WICK STRUCTURE FOR A HEAT TRANSFER DEVICE
Field of Invention
[001] The present invention relates to the field of heat
transfer devices. Particularly, the present invention is directed to a wick structure of cylinders and plates, for heat transfer devices where capillary-rise liquid pathways are formed by near zero-radii contacts of the cylinders and plates.
Background of the invention
[002] A heat pipe (HP) is used for high heat transfer across
very low temperature difference and is a significant component of electronic devices. Generally, a heat pipe includes a wick, a porous medium containing the evaporating liquid, which spans throughout the length of the heat pipe. A portion of the heat pipe is supplied with heat, conductively through its casing leading to evaporation of liquid from the wick. The vapours thus generated travel through the empty space (straight path) axially and get condensed at the other end of the HP. The condensed liquid is again transported to the heating zone by the wick in turn maintaining a cycle. Loop Heat Pipe (LHP) and Capillary Pumped Loops (CPL) are used in spacecrafts and are modified variants of a heat pipe. In LHP & CPL, the wick is limited to the evaporator section while the vapours generated after evaporation travel to a different location through smooth tubes where they are condensed and fed back to the evaporator section by pressure difference created by the liquid-vapour (L-V) meniscus in the wick. The process hence forms a close loop in all these devices and is supposed to be self-sustaining.

[003] LHP & CPL, which are two-phase heat transfer
devices, are designed to last longer as they do not having moving parts. Wicks have been constructed with single size spheres, multiple size spheres, nanochannels, wire mesh, separated microwires, and pins. Recently biporous materials, which are sintered materials, have also been used as the wicking material.
[004] In all such heat dissipation systems (HP/LHP/CPL),
the evaporation occurs from the liquid-vapour (L-V) menisci formed within the wick. The L-V menisci generate a capillary pressure in such systems and are required to be higher than the total pressure drop of the system. However, in such heat dissipation systems having an increased heat load (of the order of 104-106 W/m2), the L-V menisci tend to recede deeper in the wick. Whereas, in the most adverse condition (very high heat load), the wick will not be in a position to support the required evaporative demand which leads to dry-out of the wick. In case of a heat pipe there is also an additional requirement of immediate transportation of condensed liquid from the condenser section to the evaporator section. Therefore, a preferred wick in these systems is the one that does not dry up irrespective of the heat load.
[005] The wick structure is also required to display the
following physical properties for successful working of the HP/LHP/CPL. Firstly, a low thermal resistance is required at the evaporator end and secondly, to transport the liquid from the condenser to the evaporator, a high capillary pumping pressure is desired.

[006] It is also known in the art that surface tension force
on which capillarity depends is weak, posing a limitation for strong capillary forces to develop in the wick structure.
Objects of the present invention
[007] The primary object of the present invention is to
provide a wick structure for heat transfer devices, having a plurality of cylinders with smooth surfaces that are in abutting engagement with one another.
[008] An object of the present invention is to provide is to
provide a wick structure for heat transfer devices, having a plurality of cylinders and plates with smooth surfaces that are in abutting engagement with one another.
[009] Another object of the present invention is to provide
a wick structure for heat transfer devices, having a plurality of
linear members with capillary-rise liquid pathways disposed
between the adjacent pair of linear members, through the
formation of near-zero radii of contacts between the cylinders.
[010] It is also an object of the present invention to
provide a wick structure for heat transfer devices, where liquid encounters a substantially lower resistance and higher transportation rates, due to the provisioning of capillary-rise liquid pathways having no tortuosity, while the liquid is transported from one end to the other end of the cylinders.
Summary of the present invention
[011] Accordingly, the present invention provides
a wick structure, comprising a plurality of cylinders with smooth surfaces that are oriented in a parallel-configuration, with at least two or more cylinders in abutting engagement with the smooth surfaces of the cylinders, to define contact lines between

the adjacent cylinders. Non-tortuous capillary-rise liquid pathways are disposed along the contact lines of the cylinders. When a liquid is permitted to flow through the capillary-rise pathways of the wick structure, the liquid encounters a substantially lower resistance and higher transportation rates, due to non-tortuous capillary-rise pathways.
Brief description of the drawings
[012] FIG.1(a) is a perspective schematic illustration of
the wick structure of the present invention with cylinders arranged in a parallel configuration.
[013] FIG.1(b) is a planar schematic illustration of a unit
of cylinders of wick structure of the present invention.
[014] FIG.1(c) is another schematic illustration of a cross-
sectional view (B-B cross section) of the wick structure, as shown in FIG.1(b), illustrating the formation of near-zero radius corner L-V menisci between the adjacent linear members of the wick structure.
[015] FIG.1(d) is a schematic horizontal cross-sectional
(C-C cross section) of FIG.1(b), depicting zero radii corner L-V menisci, whose radius of curvature increases with the distance away from the zero-radii contact.
[016] FIG.1(e) is another schematic illustration of a cross-
sectional view of the wick structure with elliptically-shaped cylinders, illustrating the formation of near-zero radius corner L-V menisci between the adjacent linear members of the wick structure.
[017] FIG.2(a) is a perspective schematic illustration of
the wick structure of the present invention with curved cylinders that are arranged in a parallel configuration.

[018] FIG.2(b) is a perspective schematic illustration of
the wick structure of the present invention with a combination of
cylinders and plates.
[019] FIG.3(a) is a schematic cross-sectional view of the
wick structure as shown in FIG.2(a), where the abutting
cylinders are of variable diameter and the contact formed by two
curves whose centres are on the either side of the contact.
[020] FIG.3(b) is a schematic cross-sectional view of the
wick structure as shown in FIG.2(b), where near-zero radii
contacts are formed by an arrangement of cylinders and plates.
[021] FIG.3(c) is a partial enlarged view of FIG.3(b) to
show a typical contact formed between the cylinder and the
plate.
[022] FIG.3(d) is a schematic cross-sectional view of the
wick structure with a combination of solid and hollow cylinders to
form near-zero radii contacts.
[023] FIG.3(e) is a partial enlarged view of FIG.3(d)
demonstrating a contact that is formed by two curves whose
centres are on the same side of the contact.
[024] FIG.4 is a perspective schematic illustration of wick
structure of movable cylinders of the present invention arranged
in a parallel configuration.
[025] FIG.5(a) is a perspective schematic illustration of
wick structure of cylinders of the present invention with vapour
draining zones.
[026] FIG.5(b) is a schematic horizontal cross-sectional
(C-C cross section) of FIG.5(a) with a heating arrangement,
depicting zero radii corner L-V menisci, whose radius of

curvature increases with the distance away from the zero-radii contact.
[027] FIG.6(a) is a perspective schematic illustration of
wick structure of the present invention where the porous
cylinders are arranged in a parallel configuration.
[028] FIG.6(b) is another schematic illustration of a cross-
sectional view (B-B cross section) of the wick structure, as shown in FIG.6(a), illustrating the formation of near-zero radius corner L-V menisci between the adjacent linear members of the wick structure.
[029] FIG.6(c) is a schematic horizontal cross-sectional
(C-C cross section) of FIG.6(a), depicting zero radii corner L-V menisci, whose radius of curvature increases with the distance away from the zero-radii contact.
[030] FIG.7(a) is a perspective schematic illustration of
wick structure of cylindrical capillaries of the present invention.
[031] FIG.7(b) is another schematic illustration of a cross-
sectional view (B-B cross section) of the wick structure, as shown in FIG.7(a), illustrating the formation of near-zero radius corner L-V menisci between the adjacent linear members of the wick structure.
[032] FIG.7(c) is a schematic horizontal cross-sectional
(C-C cross section) of FIG.7(a), depicting zero radii corner L-Vmenisci, whose radius of curvature increases with the distance away from the zero-radii contact.
[033] FIG.8(a) is a perspective schematic illustration of
wick structure of porous cylinders of the present invention arranged in a parallel configuration along with vapour draining zones.

[034] FIG.8(b) is a schematic horizontal cross-sectional
(C-C cross section) of FIG.8(a), depicting zero radii corner L-V menisci, whose radius of curvature increases with the distance away from the zero-radii contact.
[035] FIG.9(a) is a perspective schematic illustration of
wick structure of cylindrical capillaries of the present invention arranged in a parallel configuration along with vapour draining zones.
[036] FIG.9(b) is a schematic horizontal cross-sectional
(C-C cross section) of FIG.9(a) with a heating arrangement, depicting zero radii corner L-V menisci, whose radius of curvature increases with the distance away from the zero-radii contact.
[037] FIG.10(a) is a perspective schematic illustration of
wick structure of cylindrical capillaries of the present invention arranged in a parallel configuration along with vapour draining zones.
[038] FIG.10(b) is a schematic horizontal cross-sectional
(C-C cross section) of FIG.10(a), depicting L-V menisci, at that cross section.
[039] FIG.10(c) is a schematic vertical cross-sectional (B-
B cross section) of FIG.10(a), depicting zero radii corner L-V menisci, whose radius of curvature increases with the distance away from the zero-radii contact.
[040] FIG.11(a) is a perspective schematic illustration of
wick structure of cylinders with a cylindrical capillary of the present invention arranged in a parallel configuration along with vapour draining zones.

[041] FIG.11(b) is a top view of the wick structure as
illustrated in FIG.11(a), along with a cylindrical capillary.
[042] FIG.11(c) is a schematic vertical cross-sectional (A-
A cross section) of FIG.11(b), depicting liquid and vapour flows across the wick structure.
[043] FIG.12 is a schematic cross sectional view of
illustrating the functional aspects of the wick structure of the
present invention as used in conjunction with a LHP/CPL device.
[044] FIG.13 is graphical depiction of comparative
experimental results of the rate of liquid evaporation of the wick structure of the present invention vis-à-vis other known wick structure.
Detailed description of the invention
[045] The preferred embodiments of the present invention
are now described, by referring to the accompanied drawings, where the wick structure as shown in FIGs.1(a) and 1(b), is for use in two-phase heat dissipation or heat transfer systems, particularly along with loop heat pipe (LHP) and capillary pumped loop (CPL) devices.
[046] The wick structure 100 of the present invention
includes a plurality of cylinders 101, with proximal and distal ends that are oriented in a parallel configuration as shown in FIGs.1(a) and 1(b). The proximal ends are those, which are in proximity to a reservoir section having a liquid and the distal ends at a heater or an evaporator section of LHP/ CPL devices (not shown in FIGs.1(a) and 1(b)). Some of the exemplary liquids include water, fluorocarbons, alcohols, ketones, and ammonia.

[047] The cylinders 101 are exemplarily shown as solid
rods made up of any suitable material such as glass, metal, and ceramics. The surface of each of the cylinders 101 is preferably provided with texture as smooth as possible. The cylinders 101 are advantageously provided with uniform cross sections. However, the cylinders 101 with non-uniform cross sections can also be adapted for use. Accordingly, in FIGs.1(a) and 1(b), the cylinders 101 are shown, in an exemplary manner, with circular cross sections. Other suitable cross sections such as elliptical or a combination of these cross sections can also be used for cylinders 101 as shown in FIGs.1(e). In other words, any type of cross-sections, for example convex-convex or convex-concave, which can provide a near-zero radius contacts between the cylinders 101 can be suitably adapted for use.
[048] Each of the cylinders 101 is arranged along the
respective central axis "A" and are abutted against each other to form a stack 100 as shown in FIG.1(a). In other words, at least two or more cylinders 101are in abutting engagement along their central axes "A", so that near zero-radii contacts 102 are formed between the cylinders 101. These types of contacts are substantially lines having zero thickness. The surfaces of the cylinders 101 are advantageously provided with a smooth texture so that contacts between the two adjacent cylinders 101 are limited to the frictional level along their axial length, thereby facilitating liquid aspirations on their surfaces. The near zero-radii contacts 102 between the cylinders 101 are near zero, since the surface texture of the linear members is smooth and uniform.

[049] As particularly shown in FIG.1(d), the near zero-
radii contacts 102 are formed between the abutting surfaces of the adjacent cylinders 101. The near zero-radii contacts 102 extend along the axial lengths of the cylinders 101, as shown in FIG.1(a). The contact line exists and extends as long as surfaces of adjacent cylinders are in contact.
[050] Non-tortuous capillary-rise liquid pathways 103 are
formed along the near zero-radii contacts 102 of the cylinders
101, as particularly shown in FIGs.1(c) and 1(d). The non-tortuous capillary-rise liquid pathways 103 are formed in between the adjacent pair of cylinders 101 in the region of near-zero radii contacts 102. The non-tortuous capillary-rise liquid pathways 103 act as conduit spaces for a rapid flow of liquid through the wick structure 100, during heat transfer process. The capillary-rise liquid pathways 103 are straight pathways so as to facilitate the flow of liquid in the wick structure 100, with a substantially reduced resistance, due to the presence of straight capillary rise paths between each pair of the cylinders 101, without forming a tortuous liquid flow path between the two adjacent cylinders 101. The non-tortuous capillary-rise liquid pathways 103 that are formed from near zero-radii contacts
102, in principle, can lead to infinite capillary rise (often called ‘Corner Flow’) through the non-tortuous capillary-rise liquid pathways 103, until the heat transfer system encounters cavitation or evaporation, which is limited by a contact angle of near-zero radii contacts. Therefore, in the wick structure 100 of the present invention, liquid encounters a substantially lower resistance and higher transportation rates, due to the provisioning of capillary-rise liquid pathways 103 having no

tortuosity, while the liquid is transported from one end to the other end of the cylinders 101.
[051] In an arrangement where the wick structure 100 of
the present invention is employed in functional connectivity with
LHP/CPL devices having an evaporator section with heat flux
generating sources, condensing and reservoir sections, the liquid
transport 104 is conducted from the reservoir section through
the non-tortuous capillary-rise liquid pathways 103, as shown in
FIG.1(d). Once the cylinders 101 of the wick structure 100 are
in flow communication with the liquid in the reservoir, a liquid-
vapour interface (L-V) 105 is formed on the liquid surface of the
reservoir. Simultaneously, corner liquid-vapour (L-V) menisci
106 also appear in the non-tortuous capillary-rise liquid
pathways 103. Significantly, these liquid-vapour (L-V) menisci
106 are maintained substantially at the top surfaces of the
cylinders, as illustrated in FIG.1(d), from where about 90-95%
of evaporation of the liquid takes place. Accordingly, the abutting
engagement of the cylinders 101, through their near-zero-radii
contact surfaces, exhibit the formation of near-zero radii liquid-
vapour (L-V) menisci 106 between the cylinders.
[052] Whereas, the vapourized liquid (vapour) 107 is
channelized from the L-V menisci 106 towards the heater
section. The near-zero radii contacts 102 between the cylinders
101 not only lead to an infinite capillary rise through the non-
tortuous capillary-rise liquid pathways 103 but also lead to
faster liquid rise, through the wick structure 100.
[053] In an exemplary aspect, the wick structure 100 is
provided with cylinders 101 with elliptical configuration as shown in FIG.1(e). The near zero-radii contacts 102 are formed

between the abutting surfaces of the adjacent cylinders 101. The near zero-radii contacts 102 extend along the axial lengths of the cylinders 101. Non-tortuous capillary-rise liquid pathways 103 are formed along the near zero-radii contacts 102 of the cylinders 101, where the near zero-radii contacts 102 facilitate the formation of the non-tortuous capillary-rise liquid pathways 103. Once the cylinders 101 of the wick structure 100 are in flow communication with the liquid, corner liquid-vapour (L-V) menisci 106 appear in the non-tortuous capillary-rise liquid pathways.
[054] In another aspect of the present invention, a wick
structure 200, having curved cylinders 201 where the curved cylinders 201 are arranged along the respective central axis "A", are abutted against each other to form the wick structure 200 as shown in FIG.2(a). In other words, at least two or more cylinders 201 are in abutting engagement along their central axes "A", so that near zero-radii contacts are formed between the cylinders 201. The surfaces of the cylinders 201 are advantageously provided with a smooth texture so that contacts between the two adjacent cylinders 201 are limited to the frictional level along their axial length, thereby facilitating liquid aspirations on their surfaces. The near zero-radii contacts 202 are formed between the abutting surfaces of the adjacent cylinders 201. The near zero-radii contacts 202 extend along the axial lengths of the cylinders 201, as shown in FIG.2(a). The near zero-radii contacts 202 are near zero, since the surface texture of the linear members are smooth and uniform. Non-tortuous capillary-rise liquid pathways are formed along the near

zero-radii contacts 202 of the cylinders 201, in the manner as described above.
[055] In another illustrative embodiment as shown in
FIG.2(b), In another aspect of the present invention, a wick structure 200, where linear cylinders 201 are abutted to one another along their central axes to form a cluster of the joined linear cylinders 201. The clusters of the linear cylinders 201 are joined by plates 217, where the plates 217 separate the cylinders 201 along their horizontal axes, as shown in FIG.2(b). The cylinders 201 and plates 217 are made up of any suitable material such as glass, metal and ceramics. Accordingly, in this exemplary embodiment the cylinders 201 are in abutting engagement along their central axes, so that near zero-radii contacts are formed between the cylinders 201. In addition, near zero-radii contacts are also formed between the surfaces of the plates 217 and the cylinders 201. The surfaces of the cylinders 201 and plates 217 are advantageously provided with a smooth texture so that contacts between the two adjacent cylinders 201 are limited to the frictional level along their axial length, thereby facilitating liquid aspirations on their surfaces. The near zero-radii contacts 202 are formed between the abutting surfaces of the cylinders 201 and plates 217. The near zero-radii contacts 202 are near zero, since the surface texture of the cylinders and plates are smooth and uniform. Non-tortuous capillary-rise liquid pathways are formed near the zero-radii contacts 202 of the cylinders 201 and the plates 217, in the manner as described above.
[056] A wick structure 300 with arrangements of stacks of
cylinders 301 and a combination of cylinders 301 and plates

317, defining various types of near-zero radii contacts are shown in FIG.3(a)-(e). FIG.3(a) shows assembly 300 consisting of rods 301 creating near-zero radii contacts 302 leading to the formation of corner menisci 303. In this exemplary aspect of the wick structure 300, the near-zero radii contacts 302 formed by curvilinear members 301, whose centres are on the either side of the near-zero radii contact 302. In yet another exemplary aspect, the wick structure 300 as shown in FIG.3(b) is formed by an abutting arrangement of cylindrical rods 301 and plates 304 to render near-zero radii contacts 302. The formation of corner meniscus 303 as a result of the near-zero radius of contact 302 that is established between the curved member 301 and the plate 304. In yet another exemplary aspect the wick structure 300 as shown in FIG.3(d) includes a stack solid members (cylinders) 301 are arranged so as to establish surface contact with each other, along their central axes. The stack of cylinders 301 are arranged in another hollow members or cylinder 305, so as to form near-zero radii contact 302 and the corresponding corner meniscus 303, as shown in FIG.3(e). The formation of corner meniscus 303 is thus formed from a combination of solid member 301 and a concave surface of the hollow member 305.
[057] Hitherto, embodiments pertaining to the wick
structure, where the cylinders are stationary are described. Now, by referring to FIG.4, embodiments of the wick structure
400 with movable cylinders 401 are described. The cylinders
401 are exemplarily shown as solid rods made up of any suitable material as aforementioned and the surface of each of the cylinders 401 is preferably provided with a smooth texture. Each

of the cylinders 401 is arranged along the respective central axis "A" and is rotatably abutted against each other to form the wick structure 400 as shown in FIG.4. The cylinders 401 are rotatable in both clockwise and counter clockwise directions along the cylindrical axes of the cylinders 401. The rotation of the cylinders 401 can be actuated with any suitable known contraptions such as rotary actuators with constant or variable speeds. In other words, at least two or more cylinders 101 are in rotatable abutting engagementalong their central axes "A", so that near zero-radii contacts 102 are formed between the cylinders 401. The surfaces of the cylinders 401 are advantageously provided with a smooth texture so that contacts between the two adjacent cylinders 401 are limited to the frictional level along their axial length, thereby facilitating liquid aspirations on their surfaces. The near zero-radii contacts 402 of the cylinders 401 are near zero, since the surface texture of the each of the cylinder 401 is smooth and uniform. Contact lines 402 are formed between the abutting surfaces of the adjacent cylinders 401. The near zero-radii contacts 402 extend along the axial lengths of the cylinders 401. Non-tortuous capillary-rise liquid pathways are also formed along the near zero-radii contacts 402 of the cylinders 401. The non-tortuous capillary-rise liquid pathways are formed in between the adjacent pair of cylinders 401 in the region of the near-zero radii contacts 402. The non-tortuous capillary-rise liquid pathways act as conduit spaces for a rapid flow of liquid through the wick structure 400, during heat transfer process. The non-tortuous capillary-rise liquid pathways are straight pathways so as to facilitate the flow of liquid in the wick structure 400, with a substantially reduced

resistance, due to the presence of straight capillary rise paths between each pair of the cylinders 401, without forming a tortuous liquid flow path between the two adjacent cylinders 401. The non-tortuous capillary-rise liquid pathways that are formed from the near zero-radii contacts 402, in principle, can lead to infinite capillary rise through the non-tortuous capillary-rise liquid pathways, until the heat transfer system encounters cavitation or evaporation.
[058] In yet another aspect of the present invention, the
preferred embodiments of the wick structure 500, where the cylinders are configured to have vapour draining zones to direct the flow of vapour, are now described, by particularly referring FIG.5(a) and FIG.5(b). The wick structure 500 includes a plurality of cylinders 501, with proximal and distal ends that are oriented in a parallel configuration as shown in FIG.5(a). The proximal ends are those, which are in proximity to a reservoir section having a liquid and the distal ends at a heater or an evaporator section of LHP/ CPL devices (not shown in FIG.5(a). The cylinders 501 are exemplarily shown as solid rods made up of any suitable material and the surface of each of the cylinders 501 is preferably provided with a smooth texture. The cylinders 501 are advantageously provided with uniform cross sections. However, the cylinders 501 with non-uniform cross sections can also be adapted for use. Each of the cylinders 501 is arranged along the respective central axis "A" and are abutted against each other to form a stack 100 as shown in FIG.5(a). In other words, at least two or more cylinders 501 are in abutting engagement along their central axes "A", so that near zero-radii contacts 502 are formed between the cylinders 501. The near

zero-radii contacts 502 are formed between the abutting surfaces of the adjacent cylinders 501. The near zero-radii contacts 502 extend along the axial lengths of the cylinders 501. The surfaces of the cylinders 501 are advantageously provided with a smooth texture so that contacts between the two adjacent cylinders 501 are limited to the frictional level along their axial length, thereby facilitating liquid aspirations on their surfaces. The near zero-radii contacts 502 of the cylinders 501 are near zero, since the surface texture of the linear members is smooth and uniform. Non-tortuous capillary-rise liquid pathways are formed along the near zero-radii contacts 502 of the cylinders 501, as described above, to act as conduit spaces for a rapid flow of liquid through the wick structure 500, during heat transfer process.
[059] Vapour draining zones 508 of the cylinders 501 are
formed at the distal ends of the cylinders 501, which when used in conjunction with HP/LHP/CLP devices are in proximity to an evaporator section, having heat sources that generate heat flux. In an exemplary aspect as shown in FIG.5(a), the vapour draining zones 508 are with reduced cross sections, as compared to the other portions of the cylinders 501. The reduced cross sections of vapour draining zones 508 of the cylinders 501 are advantageously obtained through the processes of machining, casting, sintering, debossing, grooving or any other suitable means. In this exemplary aspect, the vapour draining zones 508 are shown as grooves formed at the distal terminal ends of the cylinders 501, to facilitate passage for liquid vapour that is formed after evaporation of liquid from the corner L-V menisci 506, which absorbs heat from the heater

section. The liquid vapour from the heater section is directed towards a condensation section, of the loop heat pipe (LHP) and capillary pumped loop (CPL) devices (not shown in this figure).
[060] As shown in FIG.5(b), the near zero-radii contacts
502 are formed between the abutting surfaces of the adjacent cylinders 501. The near zero-radii contacts 502 extend along the axial lengths of the cylinders 501, as shown in FIG.5(b). Non-tortuous capillary-rise liquid pathways 503 are thus formed along the near zero-radii contacts 502 of the cylinders 501. The non-tortuous capillary-rise liquid pathways 503 are formed in between the adjacent pair of cylinders 501 in the region of near-zero radii contacts 502. The non-tortuous capillary-rise liquid pathways 503 act as conduit spaces for a rapid flow of liquid through the wick structure 500, during heat transfer process. The capillary-rise liquid pathways 503 are straight pathways so as to facilitate the flow of liquid in the wick structure 500, with a substantially reduced resistance, due to the presence of straight capillary rise paths between each pair of the cylinders 501, without forming a tortuous liquid flow path between the two adjacent cylinders 501. The non-tortuous capillary-rise liquid pathways 503 that are formed from near zero-radii contacts, in principle, can lead to infinite capillary rise (often called ‘Corner Flow’) through the non-tortuous capillary-rise liquid pathways 503, until the heat transfer system encounters cavitation or evaporation (and contact angle) limits it.
[061] In an arrangement where the wick structure 500 of
the present invention is employed in functional connectivity with HP/LHP/CPL devices having an evaporator section with heat flux sources, condensing and reservoir sections, the liquid transport

504 is conducted from the reservoir section through the non-
tortuous capillary-rise liquid pathways 503, as shown in
FIG.5(b). Once the cylinders 501 of the wick structure 500 are
in flow communication with the liquid in the reservoir, a liquid-
vapour interface (L-V) 505 is formed on the liquid surface of the
reservoir. Simultaneously, corner liquid-vapour (L-V) menisci
506 also appear in the non-tortuous capillary-rise liquid
pathways 503. Significantly, these liquid-vapour (L-V) menisci
506 are maintained substantially at the top surfaces of the
cylinders, as illustrated in FIG.5(b), from where about 90-95%
of evaporation of the liquid takes place. Accordingly, the abutting
engagement of the cylinders 501, through their near-zero-radii
contact surfaces, exhibit the formation of near-zero radii liquid-
vapour (L-V) menisci 506 between the cylinders.
[062] Whereas, the vapourized liquid 507 is channelized
from the L-V menisci 506 towards the heater section, through the vapour draining zones 508. The vapour draining zones provide an easy path that may be led to the condenser section (not shown) of HP/LHP/CPL. The near-zero radii contacts 502 between the cylinders 501 not only lead to an infinite capillary but also lead to faster liquid rise.
[063] In yet another aspect of the present invention, the
wick structure 600 with porous configuration is as shown in FIGs.6(a), (b) and (c). The cylinders 601 are arranged along their central axes and are abutted against each other to form the stack or structure 600 as shown in FIG.6(a). The surfaces of the cylinders 601 are mutually connected along their central axes, so as to form capillary rise pathways 603 between the cylinders 601, as result of near zero-radii contacts that are

formed between the adjacent cylinders 601. In this aspect, the cylinders 601 are with pores 609 and exemplary circular cross sections. The pores 609 are with uniform pore diameters or with variable pore diameters. The pores 609 act as drains to permit the flow of vapours through the pores 609. The pores 609 also hold the liquid and a L-V interface 610 thus forms within the porous cylinders 601. The geometries of the pores 609 can also be suitably varied. For instance, the pores with non-circular, such as slits, non-circular, and a combination of various geometries, can also be used. The cylinders 601 are abutted to each other to form capillary rise pathways 603 for the liquid, between the cylinders 601. The corner liquid-vapour (L-V) menisci 605 are formed in the near-zero radii contacts of the cylinders as shown in FIG.6(b). The liquid evaporates from these corner liquid-vapour (L-V) menisci 605, while the reservoir supplies the liquid thus maintaining a close loop in the steady state.
[064] As particularly shown in FIG.6(c), the corner liquid-
vapour (L-V) menisci 605, which are formed in the near-zero radii contacts 602 of the cylinders 601 with pores 609, whose radii of curvature increases with the distance away from the contact surfaces of the cylinders 601. The liquid evaporates from these corner liquid-vapour (L-V) menisci 605 and through the pores 609, while the reservoir supplies the condensed liquid, thereby maintaining a close loop in the steady state, in HP/LHP/CLP devices.
[065] In yet another aspect of the present invention, the
wick structure 700 includes cylinders, which are solid cylindrical capillaries as shown in FIGs.7(a), (b) and (c). The cylinders

701 are arranged along their central axes and are abutted against each other to form the stack or structure 700 as shown in FIG.7(a). The outer surfaces of the cylinders 701 are mutually connected along their central axes, so as to form capillary rise pathways 703 between the cylinders 701, as result of near zero-radii contacts 702 that are formed between the adjacent cylinders 701. The cylinders 701 are abutted to each other to form non-tortuous capillary-rise liquid pathways 703 formed in between the adjacent pair of cylinders 701 in the region of near-zero radii contacts 702. The non-tortuous capillary-rise liquid pathways 703 act as conduit spaces for a rapid flow of liquid through the wick structure 700, during heat transfer process. The corner liquid-vapour (L-V) menisci 705, are formed in the non-tortuous capillary-rise liquid pathways 703 of the cylinders 701 as shown in FIGs.7 (b) and (c). The liquid evaporates from these corner liquid-vapour (L-V) menisci 705, while the reservoir supplies the liquid thus maintaining a close loop in the steady state, while the wick structure 700 is used in conjunction with LHP/CLP devices.
[066] As particularly shown in FIG.7(c), the liquid 704
rises through the cylinders (capillaries) and the corner liquid-vapour (L-V) menisci 705, which are formed in the near-zero radii contacts 702 of the cylinders 701, whose radii of curvature increases with the distance away from the contact surfaces of the cylinders 701. The liquid evaporates from these corner liquid-vapour (L-V) menisci 705, while the reservoir supplies the condensed liquid, thereby maintaining a close loop in the steady state, in LHP/CLP devices. The corner L-V meniscus 705 is

hydraulically connected to the L-V meniscus 706 in the capillary which aids to the liquid flow 704.
[067] In yet another aspect of the present invention, the
preferred embodiments of the wick structure of the present invention, where the porous cylinders are configured to have vapour draining zones to direct the flow of vapour, are now described by particularly referring FIGs.8(a) and 8(b). The wick structure 800 of the present invention, includes a plurality of cylinders 801 with pores 809 and the cylinders 801 are with proximal and distal ends, which are oriented in a parallel configuration as shown in FIG.8(a). The proximal ends are those, which are in proximity to a reservoir section having a liquid and the distal ends at a heater or an evaporator section of LHP/ CPL devices (not shown in FIG.8(a). The cylinders 801 are exemplarily shown as solid rods made up of any suitable material and the surface of each of the cylinders 801 is preferably provided with a smooth texture. The cylinders 801 are advantageously provided with uniform cross sections. However, the cylinders 801 with non-uniform cross sections can also be adapted for use. Each of the cylinders 801 is arranged along the respective central axis "A" and are abutted against each other to form a stack 800 as shown in FIG.8(a). In other words, at least two or more cylinders 801 are in abutting engagement along their central axes "A", so that near zero-radii contacts are formed between the cylinders 801. The surfaces of the cylinders 801 are advantageously provided with a smooth texture so that contacts between the two adjacent cylinders 801 are limited to the frictional level along their axial length, thereby facilitating liquid aspirations on their surfaces. The near zero-radii contacts

of the cylinders 801 are near zero, since the surface texture of the linear members are smooth and uniform. Contact lines 802 are formed between the abutting surfaces of the adjacent cylinders 801. The contact lines 802 extend along the axial lengths of the cylinders 801. Non-tortuous capillary-rise liquid pathways are formed along the contact lines 802 of the cylinders 801, as described above, to act as conduit spaces for a rapid flow of liquid through the wick structure 800, during heat transfer process.
[068] Vapour draining zones 808 of the cylinders 801 are
formed at the distal ends of the cylinders 801, which when used in conjunction with LHP/CLP devices are in proximity to an evaporator section, having heat sources that generate heat flux. In an exemplary aspect as shown in FIG.8(a), the vapour draining zones 808 are with reduced cross sections, as compared to the other portions of the cylinders 801.The reduced cross sections of vapour draining zones 808 of the cylinders 801 are advantageously obtained through the processes of machining, casting, sintering, debossing, grooving or any other suitable means. In this exemplary aspect, the vapour draining zones 808 are exemplarily shown as grooves formed at the distal terminal ends of the cylinders 801, to facilitate passage for liquid vapour that is formed after evaporation of liquid from the corner L-V menisci 806which absorbs heat from the heater section. The liquid vapour from the heater section is directed towards a condensation section, of the loop heat pipe (LHP) and capillary pumped loop (CPL) devices (not shown in this figure).
[069] As illustrated in FIG.8(b), contact lines 802 are
formed between the abutting surfaces of the adjacent cylinders

801. The contact lines 802 extend along the axial lengths of the cylinders 801, as shown in FIG.8(b).Non-tortuous capillary-rise liquid pathways 803 formed along the contact lines 802 of the cylinders 801. The non-tortuous capillary-rise liquid pathways 803 are formed in between the adjacent pair of cylinders 801 in the region of near-zero radii contacts. The non-tortuous capillary-rise liquid pathways 803 act as conduit spaces for a rapid flow of liquid through the wick structure 800, during heat transfer process. The non-tortuous capillary-rise liquid pathways
803 are straight pathways so as to facilitate the flow of liquid in
the wick structure 800, with a substantially reduced resistance,
due to the presence of straight capillary rise paths between each
pair of the cylinders 801, without forming a tortuous liquid flow
path between the two adjacent cylinders 801. The non-tortuous
capillary-rise liquid pathways 803 that are formed from near
zero-radii contacts, in principle, can lead to infinite capillary rise
(often called ‘Corner Flow’) through the non-tortuous capillary-
rise liquid pathways 803, until the heat transfer system
encounters cavitation or evaporation (and contact angle) limits
it.
[070] In an arrangement where the wick structure 800 of
the present invention is employed in functional connectivity with LHP/CPL devices having an evaporator section with heat flux sources, condensing and reservoir sections, the liquid transport
804 is conducted from the reservoir section through the non-
tortuous capillary-rise liquid pathways 803, as shown in
FIG.8(b). Once the cylinders 801 of the wick structure 800 are
in flow communication with the liquid in the reservoir (not shown
in the Figure), a liquid-vapour interface (L-V) 805 is formed on

the liquid surface of the reservoir. Simultaneously, corner liquid-vapour (L-V) menisci 806 also appear in the non-tortuous capillary-rise liquid pathways 803. Significantly, these liquid-vapour (L-V) menisci 806 are maintained substantially at the top surfaces of the cylinders, as illustrated in FIG.8(b), from where about 90-95% of evaporation of the liquid takes place. Accordingly, the abutting engagement of the cylinders 801, through their near-zero-radii contact surfaces 802, exhibit the formation of near-zero radii liquid-vapour (L-V) menisci 806 between the cylinders.
[071] A L-V interface 810 is formed within each of the
porous cylinders 801. Whereas, the vapourized liquid 807is transported out from the pores 809 from within the porous cylinders 801 along with the vapourized liquid 807that is channelized from the L-V menisci 806, towards the heater section, through the vapour draining zones 808. The near-zero radii contacts 802 between the cylinders 801 not only lead to an infinite capillary but also lead to faster liquid rise.
[072] In yet another aspect of the present invention, the
preferred embodiments of the wick structure of the present invention, where the cylinders, which are cylindrical capillaries, are configured to have vapour draining zones to direct the flow of vapour, are now described by particularly referring FIGs.9(a) and 9(b). The wick structure 900 of the present invention, includes a plurality of cylinders 901, with proximal and distal ends that are oriented in a parallel configuration as shown in FIG.9(a). The proximal ends are those, which are in proximity to a reservoir section having a liquid and the distal ends at a heater or an evaporator section of LHP/ CPL devices (not shown

in FIG.9(a). The cylinders 901 are exemplarily shown as solids made up of any suitable material and the outer surface of each of the cylinders 901 is preferably provided with a smooth texture. The cylinders 901 are advantageously provided with uniform cross sections. However, the cylinders 901 with non-uniform cross sections can also be adapted for use. Each of the cylinders 901 is arranged along the respective central axis "A" and are abutted against each other to form a stack 900 as shown in FIG.9(a). In other words, at least two or more cylinders 901 are in abutting engagement along their central axes "A", so that near zero-radii contacts are formed between the cylinders 901. The outer surfaces of the cylinders 901 are advantageously provided with a smooth texture so that contacts between the two adjacent cylinders 901 are limited to the frictional level along their axial length, thereby facilitating liquid aspirations on their surfaces. The near zero-radii contacts of the cylinders 901 are near zero, since the surface texture of the linear members is smooth and uniform. Contact lines 902 are formed between the abutting surfaces of the adjacent cylinders 901. The contact lines 902 extend along the axial lengths of the cylinders 901. Non-tortuous capillary-rise liquid pathways 903are formed along the contact lines 902 of the cylinders 901, as described above, to act as conduit spaces for a rapid flow of liquid through the wick structure 900, during heat transfer process.
[073] Vapour draining zones 908 of the cylinders 901 are
formed at the distal ends of the cylinders 901, which when used in conjunction with LHP/CLP devices are in proximity to an evaporator section, having heat sources that generate heat flux.

In an exemplary aspect as shown in FIG.9(a), the vapour draining zones 908 are with reduced cross sections, as compared to the other portions of the cylinders 901.The reduced cross sections of vapour draining zones 908 of the cylinders 901 are advantageously obtained through the processes of machining, casting, sintering, debossing, grooving or any other suitable processes. In this exemplary aspect, the vapour draining zones 908 are exemplarily shown as grooves formed at the distal terminal ends of the cylinders 901, to facilitate passage for liquid vapour that is formed after evaporation of liquid from the corner L-V menisci 906, which absorbs heat from the heater section. The liquid vapour from the heater section is directed towards a condensation section, of the loop heat pipe (LHP) and capillary pumped loop (CPL) devices (not shown in this figure).
[074] As illustrated in FIG.9(b), contact lines 902 are
formed between the abutting surfaces of the adjacent cylinders 901. The contact lines 902 extend along the axial lengths of the cylinders 901, as shown in FIG.9(b). Non-tortuous capillary-rise liquid pathways 903 formed along the contact lines 902 of the cylinders 901. The non-tortuous capillary-rise liquid pathways 903 are formed in between the adjacent pair of cylinders 901 in the region of near-zero radii contacts. The non-tortuous capillary-rise liquid pathways 903 act as conduit spaces for a rapid flow of liquid through the wick structure 900, during heat transfer process. The capillary-rise liquid pathways 903 are straight pathways so as to facilitate the flow of liquid in the wick structure 900, with a substantially reduced resistance, due to the presence of straight capillary rise paths between each pair of the cylinders 901, without forming a tortuous liquid flow path

between the two adjacent cylinders 901. Then on-tortuous capillary-rise liquid pathways 903 that are formed from near zero-radii contacts, in principle, can lead to infinite capillary rise (often called ‘Corner Flow’) through the non-tortuous capillary-rise liquid pathways 903, until the heat transfer system encounters cavitation or evaporation is limited by contact angle.
[075] In an arrangement where the wick structure 900 of
the present invention is employed in functional connectivity with
LHP/CPL devices having an evaporator section with heat flux
sources, condensing and reservoir sections, the liquid transport
904 is conducted from the reservoir section through the non-
tortuous capillary-rise liquid pathways 903, as shown in
FIG.9(b). Cylinders 901 of the wick structure 900 are
hydraulically connected to the liquid in the cylindrical capillaries.
A separate liquid-vapour interface (L-V) 905 is formed inside the
capillaries which act as a reservoir for the corner L-V meniscus
906. Simultaneously, corner liquid-vapour (L-V) menisci 906
also appear in the non-tortuous capillary-rise liquid pathways
903. Significantly, these liquid-vapour (L-V) menisci 906 are
maintained substantially at the top surfaces of the cylinders, as
illustrated in FIG.9(b), from where about 90-95% of
evaporation of the liquid takes place. Accordingly, the abutting
engagement of the cylinders 901, through their near-zero-radii
contact surfaces, exhibit the formation of near-zero radii liquid-
vapour (L-V) menisci 906 between the cylinders.
[076] Whereas, the vapourized liquid 907 is channelized
from the L-V menisci 906 towards the heater section, through the vapour draining zones 908. The near-zero radii contacts 902

between the cylinders 901 not only lead to an infinite capillary but also lead to faster liquid rise.
[077] In yet another aspect of the present invention, a
wick structure 1000, for a particular use in conjunction with heat pipe (HP) device, is described by referring to FIG.10(a)-(c). The wick structure 1000, shown in FIG.10(a), includes a plurality of cylinders 1001, with proximal and distal ends that are positioned along the central axis. The cylinders 1001 are exemplarily shown as cylindrical capillaries. The surface of the cylinders 1001 are provided with smooth texture. The cylinders 1001 are advantageously provided with uniform cross sections. However, the cylinders 1001with non-uniform cross sections can also be adapted for use. The proximal and distal ends of the cylinders 1001 that are in proximity to the evaporator region and condenser region respectively are provided with vapour draining zones 1008. The vapour draining zones 1008 are arranged to provide escape routes for liquidvapour after evaporation of liquid, which absorbs heat from the heater section.At the proximal ends of the cylinders 1001, the vapour draining zones 1008 are vapour entry slits, to permit the entry of liquid vapour during heat dissipation or transfer process into the cylinders 1001. Whereas, at the proximal ends of the cylinders 1001 the vapour draining zones 1008 are vapour exit slits, to facilitate the exit of liquid vapours from the cylinders 1001 and transport the liquid vapours to the condensing region. The slits can also be placed horizontally along the circumference of the distal ends of the linear members cylinders. The vapour draining zones 1008 facilitate a rapid transport of the liquid

[078] As shown in FIG.10(b), the wick structure 1000
includes cylindrical capillaries 1001 with multiple slits 1008. Liquid evaporates from the corner L-V menisci 1005 while the generated liquid vapours travel through 1007 the nearby slits and reach the condenser end via the inner space of the capillaries. The cylinders 1001 are arranged along their central axes and are abutted against each other to form the wick structure 1000. In other words, the surfaces of the cylinders 1001 are mutually connected along their central axes, so that near zero-radii are formed between the cylinders 1001. The outer surface of the cylinders 1001 are advantageously provided with a smooth texture so that contacts between two adjacent cylinders 1001 are limited to the frictional level along their length, thereby facilitating aspirations on their surfaces. The radii of the length-wise contacts of cylinders 1001 are near zero, since the surface texture of the cylinders 1001 is smooth and uniform. Non-tortuous capillary-rise liquid pathways 1003 are formed in between the adjacent pair of cylinders 1001having near-zero radii contacts. These near-zero radii contacts 1002 facilitate the formation of non-tortuous capillary-rise liquid pathways 1003 and facilitate rapid flow of liquid through contacts of the wick structure 1000, as shown in FIG.10(c). Near-zero radii L-V (corner) menisci 1005 form along the theoretical line contact 1002, between the cylinders 1001 as seen in FIG.10(c). Liquid evaporates from these corner films 1005 and gets converted into vapours 1007 which enter into the cylinders 1001 through the vapour entry slits 1008 that are provided near the evaporator end in the cylinders 1001. The liquid vapours move within the cylinders 1001 and exit out at

condenser region. A mixture of liquid (after condensation of vapours) and vapour move through the vapour exit slits, while undergoing further condensation. After getting fully condensed the liquid moves to the evaporator end via the corner flow induced by the near-zero radii contacts 1002 of the cylinders 1001. The liquid flow path 1004 is thus maintained and the process keeps running.
[079] In yet another aspect of the present invention, a
wick structure 1100, for a particular use in conjunction with heat pipe (HP) device, is described by referring to FIG.11(a)-(c). The wick structure 1100 includes a plurality of cylinders 1101, with proximal and distal ends that are positioned along the central axis. The cylinders 1101 are exemplarily shown as cylindrical solid rods. The surface of the cylinders 1101 are provided with smooth texture. The cylinders 1101 are advantageously provided with uniform cross sections. However, the cylinders 1101 with non-uniform cross sections can also be adapted for use. The distal ends of the cylinders 1101 that are in proximity to the evaporator region and condenser region are provided with vapour draining zones and liquid draining zones at the proximal end 1108. The vapour and liquid draining zones 1108 are with reduced cross-sectional area, as compared to the other portions of the cylinders 1101. In this exemplary aspect, the vapour and liquid draining zones 1108 are exemplarily shown as grooves, which are arranged to provide escape routes for liquid and for liquid vapour, formed while condensing at the proximal end and while absorbing the heat from a heat source in the evaporator section. The cylinders 1101 are arranged along their central axes and are abutted against each other to form the

stack. In other words, the surfaces of cylinders 1101 are mutually connected along their central axes, so that near zero-radii contacts 1102 are formed between the cylinders 1101. The surface of the cylinders 1101are advantageously provided with a smooth texture so that contacts between two adjacent cylinders
1101 are limited to the frictional level along their length, thereby facilitating aspirations on their surfaces. The radii of the length-wise contacts of the cylinders 1101 are near zero, since the surface texture of the cylinders 1101 is smooth and uniform. Non-tortuous capillary-rise liquid pathways 1103 are formed in between the adjacent pair of cylinders 1101 having near-zero radii contacts. These near-zero radii contacts form capillary rise pathways and facilitate rapid flow of liquid through contacts
1102 of the wick structure 1100, as shown in FIG.11(c). An empty cavity 1110 is disposed, in the stack of the cylinders 1101, as shown in FIG.11(b)&(c). After evaporation of the liquid in the corner L-V meniscus liquid vapours travels through the cut-outs 1108 and reaches the cavity 1110. The cavity 1110 acts as a guide to transport the liquid vapours 1107 originating from the evaporator region of the HP to the condenser region. As a result of condensation the evaporating liquid 1105 accumulate in and near the condenser region after which the ‘corner’ flow ensures the rapid capillary rise along the liquid path 1104. In this exemplary embodiment a single cavity 1110 is shown in the middle of the stack of cylinders 1101. However, it is within the purview of this invention to position the cavity 1110, at any other region of the stack. Further, the number of cavities can be suitably varied and arranged at

various positions of the stack to facilitate faster rate of transport
of vapour, from the evaporator region to the condenser region.
[080] Functional aspects of the wick structure 1200 of the
present invention, are now described, exemplarily, where the wick structure is used in conjunction with LHP or CPL devices, by particularly referring to FIG.12, where the cylinders of the wick structure are cylindrical solid rods 1201. During, the heat transfer or heat dissipation, while the wick structure is in use, the distal ends of the cylinders are exposed to a heat flux and the heat is conducted by the cylinders, the liquid as present in the reservoir rises 1204 through the capillary rise pathways of the cylinders due to ‘corner’ flow and reaches the distal end; evaporating region of the wick 1200. The liquid evaporates from the corner L-V menisci and the vapours 1207 generated are directed to travel through the vapour drain zones 1208 that are disposed at the distal ends of the linear members 1201 and exit through the evaporation section of the LHP or CPL device. The exited vapour 1207 then travels through the vapour line 1215 and enter the condenser unit 1214, where the vapour is converted again into liquid and is transported through the liquid line 1216. The liquid line, hosing condensed liquid, passes through the outer casing 1213, and ends into a liquid spreader 1212, which distributes the liquid evenly among the proximal ends of the members 1201. The liquid spreader is preferably a thin porous medium such as a wire-mesh. The liquid spreader is directly connected to the proximal ends of the linear members, where the corner flow ensures faster transportation 1204 of the liquid to the evaporating end through the capillary rise pathways, thereby forming a close loop of liquid-vapour circulation. The

liquid spreader 1212 might be hydraulically connected with a
reservoir as per the demand and we may get a bulk L-V interface
1205 depending on the cooling load. The distal end of the wick
1200 is shown to be slightly away from the heating end leaving
a gap 1211. It should not be misinterpreted, since the gap 1211
is intended for clarity of the flow diagram. For all practical
purposes, the gap 1211 would be of zero dimension.
[081] Therefore, the present invention provides a
wick structure having a plurality of cylinders with smooth
surfaces that are oriented in a parallel-configuration. At least two
or more of these cylinders are in abutting engagement with the
smooth surfaces, to define contact lines between the adjacent
cylinders. In wick structure of the present invention non-tortuous
capillary-rise liquid pathways are disposed along the contact
lines of the cylinders.
[082] In an aspect of the present invention, the cylinders
of the wick structure are in abutting engagement with a plurality
of plates, so as to form contact lines, resulting from the
combination of straight and curved surfaces.
[083] In another aspect of the present invention, the
contact lines are effective zero radii contacts.
[084] In yet another aspect of the present invention, the
cylinders of the wick structure are linear or curved.
[085] In another aspect of the present invention, at least
one of the abutting surfaces of the cylinders of the wick structure
is curved.
[086] In yet another aspect of the present invention, the
cylinders of the wick structure are rotatable along their central
axes.

[087] In further aspect of the present invention, the
cylinders are solid, porous, or hollow or a combination thereof.
[088] It is also an aspect of the present invention where
the vapour draining zones are disposed at least at one of the terminal ends of cylinders and the vapour draining zones are cut¬outs or slits.
[089] It is also an aspect of the present invention, where a
cavity is disposed in the stack of cylinders.
[090] The efficacy of the stack of wick structure of the
present invention is now described by comparing with known
structures, in the form of a following non-limiting example.
[091] The functional advantages of the wick structure of
the present invention are now illustrated by a non-limiting example and the results are plotted as shown in FIG.13. As shown in FIG.13 the curves are for relative evaporation rates from the wick structures versus the relative content of liquid (water) within them. The relative evaporation rates are obtained by normalizing the real time evaporation with its maximum value for individual experiments. A known wick structure form by substantially mono-disperse spheres, having 0.70-0.85 mm diameter glass beads (GB) and an initial height of about 87 mm. Experiments are conducted with the wick structures in accordance with present invention such as, glass rods (2 mm & 3mm diameter), pencil rods (0.7 mm diameter), and capillaries having inside/outside diameter as 1.1 mm/1.5 mm respectively. The heights all these wicks were 75 mm. It is to be noted that the experiments are conducted, while heating these saturated wicks with infrared radiation. The mass release mechanism is not altered much even if the heat required for evaporation is

supplied through conduction. The conventional wick is seen to
sustain higher evaporation rates till a saturation value of nearly
0.7 which corresponds to an average water depth of nearly 30
mm. On the contrary all the wicks of the present invention
containing rods and capillaries have maintained evaporation
rates till a much larger water depths; nearly 70 mm. Even
though the present experiments is focused on the transient
behaviour of wicks, the wicks surprisingly sustains higher and
extended evaporation rates, independent of the diameter,
compared to a conventional wick structures made of spheres.
[092] As many apparently widely different embodiments of
this invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.
[093] It is also understood that the following claims are
intended to cover all the generic and specific features of the invention herein described and all statements of the scope of the invention, which as a matter of language might be said to fall there between.

We claim:
1. A wick structure, comprising:
- a plurality of cylinders with smooth surfaces are oriented in a parallel-configuration, with at least two or more cylinders are in abutting engagement with the smooth surfaces, to define contact lines between the adjacent cylinders, and
- non-tortuous capillary-rise liquid pathways are disposed along the contact lines.

2. The wick structure as claimed in claim 1, wherein said plurality of cylinders are in abutting engagement with a plurality of plates.
3. The wick structure as claimed in claim 1, wherein the contact lines are effective zero radii contacts.
4. The wick structure as claimed in claim 1, wherein the cylinders are linear or curved.
5. The wick structure as claimed in claim 1, wherein at least one of the abutting surfaces of the cylinders is curved.
6. The wick structure as claimed in claim 1, wherein the cylinders are rotatable along their central axes.
7. The wick structure as claimed in claim 1, wherein the cylinders are solid, porous, or hollow or a combination thereof.
8. The wick structure as claimed in claim 1, wherein vapour draining zones are disposed at least at one of the terminal ends of cylinders and the vapour draining zones are cut-outs or slits.

9. The wick structure as claimed in claim 1, wherein a cavity is disposed in the stack of cylinders.