FIELD OF THE INVENTION
The present invention relates to a thermal barrier for enclosure of electronic
devices kept in the innermost shell and operating at a temperature of 60
degree Celsius while the outside temperature of the enclosure is high
temperature of 1200-1400 degree Celsius.
BACKGROUND OF INVENTION
Insulating materials are characterized by lower thermal conductivity. It is the
consistent endeavour of the research community to devise new materials of
possible lowest thermal conductivity. Conventionally insulation materials in use
are fibers, foams, powders to suppress convection as insulating materials
contains sub-mm cells or pores. Typical values of thermal conductivity of above
mentioned materials are in the range of 0.035 to 0.060 Wm-1k-1. The current
limitation for the development of better insulation system in the world is the non-
availability of effective high temperature insulation.

In general, all thermal insulation materials work on the basic principle of heat
transfer from warmer to colder areas. Insulating materials with the passage of
time retards or slows this process of heat transfer. Tiny pockets of trapped gas
generated in the insulating materials resist the transfer of heat without the
complete blocking of the loss or grain of heat.
All thermal insulating materials, therefore, are generally designed to control the
different components of heat transfer for example,
• Conduction through building material or any enclosing space.
• Convection via air movement, which can be achieved by
incorporating a structure of a cellular space or small cells or high
voids. Small cells or voids slows down convection mechanism and
neighbouring cells are less excited or agitated.
• Thermal radiation
Hence inhibition of the above mechanism, i.e., conduction, convection and
radiation can be achieved by

1) Inhibition of conduction by formulating a small ratio of solid volume
to void. Also, movement of solids by the use of inert gases rather
than still air, retards the conduction. Any material having thin wall
matrix, a discontinuous matrix or a matrix of elements with
minimum point contacts would be an excellent insulator for
conduction.
2) Radiation can be reduced to a large extent by placing an insulating
material in close contact with a hot surface. Inhibition of radiation
heat transfer is obtained by the use of bright aluminium foil in the
form of multi-corrugated sheets.
Thermal insulation used for building is aimed to maintain a constant and
comfortable temperature in a house/enclosing space by preventing heat transfer
between indoor and outdoor space. For insulating purposes, the roofs of
buildings, insulating materials are used for a long time. As a consequence of
development of lower thermal conductivity materials with a thermal conductivity
in the range of 0.02 w/m2K from 0.04 w/m2K, the thickness of thermal insulation
of building materials have increased from 0.02 m to 0.15 m. For high
temperature insulation, silica brick has been found to be extensively employed in
the blast furnace and different industrial furnaces and many hot conditions in
steel plants. Insulations fitted to the furnace wall retard the heat transfer from
the furnace.

The normal temperature of reheating furnace ranges from 1200-1330 Degree
Celsius. In industrial applications, the furnace walls are covered by insulation,
especially blast furnace and reheating furnace in steel industry require insulation
suitable for withstanding high temperature. The interior of high temperature
furnaces of steel industries are generally covered with ceramic fibres. Earlier,
dense fireclay bricks were used for lining in heat treating furnaces, ceramic kilns
and brick kilns. Later on, insulating firebrick has been employed for the reason of
lighter weight coupled with improved insulating properties. The recent
replacement by ceramic fibre material from layers alumina and silica in the form
of blanket, works as a superior insulator and is used as the lining of furnaces.
However, as a result of high temperature effect, the shrinkage effect of the fibre
blanket causes the deterioration of insulating properties due to the reduction of
the gap between the ends of the blankets or modules.
Also, development of hybrid ceramic was attempted to achieve further
improvement in insulation system which posed serious problem with the uniform
arrangement of all the components. Commercially available SOLIMIDE polyimide
foams, combined with a variety of vapor barriers, coatings and facings has been

found to provide long lasting, lightweight thermal/ acoustic insulation packages
with superior fire resistance and it offers an advantage over the competitive
traditional insulation materials, making them the products suitable for critical
solutions aboard marine vessels, and aircrafts and in industries worldwide.
Another commercial insulations, Foamfrax, which is used for insulation of metal,
refractory and ceramic fibre surface, is enabled to withstand a higher
temperature of 1345°C and offers good lining performance. Instead of using
conventional blanket or module linings, monolithic insulation consisting of bulk
ceramic, an inorganic binder (colloidal silica) and an organic foaming binder, is
used for upgradation / repair of existing furnace surface linings.
Apart from insulating materials, phase change materials (PCM) are known to be
utilized for insulation purposes in buildings where the phase change materials are
incorporated inside the brick cavities. Phase Change Materials (PCM) are latent
heat storage materials, which work on the principle of "Passive Cooling", i.e.,
they absorb heat while melting and the source temperature rises, the chemical
bonds within the PCM break up with the material changing their phase

from solid to liquid, and release the same while solidifying. The phase change is
a heat-seeking (endothermic) process and therefore, the PCMs absorb heat. Or,
in other words, they release or absorb large quantities of (latent) heat during the
change of phase or state. The PCM thermal heat transfer control system used in
many purposes consists primarily of a container filled with PCMs and the PCM will
absorb excess heat through melting. During the decrease of the temperature,
the heat flow reverses from PCM and PCM solidifies. The latent heat associated
with the phase change provides a large thermal inertia as the temperature of the
equipment passes through the melting point. During the addition or subtraction
of the heat from the phase change material, its temperature remains constant on
reaching the phase transformation point until the transformation of material is
completed. There is no change in temperature change in the PCMs during the
addition or removal of latent heat, by definition.
Only recently, the PCMs have been used as a storage media for space cooling.
Apart from the use of ice as a commercial PCM for years, Paraffin wax is the
most-used commercial organic heat storage PCM. The ideal PCM would have the

features such as high heat of fusion. Patented microencapsulated phase change
materials (PCM) incorporated inside textile fibres [7] improves the thermal
performance of textile fibres and the encapsulated PCMs, can dramatically
increase the capacity of materials to store energy. Apart from the above, it has
been found that the phase change materials have been tested for the thermal
insulation in the bricks used for large building especially, where a molecular alloy
resulting from the blend of three normal alkanes: hexadecane (C16H34),
heptadecane (C17H36) and octadecane (C18H38) has been employed as phase
change material.
US patent No.4598005 discloses a thermal insulation with a double-walled
housing, between the two hosing of which an evacuated space is provided which
contains fibre like insulating material. The insulated material is comprised of two
different glass materials and can withstand temperature above 400 degree
Celsius.

US patent No.5017209 describes a thermal insulation comprising of plural
anisotropic parts which uses its anisotropy property in heat transfer around a
cylindrical heater for a furnace. The insulation comprised of plural anisotropic
parts arranged in such a way that the direction along which thermal conductivity
is low retards the heat transfer from a direction along which the thermal
conductivity of another part is high for the another part.
US patent 5626936 describes a phase change insulation system where one side
is exposed to high temperature change while the other side is exposed to a very
low temperature change. The insulation system contains an intermediate layer
containing phase change material sandwiched between one thicker insulation
layer and a thinner insulation layer and the phase change material is generally
subjected to a phase change between solid and liquid.
In many instances, materials used for conventional insulation are fibres, powder
or foams. The reason for their use is that they suppress the convection that
arises from the partition of the insulation spacings into the pores. Insulation
materials used for cryogenic purposes may be divided into three categories

based on their thermal conductivity. The first category is around 30 mW/m-K for
materials at ambient pressure, while second one is about 1.5 mW/m-K for bulk
fill materials at good vacuum, and below 0.1 mW/m-K at high vacuum. However,
it is quite difficult to maintain vacuum.
Non-asbestos Calcium Silicate, Cellulose insulations, Fibre glass insulation and
mineral wool Polyurethane insulation, Polystyrene Insulation are also used as
insulation. Non-asbestos Calcium-silicate is used for the reason of its low thermal
conductivity.
Very few efforts on experimental work dealing with insulation of such a high
temperature of furnace has been found in reality.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an insulation system for
protecting enclosure of electronic devices operating under high temperature of
1200-1400°C for retarding the heat flow from high radiating -environment.

Another object of the invention is to propose an insulation system for protecting
enclosure of electronic devices operating under high temperature of 1200-
1400°C for retarding the heat flow from high radiating hot environment, which is
enabled to retard heat flows from a high temperature of around 1200°C to a
temperature of about 60°C in an innermost space of an enclosure across a
thickness of 30-40 mm.
A still another object of the invention is to propose an insulation system for
protecting enclosure of electronic devices operating under high temperature of
1200-1400°C for retarding the heat flow from high radiating hot environment,
which maintains an innermost space of an enclosure unaffected from high
temperature of 1200°C.
A further object of the invention is to propose an insulation system for protecting
enclosure of electronic devices operating under high temperature of 1200-
1400°C for retarding the heat flow from high radiating hot environment, which is
capable of achieving a sharp drop in temperature or the temperature gradient.

Yet another object of the invention is to propose an insulation system for
protecting enclosure of electronic devices operating under high temperature of
1200-1400°C for retarding the heat flow from high radiating hot environment, in
which the insulation material used constitutes a combination of high insulating
materials and phase change material to maintain the temperature of the
innermost space at a room temperature of 60 degree Celsius.
A still further object of the invention is to propose an insulation system for
protecting enclosure of electronic devices operating under high temperature of
1200-1400°C for retarding the heat flow from high radiating hot environment,
which prevents the hot gases from the hot-medium or harsh environment of
1200 to 1400 degree Celsius to come into direct contact with the innermost
spaces maintained at 60-80 degree.
Yet further object of the invention is to propose an insulation system for
protecting enclosure of electronic devices operating under high temperature of
1200-1400°C for retarding the heat flow from high radiating hot environment, in
which the phase change materials augment the retardation of heat transfer.

SUMMARY OF THE INVENTION
According to the invention, the heat conductivity of used ceramic fibre is selected
in such a manner that the lowest possible thermal conductivity can be achieved,
and the selected ceramic fibre is placed in such a manner so as to achieve a
sharp temperature gradient across the smallest possible thickness in an
enclosure containing electronic device and back up battery. Thus, the inventive
system is intended to protect an electronic device for data acquisition inside an
enclosure, the enclosure being operable inside a high temperature furnace of
1200 to 1400 degree Celsius. The system is also designed to maintain the
innermost space of the enclosure at a room temperature of 60 degree Celsius.
The present invention illustrates the construction of a heat resistant enclosure to
use it as an insulated system which is enabled to act as repository for electronics
devices at a room temperature of 60 degree Celsius, such as, data acquisition
system and a battery. This ensures the safety and longevity of the instruments at
a high temperature of 1200-1400 Degree Celsius, or the environment similar
to the conditions of a reheating furnace.

Accordingly, the invention provides a thermal barrier that is enabled to protect
the electronics devices such as microprocessor and its battery backup. This
barrier sustains the inner temperature at around its operating temperature of the
electronics (0 to 60 C) for a period of 4-5 hours while outside environment
temperature is about 1200-1400 C. The thermal barrier is designed on the basic
principles of thermal insulation and heat absorption due to phase transformation.
According to the invention, the system comprises of a heat insulating unit,
containing layers of insulating materials, and a combination of insulating
materials and phase change material. The temperature gradient is quite stiff in
view of substantial temperature difference across the thickness of the enclosure
considered.
The steps in the cooling method involved are:
• providing an enclosure;
• configurating a cover for the enclosure to access from outside;

• selecting insulating materials including the thickness to be built-up;
• applying the combinations of insulating materials;
• applying the layers of phase change materials (PCMs);
• exposing the unit to severe high temperature environment; and
• checking the operation of the electronic device along with the
battery back up.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - represents a generic illustration of heat transfer through a composite
wall by conduction, radiation and phase change materials.
Figure 2 - represents a block diagram of an insulation system according to the
invention.

DETAILED DESCRIPTION OF THE INVENTION
An enclosure, as shown in Fig.2, is prepared from stainless steel (SS-316)
material. Commercially available insulating materials are used for insulating
purpose. The present invention will be better understood from the following brief
description of the system in conjunction with the reference to the accompanying
drawings, viz. Fig. 2.
Referring to Fig. 2, there is an enclosure where outside chamber and four inner
layer chambers have been provided. A metallic enclosure, fabricated from
stainless steel (SS) material, is used in the form of a cylindrical shape where the
height is relatively smaller. Initially, 2-3 layers of commercially available
insulating materials is packed to form the material next to the outside boundary
of the metallic body, which is exposed during the operation to the direct high
temperature environment of 1200-1400 degree Celsius. There are layers of
ceramic fibres where the fibres have different thermal properties. In addition to
the layers of conventional insulating materials, phase change materials have

been used to augment the retardation of heat transfer from harsh outside
environment. There will be temperature drop across the insulating materials
followed by movement of the heat in the region of phase change materials.
Ultimately, the inner most space is targeted to achieve a temperature of 60
degree Celsius. The inner most space is a space where the electronic device or
the data acquisition device and the battery of size AA can be fitted easily.
In all above mentioned cases, the high temperature ceramic fibres with the4
capability of resisting high temperature have been used.
REFERENCES
[1] K. Naplocha, K. Granat, The structure and properties of hyhrid performs
for composites, Journal of Achievements in Materials and Manufacturing
engineering, Vol. 22, Issue 2, June 2007, pp. 35-38.
[2] US patent 5017209, High temperature furnace with Thermal insulation, I
Yoshimura.

[3] US patent 4598005, Thermal Insulation, B. Ziegenbein., July 1,1986.
[4] US patent No. 5626936, May 6, 1997, Phase change insulation system,
Robert J. Alderman,
[5] Futschik, M.W.,1993, "Analysis of Effective Thermal Conductivity of
Fibrous Materials," M.S.E. thesis, University of Houston, Houston, TX, USA.
[6] Thermal Insulation of Buildings using Phase Change Materials, V.
Metivaud, L. Ventola, T. Calvet, M.A. Cuevas-Diarte, D. Mondieig, 6th Expert
Meeting and Workshop of Annex 17, 2004-06-07—09, Arvika, Sweden.
[7] Bryant YG, Colvin DP. Fibers with enhanced reversible thermal energy
storage properties, Techtextile Symposium, 1992.p.l-8.

WE CLAIM:
1. A system of insulating an enclosure accommodating electronic devices
operating at high temperature between 1200-1400°C by adapting different layers
of high performing insulating materials and phase change materials, the system
comprising:
an enclosure made of an innermost chamber, an intermediate
chamber and an outer chamber, the innermost chamber being the
space for disposing the electronic devices along with the
accessories;
an intervening space between the inner chamber and an outside
boundary of the system filled with combinations of insulating
materials and phase change materials (PCMs).
2. The system as claimed in claim 1, wherein the innermost chamber is an
open space and invisible from outside the system, the open space chamber
arranged to accommodate the electronic device or data acquisition device along
with the accessories.

3. The system as claimed in claim 1, wherein the insulated enclosure is
enabled to sustain an external environment of 1200-1400 degree Celsius.
4. The system as claimed in claim 1 and 2, wherein the inner chamber in
combination with insulating means maintains the temperature of the innermost
hollow space, which houses the electronic devices at a maximum temperature of
60 degree Celsius.
5. The system as claimed in claim 1, wherein the system is augmented to
have a higher heat insulating power by the addition of said phase change
materials (PCMs) through a mechanism of heat absorption during the phase
transformation.
6. A method in a system to maintain electronic devices operating under high
temperature between 1200 to 1400°C, the method comprising the steps of:

• providing a thermocouple enclosure;
• configurating a cover for the thermocouple enclosure to access
from outside;

• selecting an insulating material including the thickness to be built-
up;
• applying the combinations of insulating materials;
• applying the phase change materials;
• exposing the unit to severe high temperature environment; and
• checking the operation of the electronic device along with the
battery back up.
7. A system of insulating an enclosure under accommodating electronic
devices operating high temperature between 1200-1400°C by adapting different
layers of high performing insulating materials and phase change materials and
the system substantially as herein described and as illustrated in the
accompanying drawings.

A system of insulating an enclosure accommodating electronic devices operating
at a temperature of 60 degree Celsius while the temperature outside of the
enclosure is as at high temperature between 1200-1400°C by adapting different
layers of high performing insulating materials and phase change materials, the
system comprising: an enclosure made of an innermost chamber, one or more
than one intermediate chambers and an outer chamber, the innermost chamber
being the space for disposing the electronic devices along with the accessories;
an intervening space between the inner chamber and an outside boundary of the
system filled with combinations of insulating materials and phase change
materials (PCMs).
FIG. 2