CLIAMS:I/We claim:
1. A solar air-heater comprising:
a multi-wall sheet 101;
a plurality of composite conduits 102, positioned below the multi-wall
sheet 101, wherein the plurality of composite conduits are placed in
a multilayer form;
a fluid inlet 103, integrated into a side frame 107, along either width or length of the multi-wall sheet 101;
a mesh filter 104 is releasably fixed between the side frame 107 and an insulation panel 106b;
a central hot fluid header 105 positioned at the centre or with an offset with respect to the multi-wall sheets 101, and connecting the plurality of composite conduits 102; and
a plurality of rigid insulation panels like 106a and 106b enclosing the plurality of composite conduits102.

2. The solar air-heater as claimed in claim 1, wherein said multi-wall sheet 101 is bent at an angle, wherein the bend is adjacent to the side and constitutes to a depth of the solar air heater.

3. The solar air-heater as claimed in claim 1, wherein the composite conduits 102 are positioned below the multi-wall sheet 101 parallel to a longer length of solar air heater .

4. The solar air-heater as claimed in claim 1, wherein the composite conduits 102 are positioned below the multi-wall sheet 101 parallel to a shorter length of solar heater.

5. The solar air-heater as claimed in claim 1, wherein the composite conduits 102 are fabricated in a form of a tubular passage, or an extruded section

6. The solar air-heater as claimed in claim 5, wherein the plurality of composite conduits 102, either individually located or interlocked with each other, further comprise an outer surface.

7. The solar air-heater as claimed in claim 6, wherein the outer surface has a corrugated structure.

8. The solar air-heater as claimed in claim 5, wherein the plurality of composite conduits, either individually located or interlocked with each other, further comprise an inner surface.

9. The solar air-heater as claimed in claim 8, wherein the inner surface has internal fins.

10. The solar air-heater as claimed in claim 1, wherein the multi-wall sheet/s 101 is made from at least one material selected from a polycarbonate, or a translucent plastic, or a glass, or aerogel insulation.

11. The solar air-heater as claimed in claim 1, wherein the plurality of composite conduits 102 are made from at least one material selected from a blackened aluminium, or copper, or iron, or stainless steel, or alloys of aluminium, copper or iron, or plastic.

12. The solar air-heater as claimed in claim 1, wherein the plurality of rigid insulation panels 106 are made from at least one material selected from a Polyisocyanurate, or a Polyurethane Foam, or a Phenolic Foam and lined with at least one material selected from a thin sheet of paper, or metal foil, or plastic film as cover.
13. The solar air-heater as claimed in claim 1, wherein said side frame 107 is mounted on atleast two sides of solar air heater.

14. The solar air-heater as claimed in claim 1, wherein said mesh filter 104 is in multi-layered form made from at least one material selected from metal, or plastic, or ceramic fibre.

15. The solar air-heater as claimed in claim 1, wherein said central hot fluid header 105 have at least one hot air outlet/s 108 through which hot air is drawn out from the solar air heater.
,TagSPECI:Field of Invention:

The present disclosure relates generally to a solar heater and more specifically to a light weight solar air-heater.

Background of the Invention:

Presently various methods and alternative configurations have been tried to subdue some of the drawbacks associated with conventional solar air heaters. Some of the drawbacks of the conventional solar air heater are high top losses resulting from high absorber surface temperature due to low air side heat transfer coefficients, or reduced efficiency of solar air heaters, or limited rise in temperature of air across a single solar air heater panel due to moderate to high air velocity, or high pressure drop on air side resulting in increased blower/fan power and thereby increased initial investment, or high weight and cost due to the presence of inlet and outlet headers, or heat transfer surface enhanced by use of perforated sheets, corrugated sheets, turbulators, usually made of metal, or presence of metallic plate as back cover for supporting insulation and protecting the lower side of the collector panel, or need for decoupled heat transfer and pressure drop to achieve high heat transfer coefficients, high collector efficiency while reducing pressure drop in fluid passages.

Indian Patent Application No. 2792/MUM/2012, titled “A novel method and apparatus for double pass solar air heater” uses aluminium nets to enhance absorber area, thermal mass/heat capacity, heat transfer area and heat transfer coefficient as air passes through the net in a double pass air heater. Its performance is limited due to increased absorber area, which also reradiates absorbed energy; increase in air temperature and heat transfer coefficient will be limited due to very large air side flow cross section area and hydraulic diameter; this necessitates use of high velocities to realize reasonable heat transfer coefficients, due to this the pressure drop on air side will be high per unit temperature rise, this also increases parasitic power needed to heat air, fabrication is not very easy.

US Patent 4,085,729 by Schmidt, 1978 titled “Solar air heater” describes an improved low cost solar air heater which utilizes an array of holes or jets in an intermediate solar window to produce impingement of the air on the upper or solar energy absorbing surface of the absorber plate to enhance heat transfer efficiency and reduce convection losses from the system. This type offers limited temperature rise on air side.

US patent 4,019,494 by Safdari, 1977 titled “Solar air heater assembly” This discloses a solar heater assembly for heating air or other gases having increased efficiency in the transfer of solar energy falling on an assembly to a gas stream and to a heat exchange plate used in the assembly.

Indian patent 234,778 by Rane, 2010 “Flat plate solar fluid heating device”, this simple, light weight and energy efficient design is easy to install. It can deliver hot air at 20 to 40oC above ambient temperature at 50 to 60% efficiency.

US Patent 7,434,577 B2 by Doherty, 2008 titled “Solar air heater”, features a housing partitioned into essentially isolated sections wherein the sections are in fluid communication with each other through multiple channels located within the partition.

US Patent 8,555,872 B2 by Dolphin & Finney, 2013 titled “Solar heater”, for space heating discloses absorber plate directly molded into the frame and sealed by the frame and housing. Since air flow passages are formed by the space between the absorber plate and the housing flow cross section area is large and multiple solar heaters have to be deployed in series to enable heating air through large temperature rise, which will result in high pressure drop and high parasitic power requirement.

There is thus a requirement in the industry to mitigate some of the foregoing problems

Object of the invention:

It is the primary object of the present invention to provide a low cost light weight solar air-heater.

It is another object of the present invention to enhance the heat transfer in solar air-heater.

It is another object of the present invention to provide a solar air-heater with efficiency in the range of 50 to 80% while heating air from ambient to 75°C.

It is another object of the present invention to reduce the air velocities resulting in low pressure drop in solar air-heater.

Summary of the invention:

This summary is provided to introduce concepts related to systems and methods for a solar air heater and the concepts are further described below in the detailed description. This summary is not intended to identify essential features of the claimed subject matter nor is it intended for use in determining or limiting the scope of the claimed subject matter.

According to an aspect of the present disclosure a solar air-heater is disclosed. The solar air heater may comprise a multi-wall sheet 101 positioned on top of a plurality of composite conduits 102. The plurality of composite conduits may be placed a multilayer form, wherein the plurality of conduits are adjacent to each other in an interlocked, or in a non-interlocked form adjacent to an insulation layer. Further, the plurality of conduits 102 can be positioned below the multi-wall sheet 101 parallel to longer length of solar air heater or parallel to shorter length of solar air heater. The system may further comprise at least one fluid inlet 103, integrated into a side frame 107, along either the width or the length of the multi-wall sheets 101. Further a mesh filter 104 may be releasably fixed between the frame 107 and insulation 106b. Additionally another filter may be mounted auxiliary to the mesh filter either externally or internally for ease of removal, cleaning and refitting. The system may comprise a central hot fluid header 105 preferably positioned centrally with respect to the said multi-wall sheets 101, connecting the plurality of composite conduits 102. Further the solar air heater may comprise a plurality of rigid insulation panels 106a and 106b enclosing the plurality of composite conduits102.

Brief description of the Drawings:

Figure-1A shows isometric cut section of solar air-heater in accordance with an example embodiment.

Figure-1B shows enlarged view of section 1B in Figure-1A in accordance with an example embodiment.

Figure-1C is enlarged view of section 1C in Figure-1A in accordance with an example embodiment.

Figure-1D is enlarged view of section 1D in Figure 1A in accordance with an example embodiment.

Figure-2A shows isometric cut section of solar air heater with aluminium header and aluminium frame at all four sides in accordance with an example embodiment.

Figure-2B shows enlarged view of section 2B in Figure-2Ain accordance with an example embodiment.

Figure-2C is enlarged view of section 2C in Figure-2A in accordance with an example embodiment.

Figure-2D is enlarged view of section 2D in Figure-2A in accordance with an example embodiment.

Figure-3a shows cross sectional enlarged view of fluid passages on one of the sides of the solar air heater in accordance with an example embodiment.

Figure-3b shows side enlarged view of fluid inlet in accordance with an example embodiment.

Figure-4a shows a circular tubular composite conduit absorber with internal grooves in accordance with an example embodiment

Figure-4b shows a square tubular composite conduit absorber with internal grooves in accordance with an example embodiment

Figure-4c shows an extruded profile of composite conduit absorber with internal corrugations in accordance with an example embodiment.

Figure-4d shows an extruded profile of composite conduit absorber with internal corrugations and locking arrangement in accordance with an example embodiment.

Figure-4e shows an extruded profile of composite conduit absorber with internal and external corrugations and with locking arrangement in accordance with an example embodiment.

Figure-5 shows hot air outlet header in accordance with an example embodiment.

Detailed description of the invention:

The present disclosure relates to solar air-heater and is explained below with reference to the accompanying drawings in accordance with an embodiment of the present disclosure.

Figures 1A, 1B, 1C and 1D illustrate an aspect of the present disclosure. The solar air-heater comprises a multi-wall sheet 101 made of polycarbonate, translucent plastic, glass, or aerogel insulation. The multi-wall sheet 101 may be bent at an angle, wherein the bend is preferably along a longer side and may constitutes towards a depth of the solar air heater covering from top. The solar air heater may further comprise a plurality of composite conduits 102, placed in multilayer form. The plurality of composite conduits may be made from blackened aluminium, aluminium alloy, copper, copper alloy, iron, iron alloy, stainless steel, plastic or composite material as an absorber. The plurality of composite conduits 102 could be in a form of tubular passages or extruded sections, further a surface of the plurality of composite conduits 102 may be plain or corrugated. In an embodiment the surface is preferably corrugated so as to increase heat transfer surface area. Further, the solar air heater may comprise a fluid inlet 103 integrated in a side frame 107. The integration of fluid inlet into the side frame may enable heat transfer from the side frame to preheat the incoming fluid to be heated. The side frame 107 may be mounted on any two sides of the multi-wall sheet 101, with the top cover itself bent to form the side cover for the other two sides of the multi-wall sheet 101. Further the air solar heater may comprise at least one multilayer mesh filter 104 made of metal, or plastic, or ceramic fibre. At least one multilayer mesh filter may be located along the side frames 107 for air heating application. The solar air heater may further comprise a central hot fluid header 105. The solar air heater may be positioned centrally or at an offset with respect to the multi-wall sheet 101, and maybe connected to the plurality of composite conduits 102. To reduce heat losses the solar air heater may further comprises a plurality of rigid insulation panels 106a and 106b with thin metallic or paper or plastic foils as covers. A light weight rigid insulation sheets, of Polyisocyanurate – PIR, Polyurethane Foam – PUF, Phenolic Foam - PF, offer durable back support and eliminate the need for additional metal sheet cladding in solar air-heater.

Ambient air maybe taken in from bottom side of the solar air-heater through the mesh filter 104 and the fluid inlet 103 integrated in the side frame 107, which is painted black and this preheats the inlet air. Preheated air then enters in blackened plurality of composite conduits 102 and heated up to desired temperature, utilizing absorbed solar energy, in a single pass. Each composite conduit/absorber tube from plurality of composite conduits 102 may have semi rectangular slot at the centre along a length of the plurality of composite conduit to discharge/deliver hot air in central hot fluid header 105. The central hot fluid header may either be made from aluminium pipe or carved at a bottom of an insulation panel 106a. Central hot fluid header may have one or multiple hot air outlets 108 through which hot air maybe drawn out from the solar air heater.

In an embodiment the absorber area i.e. the surface area of the plurality of composite conduits maybe enhanced by using circular tubes with internal grooves or corrugated multiwall surface. This enables higher heat transfer area per unit aperture area, the enhancement is 2.5 to 6 times, that of heat transfer area i.e. 2.5 to 6 times the aperture area; this along with high heat transfer coefficients in the range of 27 to 60 W/m2.K are realized even in laminar flow regime due to reduced hydraulic diameter, which may range from 2 to 4.5 mm; typical temperature difference between a hot absorber surface and air is reduced by a factor of 2 to 3 which helps in reducing absorber surface temperature which in turn reduces top loss and increases solar air heater efficiency in the range of 50 to 80% while heating air from ambient to 75°C in a single pass.

Further effective decoupling of heat transfer coefficient and air velocity by operating in laminar flow regime enables reducing air flow rate per unit aperture area, while still achieving high heat transfer coefficients, which helps increase rise in temperature of air in a small length of absorber passage, this also reduces pressure drop and parasitic power required for air circulation.

High air flow cross-section area, absence of air inlet header and liberal sizing of hot air outlet header carved out in the insulation panel 106a along with low air velocity help reduce pressure drop.

Judiciously avoiding inlet header, integrating outlet header in the thick but light-weight foam insulation with sandwich construction having thin foil as the outer protective surface reduces the weight and cost, suitably bending the multi-wall top transparent cover eliminate the need for metallic frame on two sides of the solar collector panel, while eliminating the need to seal the two sides, also this helps reduce weight and cost, reduces back heat loss and increases collector efficiency.

Figures 2A, 2B, 2C and 2D illustrate another aspect of present disclosure wherein aluminium side frame 107 is mounted on all side of the solar Air heater. The multi-wall sheet 101 may cover a plurality of composite conduits 102 from top. The plurality of composite conduits may be placed in multilayer form, along the shorter length of solar air heater. Said composite conduits 102 may be fabricated from blackened aluminium, aluminium alloy, copper, copper alloy, iron, iron alloy, stainless steel, plastic or composite material as an absorber, wherein the plurality of composite conduits 102 could be in the form of tubular passages or extruded sections, also surface of the plurality of composite conduits 102 can be plain or corrugated, according to an embodiment the surface of the plurality of composite conduits is preferably corrugated to increase heat transfer surface area. A fluid inlet 103 integrated in the side frame 107 mounted on longer length of solar air heater enables heat transfer from the frame to preheat the incoming fluid to be heated. A one or multilayer mesh filter 104 made of metal or plastic or ceramic fibre may be located along the side frames 107 for air heating application, a central hot fluid header 105 is positioned centrally or at an offset with respect to the multi-wall sheet 101, connected to the plurality of composite conduits 102. To reduce heat losses the solar air heater may further comprise a plurality of rigid insulation panels 106a and 106b with thin metallic or paper or plastic foils as covers. A light weight rigid insulation sheets, of Polyisocyanurate – PIR, Polyurethane Foam – PUF, Phenolic Foam - PF, offer durable back support and eliminate the need for additional metal sheet cladding in solar air-heater.

Figure-3A shows cross sectional enlarged view of fluid passages on one of the sides of the solar air heater. Figure 3B illustrates side view of fluid inlet 103. Ambient air entering in the solar air heater is first passed through metallic, plastic or ceramic fibre based filter mesh 104 and then via fluid inlet 103. Fluid inlet is integrated in side frame 107 of solar air-heater.

Integrated fluid inlet 103 helps reduce side losses as ambient air entry section may be along the width of the solar air heater which maintains side frame temperature closer to ambient and thus convection losses are reduced. Blackened side frame may act as an absorber for beam as well as diffused solar radiation which preheats ambient air flowing through fluid inlet 103, integrated in the side frame107. Such preheating may help increase air temperature at collector outlet or increase volume flow rate of air through the device which in turn leads to increase in efficiency. Ends of the composite conduits 102 may have a 45° edge to increase the cross section area while air enters in the composite conduits. Increased cross section reduces air velocity which in turn reduces entry region pressure drop.

Figures 4A, 4B, 4C, 4D and 4E illustrates various extrusion profiles for composite conduits 102, they may have configurations like, tubular with or without inner grooves, corrugated tubular with or without internal fins, extruded profiles with corrugations with or without internal fins are used to reduce the hydraulic diameter of the air/fluid passages while maintain large flow cross section areas.

Reducing the hydraulic diameter helps increase heat transfer coefficients. Heat transfer coefficient is inversely proportional to area of cross section. Operating in the laminar flow regime with small hydraulic diameters enables realizing high heat transfer coefficients while keeping fluid velocities low. Keeping low fluid velocities enable keeping fluid pressure drop and circulation power low.

Figure 5 illustrates hot air outlet header 105. Hot air from each composite conduits is delivered in hot air outlet header105. Liberally sized polygonal cross section helps reduce pressure drop. It may be carved out in the insulation panel 106a which is primarily used to prevent heat loss. Multilayer rigid foam insulation sheets with aluminium, steel or plastic liner (preferably aluminium) on the exposed side helps assure weather protection while keeping the weight and cost low.

Example:

Assuming fluid flow passage of hydraulic diameter dh = 5 to 3 mm and constant heat flux condition where Nu = 4.36 = h dh/k.
If air is the working fluid then air side heat transfer coefficient, ha, in the range of 24 to 40 W/m2.K can be achieved with laminar flow regime.
As the flow velocities are reduced the fluid temperature rise from inlet to the outlet increases. Air temperature rise achieved in 0.5 to 1 m passage length of 3 to 5 mm hydraulic diameter has been in the range of 45 to 90oC. The pressure drop on the airside is as low as 20 Pa.

Since the pressure drop within the passages and passage length itself is very less, power required for working fluid circulator will be small and PV operated blower can be cost effectively deployed in off grid conditions.