Title of Invention	"AN AIR COOLING DEVICE"
Abstract	This invention relates to an air cooling device with a capacity to cold hot ambient air (upto 50°C) to 37°C without using any conventional methods of cooling like water evaporation or compression-expansion cycle of fluoro carbon gases.

Full Text

FIELD OF INVENTION : The present invention relates to an air cooling device based on phase change material (PCM). PRIOR ART: Air cooling is essential during summer in tropical hot regions to provide comfort to human beings. It is also required to withdraw heat from certain heat generating devices like electrical/electronic equipments for their safe and efficient operation. Conventional air cooling methodologies are based on compression - expansion cycles of fluoro-carbon gases, as utilised in air conditioners or on heat loss by water evaporation, as utilised in air cooler. One of the disadvantages of conventional air cooling devices based on electrical compression expansion cycle of gases is their high requirement of electrical power. Another disadvantage of these devices is that they are quite expensive. Yet another disadvantage of these devices based on compression expansion cycle of gases is that they are not suitable in field conditions. Another type of conventional air cooling devices are based on water evaporation. The main disadvantage of water based air cooling device is their requirement of water which may not be available due to water shortage in field conditions. Another disadvantage of water based air cooling device is that they increase level of humidity in cooled air hence they become ineffective when atmospheric humidity and temperature rises beyond a certain limit. Yet another disadvantage of water base air cooling device is high corrosion of the metallic bodies, requiring regular high maintenance. The other cooling devices are made by using Phase change material (PCM) which absorb a good quantity of heat during phase change. The absorbed heat is released back in environment when environment temperature falls below phase change temperature. This phase change can be solid to solid or solid to liquid, reversible or irreversible. Thus PCM does not require compression - expansion cycles of fluoro-carbon gases or water evaporation, and can be used for controlling heat in limited volumes. According to US patent No. 6,241,910 PCM like formaldehyde (methanol), acetaldehyde (ethanol), propanaldehyde (Propanal), n-butyraldehyde (butanal), benzaldehyde, p-nitrobenzaidehyde, o-tolualdehyde etc. have been used for absorbing heat from a heat generating source like electronic/electrical equipment by placing the material inbetween heat generator and heat sensitive device. According to yet another US patent No. 6235216 the increase of temperature in heat sensitive device showing heat generating conditions is prevented through the absorption of heat by providing a bicarbonate salt such as Lithium bicarbonate, sodium bicarbonate etc. Here irreversible decomposition reaction have been used for one time heat absorption purpose. Yet another US patent No. 6181558 describe use of micro-encapsulated PCM for heat absorbing in electrical apparatus which produce heat while in operation. The main disadvantage of above phase change materials is that phase transformation temperature of materials used does not lie within natural ambient temperature cycle (33°C-50°C) observed during hot summer days. Thus the material is not suitable for ambient air cooling. Yet another disadvantage of many PCM known in the art, is their irreversible nature of phase change which makes them unsuitable to repetitive heat absorption purposes as needed in ambient air cooling devices. OBJECTS OF INVENTION The main object of the present invention is to provide an air cooling device which utilize phase change material (PCM), as heat absorbing material. Another object of the present invention is to provide an air cooling device which requires around 60-100 watt of electricity only. Still another object of the present invention is to provide an air cooling device which facilitate transfer of heat from hot ambient air to phase change materials used as heat sink. Yet another object of the present invention is to provide an air cooling device which cools hot air upto 50°C to 37°C Further object of the present invention is to provide an air cooling device wherein the phase change material can be used repeatedly. Yet further object of the present invention is to provide an air cooling device which does not require any water. Still further object of the present invention is to provide an air cooling device which can be used in field conditions with temperature about 50°C. STATEMENT OF INVENTION: According to this invention there is provided an air cooling device based on phase change material comprising of a heat exchanger cum heat sink unit and an electrical air blowing unit; the said heat exchanger cum heat sink unit comprising of an and inner casings shielded from an metallic outer casing by a heat insulating material' the said metallic inner casing having phase change material disposed therein, a heat exchange tube disposed within said inner casing and connected to a blower. The device of the present invention utilizes phase change materials as heat absorbing media and it absorbs heat from hot air during day time and releasing back stored energy to environment during night time. The phase change temperature of these materials lies inbetween temperature range observed in daily ambient temperature cycle of hot summer day in tropical regions. In the present device a copper heat exchanger is surrounded by suitable phase change material such as hydrated salts of zinc and calcium. When hot ambient air (around 50°C) during summer day time is passed through heat exchanger with the help of a normal conventional electric fan or air blower, the heat from hot air is exchanged through heat exchanger wall to surrounding phase change materials and cooled air (below 40°C-35"C) comes out of heat exchanger. Exchanged heat is stored in phase change material as its latent heat of phase transformation. Quantity of phase change material is calculated so that it is capable of absorbing heat as latent heat through out the long summer day when ambient temperature is above phase transformation temperature of PCM. During night when ambient temperature falls below phase transformation temperature of PCM, heat flows back to environment and PCM returns back to its original phase to be reused again next day. The PCM selected and its quantity and design of device is such that all the heat stored in PCM as latent heat during day time is compulsorily released back to environment during night time. DESCRIPTION OF FIGURES: The design of air cooling device as claimed in the present invention is illustrated by the accompanying figures where in: Figure-1 shows the schematic view of air cooling device. Figure- U(a) shows the sectional top view of heat exchanger. Figure- II(b) shows the sectional front view of heat exchanger. DETAILED DESCRIPTION WITH RESPECT TO DRAWINGS : Referring to figure-I, the air cooling device based on phase change material comprises of a heat exchanger cum heat sink unit (1) and an electrical air blowing unit (2). Referring to figure- ll(a) and figure-II(b), the air cooling device based on PCM consists of two metallic casings, an outer casing(8) and an inner casing(6) made preferably of aluminium A heat insulating layer(5) in between the two metallic outer casing(8) and inner casing(6), preferably glass wool, to stop heat inflow from outside environment. The metallic inner case(6) is filled with phase change material(7) as a heat sink. Any phase change material such as Calcium chloride hexahydrate, Calcium bromide hexahydrate, Arsenic bromide, 1- Methycyclopentanol, 2,2-Dimethylpropanoic acid, P-Cresol, M-nitroanisol and preferably Calcium nitrate hexahydrate, having phase transformation (solid to solid or solid to liquid) temperature within 30°C- 40°C is used in present air cooling device. A heat exchange tube (3) made of heat conducting material preferably copper is immersed in the PCM surrounding. Copper fins (4) are attached to the copper tube which extend into the PCM, to facilitate heat transfer from the air flowing inside the tube to the PCM. The phase change materials(PCM) used preferably are hydrated calcium nitrate Ca(NO3)2 6 H2O having solid to liquid phase transformation at 39.7°C, hydrated zinc nitrate Zn (NO3)2 4H2O with phase change temperature 36.4°C, paraffin hydrocarbons having phase change temperature 30°C-40°C, n-Heneicosane having phase change temperature 40.5°C, N-Ei cosane having phase change temperature 36.8°C. Preferably a mixture of hydrated calcium nitrate and zinc nitrate in the ratio (by weight) of 2:1 to 6:1 preferably 5:1 which gives maximum heat absorption around 37°C is used as the PCM. The amount of PCM (m) to be used as heat sink in the heat exchanger is calculated as, m = Rate of heat transfer through the heat exchanger (KJ/hr.) X Total duration of operation per day (hr.)/ Latent heat of phase transformation (solid to liquid) of the PCM (KJ/Kg) The length of the copper tube is calculated based on the total heat transfer area required to obtain a maximum temperature drop of 13°C (50°C - 37°C = 13°C) for desired air flow. Reynold's number is calculated for the desired air flow by using following formula:- Re = PVd (1) M. where, P = density of air V = velocity of air d = dia of the tube µ = co-efficient of viscosity Depending upon value of Reynold number nature of air flow (laminar/semi turbulent/ turbulent) is decided and for that particular type of flow average heat transfer coefficient (U) of air for copper surface is calculated using formula :- U - NuxK/d (2) where, Nu = Nusselt Number K = thermal conductivity of air Total heat transfer area required for desired cooling is calculated using formula :- Q - U A (Ata - ATb) / In A Ta/A Tb) (3) where , A Tb, A Ta = temperature difference between two heat exchanging materials at outlet and inlet of the tube respectively = rate of heat transfer through the heat exchanger. From desired heat transfer area length of the tube required is calculated for a given diameter tube from A=TtDL - (4) where, L = Length of tube D = diameter of tube It is to be understood that the present invention is susceptible to modifications, adaptations, changes by those skilled in the art. Such modifications, adaptations, changes are intended to be within the scope of the present invention., which is set forth under the following claims: WE CLAIM 1. An air cooling device based on phase change material comprising of a heat exchanger cum heat sink unit (1) and an electrical air blowing unit (2), the said heat exchanger cum heat sink unit (1) comprising of an and inner casings (6) shielded from an metallic outer casing (8) by a heat insulating material (5), the said metallic inner casing (6) having phase change material (7) disposed therein, a heat exchange tube (3) disposed within said inner casing and connected to a blower. 2. An air cooling device as claimed in claim 1 wherein said phase change material comprises Calcium nitrate hexahydrate, preferably a mixture of Calcium nitrate hexahydrate and Zinc nitrate tetrahydrate mixed in the ratio (by weight) of 2.1 to 6:1 preferably in the ratio of 5:1 as phase change material. 3. An air cooling device wherein the said heat exchange tube (3) has fins (4) extending onto said material. 4. An air cooling device substantially as herein described and illustrated herein.

Documents:

734-DEL-2003-Abstract-(05-03-2008).pdf

734-del-2003-abstract.pdf

734-DEL-2003-Claims-(05-03-2008).pdf

734-del-2003-claims.pdf

734-DEL-2003-Correspondence-Others-(05-03-2008).pdf

734-del-2003-correspondence-others.pdf

734-del-2003-correspondence-po.pdf

734-DEL-2003-Description (Complete)-(05-03-2008).pdf

734-del-2003-description (complete).pdf

734-del-2003-drawings.pdf

734-del-2003-form-1.pdf

734-del-2003-form-18.pdf

734-DEL-2003-Form-2-(05-03-2008).pdf

734-del-2003-form-2.pdf

734-DEL-2003-Form-3-(05-03-2008).pdf

734-del-2003-form-3.pdf

734-del-2003-gpa.pdf