Phase change material pack

Abstract

A phase change material (PCM) pack ( 1 ) for an air conditioning system comprises phase change material sealed between a first thermally conductive layer ( 2 ) forming a first outer surface of the PCM pack and a second thermally conductive layer ( 2 ) forming a second outer surface of the PCM pack. At least the first or second outer surface of the PCM pack takes the form of a substantially planar surface having defined therein a plurality of depressions ( 4 ) deviating from the planar surface towards the interior of the PCM pack in a direction perpendicular to the planar surface. The depressions improve heat transfer between the pack and an airflow passing over the surface of the PCM pack.

1 . A phase change material (PCM) pack for an air conditioning system, the pack comprising phase change material sealed between a first thermally conductive layer forming a first outer surface of the PCM pack and a second thermally conductive layer forming a second outer surface of the PCM pack, wherein at least the first or second outer surface of the PCM pack takes the form of a substantially planar surface having defined therein a plurality of depressions deviating from the planar surface towards the interior of the PCM pack in a direction perpendicular to the planar surface. 
     
     
         2 . A PCM pack as claimed in  claim 1 , wherein both the first and second outer surfaces of the PCM pack each take the form of a substantially planar surface having defined therein a plurality of depressions deviating from the planar surface towards the interior of the PCM pack in a direction perpendicular to the planar surface. 
     
     
         3 . A PCM pack as claimed in  claim 1 , wherein the plurality of depressions is arranged in a regular array over the outer surface. 
     
     
         4 . A PCM pack as claimed in  claim 1 , wherein each outer surface of the pack provided with said depressions comprises at least ten depressions. 
     
     
         5 . A PCM pack as claimed in  claim 1 , wherein the depressions occupy more than 15% of the planar surface area of the outer surface provided with said depressions. 
     
     
         6 . A PCM pack as claimed in  claim 1 , wherein the planar surface area of the outer surface occupied by each depression is less than 5% of the total planar surface area of the outer surface. 
     
     
         7 . A PCM pack as claimed in  claim 1 , wherein the maximum depth of each depression in the direction perpendicular to the planar surface of the PCM pack is less than 75% of the square root of the planar surface area of the outer surface occupied by the depression. 
     
     
         8 . A PCM pack as claimed in  claim 1 , wherein the maximum depth of each depression in the direction perpendicular to the planar surface of the PCM pack is greater than 10% of the square root of the planar surface area of the outer surface occupied by the depression. 
     
     
         9 . A PCM pack as claimed in  claim 1 , wherein the cross section of each depression in a plane perpendicular to the planar surface of the pack forms a smooth curve. 
     
     
         10 . A PCM pack as claimed in  claim 1 , wherein the depressions have a substantially circular shape in the plane of the planar outer surface. 
     
     
         11 . A PCM pack as claimed in  claim 1 , wherein the depressions are defined by a substantially spherical surface. 
     
     
         12 . A PCM pack as claimed in  claim 1 , wherein the phase change material comprises at least one of a salt hydrate, urea or paraffin. 
     
     
         13 . A PCM pack as claimed in  claim 1 , wherein the phase change material has a melting point in the range −5 to 35 degrees centigrade. 
     
     
         14 . A PCM pack as claimed in  claim 1 , wherein the thermally conductive material comprises aluminium or stainless steel. 
     
     
         15 . A PCM pack as claimed in  claim 1 , wherein the thermally conductive material comprises a metal-plastics composite. 
     
     
         16 . An air conditioning system comprising a plurality of PCM packs as claimed in  claim 1  arranged in a stack with spacing between adjacent packs to allow air flow over the outer surface of each pack. 
     
     
         17 . An air conditioning system as claimed in  claim 16 , wherein the maximum depth of each depression in the direction perpendicular to the planar surface of each PCM pack is less than 75% of the spacing between adjacent packs. 
     
     
         18 . An air conditioning system as claimed in  claim 16 , wherein the maximum depth of each depression in the direction perpendicular to the planar surface of each PCM pack is greater than 25% of the spacing between adjacent packs.