Minimising frost growth on cold surfaces exposed to humid air by means of crosslinked hydrophilic polymeric coatings

Experiments have shown that frost growth on cold surfaces exposed to warm humid air streams can be reduced significantly by means of crosslinked hydrophilic polymeric coatings. This derives from the ability of these materials, under frosting conditions, to absorb available water, and hence retard the growth of frost when compared to an uncoated metallic surface. The extent of reduction of frost growth appeared to vary with the water absorbing potential of the polymer-coat, as well as its water content prior to frosting. In general, measurements in over two hours of testing, indicated that the reduction in frost growth rate and subsequently frost thickness lies in the range, 10-30%. The absorbed water improves the thermal conductivity of the polymeric coating. This, consequently, lowers the total thermal resistance between the air stream and the cold plate, and hence retards the frost surface temperature in its rise towards 0 degrees C, an effect that would prolong the effective operation time of the thermal process before there is need for defrosting. Further observations made in this study tend to suggest that the nature of the frost formed with an air stream of low relative humidity (RH) differed from that resulting from a high RH air stream. (C) 2000 Elsevier Science Ltd. All rights reserved.