Abstract
In general, ice growth during industrial manufacturing of ice is governed by heat conduction and/or heat convection. Although radiation cooling is observed in nature, e.g., ice formation on roads under cold conditions, radiation cooling has not been employed in the manufacture of ice. The aim of this research is to investigate ice growth under radiation cooling. First of all, an experimental setup is developed and tested. The experimental apparatus consists of a low-temperature heat source, a water tank, and an insulation box. The insulation box is placed between the cold heat source and the water tank in order to prevent conduction and convection of heat between them. The formation of frost on the cold heat source is prevented by reducing the pressure inside the insulation box. Experiments are carried out in a low-temperature room in which the temperature maintained at approximately 2℃. The ice formed is photographed at various stages of its growth using a CCD camera. The first crystal forms spontaneously several hours after the cooling is started. The ice growth rate is almost constant along the vertically direction, and the ice formed is approximately 20-mm thick after 40 h. The average growth rate of ice is found to be 0.56 mm h -1 . The ice formed appears to be almost perfectly transparent with no bubbles. A cross section of 50 mm × 50 mm of the ice is found to be composed of a single crystal with the c-axis along the vertical direction. The growth rate of ice under conduction cooling reduces with increasing ice thickness, although it under radiation cooling is maintained almost constant. Involving bubbles inside of the ice under radiation cooling is smaller than them under conduction cooling.
