Abstract
When producing ice in ice ponds with layer-by-layer applications of constant thickness water sheets, the simplest method to determine water spray intervals is obtained by considering the amount of “coldness”. This study considered that both outdoor air temperatures and wind velocities affect ice formation rate greatly, and we developed equations of the relationships by experiments. A computer program to automatically control water spray intervals with the newly introduced coldness values was developed, and the study yielded the following results:
1) The degree hours of frost on the ice surface to freeze a water sheet decreases exponentially with wind velocity at the ice surface.
2) The 1.5m-height outdoor temperature and the 3m-height wind velocity yields a similar relationship between wind velocity and degree hours of frost necessary for freezing a, water sheet.
3) The overall heat transfer coefficient increases with outdoor wind velocity, mainly because the convection heat transfer coefficient increases with wind velocity. Changes in nocturnal radiation due to cloud cover accounts for about 10% of the variation in overall heat transfer.
4) A factor evaluating coldness (Fe) considering the contribution of wind velocity (V) on the ice formation is expressed by Fe=2.370V0.288. A temperature-wind integrated number, TWIN, is defined by multiplying the degree hours of frost by Fe. The TWIN value required for freezing a unit thickness of water is 8.6K·h·mm-1.
5) The computer program for automatically controlling spray intervals during ice making operates in two modes. The ice-making mode is usually employed and the time to complete freezing of a water sheet is estimated with TWIN, to trigger the following water application. During snow falls the program changes to the snow-melting mode and snow is melted by the water spray to form slush, and the following water application takes place after the TWIN necessary for freezing the equivalent thickness of sprinkled water is reached.
6) This program controls water spray intervals in ice-pond ice-making systems according to outdoor temperature and wind velocity, and results in effective ice production.
