Heat is transferred from the ice surface to the cold air by evaporation, Q evap , and also by melt-water runoff, Q melt . The efficiency of the radiant heaters is affected by wind, height, and the geometric shape factor. This shape factor is the fraction of the radiant energy produced by the heater elements which actually reaches the ice to melt it. Considering the geometric shape factor and the measured melt rates with the latent heat required, overall efficiencies ranged from about 5 to 15 percent for these tests. During cold weather, they are lowered to about 3 ft above the ice, where the ice can be prevented from growing.
Care is taken to prevent water spray from getting on the heater elements.
Given the required circumstances, ice can grow from 4 to 12 in. around the gear area. This accumulation can be melted off in about a day with the heater setup being used at this facility. At Lock and Dam 10, radiant heaters are being used on four roller gates. Without the heaters, water-level changes cause ice formation in this area. At Lock and Dam 9, radiant heaters have been placed near the gear area and also around the seals just above the roller gates.