6.Ill VI.I.6: WATER H 2 0 is selected primarily for safety reasons, and for its high critical temperatue (647°K}. Its disadvantages are low pressure in the temperature range anticipated in the evaporator, and low molecular weight, which causes a high leakage rate. From a temperature entropy diagram for steam (6.17} and steam tables (6.IB}: State 1: dry saturated vapor p 1 Pevap = .15 psia h 1 1055 Btu/lbm s 1 = 2.14 Btu/lbm- 0 R State 2: superheated vapor . T 2 = 1088°K (picked to have the radiator inlet temp. as high as possible} p 2 prad = 60 psia h 2 1810 Btu/lbm s 2 = s 1 = 2.14 Btu/lbm- 0 R State 2': dry saturated vapor T 2 ,= 418°K (less than the critical temp. 647°K}
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