Fig. 4-67. Radiator System Modeling Each block labeled "t" or "T' represents a parametric relationship. Longer blocks represent equations. The Greek letter rho indicates the ratio of the two inputs; the Greek letter pi indicates product. + and - indicate addition and subtraction. Blocks with the lower right hand corners shaded are independent input variables. Note that the radiator mass is the sum of the mass of all feeders, headers and radiator panels (and the NaK therein) and the associated motors and pumps. Other significant factors include the total power to be radiated and the inlet and outlet temperatures. An independent variable of prime importance is "D HEAD," the diameter of the header manifolds. As this diameter is reduced, the stress in the headers tends to reduce, the area of metal reduces, and the volume of NaK (a significant mass factor) also reduces. However, the pressure drop in the manifolds increases, so that the sum of the pressure drops around the loop ("P3") increases, tending to increase the inlet pressure, which increases the stress in the manifolds. Higher inlet pressures require more pump power, so that the pumps and associated motors become heavier. More pump power also means more busbar power, so that more solar concentrator, cavity, etc., are required. Figure 4-68 shows one of the parametric relationships used in the radiator modeling exercise; it was itself derived from computer analysis. It shows the effective temperature; i.e., temperature of an isothermal area equal in size to the radiator which rejects the same amount of energy. T5 is the radiator inlet temperature; To is the outlet temperature. Figure 4-69 shows total radiator system mass for the range of primary variables judged to be potentially applicable to power satellite usage. For each inlet temperature there is a temperature drop across the radiator (AT) which yields minimum mass. Note the drop in mass as inlet temperature is increased up to 1150K (1611°F); beyond this point the trend is less dramatic. This is because the
RkJQdWJsaXNoZXIy MTU5NjU0Mg==