Fine Temperature Control of Coupled Fluid-Looped Radiators Operating Under Differently Varying Sink Conditions 2001-01-2260

Thermal/hydraulic analyses are made for optimal design and in-orbit operations of a fluid-looped two-radiator system, which could be used for tighter temperature control of a thermoelectrically-cooled mission equipment. Analysis results are mathematically rearranged to construct a plain algorithm suited to design calculations. Computations upon that algorithm provide us with several groups of curves applicable to preliminary design of fluid loops with serially-connected radiators. All such curves are actually used in reasonably determining design specifications of an ammonia/propylene-based cooling loop of our concern. A simplified solution method is then introduced for off-design operations problems to readily find the resulting heat rejection, the required pumping power, the required pump speed, the resulting temperature drop, the resulting cold plate temperature, and so on. Solutions under various sink conditions, ranging from the coldest to the hottest, are graphically shown in the figures. A cascade controller, consisting of a state predictor and a proportional-integral regulator, is proposed for pump speed modulation met to varying orbital heat inputs. The steady-state solutions are compiled as a computational basis of the predictor. Linearized governing equations are Laplace-transformed to yield a transfer function, which is reduced to an exponentially-modified fractional expression. The lag time and the dead time characterizing that expression are displayed in the figures, from which one may easily derive a suitable set of the proportional gain and the reset time of the regulator.