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Technical Paper

Trade-Off Study of Heat Rejection Systems for Two-Stage Stirling Cooler

A combined two-stage Stirling and Joule-Thomson cycle refrigerator has been developed for advanced celestial observation missions. The specified cooling capacity is 40 mW at the final 4 K stage and 200 mW at the second 20 K stage. The precooler compressor power amounts to about 100 W, most of which is thermally dissipated. This study has therefore been made to propose a most suitable method of the waste heat rejection. Proposed are a loop heat pipe (LHP) and a mechanical pump loop (MPL). Computational sizing procedures of the two are presented with mass estimate models. Also presented is an empirically obtained relation between the cooling efficiency and the ambient temperature. This algebraic expression is then used to find the required electrical power for the 20 K stage cooling. Numerical results of the LHP/MPL design calculations are displayed in the figures as a function of the ambient temperature ranging from 150 K to 310 K.
Technical Paper

Analysis of Loop Heat Pipe Operation with Radiators of Different Orientation

A performance analysis model is presented to investigate operability of a loop heat pipe (LHP) with two differently oriented radiators. Analytical modeling has been made under particular conditions that the LHP of concern is used to reject waste heat generated by thermoelectrical cooling devices. The model is expressed in comparative dimensionless form normalized by specified design parameter values, thus permitting off-design state predictions of an LHP with one evaporator and two condensers. Condidered in that model are Peltier cooling power consumption holding most of the heat load, coupled radiator sink temperatures, a conductive loss and bubble generation in the evaporator wick, an extent of the condenser two-phase region length, a degree of the liquid subcooling, a change of the radiative conductance, a capillary pump head increase/decrease compensating a total pressure loss change, and a hydraulic balance between the condensers arranged in a row.
Technical Paper

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

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.
Technical Paper

Preparatory Study for Development of a Hybrid Capillary Pumped Loop with a Retractable Flexible Radiator

This paper gives an outline of conceptual design works for prospective development of mechanically/capillary pumped two-phase fluid loops with space radiators. Considered first are two types of capillary pump evaporators configured as a cold plate. They basically consist of porously separated vapor/liquid channels, taking a double pipe array or a tube-included rectangular duct in shape. A newly devised sizing procedure for the two is mathematically described in the table together with empirically-determined practical design formulas. Four types of deployable/retractable rigid/flexible radiators are then considered as variable capacitance heat rejection systems feasible in the existing state of technology. A unified design/performance analysis procedure for the four is also given in the table, arranged in a convenient way for comparison.
Technical Paper

Reduced Expressions for Thermophysical Properties of Fluid Loop Used Non-CFC Coolants

Investigated in this study are thermodynamic and transport properties of FC-72, -84, -77, -75, -40, -43, -70; FX-3250, -3300; PF-5050, -5060, -5070, -5080; and DF134a. All the fourteen are non-CFCs(non-chlorofluorocarbons), substitutable for commonly used coolants like Freons and not destroying ozon layers. The collected property data has mathematically been handled to reduce to proposed empirical formulas. Finally obtained are temperature-dependent algebraic expressions for the saturated vapor pressure, the saturated liquid density, the specific heat at constant pressure of liquid, the thermal conductivity of liquid, the kinematic viscosity of liquid, the surface tension of liquid, the latent heat of vaporization, the specific enthalpy of liquid, and that of vapor. All the coefficient values are listed in the tables along with applicable temperature ranges and prediction errors.
Technical Paper

Application of Classical Control Theory to Off-Design Operations of a Fluid Loop System

Off-design operation problems of a cold plate row and of a space radiator row, encountered in fluid loop control, are solved to find possible inlet/outlet temperatures or to specify a required flow rate. Solutions of the problems are given in the form suitable for numerical computations and are graphically shown in the figures for various combinations of control variables. Mathematical analyses are then made to yield transfer functions of a cold plate and of a space radiator. They are expressed as a second-order delay system, mainly dependent on the heat transfer unit number and the heat capacity rate ratio. The expressions are generalized so as to be applicable to a series of cold plates or space radiators. A further analysis based on such generalized transfer functions is made to develop a method of feedback/feedforward control. Numerical results of the analysis are summarized in the table and also are displayed in the figures.
Technical Paper

Advanced Computational Analyses for Design and Control of Pumped Liquid Loop Systems

Computational procedures are clearly shown in the tables in such a staged way as one may easily proceed design calculations of cold plates, space radiators, and single-phase fluid loop systems. All the procedures are incorporated into a design code which can deal with two types of cold plates, five types of space radiators, and five configurations of a fluid loop mechanically driven by either rotodynamic or volumetric displacement one. Equivalent hydraulic diameters, heat transfer area densities, dry weights, and pressure losses are calculated over a wide range of parameters to give demonstrative examples of design practices. For cold plate design optimization, the weight and the pressure loss are displayed in the figures as functions of baseplate area, width to length ratio, or diameter to diameter/height ratio.