Analysis and optimization of a jet-pumped combined power/refrigeration cycle.

摘要

The objectives of this study were to analyze and optimize a jet-pumped combined refrigeration/power system, and assess its feasibility, as a thermal-management system, for various space missions. A mission is herein defined by the cooling load temperature, environmental sink temperature, and solar irradiance which is a function of the distance and orientation relative to the sun. The cycle is referred to as the Solar Integrated Thermal Management and Power (SITMAP) cycle. The SITMAP cycle is essentially an integrated vapor compression cycle and a Rankine cycle with the compression device being a jet-pump instead of the conventional compressor.;This study presents a detailed component analysis of the jet-pump, allowing for two-phase subsonic or supersonic flow, as well as an overall cycle analysis. The jet-pump analysis is a comprehensive one-dimensional flow model where conservation laws are applied and the various Fabri choking regimes are taken into account. The objective of the overall cycle analysis is to calculate the various thermodynamic state points within the cycle using appropriate conservation laws. Optimization techniques were developed and applied to the overall cycle, with the overall system mass as the objective function to be minimized. The optimization technique utilizes a generalized reduced gradient algorithm.;The overall system mass is evaluated for two cases using a mass based figure of merit called the Modified System Mass Ratio (MSMR). The first case is when the only output is cooling and the second is when the system is producing both cooling and work. The MSMR compares the mass of the system to the mass of an ideal system with the same useful output (either cooling only or both cooling and work).;It was found that the active SITMAP system would only have an advantage over its passive counterpart when there is a small difference between the evaporator and sink temperatures. Typically, the minimum temperature difference was found to be about 5 degrees for the missions considered. Three optimization variables proved to have the greatest effect on the overall system mass, namely, the jet-pump primary nozzle area ratio, Ant/Ane, the primary to secondary area ratio, Ane/Ase, and the primary to secondary stagnation pressure ratio, Ppo/Pso. SMR and MSMR as low as 0.27 was realized for the mission parameters investigated. This means that for the given mission parameters the overall SITMAP system mass can be as low as 27% of the mass of an ideal system, which presents significant reduction in the operating cost per payload kilogram. It was also found that the work output did not have a significant effect on the system performance from a mass point of view, because the increase in the system mass due to the additional work output is offset by the increase in the mass of the Carnot power system that produces the same amount of work.