This effort will design and demonstrate by a computer simulation a typical spacecraft temperature-control system that uses a non-azeotropic, two-phase fluid as the working medium. The innovation lies in the use of the non-azeotropic fluid. Existing research and existing designs are based on having conventional, single-component or azeotropic fluids as the working medium. Non-azeotropic fluids, a class of mixtures of fluids, boil not at a fixed temperature but over a small range in temperature (at a fixed pressure). Therefore, the amount of fluid that has been evaporated (i.e., the thermodynamic quality) can be readily determined by sensing the easily measured temperaure. Therefore, also, the quality of the fluid leaving an evaporator can be controlled to, for example, 80%. The following advantages result: simpler and more reliable control systems, faster control system response, higher average evaporator and condenser heat-transfer coefficients, smaller evaporators and condensers, reduced fluid flow rates, lighter temperature control systems, and less power consumption for temperature control. Systems with conventional fluids have no practical means for measuring quality. The sensor is heavy and costly and the response time is long. Instead, either the fluid is super-heated and poor heat-transfer coefficients are accepted or the plate temperature is measured and the control system response time is slow.
