Temperature Control Strategies in a Rectified Continuous Flow Loop for the Thermal Management of Large Structures
H. Skye1, D. Hoch1, S. Klein2, G. Nellis2, J. Maddocks3, T. Roberts4
1Univ. of Wisconsin, Madison, WI, 2University of Wisconsin-Madison, Madison, WI, USA, 53706, 3Atlas Scientific, San Jose, CA, 4AFRL, Kirtland AFB, NM
AbstractDistributed loads are frequently encountered in large deployable structures used in space applications, such as optical mirrors, actively cooled sunshades, and focal plane electronics, or in zero boil-off cryogenic storage systems. An innovative mechanism for providing distributed cooling is via an oscillatory cryocooler such as a pulse-tube that is integrated with a fluid rectification system consisting of check-valves and buffer volumes in order to extract a small amount of continuous fl ow of cold gas. This continuous flow allows relatively large loads to be accepted over a long distance with a small temperature difference and has advantages relative to vibration and electrical isolation. Also, it is possible to provide rapid and precise temperature control via modulation of the flow rate. The same working fluid, for example helium, can be used throughout the entire system, reducing complexity and simplifying the contamination control process.
This paper describes a theoretical investigation of the ability of the rectifying interface to precisely control the temperature of a distributed load under dynamically changing conditions. The precise temperature regulation is enabled using temperature feedback control of a throttle valve placed in the loop. Flow modulation using the throttle valve is governed by a Proportional-Integral (PI) controller with gains that are selected to meet design temperature control criteria; specifically, a maximum temperature fluctuation and settling time. A linear thermal model based on experimental data is used to develop the control algorithm. The model demonstrates the ability to regulate the distributed load temperature under rapid load changes.