Temperature Control With Two Parallel Small Loop Heat Pipes for GLM Program

Abstract

The concept of temperature control of an electronic component using a single Loop Heat Pipe (LHP) is well established for Aerospace applications. Using two LHPs is often desirable for redundancy/reliability reasons or for increasing the overall heat source-sink thermal conductance. This effort elaborates on temperature controlling operation of a thermal system that includes two small ammonia LHPs thermally coupled together at the evaporator end as well as at the condenser end and operating "in parallel". A transient model of the LHP system was developed on the Thermal Desktop TM platform to understand some fundamental details of such parallel operation of the two LHPs. Extensive thermal-vacuum testing was conducted with two thermally coupled LHPs operating simultaneously as well as with only one LHP operating at a time. This paper outlines the temperature control procedures for two LHPs operating simultaneously with widely varying sink temperatures. The test data obtained during the thermal-vacuum testing, with both LHPs running simultaneously in comparison with only one LHP operating at a time, are presented with detailed explanations.

Dynamic state-space modeling and model-based control design for loop heat pipes

“…with the thermal resistance R wick of the wicks. By inserting (9), the ideal gas law (10), the Clausius-Clapeyron equation (11), and the mass balance ( 13) into ( 14), the energy balance of the CC can be rewritten as:…”

“…Simple control algorithms for the control heater are used experimentally to control the LHP operating temperature (heuristic PID controllers ( [16], [15]) and two-point controllers ( [10], [16])). However, model-based controllers for control heaters to overcome the complex performance characteristics of LHPs are rare in the literature owing to the fact that most LHP models (e.g.…”