A control system that includes a single thermal source has been designed to afford precise control of the temperature of a fluid flowing in a closed-loop system. Similar control systems could make it possible to increase production levels and to reduce risks in industrial situations in which temperatures must be strictly maintained - especially situations that involve aggressive or hazardous materials that exhibit safety-related, temperature-dependent properties. For example, in the photographic and other chemical industries, control of temperature is vital for manufacturing products and for safety of manufacturing processes; for another example, the ability to control temperature is a major concern for manufacturers of heating and cooling equipment. Overall, precise temperature-control systems like the present one can serve as valuable tools that will insure both production and safety in affected industries, in the armed services, and in the U.S. space program.

The operation of this system includes monitoring of the flow(s) of thermal (heating and/or cooling) fluid(s). Control of mass flows of thermal fluids is basic to heat-exchange systems. In traditional heating and cooling systems, constant-thermal-fluid-flow sources (e.g., pumps) and on/off valves are used to maintain temperatures at acceptable levels; this practice is expensive and is fraught with production irregularities and safety risks.

In other temperature-control systems, hot and cold fluids are constantly mixed to keep temperatures within optimum bands. In the present system, a variable flow from a single thermal source (a circulation heater or a circulation chiller, depending on whether heating or cooling is needed at the time) is used to effect precise control of the temperature of a fluid circulating in a closed-loop system. Although the system is rated to maintain the temperature within ±1 °F (≈0.6 °C) of the set point, the designer's specification predicts a range of±0.5 °F (≈0.3 °C).

The system has been installed in a space-station simulator in St. Louis, Missouri. The specification for the simulator requires that temperature be maintained within ±0.5 °F (≈0.3 °C). Because the temperature tolerance for this simulator is almost as restrictive as are the temperature tolerances in other industries (including the photographic and chemical industries, heating-equipment manufacturers, and branches of the U.S. armed services), this system could also be put to good use in those industries.

This work was done by Thomas J. Poteat of McDonnell Douglas for Johnson Space Center. MSC-22774


NASA Tech Briefs Magazine

This article first appeared in the September, 1999 issue of NASA Tech Briefs Magazine.

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