and 400K. These span a temperature range for virtually any heat rejection requirement in space. Moreover, the LDR is scalable over a wide thermal power 3 9 range (10 -10 W, depending on the liquid) and is virtually immune from permanent damage due to micrometeoroids. Several applications, including thermal engines, active cooling of photovoltaic cells, and refrigeration have been investigated. Emphasized in this paper is the need for lightweight structures and fluidhandling components for an LDR system, to take best advantage of the low mass of the droplet sheet itself. Title: The 1 i qui d... dropl et heat exchanger Source: Proceedings of the AFOSR Special Conference on Prime-Power for High Energy Space Systems, Norfolk, Virginia, USA, Feb. 22-25, 1982. (Paper No. X-3) Authors: Bruckner, A. P. ; 'University of Washington, Seattle, WA 98195> Date: 02-22-82 Classification: u Keywords: thermal control, materials and coatings, space energy conversion Abstracts Direct contact heat exchange between a gas and a molten metal dispersed into droplets offers an attractive new approach to increasing the efficiency and decreasing the specific weight of thermal power cycles for space applications. The ability of a droplet heat exchanger to transfer heat directly ATTACHMENT : from a liquid metal to a working gas over a wide temperature range circumvents many of the material limitations of conventional tube-type heat exchangers and does away with complicated plumbing systems and their tendency toward single point failure. Droplet heat exchangers offer large surface to volume ratios in a compact geometry, very low pressure drop, and high effect!veness. In the simplest configuration the molten material is sprayed axially through a counterflowing, high pressure inert working gas in an insulated cylindrical chamber. The droplets transfer heat directly to the gas by convection as they traverse the heat exchanger and are subsequently collected for recycling through the heat source. A number of suitable liquid metals and eutectic alloys having negligibly low vapor pressures in the temperature range of 350 - 1300 K have been identified. Experimental studies of droplet formation with mercury have demonstrated that near perfect control of droplet size can be easily achieved. While studies of the droplet heat exchanger have shown it to be very promising for a variety of Earth-based appl ications, the zero "g" environment of space can lead to entrainment of the droplets in the gas flow. This problem can be circumvented by the applicaion of artificial "g" fields and/or by using the principle of the cyclone? dust separator. By configuring the heat exchanger to produce a vortex flow, the droplets can be driven through the swirling gas by ATTACHMENT : the induces centrifugal forces. Since excellent uniformity of droplet size is possible, the separation efficiency of such a cyclonic heat exchanger can in principle be made nearly perfect. Heat transfer in a droplet heat exchanger can occur in either direction— i.e., gas can be heated by hot droplets or cold droplets can be used to extract waste heat from a working gas. In the latter case the droplet heat exchanger can be integrated with a droplet space radiator to make a complete heat rejection loop based entirely on the droplet concept. Title: The need for improved heat pipe fluids Source: Proceedings of the AFOSR Special Conference on Prime-Power for High Energy Space Systems, Norfolk, Virginia, USA, Feb. 22-25, 1982. (Paper No. X~4) Authors: Ernst, D. M. ; Eastman, 8. Y. ; <Thermacore, Inc., Lancaster, PA>
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