Heat transfer and hydrodynamics in heat exchangers of independent electric microsources (IEM)

Abstract

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.IPMs are increasingly used as power plants (PP) for decentralized energy supply, robotics, transportation, gas pipelines, micro vehicle, etc. applications. IPM’s efficiency is ensured by the increased working media initial temperature TIT and the use of efficient miniature air heaters (μAH), which compactness and low material consumption are achieved through the use of some structural materials that do not require cooling at temperatures up to 1350ºC, and application of some novel technologies of implementation of micro channels in its matrix with the hydraulic diameter of less than 1.5 mm (dh <1.5 mm). The reliability and efficiency of the μAH and gas turbine engine are generally provided at the design stage. This is accomplished using reliable computational relationships repeatedly proven by compact heat exchanger development practice. Reducing the hydraulic diameter of the micro channel causes a significant reduction in the Reynolds numbers Re that determine the hydrodynamic flow condition of gas/air in the μAH paths. Condition changing affects their hydraulic resistance and heat exchange intensity. As a rule, micro channels have an arbitrary cross-sectional shape, while the absolute roughness of the walls of any structure is commensurable with the absolute size of their cross section. In connection with this, for development of a miniature air heater for IPM, it is first necessary to identify the factors that have a significant impact on the mass and heat transfer in their micro channels and to establish the applicability of the "classical" equations of thermal and hydrodynamic similarity for the thermal hydraulic calculations of μAH. In this paper, a survey of experimental and theoretical studies on the hydrodynamics and heat transfer in μCs for μAH and results of the thermal-engineering tests of the metal model of μAH is presented, this μAH having a matrix containing the microchannels of the same dimensions and configuration of the cross-section as are in the matrix of a full-scale μAH. Analysis of the published material from a number of studies and experimental data obtained on the metal models has shown that "classic" calculation relationships of an acceptable accuracy [1], used for "normal" channels, can also be used for the thermal-hydraulic calculations of μAH.