Numerical Study of Entropy Generation Within Thermoacoustic Heat Exchangers with Plane Fins

Abstract

Abstract:In this paper a simplified two-dimensional computational model for studying the entropy generation characteristics of thermoacoustic heat exchangers with plane fins is presented. The model integrates the equations of the standard linear thermoacoustic theory into an energy balance-based numerical calculus scheme. Relevant computation results are the spatial distribution of the time-averaged temperature, heat fluxes and entropy generation rates within a channel of a parallel-plate stack and adjoining heat exchangers. For a thermoacoustic device working in the refrigeration mode, this study evidences as a target refrigeration output level can be achieved selecting simultaneously the heat exchangers fin length and fin interspacing for minimum entropy generation and that the resulting configuration is a point of maximum coefficient of performance. The proposed methodology, when extended to other configurations, could be used as a viable design tool for heat exchangers in thermoacoustic applications.

Mode transition in a standing-wave thermoacoustic engine: A numerical study

“…Based on the acoustic field, TAEs can be classified into standing-wave and travellingwave types [8][9][10]. Standing-wave TAEs rely on imperfect heat conduction to realize Brayton-like thermodynamic cycles within the boundary layers [11][12][13] whereas travelling-wave TAEs require perfect heat conduction to execute Stirling-like cycles [14][15][16]. Although standing-wave TAEs are less efficient from a thermodynamic perspective, they are simple in structure, compact in size and, most importantly, cheap to fabricate, therefore remaining competitive with their travelling-wave counterparts regarding cost-effectiveness.…”

Convection Heat Transfer Coefficients in Thermoacoustic Heat Exchangers: An Experimental Investigation

“…Therefore, an arbitrary increase in the HX length could not automatically lead to an increase of the heat transfer area but, eventually, only to an increase of the thermoviscous dissipation [4]. Therefore, when designing efficient HXs, the HX length must be simultaneously optimized with the pore hydraulic diameter and the fin thickness (or, equivalently, the HX blockage ratio) in order for the target heat load to be transferred under a small gas-solid temperature difference in conjunction with low pressure drop [5,6].…”

Comparative Performance of Thermoacoustic Heat Exchangers with Different Pore Geometries in Oscillatory Flow. Implementation of Experimental Techniques

“…Their porous structure entails, in fact, considerable flow resistance while steep thermal gradients are generally imposed on them to sustain the required heat fluxes. When designing efficient HXs aimed at transferring a target heat load the HX length along the direction of acoustic oscillation and the pore hydraulic radius should be simultaneously optimized in order to: -Provide the heat transfer surface area compatible with minimum acoustic power loss caused by thermal and viscous dissipation; -Provide the temperature drop between the HX and the adjacent fluid compatible with minimum thermal irreversibility associated to heat transfer [9,10]. An optimized HX should be able to achieve high transfer rates under small temperature differences in conjunction to low acoustic dissipation.…”