Development and Selection of Gas-Liquid High Pressure Heat Exchangers for External Combustion Heat driven Heat Pumps

摘要

Vuilleumier heat pumps (VHPs) are the heat energy driven heat pumps that work on the Vuilleu mier cycle. The Vuilleumier heat pump is a closed system that captures heat at lower temperatures and deposits the captured heat energy to some intermediate temperature at the expense of high temperature heat energy. The heat energy is the input to the system by burning fuel externally. Due to the interfacing between the heat pump and the outside heat sources and heat sinks, heat exchangers represent critical components in the VHP and have a major impact on overall coefficient of performance. High operating pressures, minimal dead volume and minimal pressure drop are several key challenges that need to be addressed during the down-selection of heat exchangers for Vuilleumier heat pumps. This paper focuses on the analysis and configuration selection of the VHP heat exchangers using simplified 2D models and tailored analysis techniques to evaluate the performance of the heat exchangers. Cross- flow heat exchangers are generally well suited for their application in VHPs because of their robust structure and as they are compact in size. Because the fluid flow in cross flow heat exchangers predominantly covers all three dimensions, simulating the fluid flow in 3D becomes an integral part of CFD modelling and thermal analysis. 3D CFD models are particularly computational intensive due to the involvement of large number of elements in the mesh. Appropriately developed 2D models can replicate 3D models efficiently in many ways (particularly for cross flow heat exchangers).They tend to save considerable computational time and can also maintain good levels of accuracy. The appropriate simplifying of 3D models, however, require good approximation techniques and use of analytical and numerical methods to converge on a solution. The literature describes efficient techniques of blending analytical and numerical methods to derive the solution.