| China is the largest energy source consumption country of the world. It’s of great importance to relieve energy crisis how to collect and utilize waste heat efficiently. Vuilleumier(abbr. VM) cycle heat pump can use waste heat as driven heat source both for refrigeration and heating. In this paper, taking VM heat pump as subject, the performance is analyzed and optimized.First, a VM heat pump model is built. Under given working condition, the thermodynamic calculations of theoretical and actual process are presented. The result shows theoretical COP(coefficient of performance) and actual COP respectively are 2.4 and 1.5, theoretical exergy efficiency and actual exergy efficiency respectively are 0.23 and0.15. The theoretical performance is almost two times larger than actual performance, because there exists lots of losses in actual process, including reheat loss, flow resistance loss, shuttle loss, pumping loss, heat exchange loss of heat exchanger, cooling loss etc.. Among these losses, reheat loss and flow resistance loss account for 83% of the total loss.Then, three common working fluids used in VM heat pump are analyzed and compared. Result shows helium is better than hydrogen and nitrogen in terms of safety and performance. Using helium as working fluid, keeping other parameters constant, the effect of one parameter to the actual performance of VM heat pump is studied. The result shows low heat source temperature attributes to larger actual exergy efficiency. When heat source temperature is at the range of 800~900K, the actual COP is the largest. Cycle pressure at the range of(6~6.5)×108Pa, both the actual COP and exergy efficiency attain the maxium. The actual COP and exergy efficiency is optimal when volume ratio is about 15. When speed is 200~300rpm, the actual COP and exergy efficiency reach the maxium.Finally, the optimization of VM heat pump is made. According to the analysis and results above, medium and low temperature waste heat is rather suitable for the driven heat source of VM heat pump. Regenerators with shorter length, larger diameter, bigger porosity and packing of larger diameter lead to less flow resistance loss. The way to reduce reheat loss effectively includes increasing heat exchange area and strengthening heat exchange process. The sum of shuttle loss and pumping loss is the least when the displacer length is 0.83 m and the radial clearance between displacer and cylinder is 0.6×10-3m. |
