A Novel Gravity System For Heat To Work Conversion And Improvement Of A Combined Power And Cooling Using Ammonia-water Mixture

Energy shortage and environment pollution have become common problemshuman faced. Using low-grade clean energy has already been paid more attention.China is rich in all kinds of low-grade energy sources such as industrial waste heat,geothermal energy, ocean energy, solar energy resources and so on. There is still a lot ofspace for development and utilization for those low-grade resources. As the temperatureof low-grade heat sources is usually low, the efficiency of heat to work conversionprocess is very low. Improving the efficiency of conversion process has been the keyproblem.In this paper, a novel gravity system for heat to work conversion and improvementof a combined power and cooling using ammonia-water mixture proposed by Goswamihave carried out. This paper studies the performance of these two systems bythermodynamic analysis.(1) A novel gravity system for heat to work conversion was proposed for furtherimprovement and research. Meanwhile, physical model and mathematical model of themain process that the rising process were given. The ascending process of working fluidwas numerically simulated obtaining the effect of variation of pipe diameter, mass flow,inlet temperature of the pipe and working fluid on the main parameters of working fluiddistribution and critical height.The results show:a. The temperature, pressure, density and enthalpy of the working fluid in the pipedecreases with increasing altitude. The speed and Ma of the working fluid in the pipeincrease with increasing altitude.b. The fluid flow can reach a critical height, and there would be positive effect on theparameters profile and critical height with the pipe’s diameter increasing, mass flowdecreasing, degree of superheat decreasing and low-critical-pressure working fluid.c. The main determinant of the thermal efficiency of this system is lift height of theworking fluid. Therefore the working fluid at pipe’s inlet parameters and pipe(2) Based on a combined power and cooling using ammonia-water mixtureproposed by Goswami, further improvement is presented in this paper. The technicallyavailable two-phase screw expander is used to recover the expansion work. Twodifferent layouts of the two-phase expander are analyzed, and a comparison between this two modified cycles is performed (A-modified cycleå'ŒB-modified cycle). Theparametric sensitive analysis is performed to evaluate the effects of each majorparameter on the combined cycle performance, such as heat source temperature, turbineinlet pressure, and basic ammonia concentration. When one specific parameter isstudied, other parameters are kept constant.The results show:a. Different characters appear in the two modified cycles. The main function ofA-modified cycle is work output. Higher exergy efficiency can be got in the cycle. Themain function of B-modified cycle is refrigeration output. Higher first efficiency can begot in the cycle.b. There would be positive effect on the first efficiency, exergy efficiency, work outputand refrigeration output of A-modified cycle with heat source temperature increasing,turbine inlet pressure increasing, and basic ammonia concentration decreasing. Therewould be positive effect on the first efficiency, exergy efficiency, work output andrefrigeration output of B-modified cycle only with heat source temperature increasing.Although there would be positive effect on the work output and exergy efficiency ofB-modified cycle with turbine inlet pressure increasing and basic ammoniaconcentration decreasing, there would be negative effect on the first efficiency andrefrigeration output of B-modified cycle with turbine inlet pressure increasing and basicammonia concentration decreasing.