Calculation and analysis of compression and expansion in a piston hybrid power machine with regenerative heat exchange in pump mode

Abstract

Based on the analysis of existing studies on the calculation of the process of compression of a droplet liquid in a displacement pump, we developed a method for assessing the effect of external heat transfer, deformation work and mixing heat transfer on the working fluid heating in the pump. Using the results of a numerical experiment on the increase in pressure and temperature during compression in a positive displacement pump, it was found that the greatest influence on the increase in pressure during compression is by deformation processes (an increase in pressure due to a change in volume ranges from 80 to 92%), then there is mass transfer (pressure increase is from 7 to 16%) and heat exchange, the values of which are about 2.5%. The decisive effect on the working fluid heating in the working chamber of the pump is the conversion of deformation work into heat (from 92 to 95%), the values of external and mixing heat transfer are approximately the same and range from 2.5% to 3.5% each. The nature of the effect of the independent variables used (discharge pressure, crankshaft speed, radial clearance in the cylinder-piston group and the average temperature of the working chamber surface) on each of the components of the relative change in pressure and temperature during the compression process has been established. We established that the crankshaft revolutions has the greatest effect on the relative increase in pressure and temperature during compression, followed by the value of the radial clearance and discharge pressure. The average temperature of the surface of the working chamber has practically no effect on the increase in pressure due to the processes of deformation, mass transfer and heat interaction and only affects the relative change in temperature due to external heat transfer.