The theoretical and experimental research on the thermodynamic process in transcritical carbon dioxide piston compressor

Abstract

The general mathematical model of the transcritical CO2 compressor was presented to assess the compressor efficiencies including isentropic efficiency and volumetric efficiency based on the thermodynamic theories and compressor structures. Furthermore, the prototype of the transcritical CO2 system was established and relative measurements were carried out to evaluate the precision of the simulation. Results showed that the volumetric efficiency of the compressor kept decreasing while the isentropic efficiency increased first and then kept almost constant and even declined with the increase in the pressure ratio. Besides, the indicated efficiency and volumetric efficiency declined slightly with the decrease in the suction density corresponding to the increase in suction superheating. As for the effects of compressor structures on the performances, the indicated efficiency increased sharply and then decreased gradually, while the volumetric efficiency kept declining with the increase in the cylinder diameter-to-height ratio, respectively.

Investigation of the Impact Factors on the Optimal Intermediate Temperature in a Dual Transcritical CO2 System with a Dedicated Transcritical CO2 Subcooler

“…It can be seen that, except for the gas-cooler model and internal heat exchanger model, the simulation processes of the auxiliary and main sub-cycles are completely independent. The mathematical models of the components adopted in this study are basically drawn from open literature on the CO 2 compression process [27], the heat transfer in the internal heat exchanger [3,28], the supercritical CO 2 cooling process in the gas cooler [29,30], the subcritical CO 2 evaporating process [31], and the heat-transfer correlations of air and water sides [32]. The main equations and correlations of those components' simulation models are summarized in Table 1.…”

“…Detailed Models CO 2 compression model [27] Each time step was divided into: 1) the isentropic process with constant mass (1-2*); 2) the inner change with constant volume (2*-2).…”

Thermodynamic performance study on a novel trans-critical CO2 heat pump cycle integrated with expander and internal heat exchanger

“…Carbon dioxide is an ideal refrigerant, which has many advantages, such as non-toxic, non-flammable, zero ozone depletion potential (ODP) and negligible global warming potential (GWP). 3 Additionally, compared with traditional refrigerant, the process of CO 2 releasing heat doesn't in the tow-phase region but in where it exceeds critical point. 4,5 In this exothermic process, the temperature is constantly changed and has a large glide, which means that the exothermic process can be matched with the changing high temperature heat source and forms a special Lorentz cycle which has a good performance.…”