NUMERICAL STUDY AND EXPERIMENTAL VALIDATION OF A TRANSCRITICAL CARBON DIOXIDE REFRIGERATING CYCLE

摘要

The present work is a numerical study of a transcritical carbon dioxide refrigerating cycle. The heat exchangers in particular, and the whole cycle in general, are simulated under a carbon dioxide refrigerating system. The experimental unit, specially designed to be used with carbon dioxide as refrigerant fluid, has allowed validate the numerical results obtained. A detailed numerical simulation of the thermal and fluid-dynamic behavior of a single stage vapour compression refrigerating unit has been developed. The modelization consists of a main program that sequentially calls different subroutines until convergence is reached. The different subroutines modelize the physical flow phenomena produced inside all the different elements that make up the compression cycle. The governing equations of the flow in the heat exchangers are solved by means of the Step by Step method. Some empirical information is required for the evaluation of the con-vective heat transfer, shear stress and void fraction. The compressor model is obtained using an advanced hermetic compressor numerical simulation model. An expansion valve device is modeled by means of the characteristic parameters. The software allows the analysis, in transient or steady state, of a wide range of situations, taking into account different working fluids, geometries and boundary conditions. The software gives the flow variables distribution, which are evaluated at each point of the discretized domain.