Development of a simulation model for a refrigerated transport unit working with CO2 and other refrigerants

Development in Matlab environment of different algorithms to study the refrigerating cycle of a refrigerated transport unit with different refrigerants. These algorithms allow to study the cycle at different external temperatures or different temperatures in the unit. The standard condition of the cycle is 0°C in the unit and 30°C in the external ambient. From the standard condition the temperature of the unit can decrease down to -20°C and the ambient temperature can increase up to 56°C. Each algorithm calculates the conditions of the cycle through iteratives calculations which consider: the heat exchangers dimensions, using correlations to evaluate the heat transfer coefficient and the power required by the fans. One of the algorithms developed has an economizer and a compressor with injection, this algorithm have been validated comparing the results while using R452A as refrigerant with the machine Exigo produced by Zanotti S.p.A.. This algorithm can work with pure, azeotropic and zeotropic refrigerants in subcritical conditions. The refrigerants that have been analyzed in this work are R32, R452A and R290; among those, propane have been found to be the best one in terms of EER, as it was expected. The others algorithms developed can work with transcritical carbon dioxide, in particular the layout that have been analyzed, works with a separator liquid-vapor and/or external mechanical subcooling which is done by a basic refrigerated cycle, in the case considered using R290. The comparison of these cycle showed that a layout with a separator liquid-vapor and external mechanical subcooling have higher EER.