Heat transfer and pressure drop penalization terms (exergy losses) during flow boiling of refrigerants

Heat transfer coefficient and pressure drop correlations are used to analyse the boiling heat transfer performance potentials in plain evaporator tubes of several conventional refrigerants and two newer fluorinated propene isomers possessing low global warming potentials. These correlations are used to calculate two penalization quantities expressed in terms of the refrigerant saturation temperature drop due to pressure drop and the driving temperature difference. These penalization terms are combined into a single Performance Evaluation Criterion dubbed Total Temperature Penalization (TTP). Using the two penalization terms and the TTP, several refrigerants, including the newer alternatives R1234yf (CF3CF=CH2) and R1234ze(E) (CF3CH=CHF), are evaluated for their boiling heat transfer performance potentials in plain evaporator tubes. Furthermore, the usefulness of the technique is illustrated through several examples of the optimization of evaporator tube length.