Condensation of refrigerants in smooth tubes: a new heat transfer model for heat exchangers design

This paper proposes a method to determine the condensation heat transfer coefficient of fluids flowing into horizontal smooth tubes with internal diameters D > 3 mm. The method has been drawn up as simple as possible, ready to use in heat exchanger modeling and design applications, and suitable to work very well with old and new fluids used in refrigeration, air conditioning and heat pump industry. Particular attention is given to the accuracy: it has been tested over a wide updated experimental database, coming from many different independent researchers and with reduced experimental uncertainties. In order to obtain an easy structure, only two equations are employed, related respectively to a DT-independent and to a DT-dependent fluid flow. All the parameters that influence the condensation heat transfer have been included. A comparison was conducted against data relative to HCFCs, HFCs, HCs, carbon dioxide, ammonia and water. Also zeotropic mixtures with two and three components are considered: in order to calculate the relative heat transfer penalization, the model is applied with the Bell and Ghaly [1] correction. With a total of 5478 data points, the comparison gives an average deviation eR = +2 %, an absolute mean deviation eAB = 14 %, and a standard deviation sN = 19 %. In all cases, the effort of coupling a very high accuracy with an easy structure has given very satisfactory results.