Condensation heat transfer in smooth tubes: a simple equation to determine the flow regime and the heat transfer coefficient

In this paper a new method to determine the condensation heat transfer coefficient inside horizontal smooth tubes with internal diameters D > 3 mm is proposed. The method is very simple and ready to use in heat exchanger modeling and design applications, suitable to work very well with old and new fluids used in refrigeration, air conditioning and heat pump industry. In order to obtain an easy structure and to take into account the current two-phase flow category, two equations for the heat transfer coefficient and one for the fluid flow transition are employed. All the possible flow configurations are grouped in two main categories, respectively independent and dependent from the temperature difference T between the saturated fluid and the internal tube wall. The model has been tested over a wide updated experimental database, coming from many different independent researchers and with reduced experimental uncertainties. The 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: the model is applied with an appropriate correction in order to calculate the relative heat transfer penalization. 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 N = 19 %.