Thermal analysis of heat transfer performance in a horizontal tube bundle

The thermal analysis is demonstrated for the case where steam is condensing inside a horizontal tube bundle, while simultaneously thin water films are evaporating outside the tubes generating vapor that flows across the tubes. Three experiments are carried out each coming up with a valid model to predict the impact of the corresponding parameters on the heat transfer performance or flow characteristics. Then, a collective two-dimensional model is established according to the models from those experiments to simulate the thermal and hydrodynamic performance of the evaporator. This model consists of three parts corresponding to the three models obtained from the experiments mentioned above: the water film evaporation model, the inside-tube steam model, and the intertube vapor model. The operating conditions include the water mass rate, saturation temperatures, and overall temperature difference. Calculations are carried out for water mass rate between 0.03 and 0.09 kg/m s, inlet steam temperature between 53 and 73˚C, and overall temperature difference between 1.5 and 4˚C. Results of the analysis show that the overall heat transfer coefficient and vapor temperatures have uneven distributions within the tube bundle. The variation of vapor temperature affects the distribution of heat transfer rate and the steam inlet velocity. The utilizations of the initial temperature difference with the change of tube bundle column numbers are also analyzed. It shows that the more column numbers the tube bundle includes, the more heat transfer area will lose a certain amount of initial temperature difference.