Use of Artificial Neural Networks for Prediction of Convective Heat Transfer in Evaporative Units

Convective heat transfer prediction of evaporative processes is more complicated than the heat transfer prediction of single-phase convective processes. This is due to the fact that physical phenomena involved in evaporative processes are very complex and vary with the vapor quality that increases gradually as more fluid is evaporated. Power-law correlations used for prediction of evaporative convection have proved little accuracy when used in practical cases. In this investigation, neural-network-based models have been used as a tool for prediction of the thermal performance of evaporative units. For this purpose, experimental data were obtained in a facility that includes a counter-flow concentric pipes heat exchanger with R134a refrigerant flowing inside the circular section and temperature controlled warm water moving through the annular section. This work also included the construction of an inverse Rankine refrigeration cycle that was equipped with measurement devices, sensors and a data acquisition system to collect the experimental measurements under different operating conditions. Part of the data were used to train several neural-network configurations. The best neural-network model was then used for prediction purposes and the results obtained were compared with experimental data not used for training purposes. The results obtained in this investigation reveal the convenience of using artificial neural networks as accurate predictive tools for determining convective heat transfer rates of evaporative processes. La predicción de la transferencia de calor en procesos de evaporación es una tarea complicada comparada con la de un proceso sin cambio de fase, ya que la física del fenómeno de evaporación es mucho más diversa y se modifica continuamente conforme la calidad del vapor aumenta. Las correlaciones tradicionales basadas en leyes de potencia que se utilizan para la determinación de la transferencia de calor en evaporadores han probado su falta de efectividad cuando se requie re la predicción correcta de absorción de calor del proceso de evaporación. En este trabajo se utilizaron modelos basados en redes neuronales artificiales para predecir el desempeño térmico de unidades evaporadoras y, para ello, se obtuvieron datos experimentales en un módulo de pruebas consistente en un evaporador tipo intercambiador de calor de doble tubo a contraflujo, por cuya sección circular fluye refrigerante R134a y por cuya sección anular fluye agua a una temperat