José Gonzálvez

Semiexplicit method for wall temperature linked equations (SEWTLE) : A general finite-volume technique for the calculation of complex heat exchangers

An in-depth analysis has been carried out on the discretization of a heat exchanger, the discretization of the governing equations, and the solution strategy for the resulting system of equations. An iterative global method to perform analysis of heat exchangers is proposed, called SEWTLE. This method provides flexibility to any flow arrangement or geometry, consideration of multiple streams, local evaluation of properties, friction factor, and heat transfer coefficient, and is characterized by good accuracy, high robustness, and fast computation time. In addition, three different numerical schemes for the discretization of the fluid and wall conservation equations at the cell level have been studied, and their advantages and disadvantages fully discussed.An in-depth analysis has been carried out on the discretization of a heat exchanger, the discretization of the governing equations, and the solution strategy for the resulting system of equations. An iterative global method to perform analysis of heat exchangers is proposed, called SEWTLE. This method provides flexibility to any flow arrangement or geometry, consideration of multiple streams, local evaluation of properties, friction factor, and heat transfer coefficient, and is characterized by good accuracy, high robustness, and fast computation time. In addition, three different numerical schemes for the discretization of the fluid and wall conservation equations at the cell level have been studied, and their advantages and disadvantages fully discussed.

Two-phase heat transfer analysis of evaporators

Abstract Customary evaporator or condenser characterisation provides data concerning the circulating mass flow rate and inlet and outlet conditions for each fluid flow. This paper analyses the estimation, from those typical experimental results, of the average heat transfer coefficient (HTC) taking place during the phase change region and its corresponding uncertainty. This analysis shows the influence of the typical measurement uncertainties of different measured magnitudes (temperatures, pressures and mass flow rates) and of operating conditions on the total uncertainty in the estimation of the two-phase HTC (2PhHTC). Additionally, the influence of the choice of heat exchanged, by the refrigerant or by the water, on the estimation of the 2PhHTC is also considered. The study is applied to a brazed plate heat exchanger (BPHE) working as an evaporator at both basic flow arrangements: co-current and counter-current. The results clearly show that the operating conditions in which this kind of equipment is typically characterised (and used) makes the estimation of the 2PhHTC difficult. The influence of the model used for the data reduction is also discussed. Finally, a sample of values of the 2PhHTC obtained from the analysis of the characterisation campaign results of a BPHE evaporator working with R22 is presented and briefly discussed.