Numerical Model for Pressure Drop and Flow Distribution in a Solar Collector with Horizontal U-Connected Pipes
Abstract
The development of a numerical model for calculating the pressure drop and flow distribution across a solar collector in isothermal conditions is described in this paper. More specifically, the considered collector layout is that of a harp collector with U-type configuration. The different hydraulic resistances causes unbalance of flow distribution in the absorber pipes, so this aspect had to be considered in order to correctly evaluate the pressure drop. The model was written in Matlab and makes use of pressure drop correlations found in literature for both friction losses and local losses. The model was compared in terms of overall pressure drop against measurements which were performed on an Arcon Sunmark HT 35/10 collector. Different flow rates, temperatures and fluid types were tested during this validation process. In case of pressure drops larger than 1 kPa, the relative error between model and measurements was no larger than 7%, while the absolute average value no larger than 3%. For smaller pressure drops the relative difference was usually larger, but still within the accuracy of the differential pressure sensor. Concerning the flow distribution, it was found that the flow regime was the main parameter affecting the results. Turbulent regime resulted in a much more uniform flow distribution across the absorber pipes compared to laminar regime.
Keywords
Solar collector, Pressure drop, Flow distribution, Friction losses, Propylene glycol, Heat transfer fluid, Temperature, Flow rate.