Abstract

Low and medium solar heating systems used for domestic and industrial applications, such as water and space heating, usually utilize solar flat plate collectors in order to absorb solar thermal energy converting it into heat and then transferring the heat to a fluid (usually water or air) that flows through it. The aim of this study is to evaluate the solar flat plate collector’s efficiency and the fluid behavior inside the pipeline with three different cross sections, whose hydraulic diameters are 10, 5.12 and 6.16 mm, by using ANSYS Fluent. The results obtained from the Computational Fluid Dynamics (CFD) tool showed that the collector with the Type I cross section reached temperatures up to 330 K at the pipe outlet obtaining an efficiency of 68 %, higher than those of Types II and III, whose efficiencies were 51 % and 60 %, respectively. Type I cross section also presented the lowest values in both speed and pressure drop, these being 0.266 m/s and 108.3 Pa, respectively.

Abstract

A solar desalination system with heat recovery has been developed for coastal areas of Ecuador with a shortage of freshwater. The prototype consists of a 3-stage distillation tower connected to a flat plate solar collector. The solar energy absorbed by the collector is transferred by natural circulation to the distillation tower, wherein the heat of condensation of water is recovered in each stage to increase distillate output. The modular design of the equipment allows water production to be varied, from a few liters to more than a cubic meter per day. The prototype has few moving parts and can be rapidly disassembled and assembled, greatly facilitating its operation and maintenance. The average monthly production of the desalination unit varies between 4.3 and 5.8 liters per day (2.44 and 3.29 kg/m2). A mathematical model was created to analyze system performance. The accuracy of this model was improved by experimentally evaluating the convection heat transfer coefficients in the distillation tower. A simulation program was developed in Matlab-Simulink to predict the temperature profiles, distillate output, and heat flows in the unit. The simulation results for one day of prototype operation were very satisfactory, with a difference of only 7.7 % between theoretical and experimental data. The simulation was also used to analyze improvements in equipment performance, which determined that freshwater yield could be increased by up to 107 %.