MODELING OF A SOLAR WATER COLLECTOR OF A MULTIFUNCTIONAL HELIOTECHNICAL SYSTEM

A mathematical model based on energy balance equations is developed to describe the transient thermal behavior of a flat-plate solar water collector. The proposed model enables the determination of the time-dependent temperature variations of the transparent cover, air gap, absorber plate, insulation layer, and working fluid (water). The collector is divided into several control volumes perpendicular to the fluid flow direction, and distributed-parameter energy balance equations are formulated for each component. The resulting system of coupled differential equations is solved numerically using the implicit finite difference method. Thermophysical properties of the working fluid, absorber, and air layer are evaluated as temperature-dependent parameters, while heat transfer coefficients are determined dynamically in real time. The model is applied to simulate the performance of the collector under actual operating conditions. Theoretical results indicate that the average outlet water temperatures on May 17 and May 18, 2025, reach 54.4 °C and 60.7 °C, respectively. The developed approach provides an effective tool for predicting the thermal performance of flat-plate solar collectors and can be used for their design optimization and operational analysis.