Impact of the Coolant Flow Velocity on the Thermal Condition of Flat-Plate Solar Collectors

The issues of effective operation of flat-plate solar collectors in the Voronezh region and under other RF climatic conditions have been considered. The impact of the coolant flow velocity in the absorber tubes on the radiation-generated thermal condition has been estimated, exemplified by a solar energy utilization system for the hot water supply of cottages in the warm season. The results of calculations and analysis of the water flow rate and velocity impact on the temperature difference occurring in a standard solar collector are provided. Studies have shown that to achieve the required coolant temperature, the velocity should be within 0.02–0.03 m/s, which corresponds to a flow rate of 0.001–0.0015 kg/s in a meander-type absorber. The values of the optimal interval of the coolant velocity in the tubes leads to an increase in the efficiency of the collector, since it does not cause a drop in efficiency due to approaching the stagnation temperature. Dependence has been proposed for designing solar systems installed in the northern latitude regions, which allows justifying the choice of the circulating coolant velocity and, consequently, total flow rate in the absorption tubes.