Increase in dependability and efficiency of self-draining water systems of solar heat supply
Abstract
It is shown in the paper that the reliability and efficiency of self-draining systems of the drainback syphon type depend on the atmospheric pressure and heating temperature of the heat carrier in the solar collectors, which affect the value of the allowable drop of the atmospheric pressure in the upper point of the system after it is filled with the heat carrier and achieves the specified heat operation mode. In such systems, the drop of the atmospheric pressure and growth of the heating temperature of the heat carrier lead to an increase in the power consumption for the heat carrier circulation owing to the interruption of the jet in the syphon because of the boiling of the heat carrier. An improved structure of the self-draining solar circuit with an active element in the form of a Venturi tube was developed in which there are no such drawbacks under atmospheric pressure. Compared to the common self-draining system of the drainback syphon type, the power consumption for the heat carrier circulation is reduced to 65-80%. The calculated dependencies are given to define the necessary degree of the flow contraction in the Venturi tube and its resistance coefficients. The article considers experimental studies of the hydrodynamic characteristics of the active section of the self-draining solar loop of a heating system. This element is designed as a flow constrictor referred to as a Venturi tube, with a high degree of flow constriction of 2–5 in.the region with strong viscous resistance. The experimental data are processed in a criteria form, the general type obtained by dimensional technique and compared with data from other authors. The obtained criteria dependencies can be used to calculate the hydrodynamic characteristics of the active section of the self-draining solar loop of a heating system.