Three-dimensional CFD simulations of natural and forced convection solar domestic water heating systems.

摘要

The objective of the thesis is to study the thermal performance of the open loop natural convection and closed loop forced convection solar water heating system. The 3 dimensional (3D) numerical models were made in the Computer aided design (CAD) package and were simulated for the 12 hours of day time. Analysis was performed using the Computational fluid dynamics (CFD) software package Star-CD. The physical system of natural convection can be used for the purpose of heating domestic hot water without the use of a circulating pump. The closed loop forced circulation system is simulated to study the numerical behavior of the system with respect to time which can further predict the performance of the system when it is connected to the water mains for actual residential applications.; The solar water heater that is being simulated is a truly flat surface collector where the water is allowed to flow in a thin rectangular channel cross-section. The CFD simulations are performed to predict the velocity and temperature of the water in these systems. An accurate relationship between density and temperature of water is implemented for the purpose of predicting the buoyancy effects in the natural convection case. It is felt that the continuous rectangular cross-section chosen will tend to reduce the overall heat losses from the collector hence increasing the thermal performance as the average collector surface temperature will be reduced compared to a typical plate and tube solar collector.; The open loop system is defined as the system in which the solar water heater is connected to the water mains. The cold water from the tap can be fed to the system and the hot water can be extracted from the system for utilization. The closed loop system is defined as the system in which water is circulated inside the system itself and there is no feeding or extraction of water from the system.