An Investigation On Vortex Generator Characteristic Of Small-Scale Solar Absorption Refrigeration System

As one method of refrigeration, which is driven by heat energy and has no damage on the ozone layer, absorption refrigeration technology has attracted more and more attention from industry and related researchers. Solar absorption refrigeration has become the researching emphases of absorption refrigeration because which can use the low-grade heat source or the renewable energy. But the improvement of the coefficient of performance (COP) of the solar refrigeration system is limited due to the lower temperature of the heat source, thus can not be widely used. In this paper, according to the vortex flow theory, a new dual chamber vortex generator model is suggested to improve the COP of the absorption refrigeration system. The vortex generator uses the rotating flow of the fluid to reduce the evaporation pressure and temperature at the generator. The main purpose is that at no additional external heat source to increase the refrigerant vapor and improve the COP of the solar absorption refrigeration system.Absorption refrigeration cycle is the use of phase change accompanied by the absorption process, to obtain low-temperature heat and consume the thermal energy for cooling. In the absorption cycle, the chemical and physical properties of the working pair play a key role for the system performance. In the paper, the relationship of the pressure, temperature and concentration of lithium bromide solution has been set up. At the same time, the heat and mass balance of the small-scale solar absorption system which uses the dual chamber vortex generator is analyzed.A new generator model which has a tangential inlet is set up. The optimum structure of the dual chamber vortex generator has been obtained through using the CFD software to simulate the flow and heat characteristics of different structure vortex generator. The results of the study showed that fluid entered the generator through the tangential inlet produced a strong rotation and the Rankin vortex at the center of the generator. The pressure distribution is parabola regulation. At the center the pressure is lower than around of the generator. The pressure decreased with the fluid inlet velocity increased and the inlet diameter decreased. According to the characteristic of the Lithium Bromide solution the evaporation temperature decreased in the generator with the fluid inlet velocity increased and the inlet diameter decreased. A low pressure region is created because of the vortex flow which will help the evaporation of Lithium Bromine solution at low temperature. The available temperature difference of lower-temperature heat source from an external resource increased to generate more refrigerant vapor and improve the COP of the solar absorption chiller.A novel dual chamber vortex generator which consisted of a lower chamber and upper chamber is designed in according to the numerical simulation. The lower chamber is composed of a cylinder and a cone part whose conic angle is 20°with a tangential inlet. The tangential inlet is composed of three parts to ensure the rotating flow of the fluid in the generator. The upper chamber is a cylinder with a central inlet at the bottom and two outlets at the side. Due to the rotating flow, the pressure was reduced toward the central portion of the lower chamber. And the refrigeration vapor which produced in the lower chamber came back the condensing pressure in the upper chamber. In order to investigating the flow and heat transfer characteristic, a small solar absorption chiller testing system is set up. Main four flow loops of the experiment system and the parameters of apparatus are introduced. In the thesis a novel dual chamber vortex generator was investigated under different temperatures and solution mass flow rates. The experiments and analysis results showed that the fluid enters the vortex generator to create a strong rotation.The lower pressure developed in the lower chamber could help the evaporation in the generator. The higher the pressure difference, the lower the saturated temperature which can utilize heat source to generate more refrigerant. And the higher the inlet temperature, the larger the available temperature difference. The higher the inlet temperature, the higher the vapor mass flow rate and the evaporation ratio. As solution mass flow increases, the evaporation ratio decreases and the vapor mass flow rate increases The COP increases as the solution inlet temperature increases. When the inlet temperature is 90℃, the COP can reach 0.83, which is higher than that of a conventional absorption chiller by 22%. The experiment research has depicted that the COP can be improved much higher by using the novel dual chamber vortex generator in the solar absorption chiller.