| The contradiction between supply and demand of global energy becomes increasingly prominent at present. It is particularly important to research and apply energy saving technology. Recently, an innovatory idea called "Liquid-vapor separation condensing" was proposed to enhance the condensation heat transfer by separating liquid from gas-liquid mixture during condensing. This method realized the liquid separation of steam and condensate and timely discharge of the condensate by a special setting of the header with porous baffles. When the wet steam enter into the header, the condensate separate from the steam and flow down to the baffle due to the effects of the gravity and inertia force because the density difference between the gas and liquid is very large. Then a liquid film accumulates on the porous baffle plate and the liquid flows through the holes on the baffle. The liquid film could prevent gas to flow out from the holes, so the steam could better contact with the tube wall when flowed into the next tube pass. Higher heat transfer coefficient was obtained by using condensation heat transfer process, and then high performance of the heat exchanger would be achieved. Up till now, there was no systematical research of the phenomenon and process characteristics during liquid-gas separation process in this kind of header. In this study, liquid-gas separation and liquid discharged process were investigated in-depth to established the theory basis for the header design and the design of the liquid-vapor separation condenser (LSC), and the system characters of an air conditioning system with LSC was verified.Firstly, the basic principle of liquid-gas separation and liquid discharge process were explored. A visualization cold state test system was set up, using air and water as the working fluids. The header was manufactured from transparent acrylic resin. The method of dyeing tracer and high-speed camera were adopted to record the gas and water flow process in the header. The results of four kinds of flow pattern in the header were analyzed, and the mechanism of the effects of gas and liquid superficial velocities on the morphology and movement of the liquid film was revealed. Based on the change of the liquid level height, two limits (flooding limit and drain limit) were introduced and the working condition was divided into five situations. The dimensionless Re and modified We number were introduced by forces analyzing to describe the gas-liquid separation characteristics. The results could provide theoretical guidance for the header design.On the basis of theoretical analysis, effects of operation conditions and structure parameters on the gas-liquid separation characteristics of the header were studied. The effects of the operation conditions and structure parameters on liquid level height, water seepage flow rate and liquid separation efficiency were discussed at different gas and liquid superficial velocities, air pressure, header diameter, space between the baffle and the outlet pipe, diameter of the liquid-gas separation hole, number of the liquid-gas separation hole, combined effects of the diameter and number of the liquid-gas separation holes on the self-built cold state test system. The flow characteristics in the header were observed by a PIV velocity measuring system to analyze the influence of flow patterns on the drain limit and the liquid separation. The results showed that under the experimental condition, the header showed capabilities of good liquid-gas separation; the liquid separation efficiency changed with different inlet flow patterns; it was higher than45%and80%respectively for annular flow inlet and for slug flow inlet at low liquid inlet superficial velocities, and close to100%for a stratified flow inlet. Modified We number were used to discuss the two limit conditions, and dimensionless correlations were obtained for predicting the limits. It was found that the liquid level height, water seepage flow rate and liquid separation efficiency increased with increased header diameter, spacing between baffle and outlet pipe and reduced diameter of the liquid-gas separation hole, number of the liquid-gas separation hole, The modified We number was suitable for analyzing two unexpected phenomenon:one was the increase of liquid level height with increasing header diameter at the same inlet conditions. The other was the decrease of water seepage flow rate with increasing the number of the liquid-gas separation holes.Headers were designed according to the analysis of the results of gas-liquid separation characteristics of the header in the cold state experiments. The tube path was reasonable designed based on the principle that maintaining all the steam flow rates basically remain unchanged to avoid heat transfer weakening caused by reduced steam. The baffles with liquid-gas separation holes were designed according to the relationship between water seepage flow rate and modified We number. The system performance characteristics of air conditioning systems with liquid-vapor separation condenser (LSC) were invested in a standard air enthalpy difference test room. The results indicate that, the designs of refrigerant flow path and the holes in the baffles of the LSC affected the system performance, among three tested LSC systems, the best LSC had the most uniform wall temperature distribution and the smallest pressure drop. The cooling capacity and EER(Energy Efficiency Ratio) of the best LSC system were8.04%and11.11%higher than those of the worst of the three tested LSC systems. Compared to the baseline system, although the LSC had only67%of the heat transfer area of the baseline condenser, the cooling capacity and EER of the LSC system were only1.6%and2.8%less than those of the baseline system at the nominal operating condition. |
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