Pure Refrigerants R245fa Level Tube Flow Boiling Heat Transfer Characteristics Of Experimental Research

Energy consumption increases with the development of economic, however, a large number of energy is wasted by the form of hot gas and water emission. This kind of phenomenon widely exists in some industries, such as chemical, petroleum, metallurgy, nuclear power, refrigeration and so on. Taking the smelter in Kunming Iron & Steel Group Co., Ltd as an example, a large number of flue gas, waste steam, waste hot water which lower 300～400℃are uninterruptedly discharged every day. Organic Rankine cycle power generation using low-boiling point organic working fluids is an effective way for low-grade heat recovery. To choice suitable working fluids for Organic Rankine cycle, the basic requirements including environmental performance, chemical stability, security, thermodynamic performance, cost, heat transfer and flow performance must be satisfied.Accurate calculation of working fluid heat transfer coefficient is the foundation of heat exchanger design and safe operation of equipment. Heat transfer performances of organic fluids R245fa are studied in this paper. The main purpose is to provide a reliable heat transfer design basis for the design and optimization of heat transfer equipments of Organic Rankine cycle power generation using low-boiling point organic working fluids.Some basic parameters of gas-liquid two-phase flow inside a horizontal tube have been analyzed, including cross-section gas rate and liquid rate, mass flow, vapor content, mass flow rate; volumetric flow; volumetric fraction, real gas velocity, gas superficial velocity, sliding ratio; sliding speed, the average density of gas-liquid two-phase flow, the average velocity of gas-liquid two-phase flow and so on.Basic flow patterns of gas-liquid two-phase flow inside a horizontal tube have been analyzed, including single-phase liquid, fine bubbly flow, gas plug-like flow, gas slug flow, wavy stratified flow, annular flow.The correlations of calculation two-phase forced convection heat transfer coefficients were summarized and analyzed. In general, there are two categories:the first, models distinguished by flow patterns, organic refrigerant evaporation heat transfer in the pipe roughly divided into two heat transfer areas in this model that are Pulverescent-boiling heat transfer area and the two-phase forced convection heat transfer area, respectively. The second, models of homogeneous flow patterns,There are three main calculation methods in this model:1,superposition method, a representative of the correlation with Gungor and Wingterton the formula, Chen formula, Jung formula; 2,progressive line method, a representative of the correlation with Liu and Winterton formula, Wattelet formula; 3,enhancement method, a representative of the correlation with Shah formula, Kandlikar formula. And using neural network model calculations tube two-phase forced convection heat transfer coefficient was analyzed.Based on the above theoretical study, convective boiling heat transfer characteristics of R245fa inside horizontal tube are investigated at various mass flow rates of hot water, working fluids and at various evaporation temperatures. The investigation results show that convective boiling heat transfer coefficients goes up with the increase of hot water and working fluid mass flow rate, but it is contrary to evaporation temperature.By comparisons of the experimental local heat transfer coefficients with that predicted by Chen correlation, Liu-Winterton correlation and Shah correlation, it is concluded that deviations of these three correlations are 31.6%,6.3%,37.4% respectively. Liu-Winterton correlation is more precise to predict convective boiling heat transfer coefficients of R245fa than Chen correlation and Shah correlation.