Experimental Study On Flow-boiling Heat Transfer In A Tube Enhanced By A Horizontal Composite Structure

Under the background of the rapid development of the world economy,the problems of environment,ecology and energy are becoming more and more serious,the energy problem has been paid great attention by all mankind.To improve the efficiency of traditional energy use and promote the development and use of clean energy will become the core theme of the development of China's energy field in the next few decades.In the context of carbon peaking and carbon neutrality goals,the development of enhanced heat transfer technology provides a very important value in energy saving,environmental protection and cost reduction.In all kinds of research in the field of enhanced heat transfer technology,the design and development of innovative enhanced heat transfer tube has become one of the important directions of development.In this paper,single-phase and flow boiling heat transfer characteristics of refrigerant R410a in four heat exchanger tubes with different structures were studied by experiments.The experimental results include the comparison of heat transfer coefficient and friction pressure drop loss.The four heat exchanger tubes involved are smooth tube ST,enhanced tube EHT?HB with inner herringbone,enhanced tube EHT?DIM with inner convex,and compound structure enhanced tube EHT?HB/DIM with both herringbone and convex.The experiment of single-phase heat transfer is conducted at 311K and the range of mass flux is between 25 kg/(m~2s)and 225kg/(m~2s),and the saturation temperature of flow boiling heat transfer is 279K at variable mass flux which is between 50 and 205kg/(m~2s).In order to explore the characteristics of local heat transfer coefficient under the flow boiling heat transfer,the thermal-hydraulic characteristics were investigated under three different mass flow rates(100 kg/(m~2s),150 kg/(m~2s),200 kg/(m~2s))respectively,vapor quality ranges from 0.3 to 0.8 and saturation temperature is 279K.The experimental results show that the enhanced tube EHT?HB/DIM with composite structure performs the best enhanced heat transfer effect in all experiments conducted.In the single-phase experiments,the average heat transfer coefficient of EHT?HB/DIM tube is about 53%higher than that of smooth tube;under the experimental condition of flow boiling with variable mass flux,the average heat transfer coefficient of EHT?HB/DIM tube is about 43.75%higher than that of smooth tube.Under the condition of variable vapor quality flow boiling heat transfer at the same mass flux,the maximum heat transfer coefficient of EHT?HB/DIM tube is about 50%higher than that of smooth tube.It is worth noting that the friction pressure drop loss of EHT?HB/DIM tube is also the largest among all the tested tubes,especially under the conditions of high mass flux and high vapor quality.Four classical prediction models of heat transfer coefficient in horizontal smooth tube and two typical prediction models of heat transfer coefficient in horizontal micro-fin tube are selected to predict the experimental data.It showed that the prediction accuracy of Kandlikar model and Kattan model is relatively high.Therefore,based on the original model of Kandlikar and Kattan,a new heat transfer correlation is developed after fitting the experimental data with Matlab software.The comparison results show that the new correlation performs better prediction accuracy of the experimental data.