The thermal transmission coefficient for a micro-ribbed tube has been determined using theoretical relationships and the outcomes of such calculations have been compared with experiments conducted using a R1234yf refr...The thermal transmission coefficient for a micro-ribbed tube has been determined using theoretical relationships and the outcomes of such calculations have been compared with experiments conducted using a R1234yf refrigerant undergoing condensation.In particular four theoretical single-phase flow and three multi-phase flow models have been used in this regard.The experimental results show that:the Oliver et al.criterion equation overestimates the experimental results as its accuracy is significantly affected by the specific conditions realized inside micro-fin tubes;the Miyara et al.criterion equation prediction error is less than 15%;the Cavallini et al.approach gives the highest prediction accuracy;the Goto et al.model overestimates the test data.Such results are critically discussed and some indications for the improvement of such models are provided.展开更多
Experiments and simulations on flow and heat transfer behavior of Therminol-55 liquid phase heat transfer fluid have been conducted in a ribbed tube with the outer diameter and inner diameter 25.0 and 20.0 mm,pitch an...Experiments and simulations on flow and heat transfer behavior of Therminol-55 liquid phase heat transfer fluid have been conducted in a ribbed tube with the outer diameter and inner diameter 25.0 and 20.0 mm,pitch and rib height of 4.5 and 1.0 mm.respectively.Experimental results show that the heat transfer and thermal performance of Therminol-55 liquid phase heat transfer fluid in the ribbed tube are considerably improved compared to those of the smooth tube.The Nusselt number increase with the increase of Reynolds number.The increase in heat transfer rate of the ribbed tube has a mean value of 2.24 times.Also,the pressure drop results reveal that the average friction factor of the ribbed tube is in a range of 2.4 and 2.8 times over the smooth tube.Numerical simulations of three-dimensional flow behavior of Therminol-55 liquid phase heat transfer fluid are carried out using three different turbulence models in the ribbed tube.The numerical results show that the heat transfer of ribbed tube is improved because vortices are generated behind ribs,which produce some disruptions to fluid flow and enhance heat transfer compared with smooth tube.The numerical results prove that the ribbed tube can improve heat transfer and fluid flow performances of Therminol liquid phase heat transfer fluid.展开更多
A new type of cooling stave with internal ribbed tube was proposed,and the heat transfer performance of the stave was studied by means of thermal test and numerical simulation.The temperature of cooling stave was moni...A new type of cooling stave with internal ribbed tube was proposed,and the heat transfer performance of the stave was studied by means of thermal test and numerical simulation.The temperature of cooling stave was monitored in the conditions of furnace gas temperature of 200-700 C and cooling water velocity of 0.2-1.0 m/s.The thermal test results show that the internal rib structure can form swirl in the water pipe and improve the cooling capacity of the cooling stave.The higher the furnace temperature or the lower the cooling water flow rate,the more obvious the advantage of the cooling stave with internal ribbed tube.The mathematical model of the cooling stave with internal ribbed tube was established by FLUENT software,and the influence of the internal rib structure parameters on the heat transfer performance of the cooling stave was discussed.It is suggested that the parameters of the internal ribbed tube should be 4 ribs,1 mm in height,5-7 mm in width,and 20-30 mm in lead.In the same common working conditions of the cooling stave,the maximum temperature of the newly designed cooling stave with internal ribbed tube is reduced by 5.6%compared with that of common cooling stave with round tube.The water flow rate in the internal ribbed tube only needs 0.9 m/s to reach the cooling effect of 2 m/s in the common tube cooling stave,which can save 55%of water.In case of water shortage accident of cooling stave,the maximum temperature of the cooling stave with internal ribbed tube is decreased by 22.4%compared with that of common round tube,which can effectively reduce the harm of water shortage and protect the cooling stave.展开更多
Using the upper bound element technique (UBET), a numerical model was proposed for analyzing the metal deformation behavior in the extrusion process of ribbed thin wall pipes through a porthole die. Optimization param...Using the upper bound element technique (UBET), a numerical model was proposed for analyzing the metal deformation behavior in the extrusion process of ribbed thin wall pipes through a porthole die. Optimization parameters were contained in the numerical model and determined through minimizing the total work of metal deformation. Taking the extrusion process of thin wall pipe with one rib as an example, the calculated results using the proposed model are as follows: the extrusion pressure p is linearly related to the extrusion ratio R by p = a+bR 0.683 , where a = 14.13, b = 0.911. When the length of the billet remaining in container is shorter than a quarter of the container diameter, the plastic region extends over the whole of the remained billet and the extrusion process reaches the state of funnel deformation. There exists an optimum depth of welding chamber in respect of the extrusion pressure, and to the calculated example the optimum depth is about 10% of the circumscribed diameter of portholes. To obtain more equitable metal flow in welding chamber, it is required to make the dividing planes in container to be consistent with corresponding welding planes in the chamber ( θ max i = θ′ max i ) through choosing different entering area for each of the portholes.展开更多
Experiments about heat transfer in the presence of a two-phase flow due to the condensation of a R1234yf refrigerant have been performed considering a smooth tube and two micro-fin tubes.The following experimental con...Experiments about heat transfer in the presence of a two-phase flow due to the condensation of a R1234yf refrigerant have been performed considering a smooth tube and two micro-fin tubes.The following experimental conditions have been considered:Condensation temperatures of 40℃,43℃ and 45℃,mass fluxes of 500–900 kg/(m^(2)·s),vapor qualities at the inlet and outlet of the heat transfer tube in the ranges 0.8–0.9 and 0.2–0.3,respectively.These tests have shown that:(1)The heat transfer coefficient increases with decreasing the condensation temperature and on increasing the mass flux;(2)The heat transfer coefficient inside the micro-fin tube is larger than that for the smooth tube;(3)The heat transfer enhancement factors for the micro-fin tube with a fin helical angle of 8°and 15°are 2.51–2.89 and 3.11–3.57,respectively;both are higher than the area increase ratio.These experimental results have been compared with correlations available in the literature:the Cavallini et al.correlation has the highest accuracy in predicting the heat transfer coefficient inside the smooth tube,the related percentage error and the average prediction error are±8%and 0.56%,respectively;for the micro-fin tube these become±25%and 6%,respectively.展开更多
基金supported by the National Natural Science Foundation of China(No.41877251)Major Science and Technology Projects of Xinxiang City(No.21ZD012).
文摘The thermal transmission coefficient for a micro-ribbed tube has been determined using theoretical relationships and the outcomes of such calculations have been compared with experiments conducted using a R1234yf refrigerant undergoing condensation.In particular four theoretical single-phase flow and three multi-phase flow models have been used in this regard.The experimental results show that:the Oliver et al.criterion equation overestimates the experimental results as its accuracy is significantly affected by the specific conditions realized inside micro-fin tubes;the Miyara et al.criterion equation prediction error is less than 15%;the Cavallini et al.approach gives the highest prediction accuracy;the Goto et al.model overestimates the test data.Such results are critically discussed and some indications for the improvement of such models are provided.
基金Supported by the National Natural Science Foundation of China(11472093 and21276056)
文摘Experiments and simulations on flow and heat transfer behavior of Therminol-55 liquid phase heat transfer fluid have been conducted in a ribbed tube with the outer diameter and inner diameter 25.0 and 20.0 mm,pitch and rib height of 4.5 and 1.0 mm.respectively.Experimental results show that the heat transfer and thermal performance of Therminol-55 liquid phase heat transfer fluid in the ribbed tube are considerably improved compared to those of the smooth tube.The Nusselt number increase with the increase of Reynolds number.The increase in heat transfer rate of the ribbed tube has a mean value of 2.24 times.Also,the pressure drop results reveal that the average friction factor of the ribbed tube is in a range of 2.4 and 2.8 times over the smooth tube.Numerical simulations of three-dimensional flow behavior of Therminol-55 liquid phase heat transfer fluid are carried out using three different turbulence models in the ribbed tube.The numerical results show that the heat transfer of ribbed tube is improved because vortices are generated behind ribs,which produce some disruptions to fluid flow and enhance heat transfer compared with smooth tube.The numerical results prove that the ribbed tube can improve heat transfer and fluid flow performances of Therminol liquid phase heat transfer fluid.
基金funded by the National Natural Science Foundation of China(51574179)Nantong Science and Technology Project(JC2019154).
文摘A new type of cooling stave with internal ribbed tube was proposed,and the heat transfer performance of the stave was studied by means of thermal test and numerical simulation.The temperature of cooling stave was monitored in the conditions of furnace gas temperature of 200-700 C and cooling water velocity of 0.2-1.0 m/s.The thermal test results show that the internal rib structure can form swirl in the water pipe and improve the cooling capacity of the cooling stave.The higher the furnace temperature or the lower the cooling water flow rate,the more obvious the advantage of the cooling stave with internal ribbed tube.The mathematical model of the cooling stave with internal ribbed tube was established by FLUENT software,and the influence of the internal rib structure parameters on the heat transfer performance of the cooling stave was discussed.It is suggested that the parameters of the internal ribbed tube should be 4 ribs,1 mm in height,5-7 mm in width,and 20-30 mm in lead.In the same common working conditions of the cooling stave,the maximum temperature of the newly designed cooling stave with internal ribbed tube is reduced by 5.6%compared with that of common cooling stave with round tube.The water flow rate in the internal ribbed tube only needs 0.9 m/s to reach the cooling effect of 2 m/s in the common tube cooling stave,which can save 55%of water.In case of water shortage accident of cooling stave,the maximum temperature of the cooling stave with internal ribbed tube is decreased by 22.4%compared with that of common round tube,which can effectively reduce the harm of water shortage and protect the cooling stave.
文摘Using the upper bound element technique (UBET), a numerical model was proposed for analyzing the metal deformation behavior in the extrusion process of ribbed thin wall pipes through a porthole die. Optimization parameters were contained in the numerical model and determined through minimizing the total work of metal deformation. Taking the extrusion process of thin wall pipe with one rib as an example, the calculated results using the proposed model are as follows: the extrusion pressure p is linearly related to the extrusion ratio R by p = a+bR 0.683 , where a = 14.13, b = 0.911. When the length of the billet remaining in container is shorter than a quarter of the container diameter, the plastic region extends over the whole of the remained billet and the extrusion process reaches the state of funnel deformation. There exists an optimum depth of welding chamber in respect of the extrusion pressure, and to the calculated example the optimum depth is about 10% of the circumscribed diameter of portholes. To obtain more equitable metal flow in welding chamber, it is required to make the dividing planes in container to be consistent with corresponding welding planes in the chamber ( θ max i = θ′ max i ) through choosing different entering area for each of the portholes.
基金supported by the National Natural Science Foundation of China(No.41877251).
文摘Experiments about heat transfer in the presence of a two-phase flow due to the condensation of a R1234yf refrigerant have been performed considering a smooth tube and two micro-fin tubes.The following experimental conditions have been considered:Condensation temperatures of 40℃,43℃ and 45℃,mass fluxes of 500–900 kg/(m^(2)·s),vapor qualities at the inlet and outlet of the heat transfer tube in the ranges 0.8–0.9 and 0.2–0.3,respectively.These tests have shown that:(1)The heat transfer coefficient increases with decreasing the condensation temperature and on increasing the mass flux;(2)The heat transfer coefficient inside the micro-fin tube is larger than that for the smooth tube;(3)The heat transfer enhancement factors for the micro-fin tube with a fin helical angle of 8°and 15°are 2.51–2.89 and 3.11–3.57,respectively;both are higher than the area increase ratio.These experimental results have been compared with correlations available in the literature:the Cavallini et al.correlation has the highest accuracy in predicting the heat transfer coefficient inside the smooth tube,the related percentage error and the average prediction error are±8%and 0.56%,respectively;for the micro-fin tube these become±25%and 6%,respectively.
