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Radiation convective heat transfer in channel of a heat exchanger with an intermediate screen
Summaries of other CHISA papers
467
perforated jacket, and also at body location (disc, plate, ball) in a finely dispersed filling affected by vibration. It is established that heat transfer increases with the increase of cylinder vibration amplitude and reduction of the gap between its surface and the jacket, and reaches the maximum with the increase of vibration frequency and hole diameters. For single row perforation heat exchange intensity depended also on the angle distance ~, from the upper cylinder generatrix. At vertically directed cylinder vibration heat transfer maximum was reached at ~b = 33--45°C and minimum at ¢, = 90°C. The results of experimental definition of heat transfer factors at a critical point for a single row perforated are given as a criterion equation. A similar mode of heat transfer is observed at body immersed into a vibrating filling of finely dispersed material, in which appear alternating direction pulsations of gas pressure and consequently flow rates. The circulating material complicates the heat transfer process as compared to that at fixed performation arrangement. At free floating of bodies in such a bed the advantage of jet heat transfer becomes fully apparent, as the natural jets rearrangement, their small dia. equal to the pore size between the particles, and a great number of jets per body surface unit contribute to high heat transfer intensity. In particular for a free floating disc (0 30 x 5 ram) and a ball (0 ! 6 mm) made of copper the heat transfer coefficient were in the range of 600 + 950 W m- 2 K- i. Data on the effect of free floating bodies size and shape, vibration parameters, filling particle size on heat transfer are obtained.
RADIATION CONVECTIVE HEAT TRANSFER IN CHANNEL OF A HEAT EXCHANGER WITH AN INTERMEDIATE SCREEN A. A. KHALAI'OV,R. SH. VAINBERGand A. L. SATANOVSKII Inst. Eng. Thermophys., Ukr. Acad. Sci., Kiev, USSR
One of the efficient and simple construction methods for heat transfer intensification in a heat exchanger channel at high temperatures is the application of intermediate screens that are placed along the flow between the heated walls. In this case the surface cooling is realized both by radiation and convection, the radiation component of the heat flow transferred to the screen being transmitted to the air flow by convection. The results of theoretical and experimental study of radiation-convective heat transfer at air flow motion in a flat channel are presented in the paper. Equations describing the wall and screen temperature state at different values of the basic parameters are obtained. Two practically important cases--equal heat flows and equal surface temperatures--have been theoretically analysed for two situations--with and without the screen. An expression characterising the surface temperature reduction as a result of screen application has been obtained for the first case. For the second case an equation determining the increase of heat flow at constant wall temperature has been obtained. Graphical dependencies for both cases characterising the efficiency of the screen application have been plotted. The results of the numerical analysis of one practically important case are presented. The experimental study results confirm the theoretical conclusion that intermediate screens are highly effective. In the most interesting range of the characteristic parameter changes the average surface temperature reduction was 4.0~, the heat flow increase being up to 10~. The effectiveness of screens is shown to increase with the heat flow rise and Reynolds number reduction. The technical and economical analysis of one installation with an intermediate screen is presented.
467
perforated jacket, and also at body location (disc, plate, ball) in a finely dispersed filling affected by vibration. It is established that heat transfer increases with the increase of cylinder vibration amplitude and reduction of the gap between its surface and the jacket, and reaches the maximum with the increase of vibration frequency and hole diameters. For single row perforation heat exchange intensity depended also on the angle distance ~, from the upper cylinder generatrix. At vertically directed cylinder vibration heat transfer maximum was reached at ~b = 33--45°C and minimum at ¢, = 90°C. The results of experimental definition of heat transfer factors at a critical point for a single row perforated are given as a criterion equation. A similar mode of heat transfer is observed at body immersed into a vibrating filling of finely dispersed material, in which appear alternating direction pulsations of gas pressure and consequently flow rates. The circulating material complicates the heat transfer process as compared to that at fixed performation arrangement. At free floating of bodies in such a bed the advantage of jet heat transfer becomes fully apparent, as the natural jets rearrangement, their small dia. equal to the pore size between the particles, and a great number of jets per body surface unit contribute to high heat transfer intensity. In particular for a free floating disc (0 30 x 5 ram) and a ball (0 ! 6 mm) made of copper the heat transfer coefficient were in the range of 600 + 950 W m- 2 K- i. Data on the effect of free floating bodies size and shape, vibration parameters, filling particle size on heat transfer are obtained.
RADIATION CONVECTIVE HEAT TRANSFER IN CHANNEL OF A HEAT EXCHANGER WITH AN INTERMEDIATE SCREEN A. A. KHALAI'OV,R. SH. VAINBERGand A. L. SATANOVSKII Inst. Eng. Thermophys., Ukr. Acad. Sci., Kiev, USSR
One of the efficient and simple construction methods for heat transfer intensification in a heat exchanger channel at high temperatures is the application of intermediate screens that are placed along the flow between the heated walls. In this case the surface cooling is realized both by radiation and convection, the radiation component of the heat flow transferred to the screen being transmitted to the air flow by convection. The results of theoretical and experimental study of radiation-convective heat transfer at air flow motion in a flat channel are presented in the paper. Equations describing the wall and screen temperature state at different values of the basic parameters are obtained. Two practically important cases--equal heat flows and equal surface temperatures--have been theoretically analysed for two situations--with and without the screen. An expression characterising the surface temperature reduction as a result of screen application has been obtained for the first case. For the second case an equation determining the increase of heat flow at constant wall temperature has been obtained. Graphical dependencies for both cases characterising the efficiency of the screen application have been plotted. The results of the numerical analysis of one practically important case are presented. The experimental study results confirm the theoretical conclusion that intermediate screens are highly effective. In the most interesting range of the characteristic parameter changes the average surface temperature reduction was 4.0~, the heat flow increase being up to 10~. The effectiveness of screens is shown to increase with the heat flow rise and Reynolds number reduction. The technical and economical analysis of one installation with an intermediate screen is presented.