端部圆角结构提升带针肋微通道热沉均温性
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摘要
布设针肋的微通道因其具有较高的强化传热传质效率而得到了广泛应用,但针肋背风侧端部存在的局部高温区域和整体较差的均温性将会提升换热表面的温度梯度,产生额外扩展热阻,将在很大程度上影响系统的调制响应,以及设备的经济性和可靠性.为解决上述问题,本文提出了采用端部圆角结构改进带针肋微通道热沉均温性的研究思路,并详细分析了其周期性层流流动换热性特性,由结果可见,Re=0~120时该新型针肋强化了微通道内的展向和法向二次流,提升了外侧换热面和针肋表面的均温性,有效消除了针肋背风侧端部的局部高温区域,并且随着圆角半径的增加,上述效应逐渐增强,通道努塞尔数最大增加了16.93%;而与传统带针肋微通道热沉相比,该新型微通道的阻力系数并未明显增加,因此,通道综合热性能系数最大增加了16.22%.此外,随着Re数继续增加,圆角结构对通道换热性能的影响逐渐减弱.
Energy and mass transfer process are involved in many industries, such as energy, transportation, aeronautics and astronautics, electronic, manufacturing, among which, the heat exchanger plays a very key role. With the development of science and technology and the increasing requirements for energy conservation and emission reduction, the efficiency of heat exchange system has to be promoted to meet the demand of higher heat intensity and thermal load. The high-efficient and energy-saving compact heat exchanger such as microchannel heat sink has gained more attractions in academic researches and engineering applications. Microchannel with pin-fin is widely used in engineering applications due to its high efficiency in heat and mass transfer, but the high temperature region formed in the rear of the cylinder and the non-uniformity temperature field increase the temperature gradient and generate extra thermal spreading resistance, which would, to a large extend, influence the regulation of the system and the economy and reliability of the equipments. Therefore, the endwall fillet structure is proposed in this work, based on researches about the performance of CDA(controlled diffusion airfoil) blade with fillet, to improve the temperature uniformity and heat transfer performance of microchannel with pin-fin. The periodical laminar flow and heat transfer performances are comparatively studied. The results show that the flow resistance coefficient f of the microchannel with filleted pin-fin does not increase significantly compared to traditional pin-fined microchannel, which means the introducing of the fillet will enhance the heat transfer while f of the microchannel is almost a constant. The maximum increase of f is only 2.03%. Moreover, two separate symmetrical secondary flows develop in microchannel with smooth cylinder, with one on the top of the other. After adding the proposed structures, at low Reynolds number, the lower span-wise secondary flow is enhanced as the radius increases and these two span-wise secondary flows gradually merge into one which develops along the normal direction. At high Reynolds number, the mainstream low-temperature core region is obvious asymmetry: it moves downwards gradually as Reynolds number increases. Besides, at low Reynolds number(0–120), the fillet improves the heat and mass transfer between the main stream core and areas near the wall, enhances the thermal uniformity of the pin-fin and heated walls, improves the heat transfer performance of the rear of the cylinder and eliminates the high temperature area in the pin-fin. And local high-temperature region on the top half of the microchannel decreases, which contributes to the extension of low-temperature region and the decrease of average temperature. As the radius of the fillet increases, the effects mentioned above are gradually enhanced. The heat transfer coefficient of the channel reaches a maximum augmentation of 16.93%, and the flow resistance coefficient of the microchannel with filleted pin-fin does not increase significantly. Comparing with the synthetical thermal performance coefficient of pin-fined microchannel heat sink, that of the proposed filleted pin-fin microchannel increases 16.22% at most. As the Reynolds number increases, the influence of the fillet structure decreases. The study motivation of combining separation flow researches of rotatory machines with heat transfer enhancement, as well as the resulting design are a beneficial attempt for scientific research and engineering application.
Energy and mass transfer process are involved in many industries, such as energy, transportation, aeronautics and astronautics, electronic, manufacturing, among which, the heat exchanger plays a very key role. With the development of science and technology and the increasing requirements for energy conservation and emission reduction, the efficiency of heat exchange system has to be promoted to meet the demand of higher heat intensity and thermal load. The high-efficient and energy-saving compact heat exchanger such as microchannel heat sink has gained more attractions in academic researches and engineering applications. Microchannel with pin-fin is widely used in engineering applications due to its high efficiency in heat and mass transfer, but the high temperature region formed in the rear of the cylinder and the non-uniformity temperature field increase the temperature gradient and generate extra thermal spreading resistance, which would, to a large extend, influence the regulation of the system and the economy and reliability of the equipments. Therefore, the endwall fillet structure is proposed in this work, based on researches about the performance of CDA(controlled diffusion airfoil) blade with fillet, to improve the temperature uniformity and heat transfer performance of microchannel with pin-fin. The periodical laminar flow and heat transfer performances are comparatively studied. The results show that the flow resistance coefficient f of the microchannel with filleted pin-fin does not increase significantly compared to traditional pin-fined microchannel, which means the introducing of the fillet will enhance the heat transfer while f of the microchannel is almost a constant. The maximum increase of f is only 2.03%. Moreover, two separate symmetrical secondary flows develop in microchannel with smooth cylinder, with one on the top of the other. After adding the proposed structures, at low Reynolds number, the lower span-wise secondary flow is enhanced as the radius increases and these two span-wise secondary flows gradually merge into one which develops along the normal direction. At high Reynolds number, the mainstream low-temperature core region is obvious asymmetry: it moves downwards gradually as Reynolds number increases. Besides, at low Reynolds number(0–120), the fillet improves the heat and mass transfer between the main stream core and areas near the wall, enhances the thermal uniformity of the pin-fin and heated walls, improves the heat transfer performance of the rear of the cylinder and eliminates the high temperature area in the pin-fin. And local high-temperature region on the top half of the microchannel decreases, which contributes to the extension of low-temperature region and the decrease of average temperature. As the radius of the fillet increases, the effects mentioned above are gradually enhanced. The heat transfer coefficient of the channel reaches a maximum augmentation of 16.93%, and the flow resistance coefficient of the microchannel with filleted pin-fin does not increase significantly. Comparing with the synthetical thermal performance coefficient of pin-fined microchannel heat sink, that of the proposed filleted pin-fin microchannel increases 16.22% at most. As the Reynolds number increases, the influence of the fillet structure decreases. The study motivation of combining separation flow researches of rotatory machines with heat transfer enhancement, as well as the resulting design are a beneficial attempt for scientific research and engineering application.
引文
1 Ma J,Sun Y S,Li B W.Simulation of combined conductive,convective and radiative heat transfer in moving irregular porous fins by spectral element method.Int J Therm Sci,2017,118:475-487
2 Vafai K,Zhu L.Analysis of two-layered micro-channel heat sink concept in electronic cooling.Int J Heat Mass Tran,1999,42:2287-2297
3 Peles Y,Ko?ar A,Mishra C,et al.Forced convective heat transfer across a pin fin micro heat sink.Int J Heat Mass Tran,2005,48:3615-3627
4 Fan C,Sun F,Yang L,et al.Experimental investigation of flat miniature heat pipes with three kinds of micro grooves.J Enhanc Heat Transf,2004,11:467-476
5 Wei X J,Joshi Y K,Ligrani P M.Numerical simulation of laminar flow and heat transfer inside a microchannel with one dimpled surface.J Electron Packaging,2007,129:63-70
6 Li P,Xie Y,Zhang D.Laminar flow and forced convective heat transfer of shear-thinning power-law fluids in dimpled and protruded microchannels.Int J Heat Mass Tran,2016,99:372-382
7 Ko?ar A,Mishra C,Peles Y.Laminar flow across a bank of low aspect ratio micro pin fins.J Fluids Eng-T ASME,2005,127:419-430
8 Ko?ar A,Peles Y.Thermal-hydraulic performance of MEMS-based pin fin heat sink.J Heat Transf,2006,128:121-131
9 Marques C,Kelly K W.Fabrication and performance of a pin fin micro heat exchanger.J Heat Transf,2004,126:434-444
10 Vanapalli S,Ter Brake H J M,Jansen H V,et al.Pressure drop of laminar gas flows in a microchannel containing various pillar matrices.J Micromech Microeng,2007,17:1381-1386
11 Wang Y,Houshmand F,Elcock D,et al.Convective heat transfer and mixing enhancement in a microchannel with a pillar.Int J Heat Mass Tran,2013,62:553-561
12 Curlett B P.The aerodynamic effect of fillet radius in a low speed compressor cascade.NASA Technical Memorandum,Washington D C,1991.105347
13 Hoeger M,Schmidt-Eisenlohr U,Gomez S,et al.Numerical simulation of the influence of a fillet and a bulb on the secondary flow in a compressor cascade.Task Quart,2002,6:25-37
14 Hoeger M,Baier R D,Müller R,et al.Impact of a fillet on diffusing vane endwall flow structure.In:Proccedings of the 11th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery.Honolulu,2006.ISROMAC 2006-05
15 Kügeler E,Nürnberger D,Weber A,et al.Influence of blade fillets on the performance of a 15 stage gas turbine compressor.In:Proceedings of ASME Turbo Expo:Power for Lan,Sea and Air.Berlin,2008.GT2008-50748
16 Goodhand M N,Miller R J.The impact of real geometries on three-dimensional separations in compressors.J Turbomach,2012,134:021007
17 Meyer R,Schulz S,Liesner K,et al.A parameter study on the influence of fillets on the compressor cascade performance.J Theor Appl Mech,2012,50:131-145
18 Li P,Zhang D,Xie Y.Heat transfer and flow analysis of Al2O3-water nanofluids in microchannel with dimple and protrusion.Int J Heat Mass Tran,2014,73:456-467
19 Shah R K,London A L.Laminar Flow Forced Convection in Ducts.New York:Academic Press,1978
20 Xie G,Liu J,Zhang W,et al.Numerical prediction of flow structure and heat transfer in square channels with dimples combined with secondary half-size dimples/protrusions.Numer Heat Tr A-Appl,2014,65:327-356
21 Murata A,Mochizuki S.Centrifugal buoyancy effect on turbulent heat transfer in a rotating two-pass smooth square channel with sharp180-deg turns.Int J Heat Mass Tran,2004,47:3215-3231
2 Vafai K,Zhu L.Analysis of two-layered micro-channel heat sink concept in electronic cooling.Int J Heat Mass Tran,1999,42:2287-2297
3 Peles Y,Ko?ar A,Mishra C,et al.Forced convective heat transfer across a pin fin micro heat sink.Int J Heat Mass Tran,2005,48:3615-3627
4 Fan C,Sun F,Yang L,et al.Experimental investigation of flat miniature heat pipes with three kinds of micro grooves.J Enhanc Heat Transf,2004,11:467-476
5 Wei X J,Joshi Y K,Ligrani P M.Numerical simulation of laminar flow and heat transfer inside a microchannel with one dimpled surface.J Electron Packaging,2007,129:63-70
6 Li P,Xie Y,Zhang D.Laminar flow and forced convective heat transfer of shear-thinning power-law fluids in dimpled and protruded microchannels.Int J Heat Mass Tran,2016,99:372-382
7 Ko?ar A,Mishra C,Peles Y.Laminar flow across a bank of low aspect ratio micro pin fins.J Fluids Eng-T ASME,2005,127:419-430
8 Ko?ar A,Peles Y.Thermal-hydraulic performance of MEMS-based pin fin heat sink.J Heat Transf,2006,128:121-131
9 Marques C,Kelly K W.Fabrication and performance of a pin fin micro heat exchanger.J Heat Transf,2004,126:434-444
10 Vanapalli S,Ter Brake H J M,Jansen H V,et al.Pressure drop of laminar gas flows in a microchannel containing various pillar matrices.J Micromech Microeng,2007,17:1381-1386
11 Wang Y,Houshmand F,Elcock D,et al.Convective heat transfer and mixing enhancement in a microchannel with a pillar.Int J Heat Mass Tran,2013,62:553-561
12 Curlett B P.The aerodynamic effect of fillet radius in a low speed compressor cascade.NASA Technical Memorandum,Washington D C,1991.105347
13 Hoeger M,Schmidt-Eisenlohr U,Gomez S,et al.Numerical simulation of the influence of a fillet and a bulb on the secondary flow in a compressor cascade.Task Quart,2002,6:25-37
14 Hoeger M,Baier R D,Müller R,et al.Impact of a fillet on diffusing vane endwall flow structure.In:Proccedings of the 11th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery.Honolulu,2006.ISROMAC 2006-05
15 Kügeler E,Nürnberger D,Weber A,et al.Influence of blade fillets on the performance of a 15 stage gas turbine compressor.In:Proceedings of ASME Turbo Expo:Power for Lan,Sea and Air.Berlin,2008.GT2008-50748
16 Goodhand M N,Miller R J.The impact of real geometries on three-dimensional separations in compressors.J Turbomach,2012,134:021007
17 Meyer R,Schulz S,Liesner K,et al.A parameter study on the influence of fillets on the compressor cascade performance.J Theor Appl Mech,2012,50:131-145
18 Li P,Zhang D,Xie Y.Heat transfer and flow analysis of Al2O3-water nanofluids in microchannel with dimple and protrusion.Int J Heat Mass Tran,2014,73:456-467
19 Shah R K,London A L.Laminar Flow Forced Convection in Ducts.New York:Academic Press,1978
20 Xie G,Liu J,Zhang W,et al.Numerical prediction of flow structure and heat transfer in square channels with dimples combined with secondary half-size dimples/protrusions.Numer Heat Tr A-Appl,2014,65:327-356
21 Murata A,Mochizuki S.Centrifugal buoyancy effect on turbulent heat transfer in a rotating two-pass smooth square channel with sharp180-deg turns.Int J Heat Mass Tran,2004,47:3215-3231