共查询到20条相似文献,搜索用时 343 毫秒
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为了获得开缝布置方式对开缝翅片管换热器传热与阻力特性的影响规律,对5种不同翅片管换热器进行了数值模拟研究,并进行了模化试验验证。结果表明:增加开缝会提高翅片管换热器的传热性能,但阻力也随之增加;与开缝位置相比,开缝数量对开缝翅片管换热器传热与阻力特性的影响更大;在Re=4800~7500日时,开缝翅片管换热器综合流动传热性能 随着Re数的增大而增大;在5种翅片中,开缝翅片的综合流动传热性能高于普通平直翅片;数值模拟与试验结果偏差较小,采用数值模拟方法能够比较准确地分析开缝翅片管换热器的传热与阻力特性。 相似文献
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通过对不同开缝数量、不同相对开缝高度的单向开缝翅片管换热器进行模拟,分析开缝数量、相对开缝高度对单向开缝翅片管换热器传热与阻力性能的影响规律。结果表明:在开缝数量为3~7片时,翅片侧Nu和f因子随着开缝数量的增加而增大,但Nu增幅逐渐减小;将开缝的数量取为5片能得到最好的综合性能;在相对开缝高度为0.3~0.7时,翅片侧Nu和f因子随着相对开缝高度的增加而增大,但当相对开缝高度在0.5~0.7范围内,翅片侧Nu的增幅减小;将相对开缝高度取为0.5能得到最好的综合性能。 相似文献
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Effects of thermal property variations on the liquid flow and heat transfer in microchannel heat sinks 总被引:1,自引:0,他引:1
Zhigang Li Xiulan Huai Yujia Tao Huanzhuo Chen 《Applied Thermal Engineering》2007,27(17-18):2803-2814
Three-dimensional conjugate numerical simulations using the inlet, average and variable thermal properties respectively were performed for the laminar water flow and heat transfer in rectangular microchannels with Dh of 0.333 mm at Re of 101–1775. Both average and variable properties are adopted in data reduction. The calculated local and average characteristics of flow and heat transfer are compared among different methods, and with the experiments, correlations and simplified theoretical solution data from published literatures. Compared with the inlet property method, both average and variable property methods have significantly lower fapp, but higher convective heat transfer coefficient hz and Nuz. Compared with the average property method, the variable property method has higher fappReave and lower hz at the beginning, but lower fappReave and higher hz at the later section of the channel. The calculated Nuave agree well with the Sieder-Tate correlation and the recently reported experiment, validating the traditional macroscale theory in predicting the flow and heat transfer characteristics in the dimension and Re range of the present work. 相似文献
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Using the Buckingham Pi theorem, this study derives dimensionless correlations to characterize the heat transfer performance of the corrugated channel in a plate heat exchanger. The experimental data are substituted into these correlations to identify the flow characteristics and channel geometry parameters with the most significant influence on the heat transfer performance. Simplified correlations by omitting the factors with less influence are then obtained. The results show that Nux is affected primarily by Re, R/Dh, x/Dh, and β. Neglecting the minor effect of factors on Nux, it is shown that Num is determined primarily by Re, R/Dh and β. 相似文献
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Mixed convection heat transfer in a cubical cavity with an isothermally heated blockage inside filled with a hybrid nanofluid (HBNF) is numerically studied. The natural convection is created by the temperature difference between the hot block and the cold lateral walls, while the forced convection is generated by moving the upper wall. The influence of some variables, like the aspect ratio (0.1 ≤ r ≤ 0.5), Richardson number (0 ≤ Ri≤ 20), Reynolds number (50 ≤ Re ≤ 200), volume concentration of nanoparticles (0 ≤ ϕ ≤ 0.06), and the concentration ratio (2:8, 5:5, and 8:2) on the flow field and heat transfer is analyzed. A comparison between hybrid and mono nanofluids (NFs) is realized to investigate the energy transport enhancement. Results show that the increase of each parameter causes an increase of average Nusselt number Nuavg and improves the heat transfer; besides the use of HBNF gives better Nuavg values. Three correlations of the effect of r, ϕ, Ri, and Re on Nuavg are determined for both hybrid and mono NFs. 相似文献
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The present work experimentally investigates the effect of vortex generators, in the form of small tabs projecting normally into the flow at the nozzle exit, on the fluid flow and heat transfer characteristics of an axisymmetric impinging air jet in the subcritical Reynolds number range. With this comes the expectation of a large eddy structure variation and the possibility of active control. Local heat transfer and static pressure were measured on a target plate for a round air jet issuing from a circular nozzle with rectangular tabs whose numbers and lengths changed at a constant nozzle‐to‐plate gap (L/d = 8) and jet Reynolds number (Re = 34,000). The main results are the following: When two tabs were set at the exit of the circular nozzle, Cpw and Nu profiles flatten in the direction of the tab setting. In the case of three tabs, however, among both Cpw and Nu profiles a concentric profile is found, as well as in the case without any tabs. © 2001 Scripta Technica, Heat Trans Asian Res, 30(7): 561–570, 2001 相似文献
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Forced convection in channels filled with packed beads with internal heat source was numerically analyzed by using the extended Darcy model for the flow and energy conservation equations with nonthermal equilibrium (NTE). The temperature difference between the matrix and fluid phases was discussed with three dimensionless parameters (Rep, H/dp, and ks/kf). It is concluded that the thermal equilibrium assumption may be adopted for the situation when the solid conduction dominated over the convection or when the heat transfer coefficient between the two phases is large at large Rep. The Nusselt number at the wall with the variation of Rep for different ks/kf was also investigated. © 2001 Scripta Technica, Heat Trans Asian Res, 30(3): 213–221, 2001 相似文献
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Present paper is performed to investigate the heat and exergy transfer characteristics of forced convection flow through a horizontal rectangular channel where open-cell metal foams of different pore densities such as 10, 20 and 30 PPI (per pore inches) were situated. All of the bounding walls of the channel are subjected to various uniform heat fluxes. The pressure drop and heat transfer characteristics are presented by two important parametric values, Nusselt number (NuH) and friction factor (f), as functions of Reynolds number (ReH) and the wall heat flux (q). The Reynolds number (ReH) based on the channel height of the rectangular channel is varied from 600 to 33?000, while the Grashof number (GrDh) ranged from approximately 105–107 depending on q. Based on the experimental data, new empirical correlations are constructed to link the NuH. The results of all cases are compared to that of the empty channel and the literature. It is found that the results are in good agreement with those cited in the references. The mean exergy transfer Nusselt number (Nue) based on the ReH, NuH, Pr and q for a rectangular channel with constant heat flux is presented and discussed. 相似文献
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This experiment was carried out using delta winglet arrays of vortex generators (VG) with inline arrangement in a tube heat exchanger to study enhanced heat transfer and flow behaviour. The experiment was conducted for the turbulent flow (Re = 6000 to 27000). In this experiment, different parameters, pitch ratios (PR = 1.6, 2.4, and 4.8), lengths (L = 10, 15, and 20 mm), and attack angles (B = 0°, 10°, 20°, 30°, and 45°) were studied and then their effect on thermal performance was observed. Results indicate that the PR affected f and Nu significantly. For PR = 1.6, VGs showed the highest f and Nu for all of the cases. Vortex generators with L10 B45 PR4.8 achieved the best TPE with 1.23 at Re = 6000. Attack angle B indicated a significant impact on thermal performance and 45 degree showed the TPE of 1.23 at lower Re. Oil film flow and smoke flow visualization were employed to identify the flow vortices and understand flow mechanism. The oil film flow and smoke flow visualization clearly traced longitudinal vortex, and induced vortex, which induced impingement flow and recirculation zone that lead to significant heat transfer enhancement. 相似文献
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This paper examines experimentally the effect of jet vortex technology on enhancing the heat transfer rate within a double pipe heat exchanger by supplying the heat exchanger with water at different vortex strengths. A vortex generator with special inclined holes with different inlet angles was designed, manufactured, and integrated within the heat exchanger. In this study, four levels of Reynolds number for hot water in the annulus (Reh) were used, namely, 10,000; 14,500; 18,030; and 19,600. Similarly, four levels of Reynolds number for cold water in the inner tube (Rec) were used, namely, 12,000; 17,500; 22,500; and 29,000. As for the inlet flow angle (θ), four different levels were selected, namely, 0°, 30°, 45°, and 60°. The temperature along the heat exchanger was measured utilizing 34 thermocouples installed along the heat exchanger. It was found that increasing the inlet flow angle (θ) and/or the Reynolds number results in an increase in the local Nusselt number, the overall heat transfer coefficient, and the ratio of friction factor. It is revealed that the percentage increase in the average Nusselt number due to swirl flow compared to axial flow was 10%, 40%, and 82% for an inlet flow angle of 30°, 45°, and 60°, respectively. 相似文献
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Qiang Yu Dawen Peng Yuting Wu Chongfang Ma 《Numerical Heat Transfer, Part A: Applications》2013,63(10):1666-1684
AbstractTo analyze the natural convection heat transfer of molten salt nanofluids around vertical array of horizontal cylinders, a numerical simulation is performed with cylinder numbers in the range of N?=?2–8 and pitches in the range of S/D?=?5–10. The results show that the heat transfer of nanofluids around each cylinder is affected by the position in the tube row and its distance from the adjacent cylinder. The average Nusselt number (Nua) of the natural convection heat transfer over the whole array of cylinders is determined by cylinder spacing S/D, cylinder number N, and Ra. When S/D?=?5, Nua decreases as the cylinder number increases. When S/D?=?10, Nua increases as the cylinder number increases. Compared with the molten salts, the natural convection heat transfer of nanofluids is enhanced. This study provides a theoretical basis for the design of a single-tank energy storage system. 相似文献
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A steady-state three-dimensional numerical model was used to study the heat transfer and pressure drop characteristics of an offset strip fin heat exchanger. Water was the heat transfer medium, and the Reynolds number Redh ranged from 10 to 3500. Variations in the Fanning friction factor f and the Colburn heat transfer factor j relative to Redh were observed. General correlations for the f and j factors were derived, and these could be used to analyze fluid flow and heat transfer characteristics of offset strip fins in the laminar, transition, and turbulent regions. Finally, three performance criteria (j/f, j/f1/3, and JF) were adopted, and the best performance criteria for the cases Pr = 7 and Pr = 50 were chosen to be JF and j/f1/3, respectively. 相似文献