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Two‐dimensional conjugate conduction/convection numerical simulations were carried out for flow and thermal fields in a unit model of a counter‐flow‐type corrugated thin plate heat exchanger core. The effects of the thermal resistance of the solid plate, namely the variation of the plate thickness and the difference of the plate material, on the heat exchanger performance were examined in the Reynolds number range of 100<Re<400. Higher temperature effectiveness was obtained for a thicker plate at any Reynolds number, which was a unique feature of corrugated thin plate geometry. Detailed discussions on the thermal fields revealed that restricting the heat conduction along the plate by making the plate thinner or choosing a low thermal conductivity material causes a larger plate temperature variation along the plate, and, consequently, a smaller amount of thermal energy exchanged between two fluids. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(3): 209–223, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20110 相似文献
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Jun Liu Fenghao Wang Wanlong Cai Zhihua Wang Qingpeng Wei Jiewen Deng 《国际能源研究杂志》2019,43(12):6337-6352
Deep borehole heat exchanger (DBHE) is attracting attention intensively owing to much more geothermal extraction, higher efficiency for heat pumps, and lesser land demand compared with shallow borehole heat exchanger. DBHE is usually dipped into several thousand meters in the subsurface, having a complicated heat transfer with surrounding rock–soil. However, the heat transfer characteristics below surface under different conditions are rarely studied. In this study, a numerical model considering the comprehensive effects of geothermal gradients and heat loss from inner pipe was proposed. The model was validated with experimental data and Beier analytical solution. Based on the model, the effects of primary design parameters on the heat transfer performance below surface along the pipe were investigated. The results indicate that temperature at pipe bottom increases with inlet flow rate decreasing, while the heat load cannot be extracted fully to the surface because of the heat loss of inner pipe. When the inlet flow rates decrease from 41.39 to 4.52 m3/h, the heat loss ratio increases from 25.5% to 63.7%. It is an effective way of insulating inner pipe to reduce heat loss under low inlet flow rates. Increasing the velocity in inner pipe by lessening the inner pipe diameter can also decline the heat loss well. While by this way, the increasing pumping power resulting from the higher velocity in inner pipe has to be considered. This study is significant to effective optimization of DBHE and energy conservation of buildings. 相似文献
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《International Journal of Heat and Mass Transfer》1986,29(5):761-767
Duplex heat exchanger tubes consist of two concentric cylinders assembled in a state of prestress by shrink fitting. During operation, thermal expansion changes the interface pressure and this can cause a substantial increase in the thermal resistance of the tube. Under certain circumstances, more than one steadystate solution can be obtained. In this paper, the effect of this mechanism on the axial temperature variation in parallel or counterflow heat exchangers is analyzed. A method is developed for integrating the controlling equations for an arbitrary, non-linear, pressure-dependent contact resistance without iteration and the effect ofprestress and other parameters on the occurrence of in ultiple solutions is discussed. 相似文献
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The heat transfer enhancement performance of a phase change buried tubes thermal storage system is influenced by major parameters such as arrangement of heat transfer tubes, fin structure and fin geometry size. We developed a three-dimensional numerical model with two different arrangements and five different enhanced heat transfer structures respectively. For the sake of analysis the effects of arrangement of heat transfer tubes, fin structure and fin geometry size. In addition, we applied the enthalpy-transforming model to obtain the liquid fraction and location of the solid-liquid interface at different time in the phase change process. The numerical results show that the melting time of the thermal storage system model with a triangle arrangement is about 6.1% longer than that of the model with a square arrangement. Besides, the melting time of the model with 55 mm tube pitch is about 16.7% shorter than that of tube pitch with 60 mm. Moreover, the buried tube thermal storage system models with circle fins have the shortest melting time, which is 18 seconds. Melting time of the model with circle fins is about 40% shorter than that of the model with smooth tube. In addition, the melting time of the model with 3 mm fin thickness is 10 seconds, which is the shortest. The model with thicker fins means the shorter time of melting process. Moreover, the melting time of the model with 10.5 mm fin spacing is about 23.5% shorter than that of the model with 12.5 mm fin spacing, which is 13 seconds. In conclusion, the main factor of the melting time is the heat transfer area. It provides a guidance for the design and reconstruction of the type of heat storage structure. 相似文献
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M.G. Rodio M.G. De Giorgi A. Ficarella 《International Journal of Heat and Mass Transfer》2012,55(23-24):6538-6554
The accuracy of numerical simulations for the prediction of cavitation in cryogenic fluids is of critical importance for the efficient design and performance of turbopumps in rocket propulsion systems. One of the main remaining challenges is efficiency in modeling of the physics, handling the multi-scale properties involved and developing robust numerical methodologies. Such flows involve thermodynamic phase transitions and cavitation bubbles that are on a smaller scale than the global flow structure. Cryogenic fluids are thermo-sensitive, and therefore, thermal effects and strong variations in fluid properties can alter the cavitation properties. The aim of this work is to address the challenge posed by thermal effects. The Rayleigh–Plesset equation is modified by the addition of a term for convective heat transfer at the interface between the liquid and the bubble coupled with a bubbly flow model to assess the prediction of thermal effects. We perform a parametric study by considering several values of and models for the convective heat transfer coefficient, hb, and we compare the resulting temperature and pressure profiles with the experimental data. Finally, the results of a 2D simulation with a commercial CFD code are presented and compared with the previous results. We note the importance of the choice of hb for the correct prediction of the temperature drop in the cavitating region, and we assess the most efficient models, underlining that the choice of hb estimation model in a cryogenic cavitating flow is more important in the bubble growth phase than in the bubble collapse phase. 相似文献
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A hot wind tunnel of annular cascade test rig is established for measuring temperature distribution on a real gas turbine blade surface with infrared camera. Besides, conjugate heat transfer numerical simulation is performed to obtain cooling efficiency distribution on both blade substrate surface and coating surface for comparison. The effect of thermal barrier coating on the overall cooling performance for blades is compared under varied mass flow rate of coolant, and spatial difference is also discussed. Results indicate that the cooling efficiency in the leading edge and trailing edge areas of the blade is the lowest. The cooling performance is not only influenced by the internal cooling structures layout inside the blade but also by the flow condition of the mainstream in the external cascade path. Thermal barrier effects of the coating vary at different regions of the blade surface, where higher internal cooling performance exists, more effective the thermal barrier will be, which means the thermal protection effect of coatings is remarkable in these regions. At the designed mass flow ratio condition, the cooling efficiency on the pressure side varies by 0.13 for the coating surface and substrate surface, while this value is 0.09 on the suction side. 相似文献
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《Applied Energy》2001,68(1):31-42
This paper reports on a method which has been developed to improve the efficiency of the numerical simulation of built environment earth-contact heat transfers. This method modifies a numerical method by incorporating elements of the response factor method. Additionally, this paper reports on the use of extrapolation techniques to further speed up one stage of the simulation. Essentially, the method requires that a numerical technique be initially used to generate a certain number of simulated hours for use as a time-series by the response factor element of the method. This first (‘pre-processing’) part of the procedure takes a certain time and this time can be significantly reduced by means of the extrapolation techniques described in the paper. However, assuming that the earth-contact domain remains unchanged from then on, this ‘pre-processing’ does not need to repeated, and every subsequent simulation that is performed to calculate the effect on the earth-contact heat transfer of changing another parameter (i.e. during a parametric analysis) takes only a few seconds. Reductions in run-time for these successive simulations are of the order of 1000 times faster than the full finite volume technique whilst still retaining the flexibility and accuracy of this method. 相似文献
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《International Journal of Hydrogen Energy》2021,46(55):28200-28213
The inherent nature concerning the intermittency of concentrating solar power (CSP) plants can be overcome by the integration of efficient thermal energy storage (TES) systems. Current CSP plants employ molten salts as TES materials although metal hydrides (MH) have proven to be more efficient due to their increased operating temperatures. Nonetheless, the heat exchange between the MH bed and the heat transfer medium used to operate a heat engine is a critical factor in the overall efficiency of the TES system. In this work, a computational study is carried out to investigate the performance of a magnesium hydride TES packed bed using a multiphase (boiling) medium instead of single-phase heat absorption methods. The boiling heat transfer behaviour is simulated by using the Eulerian two-fluid framework. The simulations are conducted at a transient state using SST-k-ω Reynolds-Averaged Navier-Stokes equations. It is observed that, unlike the single-phase heat collection method, the multiphase heat absorption method maintains a constant temperature in the heat transfer fluid throughout the reactor. Consequently, a higher temperature gradient is realised between the MH bed and heat transfer fluid (HTF), leading to improvements in the overall reaction rate of the hydrogenation process. 相似文献
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A new complete numerical model for the prediction of thermal performance of the earth-to-air heat exchangers is presented. The model describes the simultaneous heat and mass transfer inside the tube and into the soil accounting for the soil natural thermal stratification. The model is validated against an extensive set of experimental data and it is found accurate. The proposed algorithms are suitable for the calculation of the temperature and humidity variation of the circulating air and for the temperature and humidity distribution inside the ground. The presented model was developed within the TRNSYS environment and can be easily coupled with building or greenhouse simulation codes in order to describe the impact of the earth-to-air heat exchangers to indoor environments. 相似文献
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基于航空航天等领域对环路热管长距离传热的需求,设计制造了一套传热距离8.1m的圆柱型蒸发器环路热管,试验了不同加热功率、不同冷凝温度下该环路热管的启动和变工况运行性能,并对其热阻及最大传热能力进行了分析。研究结果表明:当其他条件一致、初始气液分布相同和不同时,加热功率由100W增大至160W后,本研究中的环路热管启动时间和启动温升均发生一定程度的下降;加热功率100W时,冷凝温度由10℃降低至-10℃使得环路热管启动时间增加,加热功率160W时,冷凝温度由10℃降至-10℃对环路热管的启动时间影响不大。在冷凝温度0℃下,该环路热管在100~500W范围内均能稳定运行,且200W时环路热管传热效率最高,传热温差最小,稳定运行温度最低;另外,由于系统传输距离较长,每个工况达到稳定所需要的时间也较长,分布于1000至3500S内。随着加热功率的增大,环路热管热阻先减小后逐渐增大,该环路热管传热热阻最大不超过0.09℃/W,最小为0.024℃/W;随着传热距离的增大,管路的热损失增加,总压降和热阻也变大。当传热距离基本相同时,蒸发器容积的大小、冷凝器的冷凝能力及气液管线的布置形状均在一定程度上影响环路热管的最大传热能力。 相似文献
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A thermo-economic performance analysis and optimization has been carried out for an irrversible solar-driven heat engine with losses due to heat transfer across finite temperature differences, heat leak and internal irreversibilities. In the considered heat engine model, heat transfer from the hot reservoir is assumed to be simultaneous radiation and convection mode and the heat transfer to the cold reservoir is assumed to be convection mode. The effects of the technical and economical parameters on the thermo-economic performance have been investigated in order to see the collective effects of the radiation and convection modes of heat transfer. Also the optimal performance parameters of the heat engine, such as the thermal efficiency, temperatures of the working fluid and the ratio of heat transfer areas have been discussed in detail. 相似文献
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The efficiency bounds at maximum profit are obtained from finite-time exergoeconomic analysis for three common heat transfer laws: Newton's law (n = 1), a linear pheomenological law in irreversible thermodynamics (n = 1), and the radiative heat law (n = 4). The relation between optimal profit and efficiency of an endoreversible Carnot engine is derived on the basis of the general heat-transfer law q∝Δ(Tn). 相似文献
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The effect of SiO2 particles on heat transfer performance of a pulsating heat pipe(PHP) was investigated experimentally.DI water was used as the base fluid and contrast medium for the PHP.In order to study and measure the character,there are SiO2 /H2 O nanofluids with different concentration and applying with various heating powers during the experiment investigation.According to the experimental result,the high fraction of SiO2 /H2 O will deteriorate the performance of PHP compared with DI water,i.e.the thermal resistance and the temperature of evaporation section increases.It is in contrary in the case of low fraction of SiO2 /H2 O.Finally,the comparison of the thermal performances between the normal operation system and the static settlement system is given.It is found that both the thermal resistance of nanofluid PHP and the temperature of the evaporation section increase after standing for a period,and it is the same trend for the temperature fluctuation at the identical heating power for PHP. 相似文献
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《International Communications in Heat and Mass Transfer》1994,21(1):53-63
The present study is aimed to extend the theoretical model of the maximum-slope single-blow transient testing method[4,5,8], which is frequently used in evaluating the thermal performance of heat transfer surfaces in heat exchangers, by additionally considering the effects of longitudinal diffusion and thermal capacity of fluid. Energy equations are solved by the finite-difference methods to examine the transient variation of the solid and fluid temperatures within the solid matrix. Results show that the neglect of these fluid properties in the earlier models may cause a considerable error in the evaluation of thermal performance of surfaces and hence, limits the accuracy and applicability of this testing method. 相似文献