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搭建以R134a为制冷工质的闭式喷雾冷却试验台,试验研究喷雾冷却瞬态传热过程,建立了准确描述其传热过程的试验曲线,分析了蒸发压力对传热性能的影响,并阐述了每个瞬态传热阶段的传热机理。试验蒸发压力变化范围为0.207~0.331 MPa,流量范围为0.140~0.164 L/min。结果表明:膜态沸腾区在瞬态冷却过程中所占时间最长,且表面温度冷却速率保持在0.10 ℃/s,热流密度维持在20 W/cm2以下,故穿越膜态沸腾区的耗时决定着喷雾冷却瞬态过程的冷却速率;增加蒸发压力,可以提升冷却速率,当蒸发压力从0.207 MPa增加到0.331 MPa时,表面温度从130 ℃冷却至30 ℃所需的时间从508 s降至381 s;喷雾冷却瞬态过程在过渡沸腾区存在表面温度突变点,随着蒸发压力提高,突变点对应温度增加。 相似文献
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以表面式间接空冷散热器为例,建立了间接空冷散热器冷却单元的一维传热数学模型。通过该模型,计算并分析了冷却水流量、温度及空气进口温度(环境温度)、流速等对空冷散热器传热性能的影响。计算结果显示,随着冷却水流量、温度和空气流速、温度的增大,散热器总传热系数逐渐增大;散热器总传热系数更接近于空气侧表面传热系数,其中空气流速对总传热系数的影响尤为明显;积灰对散热器传热性能的负面影响较大,积灰越厚,散热器总传热系数越小。另外,利用本文模型,得到了一定条件下间接空冷系统冷却水最佳流量,为间接空冷机组的运行了提供一定的理论依据。 相似文献
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以表面式间接空冷散热器为例,建立了间接空冷散热器冷却单元的一维传热数学模型。通过该模型,计算并分析了冷却水流量、温度及空气进口温度(环境温度)、流速等对空冷散热器传热性能的影响。计算结果显示,随着冷却水流量、温度和空气流速、温度的增大,散热器总传热系数逐渐增大;散热器总传热系数更接近于空气侧表面传热系数,其中空气流速对总传热系数的影响尤为明显;积灰对散热器传热性能的负面影响较大,积灰越厚,散热器总传热系数越小。另外,利用本文模型,得到了一定条件下间接空冷系统冷却水最佳流量,为间接空冷机组的运行了提供一定的理论依据。 相似文献
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喷雾冷却发热壁面温度非均匀性实验研究 总被引:3,自引:0,他引:3
喷雾冷却是一种新型的高热流密度换热方式,利用可视化手段对喷雾冷却中发热体壁面温度非均匀性进行了实验研究。采用热电偶多点测温及红外成像相结合的方法测量发热体壁面温度,通过分析提出了温度不均匀度现象;结合壁面液膜特性及多普勒激光测速仪所测之液滴参数的空间分布,分析阐述了温度非均匀现象的成因与影响因素。研究结果表明,发热壁面温度的不均匀来自于喷雾特性的变化,通过选择合适的喷雾高度使工质从壁面中心向四周附壁流出,可以克服喷嘴空心回流区影响、增强壁面中心的换热,使发热壁面温度更均匀、同时提高冷却效果。本文突破了将壁面温度分布视为均匀的传统观点,为喷雾冷却的性能评估提供了新的途径,对喷雾冷却特性进一步的科学研究和工程应用具有参考价值。 相似文献
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在油区地热资源开发过程中,应用井内换热和尾水回灌的对井供热系统可以提高地热资源开发效益、避免地热水资源浪费和实现可持续发展。文章使用了地热储二维分布模型和井筒传热模型.通过对地热储的数值模拟预测了尾水回灌过程中地热储的压力响应和冷却效应,通过对井筒的热力计算得到了井内换热器的最优设计方法。计算结果表明,地热储对尾水回灌的压力响应非常迅速,压力场能很快达到稳定;回灌冷水的影响区集中在回灌井的周围,冷区半径增长的速度越来越慢。井内换热器在最佳设置深度时,经济效益达到最大值;井内换热器设置深度不变,增大载热水的流量经济效益将增加,但是获得的热能温度下降。 相似文献
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《International Journal of Heat and Mass Transfer》2006,49(5-6):962-974
Experiments were performed to evaluate the evaporative heat transfer characteristics of spray cooling of water on plain and micro-structured silicon surfaces at very low spray mass fluxes. The textured surface is made of an array of square micro-studs. It was found that the Bond number of the microstructures is the primary factor responsible for the heat transfer enhancement of evaporative spray cooling on micro-structured silicon surface in the present study. A qualitative study of evaporation of a single water droplet on plain and textured silicon surface shows that the capillary force within the microstructures is effective in spreading the deposited liquid film, thus increasing the evaporation rates. Four distinct heat transfer regimes, which are the flooded, thin film, partial dryout, and dryout regimes, were identified for evaporative spray cooling on micro-structured silicon surfaces. The microstructures provided better cooling performance in the thin film and partial dryout regime and higher liquid film breakup heat flux, because more water was retained on the heat transfer surface due to the capillary force. Heat transfer coefficient and temperature stability deteriorated greatly once the liquid film breakup occurred. The liquid film breakup heat flux increases with the Bond number. Effects of surface material, system orientation and spray mass flux were also addressed in this study. 相似文献
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An experimental facility was developed to investigate the nonboiling heat transfer performance of water spray cooling. The effects of mass flux and wall temperature on heat transfer coefficient and heat flux were experimentally studied. It was found that heat transfer coefficient increased with the increasing of mass flux and wall temperature. Generalized correlations were developed for the Nusselt number related to wall temperature and the average Nusselt number as a function of the spray Reynolds number and the nondimensional temperature with an absolute error of 4% and 15% when the Reynolds number is more than 440. Compared with the data of Oliphant et al., it was observed that the usage field of the correlations could be extended to Reynolds number greater than 240. 相似文献
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Experiments were conducted to study the effects of enhanced surfaces on heat transfer performance during water spray cooling in non-boiling regime. The surface enhancement is straight fin. The structures were machined on the top surface of heated copper blocks with a cross-sectional area of 10 mm×10 mm. The spray was performed using Unijet full cone nozzles with a volumetric flux of 0.044–0.053 m3/(m2·s) and a nozzle height of 17 mm. It is found that the heat transfer is obviously enhanced for straight fin surfaces relative to the flat surface. However, the increment decreases as the fin height increases. For flat surface and enhanced surfaces with a fin height of 0.1 mm and 0.2 mm, as the coolant flux increases, the heat flux increases as well. However, for finned surface with a height of 0.4 mm, the heat flux is not sensitive to the coolant volumetric flux. Changed film thickness and the form of water/surface interaction due to an enhanced surface structure (different fin height) are the main reasons for changing of the local heat transfer coefficient. 相似文献
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In this study, a test system for spray cooling, in which the heating surface temperatures were simultaneously measured by thermocouples and an infrared imager, was set up. A mathematical model of spray cooling heat transfer characteristics was presented based on the fundamentals of dynamics and heat transfer. The temperature distribution on the heating surface was investigated by the experimental and theoretical methods, the surface temperature non-uniformity and its influencing factors were analyzed. The predictions by the model coincided with the experimental results well, and a comparison was demonstrated with a deviation below 10%. It can be concluded that the surface temperature non-uniformity is influenced by the spray characteristics, nozzle-to-surface distance, inlet pressure, heat flux, spray angle and the system pressure. In the case of the same heat flux, the surface temperature non-uniformity can be reduced by the small spray angle, low system pressure, low nozzle-to-surface distance, and the high inlet pressure. 相似文献
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Heat transfer characteristics of spray cooling in a closed loop 总被引:2,自引:0,他引:2
Lanchao Lin Rengasamy Ponnappan 《International Journal of Heat and Mass Transfer》2003,46(20):3737-3746
A closed loop spray cooling test setup is established for the cooling of high heat flux heat sources. Eight miniature nozzles in a multi-nozzle plate are used to generate a spray array targeting at a 1 × 2 cm2 cooling surface. FC-87, FC-72, methanol and water are used as the working fluids. Thermal performance data for the multi-nozzle spray cooling in the confined and closed system are obtained at various operating temperatures, nozzle pressure drops (from 0.69 to 3.10 bar) and heat fluxes. It is exhibited that the spray cooler can reach the critical heat fluxes up to 90 W/cm2 with fluorocarbon fluids and 490 W/cm2 with methanol. For water, the critical heat flux is higher than 500 W/cm2. Air purposely introduced in the spray cooling system with FC-72 fluid has a significant influence on heat transfer characteristics of the spray over the cooling surface. 相似文献
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Z.Z. Xia C.J. Chen R.Z. Wang 《International Journal of Heat and Mass Transfer》2011,54(11-12):2367-2374
A closed wet cooling tower with novel design was proposed and numerically investigated. The studied cooling tower consists of two main parts: one heat and mass transfer unit (HMTU) and one heat transfer unit (HTU). In the HMTU, copper tubes are arranged as heat transfer tubes while plastic tubes are collocated to enlarge the mass transfer area between the spray water and the airflow. In the HTU, only copper tubes are adopted as heat transfer tubes. Heat and mass transfer process takes place among the process water, airflow and spray water in the HMTU, while in the HTU only heat transfer between the process water and the spray water is observed. A transient one dimensional distributed-parameter model was adopted to evaluate the cooling tower performance under different operating conditions. Determination of heat and mass transfer coefficients, as well as the influence of Lewis number on the cooling tower performance, was presented. 相似文献
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In recent years,the problem of heat dissipation in airborne directed energy weapons has attracted considerable research interest.Spray cooling can be applied to cool airborne directed energy weapons,owing to its several advantages such as a large heat transfer coefficient,absence of boiling hysteresis and uniform surface temperature.To examine the potential of an airborne spray cooling system,the typical high heat flux dissipation methods were compared,and the state of the art research on spray cooling was reviewed.This review was focused on studies related to the spray cooling hydrodynamic mechanism,experimental studies of closed loop spray cooling,numerical simulation studies about spray cooling and the identification of the factors influencing spray cooling systems,and investigations related to the multiple nozzle spray cooling technology and heat transfer correlation predictions.Overall,there is a need for further research to investigate the failure phenomenon after the critical state,matching operation of the total system and microscopic characteristics of airborne specific parameters. 相似文献
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《International Journal of Thermal Sciences》2000,39(5):582-591
A systematic experimental study was conducted to examine the heat transfer characteristics from the hot die surface to the water spray involved in high pressure die casting processes. Temperature and heat flux measurements were made locally in the spray field using a heater made from die material H-13 steel and with a surface diameter of 10 mm. The spray cooling curve was determined in the nucleate boiling, critical heat flux, as well as the transition boiling regimes. The hydrodynamic parameters of the spray such as droplet diameters, droplet velocities, and volumetric spray flux were also measured at the position in the spray field identical to that of the test piece. Droplet size and velocity distribution were measured using a PDA system. A new empirical correlation was developed to relate the spray cooling heat flux to the spray hydrodynamic parameters such as liquid volumetric flux, droplet size, and droplet velocity in all heat transfer regimes. The agreement between experimental data and predicted results is satisfactorily good. 相似文献
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Drazen Fabris Sergio Escobar-Vargas Jorge E. Gonzalez Ratnesh Sharma Cullen Bash 《传热工程》2013,34(14):1161-1169
Spray cooling is an effective method to remove high heat fluxes from electronic components. To understand the physical mechanisms, this work studies heat transfer rates from single and dual nozzle distilled water sprays on a small heated surface (1.3 mm × 2 mm). Thermal ink jet atomizers generate small droplets, 33 μm diameter, at known frequencies, leading to controlled spray conditions with a monodisperse stream of droplets interacting with the hot surface. Of particular interest in this work is the dissipated heat flux and its relation to the liquid film thickness, the surface superheat, and the cooling mass flow rate. Experimental results show the heat flux scales to the cooling mass flow rate. In comparison to published spreading–splashing correlations, these experiments indicate that the drops impinge on the liquid film and spread without generating splashing, leading to high-efficiency stable heat transfer. Surface temperatures range from 120 to 140°C. In addition, the liquid film thickness is investigated in relation to the heater superheat and a stable thin film is seen at superheats beyond 20°C. The efficiency of the spray system is inversely related to the film thickness and may be due to ejection of liquid from the surface due to bursting of vapor bubbles. 相似文献