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本文采用瞬态实验法对8种不同孔隙率的波纹板蓄热元件的传热和阻力性能进行了研究(500Re11 000)。试验得到8种孔隙率的波纹板组件对应火用损和火用损系数随雷诺数Re变化的曲线。通过计算和比较不同孔隙率的试验元件在2 000Re9 000范围内的平均火用损EL,avg和平均火用损系数Ravg,得出孔隙率对试验元件火用损特性的影响规律,结果显示孔隙率P为6.8%和11.8%时平均火用损均较小为33.0 k J左右,孔隙率P=4.6%平均火用损最大达到41.5 k J。平均火用损系数随孔隙率的变化趋势与平均火用损类似,在52.4%~85.8%之间浮动。不同孔隙率试验元件对应的火用损和火用损系数随雷诺数变化曲线都呈先升高后降低的趋势,峰值点也即转捩点出现在2 000Re4 500之间,此时流动处于过渡态,热能的品位恶化最严重。实验结果表明:孔隙率6.8%的波纹板具有较好的经济性和传热性能。考虑到不同孔隙率波纹板火用损失转捩点的差异,应尽量避免使工况处在Re2 000或Re6 000的范围以保证蓄热波纹板的火用损和火用损系数处于较低的水平。 相似文献
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为了探讨糖厂的烟气水膜除尘耦合换热技术实施的可行性,建立了带水膜湿烟气与空气之间的换热实验装置,进行带水膜湿烟气的对流传热实验研究。在该换热装置中,烟气在矩形通道中流动并喷入雾化热水,通过换热面加热另一侧的空气,同时,在烟气侧通道安装波纹板强化单元,以强化热质传递。实验确定最佳液气比,通过改变波纹板峰高、波纹段高、段数及烟气流速,研究带水膜饱和烟气的对流传热系数。结果表明:饱和烟气对空气的换热量显著;最佳液气比为3.3~4.2 L/m~3;烟气流速和波纹板添加段数的增加显著增大对流传热系数。回归了最佳液气比下的传热准则关联式。 相似文献
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文章设计了一种以石蜡为相变材料的圆柱形等距螺旋盘管式相变蓄热装置,并通过实验分析了该装置的传热特性,以及传热流体入口温度、入口流量对石蜡的融化特性、相变蓄热装置的蓄热量及相变蓄热系统总传热系数的影响。分析结果表明:融化后期,石蜡的融化速率会明显加快;当传热流体入口温度一定时,随着入口流量逐渐增大,蓄热装置的最终显热蓄热量略微升高;与传热流体入口流量相比,传热流体入口温度对石蜡融化速率影响较大;相变阶段,石蜡的传热性能较强,传热流体入口温度越高,石蜡的传热性能越不稳定。 相似文献
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采用CFD软件对氦气冲刷螺旋管束的传热特性进行了数值模拟。计算时采用了轴对称简化模型;湍流模拟采用低Re k-ε模型。通过与实验数据对比,发现低Re模型比壁面函数法更适合计算冲刷管束类型的流动。计算结果表明,顺排管束前几层平均Nu高于叉排管束,而深层管平均Nu低于叉排管束;管列距离较大时排列方式对深层管的传热影响很小;管束与边界距离约为管束中心部分氦气流道宽度的一半时,各列传热管传热和氦气出口温度都较为均匀;管束横向位置发生偏移将导致管束内流动、传热出现不均匀。结果对于螺旋管蒸汽发生器设计具有参考意义。 相似文献
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为了利用螺旋流动强化传热的特性并简化换热器结构,结合螺旋折流板换热器的结构和流体流动特点,开发了一种螺旋肋片自支撑换热器.为了掌握螺旋肋片自支撑换热器的传热和压降综合性能,建立了换热器的试验模型和试验装置.在相同的试验条件下与折流杆换热器进行对比试验,结果表明:当雷诺数Re=6000时螺旋肋片换热器的总传热系数比折流杆换热器提高13.3%,并随着雷诺数增大强化传热效果更加显著;而同时压力梯度却降低了87.5%,并随雷诺数增大二者的压力梯度差值变大.在试验雷诺数2 000~6 500的范围内,螺旋肋片换热器的综合性能K/▽P值是折流杆换热器的1.4~2倍.可见,螺旋肋片换热器具有较高的传热系数和较低的压降,因而具有良好的发展及应用前景. 相似文献
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Kiyoshi Kawaguchi Kenichi Okui Takahiro Shimoura Takaki Ohkouchi Hiroyuki Osakabe Tosihide Ninagawa 《亚洲传热研究》2007,36(4):215-229
In recent years the requirement for reduction of energy consumption has been increasing to solve the problems of global warming and the shortage of petroleum resources. A latent heat recovery type heat exchanger is one of the effective methods of improving thermal efficiency by recovering latent heat. This paper described the heat transfer and pressure loss characteristics of a latent heat recovery type heat exchanger having a wing fin (fin pitch: 4 mm, fin length: 65 mm). These were clarified by measuring the exchange heat quantity, the pressure loss of heat exchanger, and the heat transfer coefficient between outer fin surface and gas. The effects of condensate behavior in the fins on heat transfer and pressure loss characteristics were clarified. Furthermore, the equations for predicting the heat transfer coefficient and pressure loss which are necessary in the design of the heat exchanger were proposed. ©2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(4): 215–229, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20154 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 simplified model predicting the heat transfer performance of a heat sink base with a high thermal conductivity was developed. Numerical analysis was performed using the commercial software FLUENT. The investigation indicates that for heat sink bases with a high effective thermal conductivity, such as the base embedded with a typical heat pipe, the entire heat sink can be modeled as a flat plate with a uniform temperature and an effective convection heat transfer coefficient. This simplified model can be used to determine the heat transfer performance of a heat sink embedded with a typical heat pipe or vapor chamber. 相似文献
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介绍回收热泵压缩机散热的4种技术方案:利用待加热的低温气体吹过压缩机表面,利用待加热的低温液体流过压缩机表面的换热器,利用低温热泵工质液体喷入压缩机内部的工作部件表面,利用特定性质的热泵工质降低压缩过程中热泵工质的温度。对各方案的实施方法进行了分析与探讨。 相似文献
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Experimental research was conducted to understand heat transfer characteristic of pulsating heat pipe in this paper, and the PHP is made of high quality glass capillary tube. Under different fill ratio, heat transfer rate and many other influence factors, the flow patterns were observed in the start-up, transition and stable stage. The effects of heating position on heat transfer were discussed. The experimental results indicate that no annular flow appears in top heating condition. Under different fall ratios and heat transfer rate, the flow pattern in PHP is transferred from bulk flow to semi-annular flow and annular flow, and the performance of heat transfer is improved for down heating case. The experimental results indicate that the total heat resistant of PHP is increased with fill ratio, and heat transfer rate achieves optimum at filling rate 50%. But for pulsating heat pipe with changing diameters the thermal resistance is higher than that with uniform diameters. 相似文献
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氟塑料换热器以其耐腐蚀、耐磨损等优点而备受关注,但氟塑料热导率较低,换热能力差,限制了其广泛应用。石墨烯-PFA复合材料兼具石墨烯优异的导热性和可熔性聚四氟乙烯(PFA)良好的耐酸碱腐蚀性,是新一代的换热器材料。搭建了余热回收测试实验台,对石墨烯-PFA复合材料换热器和金属换热器的传热性能进行对比。研究了不同烟气流速、不同进口烟气温度以及不同石墨烯配比对复合材料传热性能的影响。结果表明:对于金属换热器和复合材料换热器,当烟气流速从2.0增加到4.0 m/s时,传热系数分别增加到原来的1.19和1.34倍;随着进口烟温的升高,两种材质的传热系数分别降低了15.6%和14.7%;随着石墨烯含量增加,复合材料的导热系数以及传热系数均增加。 相似文献
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This paper presents an experimental study on the effects of initial concentration on the critical heat transport rate of an osmotic heat pipe operated under atmospheric pressure. In this experiment, an aqueous polyethylene glycol 600 solution was used as the working fluid and 18 tubular acetyl cellulose membranes were used as the osmotic membranes. The initial concentration was varied between 0.1 to 1.0 kmol/m3 in 0.1 kmol/m3 steps. Consequently, the existence of an optimum initial concentration for the critical heat transport rate was revealed. In addition, solution concentrations in the solution riser and downcomer were found to be related to the initial concentration and solvent contact height. © 1999 Scripta Technica, Heat Trans Asian Res, 29(1): 59–71, 2000 相似文献