共查询到19条相似文献,搜索用时 140 毫秒
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《内燃机学报》2021,39(4)
活塞是内燃机中热负荷和机械负荷最大的零部件之一,为了确保内燃机活塞的可靠性和寿命,大型船用柴油机往往采用振荡强化传热的方式进行活塞的冷却.为了理解振荡冷却的强化机制,首先进行了活塞冷却油腔壁面对流换热系数的分析,分解出常规流动换热分量、振荡强化换热分量和射流冲刷换热分量,并具体分析了振荡强化换热分量、射流冲刷换热分量和常规流动换热分量的分布特征.随后,基于正交设计方法,研究了活塞振荡腔不同结构参数对活塞内、外冷却油腔填充率和壁面对流换热系数的影响规律,为后续的活塞振荡冷却能力优化提供了方向.最后,针对原型活塞中内冷却油腔冷却能力不够的问题,进行了活塞振荡腔结构的优化. 相似文献
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为研究柴油机活塞环形油腔周向振荡冷却特性,在非惯性坐标系下应用流体体积函数(VOF)多相流模型,对活塞环形油腔振荡冷却进行了瞬态换热研究,得到了环形油腔周向壁面平均换热系数的变化规律,发现壁面平均换热系数的振荡幅度最大的并不是入口冲击的周向10°区域,而是周向20°区域.一个周期内油腔周向区域的壁面平均换热系数整体呈类"对数"减小的趋势,在周向10°~30°区域急剧减小,而后随着远离入口段,其值呈现先增大后减小的变化规律.最后通过两种方法计算活塞温度场并进行对比,发现使用18周向区域的壁面平均换热系数所计算的活塞温度场的顶部温度波动更大,更符合实际情况. 相似文献
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《内燃机与动力装置》2017,(3):37-40
某型柴油机单缸功率由140k W提升到150k W后,活塞出现了拉缸问题。针对该问题,本文从增强活塞的冷却入手,对活塞的冷却方式及冷却油道结构等方面进行分析,对机油供油压力、供油喷孔大小及活塞进、出油口尺寸进行了优化改进;通过CFD仿真计算,活塞油腔的机油填充率从优化前的34%提高到优化后的46%,接近50%的理想机油填充率;最终经柴油机耐久试验验证:活塞冷却良好,无拉缸现象。 相似文献
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为深入了解振荡条件下的两相流运动过程与流动换热特性,采用数值仿真研究方法,摒弃活塞复杂的结构因素,以简化模型为研究对象,从基础问题出发探索各因素对两相流振荡换热过程的影响。通过一系列的数值模拟,直观地展现了油腔内两相流运动过程是高度紊乱的不对称流动。研究结果表明:除活塞二阶运动产生偏离外,油腔上下运动引起的压力变化也将引起油柱倾斜,造成喷油与油腔入口偏离;活塞运动产生的强制振荡是影响腔内流动换热波动的决定性因素,油腔表面传热系数、填充率等的波动频率都与活塞运动频率完全吻合。此外,研究还发现喷油速率、活塞转速等参数对填充率和传热系数都会产生显著的影响,但这些影响因素可能并不是单一作用而是相互耦合的。喷油油柱在进入油腔时的速度与活塞的最大运动速度之间的匹配度可能是影响油腔填充率及传热系数的一个关键因素;当喷油的绝对速度与活塞最大速度接近或大于活塞最大速度时,将达到较为理想的填充率和传热系数。 相似文献
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本文利用CFD软件Fluent对活塞的喷油强制冷却进行了三维数值计算,模拟了活塞处于不同位置时,冷却机油在内冷油腔和活塞顶内壁空腔内的流动与分布,得到了不同位置时冷却机油在内冷油腔内的体积分数和质量流量。模拟结果为活塞冷却油腔的优化设计提供了依据。 相似文献
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利用量纲为1的基础关联式,考虑活塞内冷油腔结构、两相流的物理特性和局部流动特性对传热系数的影响,分析不同缸径活塞在不同发动机转速时内冷油腔内流体的流动特性,建立对流换热系数的预测模型.结果表明:雷诺数和普朗特数乘积的自然对数值随发动机转速的增加而增大;在发动机转速相同时,随着内燃机活塞缸径的增加,内冷油腔内流体的雷诺数和普朗特数乘积的自然对数值随之增大.通过对比数值模拟和硬度塞试验测试结果可知,对流换热系数预测模型可有效预测内冷油腔的传热系数,能为内冷油腔的设计提供一定的理论依据. 相似文献
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《International Journal of Heat and Mass Transfer》2007,50(3-4):492-501
The characteristics of the flow and convective heat transfer on the conditions of both developed laminar and turbulent flow in bilaterally heat narrow annuli were investigated. Investigations show that the ratio of heating flux at the inner wall to that at the outer wall, and the gap size of narrow annuli as well, have great influences on the heat transfer characteristics during flowing in bilaterally heated narrow annuli. Under laminar flow condition, the decreases of the gap size will lead to the heat transfer deterioration both on the inner and outer walls. However with respect to the case of the turbulent flow conditions, it is quite different. The decrease of the gap size will yield heat transfer deterioration on the inner wall, but it will enhance the heat transfer coefficient on the outer wall. In addition, whether the convective heat transfer is enhanced or reduced depends on the combination effect of the heat-flux ratio and the Reynolds number. The decrease of the gap size will reduce the convective heat transfer when the heat-flux ratio is smaller, and enhance the heat transfer coefficient when the heat-flux ratio becomes greater under a certain Reynolds number. Predicted friction coefficients and heat transfer coefficients were compared to experimental data as well, and they were found to be in good agreement. 相似文献
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目的探讨房室间隔缺损介入治疗失败后外科手术的原因及效果,以提高手术成功率。方法选择2000年1月至2007年12月接受经导管介入治疗房间隔缺损(ASD)和室间隔缺损(VSD)失败后,需行外科手术的13例病例进行回顾性分析。外科手术指征为封堵器脱落7例、Ⅲ°房室传导阻滞(AVB)3例、瓣膜关闭不全2例(其中1例同时合并Ⅲ°AVB)、残余漏1例、封堵失败1例。手术均在体外循环下进行,取出封堵器,修复心内畸形,术后入ICU监护。结果ASD介入治疗患者中,手术探查ASD直径平均31mm,较术前诊断的平均26mm增大,两者相比差异有统计学意义(P<0.05)。ASD部位为中央型3例,下腔型6例,与术前诊断符合率为41.7%,不符合率为58.3%(P>0.05)。3例Ⅲ°AVB者术后均恢复窦性心律。心内畸形修复完善,无手术死亡。结论及时采取外科手术治疗介入封堵失败后并发症,效果良好,安全可靠,可避免治疗失败及术后并发症。 相似文献
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对采用绕簧管的立式电机轴承油冷却器进行了传热性能实验.根据实验数据对冷却器油侧和水侧换热热阻进行了分离,结果显示,油侧换热热阻为水侧的4~12倍.实验结果表明:油流量对冷却器传热系数的影响较大,油流量每增加10 L·min~(-1),总传热系数增大60~70 W·m~(-2)·K~(-1);水流速对冷却器换热系数的影响相对较小;增加换热管的翅化比或提高油流速以降低油侧的换热热阻是提高油冷却器传热性能的关键;采用绕簧管的立式电机轴承油冷却器的传热系数要优于常规采用双金属轧制式翅片管的油冷却器. 相似文献
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Using ethanol or acetone as the working fluid, the performance of starting up and heat transfer of closed-loop plate oscillating heat pipe with parallel channels(POHP-PC) were experimentally investigated by varying filling ratio, inclination, working fluids and heating power. The performance of the tested pulsating heat pipe was mainly evaluated by thermal resistance and wall temperature. Heating copper block and cold water bath were adopted in the experimental investigations. It was found that oscillating heat pipe with filling ratio of 50% started up earlier than that with 70% when heating input was 159.4 W, however, it has similar starting up performance with filling ratio of 50% as compared to 70% on the condition of heat input of 205.4 W. And heat pipe with filling ratio of 10% could not start up but directly transit to dry burning. A reasonable filling ratio range of 35%-70% was needed in order to achieve better performance, and there are different optimal filling ratios with different heating inputs- the more heating input, the higher optimal filling ratio, and vice versa. However, the dry burning appeared easily with low filling ratio, especially at very low filling ratio, such as 10%. And higher filling ratio, such as 70%, resulted in higher heat transfer( dry burning) limit. With filling ratio of 70% and inclination of 75°, oscillating heat pipe with acetone started up with heating input of just 24 W, but for ethanol, it needed to be achieved 68 W, Furthermore, the start time with acetone was similar as compared to that with ethanol. For steady operating state, the heating input with acetone was about 80 W, but it transited to dry burning state when heating input was greater than 160 W. However, for ethanol, the heating input was in vicinity of 160 W. Furthermore, thermal resistance with acetone was lower than that with ethanol at the same heating input of 120 W. 相似文献
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为解决能源桩传热分析中一般将桩土视为相同介质而引起误差的问题,建立一种可考虑桩体与土体之间热物性差异的U型埋管能源桩非稳态传热模型,将其与线热源模型进行对比,验证该模型的准确性。在此基础上,通过级数展开得到近似简化的能源桩热响应半径表达式。最后,对单位桩长换热量、桩体的热扩散系数、桩径以及土体类型进行分析,利用“储热比”评价上述参数对能源桩传热过程的影响。结果表明:该模型较线热源模型可更精准地描述能源桩传热过程,可有效避免传热初期低估桩壁过余温度以及传热稳定期高估桩体温度的问题;在典型的能源桩运行周期内,所提出的热响应半径计算方法误差在0.1 ℃以内,符合工程要求;能源桩传热过程中,土体的储热比随桩体热容、桩土间热扩散系数相对差异的减小而增大;桩壁过余温度及土体储热比均随桩径的增大而减小,随着传热时间的增加,不同桩径对应的桩壁过余温度差逐渐加大,土体储热比差值逐渐减小;相同换热功率作用下能源桩桩壁过余温度的变化率几乎不随传热时间增长而变化;传热90 d后,桩径对能源桩传热过程中能量传递分布影响不大。 相似文献