共查询到17条相似文献,搜索用时 109 毫秒
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王勤何巍王世宽郝楠徐象国陈光明徐璐陈达 《工程热物理学报》2014,(6):1053
本文搭建了带溶液泵的循环实验装置,并进行了提升管直径分别为6 mm、8 mm和12 mm的气泡泵用于输送12.5%、15%和17.5%三个质量浓度R134a-DMF溶液的性能实验。结果表明,在相同的R134a浓度下,三种管径气泡泵的气相流量随着输入功率的增加均呈大致线性增加趋势,提升效率随着气相流量的增加均明显减少,发生温度均随着输入功率的增加而线性增加,而输入功率对系统压力的影响不大。在相同的R134a浓度和相同气相流量下,8 mm管径气泡泵的提升效率最高,6 mm管径气泡泵的提升效率最低,R134a的浓度对提升效率的影响不明显。随着提升管直径的增大,气泡泵的启动加热量在所有R134a浓度下均增加,R134a的浓度对发生温度的影响不明显,但对系统压力的影响很大。这些实验结果对扩散吸收制冷系统的气泡泵设计具有重要参考价值。 相似文献
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为了进一步提高能源利用效率和实现其空冷化,在双效溴化锂吸收式制冷系统中利用两级气泡泵代替溴化锂吸收制冷系统中传统的机械溶液泵。本文重点对两级溴化锂气泡泵的泵起时间及其影响因素做相关的实验研究,并得出以下的主要研究结果:1)对于不同的管径,两级气泡泵的泵起时间随着加热功率、浸没高度、工质浓度的变化趋势是基本一致的;2)加热功率越大越有利于气泡泵的泵起;3)随着浸没高度的增大气泡泵的泵起时间逐渐减小;4)工质浓度的增大也会使气泡泵的泵起时间增大,但当溴化锂溶液浓度大于54%后影响不明显;5)一级气泡泵的气液成分及中间溶液的闪发一定程度上影响两级气泡泵的泵起时间,因而造成局部区域与上述规律的偏离。 相似文献
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《工程热物理学报》2016,(5)
本文搭建了两级气泡泵与溴化锂制冷系统耦合特性实验台,进行了实验研究,实验中用气泡泵代替了传统的溶液泵,以进一步提高能源的利用率。实验结果表明:1)装置运行初期,因气泡泵本身的间歇性以及气泡泵流型转换的影响,系统参数,如一次冷剂蒸汽和稀溶液流量等参数,表现出不稳定性。随着装置继续运行,当气泡泵中的流型为环状流时,系统参数趋于稳定。2)在稀溶液浓度为53%时,1740 W的加热功率对系统性能系数(COP)影响最大,超过1740 W后,增加加热功率的影响不再显著。3)在无热交换器的情况下,加热功率为1740 W,稀溶液浓度为53%,管径为9.5mm,冷凝器温度为38~42℃,蒸发器温度为15~18℃时,系统的制冷系数为0.62~0.68。 相似文献
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《工程热物理学报》2020,(5)
电力供给侧面临热源高效利用和电网侧波峰波谷对电厂变负荷运行的要求,本文针对发电系统变负荷运行工况,在实验热源功率及温度分别为100 kW和110℃下,研究负载和膨胀机转速变化时,有机朗肯循环发电系统净效率及部件实际运行特性的变化规律。主要结论为:系统净效率随着负载功率和膨胀机转速的增大而增大,当负载为6 kW和膨胀机转速为3000 r/min时,系统发电净效率最大,为4.8%。膨胀比和工质泵等熵效率随负载功率和转速的增加而增大,膨胀机入口处过热度的变化规律与之相反;当系统效率最大时,膨胀机膨胀比、等熵效率与入口过热度分别为4.4、53.5%及8.8℃。 相似文献
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以蒸馏水为冷却工质,对冷凝器内置的封闭式光滑表面喷雾冷却系统进行了启动时间变化规律的实验研究,结果表明喷雾系统不同模块最优启动顺序为冷凝器、泵和加热器。采取6种不同的启动顺序,启动后加热表面的温度不均匀度均小于0.25 ℃。在最优启动顺序下,研究了冷却水流量、泵高度、加热功率和喷雾流量对启动时间的影响。随冷却水流量和喷雾流量增加启动时间缩短,随泵高度增加启动时间略微增大,随加热功率增大启动时间先增大后减小。启动时间影响程度由大到小的因素依次为喷雾流量、冷却水流量、加热功率及泵相对于加热表面的高度。喷雾工质流量由10 mL/min增大到35 mL/min时,封闭式喷雾系统的启动时间缩短了5 000 s。同样操作条件下,封闭式系统的启动时间比开放式系统延长15%~20%。 相似文献
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本文采用微加热器对液滴进行局部加热,并对其蒸发沸腾现象进行了可视化研究。液滴局部加热后产生局部沸腾现象,内部生成单气泡,气泡附着在加热基板上,持续生长,当达到某个临界点气泡破裂。在加热初期,气泡生长速度很快,随着加热过程的不断进行,气泡的生长速度逐渐放缓;随着气泡生长顺序的不断推迟,最大直径减小;加热功率的提升会增加气泡的生长速度,缩短气泡的生长时间。通过对气泡破裂过程的研究,气泡破碎过程开始于气泡上方的液膜断裂,形成不稳定的瑞利流和向上喷射的液滴,在表面张力的作用下,恢复初始状态,气泡破裂直径大小会影响液滴的波动幅度与周期。 相似文献
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We provide the high speed flow visualization and dynamic measurement results for the U-shaped and the inverted U-shaped heat driven pumps. The U-shaped heat driven pumps at the high heating powers consist of a succession of tiny bubble nucleation, growth and coalescence process. Once the “larger” spherical bubble or the bubble slug forms, it expands quickly in both upstream and downstream directions. The increased pressure leads to the liquid discharge through the outlet check valve. When the advancing vapor/liquid interface reaches a higher position in the vertical discharge branch, the condensation heat transfer in the discharge branch shrinks the bubble slug, leading to the decreased pressure and initiating the open of the inlet check valve. Thus the fresh liquid can be sucked into the system. Heat driven pumps operating at the low heating powers display the similar process. However, two major differences are identified: (1) A full cycle includes a set of positive pressure pulses corresponding to a set of tiny bubble nucleation, growth and coalescence process in each substage. Only at the end of the cycle, an apparent negative pressure pulse is created. (2) For each substage in each cycle, when the newly formed bubble slug is chasing the ahead “old” bubble slug, the deformed liquid bridge is formed due to the gravity force effect. When the two bubble slugs are merging together, a wave vapor/liquid interface occurs along the bottom of the capillary tube. For the inverted U-shaped heat driven pumps, there are fewer positive pressure pulses included, corresponding to lesser number of new bubble nucleation, growth, and coalescence process. The bubble slug in the capillary tube is very standard with the smooth vapor/liquid interface. The cycle periods and the pumping flow rates are given versus the heating powers. 相似文献
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This study investigates flow boiling heat transfer of aqueous alumina nanofluids in single microchannels with particular focuses
on the critical heat flux (CHF) and the potential dual roles played by nanoparticles, i.e., (i) modification of the heating
surface through particle deposition and (ii) modification of bubble dynamics through particles suspended in the liquid phase.
Low concentrations of nanofluids (0.001–0.1 vol.%) are formulated by the two-step method and the average alumina particle
size is ~25 nm. Two sets of experiments are performed: (a) flow boiling of formed nanofluids in single microchannels where
the effect of heating surface modification by nanoparticle deposition is apparent and (b) bubble formation in a quiescent
pool of alumina nanofluids under adiabatic conditions where the role of suspended nanoparticles in the liquid phase is revealed.
The flow boiling experiments reveal a modest increase in CHF by nanofluids, being higher at higher nanoparticle concentrations
and higher inlet subcoolings. The bubble formation experiments show that suspended nanoparticles in the liquid phase alone
can significantly affect bubble dynamics. Further discussion reveals that both roles are likely co-existent in a typical boiling
system. Properly surface-promoted nanoparticles could minimize particle deposition hence little modification of the heating
surface, but could still contribute to the modification in heat transfer through the second mechanism, which is potentially
promising for microchannel applications. 相似文献
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