Analysis and comparison of internal and external temperature measurements of a tubular oscillating heat pipe
Analysis and comparison of internal and external temperature measurements of a tubular oscillating heat pipe
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管式振荡热管内外温度测量分析与比较
DOI：
10.1016/j.expthermflusci.2017.01.020
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发表时间：
2017
影响因子：
3.2
通讯作者：
Thompson, Scott M.
中科院分区：
文献类型：
--
作者：
Monroe, J. Gabriel;Aspin, Zachary S.;Fairley, John D.;Thompson, Scott M.
本研究考察了管式振荡热管(T-OHP)在不同的热输入下，沿绝热段的内部/流体温度测量与外部/壁面温度测量之间的关系。温度测量是使用放置在蒸发器和冷凝器之间的OHP壁内或沿壁的T型热电偶来实现的。通过测量来阐明壁面热容、外壁温度梯度和内部流体平流的影响。估算了OHP的内部单相换热系数，确定了OHP的有效导热系数。将4圈铜T-OHP(3.25 mm内径)装入水(体积比为75%)，并在底部加热条件下进行测试。热输入以25W为增量从60W到300W变化。结果表明，外部热电偶无法捕获大于∼1 GHz的频率分量。内部测量表明，平均蒸发器侧流体振荡频率在60瓦时为∼1.5赫兹，在300瓦时为∼2.5赫兹，而冷凝器侧频率在∼0.5赫兹时保持相当恒定。与内部/外部热电偶之间的热阻网络相对应的频率传递函数在所有测试的功率输入上都是恒定的。与整体流体运动相关的内部温度的低频、大幅度变化不是立即在OHP管外表面测量到的。仅使用外部温度测量计算的有效导热系数比使用内部测量计算的有效导热系数低4-12%。使用内部或外部温度测量计算的最大有效导热系数分别为15,300W/m·K和14,000 W/m·K。产生这种差异的原因是，由于OHP换热的强烈平流分量，沿流体柱的纵向温度梯度比沿管壁的温度梯度小。管壁导热占总换热的2-10%，在较高的热输入下，随着流体平流度的增加，管壁导热的重要性降低。对于大于100W的功率输入，OHP内部单相流体振荡的换热系数估计为∼1000W/M2K；对应于4至6之间的努塞尔数。
The current study examines the relationship between internal/fluidic and external/wall temperature measurements along the adiabatic section of an operating tubular oscillating heat pipe (T-OHP) for varying heat inputs. Temperature measurements were achieved using type-T thermocouples located either inside or along the OHP wall in the region between the evaporator and condenser. Measurements were utilized to elucidate the effects of wall thermal capacitance, external wall temperature gradient, and internal fluid advection. The internal, single-phase heat transfer coefficient was estimated, and the effective thermal conductivity of the OHP was determined. A 4-turn copper T-OHP (3.25 mm ID) was charged with water (75% by volume) and tested in the bottom-heating condition. Heat input was varied in increments of 25 W from 60 W to 300 W. Results indicate that the external thermocouples were unable to capture frequency components larger than ∼1 Hz. Internal measurements indicate that average, evaporator-side fluid oscillation frequencies varied from ∼1.5 Hz at 60 W to ∼2.5 Hz at 300 W, whereas condenser-side frequencies remained fairly constant at ∼0.5 Hz. The frequency transfer function corresponding to the thermal resistance network between the internal/external thermocouples was found to be constant across all tested power inputs. The low-frequency, large-amplitude changes in internal temperature associated with bulk fluid motion were not immediately measured at the external OHP tube surface. The effective thermal conductivity calculated using only external temperature measurements was found to be 4–12% lower than that calculated using internal measurements. The maximum, calculated effective thermal conductivity using internal or external temperature measurements was 15,300 W/m·K and 14,000 W/m·K, respectively. This difference arises from there being a smaller, length-wise temperature gradient along the fluid columns than along the tube wall due to the strong advection component of OHP heat transfer. Tube wall conduction was found to account for 2–10% of the overall heat transfer, with its significance decreasing as fluid advection increased at higher heat inputs. The heat transfer coefficient for single-phase fluid oscillation inside the OHP was estimated to be ∼1000 W/m2K for power inputs larger than 100 W; corresponding to Nusselt numbers between 4 and 6.
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通讯作者：
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