低温混合工质大质流密度流动传热试验系统

针对目前大质流密度条件绕管式换热器试验数据缺乏的现状,本研究搭建了可实现低温混合工质大质流密度条件试验工况控制和数据测试需求的试验系统。试验系统包括压缩机、冷却塔、冷水和冷冻机组、低温液化换热器等关键装备,可进行混合工质的压缩-冷却液化-相变传热流动控制和可视化等测试研究。试验平台可实现质量流量密度在20~140 kg/(m^(2)·s)范围内测试,系统温度误差为±0.1℃,压力误差小于10 kPa,压降误差小于2 kPa,干度误差小于1.4%。在预冷段试验区域干度为0.4,质流密度120 kg/(m^(2)·s)下实现了平稳运行,获得了稳定循环数据验证。

回热对低温大质流密度实验系统能耗影响

以绕管式换热器为测试件,设计搭建了带回热的大质流密度流动传热特性实验系统。该实验系统包括主测试循环回路、冷却回路、控制系统和安全通风系统。本文实验系统能够覆盖的实验工况范围如下:蒸发压力为0.15~0.85 MPa,质流密度为20~120 kg/(m^(2)·s),干度为0~1.0,热流密度为0~10 kW/m^(2),温度可达-180℃。构建了实验系统热力学模型,获得了实验工况条件下各节点温度、压力数据和设备负荷参数。对该系统能耗进行了对比分析,研究发现,有回热系统在各个干度情况下均比无回热系统的能耗低,干度为0.1时,能耗减少75%,在干度为0.5时,能耗减少43%,在干度为1时,能耗减少3%。

Critical Heat Flux with Subcooled Flowing Water in Tubes for Pressures from Atmosphere to Near-Critical Point

During last 45 years, two groups of the experimental data on critical heat flux were obtained in bare tubes, covering the pressures from atmosphere to near-critical point. One group of the data were obtained in the inner diameter of 2.32, 5.16, 8.05, 10.0 and 16.0 mm, respectively, with the ranges of pressure of 0.1-1.92 MPa, velocity of 1.47-23.3 m/s, local subcooling of 3.7-108.7 ℃ and heat flux of up to 38.3 MW/m2. Another group of the data were obtained in the inner diameter of 4.62, 7.98 and 10.89 mm, respectively, with the ranges of pressure of 1.7-20.6 MPa, mass flux of 454-4,055 kg/（m2.s） and inlet subcooling of 53-361 ℃. The results showed complicated effects of the pressure, mass flux, subcooling and diameter on the critical heat flux. They were formulated by two empirical correlations. A mechanistic model on the limit of heat transfer capability from the bubbly layer to the subcooled core was also proposed for all the results.