Single-phase pressure drop and heat transfer characteristics of turbulent liquid nitrogen flow in micro-tubes |
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| Affiliation: | 1. Institute of Refrigeration and Cryogenics, Shanghai Jiao Tong University, Shanghai 200240, China;2. School of Life Sciences and Technology, Shanghai Jiao Tong University, Shanghai 200240, China;1. Department of Mechanical Engineering, Azad Islamic University, Science and Research Branch, Tehran, Iran;2. School of Mechanical Engineering, Northwestern Polytechnical University, Xi’an 710129, PR China;3. Division of Heat Transfer, Department of Energy Sciences, Lund University, P.O. Box 118, SE-22100 Lund, Sweden;1. Mechanical Engineering Department, College of Engineering, Universiti Tenaga Nasional, Jalan IKRAM-UNITEN, 43000 Kajang, Selangor, Malaysia;2. Department of Thermofluids, Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor Bahru, Malaysia;1. Wolfson School of Mechanical, Electrical and Manufacturing Engineering, Loughborough University, Leicestershire LE11 3TU, UK;2. Clean Cold Power UK Ltd, Unit 5, Stafford Cross Business Park, Stafford Rd, Croydon CR0 4TU, UK |
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| Abstract: | Experiments have been conducted to investigate the single-phase pressure drop and heat transfer characteristics of liquid nitrogen in four micro-tubes with the diameters of 1.931, 1.042, 0.834 and 0.531 mm. The friction factors are compared with the conventional correlations over a Reynolds number range of 10,000–90,000. The effect of the variable thermal properties of liquid nitrogen, i.e., viscosity and thermal conductivity, on the flow and local heat transfer in the micro-tubes is clarified. The average Nusselt numbers are determined and compared with the correlations for the conventional channels and micro-channels, respectively. It is found that large roughness of the micro-tube causes high friction factor, and the modified Colebrook correlation can well predict the experimental friction factors by using the measured surface roughness. With the increase of liquid nitrogen temperature, the pressure drop decreases as a result of the lower viscosity. Opposite to water, the local heat transfer coefficient of liquid nitrogen flow in the micro-tube drops by 12.5% along the tube. The experimental data show that the average Nusselt numbers for the micro-tubes are higher than those predicted by the correlations for the conventional channels. Taking into account the effect of surface roughness of the micro-tubes on the heat transfer, the modified Gnielinski correlation enables to predict the experimental Nusselt numbers with a mean absolute error (MAE) of 6.4%. |
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