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Pool boiling heat transfer in a vertical annulus with a stepped outside tube |
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| Authors: | Myeong-Gie Kang |
| Affiliation: | 1. School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan, China;2. CAD Center, Huazhong University of Science and Technology, Wuhan, China;1. CERN European Organization for Nuclear Research, 1211 Geneva 23, CH;2. ASSYSTEM France, Succursale de Genève, ch. Franck-Thomas 36, 1208 Geneva 6, CH;3. Institute of Scientific Instruments of the ASCR, Kralovopolska 147, 61264 Brno, CZ;1. Department of Thermodynamics, Theory of Machines and Thermal Systems, Faculty of Mechanical and Power Engineering, Wroc?aw University of Science and Technology, Wybrze?e Wyspiańskiego 27, 50-370 Wroc?aw, Poland;2. National Institute for Fusion Science, 322-6 Oroshi cho, Toki, Gifu 509-5292, Japan;3. High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan;4. University of Tsukuba, 1 Chome-1-1 Tennodai, Tsukuba, Ibaraki 305-8571, Japan |
| Abstract: | Effects of a stepped outside tube on nucleate pool boiling heat transfer in a vertical annulus with closed bottoms have been investigated experimentally. For the study saturated water at atmospheric pressure and a heated tube of 200 mm length and 19 mm diameter were used. The shape of an outside tube of the annulus has step geometry and the ratio between the upper and lower regions are varied from 0.23 to 4.43. The existence of the stepped outside tube changes heat transfer characteristics and its effect becomes evident as the gap ratio is smaller than 1. For the tested gap ratios heat transfer deterioration is observed as the heat flux is higher than 80 kW/m2 comparing to the single unrestricted tube. The major cause for the tendency is attributed to the loss of liquid agitation intensity around the stepped regions of the annulus. |
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