Temperature distribution and variation with time has been considered in the analysis of the influences of the initial level of immersion of a horizontal metallic mesh tube in the liquid on combined buoyant and thermo-capillary flow. The combined flow occurs along with the rising liquid film flow on the surface of a horizontal metallic mesh tube. Three different levels of immersion of the metallic mesh tube in the liquid have been tested. Experiments of 60 min in duration have been performed using a heating metallic tube with a diameter of 25 mm and a length of 110 mm, sealed outside with a metallic mesh of 178 mm by 178 mm, and distilled water. These reveal two distinct flow patterns. Thermocouples and infrared thermal imager are utilized to measure the temperature. The level of the liquid free surface relative to the lower edge of the tube is measured as angle q. The results show that for a smaller q angle, or a low level of immersion, with a relatively low heating power, it is possible to near fully combine the upwards buoyant flow with the rising liquid film flow. In this case, the liquid is heated only in the vicinity of the tube, while the liquid away from the flow region experiences small changes in temperature and the system approaches steady conditions. For larger q angles, or higher levels of immersion, a different flow pattern is noticed on the liquid free surface and identified as the thermo-capillary (Marangoni) flow. The rising liquid film is also present. The higher levels of immersion cause a high temperature gradient in the liquid free surface region and promote thermal stratification; therefore the system could not approach steady conditions.
GOMES(马努尔.戈梅斯) Manuel J., MEI Ning. 水平金属丝网管表面上升液膜流动的浮力和热毛细混合流动的试验研究[J]. Frontiers in Energy, 2020, 14(1): 114-126.
Manuel J. GOMES, Ning MEI. Experimental study on combined buoyant-thermocapillary flow along with rising liquid film on the surface of a horizontal metallic mesh tube. Front. Energy, 2020, 14(1): 114-126.
Level of the liquid free surface relative to the lower edge of the tube
ϵ
Emissivity of water
DT
Temperature difference/°C
q
Heat flux density on the surface of the smooth metallic tube/(W·m–2)
U
Power source voltage/V
R
Resistance of the metallic tube/W
D
Diameter of the smooth metallic tube/m
L
Length of the metallic tube/m
T
Thermocouple
CTD
Circumferential temperature distribution/°C
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