This paper presents results of an experimental investigation of convective heat transfer in liquids placed between two horizontal plates and heated from below. The liquids used were water, silicone oils of 1.5, 50, and 1000 centistoke kinematic viscosities, and mercury.
The experiments covered a range of Rayleigh numbers between 1.51(10)5 and 6.76(10)8. and Prandtl numbers between 0.02 and 8750.
Tests were made in cylindrical containers having copper tops and bottoms and insulating walls. For water and silicone oils the container was 5 in. in diam and 2 in. high. For mercury, two containers were used, both 5.28 in. in diameter, but one 1.39 in. high and another 2.62 in. high. In all cases the bottom plates were heated by electric heaters. The top plates were air-cooled for the water and silicone-oil experiments and water-cooled for the mercury tests. To prevent amalgamation, the copper plates of the mercury container were chromium plated.
Surface temperatures were measured by thermocouples embedded in the plates.
The test results indicate that the heat-transfer coefficients for all liquids investigated may be determined from the relationship Nu=0.069Ra13Pr0.074
In this equation the Nusselt and Rayleigh numbers are based on the distance between the copper plates.
The results of this experiment are in reasonable agreement with the data reported by others who used larger containers and different fluids.
This paper presents results of an experimental investigation of convective heat transfer in liquids confined by two parallel plates and inclined at various angles with respect to the horizontal. The experiments covered a range of Rayleigh numbers between 5(10)4 and 7.17(10)8, and Prandtl numbers between 0.02 and 11,560. Tests were made in rectangular and circular containers having copper plates and insulating walls. The liquids used were water, silicone oils, and mercury. The test results indicate that the heat transfer coefficients for all liquids investigated at the various angles, from horizontal to vertical, may be determined from the relationship Nu=C(Ra)1/3(Pr)0.074 The constant, C, is a function of the angle of inclination. It varies from C = 0.069 for the horizontal case when heated from below to C = 0.049 for the vertical case. For the test cells used, no effect on the Nusselt number had been detected for the vertical case by the change of the ratio of height of cell to distance between plates. The ratio for these tests was varied from 4.41 to 16.56.
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