Measurements and Calculations of Transient Natural Convection in Water

1982 ◽  
Vol 104 (4) ◽  
pp. 644-648 ◽  
Author(s):  
B. Sammakia ◽  
B. Gebhart ◽  
Z. H. Qureshi
Keyword(s):  
Natural Convection ◽  
Temperature Response ◽  
Vertical Surface ◽  
Constant Heat Flux ◽  
Thermal Capacity ◽  
Transient Natural Convection ◽  
Heating And Cooling ◽  
Dependent Form ◽  
Induced Flow ◽  
Explicit Finite Difference

Transient natural convection adjacent to a flat vertical surface with appreciable thermal capacity is investigated both experimentally and numerically. The surface is immersed in initially quiescent water, and has the same uniform temperature distribution. It is then suddenly loaded with a uniform and constant heat flux thereby generating a buoyancy induced flow adjacent to the surface. Surface temperature response was recorded by means of thermocouples embedded inside the surface, and boundary layer temperature measurements were also taken. An explicit finite difference numerical scheme is used to obtain solutions to the partial differential equations describing the conservation of mass, momentum, and energy in their time dependent form. Good agreement between the calculated and measured results is observed for both the heating and cooling transient processes.

Measurements of Transient Natural Convection on Flat Vertical Surfaces

1963 ◽  
Vol 85 (1) ◽  
pp. 25-28 ◽  
Author(s):  
B. Gebhart ◽  
D. E. Adams
Keyword(s):  
Natural Convection ◽  
Thermal Capacity ◽  
Complete Agreement ◽  
Experimental Measurements ◽  
Integral Analysis ◽  
Transient Natural Convection ◽  
Surface Temperatures ◽  
Input Flux ◽  
Wide Range ◽  
Infrared Techniques

Experimental measurements of natural convection transients in air and in water are compared with the results of the integral analysis presented by the first author. An application of infrared techniques to the measurement of transient surface temperatures is described. The measurements, over a wide range of thermal capacity, are reduced to the variables which arose in the analysis and the measured responses are in essentially complete agreement with the results of that analysis for the case of a step in input flux. None of the measurements of natural convection transients on vertical plates has indicated temperature overshoot for the step condition.

Transient Natural Convection From Vertical Elements

1961 ◽  
Vol 83 (1) ◽  
pp. 61-70 ◽  
Author(s):  
B. Gebhart
Keyword(s):  
Natural Convection ◽  
Prandtl Number ◽  
Surface Temperature ◽  
Extreme Case ◽  
Transient Behavior ◽  
Thermal Capacity ◽  
Average Surface ◽  
Transient Natural Convection ◽  
Average Surface Temperature ◽  
Prandtl Numbers

The transient natural-convection process is analyzed using an integral method of analysis. Differential equations are derived which relate average surface temperature and time for either heating or cooling for vertical elements having arbitrary thermal capacity. The equations are applicable to laminar flow for all fluids. The coefficients are Prandtl number dependent and are estimated for Prandtl numbers in the range 0.01 to 1000. A solution of the equations is presented for the extreme case of a vertical plate of negligible thermal capacity subjected to a step in flux at its surface. Fluids having Prandtl numbers of 0.01, 0.1, 0.72, 1.0, 5, 10, 100, and 1000 are considered. The results, in terms of generalized variables, are practically independent of Prandtl number. Simple one-dimensional transient behavior is followed for approximately 20 per cent of the transient with a subsequent quick approach to the asymptotic value. The results show no substantial overshoot of the average surface temperature. It is doubted that significant temperature overshoot actually occurs for vertical surfaces even for a step in flux.

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