scholarly journals Two-Dimensional Thermal Boundary Layer Corrections for Convective Heat Flux Gauges

2007 ◽  
Vol 21 (3) ◽  
pp. 543-547 ◽  
Author(s):  
M. Kandula ◽  
G. Haddad
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Convective Heat ◽  
Thermal Boundary Layer ◽  
Two Dimensional ◽  
Convective Heat Flux

Contrasting suspended covers reveal the impact of an artificial monolayer on heat transfer processes at the interfacial boundary layer

2015 ◽  
Vol 72 (9) ◽  
pp. 1621-1627 ◽  
Author(s):  
P. Pittaway ◽  
V. Martínez-Alvarez ◽  
N. Hancock
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Wind Speed ◽  
Diurnal Variation ◽  
Water Temperature ◽  
Convective Heat ◽  
Wave Turbulence ◽  
Convective Heat Flux ◽  
Interfacial Boundary ◽  
Reduced Temperature

The highly variable performance of artificial monolayers in reducing evaporation from water storages has been attributed to wind speed and wave turbulence. Other factors operating at the interfacial boundary layer have seldom been considered. In this paper, two physical shade covers differing in porosity and reflectivity were suspended over 10 m diameter water tanks to attenuate wind and wave turbulence. The monolayer octadecanol was applied to one of the covered tanks, and micrometeorological conditions above and below the covers were monitored to characterise diurnal variation in the energy balance. A high downward (air-to-water) convective heat flux developed under the black cover during the day, whereas diurnal variation in the heat flux under the more reflective, wind-permeable white cover was much less. Hourly air and water temperature profiles under the covers over 3 days when forced convection was minimal (low wind speed) were selected for analysis. Monolayer application reduced temperature gain in surface water under a downward convective heat flux, and conversely reduced temperature loss under an upward convective heat flux. This ‘dual property’ may explain why repeat application of an artificial monolayer to retard evaporative loss (reducing latent heat loss) does not inevitably increase water temperature.

Unsteady Stagnation Point Heat Transfer

1965 ◽  
Vol 87 (2) ◽  
pp. 221-230 ◽  
Author(s):  
B. T. Chao ◽  
D. R. Jeng
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Flux ◽  
Surface Temperature ◽  
Thermal Boundary Layer ◽  
Essential Feature ◽  
Step Change ◽  
Stream Velocity ◽  
Two Dimensional ◽  
Time Solution

An analysis is presented for the unsteady laminar, forced-convection heat transfer at a two-dimensional and axisymmetrical front stagnation due to an arbitrarily prescribed wall temperature or heat flux variation. The flow is incompressible and steady. The procedure begins with a consideration of the thermal boundary-layer response caused by either a step change in surface temperature or heat flux. Two appropriate asymptotic solutions, valid for small and large times, respectively, are found and satisfactorily joined for Prandtl numbers ranging from 0.01 to 100. The key to the small time solution is the transformation of the energy equation in the Laplace transform plane to an ordinary differential equation with a large parameter. An essential feature of the large time solution is the use of Meksyn’s transformation variable and the method of steepest descent in the evaluation of integrals. It is found that, for both two-dimensional and axisymmetrical stagnation, the time required for the thermal boundary layer to attain steady condition, for either a step change in surface temperature or heat flux, varies inversely with the free stream velocity and directly with 1/4 power of the Prandtl number of the fluid.

Effect of Edge Conditions on Natural Convective Heat Transfer From a Narrow Vertical Flat Plate With a Uniform Surface Heat Flux

2007 ◽  
Author(s):  
Patrick H. Oosthuizen ◽  
Jane T. Paul
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Surface Heat Flux ◽  
Three Dimensional ◽  
Surface Heat ◽  
Heated Plate ◽  
Two Dimensional ◽  
Adiabatic Surface

Two-dimensional natural convective heat transfer from vertical plates has been extensively studied. However, when the width of the plate is relatively small compared to its height, the heat transfer rate can be greater than that predicted by these two-dimensional flow results. Because situations that can be approximately modelled as narrow vertical plates occur in a number of practical situations, there exists a need to be able to predict heat transfer rates from such narrow plates. Attention has here been given to a plate with a uniform surface heat flux. The magnitude of the edge effects will, in general, depend on the boundary conditions existing near the edge of the plate. To examine this effect, two situations have been considered. In one, the heated plate is imbedded in a large plane adiabatic surface, the surfaces of the heated plane and the adiabatic surface being in the same plane while in the second there are plane adiabatic surfaces above and below the heated plate but the edge of the plate is directly exposed to the surrounding fluid. The flow has been assumed to be steady and laminar and it has been assumed that the fluid properties are constant except for the density change with temperature which gives rise to the buoyancy forces, this having been treated by using the Boussinesq approach. It has also been assumed that the flow is symmetrical about the vertical centre-plane of the plate. The solution has been obtained by numerically solving the full three-dimensional form of the governing equations, these equations being written in terms of dimensionless variables. Results have only been obtained for a Prandtl number of 0.7. A wide range of the other governing parameters have been considered for both edge situations and the conditions under which three dimensional flow effects can be neglected have been deduced.

Schmidt-Boelter Heat Flux Gage Sensitivity Coefficients in Radiative and Convective Environments

2011 ◽  
Author(s):  
James T. Nakos ◽  
Alexander L. Brown
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Convective Heat ◽  
Radiative Heat ◽  
Sensitivity Coefficient ◽  
Calibration Standard ◽  
Convective Heat Flux ◽  
Sensitivity Coefficients ◽  
Theoretical Sensitivity ◽  
Flux Calibration

Commercial Schmidt-Boelter heat flux gages are always calibrated by using a radiative heat flux source where convection is minimized. This is because one can establish a reliable link to a National Institute of Standards and Technology (NIST) calibration standard. To the authors’ knowledge, no NIST traceable link exists for convective heat flux calibration. When heat flux gages are used in typical applications, convection is often not negligible. It has been common practice to assume that the sensitivity coefficient supplied by the manufacturer also applies for convective environments. This assumption is believed to be incorrect. If incorrect, this would result in uncertainties larger than typically reported (e.g., ±3%). This paper analyzes the heat transfer from an idealized Schmidt-Boelter heat flux gage. The analysis shows that the theoretical sensitivity coefficients in purely radiative and convective environments are not the same and, in fact, differ by the emissivity of the gage surface. The implication of this difference is that the accuracy specification supplied by the manufacturer (typically ± 3%) is not correct for measurement applications where convection is not negligible.

Sign in / Sign up

Export Citation Format

Share Document