Inverse Estimation of Heat Transfer Coefficient and Reference Temperature in Jet Impingement

2020 ◽  
Vol 142 (9) ◽  
Author(s):  
Anil Ramkishanrao Kadam ◽  
Vijaykumar Hindasageri ◽  
G. N. Kumar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Steady State ◽  
Transfer Coefficient ◽  
Jet Impingement ◽  
Impinging Jets ◽  
Reference Temperature ◽  
Present Technique ◽  
Transient Heat Flux

Abstract Applications of impinging jets are wide-ranging from cooling to heating in industrial as well as domestic field. Most of the reported heat transfer distribution data to and from impinging jets have been found from steady-state measurements. This study utilizes the solution to three-dimensional (3D) inverse heat conduction problem to estimate transient temperatures on the impingement side. Then, the temperature gradient is determined near the impingement wall (∼0.01 mm inside) with which transient heat flux is estimated on the impingement side. Instead of steady-state values, transient heat flux and corresponding wall temperatures are utilized in a thin foil technique to find out heat transfer coefficient and reference temperature simultaneously. The scope of the present technique is examined through its application to impinging jets with various configurations such as laminar jet, turbulent jet, hot jet, cold jet, and multiple jets. In all cases, estimations are reasonably close. The application of this inverse technique can be extended to any configuration of jet impingement irrespective of geometry of nozzle (circular/rectangular), the orientation of nozzle (orthogonal/inclined), the temperature of a jet (hot/cold), Reynolds numbers (laminar/turbulent), the nozzle-to-plate spacing (any Z/d), and roughness of the plate surface. The effect of plate thickness on the accuracy of the present technique is also studied. Up to 5 mm thick plates can be used in impinging jet applications without worrying much on accuracy. The use of the present technique significantly reduces the experimental cost and time since it works on transient data of just a few seconds.

Casing Convective Heat Transfer Coefficient and Reference Freestream Temperature Determination Near an Axial Flow Turbine Rotor

2011 ◽  
Vol 133 (8) ◽  
Author(s):  
C. Camci ◽  
B. Gumusel
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Steady State ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Convective Heat Transfer Coefficient ◽  
Axial Flow ◽  
Reference Temperature ◽  
Steady State Heat Transfer

The present study explains a steady-state method of measuring convective heat transfer coefficient on the casing of an axial flow turbine. The goal is to develop an accurate steady-state heat transfer method for the comparison of various casing surface and tip designs used for turbine performance improvements. The freestream reference temperature, especially in the tip gap region of the casing, varies monotonically from the rotor inlet to rotor exit due to work extraction in the stage. In a heat transfer problem of this nature, the definition of the freestream temperature is not as straightforward as constant freestream temperature type problems. The accurate determination of the convective heat transfer coefficient depends on the magnitude of the local freestream reference temperature varying in axial direction, from the rotor inlet to exit. The current study explains a strategy for the simultaneous determination of the steady-state heat transfer coefficient and freestream reference temperature on the smooth casing of a single stage rotating turbine facility. The heat transfer approach is also applicable to casing surfaces that have surface treatments for tip leakage control. The overall uncertainty of the method developed is between 5% and 8% of the convective heat transfer coefficient.

Experimental Study of Thickness Effects on Evaporation/Boiling on Thin Sintered Copper Mesh Surfaces

2005 ◽  
Author(s):  
Chen Li ◽  
G. P. Peterson ◽  
Yaxiong Wang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Steady State ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Thermal Contact Resistance ◽  
Thermal Contact ◽  
Boiling Heat Transfer Coefficient ◽  
Copper Mesh

Evaporation/boiling from surfaces coated with multiple, uniform layers of sintered, isotropic, copper-mesh is studied experimentally. The investigation focuses on the effect of the wick thickness on the steady-state evaporation/boiling heat transfer coefficient and the critical heat flux under atmospheric pressure conditions. An optimal sintering process was developed and employed to prepare the test articles. This process minimizes the interface thermal contact resistance between the heated wall and wick, as well as enhancing the contact conditions between the layers of copper mesh. Due to the reduction in the thermal contact resistance between the wall and copper mesh, extremely high evaporation/boiling heat transfer coefficients were achieved. These values, which varied with input heat flux and wick thickness, were from 5 to 20 times higher than those previously reported by other researchers. The critical heat flux (CHF) was also significantly enhanced. The experimental results also indicated that while the evaporation/boiling heat transfer coefficient is not affected by wick thickness, the CHF for steady-state operation is strongly dependent on the wick layer thickness. In addition, the CHF increases proportionally with the wick thickness when the wick structure, porosity and pore size are held constant. Sample structure and fabrication processes as well as test procedures are described and discussed in detail and the experimental results and observations are systematically presented and analyzed. Evaporation/boiling Heat transfer regimes from these wick structures are identified and discussed based on the visual observations of the phase-change phenomena and the relative relationship between the heat flux and superheat.

On Selection of Reference Temperature of Heat Transfer Coefficient for Complicated Flows

2007 ◽  
Author(s):  
X. C. Li ◽  
J. Zhou ◽  
K. Aung
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Surface Temperature ◽  
Transfer Coefficient ◽  
Wall Temperature ◽  
Convective Heat Transfer Coefficient ◽  
Internal Heat ◽  
Reference Temperature ◽  
The Heat Transfer Coefficient

One of the most fundamental concepts in heat transfer is the convective heat transfer coefficient, which is closely related with the flow Reynolds number, flow geometry and the thermal conditions on the heat transfer surface. To define the heat transfer coefficient, a reference temperature is needed besides the surface temperature and heat flux. The reference temperature can be chosen differently, such as the fluid bulk mean temperature (for internal flows) and the temperature at the far field (for external flows). For complicated flows, the adiabatic wall temperature, defined as the wall temperature when the surface heat flux is zero, is commonly adopted as the reference temperature. Other options can also be applied to complicated flows. This paper analyzed some of the potential selections of the reference temperature for different flow settings, including film cooling, jet impingement with cross flows and a mixing flow in a straight duct with or without internal heat source. Both laminar and turbulent flows are considered with different boundary conditions. Dramatic changes of heat transfer coefficient are observed with different reference temperatures. In some special conditions the heat transfer coefficient becomes negative, which means the heat flux has a different direction with the driving temperature difference defined. An innovative method is proposed to calculate the heat transfer coefficient of complicated flows with constant surface temperature.

Alternative and Relevant Representation to Heat Transfer Coefficient for Modeling the Heat Transfer Between a Fluid and a Non-Isothermal Wall in Transient Regime

2010 ◽  
Author(s):  
Benjamin Remy ◽  
Alain Degiovanni
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Steady State ◽  
Boundary Conditions ◽  
Transfer Coefficient ◽  
Flat Plate ◽  
Temperature Difference ◽  
Interfacial Heat Transfer ◽  
Thermal Boundary Conditions

This paper deals with the relevant model that can be proposed for modeling the interfacial heat transfer between a fluid and a wall in the case of space and time varying thermal boundary conditions. Usually, for a constant and uniform heat transfer (unidirectional steady-state regime), the problem can be solved introducing a heat transfer coefficient h, uniform in space and constant in time that linearly links the surface heat flux and the temperature difference between the wall temperature Tw and an equivalent fluid temperature Tf. The problem we consider in this work concerns the heat transfer between a steady-state fluid flow and a wall submitted to a transient and non uniform thermal solicitations, as for instance a steady-state flow on a flat plate submitted to a transient and space reduced heat flux. We will show that the more interesting representation for describing the interfacial heat transfer is not to define as usually done a non-uniform and variable heat transfer coefficient h(x,t) because as it depends on the thermal boundary conditions, it is not really intrinsic. We propose an alternative approach, which consists in introducing a generalized impedance Z(ω,p) that links in space and time domain the heat flux and the temperature difference through a double convolution product instead of a scalar product. After the presentation of the general problem, the simple case of a stationary piston flow that can be solved analytically will be considered for validation both in thermal steady-state and transient regimes. To conclude and show the interest of our approach, a comparison between a global approach and a numerical simulation in a more complex and realistic case taking into account the thermal coupling with a flat plate will be presented.

Experimental Study of Boiling Heat Transfer From a Sphere Embedded in a Liquid-Saturated Porous Medium

1990 ◽  
Vol 112 (3) ◽  
pp. 736-743 ◽  
Author(s):  
V. X. Tung ◽  
V. K. Dhir
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Particle Size ◽  
Porous Medium ◽  
Heat Transfer Coefficient ◽  
Steady State ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Maximum Heat ◽  
Maximum Heat Flux

Boiling heat transfer from a sphere embedded in a porous medium composed of nonheated glass particles was studied under steady-state and transient quenching conditions. In the experiments, the diameter of the nonheated glass particles forming the porous layers was varied parametrically. Freon-113 was used as the test liquid. Experimental results showed that the maximum heat flux increased monotonically with increasing glass particle diameter and approached an asymptotic value corresponding to the maximum heat flux obtained in a pool free of glass particles. It was also observed that the minimum heat flux was nearly insensitive to the particle size and the film boiling heat transfer coefficient increased slightly with decreasing particle size. In the nucleate boiling region, the heat transfer coefficient showed a much weaker dependence on wall superheat in the presence of particles. Transient data indicated that the surface temperature was not uniform during quenching. Therefore, different maximum heat fluxes were obtained depending on the location of the thermocouple whose temperature history was employed in recovering the transient boiling curve. However, for some applications, cooling rates predicted by imposing the steady-state boiling curve may not be in large error.

Heat Transfer Experiments in a Confined Jet Impingement Configuration Using Transient Techniques

2011 ◽  
Vol 133 (9) ◽  
Author(s):  
Florian Hoefler ◽  
Nils Dietrich ◽  
Jens Wolfersdorf
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Jet Impingement ◽  
Fast Response ◽  
Heat Fluxes ◽  
Thermochromic Liquid Crystal ◽  
Turbine Blade Cooling ◽  
Transient Techniques

A confined jet impingement configuration has been investigated in which the matter of interest is the convective heat transfer from the air flow to the passage walls. The geometry is similar to gas turbine blade cooling applications. The setup is distinct from usual cooling passages by the fact that no crossflow and no bulk flow directions are present. The flow exhausts through two staggered rows of holes opposing the impingement wall. Hence, a complex 3-D vortex system arises, which entails a complex heat transfer situation. The transient thermochromic liquid crystal (TLC) method was used in previous studies to measure the heat transfer on the passage walls. Due to the nature of these experiments, the fluid as well as the wall temperature vary with location and time. As a prerequisite of the transient TLC technique, the heat transfer coefficient is assumed to be constant over the transient experiment. Therefore, it is the scope of this article to qualify this assumption and to validate the results at discrete locations. For this purpose, fast response surface thermocouples and heat flux sensors were applied, in order to gain information on the temporal evolution of the wall heat fluxes. The linear relation between heat flux and temperature difference could be verified for all measurement sites. This validates the assumption of a constant heat transfer coefficient. Nusselt number evaluations from independent techniques show a good agreement, considering the respective uncertainty ranges. For all investigated sites, the Nusselt numbers range within ±9% of the values gained from the TLC measurement.

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