scholarly journals HEAT TRANSFER FOR FILN BOILING OF A LIQUID ON A VERTICAL HEATED WALL IN A POROUS MEDIUM

2021 ◽  
Vol 43 (1) ◽  
pp. 20-29
Author(s):  
A.A. Avramenko ◽  
M.M. Kovetskaya ◽  
E.A. Kondratieva ◽  
T.V. Sorokina
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Porous Medium ◽  
Fluid Flow ◽  
Wall Temperature ◽  
Heated Wall ◽  
Film Boiling ◽  
Transfer Coefficients ◽  
Constant Wall Temperature ◽  
Heat Transfer Coefficients

The paper presents results of the modelling of heat transfer at film boiling of a liquid in a porous medium on a vertical heated wall. Such processes are observed at cooling of high-temperature surfaces of heat pipes, microstructural radiators etc. Heating conditions at the wall were the constant wall temperature or heat flux. An analytical solution was obtained for the problem of fluid flow and heat transfer using the porous medium model in the Darcy-Brinkman. It was shown that heat transfer at film boiling in a porous medium was less intensive than in the absence of a porous medium (free fluid flow) and further decreased with the decreasing permeability of the porous medium. A sharp decrease in heat transfer was observed for the Darcy numbers lower than five. The analytical predictions of heat transfer coefficients qualitatively agreed with the data [14] though demonstrated lower values of heat transfer coefficients for the conditions of the constant wall temperature and constant wall heat flux.

scholarly journals Experimental Heat Transfer Investigation of Stationary and Orthogonally Rotating Asymmetric and Symmetric Heated Smooth and Turbulated Channels

1992 ◽  
Author(s):  
H. A. El-Husayni ◽  
M. E. Taslim ◽  
D. M. Kercher
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Rotation Number ◽  
Symmetric Case ◽  
Wall Heat Flux ◽  
Heated Wall ◽  
Wall Heat Transfer ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Smooth Channel

An experimental investigation was conducted to determine the effects of variations in wall thermal boundary conditions on local heat transfer coefficients in stationary and orthogonally rotating smooth wall and two opposite-wall turbulated square channels. Results were obtained for three distributions of uniform wall heat flux: asymmetric, applied to the primary wall only; symmetric, applied to two opposite walls only; and fully-symmetric, applied to all four channel walls. Measured stationary and rotating smooth channel average heat transfer coefficients at channel location L/Dh = 9.53 were not significantly sensitive to wall heat flux distributions. Trailing side heat transfer generally increased with Rotation number whereas the leading wall results showed a decreasing trend at low Rotation numbers to a minimum and then an increasing trend with further increase in Rotation number. The stationary turbulated wall heat transfer coefficients did not vary markedly with the variations in wall heat flux distributions. Rotating leading wall heat transfer decreased with Rotation number and showed little sensitivity to heat flux distributions except for the fully-symmetric heated wall case at the highest Reynolds number tested. Trailing wall heat transfer coefficients were sensitive to the thermal wall distributions generally at all Reynolds numbers tested and particularly with increasing Rotation number. While the asymmetric case showed a slight deficit in trailing wall heat transfer coefficients due to rotation, the symmetric case indicated little change whereas the fully-symmetric case exhibited an enhancement.

scholarly journals RESEARCH ON MAXIMIZING CRITICAL AND REDUCING INITIAL HEAT FLUX DENSITIES TO ELIMINATE ANY FILM BOILING AND MINIMIZE DISTORTION DURING QUENCHING

2017 ◽  
Vol 4 ◽  
pp. 33-41 ◽  
Author(s):  
Nikolai Kobasko ◽  
Anatolii Moskalenko ◽  
Petro Lohvynenko ◽  
Volodymyr Dobryvechir
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Film Boiling ◽  
International Database ◽  
Transfer Coefficients ◽  
Mineral Oils ◽  
Heat Transfer Coefficients ◽  
Cooling Intensity ◽  
Initial Heat

In the paper the results of testing three types of FUCHS oils: Thermisol QH 120, Thermisol QH 10 and Thermisol QB 46 are discussed. The main attention is paid to critical heat flux densities evaluation because they create a basis for optimizing cooling intensity of any liquid quenchant. In the paper is underlined that any film boiling during quenching is undesirable since it is a reason for big distortion and non-uniform surface harness. It is shown that intensive quenching decreases distortion of steel parts during quenching. To eliminate film boiling during quenching in mineral oils, optimal temperature of oil should be chosen which maximize the first critical heat flux density and special additives should be used to decrease initial heat flux by creating surface micro-coating. Along with the evaluation of heat transfer coefficients, critical heat flux densities inherent to liquid quenchant must be measured first to optimize quenching processes. International DATABASE on cooling characteristics of liquid quenchants must include critical heat flux densities, initial heat flux densities, and heat transfer coefficients allowing optimizing and governing quenching processes.

Experimental Heat Transfer Investigation of Stationary and Orthogonally Rotating Asymmetric and Symmetric Heated Smooth and Turbulated Channels

1994 ◽  
Vol 116 (1) ◽  
pp. 124-132 ◽  
Author(s):  
H. A. El-Husayni ◽  
M. E. Taslim ◽  
D. M. Kercher
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Rotation Number ◽  
Symmetric Case ◽  
Wall Heat Flux ◽  
Heated Wall ◽  
Wall Heat Transfer ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Smooth Channel

An experimental investigation was conducted to determine the effects of variations in wall thermal boundary conditions on local heat transfer coefficients in stationary and orthogonally rotating smooth wall and two opposite-wall turbulated square channels. Results were obtained for three distributions of uniform wall heat flux: asymmetric, applied to the primary wall only; symmetric, applied to two opposite walls only; and fully symmetric, applied to all four channel walls. Measured stationary and rotating smooth channel average heat transfer coefficients at channel location L/Dh = 9.53 were not significantly sensitive to wall heat flux distributions. Trailing side heat transfer generally increased with Rotation number, whereas the leading wall results showed a decreasing trend at low Rotation numbers to a minimum and then an increasing trend with further increase in Rotation number. The stationary turbulated wall heat transfer coefficients did not vary markedly with the varaitions in wall heat flux distributions. Rotating leading wall heat transfer decreased with Rotation number and showed little sensitivity to heat flux distributions except for the fully symmetric heated wall case at the highest Reynolds number tested. Trailing wall heat transfer coefficients were sensitive to the thermal wall distributions generally at all Reynolds numbers tested and particularly with increasing Rotation number. While the asymmetric case showed a slight deficit in trailing wall heat transfer coefficients due to rotation, the symmetric case indicated little change, whereas the fully symmetric case exhibited an enhancement.

Heat Transfer Characteristics of Gaseous Flows in Micro-Channels With Constant Wall Temperature: Cooled From Walls

2006 ◽  
Author(s):  
Chungpyo Hong ◽  
Yutaka Asako
Keyword(s):  
Heat Transfer ◽  
Incompressible Flow ◽  
Wall Temperature ◽  
Heat Transfer Characteristics ◽  
Transfer Coefficients ◽  
Constant Wall Temperature ◽  
Gaseous Flow ◽  
Heat Transfer Coefficients ◽  
Micro Channels ◽  
Gaseous Flows

Two-dimensional compressible momentum and energy equations are solved to obtain the heat transfer characteristics of gaseous flows in micro-channels with CWT (constant wall temperature) whose temperature is lower than the inlet temperature. The combined effect of viscous dissipation and compressibility is also investigated. The numerical methodology is based on the Arbitrary-Lagrangian-Eulerian (ALE) method. The stagnation temperature is fixed at 300K and the computations were done for the wall temperature of 250K, 280K, and 290K. The bulk temperature based on the static temperature and the total temperature are compared with those of the heated case and also compared with those of the incompressible flow in a conventional sized channel. The identical heat transfer coefficients are obtained for both heated and cooled cases of the incompressible flow. However, in the case of the gaseous flow in micro-channels, different heat transfer coefficients are obtained for each heated and cooled case. A correlation for the prediction of the heat transfer rate of the gaseous flow in the micro-channel is proposed.

Cooldown Simulation for the Compact Ignition Tokamak (CIT), Poloidal Field (PF) Coils

2002 ◽  
Author(s):  
Behzad Mottahed ◽  
Harri Kyto¨maa
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Nucleate Boiling ◽  
Scale Model ◽  
Film Boiling ◽  
Type I ◽  
Type Ii ◽  
Poloidal Field ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

An experimental investigation was conducted to study the cooldown behavior of the Poloidal Field (PF) magnets. A full-scale model of a section of the cooling passages was built for this purpose. LN2, was used as the coolant in the vertical passages at mass fluxes ranging between 42 to 140 Kg/m2-s and heat fluxes from 17000 to 75000 W/m2 with nearly saturated liquid at the inlet. The heat flux was controlled with resistive heaters. Two distinct boiling regimes were observed. The first, Type I consists of film-boiling throughout the passage. Type II has nucleate boiling at the inlet, and is followed, in a short distance, to film-boiling. The equilibrium quality at the burnout point was calculated and was found to increase slightly with decreasing heat flux. The Leidenfrost temperature at which liquid Nitrogen wets the wall was measured to be about 180–200 K. Heat transfer coefficients in the order of 200–500 W/m2-K for film boiling and 5000 to 10000 W/m2-k for nucleate boiling in the type II regime were attained. Higher heat flux and mass flow rates resulted in higher heat transfer coefficients. Empirical correlations were obtained for the nucleate region of the type II regime.

Film Cooling Calculations With an Iterative Conjugate Heat Transfer Approach Using Empirical Heat Transfer Coefficient Corrections

2010 ◽  
Author(s):  
Sushant Dhiman ◽  
Savas Yavuzkurt
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Surface Temperature ◽  
Wall Temperature ◽  
Film Cooling ◽  
Conjugate Heat Transfer ◽  
Transfer Coefficients ◽  
Flat Plates ◽  
Constant Wall Temperature ◽  
Heat Transfer Coefficients

An iterative conjugate heat transfer technique has been developed to predict the temperatures on film cooled surfaces such as flat plates and turbine blades. Conventional approaches using a constant wall temperature to calculate heat transfer coefficient and applying it to solid as a boundary condition can result in errors around 14% in uncooled blade temperatures. This indicates a need for conjugate heat transfer calculation techniques. However, full conjugate calculations also suffer from inability to correctly predict heat transfer coefficients in the near field of film cooling holes and require high computational cost making them impractical for component design in industrial applications. Iterative conjugate heat transfer (ICHT) analysis is a compromise between these two techniques where the external flow convection and internal blade conduction are loosely coupled. The solution obtained from solving one domain is used as boundary condition for the other. This process is iterated until convergence. Flow and heat transfer over a film cooled blade is not solved directly and instead convective heat transfer coefficients resulting from external convection on a similar blade without film cooling and under the same flow conditions are corrected by use of experimental data to incorporate the effect of film cooling in the heat transfer coefficients. The effect of conjugate heat transfer is taken into account by using this iterative technique. Unlike full conjugate heat transfer (CHT) the ICHT analysis doesn’t require solving a large number of linear algebraic equations at once. It uses two separate meshes for external convection and blade conduction and thus problem can be solved in lesser time using less computational resources. A demonstration of this technique using a commercial CFD solver FLUENT is presented for simulations of film cooling on flat plates. Results are presented in form of film cooling heat transfer coefficients and surface temperature distribution which are compared with results obtained from conventional approach. For uncooled surfaces, the deviations were as high as 3.5% between conjugate and conventional technique results for the wall temperature. For film cooling simulations on a flat plate using the ICHT approach showed deviations up to 10% in surface temperature compared to constant wall temperature technique for a high temperature difference case and 3% for a low temperature difference case, since surface temperature is not constant over the surface when conjugate heat transfer is considered. Results show that conjugate heat transfer effect is significant for film cooling flows involving high temperature differences for the current blade materials and application of film cooling correction obtained from experimental data is very useful in obtaining realistic blade temperatures.

scholarly journals Operating temperatures of oil-lubricated medium-speed gears: Numerical models and experimental results

2003 ◽  
Vol 217 (2) ◽  
pp. 87-106 ◽  
Author(s):  
H Long ◽  
A A Lord ◽  
D T Gethin ◽  
B J Roylance
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Temperature ◽  
Rotational Speed ◽  
High Speed ◽  
Applied Load ◽  
Frictional Heat ◽  
Transfer Coefficients ◽  
Gear Teeth ◽  
Heat Transfer Coefficients

This paper investigates the effects of gear geometry, rotational speed and applied load, as well as lubrication conditions on surface temperature of high-speed gear teeth. The analytical approach and procedure for estimating frictional heat flux and heat transfer coefficients of gear teeth in high-speed operational conditions was developed and accounts for the effect of oil mist as a cooling medium. Numerical simulations of tooth temperature based on finite element analysis were established to investigate temperature distributions and variations over a range of applied load and rotational speed, which compared well with experimental measurements. A sensitivity analysis of surface temperature to gear configuration, frictional heat flux, heat transfer coefficients, and oil and ambient temperatures was conducted and the major parameters influencing surface temperature were evaluated.

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