Turbulent Heat Transfer and Friction in Pin Fin Channels With Lateral Flow Ejection

1989 ◽  
Vol 111 (1) ◽  
pp. 51-58 ◽  
Author(s):  
S. C. Lau ◽  
J. C. Han ◽  
Y. S. Kim
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Friction Factor ◽  
Lateral Flow ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Pressure Drops ◽  
Pin Fin ◽  
Straight Flow

Experiments were conducted to study the effects of lateral flow ejection on the overall heat transfer and pressure drops for turbulent flow through pin fin channels. The two test sections of the investigation were rectangular channels with staggered arrays of six and eight streamwise rows of pins, respectively. The pin length-to-diameter ratio was one and both the streamwise and spanwise pin spacings were 2.5 times the pin diameter. Heat transfer and friction data were obtained for various ejection exit geometries, for ejection ratios between 0 and 1, and for Reynolds numbers between 6000 and 60,000. The results of the study show that, for any given ejection ratio, the overall Nusselt number increases with increasing Reynolds number. However, the overall Nusselt number is reduced by as much as 25 percent as the ejection ratio is increased from 0 to 1 over the range of Reynolds number studied. The Nu–Re–ε relationship, which is insensitive to varying the ejection exit geometry, can be correlated by the equation (Nu/Nu0) = (Nu1/Nu0)ε, where Nu0 = c0Rem and Nu1 = c1Ren are the overall Nusselt numbers in the 0 and 100 percent lateral flow ejection cases, respectively. The results also show that the overall friction factor is independent of the flow Reynolds number over the range of Reynolds number studied. However, the friction factor is strongly dependent on the ejection ratio as well as the geometries of the straight flow exit and lateral ejection flow exit.

scholarly journals Effect of Pin Diameter Degressive Gradient on Heat Transfer in a Microreactor with Non-Uniform Pin-Fin Array under Low Reynolds Number Conditions

Energies ◽  
2019 ◽  
Vol 12 (14) ◽  
pp. 2702
Author(s):  
Miao Qian ◽  
Jie Li ◽  
Zhong Xiang ◽  
Chao Yan ◽  
Xudong Hu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Friction Factor ◽  
Low Reynolds Number ◽  
Hydrodynamic Characteristics ◽  
Pin Fin ◽  
Low Reynolds ◽  
Pin Fin Array

To improve the efficiency of hydrogen-producing microreactors with non-uniform pin-fin array, the influence of the pin diameter degressive gradient of the non-uniform pin-fin array (NPFA) on heat transfer and pressure drop characteristics is analyzed in this study via numerical simulation under low Reynolds number conditions. Because correlations in prior studies cannot be used to predict the Nusselt number and pressure drop in the NPFA, new heat transfer and friction factor correlations are developed in this paper to account for the effect of the pin diameter degressive gradient, providing a method for the optimized design of the pin diameter degressive gradient for a microreactor with NPFA. The results show that the Nusselt number and friction factor under a low Reynolds number are quite sensitive to the pin diameter degressive gradient. Based on the new correlations, the exponents of the pin diameter degressive gradient for the friction factor and Nusselt number were 6.9 and 2.1, respectively, indicating the significant influence of the pin diameter degressive gradient on the thermal and hydrodynamic characteristics in the NPFA structure.

Heat Transfer in Thin, Compact Heat Exchangers With Circular, Rectangular, or Pin-Fin Flow Passages

1992 ◽  
Vol 114 (2) ◽  
pp. 373-382 ◽  
Author(s):  
D. A. Olson
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Friction Factor ◽  
Heat Exchangers ◽  
Rectangular Channel ◽  
Fluid Temperature ◽  
Compact Heat Exchangers ◽  
Pin Fin

We have measured heat transfer and pressure drop of three thin, compact heat exchangers in helium gas at 3.5 MPa and higher, with Reynolds numbers of 450 to 36,000. The flow geometries for the three heat exchanger specimens were: circular tube, rectangular channel, and staggered pin fin with tapered pins. The specimens were heated radiatively at heat fluxes up to 77 W/cm2. Correlations were developed for the isothermal friction factor as a function of Reynolds number, and for the Nusselt number as a function of Reynolds number and the ratio of wall temperature to fluid temperature. The specimen with the pin fin internal geometry had significantly better heat transfer than the other specimens, but it also had higher pressure drop. For certain conditions of helium flow and heating, the temperature more than doubled from the inlet to the outlet of the specimens, producing large changes in gas velocity, density, viscosity, and thermal conductivity. These changes in properties did not affect the correlations for friction factor and Nusselt number in turbulent flow.

scholarly journals Steady interaction of a turbulent plane jet with a rectangular heated cavity

2016 ◽  
Vol 20 (5) ◽  
pp. 1485-1498
Author(s):  
Farida Iachachene ◽  
Amina Mataoui ◽  
Yacine Halouane
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Flow Structure ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heated Wall ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Potential Core

Turbulent heat transfer between a confined jet flowing in a hot rectangular cavity is studied numerically by finite volume method using the k-w SST one point closure turbulence model. The location of the jet inside the cavity is chosen so that the flow is in the non-oscillation regime. The flow structure is described for different jet-to-bottom-wall distances. A parametrical study was conducted to identify the influence of the jet exit location and the Reynolds number on the heat transfer coefficient. The parameters of this study are: the jet exit Reynolds number (Re, 1560< Re <33333), the temperature difference between the cavity heated wall and the jet exit (DT=60?C) and the jet location inside the cavity (Lf, 2? Lf? 10 and Lh 2.5<Lh?10). The Nusselt number increased and attained its maximum value at the stagnation points and then decreased. The flow structure is found in good agreement with the available experimental data. The maximum local heat transfer between the cavity walls and the flow occurs at the potential core end. The ratio between the stagnation point Nusselt numbers of the cavity bottom (NuB0) to the maximum Nusselt number on the lateral cavity wall (NuLmax) decreased with the Reynolds number for all considered impinging distances. For a given lateral confinement, the stagnation Nusselt number of the asymmetrical interaction Lh?10 is almost equal to that of the symmetrical interaction Lh=10.

Heat Transfer Prediction of a Jet Impinging a Cylindrical Deadlock Area

2014 ◽  
Vol 136 (11) ◽  
Author(s):  
Yacine Halouane ◽  
Amina Mataoui ◽  
Farida Iachachene
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Flow Behavior ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Potential Core ◽  
Numerical Predictions

The turbulent heat transfer by a confined jet flowing inside a hot cylindrical cavity is investigated numerically in this paper. This configuration is found in several engineering applications such as air conditioning and the ventilation of mines, deadlock, or corridors. The parameters investigated in this work are the Reynolds number (Re, 20,000 ≤ Re ≤ 50,000) and the normalized distance Lf between jet exit and the cavity bottom (Lf, 2 ≤ Lf  ≤ 12). The numerical predictions are performed by finite volume method using the second order one-point closure turbulence model (RSM). The Nusselt number increases and attains maximum values at stagnation points, after it decreases. For an experimental test case available in the literature Lf = 8, the numerical predictions are in good agreement. Processes of heat transfer are analyzed from the flow behavior and the underlying mechanisms. The maximum local heat transfer between the cavity walls and the flow occurs at Lf = 6 corresponding to the length of the potential core. Nusselt number at the stagnation point is correlated versus Reynolds number Re and impinging distance Lf; [Nu0=f(Re,Lf)].

scholarly journals Turbulent Heat Transfer From a Slot Jet Impinging on a Flat Plate

2013 ◽  
Vol 135 (10) ◽  
Author(s):  
Dahbia Benmouhoub ◽  
Amina Mataoui
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Flow Field ◽  
Skin Friction ◽  
Velocity Ratio ◽  
Surface Velocity ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Jet Velocity

The flow field and heat transfer of a plane impinging jet on a hot moving wall were investigated using one point closure turbulence model. Computations were carried out by means of a finite volume method. The evolutions of mean velocity components, vorticity, skin friction coefficient, Nusselt number and pressure coefficient are examined in this paper. Two parameters of this type of interaction are considered for a given impinging distance of 8 times the nozzle thickness (H/e = 8): the jet-surface velocity ratio and the jet exit Reynolds number. The flow field structure at a given surface-to-jet velocity ratio is practically independent to the jet exit Reynolds number. A slight modification of the flow field is observed for weak surface-to-jet velocity ratios while the jet is strongly driven for higher velocity ratio. The present results satisfactorily compare to the experimental data available in the literature for Rsj ≤ 1.The purpose of this paper is to investigate this phenomenon for higher Rsj values (0 ≤ Rsj ≤ 4). It follows that the variation of the mean skin friction and the Nusselt number can be correlated according to the surface-to-jet velocity ratios and the Reynolds numbers.

Simulation of Turbulent Heat Transfer in a Tube Fitted with Twisted Tape Placed Separately from the Tube Walls

2015 ◽  
Vol 751 ◽  
pp. 245-250 ◽  
Author(s):  
Niwat Piriyarungroj ◽  
Smith Eiamsa-ard ◽  
Pongjet Promvonge ◽  
Petpices Eiamsa-Ard ◽  
Chinaruk Thianpong
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Friction Factor ◽  
Transfer Rate ◽  
Reynolds Numbers ◽  
Turbulent Heat Transfer ◽  
Twisted Tape ◽  
Turbulent Heat ◽  
Clearance Ratio ◽  
Constant Wall Temperature

The effects of loose-fit twisted tape (LFT) on the heat transfer rate, friction factor, fluid phenomena and thermal performance of a tube under constant wall temperature are examined. It is observed that apart from the rise of Reynolds number, the reduction of the clearance ratio (c/D) leads to an increase in the heat transfer and pressure loss. According to the numerical results, the heat transfer and friction factor in the tubes with loose-fit twisted tape (LFT) for the smallest clearance ratio of c/D = 0.05 are higher those other clearance ratios. In addition, the thermal performances of clearance ratio c/D = 0.05 are found to be higher than those other clearance ratios (c/D) for all Reynolds numbers examined.

scholarly journals Rayeilgh number effect on the turbulent heat transfer within a parallelepiped cavity

2011 ◽  
Vol 15 (suppl. 2) ◽  
pp. 341-356 ◽  
Author(s):  
Mohamed Aksouh ◽  
Amina Mataoui ◽  
Nassim Seghouani ◽  
Zoubida Haddad
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Natural Convection ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Practical Applications ◽  
Low Reynolds

This purpose is about a three dimensional study of natural convection within cavities. This problem is receiving more and more research interest due to its practical applications in the engineering and the astrophysical research The turbulent natural convection of air in an enclosed tall cavity with high aspect ratio (AR=H/W=28.6) is examined numerically. Two cases of differential temperature have been considered between the lateral cavity plates corresponding, respectively, to the low and high Rayleigh numbers: Ra=8.6?105 and Ra=1.43?106 [1]. For these two cases, the flow is characterized by a turbulent low Reynolds number. This led us to improve the flow characteristics using two one point closure low-Reynolds number turbulence models: RNG k-e model and SST k-w model, derived from standard k-e model and standard k-w model, respectively. Both turbulence models have provided an excellent agreement with the experimental data. In order to choose the best model, the average Nusselt number is compared to the experiment and other numerical results. The vorticity components surfaces confirm that the flow can be considered two-dimensional with stretched vortex in the cavity core. Finally, a correlation between Nusselt number and Rayleigh number is obtained to predict the heat transfer characteristics.

scholarly journals Turbulent heat transfer for impinging jet flowing inside a cylindrical hot cavity

2015 ◽  
Vol 19 (1) ◽  
pp. 141-154 ◽  
Author(s):  
Yacine Halouane ◽  
Amina Mataoui ◽  
Farida Iachachene
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Average Nusselt Number ◽  
Reverse Flow ◽  
Jet Impingement ◽  
Impinging Jet ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Cavity Bottom

Convective heat transfer from an isothermal hot cylindrical cavity due to a turbulent round jet impingement is investigated numerically. Three-dimensional turbulent flow is considered in this work. The Reynolds stress second order turbulence model with wall standard treatment is used for the turbulence predictions the problem parameters are the jet exit Reynolds number, ranging from 2x104 to 105and the normalized impinging distance to the cavity bottom and the jet exit Lf, ranging from 4 to 35. The computed flow patterns and isotherms for various combinations of these parameters are analyzed in order to understand the effect of the cavity confinement on the heat transfer phenomena. The flow in the cavity is divided into three parts, the area of free jet, and the area of the jet interaction with the reverse flow and the semi-quiescent flow in the region of the cavity bottom. The distribution of the local and mean Nusselt numbers along the cavity walls for above combinations of the flow parameters are detailed. Results are compared against to corresponding cases for impinging jet on a plate for the case of the bottom wall. The analysis reveals that the average Nusselt number increases considerably with the jet exit Reynolds number. Finally, it was found that the average Nusselt number at the stagnation point could be correlated by a relationship in the form Nu=f(Lf,Re).

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