Turbulent Heat Transfer Between a Series of Parallel Plates With Surface-Mounted Discrete Heat Sources

1994 ◽  
Vol 116 (3) ◽  
pp. 577-587 ◽  
Author(s):  
S. H. Kim ◽  
N. K. Anand

Two-dimensional turbulent heat transfer between a series of parallel plates with surface mounted discrete block heat sources was studied numerically. The computational domain was subjected to periodic conditions in the streamwise direction and repeated conditions in the cross-stream direction (Double Cyclic). The second source term was included in the energy equation to facilitate the correct prediction of a periodically fully developed temperature field. These channels resemble cooling passages in electronic equipment. The k–ε model was used for turbulent closure and calculations were made for a wide range of independent parameters (Re, Ks/Kf, s/w, d/w, and h/w). The governing equations were solved by using a finite volume technique. The numerical procedure and implementation of the k–ε model was validated by comparing numerical predictions with published experimental data (Wirtz and Chen, 1991; Sparrow et al., 1982) for a single channel with several surface mounted blocks. Computations were performed for a wide range of Reynolds numbers (5 × 104–4 × 105) and geometric parameters and for Pr = 0.7. Substrate conduction was found to reduce the block temperature by redistributing the heat flux and to reduce the overall thermal resistance of the module. It was also found that the increase in the Reynolds number decreased the thermal resistance. The study showed that the substrate conduction can be an important parameter in the design and analysis of cooling channels of electronic equipment. Finally, correlations for the friction factor (f) and average thermal resistance (R) in terms of independent parameters were developed.

1995 ◽  
Vol 117 (1) ◽  
pp. 52-62 ◽  
Author(s):  
S. H. Kim ◽  
N. K. Anand

Two-dimensional laminar heat transfer between a series of parallel plates with surface mounted block heat sources was numerically studied. These channels resemble cooling passages of electronic equipment. Consideration was given only to periodically fully developed flow (PDF) and heat transfer. The computational domain was subjected to periodic condition in the streamwise direction and repeated condition in the cross-stream direction (double cyclic). The governing equations were solved by a finite volume technique. Calculations were made for a wide range of independent parameters (Re, ks/kf, s/w, d/w, H/w, and t/H). Consideration was given only to airflow (Pr=0.7). The friction factor was found to be a strong function of channel height and a weak function of block spacing. The thermal performance was studied in terms of the average Nusselt number and overall thermal resistance. For the most part, the thermal performance was independent of the Reynolds number, however, it deteriorated drastically for Re ≤ 500. The thermal resistance was found to decrease with an increase in substrate conductivity up to a particular value of ks/kf, and beyond this value thermal resistance did not decrease further. This value of ks/kf is a function of geometric parameters and occurs between 1 and 10. Correlations in terms of independent parameters were developed for friction factor, average Nusselt number, and thermal resistance.


2012 ◽  
Vol 134 (3) ◽  
Author(s):  
Nobuhide Kasagi ◽  
Yosuke Hasegawa ◽  
Koji Fukagata ◽  
Kaoru Iwamoto

Because of the importance of fundamental knowledge on turbulent heat transfer for further decreasing entropy production and improving efficiency in various thermofluid systems, we revisit a classical issue whether enhancing heat transfer is possible with skin friction reduced or at least not increased as much as heat transfer. The answer that numerous previous studies suggest is quite pessimistic because the analogy concept of momentum and heat transport holds well in a wide range of flows. Nevertheless, the recent progress in analyzing turbulence mechanics and designing turbulence control offers a chance to develop a scheme for dissimilar momentum and heat transport. By reexamining the governing equations and boundary conditions for convective heat transfer, the basic strategies for achieving dissimilar control in turbulent flow are generally classified into two groups, i.e., one for the averaged quantities and the other for the fluctuating turbulent components. As a result, two different approaches are discussed presently. First, under three typical heating conditions, the contribution of turbulent transport to wall friction and heat transfer is mathematically formulated, and it is shown that the difference in how the local turbulent transport of momentum and that of heat contribute to the friction and heat transfer coefficients is a key to answer whether the dissimilar control is feasible. Such control is likely to be achieved when the weight distributions for the stress and flux in the derived relationships are different. Second, we introduce a more general methodology, i.e., the optimal control theory. The Fréchet differentials obtained clearly show that the responses of velocity and scalar fields to a given control input are quite different due to the fact that the velocity is a divergence-free vector, while the temperature is a conservative scalar. By exploiting this inherent difference, the dissimilar control can be achieved even in flows where the averaged momentum and heat transport equations have the same form.


Author(s):  
V.V. Gorskiy ◽  
A.G. Loktionova

In order to compute the intensity of laminar-turbulent heat transfer, algebraic or differential models are commonly used, which are designed to compute the contribution of turbulent pulsations to the transfer properties of the gas. This, in turn, dictates the necessity of validating these semi-empirical models against experimental data obtained under conditions simulating the gas dynamics inherent to the phenomenon as observed in practice. The gas dynamic patterns observed during gradient flow around fragments of aircraft structure (such as a sphere or a cylinder) differs qualitatively from the patterns revealed by the flow around the lateral surfaces of these fragments, which necessitates using various semi-empirical approaches in this case, followed by mandatory validation against the results of respective experimental studies. In recent years, there appeared scientific publications dealing with modifying one of the algebraic models designed to compute the contribution of turbulent pulsations in the boundary layer to the transfer properties of the gas; this was accomplished by making use of experimental data obtained for a hemisphere at extremely high Reynolds numbers. The paper proposes a similar modification of the same turbulence model, based on fitting a wide range of experimental data obtained for lateral surfaces of spherically blunted cones. As a result of the investigations conducted, we stated a method for computing laminar-to-turbulent heat transfer over the entire surface of a blunted cone; the accuracy of the method is acceptable in terms of most practical applications. We show that the computational method presented is characterised by minimum error as compared to the most widely spread methods for solving this problem


Author(s):  
Michael J. Denninger ◽  
Ann M. Anderson

The work presented here is the first reported study to test the general correlation for turbulent heat transfer proposed by Maciejewski and Anderson (1996). A turbulent pipe flow apparatus was built for heat transfer and fluid studies. Tests were performed for a range of Reynolds numbers from 27,000 to 90,000. The heated wall temperature, adiabatic temperature, the wall heat flux and the maximum velocity fluctuations were measured at each Reynolds number. The non-dimensional groups recommended by Maciejewski and Anderson were formed and compared to the correlation. The results verify the correlation with agreement to within ±7% (as per figure 11). This study has important implications for the study of heat transfer in a wide range of fields, including the gas turbine industry. The development of a geometry independent correlation will lead to faster turn around times and improved engine design.


2020 ◽  
Vol 14 (1) ◽  
pp. 6344-6361
Author(s):  
Pankaj Srivastava ◽  
Anupam Dewan

This paper presents the effects of microchannel shape with ribs and cavities on turbulent heat transfer. Three-dimensional conjugate heat transfer using the SST k-ω turbulence model has been investigated for four different microchannels, namely, rectangular, rectangular with ribs and cavities, convergent-divergent (CD) and convergent-divergent with Ribs and Cavities (CD-RC). The flow field, pressure and temperature distributions and friction factor are analyzed, and thermal resistance and average Nusselt number are compared. The thermal performance of the CD-RC microchannel is found to be better than that of other microchannels considered in terms of an average Nusselt number increased from 16% to 40%. Heat transfer increases due to a strong fluid mixing and periodic interruption of boundary-layer. It is observed that with an increase in Reynolds number (Re), the thermal resitance drops rapidly. The thermal resistance of the CD-RC microchannel is decreased by 30% than that of the rectangular microchannel for Re ranging from 2500 to 7000. However, such design of microchannel loses its heat transfer effectiveness due to a high pumping power at high values of Re.


Author(s):  
Robert Bergant ◽  
Iztok Tiselj

Direct Numerical Simulation (DNS) of fully developed turbulent flow in a flume and channel was used to study the heat transfer near the wall. Two different geometries for numerical simulations of turbulent heat transfer in infinite channel and flume were used. Reynolds number based on friction velocity, channel half height (or flume height) and kinematic viscosity was set to Reτ = 170.8, whereas the Prandtl number was set to unity, Pr = 1. The computational domain of 2146×341.6×537 wall units and 2146×170.8×537 wall units was used for channel geometry and flume geometry, respectively. Comparison of these two different geometries with the same physics, were highlighted and discussed.


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