A Comparison of Constant Wall Temperature and Constant Heat Flux Turbulent Heat Transfer

1962 ◽  
Vol 84 (1) ◽  
pp. 90-91 ◽  
Author(s):  
M. L’Ecuyer ◽  
C. F. Warner
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Wall Temperature ◽  
Constant Heat Flux ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Constant Heat ◽  
Constant Wall Temperature

scholarly journals Laminar convective heat transfer for in-plane spiral coils of noncircular cross sections ducts: A computational fluid dynamics study

2012 ◽  
Vol 16 (1) ◽  
pp. 109-118 ◽  
Author(s):  
Jundika Kurnia ◽  
Agus Sasmito ◽  
Arun Mujumdar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Cross Sections ◽  
Wall Temperature ◽  
Heat Transfer Performance ◽  
Constant Heat Flux ◽  
Uniform Heat Flux ◽  
Transfer Performance ◽  
Constant Wall Temperature ◽  
Flux Boundary Condition

The objective of this study was to carry out a parametric study of laminar flow and heat transfer characteristics of coils made of tubes of several different cross-sections e.g. square, rectangular, half-circle, rectangular and trapezoidal. For the purpose of ease of comparison, numerical experiments were carried out base on a square-tube Reynolds number of 1000 and a fixed fluid flow rate while length of the tube used to make coils of different diameter and pitch was held constant. A figure of merit was defined to compare the heat transfer performance of different geometry coils; essentially it is defined as total heat transferred from the wall to the surroundings per unit pumping power required. Simulations were carried out for the case of constant wall temperature as well as constant heat flux. In order to allow reasonable comparison between the two different boundary conditions - constant wall temperature and constant wall heat flux - are tested; the uniform heat flux boundary condition was computed by averaging the heat transferred per unit area of the tube for the corresponding constant wall temperature case. Results are presented and discussed in the light of the geometric effects which have a significant effect on heat transfer performance of coils.

Exergy Transfer Criteria on Enhanced Heat Transfer Performance Evaluation

2006 ◽  
Author(s):  
Shuang-Ying Wu ◽  
Yan Chen ◽  
You-Rong Li ◽  
Wen-Zhi Cui ◽  
Liao Quan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Performance Evaluation ◽  
Wall Temperature ◽  
Evaluation Criteria ◽  
Constant Heat Flux ◽  
Transfer Performance ◽  
Enhanced Heat Transfer ◽  
Constant Wall Temperature ◽  
Exergy Transfer

Based on the exergy transfer performance analysis of forced convective heat transfer through a tube with constant heat flux/ constant wall temperature for thermally and hydrodynamic fully developed turbulent flow, extended performance evaluation criteria for enhanced heat transfer surfaces based on the exergy transfer theorem have been developed. An exergy transfer performance evaluation criterion ΔNue or ΔE, which is defined as the difference of exergy-transfer Nusselt number or exergy transfer rate before and after enhanced heat transfer, is put forward. By reference to spirally grooved tube, the effect of Reynolds number, structure parameters of tube, dimensionless wall temperature difference and heat flux on the exergy transfer process is discussed. The results show that the exergy transfer performance of enhanced heat transfer with constant wall temperature is quite different from that with constant wall heat flux. An effective approach for exergy transfer performance evaluation and the optimal process parameters and configuration choice of enhanced heat transfer tube are provided.

Heat Convection Within an Eccentric Annulus Heated at Either Constant Wall Temperature or Constant Heat Flux

2012 ◽  
Vol 134 (8) ◽  
Author(s):  
F. M. Mahfouz
Keyword(s):  
Heat Flux ◽  
Numerical Solution ◽  
Wall Temperature ◽  
Outer Wall ◽  
Constant Heat Flux ◽  
Heat Convection ◽  
Radius Ratio ◽  
Constant Heat ◽  
Constant Wall Temperature ◽  
Eccentric Annulus

Natural heat convection within an annular annulus bounded by two horizontal vertically eccentric long cylinders has been investigated. The annulus inner wall has been heated and maintained at either constant wall temperature CWT or constant heat flux CHF while the outer wall is cooled and maintained at constant temperature. The induced buoyancy driven flow and the associated heat convection are predicted through solving numerically the full conservation equations for mass, momentum, and energy using Fourier spectral method. Beside Rayleigh and Prandtl numbers, the heat convection process in the annulus depends on the annulus radius ratio and eccentricity (normalized by the radius difference). The study considered a moderate range of Rayleigh numbers up to 105 while Prandtl number is fixed at 0.7. The radius ratio is considered up to 3.2 while the eccentricity is varied between − 0.65 and + 0.65. The study has revealed that at certain radius ratio for a given Rayleigh number and eccentricity, the heat transfer is minimum in case of CWT and the mean inner wall temperature is maximum in case of CHF. The study has also shown, in the range considered for controlling parameters, that multiple convection cells only exist in case of CWT and only for positive eccentricity. Moreover, the study has shown that the present numerical solution of the pure conduction problem is almost identical with the newly presented analytical solution which confirms the high accuracy of the numerical solution.

Natural Convection in a Vertical Slit Microchannel With Superhydrophobic Slip and Temperature Jump

2013 ◽  
Vol 136 (3) ◽  
Author(s):  
C. Y. Wang ◽  
Chiu-On Ng
Keyword(s):  
Heat Flux ◽  
Flow Rate ◽  
Wall Temperature ◽  
Temperature Jump ◽  
Slip Surface ◽  
Critical Value ◽  
Constant Heat Flux ◽  
Constant Heat ◽  
Constant Wall Temperature ◽  
Temperature Jump Coefficient

Recent developments in microscale heat exchangers have heightened the need for the understanding of fluid flow and heat transfer in a microchannel. In this study, we look into fully-developed buoyancy-driven flow in a vertical parallel-plate microchannel, which has one wall exhibiting superhydrophobic slip and temperature jump, and another wall being a normal no-slip surface. Analytical solutions are derived for free convection in the channel, where the heating is applied to either one of the two walls, and by either constant wall temperature or constant heat flux. We examine how the superhydrophobic slip and temperature jump may affect the volume flow rate and the Nusselt number under various heating conditions. There exists a critical value of the temperature jump coefficient, above which the flow rate will be larger by heating the no-slip surface than by heating the superhydrophobic surface, whether by constant wall temperature or by constant heat flux. The opposite is true when the temperature jump coefficient is below the critical value. Also, the temperature jump can have a negative effect on the flow rate when the heating is by constant temperature on the superhydrophobic side of the channel, but will have a positive effect when the heating is on the no-slip side of the channel.

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