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.

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.

Heat-Transfer Effects on the Developing Laminar Flow Inside Vertical Tubes

1966 ◽  
Vol 88 (2) ◽  
pp. 214-222 ◽  
Author(s):  
W. T. Lawrence ◽  
J. C. Chato
Keyword(s):  
Heat Flux ◽  
Transition Process ◽  
Constant Heat Flux ◽  
Wall Heat Flux ◽  
Axial Position ◽  
Fluid Viscosity ◽  
Constant Heat ◽  
Constant Wall Temperature ◽  
Constant Wall Heat Flux ◽  
Vertical Tubes

A numerical method was developed for the calculation of entrance flows in vertical tubes for the cases of upflow or downflow and constant wall heat flux or constant wall temperature. The solutions were in excellent agreement with experimental data obtained with water flowing upward in a vertical heated tube. The results show that both the density and the viscosity have to be treated as nonlinear functions of temperature. Consequently, for the constant heat flux condition, the velocity and temperature profiles constantly change and never reach “fully developed” states. The transition to turbulent flow was also studied. The experimental measurements demonstrated that the transition process depends on the developing velocity profiles. For the constant heat flux case, transition will always occur at some axial position. For a given entrance condition, the distance to transition is fixed by the fluid flow rate and the wall heat flux. For the experimental results, a tentative transition criterion was obtained, which depends only on the velocity profile shape, fluid viscosity, and the entrance Reynolds number.

Infrared experiment on the wall temperature distribution for a particle packed channel with constant heat flux

2001 ◽  
Vol 46 (18) ◽  
pp. 1566-1568 ◽  
Author(s):  
Jianhua Du ◽  
Xuejiao Hu ◽  
Bin Ma ◽  
Wei Wu ◽  
Buxuan Wang
Keyword(s):  
Heat Flux ◽  
Temperature Distribution ◽  
Wall Temperature ◽  
Constant Heat Flux ◽  
Constant Heat

scholarly journals Experimental Investigation of Heat Transfer Enhancement by Pulsating Flow in a Minichannel

2021 ◽  
Vol 2116 (1) ◽  
pp. 012031
Author(s):  
P Kumavat ◽  
S M O’Shaughnessy
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Enhancement ◽  
Flow Rate ◽  
Wall Temperature ◽  
High Performance ◽  
Amplitude Ratio ◽  
Constant Heat Flux ◽  
Pulsating Flow ◽  
Transfer Enhancement

Abstract The increasing power density requirements of next generation high performance electronic devices has resulted in ever-increasing heat flux densities which necessitates the evolution of new liquid-based heat exchange technologies. Pulsating flow in single-phase cooling systems is viewed as a potential solution. In this study, an experimental analysis of thermally developed pulsating flow in a rectangular minichannel is conducted. The channel test setup involves a heated bottom section approximated as a constant heat flux boundary. Asymmetric sinusoidal pulsating flows with a fixed flow rate amplitude ratio of 0.9 and Womersley numbers (Wo) of 0.51 and 1.6 are investigated. The wall temperature profiles are recorded using infrared thermography. It is observed that the transverse wall temperature profile is influenced by the sudden velocity variations of such characteristic waveforms. A heat transfer enhancement of 6% was determined for asymmetric flow pulsations of Wo > 1 over the steady flow with a potential augmentation for higher flow rate amplitudes.

Effect of Nanoparticle Concentration on Thermo-Hydraulic Behavior of a Nanofluid in a Horizontal Tube with Constant Heat Flux and Mass Flow Rate

2011 ◽  
Vol 110-116 ◽  
pp. 3650-3656
Author(s):  
S. Mirmasoumi ◽  
A. Behzadmehr
Keyword(s):  
Heat Flux ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Horizontal Tube ◽  
Constant Heat Flux ◽  
Tube Length ◽  
Nanoparticle Concentration ◽  
Constant Heat ◽  
Two Phase

How nanoparticle concentration affects on thermal and hydrodynamic parameters of a nanofluid (water+Al2O3) is numerically investigated in a horizontal tube while these parameters are impressed by buoyancy force under constant heat flux and mass flow rate. Comparisons with previously published experimental and numerical works on mixed convection in horizontal tubes show good agreements between the results. Results which are obtained using the two – phase mixture model indicate that adding the nanoparticles causes changes in the properties of nanofluid and finally increases the temperature of the flow. Whereas, dimensionless pressure drop along the tube length could increase with the nanoparticle concentration.

Fully-Developed Thermal Transport in Microchannels With Streamwise Grooved Superhydrophobic Walls at Constant Heat Flux

2012 ◽  
Author(s):  
D. Maynes ◽  
J. Vanderhoff ◽  
G. Rosengarten
Keyword(s):  
Heat Flux ◽  
Nusselt Number ◽  
Thermal Transport ◽  
Average Nusselt Number ◽  
Temperature Jump ◽  
Slip Length ◽  
Relative Size ◽  
Constant Heat Flux ◽  
Constant Heat ◽  
Hydrodynamic Slip

This paper presents an analytical investigation of constant property, steady, fully-developed, laminar thermal transport in a parallel-plate channel comprised of metal superhydrophobic walls. The superhydrophobic walls considered here exhibit micro-ribs and cavities aligned in the streamwise direction. The cavities are assumed to be non-wetting and contain air, such that the Cassie-Baxter state is the interfacial state considered. The scenario considered is that of constant heat flux through the rib surfaces with negligible thermal transport through the air cavity interface. Closed form solutions for the local Nusselt number and local wall temperature are presented and are in the form of infinite series expansions. The analysis show the relative size of the cavity regions compared to the total rib and cavity width (cavity fraction) exercises significant influence on the aggregate thermal transport behavior. Further, the relative size of the rib and cavity module width compared to the channel hydraulic diameter (relative module width) also influences the Nusselt number. The spatially varying Nusselt number and wall temperature are presented as a function of the cavity fraction and the relative module width over the ranges 0–0.99 and 0.01–1.0, respectively. From these results the rib/cavity module averaged Nusselt number was determined as a function of the governing parameters. The results reveal that increases in either the cavity fraction or relative module width lead to decreases in the average Nusselt number and results are presented over a wide range of conditions from which the average Nusselt number can be determined for heat transfer analysis. Further, analogous to the hydrodynamic slip length, a temperature jump length describing the apparent temperature jump at the wall is determined in terms of the cavity fraction. Remarkably, it is nearly identical to the hydrodynamic slip length for the scenario considered here and allows straightforward determination of the average Nusselt number for any cavity fraction and relative rib/cavity module width.

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.

Sign in / Sign up

Export Citation Format

Share Document