Effects of Surface Roughness on Single Phase Fluid Flow and Heat Transfer Characteristics in Microchannels

2009 ◽  
Author(s):  
Jinli Lu ◽  
Yingli Hao
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Velocity Distribution ◽  
Shape Factor ◽  
Single Phase ◽  
Peak Position ◽  
Centerline Velocity ◽  
Heat Transfer Characteristics ◽  
Flow And Heat Transfer

A two dimensional numerical simulation is conducted to investigate the flow and heat transfer characteristics of single phase liquid laminar flow through rough microchannels. The wall roughness is simulated in a series of cases with rectangular, triangular and trapezoidal elements, respectively. Shape factor and peak position have been used to analyze the influence of roughness elements on centerline velocity distribution, pressure drop and Nusselt number. It is found that the shape factor has a significant effect on the centerline velocity distribution, pressure drop and Nusselt number. It is also found that, for a given shape factor, the effect of peak position on pressure drop is strongly than centerline velocity distribution and heat transfer. In addition, for all considered roughness element shapes, the rectangular element displays a poor heat transfer and large pressure drop.

scholarly journals Numerical Simulation of Flow and Heat Transfer in Structured Packed Beds with Smooth or Dimpled Spheres at Low Channel to Particle Diameter Ratio

Energies ◽  
2018 ◽  
Vol 11 (4) ◽  
pp. 937 ◽  
Author(s):  
Shiyang Li ◽  
Lang Zhou ◽  
Jian Yang ◽  
Qiuwang Wang
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Heat Transfer Performance ◽  
Particle Diameter ◽  
Packed Bed ◽  
Packed Beds ◽  
Transfer Performance ◽  
Heat Transfer Characteristics ◽  
Flow And Heat Transfer

Packed beds are widely used in catalytic reactors or nuclear reactors. Reducing the pressure drop and improving the heat transfer performance of a packed bed is a common research aim. The dimpled structure has a complex influence on the flow and heat transfer characteristics. In the present study, the flow and heat transfer characteristics in structured packed beds with smooth or dimpled spheres are numerically investigated, where two different low channel to particle diameter ratios (N = 1.00 and N = 1.15) are considered. The pressure drop and the Nusselt number are obtained. The results show that, for N = 1.00, compared with the structured packed bed with smooth spheres, the structured packed bed with dimpled spheres has a lower pressure drop and little higher Nusselt number at 1500 < ReH < 14,000, exhibiting an improved overall heat transfer performance. However, for N = 1.15, the structured packed bed with dimpled spheres shows a much higher pressure drop, which dominantly affects the overall heat transfer performance, causing it to be weaker. Comparing the different channel to particle diameter ratios, we find that different configurations can result in: (i) completely different drag reduction effect; and (ii) relatively less influence on heat transfer enhancement.

scholarly journals Uncertainties Analysis on the Prediction of Flow and Heat Transfer of Liquid Sodium with CFD Technology

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Zhanwei Liu ◽  
Xinyu Li ◽  
Tenglong Cong ◽  
Rui Zhang ◽  
Lingyun Zheng ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Coefficient ◽  
Liquid Sodium ◽  
Heat Transfer Characteristics ◽  
Backward Facing Step ◽  
Heating Wall ◽  
Transfer Characteristics ◽  
Cfd Models ◽  
Flow And Heat Transfer

The prediction of flow and heat transfer characteristics of liquid sodium with CFD technology is of significant importance for the design and safety analysis of sodium-cooled fast reactor. The accuracies and uncertainties of the CFD models should be evaluated to improve the confidence of the numerical results. In this work, the uncertainties from the turbulent model, boundary conditions, and physical properties for the flow and heat transfer of liquid sodium were evaluated against the experimental data. The results of uncertainty quantization show that the maximum uncertainties of the Nusselt number and friction coefficient occurred in the transition zone from the inlet to the fully developed region in the circular tube, while they occurred near the reattachment point in the backward-facing step. Furthermore, in backward-facing step flow, the maximum uncertainty of temperature migrated from the heating wall to the geometric center of the channel, while the maximum uncertainty of velocity occurred near the vortex zone. The results of sensitivity analysis illustrate that the Nusselt number was negatively correlated with the thermal conductivity and turbulent Prandtl number, while the friction coefficient was positively correlated with the density and Von Karman constant. This work can be a reference to evaluate the accuracy of the standard k-ε model in predicting the flow and heat transfer characteristics of liquid sodium.

Computation of flow and heat transfer in horizontal gas–solid flows through an adiabatic pipe

2020 ◽  
pp. 095440622093631
Author(s):  
Brundaban Patro ◽  
Kiran K Kupireddi ◽  
Jaya K Devanuri
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Solid Loading ◽  
Gas Velocity ◽  
Two Phase ◽  
Flow And Heat Transfer ◽  
Loading Ratio ◽  
Solid Temperature

The current paper deals with the studies of heat transfer and pressure drop through a horizontal, adiabatic pipe, having gas–solid flows. The inlet air temperature is 443 K, whereas the inlet solid temperature is 308 K. The numerical results are compared with the benchmark experimental data and are agreed satisfactorily. The influences of solid loading ratio, solid diameter and gas velocity on Nusselt number and pressure drop have been studied. The Nusselt number decreases and the pressure drop increases with an increase in the solid diameter. The Nusselt number decreases with an increase in the solid loading ratio at a lower solid diameter of 100 µm. However, at a higher value of solid diameter of 200 µm, the Nusselt number first decreases up to a specific solid loading ratio, and after that, it increases. The pressure drop results show different behaviours with the solid loading ratio. Both the Nusselt number and pressure drop increase with the gas velocity. Finally, a correlation is generated to calculate the two-phase Nusselt number.

Heat Transfer and Flow Structure in a Latticework Duct With Different Sidewalls

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Wei Du ◽  
Lei Luo ◽  
Songtao Wang ◽  
Jian Liu ◽  
Bengt Sunden
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Friction Factor ◽  
Flow Structure ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Pressure Side ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics

Abstract Heat transfer characteristics in a latticework duct with various sidewalls are numerically investigated. The crossing angle is 90 deg and the number of subchannels is eleven on both the pressure side and suction side for each latticework duct. The thickness of the ribs is 8 mm and the distance between adjacent ribs is 24 mm. The investigation is conducted for various Reynolds numbers (11,000 to 55,000) and six different sidewalls. Flow structure, pressure drop, and heat transfer characteristics are analyzed. Results revealed that the sidewall has significant effects on heat transfer and flow structure. The triangle-shaped sidewall provides the highest Nusselt number accompanied by the highest friction factor. The sidewall with a slot shows the lowest friction factor and Nusselt number. An increased slot width decreased the Nusselt number and friction factor simultaneously.

Numerical Study of Flow and Heat Transfer Characteristics of Impinging Jets

2010 ◽  
Author(s):  
Tarek M. Abdel-Salam
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Numerical Study ◽  
Three Dimensional ◽  
Impinging Jets ◽  
Two Dimensional ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer

This study presents results for flow and heat transfer characteristics of two-dimensional rectangular impinging jets and three-dimensional circular impinging jets. Flow geometries under consideration are single and multiple impinging jets issued from a plane wall. Both confined and unconfined configurations are simulated. Effects of Reynolds number and the distance between the jets are investigated. Results are obtained with a finite volume computational fluid dynamics (CFD) code. Structured grids are used in all cases of the present study. Turbulence is treated with a two equation k-ε model. Different jet velocities have been examined corresponding to Reynolds numbers of 5,000 to 20,000. Results of the three-dimensional cases show that Reynolds number has no effect on the velocity distribution of the center jet. Results of both two-dimensional and three-dimensional cases show that Reynolds number highly affects the heat transfer and values of the Nusselt number. The maximum Nusselt number was always found at the stagnation point of the center jet.

Buoyancy Driven Flow, Heat Transfer and Entropy Generation Characteristics for Different Heater Geometries Placed in Cryogenic Liquid: A CFD Study

2021 ◽  
pp. 1-20
Author(s):  
Someshwar Ade ◽  
Sushil Rathore
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Entropy Generation ◽  
Heat Generation ◽  
Average Nusselt Number ◽  
Cryogenic Liquid ◽  
Heat Generation Rate ◽  
Heat Transfer Characteristics ◽  
Flow And Heat Transfer

Abstract The present work reports 3D computational study of buoyancy driven flow and heat transfer characteristics for a localized heater (analogous to superconductor) submerged in cryogenic liquid nitrogen in an enclosure. Seven different heater geometries are considered and the effect of heater geometry on flow and heat transfer characteristics are illustrated. The heater is generating heat at a constant rate (W/m3). Continuity, momentum and energy equations are solved using finite volume method. Liquid flow and heat transfer features are demonstrated with the help of velocity vector and temperature contours. Rayleigh number, average Nusselt number, maximum vertical velocity of fluid flow, average velocity of fluid flow are the parameters which are considered for comparing seven different geometries of heater. Additionally, an analysis of the entropy generation owing to transfer of heat and friction due to fluid flow are reported. Furthermore, the dependency of average Nusselt number, maximum velocity of fluid, entropy generation owing to transfer of heat and fluid friction as a function of heat generation rate is illustrated graphically. The results of this study indicate that heater geometry can considerably affect the transfer of heat, fluid flow features and entropy generation under same heat generation rate in the heater. Highest average Nusselt number on heater surface is obtained when heater geometry is circular; whereas lowest value of total entropy generation in the domain is obtained when heater geometry is equilateral triangle.

Computational Modeling for a Microchannel Electronics Cooler

2007 ◽  
Author(s):  
Joseph Dix ◽  
Amir Jokar ◽  
Robert Martinsen
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Single Phase ◽  
Operating Conditions ◽  
Coolant Fluid ◽  
Working Fluid ◽  
Flow Parameters ◽  
Flow And Heat Transfer ◽  
Through Flow ◽  
Phase Fluid

The objective of this study is to analyze the single-phase fluid flow and heat transfer through a microchannel electronics cooler with a hydraulic diameter of about 300 microns. For this purpose, commercial computational fluid dynamics software was used to first characterize the existing design that uses purified water as coolant fluid. The flow parameters of the cooler were then adjusted in order to optimize the design. Geometry modifications were used next to enhance heat transfer, and to reduce pressure drop and erosion from possible impurities in the working fluid. Different working fluids were also considered to investigate possible reductions in corrosion and further increases in heat transfer. Alternative combinations of boundary and operating conditions were explored during optimization. The results of this study showed the microchannel cooler had capacity in rejecting more thermal energy with less pressure drop through flow optimization and geometry modification.

Numerical Investigation on the Flow and Heat Transfer Characteristics of the Superheated Steam in the Wedge Duct With Pin-Fins

2013 ◽  
Author(s):  
Gaoliang Liao ◽  
Xinjun Wang ◽  
Xiaowei Bai ◽  
Ding Zhu ◽  
Jinling Yao
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Three Dimensional ◽  
Heat Transfer Characteristics ◽  
Pin Fin ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Pin Fins ◽  
Steam Superheat

By using the CFX software, the three-dimensional flow and heat transfer characteristics in the cooling duct with pin-fin in the blade trailing edge were numerically simulated. The effects of pin-fin arrangements, Reynolds number, steam superheat degrees, streamwise pin density and convergence angle of the wedge duct on the flow and heat transfer characteristics were analysed. The results show that the Nusselt number on the endwall and pin-fin surfaces as well as the pin-fin row averaged Nusselt number increase with the increasing of Reynolds number, while it decreased with the with the increasing of X/D. The pressure drop increases with the increasing of Reynolds number while decreases with the increasing of X/D in the wedge duct. The degree of superheat has little effect on the pressure loss in the wedge duct. A comprehensive analysis and comparison show that the highest thermal performance is reached in the wedge duct when the value of X/D is 1.5.

Sign in / Sign up

Export Citation Format

Share Document