Heat Transfer Enhancement in a Tube Using Triangular Ribs

2008 ◽  
Author(s):  
Veysel Ozceyhan ◽  
Sibel Gunes
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Enhancement ◽  
External Surface ◽  
Numerical Study ◽  
Experimental Studies ◽  
Working Fluid ◽  
Uniform Heat Flux ◽  
Enhancement Ratio ◽  
Transfer Enhancement

A numerical study was undertaken for investigating the heat transfer enhancement in a tube with triangular cross sectioned ribs. The spacing between the ribs were kept constant as a distance of tube diameter, D. Three different rib thicknesses were considered for numerical analyses. Uniform heat flux was applied to the external surface of the tube and air was selected as working fluid. Numerical calculations were performed with FLUENT 6.1.22 code, in the range of Reynolds number 8000–36000. The results obtained from a smooth tube and rib inserted tube were compared with those from the experimental studies in literature in order to validate the numerical method. The variation of Nusselt number, friction factor and overall enhancement ratios for the tube with triangular cross sectioned ribs were presented. Consequently, a maximum gain of 1.34 on overall enhancement ratio is obtained for S/D = 0.75.

A numerical study of the effect on flow structure and heat transfer of a rectangular winglet pair in a plate fin heat exchanger

2009 ◽  
Vol 223 (9) ◽  
pp. 2109-2115 ◽  
Author(s):  
M Gupta ◽  
K S Kasana ◽  
R Vasudevan
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Transfer Enhancement ◽  
Flow Structure ◽  
Numerical Study ◽  
Vortex Generator ◽  
Working Fluid ◽  
Pair Type ◽  
Transfer Enhancement ◽  
Navier Stokes Equation

Longitudinal vortices have a great capability of disrupting the growth of boundary layers and bring about the heat transfer enhancement between the fluid and its neighbouring surface. The potential of a winglet pair type vortex generator for the heat transfer enhancement in a plate fin heat exchanger, with triangular fins as inserts, is numerically evaluated in this article. The rectangular winglet pair is mounted on the triangular fins. The numerical computations are performed by solving an unsteady, three-dimensional Navier—Stokes equation, and an energy equation by using the modified MAC method. Air is taken as the working fluid. This study shows the flow structure and the performance of the winglet pair in improving the heat transfer. The computations are performed at Re=200 and placing the winglet at an angle of attack, β=20°. The results show that the heat transfer is increased by 13 per cent, even at the exit, with the winglet pair. The heat transfer enhancement with a winglet pair for different Re=200—500 and Pr=0.71 and for varying heights of the winglet pair is also predicted.

Heat transfer enhancement in pool boiling and condensation using h-BN/DCM and SiO2/DCM nanofluids: experimental and numerical comparison

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Erdem Çiftçi ◽  
Adnan Sözen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Enhancement ◽  
Base Fluid ◽  
Pool Boiling ◽  
Working Fluid ◽  
Numerical Comparison ◽  
Comparison Study ◽  
Transfer Enhancement ◽  
Content Type

Purpose The purpose of this study is to experimentally and numerically scrutinize the heat transfer enhancement in pool boiling and condensation by changing the hydrophilicity or hydrophobicity properties of the working fluid, i.e. by use of nanofluid solution. Design/methodology/approach For specifying the effects of nanoparticle concentration on heat transfer properties, two different nanofluid solutions (h-BN/DCM and SiO2/DCM) at three different volumetric concentrations were prepared and tested under different heat flux conditions. Boiling curves, alterations in pressure with heat flux and heat transfer coefficients for both boiling and condensation processes were obtained and viscosity measurements were performed for dichloromethane (DCM) and each working fluid was prepared. In addition, a series of numerical simulations, via computational fluid dynamics approach, was performed for specifying the evaporation–condensation phenomena and temperature and velocity distributions. Findings Nanoparticle addition inside the base fluid increased the thermal characteristics of the base fluid significantly. For the experimental results of h-BN/DCM nanofluid, the increment rate in heat transfer coefficient for saturation boiling, after-saturation boiling and condensation processes was found as 27.59%, 14.44% and 15%, respectively. Originality/value The novelty of this comparison study is that there is no such experimental and numerical comparison study in literature for DCM fluid, which concentrates on thermal performance enhancement and compares the effect of different kinds of nanoparticles on heat transfer characteristics for boiling–condensation processes.

scholarly journals Effect of Actual Gas Turbine Operating Conditions on Mist/Steam Cooling Performance in a Ribbed Passage

Energies ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 2015 ◽  
Author(s):  
Jianying Gong ◽  
Tieyu Gao ◽  
Junxiong Zeng ◽  
Jianqiang Hou ◽  
Zhen Li
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Enhancement ◽  
Flux Density ◽  
Heat Flux Density ◽  
Operating Conditions ◽  
Operating Pressure ◽  
Enhancement Ratio ◽  
Transfer Enhancement ◽  
Steam Cooling

This study numerically examines the effect of actual gas turbine operating conditions on heat transfer characteristics in a ribbed passage with mist/steam cooling. A 60° ribbed passage with aspect ratio of 1/1 was investigated at Reynolds number of 300,000, and steam cooling was used to provide a contrast. Three main factors were considered: coolant temperature, operating pressure, and wall heat flux density. The heat transfer enhancement mechanism of mist/steam cooling was explored, and the results showed that the heat transfer performance of mist/steam cooling was superior to steam cooling. When the coolant temperature varied from 300 to 500 °C, the average Nusselt number of mist/steam cooling decreased by 26.6%, and the heat transfer enhancement ratio dropped from 15% to 10%. As operating pressure increased, the heat transfer performance factor of mist/steam firstly increased and then decreased. At an operating pressure of 1.5 MPa, the heat transfer achieved its optimal performance, and the heat transfer enhancement ratio achieved its maximum value of 15.9%. Larger wall heat flux density provided less heat transfer enhancement. When the heat flux density increased from 100,000 to 300,000 W·m−2, the average Nusselt number of mist/steam cooling decreased by 13.8%, while the heat transfer enhancement ratio decreased from 25.3% to 12.6%.

scholarly journals Thermal Analysis of a Solar External Receiver Tube with a Novel Component of Guide Vanes

Energies ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2253
Author(s):  
Zecan Tu ◽  
Daniela Piccioni Koch ◽  
Nenad Sarunac ◽  
Martin Frank ◽  
Junkui Mao
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Molten Salt ◽  
Heat Transfer Enhancement ◽  
Heat Transfer Performance ◽  
Smooth Tube ◽  
Uniform Heat Flux ◽  
Transfer Enhancement ◽  
Guide Vanes ◽  
Velocity Turbulence

The heat transfer performance of a solar external receiver tube with guide vanes was numerically studied under non-uniform heat flux conditions. Models of the smooth tube and the tube with guide vanes were built. The distributions of the temperature, velocity, turbulence intensity, and Nu predicted by these two models were compared to investigate the heat transfer enhancement and the mixing effect of the guide vanes. The effect of the Re and the α on the heat transfer enhancement was also studied. The results show that the guide vanes form spiraling flows, reduce the maximum tube and molten salt temperatures, and improve the heat transfer. In addition, a more uniform temperature distribution is achieved compared to the smooth tube, allowing the molten salt to work safely under higher heat flux conditions in the receiver tube with guide vanes. It was observed that a larger Re enhances the heat transfer on the tube wall and achieves a longer effective distance of enhanced heat transfer in the downstream region, while the spiraling flow, the heat transfer enhancement, and the mixing are stronger for a larger α.

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