scholarly journals Review of improvements on heat transfer using nanofluids via corrugated facing step

2018 ◽  
Vol 7 (4.13) ◽  
pp. 160 ◽  
Author(s):  
Ali Hilo ◽  
Abd Rahim Abu Talib ◽  
Sadeq R. Nfawa ◽  
Mohamed Thariq Hameed Sultan ◽  
Mohd Faisal Abdul Hamid
Keyword(s):  
Heat Transfer ◽  
Thermal Conduction ◽  
Experimental Studies ◽  
Conductivity Measurement ◽  
Measurement Methods ◽  
Laminar Flows ◽  
Transfer Enhancement ◽  
Innovative Design ◽  
Experimental Findings ◽  
The Ideal

Nanofluids are considered to offer significant advantages as thermodynamic fluids because of their admirable properties on thermal conduction, thermal convection, boiling heat transfer and stability. This paper presents numerous researches focusing on the improvement of heat transfer via facing step and corrugated channels using nanofluids and without it. Exploration on the convective heat transfer was done through numerical modeling. It was reported that experimental studies were carried out in corrugated and facing step channels through the application of nanofluids and conventional fluids for heat transfer enhancement. The turbulent and laminar flows along corrugated and facing step channels have been presented. The numerical and experimental findings in maximizing the heat transfer rate are in accord. Comparisons between thermal conductivity measurement methods were done. Innovative design of corrugated facing step channel is being proposed. The heat transfer enhancements reach 60% by using facing step channel under laminar flow with nanofluid. The dimensions of new channel such as height and width of the baffle, the height of the step, shape and height of corrugated are needed to compare that might to provide the ideal rate of heat transfer.  

Droplet and Bubble Dynamics in Saturated FC-72 Spray Cooling

2005 ◽  
Author(s):  
Ruey-Hung Chen ◽  
David S. Tan ◽  
Kuo-Chi Lin ◽  
Louis C. Chow ◽  
Alison R. Griffin ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Bubble Dynamics ◽  
Bubble Diameter ◽  
Spray Cooling ◽  
Transfer Enhancement ◽  
Secondary Nucleation ◽  
Bubble Density ◽  
Experimental Findings ◽  
Small Bubbles ◽  
Nucleation Bubble

Droplet and bubble dynamics and nucleate heat transfer in saturated FC-72 spray cooling were studied using a simulation model. Using the experimentally observed bubble growth rate, submodels were assumed based on physical reasoning for the number of secondary nuclei entrained by the impinging droplets, bubble puncturing by the impinging droplets, bubble merging and the spatial distribution of secondary nuclei. The predicted nucleate heat transfer was in agreement with experimental findings. Dynamic aspects of the droplets and bubbles, which had been difficult to observe experimentally, and their ability in enhancing nucleate heat transfer were then discussed based on the results of the simulation. These aspects include bubble merging, bubble puncturing by impinging droplets, secondary nucleation, bubble size distribution and bubble diameter at puncture. Simply increasing the number of secondary nuclei is not as effective in enhancing nucleate heat transfer as when it is also combined with increased bubble puncturing frequency by the impinging droplets. For heat transfer enhancement, it is desirable to have as many small bubbles and as high a bubble density as possible.

Heat Transfer Enhancement in Square Ducts With V-Shaped Ribs of Various Angles

2002 ◽  
Author(s):  
Rongguang Jia ◽  
Arash Saidi ◽  
Bengt Sunde´n
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Experimental Studies ◽  
Eddy Diffusivity ◽  
Heat Fluxes ◽  
Secondary Flows ◽  
Turbulent Heat ◽  
Transfer Enhancement ◽  
Transfer Coefficients

Experimental studies have revealed that both downstream and upstream pointing V-shaped ribs result in better heat transfer enhancement than transverse straight ribs of the same geometry. Secondary flows induced by the angled ribs are believed to be responsible for this higher heat transfer enhancement. Further investigations are needed to understand this. In the present study, the heat and fluid flow in V-shaped-ribbed ducts is numerically simulated by a multi-block 3D solver, which is based on solving the Navier-Stokes and energy equations in conjunction with a low-Reynolds number k-ε turbulence model. The Reynolds turbulent stresses are computed with an explicit algebraic stress model (EASM), while turbulent heat fluxes are calculated with a simple eddy diffusivity model (SED). Firstly, the simulation results of transverse straight ribs are validated against the experimental data, for both velocity and heat transfer coefficients. Then, the results of different rib angles (45° and 90°) and Reynolds number (15,000–30,000) are compared to determine the goodness of different rib orientations. Detailed velocity and thermal field results have been used to explain the effects of the inclined ribs and the mechanisms of heat transfer enhancement.

Injection, Transport and Removal of Gas Bubbles in Microchannels for Heat Transfer Enhancement

2010 ◽  
Author(s):  
Daniel Attinger
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Enhancement ◽  
Thin Liquid Film ◽  
Film Coating ◽  
Porous Membrane ◽  
Laminar Flows ◽  
Heat Fluxes ◽  
Transfer Enhancement ◽  
Segmented Flow

Liquid cooling is an efficient way to remove heat fluxes with magnitudes up to 10,000 W/cm2. One limitation of single-phase microchannel heat transfer is the relatively low Nusselt number, due to laminar flow. Several methods have been used to improve the Nusselt number such as geometric obtrusions, pins and fins and nanofluids. In this talk, we experimentally investigate the heat transfer enhancement of a heat sink where air bubbles are periodically injected. The segmented flow pattern generates recirculation loops that enhance transport phenomena. We show that segmented flow can enhance the Nusselt number of laminar flows in short channels by a factor two. Also, we demonstrate a simple and high-throughput method for removing bubbles from microchannels, using a hydrophobic porous membrane. The role of the thin liquid film coating the bubbles in the heat transfer and the bubble removal is investigated.

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.

scholarly journals Determination and measurement of some thermophysical properties of nanofluids and comparison with literature studies

2020 ◽  
pp. 239-239
Author(s):  
Adnan Topuz ◽  
Beytullah Erdoğan ◽  
Osman Aycan
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermophysical Properties ◽  
Convection Heat Transfer ◽  
Conductivity Measurement ◽  
Pumping Power ◽  
Transfer Enhancement ◽  
Convection Heat Transfer Coefficient ◽  
Volumetric Concentration ◽  
Wire Method

The thermophysical properties of nanofluids must be determined to evaluate their thermal performances like heat transfer, convection heat transfer coefficient, Nusselt number. The purpose of this study is to obtain the thermophysical properties of nanofluids. Al2O3, TiO2, and ZnO are used as a nanoparticle, while deionized water is used as base fluid. The solutions included nanoparticles in a way to be each with 0.5%, 0.7%, and 1.0% volumetric concentration were prepared. SDS was added to the solutions as a surfactant to prevent instability that occurred due to agglomeration and sedimentation. For thermal conductivity measurement, the device that works by the transient hot-wire method was used between 30-60?C temperatures. Also, for viscosity measurement, the device that works as based on the vibrating plate method was used between 20-50?C temperatures. Density and specific heat values are obtained with the help of the well-known equations while thermal conductivity and viscosity are measured. Thanks to this study, it is emphasized how thermophysical properties of nanofluids change according to temperature and volumetric concentration. Moreover, their curve fitting equations are obtained. All of the thermophysical properties compared with the studies in the literature. It is established that the thermal conductivity of nanofluids is proportional to temperature, and viscosity of it is proportional to volumetric concentrations but inversely with temperature. Finally, the effects of the augmentation in dynamic viscosity on pumping power were considered as well as the increase in thermal conductivity; thus, no abnormal heat transfer enhancement was observed.

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