scholarly journals Heat transfer enhancement of wall with a near wall cylinder in a channel at low and middle Reynolds number ranges

2020 ◽  
pp. 002029402096212
Author(s):  
Hui Xu ◽  
Yixi Cai ◽  
Guannan Xi
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Heat Transfer Enhancement ◽  
Heat Dissipation ◽  
Vortical Structure ◽  
Bottom Wall ◽  
Transitional Flow ◽  
Transfer Enhancement ◽  
Clearance Ratio ◽  
Near Wall

This paper investigated the flow performance around a near-wall cylinder and its effect on heat transfer enhancement in the laminar and early transitional flow region. The numerical model is resolved by finite volume method through FORTRAN code. The results show that the flow field becomes a transitional flow state when Re = 100 due to the insertion of a cylinder. In the transitional flow sate, the heat transfer enhancement is regional, mainly concentrating in the region of –2 ≤ x/D≤ 10, and the region increases with the increase of Re; There are three or four peaks in the distribution of instantaneous local Nusselt number. The first peak is caused by the acceleration of the fluid between the cylinder and the bottom wall. The other peaks are caused by the interaction between the cylinder wake and the bottom wall boundary layer. The vortical structure induced by the periodic instability of the fluid in the transitional flow is the main factor for explaining the local heat transfer enhancement of the cylinder downstream wall. Re has a direct impact on the vortical structure in the flow field. The greater Re, the greater the heat transfer enhancement of the cylinder downstream wall. Under the same blocking ratio of D/H, the greater Re, the smaller the optimal clearance ratio of C/D. The guidelines are suggested for the design on heat dissipation of electronic equipment.

Experimental Study of Advanced Convective Cooling Techniques for Combustor Liners

2008 ◽  
Author(s):  
Michael Maurer ◽  
Uwe Ruedel ◽  
Michael Gritsch ◽  
Jens von Wolfersdorf
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Flow Field ◽  
Transfer Coefficient ◽  
Heat Transfer Enhancement ◽  
Transfer Enhancement ◽  
Number Range ◽  
Convective Cooling

An experimental study was conducted to determine the heat transfer performance of advanced convective cooling techniques at the typical conditions found in a backside cooled combustion chamber. For these internal cooling channels, the Reynolds number is usually found to be above the Reynolds number range covered by available databases in the open literature. As possible candidates for an improved convective cooling configuration in terms of heat transfer augmentation and acceptable pressure drops, W-shaped and WW-shaped ribs were considered for channels with a rectangular cross section. Additionally, uniformly distributed hemispheres were investigated. Here, four different roughness spacings were studied to identify the influence on friction factors and the heat transfer enhancement. The ribs and the hemispheres were placed on one channel wall only. Pressure losses and heat transfer enhancement data for all test cases are reported. To resolve the heat transfer coefficient, a transient thermocromic liquid crystal technique was applied. Additionally, the area-averaged heat transfer coefficient on the W-shaped rib itself was observed using the so-called lumped-heat capacitance method. To gain insight into the flow field and to reveal the important flow field structures, numerical computations were conducted with the commercial code FLUENT™.

Heat Transfer Enhancement in Narrow Channels Using Two and Three-Dimensional Mixing Devices

1995 ◽  
Vol 117 (3) ◽  
pp. 590-596 ◽  
Author(s):  
S. V. Garimella ◽  
D. J. Schlitz
Keyword(s):  
Heat Transfer ◽  
Heat Source ◽  
Prandtl Number ◽  
Heat Transfer Enhancement ◽  
Large Scale ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Transitional Flow ◽  
Transfer Enhancement ◽  
Roughness Elements

The localized enhancement of forced convection heat transfer in a rectangular duct with very small ratio of height to width (0.017) was experimentally explored. The heat transfer from a discrete square section of the wall was enhanced by raising the heat source off the wall in the form of a protrusion. Further enhancement was effected through the use of large-scale, three-dimensional roughness elements installed in the duct upstream of the discrete heat source. Transverse ribs installed on the wall opposite the heat source provided even greater heat transfer enhancement. Heat transfer and pressure drop measurements were obtained for heat source length-based Reynolds numbers of 2600 to 40,000 with a perfluorinated organic liquid coolant, FC-77, of Prandtl number 25.3. Selected experiments were also performed in water (Prandtl number 6.97) for Reynolds numbers between 1300 and 83,000, primarily to determine the role of Prandtl number on the heat transfer process. Experimental uncertainties were carefully minimized and rigorously estimated. The greatest enhancement in heat transfer relative to the flush heat source was obtained when the roughness elements were used in combination with a single on the opposite wall. A peak enhancement of 100 percent was obtained at a Reynolds number of 11,000, which corresponds to a transitional flow regime. Predictive correlations valid over a range of Prandtl numbers are proposed.

Molecular Dynamics Simulation on the Effect of Micro-Motions of Nanoparticles in Heat Transfer Enhancement of Nanofluids

2016 ◽  
Author(s):  
Chengzhi Hu ◽  
Minli Bai ◽  
Jizu Lv ◽  
Yuyan Wang
Keyword(s):  
Heat Transfer ◽  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Shear Flow ◽  
Flow Field ◽  
Heat Transfer Enhancement ◽  
Base Fluid ◽  
Dynamics Simulation ◽  
Wall Region ◽  
Transfer Enhancement

The flow and heat transfer characteristics of nanofluids in the near-wall region were studied by non-equilibrium molecular dynamics simulation. The nanofluid model consisted of one spherical copper nanoparticle and argon atoms as base liquid. The effective thermal conductivity (ETC) of nanofluids and base fluid in shear flow fields were obtained. The ETC was increased with the increasing of shear velocity for both base fluid and nanofluids. The heat transfer enhancement of nanofluids in the shear flow field (v≠0) is better than that in the zero-shear flow field (v=0). By analyzing the flow characteristics we proved that the micro-motions of nanoparticles were another mechanism responsible for the heat transfer enhancement of nanofluids in the flow field. Based on the model built in the paper, we found that the thermal properties accounted for 52%–65% heat transfer enhancement and the contribution of micro-motions is 35%–48%.

scholarly journals Effect of the Circular Perforations on the Heat Transfer Enhancement by the Forced Convection from the Rectangular Fins

2018 ◽  
Vol 11 (3) ◽  
pp. 62-70 ◽  
Author(s):  
Wadhah Hussein Abdulrazzaq Al-Taha
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Properties ◽  
Heat Transfer Enhancement ◽  
Forced Convection ◽  
Heat Dissipation ◽  
Transfer Enhancement ◽  
Geometrical Dimensions

This study aims to investigate the effect of the circular perforation of the rectangular fin on the enhancement of the heat transfer by forced convection. The solid rectangular fin considered as a reference for comparison purpose with the perforated fin. The parameters taken into consideration are thermal properties and geometrical dimensions of the fin and its perforations. The area and heat transfer gain of the perforations fins were considered being the main parameters in this study. The results of this study showed that the heat dissipation was improved when used the perforation fins compared with the equivalent solid fin. The enhancement quantity of the heat dissipation from the fin depends on the thermal conductivity, the perforation dimension, thickness, longitudinal and lateral spacing. Finally, the perforating of the fins enhances the rate of heat dissipation as well as decreases the weight of the fin

scholarly journals Experimental and Numerical Study Effect of Using Nanofluids in Perforated Plate Fin Heat Sink for Electronics Cooling

2018 ◽  
Vol 24 (8) ◽  
pp. 1
Author(s):  
Kadhum Audaa Jehhef
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Heat Sink ◽  
Heat Dissipation ◽  
Volume Fraction ◽  
Numerical Study ◽  
Perforated Plate ◽  
Processing Unit ◽  
Transfer Enhancement

An experimental and numerical investigation of the effect of using two types of nanofluids with suspending of (Al2O3 and CuO) nanoparticles in deionized water with a volume fraction of (0.1% vol.), in addition to use three types of fin plate configurations of (smooth, perforated, and dimple plate) to study the heat transfer enhancement characteristics of commercial fin plate heat sink for cooling computer processing unit. All experimental tests under simulated conditions by using heat flux heater element with input power range of (5, 16, 35, 70, and 100 W). The experimental parameters calculated are such as water and nanofluid as coolant with Reynolds number of (7000, 8000, 9400 and 11300); the air is blown in the inlet duct across the heat sink with Reynolds number of (10500, 12300, 14200 and 16000). The distance fin-to-fin is kept constant at (2.00 mm), and the channel employed in this work has a square cross-section of (7 cm) inside. It was observed that the average effectiveness and Nusselt number of the nanofluids are higher compared with those of using conventional liquid cooling systems. However, the perforated fin plate showed higher air heat dissipation than the other configuration plate fin employed in this study. The experimental results were supported by numerical results which gave a good indication to heat transfer enhancement in studied ranges.  

Numerical Simulation of Laminar Flow Heat Transfer Enhancement Using Surface Modification

2014 ◽  
Author(s):  
Abhijit S. Paranjape ◽  
Ninad C. Maniar ◽  
Deval A. Pandya ◽  
Brian H. Dennis
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Surface Modification ◽  
Laminar Flow ◽  
Heat Transfer Enhancement ◽  
Rectangular Channel ◽  
Longitudinal Vortex ◽  
Bottom Wall ◽  
Transfer Enhancement ◽  
Smooth Channel

Heat transfer augmentation techniques have gained great importance in different engineering applications to deal with thermal management issues. In this work, a numerical investigation was carried out to see the effects of a modified surface on the heat transfer enhancement compared to a smooth surface. In the first case, spherical dimple arrays were applied to the surface. The effects were observed for dimples on the bottom wall of a channel for a laminar airflow. The effects of a 21×7 staggered array and a 19×4 inline array on the bottom wall were investigated. In the second case, the heat exchange enhancement in a rectangular channel using longitudinal vortex generators (LVG) for a laminar flow was considered. In both cases, a 3D steady viscous computational fluid dynamics package with an unstructured grid was used to compute the flow and temperature field. The heat transfer characteristics were studied as a function of the Reynolds number based on the hydraulic diameter of the channel. The heat transfer was quantified by computing the surface averaged Nusselt number. The pressure drop and flow characteristics were also calculated. The Nusselt number was compared with that of a smooth channel without surface modification to assess the level of heat transfer enhancement.

Investigation on the Multiple Jet Impingement Heat Transfer Using Al2O3-Water Nanofluid

2013 ◽  
Author(s):  
Caner Senkal ◽  
Shuichi Torii
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Transfer Enhancement ◽  
Heat Dissipation ◽  
Jet Impingement ◽  
High Heat ◽  
Experimental Results ◽  
Transfer Enhancement ◽  
Particle Volume

In recent years, increasing demands for high performance electronic devices give rise to a necessity to remove enormous amount of heat fluxes from small areas. Uniform temperature distribution and sufficient heat transfer dissipation are crucial issues for proper operation of electronic components. To cope up with thermal management of high heat dissipation devices, an efficient cooling method is required. Jet impingement cooling is one of those promising candidates which can handle heat dissipation in an effective way due to its superior heat transfer rates. In this paper, Al2O3 nanofluid heat transfer characteristics are investigated experimentally. Particle diameter of 31nm Al2O3 is taken into consideration in experiments. Impingement surface (surface area:780mm2) were made from oxygen-free copper to simulate high heat flux dissipating electronic component. The experimental results show that the suspended nanoparticles remarkably increase the convective heat transfer coefficient of the base fluid.. Nanofluids with particle volume fractions up to 4% can provide significant heat transfer enhancement, on the other hand, it has been found that high volume fractions (higher then 6%), is not appropriate for heat transfer enhancement under the free jet array configuration. Within the range of parameters considered in this study, experimental results indicated that maximum heat transfer coefficient can be obtained for the intermediate jet to heated target distance (around five times of jet diameter) and closely spaced jets (S/D = 3) for the particle volume fraction 2%. Closely spaced jets are particularly suitable for the electronics cooling applications with regards to provide temperature uniformity on the heated surface.

Flow Bifurcations and Heat Transfer Enhancement in Asymmetric Grooved Channels

2005 ◽  
Author(s):  
Amador M. Guzma´n ◽  
Fernando A. Villar
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Flow Regime ◽  
Flow Regimes ◽  
Numerical Results ◽  
Transitional Flow ◽  
Periodic Flow ◽  
Transfer Enhancement ◽  
Transition Scenario

Numerical investigations of the flow bifurcations, transition scenario and heat transfer enhancement in asymmetric grooved channels are performed by direct numerical simulations of the mass, momentum and energy equations. The governing equations are solved for laminar and time-dependent transitional flow regimes by the spectral element method in a periodic computational domain with appropriated boundary conditions. Numerical results show a flow transition scenario with two Hopf bifurcations B1 and B2, occurring in critical Reynolds numbers Rec1 y Rec2, respectively. Fundamental frequencies ω1 and ω2, and super harmonic combinations of both develop as the Reynolds number increases from a laminar to higher transitional flow regime. Numerical calculations demonstrate that the time-average mean Nusselt number (the non-dimensional heat transfer rate), increases significantly as the flow passes from a laminar to a periodic—and then to a quasi-periodic flow regime. This increase is accompanied by a reasonable increase in both the friction factor and the pumping power. The obtained behavior is comparable to other geometries and configurations as well as to previously reported numerical results for the studied geometry. This numerical investigation shows a transition scenario at the onset of turbulence, similar to the Ruelle-Takens-Newhouse scenario, which has not been found or reported by other researchers using this geometry. The numerical simulation results also show the existence of a bifurcation scenario that develops a path-dependent flow and heat transport behavior. In the vicinity of the first Hopf flow bifurcation (and consequently, the critical Reynolds number Rec1), the resulting stable time periodic flow depends on both the initial flow conditions and the way in which the incremental process to higher flow regimes is carried out.

Alumina Nanofluid for Spray Cooling Enhancement

2007 ◽  
Author(s):  
Aditya Bansal ◽  
Frank Pyrtle
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heat Dissipation ◽  
Cooling System ◽  
Spray Cooling ◽  
Open Loop ◽  
Heat Fluxes ◽  
Alumina Nanoparticles ◽  
Transfer Enhancement ◽  
Thermal Conductivities

Nanofluids have been demonstrated as promising for heat transfer enhancement in forced convection and boiling applications. The addition of carbon, copper, and other high-thermal-conductivity nanoparticles to water, oil, ethylene glycol, and other fluids has been determined to increase the thermal conductivities of these fluids. The increased effective thermal conductivities of these fluids enhance their abilities to dissipate heat in such applications. The use of nanofluids for spray cooling is an extension of the application of nanofluids for enhancement of heat dissipation. In this investigation, experiments were performed to determine the level of heat transfer enhancement with the addition of alumina nanoparticles to the fluid. Using mass percentages of up to 0.5% alumina nanoparticles suspended in water, heat fluxes and surface temperatures were measured and compared. Compressed nitrogen was used to provide constant spray nozzle pressures to produce full-cone sprays in an open loop spray cooling system. Heat fluxes were measured for single-phase and evaporative spray cooling regimes.

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