Applied Pulsed Flow for Single-Phase Convective Heat Transfer Enhancement in a Laminar Flow Cooling System

2008 ◽  
Author(s):  
Bolaji O. Olayiwola ◽  
Gerhard Schaldach ◽  
Peter Walzel
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Cooling System ◽  
Transfer Enhancement ◽  
Flow Rates ◽  
The Heat Transfer Coefficient

Experimental and CFD studies were performed to investigate the enhancement of convective heat transfer in a laminar cooling system using flow pulsation in a flat channel with series of regular spaced fins. Glycerol-water mixtures with dynamic viscosities in the range of 0.001 kg/ms–0.01 kg/ms were used. A steady flow Reynolds number in the laminar range of 10 < Re < 1200 was studied. The amplitudes of the applied pulsations are in the range of 0.25 < A < 0.55 mm and the frequency range is 10 < f < 60 Hz. Two different cooling devices with active length L = 450 mm and 900 mm were investigated. CFD simulations were performed on a parallel-computer (Linux-cluster) using the software suit CFX11 from ANSYS GmbH, Germany. The rate of cooling was found to be significant at moderate low net flow rates. In general, no significant heat transfer enhancement at very low and high flow rates was obtained in compliance with the experimental data. The heat transfer coefficient was found to increase with increasing Prandtl number Pr at constant oscillation Reynolds number Reosc whereas the ratio of the hydraulic diameter to the length of the channel dh/L has insignificant effect on the heat transfer coefficient. This is due to enhanced fluid mixing. CFD results allow for performance predictions of different geometries and flow conditions.

An Experimental Investigation of Structured Roughness Effect on Heat Transfer During Single-Phase Liquid Flow at Microscale

2012 ◽  
Vol 134 (10) ◽  
Author(s):  
Ting-Yu Lin ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Transfer Enhancement ◽  
Enhancement Factor ◽  
Roughness Element ◽  
Hydraulic Diameter ◽  
Transfer Enhancement ◽  
Roughness Elements ◽  
The Heat Transfer Coefficient

The effect of structured roughness on the heat transfer of water flowing through minichannels was experimentally investigated in this study. The test channels were formed by two 12.7 mm wide × 94.6 mm long stainless steel strips. Eight structured roughness elements were generated using a wire electrical discharge machining (EDM) process as lateral grooves of sinusoidal profile on the channel walls. The height of the roughness structures ranged from 18 μm to 96 μm, and the pitch was varied from 250 μm to 400 μm. The hydraulic diameter of the rectangular flow channels ranged from 0.71 mm to 1.87 mm, while the constricted hydraulic diameter (obtained by using the narrowest flow gap) ranged from 0.68 mm to 1.76 mm. After accounting for heat losses from the edges and end sections, the heat transfer coefficient for smooth channels was found to be in good agreement with the conventional correlations in the laminar entry region as well as in the laminar fully developed region. All roughness elements were found to enhance the heat transfer. In the ranges of parameters tested, the roughness element pitch was found to have almost no effect, while the heat transfer coefficient was significantly enhanced by increasing the roughness element height. An earlier transition from laminar to turbulent flow was observed with increasing relative roughness (ratio of roughness height to hydraulic diameter). For the roughness element designated as B-1 with a pitch of 250 μm, roughness height of 96 μm and a constricted hydraulic diameter of 690 μm, a maximum heat transfer enhancement of 377% was obtained, while the corresponding friction factor increase was 371% in the laminar fully developed region. Comparing different enhancement techniques reported in the literature, the highest roughness element tested in the present work resulted in the highest thermal performance factor, defined as the ratio of heat transfer enhancement factor (over smooth channels) and the corresponding friction enhancement factor to the power 1/3.

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™.

scholarly journals Intensified Thermal Conductivity and Convective Heat Transfer of Ultrasonically Prepared CuO–Polyaniline Nanocomposite Based Nanofluids in Helical Coil Heat Exchanger

2019 ◽  
Vol 64 (2) ◽  
pp. 271-282 ◽  
Author(s):  
Abhishek Lanjewar ◽  
Bharat Bhanvase ◽  
Divya Barai ◽  
Shivani Chawhan ◽  
Shirish Sonawane
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Base Fluid ◽  
Cuo Nanoparticles ◽  
The Heat Transfer Coefficient

In this study, investigation of convective heat transfer enhancement with the use of CuO–Polyaniline (CuO–PANI) nanocomposite basednanofluid inside vertical helically coiled tube heat exchanger was carried out experimentally. In these experiments, the effects of different parameters such as Reynolds number and volume % of CuO–PANI nanocomposite in nanofluid on the heat transfer coefficient of base fluid have been studied. In order to study the effect of CuO–PANI nanocomposite based nanofluid on heat transfer, CuO nanoparticles loaded in PANI were synthesized in the presence of ultrasound assisted environment at different loading concentration of CuO nanoparticles (1, 3 and 5 wt.%). Then the nanofluids were prepared at different concentrations of CuO–PANI nanocomposite using water as a base fluid. The 1 wt.% CuO–PANI nanocomposite was selected for the heat transfer study for nanofluid concentration in the range of 0.05 to 0.3 volume % and Reynolds number range of was 1080 to 2160 (±5). Around 37 % enhancement in the heat transfer coefficient was observed for 0.2 volume % of 1 wt.% CuO–PANI nanocomposite in the base fluid. In addition, significant enhancement in the heat transfer coefficient was observed with an increase in the Reynolds number and percentage loading of CuO nanoparticle in Polyaniline (PANI).

Heat transfer performance of steam/air flow in inverted V-shaped rib-roughened channels

2021 ◽  
pp. 095765092110161
Author(s):  
Chao Ma ◽  
Bing Ge
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Transfer Enhancement ◽  
Heat Transfer Performance ◽  
Air Flow ◽  
Transfer Performance ◽  
Transfer Enhancement ◽  
Ribbed Channel

The heat transfer performance of steam and air flow in a rough rectangular channel with different inverted V-shaped ribs was investigated by infrared thermal imaging technology. Under the conditions that the Reynolds number is in the range of 4000–15,000, the effects of the rib angle on the heat transfer enhancement of the two coolants were obtained. The rib pitch ratio of the flow channel is 10, the ratio of the rib height to the channel hydraulic diameter is 0.078, and the inverted V-shaped rib angle varies from 45° to 90°. The results show that in the inverted V-shaped ribbed channel, the Nu number on both sides of the channel is greatly increased, while the Nu number in the middle of the channel is lower. The local Nu distribution on the surface of the ribbed channel is highly related to the shape of the rib. For different medium cooling, the value and unevenness of the heat transfer coefficient are different, but the shape of the high and low heat transfer coefficient distribution is hardly affected. The heat transfer of both coolants increases as the rib angle decreases from 90° to 45°. Compared with air flow, steam flow cooling shows higher convective heat transfer enhancement. For rib angles of 45°, 60°, 75°, and 90°, under the operating condition of the Reynolds number = 12,000, the area-averaged Nusselt numbers of the steam flow is 23.6%, 27.4% and 13.9% higher than that of the air flow, respectively. Based on the experimental heat transfer data, the correlation in terms of the Reynolds number and the rib angle was developed, which is used to estimate the Nu number for steam and air cooling in the inverted V-shaped rib-roughness channels.

Experimental and Numerical Investigations on the Heat Transfer of Film Cooling With Cylindrical Holes Fed With Internal Coolant Cross Flows

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Lin Ye ◽  
Cun-Liang Liu ◽  
Dao-En Zhou ◽  
Hui-Ren Zhu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Transfer Enhancement ◽  
Cross Flow ◽  
Skewed Distribution ◽  
Transfer Enhancement ◽  
High Heat Transfer ◽  
Cylindrical Holes ◽  
The Heat Transfer Coefficient

Abstract The heat transfer coefficient of cylindrical holes fed by varying internal cross-flow channels with different cross-flow Reynolds numbers Rec is experimentally studied on a low-speed flat-plate facility. Three coolant cross flow cases, including a smooth case and two ribbed cases with 45/135-deg ribs, are studied at Rec = 50,000, and 100,000 with varying blowing ratios M of 0.5, 1.0, and 2.0. A transient liquid-crystal (LC) measurement technique is used to determine the heat transfer coefficient. At lower M, the heat transfer enhancement regions are asymmetrical for the smooth and 45-deg cases. The asymmetrical vortex is more pronounced with increasing cross-flow direction velocity, resulting in a more skewed distribution at Rec = 100,000. Conversely, the contours are laterally symmetric in the 135-deg case at varying Rec. A fork-shaped trend with a relatively high heat transfer coefficient appears upstream, and the increases in the heat transfer in the 135-deg cases are lower than those in the 45-deg cases. As M increases to 2.0, the vortex intensity increases, resulting in a stronger scouring effect upstream, especially at large Rec. The range and degree are affected by Rec at M = 2.0. The core of the heat transfer enhancement is skewed to the −Y side for both cases.

An Investigation of the Application of Roughness Elements to Enhance Heat Transfer in an Impingement Cooling System

2005 ◽  
Author(s):  
Changmin Son ◽  
Geoffery Dailey ◽  
Peter Ireland ◽  
David Gillespie
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Transfer Enhancement ◽  
Pressure Loss ◽  
Cooling System ◽  
Target Surface ◽  
Transfer Enhancement ◽  
Impingement Cooling ◽  
Roughness Elements

The inclusion of roughness elements on the target surface of a turbine aerofoil impingement cooling system is an attractive means of heat transfer enhancement. In such a system, it is important to minimise additional pressure loss caused by the roughness elements and thus their shape, size and position need to be optimised. The research showed how heat transfer enhancement is normally achieved at the expense of extra pressure loss. A hexagonal roughness element designed by the authors showed up to 10% heat transfer enhancement with minimal extra pressure loss. The present work includes shear pattern visualisation on the target surface, pressure loss measurements and heat transfer coefficient measurements for an impingement cooling system with simply shaped roughness elements-specifically cylindrical & diamond pimples. Flow visualisation results and pressure loss measurements for the above configurations provided criteria for selecting the shape, size and position of the roughness elements. The detailed heat transfer measurements on the target surface and over the roughness elements were used to explain the heat transfer enhancement mechanisms. It was found that the largest contribution to heat transfer is the impingement stagnation point and the developing wall jet regions. However, the research showed that the low heat transfer coefficient region could be made to contribute more by using strategically located roughness elements. A hexagonal rim was designed to cover the complete low heat transfer coefficient region midway between neighbouring jets. The effect of the height, cross sectional shape and wall angle of the hexagonal rim were studied using a series of heat transfer and pressure loss experiments. The transient heat transfer tests were conducted using a triple thermochromic liquid crystal technique and the thermal transient was produced by a fine wire mesh heater. The heat transfer coefficient over the pimples was measured using a hybrid transient method that analysed the thermal transient of the copper pimple. The detailed heat transfer coefficient distributions over the complete area of the target surface provided comprehensive understanding of the performance of the hexagonal rim. Tests were conducted at three different mass flow rates for each configuration. The average and local jet Reynolds numbers varied between 21500 and 31500, and 17000 and 41000 respectively.

scholarly journals Convective Heat Transfer Enhancement in Nanofluids: Real Anomaly or Analysis Artifact?

2011 ◽  
Author(s):  
Naveen Prabhat ◽  
Jacopo Buongiorno ◽  
Lin-wen Hu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Laminar Flow ◽  
Turbulent Flow ◽  
Transfer Coefficient ◽  
Temperature Dependence ◽  
Convective Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Convective Heat ◽  
Transfer Enhancement

The nanofluid literature contains many claims of anomalous convective heat transfer enhancement in both turbulent and laminar flow. To put such claims to the test, we have performed a critical detailed analysis of the database reported in 12 nanofluid papers (8 on laminar flow and 4 on turbulent flow). The methodology accounted for both modeling and experimental uncertainties in the following way. The heat transfer coefficient for any given data set was calculated according to the established correlations (Dittus-Boelter’s for turbulent flow and Shah’s for laminar flow). The uncertainty in the correlation input parameters (i.e. nanofluid thermo-physical properties and flow rate) was propagated to get the uncertainty on the predicted heat transfer coefficient. The predicted and measured heat transfer coefficient values were then compared to each other. If they differed by more than their respective uncertainties, we judged the deviation anomalous. According to this methodology, it was found that in nanofluid laminar flow in fact there seems to be anomalous heat transfer enhancement in the entrance region, while the data are in agreement (within uncertainties) with the Shah’s correlation in the fully developed region. On the other hand, the turbulent flow data could be reconciled (within uncertainties) with the Dittus-Boelter’s correlation, once the temperature dependence of viscosity was included in the prediction of the Reynolds number. While this finding is plausible, it could not be conclusively confirmed, because most papers do not report information about the temperature dependence of the viscosity for their nanofluids.

Heat Transfer Enhancement in Split and Recombine Flow Configurations: A Numerical and Experimental Study

2016 ◽  
Author(s):  
Mojtaba Jarrahi ◽  
Jean-Pierre Thermeau ◽  
Hassan Peerhossaini
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Convective Heat ◽  
Convective Heat Transfer Coefficient ◽  
Working Fluid ◽  
Transfer Enhancement

Heat transfer enhancement in laminar regime by split and recombine (SAR) mechanism, based on the baker’s transformation, is investigated. Two different heat exchangers, called SAR1 and SAR2, are studied. Their geometries are inspired from the previous studies reported in the literature. The working fluid on both, shell and tube side, is water and the temperature on the shell side is kept constant. Experiments are carried out for the Reynolds number range 100<Re<3000 when the Prandtl number is between 4.5 and 7.5. The results show that the convective heat transfer coefficient in the first element of heat exchanger SAR1 is higher than that in the second one, i.e. SAR2. However, the variation in the convective heat transfer coefficient from the first to the third element along the heat exchanger SAR2 is less significant than that observed for SAR1. Moreover, SAR2 causes a higher pressure drop, especially when Re>1000, and provides a less uniform temperature field at the outlet.

Measurement of Heat Transfer Enhancement and Pressure Drop Across Eddy Promoter Air Screens in a Liquid-to-Air-Membrane Energy Exchanger (LAMEE)

2013 ◽  
Author(s):  
Ashkan Oghabi ◽  
Davood Ghadiri Moghaddam ◽  
Carey Simonson ◽  
Robert W. Besant
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Convective Heat Transfer Coefficient ◽  
Transfer Enhancement ◽  
Membrane Energy ◽  
Air Channel

In liquid-to-air membrane energy exchangers (LAMEEs), the heat and mass transfer resistances in the air channel are dominant. An eddy promoter air screen can effectively enhance the heat and mass transfers in the air channel. In this study, the heat transfer enhancement and pressure drop across three different eddy promoter air screens in an air channel are experimentally investigated. Eddy promoter air screens are comprised of plastic ribs in the stream-wise direction and aluminum cross-bars normal to the air flow direction. A low speed wind tunnel test facility, which simulates the air channel of a LAMEE is designed to measure the friction factor and enhanced convective heat transfer coefficient in the air channel with an eddy promoter air screen. Tests were conducted at Reynolds numbers of 920, 1550, and 2160. In this paper, the effects of the spacing of the cylindrical bars and plastic ribs on the heat transfer performance are studied experimentally. Also, the performance of eddy promoter air screens as a function of enhanced heat transfer coefficient and increased pressure drop is investigated. Results show that the eddy promoter air screens have the highest efficiencies at Reynolds of 1550 and double the convective heat transfer coefficient of the air with respect to a smooth channel.

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