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 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™.

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.

scholarly journals FORCED CONVECTION HEAT TRANSFER PERFORMANCE OF AN INTERNALLY FINNED TUBE

1970 ◽  
Vol 40 (1) ◽  
pp. 54-62 ◽  
Author(s):  
Asharful Islam ◽  
A. K. Mozumder
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Friction Factor ◽  
Heat Transfer Performance ◽  
Finned Tube ◽  
Transfer Performance

Heat transfer performance of T-section internal fins in a circular tube has been experimentally investigated. The T-finned tube was heated by electricity and was cooled by fully developed turbulent air. Inside wall temperatures and pressure drop along the axial distance of the test section at steady state condition were measured for different flows having Reynolds number ranging from 2x104 to 5x104 for both smooth and finned tubes. From the measured data, heat transfer coefficient, Nusselt number and friction factor were calculated. From the measured and calculated values, heat transfer characteristics and fluid flow characteristics of the finned tube are explained; the performance of the finned tube is also evaluated. For finned tube, friction factor on an average was 5 times higher and heat transfer coefficient was 2 times higher than those for smooth tube for similar flow conditions. The finned tube, however, produces significant heat transfer enhancement. Key Words: Heat Transfer, Internal Fin, Reynolds Number, Nusselt Number, Pressure Drop. doi: 10.3329/jme.v40i1.3473 Journal of Mechanical Engineering, Vol. ME40, No. 1, June 2009 54-62

A Numerical Study on Heat Transfer Characteristics of CO2-DME Mixture Fluid

2009 ◽  
Author(s):  
Xin-Rong Zhang ◽  
Jia Liu ◽  
Hiroshi Yamaguchi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Temperature Gradient ◽  
Heat Transfer Enhancement ◽  
Mass Fraction ◽  
Heat Transfer Performance ◽  
Transfer Performance ◽  
Transfer Enhancement ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics

In response to the call for environment protection, more and more researches have been finding new alternative refrigerants which are of zero Ozone depleting potential (ODP), low global warming potential (GWP) and will be efficient, inflammable, and nontoxic to replace the HCFCs and HFCs refrigerants. Non-azeotropic mixtures of suitable fluids are becoming the important candidates of that search race. In this paper, the flow and heat transfer performance of CO2-DME (dimethyl ether) mixture refrigerants at 8.0 MPa in a horizontal tube was numerically investigated. In particular, this work has been focused upon the laminar heat transfer characteristics of CO2-DME mixture refrigerant flow with Reynolds number ranging from 180 to 1800 and the mass fraction of DME ranging from 21% to 39%. The results show that the heat transfer performance of the mixture fluid can be improved when the mass fraction of DME increases to 30%. Considering both the best heat transfer performance and the safety, the optimum component of CO2-DME (70/30, mass%) has been found in this study. And the mechanisms that are responsible for the heat transfer enhancement are obtained and they are: (1) The temperature gradient of CO2-DME mixture fluid with high mass fraction of DME is larger than that of CO2-DME mixture fluid with low mass fraction of DME; in addition, the temperature gradient increases with the mass fraction of DME; (2) The increase of thermal conductivity for CO2-DME mixtures can enhance the heat transfer performance to a large extent. (3) The self-acceleration characteristic of the supercritical mixture fluid is also beneficial to the heat transfer enhancement. Furthermore, it is found that the heat transfer performance of the mixture fluid can also be improved with Reynolds number. The viscous boundary layer of the fluid becomes thinner when the Reynolds number increases, which leads to an enhancement in heat transfer. In addition, at high Reynolds number, the flow is tend to be turbulent, which is beneficial to the heat transfer performance of mixture fluid. With regard to the flow characteristic of mixtures, first the flowing changes depend on the temperature and the density of fluid to a large extent-the high value of velocity can occur when the fluid has a high temperature and a low density. And secondly, the supercritical CO2-DME mixtures speed up along the tube and make themselves different with water flow. These results of this study have significant implications for the design of high-performance heat exchangers, using CO2-DME mixture as the working fluid.

Heat Transfer Enhancement by Insertion of Vortex Generators in Electronic Chip Cooling: A Numerical Study

2017 ◽  
Author(s):  
Mohammad Rejaul Haque ◽  
Amy Rachel Betz
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Transfer Coefficient ◽  
Heat Transfer Enhancement ◽  
Vortex Generators ◽  
Transfer Enhancement ◽  
Maximum Heat

The present work represents a 2-D numerical investigation of forced convection heat transfer over three electronic blocks (silicon chip) in an inline arrangement with elliptical shaped vortex generators (VG-copper made) placed on top of the channel, for a range of Reynolds numbers. The block is prescribed with a 1,000 W/m2 heat flux due to heating of the electronic components installed in the CPU casing. The results show that, vortex generators could effectively enhance the heat transfer in the channel. Subsequently, the effects of Reynolds number (from 500 to 1050), the number of vortex generators (baseline, 1, 2 and 3), aspect ratio of heated block (0.125, 0.15, 0.22), and aspect ratio of vortex generators (0.3125, 0.4, 0.5) on the heat transfer and fluid flow characteristics are examined. The characteristics of the performance parameters are studied numerically with the aid of computational fluid dynamics (CFD). The 3 VG demonstrates nearly 28.35% enhancement of Nusselt number compared to the 1 VG case at Re = 479. The change in pressure drop is less at low Reynolds number compared to higher Reynolds number respective to other parameters. Increasing the aspect ratio of the block increases the convection coefficient while decreasing aspect ratio of VG increases heat transfer coefficient. This enhancement is less significant for the third block as the cooling effect is predominant close to the channel inlet. Increasing consecutive distance between the blocks, enhances the heat transfer coefficient with the penalty of additional pressure drop. However, parametric studies are conducted for the maximum heat transfer enhancement.

Production Process and Heat Transfer Performance of 10/316 Clad Tube

2014 ◽  
Vol 1081 ◽  
pp. 270-274
Author(s):  
Zui Xian Yu ◽  
Xue Sheng Wang ◽  
Qin Zhu Chen
Keyword(s):  
Heat Transfer ◽  
Stainless Steel ◽  
Heat Transfer Coefficient ◽  
Carbon Steel ◽  
Transfer Coefficient ◽  
Heat Transfer Performance ◽  
Steel Tube ◽  
Stainless Steel Tube ◽  
Transfer Performance ◽  
Clad Tube

A new preparation technique of carbon steel/stainless steel clad tube was introduced, and the contact surface was well combined. Meanwhile, with the using of tube heat exchanger, the experiment on the heat transfer performance of the clad tube was done. Comparing the 10/316 clad tube and the 316 stainless steel tube, the effects on the heat transfer performance of 316 stainless steel tube attached to carbon steel was evaluated. It is showed that overall heat transfer coefficient of 10/316 clad tubes is higher than that of stainless steel tube. The average heat transfer coefficient of 10/316 clad tubes is about 18.7%~34.4% higher than that of stainless steel tube. Experimental investigation indicates that, by brazing and cold drawing, the 10/316 clad tube was well combined and the thermal conductivity was better than that of stainless steel tube.

Heat Transfer Performance of Different Nanofluids Flows in a Helically Coiled Heat Exchanger

2013 ◽  
Vol 832 ◽  
pp. 160-165 ◽  
Author(s):  
Mohammad Alam Khairul ◽  
Rahman Saidur ◽  
Altab Hossain ◽  
Mohammad Abdul Alim ◽  
Islam Mohammed Mahbubul
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Friction Factor ◽  
Heat Exchangers ◽  
Heat Transfer Performance ◽  
Volume Concentration ◽  
Transfer Performance

Helically coiled heat exchangers are globally used in various industrial applications for their high heat transfer performance and compact size. Nanofluids can provide excellent thermal performance of this type of heat exchangers. In the present study, the effect of different nanofluids on the heat transfer performance in a helically coiled heat exchanger is examined. Four different types of nanofluids CuO/water, Al2O3/water, SiO2/water, and ZnO/water with volume fractions 1 vol.% to 4 vol.% was used throughout this analysis and volume flow rate was remained constant at 3 LPM. Results show that the heat transfer coefficient is high for higher particle volume concentration of CuO/water, Al2O3/water and ZnO/water nanofluids, while the values of the friction factor and pressure drop significantly increase with the increase of nanoparticle volume concentration. On the contrary, low heat transfer coefficient was found in higher concentration of SiO2/water nanofluids. The highest enhancement of heat transfer coefficient and lowest friction factor occurred for CuO/water nanofluids among the four nanofluids. However, highest friction factor and lowest heat transfer coefficient were found for SiO2/water nanofluids. The results reveal that, CuO/water nanofluids indicate significant heat transfer performance for helically coiled heat exchanger systems though this nanofluids exhibits higher pressure drop.

Research on Heat Transfer Performance of Water Film for Outside the Tubes of the Microscale Evaporative Condenser

2009 ◽  
Author(s):  
Minghui Hu ◽  
Dongsheng Zhu ◽  
Jialong Shen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Transfer Performance ◽  
Water Film ◽  
Transfer Performance ◽  
Air Velocity ◽  
Microscale Heat Transfer ◽  
High Heat Transfer ◽  
Spray Density

It is requested to develop a microscale and high performance heat exchanger for small size energy equipments. The heat transfer performance of the water film on the condensing coils of the microscale evaporative condenser was studied for a single-stage compressed refrigeration cycle system. Under various operation conditions, the effects of the spray density and the head-on air velocity on the heat transfer performance of the water film were investigated. The results show that the microscale heat transfer coefficient of the water film αw increases with the increase of spray density and decreases with the increase of head-on air velocity. The results indicate that the key factor affecting the microscale heat transfer of the water film is the spray density. As the results, it is measured that the present device attained high heat transfer quantity despite the weight is light. In addition, via regression analysis of the experimental data, the correlation equation for calculating the microscale heat transfer coefficient of the water film was obtained, its regression correlation coefficient R is 0.98 and the standard deviation is 7.5%. Finally, the correlations from other works were compared. The results presented that the experimental correlation had better consistency with the correlations from other works. In general, the obtained experimental results of the water film heat transfer are helpful to the design and practical operation of the microscale evaporative condensers.

scholarly journals Enhanced heat transfer characteristics of conjugated air jet impingement on a finned heat sink

2017 ◽  
Vol 21 (1 Part A) ◽  
pp. 279-288 ◽  
Author(s):  
Shuxia Qiu ◽  
Peng Xu ◽  
Liping Geng ◽  
Arun Mujumdar ◽  
Zhouting Jiang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heat Sink ◽  
Heat Transfer Performance ◽  
Cooling System ◽  
Flow Characteristics ◽  
Jet Impingement ◽  
Transfer Performance ◽  
Transfer Enhancement ◽  
Air Jet

Air jet impingement is one of the effective cooling techniques employed in micro-electronic industry. To enhance the heat transfer performance, a cooling system with air jet impingement on a finned heat sink is evaluated via the computational fluid dynamics method. A two-dimensional confined slot air impinging on a finned flat plate is modeled. The numerical model is validated by comparison of the computed Nusselt number distribution on the impingement target with published experimental results. The flow characteristics and heat transfer performance of jet impingement on both of smooth and finned heat sinks are compared. It is observed that jet impingement over finned target plate improves the cooling performance significantly. A dimensionless heat transfer enhancement factor is introduced to quantify the effect of jet flow Reynolds number on the finned surface. The effect of rectangular fin dimensions on impingement heat transfer rate is discussed in order to optimize the cooling system. Also, the computed flow and thermal fields of the air impingement system are examined to explore the physical mechanisms for heat transfer enhancement.

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.

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