Heat or Mass Transfer in Laminar Flow in Conduits With Constriction

1973 ◽  
Vol 95 (3) ◽  
pp. 352-356 ◽  
Author(s):  
J. C. F. Chow ◽  
K. Soda
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Laminar Flow ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Bulk Temperature ◽  
Fluid Temperature ◽  
Entry Length ◽  
Moderate Reynolds Number ◽  
Length Changes

Analytical solutions are obtained on the effects of boundary constriction on heat or mass transfer at the entrance region in a well-developed steady laminar flow in symmetric and axisymmetric conduits subjected to uniform wall temperature or mass concentration. The solutions are limited to the fluids of constant properties with negligible viscous dissipation, moderate Reynolds number, and large Peclet or Schmidt number, and the spread of the wall constriction is large compared to the mean width or radius of the conduits. It is found that both the bulk temperature and heat transfer rate at the wall are oscillatory in nature, and their amplitudes decrease drastically as the fluid moves away from the entrance. Near thermal entry length, the bulk fluid temperature approaches its mean value with vanishing oscillation, but the heat transfer rate at the wall stays oscillatory in nature due to the irregularity of the wall. The thermal entry length changes very little from the corresponding straight-wall conduits. These results are also true for the mass transfer.

Design of a Microfin Array Heat Sink Using Flow-Induced Vibration to Enhance the Heat Transfer Rate in the Laminar Flow Regime

2001 ◽  
Author(s):  
Jeung Sang Go ◽  
Geunbae Lim ◽  
Hayong Yun ◽  
Sung Jin Kim ◽  
Inseob Song
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Heat Transfer Enhancement ◽  
Flow Regime ◽  
Heat Transfer Rate ◽  
Heat Sink ◽  
Transfer Rate ◽  
Transfer Enhancement ◽  
Air Velocity ◽  
Flow Induced Vibration

Abstract This paper presented design guideline of the microfin array heat sink using flow-induced vibration to increase the heat transfer rate in the laminar flow regime. Effect of the flow-induced vibration of a microfin array on heat transfer enhancement was investigated experimentally by comparing the thermal resistances of the microfin array heat sink and those of a plain-wall heat sink. At the air velocities of 4.4m/s and 5.5 m/s, an increase of 5.5% and 11.5% in the heat transfer rate was obtained, respectively. The microfin flow sensor also characterized the flow-induced vibration of the microfin. It was determined that the microfin vibrates with the fundamental natural frequency regardless of the air velocity. It was also shown that the vibrating displacement of the microfin is increased with increasing air velocity and then saturated over a certain value of air velocity. Based on the numerical analysis of the temperature distribution resulted from microfin vibration and experimental results, a simple heat transfer model (heat pumping model) was proposed to understand the heat transfer mechanism of a microfin array heat sink. Under the geometric and structural constraints, the maximum heat transfer enhancement was obtained at the intersection of the minimum thickness of the microfin and constraint of the bending angle.

Numerical Study of Fluid Flow and Heat Transfer Enhancement of Nanofluids over Tube Bank

2013 ◽  
Vol 388 ◽  
pp. 149-155 ◽  
Author(s):  
Mazlan Abdul Wahid ◽  
Ahmad Ali Gholami ◽  
H.A. Mohammed
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Cross Flow ◽  
Bulk Temperature ◽  
Compact Heat Exchanger ◽  
Pure Fluid ◽  
Tube Banks

In the present work, laminar cross flow forced convective heat transfer of nanofluid over tube banks with various geometry under constant wall temperature condition is investigated numerically. We used nanofluid instead of pure fluid ,as external cross flow, because of its potential to increase heat transfer of system. The effect of the nanofluid on the compact heat exchanger performance was studied and compared to that of a conventional fluid.The two-dimensional steady state Navier-Stokes equations and the energy equation governing laminar incompressible flow are solved using a Finite volume method for the case of flow across an in-line bundle of tube banks as commercial compact heat exchanger. The nanofluid used was alumina-water 4% and the performance was compared with water. In this paper, the effect of parameters such as various tube shapes ( flat, circle, elliptic), and heat transfer comparison between nanofluid and pure fluid is studied. Temperature profile, heat transfer coefficient and pressure profile were obtained from the simulations and the performance was discussed in terms of heat transfer rate and performance index. Results indicated enhanced performance in the use of a nanofluid, and slight penalty in pressure drop. The increase in Reynolds number caused an increase in the heat transfer rate and a decrease in the overall bulk temperature of the cold fluid. The results show that, for a given heat duty, a mas flow rate required of the nanofluid is lower than that of water causing lower pressure drop. Consequently, smaller equipment and less pumping power are required.

scholarly journals Numerical Investigation of Natural Convective Condensation with Noncondensable Gases in the Reactor Containment after Severe Accidents

2019 ◽  
Vol 2019 ◽  
pp. 1-12 ◽  
Author(s):  
Wen Fu ◽  
Li Zhang ◽  
Xiaowei Li ◽  
Xinxin Wu
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Mass Fraction ◽  
Transfer Processes ◽  
Noncondensable Gases ◽  
Mass Transfer Processes ◽  
Convective Condensation

The heat and mass transfer processes of natural convective condensation with noncondensable gases are very important for the passive containment cooling system of water cooled reactors. Numerical simulation of natural convective condensation with noncondensable gases was realized in the Fluent software by adding condensation models. The scaled AP600 containment condensation experiment was simulated to verify the numerical method. It was shown that the developed method can predict natural convective condensation with noncondensable gases well. The velocity, species, and density fields in the scaled AP600 containment were presented. The heat transfer rate distribution and the influences of the mass fraction of air on heat transfer rate were also analyzed. It is found that the driving force of natural convective condensation with noncondensable gases is mainly caused by the mass fraction difference but not temperature difference. The natural convective condensation with noncondensable gases in AP1000 containment was then simulated. The temperature, species, velocity, and heat flux distributions were obtained and analyzed. The upper head of the containment contributes to 35.1% of the total heat transfer rate, while its area only takes 25.4% of the total condensation area of the containment. The influences of the mass fraction of low molecular weight noncondensable gas (hydrogen) on the natural convective condensation were also discussed based on the detailed species, density, and velocity fields. The results show that addition of hydrogen (production of zirconium-water reaction after severe accident) will weaken the intensity of natural convection and the heat and mass transfer processes significantly. When hydrogen contributes to 50% mole fraction of the noncondensable gases, the heat transfer coefficient will be reduced to 45%.

Wall Roughness Effect on Heat Transfer Rate of the Turbulent Gas-Solid Flow in Inclined Pipes

2014 ◽  
Author(s):  
Adel Ebadi ◽  
Zohreh Mansoori ◽  
Majid Saffar-Avval ◽  
Goodarz Ahmadi
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Nusselt Number ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Wall Region ◽  
Fluid Temperature ◽  
Wall Roughness ◽  
Mean Flow ◽  
Inclined Pipes

The effects of wall surface roughness on the rate of heat transfer and temperature profiles in turbulent gas-solid flows in pipes at different inclination angles were studied. The earlier developed computational model for 3D flows including the four-way interactions was extended and used in this study for evaluating the mean flow, turbulence intensity and thermal fields. Interaction of particles with the rough wall was included by introducing the available stochastic wall roughness models (shadow effect model) for the dispersed phase in the computational program. It was found that changes in the particle dispersion and particle concentration altered the Nusselt number and heat transfer rate in different regions of the pipe. The Nusselt number decreased in the lower part of the duct for horizontal and inclined pipes due to the reduction in the settling velocity. The surface roughness also altered the heat transfer coefficient in the periphery of the vertical riser. The simulation results showed that the fluid temperature was reduced in the pipe core and increased near the wall region for inclined pipes. On the other hand, particle temperature increased and flattened in the entire pipe cross section.

THE EFFECT OF DIFFERENT AMBIENT TEMPERATURE TO SOLAR COOLING PERFORMANCE

2016 ◽  
Vol 78 (5-5) ◽  
Author(s):  
Dewanto Harjunowibowo ◽  
Dina Nur Adilah ◽  
Dwi Teguh Rahardjo ◽  
Danar S. Wijayanto ◽  
Fredy Surahmanto ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Ambient Temperature ◽  
Heat And Mass Transfer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Adsorption Process ◽  
Mass Transfer Rate ◽  
Cooling Performance ◽  
Solar Cooling

The density of adsorbent bed significantly contributed to solar cooling performance (COP). The density determines how well the heat and mass transfer are. Besides that, the COP is also determined by ambient temperature. This research aims to investigate the affect of temperature of a connecting pipe, as a representative of different ambient temperature against a solar cooling machine performance. The experiment will show in what condition a solar cooling is going to have a better cooling result. The data used in this case was taken experimentally and conducted using a solar cooling machine equipped with temperature measurement units such as thermocouple logger. For cold ambient temperature, in adsorption process, refrigerant vapour flows to the generator through the connecting pipe cooled by water and kept steady. The results show that the COP, heat and mass transfer of adsorbent bed of the system in the adsorption process on a warm condition are better than in a cold environment. In the warm condition the COP system is 0.24, the heat transfer rate is 0.06 °C/minute, and the mass transfer rate is 1.09 ml/minute. Whereas, in the cold condition the COP system is 0.23, the heat transfer rate is 0.05 °C/minute, and the mass transfer rate is 1.04 ml/minute. 

HEAT GENERATION AND ABSORPTION IN MHD FLOW OF CASSON FLUID PAST A STRETCHING WEDGE WITH VISCOUS DISSIPATION AND NEWTONIAN HEATING

2018 ◽  
Vol 80 (3) ◽  
Author(s):  
Imran Ullah ◽  
Sharidan Shafie ◽  
Ilyas Khan
Keyword(s):  
Heat Transfer ◽  
Skin Friction ◽  
Heat Transfer Rate ◽  
Heat Generation ◽  
Transfer Rate ◽  
Fluid Velocity ◽  
Mhd Flow ◽  
Casson Fluid ◽  
Skin Friction Coefficient ◽  
Fluid Temperature

The dissipative flow of Casson fluid in the presence of heat generation and absorption is investigated. The flow is induced due to stretching wedge. The similarity transformations were used to to transformed the governing equations into ordinary differential equations. The transformed equations are solved numerically via Keller-box method. Numerical results for skin friction coefficient are compared and found in excellent agreement with published results. The effects of pertinent parameters on velocity and temperature profiles as well as skin friction and heat transfer rate are graphically displayed and analyzed. It is noticed that fluid velocity drops with the increase of Casson fluid and magnetic parameters when the wedge is stretching faster than free stream. It is also noted that the heat transfer rate at wedge surface reduces with the increase of Eckert number, whereas the reverse trend is noted in the case of Casson and radiation parameters. Moreover, with increasing of heat generation or absorption parameter the fluid temperature rises.

scholarly journals Assisted convective heat transfer and entropy generation in a solar collector filled with nanofluid

2016 ◽  
Vol 13 (2) ◽  
pp. 135-150
Author(s):  
R. Nasrin ◽  
M.A. Alim ◽  
M. Hasanuzzzaman
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Entropy Generation ◽  
Solar Collector ◽  
Transfer Rate ◽  
Volume Fraction ◽  
Bulk Temperature ◽  
Outlet Temperature ◽  
Nanoparticle Volume Fraction ◽  
Collector Efficiency

Heat transfer phenomena of flat plate solar collector filled with different nanofluids has been investigated numerically. Galerkin’s Finite Element Method is used to solve the problem. Heat transfer rate, average bulk temperature, average sub-domain velocity, outlet temperature, thermal efficiency, mean entropy generation and Bejan number has been investigated by varying the solid nanoparticle volume fraction of water/Cu, water/Ag and water/Cu/Ag nanofluids from 0% to 3%. It is found that the solid nanoparticle volume fraction has great effect on heat transfer phenomena. It is observed that the increases of the solid volume fraction (up to 2%) enhances the heat transfer rate and collector efficiency where after 2% the rate of change almost constant. Higher heat transfer rate and collector efficiency has been obtained 19% and 13% for water/Ag nanofluid respectively.

Numerical investigations of heat transfer around a hot block subject to a cross-flow and an extended jet hole using ternary hybrid nanofluids

2021 ◽  
pp. 095440622110498
Author(s):  
Bouziane Boudraa ◽  
Rachid Bessaïh
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Laminar Flow ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Volume Fraction ◽  
Impinging Jet ◽  
Hybrid Nanofluid ◽  
Maximum Heat

In the last few years, modern heat transfer technologies significantly improved to provide more efficient systems in industries. One of those technologies is cooling electronic components in laminar flow using water nanofluids, which is interesting. This research used a ternary hybrid nanofluid with various nanoparticle forms to conduct a numerical investigation of three-dimensional heat transfer and fluid flow over a heated block exposed to a horizontal flow and an impinging jet. The effects of several variables such as the Reynolds number ratio [Formula: see text], volume fraction of nanoparticles [Formula: see text], length of extended jet hole [Formula: see text], and the influence of the inclination angle of the impinging jet inlet [Formula: see text] on the fluid flow and heat transfer were examined. Using the Ansys-Fluent 14.5 program and under laminar flow conditions, the finite-volume method was applied with the help of the SIMPLE algorithm to solve continuity, momentum, and energy equations. Several characteristics are assessed, including velocity streamline, isotherm contours, Nusselt number contours, the average Nusselt number ([Formula: see text]), the friction factor [Formula: see text], and drop pressure [Formula: see text]. The findings of the current analysis revealed that adding an impinging jet can boost the heat transfer rate up to [Formula: see text] better than a non-impingement jet. Also, a significant enhancement in the heat transfer rate was obtained when growing one of these parameters α, [Formula: see text], and E. Moreover, the ternary hybrid nanofluid with different nanoparticle forms significantly boosts the heat transfer rate compared to the traditional nanofluid. The maximum heat transfer is reached as the velocity of the impinging jet rises. Inclining the angle of the impinging jet inlet with [Formula: see text] toward the channel inlet boosted the rate of heat transfer up to [Formula: see text] compared to the perpendicular impinging jet [Formula: see text]. A strong consensus has been reached with the theoretical and experimental findings found in the literature.

On the Accuracy of Beam-Averaged Interferometric Heat Transfer Measurements

2002 ◽  
Vol 124 (5) ◽  
pp. 978-982 ◽  
Author(s):  
D. Naylor
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Three Dimensional ◽  
Laser Interferometry ◽  
Fringe Field ◽  
Fluid Temperature ◽  
Object Beam ◽  
Ideal Gases

Laser interferometry can be used in a three dimensional temperature field to measure the average fluid temperature and heat transfer rate, integrated over the length of an experimental model. However, such measurements are inherently approximate when the surface temperature varies in the direction of the test/object beam. In this study an analysis is performed to determine the accuracy of beam-averaged heat transfer rate measurements made in ideal gases. Two analysis methods are considered. The first method is based on extrapolation of the near-wall temperature field to obtain the surface gradient. In the second method, the temperature gradient at the surface is obtained directly from the gradient of the fringe field. The results show that the intrinsic error in the measurements depends strongly upon the form and magnitude of the temperature variation in the light beam direction. Although the error in the measured heat transfer rate is shown to be small for many commonly encountered conditions, it can be greater than ten percent in extreme cases.

scholarly journals Dynamic and Static Investigation of Ground Heat Exchangers Equipped with Internal and External Fins

2020 ◽  
Vol 10 (23) ◽  
pp. 8689
Author(s):  
Atefeh Maleki Zanjani ◽  
Kobra Gharali ◽  
Armughan Al-Haq ◽  
Jatin Nathwani
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Heat Exchangers ◽  
Transfer Rate ◽  
Response Times ◽  
Fluid Temperature ◽  
Physical Conditions ◽  
Ground Heat Exchangers ◽  
Numerical Studies ◽  
Operation Costs

Using fins on the inner and outer surfaces of pipes is one method to improve the heat transfer rate of ground heat exchangers (GHEs), thereby reducing the borehole depth and construction and operation costs. Results of 3D numerical studies of simple and finned U-tubes with outer and inner fins are evaluated for GHEs under similar physical conditions. Dynamic and static simulations show the effects of longitudinal fins on the thermal performance of borehole heat exchangers (BHEs) and heat transfer rate between circulating fluid and soil around pipes, while the dynamic tests include short timescale and frequency response tests. The results indicate that the maximum fluid temperature change is about 2.9% in the external finned pipe and 11.3% in the internal finned pipe compared to the finless pipe. The effects of the inlet velocity on temperature profiles, the patterns of the velocity and temperature contours due to the borehole curvature and the response times of the systems under various frequencies are also investigated in detail.

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