Buoyancy Driven Flow, Heat Transfer and Entropy Generation Characteristics for Different Heater Geometries Placed in Cryogenic Liquid: A CFD Study

2021 ◽  
pp. 1-20
Author(s):  
Someshwar Ade ◽  
Sushil Rathore
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Entropy Generation ◽  
Heat Generation ◽  
Average Nusselt Number ◽  
Cryogenic Liquid ◽  
Heat Generation Rate ◽  
Heat Transfer Characteristics ◽  
Flow And Heat Transfer

Abstract The present work reports 3D computational study of buoyancy driven flow and heat transfer characteristics for a localized heater (analogous to superconductor) submerged in cryogenic liquid nitrogen in an enclosure. Seven different heater geometries are considered and the effect of heater geometry on flow and heat transfer characteristics are illustrated. The heater is generating heat at a constant rate (W/m3). Continuity, momentum and energy equations are solved using finite volume method. Liquid flow and heat transfer features are demonstrated with the help of velocity vector and temperature contours. Rayleigh number, average Nusselt number, maximum vertical velocity of fluid flow, average velocity of fluid flow are the parameters which are considered for comparing seven different geometries of heater. Additionally, an analysis of the entropy generation owing to transfer of heat and friction due to fluid flow are reported. Furthermore, the dependency of average Nusselt number, maximum velocity of fluid, entropy generation owing to transfer of heat and fluid friction as a function of heat generation rate is illustrated graphically. The results of this study indicate that heater geometry can considerably affect the transfer of heat, fluid flow features and entropy generation under same heat generation rate in the heater. Highest average Nusselt number on heater surface is obtained when heater geometry is circular; whereas lowest value of total entropy generation in the domain is obtained when heater geometry is equilateral triangle.

scholarly journals Investigation of fluid flow and heat transfer characteristics for a thermal anti-icing system of a high-altitude and long-endurance UAV

2021 ◽  
Vol 37 ◽  
pp. 467-483
Author(s):  
Jen-Chieh Cheng ◽  
You-Ming Chen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Average Nusselt Number ◽  
Heat Transfer Characteristics ◽  
Maximum Enhancement ◽  
Hot Air ◽  
Flow And Heat Transfer ◽  
Periodic Model

ABSTRACT This research performs a three-dimensional simulation to investigate the fluid flow and heat transfer characteristics for hot-air jets impinging on the wing leading-edge surface. Both the periodic model and the whole model are proposed to examine the thermal anti-icing performance for hot air ejecting from a piccolo tube onto the impinging surface. The results show that, for the periodic model, the enhancement of the average Nusselt number can be up to 94.4%, and the enhancement of the average heat flux is up to 29.7% for 100 ≦ uj ≦ 350 m/s and 300 ≦ Tj ≦ 550 K when compared with the results of the basic case of uj = 200 m/s and Tj = 450 K. The maximum enhancement of the $\overline {Nu} $ is 62.3% as the spacing decreases from Sn = 8 to Sn = 4 and the optimum Numax and $\overline {Nu} $ occur at Si = 5 and Si = 6 for the single-array holes with 3 ≦ Si ≦ 7 and 4 ≦ Sn ≦ 8. In addition, the θh for maximum $\overline {{{Nu}}} $ is 10° and the maximum enhancement of the $\overline {{{Nu}}} $ is ∼15.7% for double-array holes and staggered-array holes as compared with single-array holes. In addition, the nonuniformity of Nusselt number and heat flux distributions are significantly improved. For the whole model, the maximum enhancement of the average Nusselt number is ∼7.5% and the optimum configuration is θh = 40°, for cases with La = 60, Dp = 8, $\dot{m}$ = 0.15 kg/s, Si = 6, 1 ≦ Nh ≦ 5, 10 ≦ Sn ≦ 30 and 10° ≦ θh ≦ 60°.

scholarly journals Free convection of a nanofluid in a square cavity with a heat source on the bottom wall and partially cooled from sides

2014 ◽  
Vol 18 (suppl.2) ◽  
pp. 283-300 ◽  
Author(s):  
Mostafa Mahmoodi ◽  
Arani Abbasian ◽  
Sebdani Mazrouei ◽  
Saeed Nazari ◽  
Mohammad Akbari
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Rayleigh Number ◽  
Average Nusselt Number ◽  
Volume Fraction ◽  
Heat Sinks ◽  
Square Cavity ◽  
Flow And Heat Transfer ◽  
Rayleigh Numbers

The problem of free convection fluid flow and heat transfer in a square cavity with a flush mounted heat source on its bottom wall and two heat sinks on its vertical side walls has been investigated numerically. Via changing the location of the heat sinks, six different arrangements have been generated. The cavity was filled with Cu-water nanofluid. The governing equations were discretized using the finite volume method and SIMPLER algorithm. Using the developed code, a parametric study was undertaken, and effects of Rayleigh number, arrangements of the heat sinks and volume fraction of the nanoparticles on fluid flow and heat transfer inside the cavity were investigated. Also for the middle-middle heat sinks arrangement, capability of five different water based nanofluids on enhancement of the rate of heat transfer was examined and compared. From the obtained results it was found that the average Nusselt number, for all six different arrangements of the heat sinks, was an increasing function of the Rayleigh number and the volume fraction of the nanoparticles. Also it was found that at high Rayleigh numbers, maximum and minimum average Nusselt number occurred for middle-middle and top-bottom arrangement, respectively. Moreover it was found that for the middle-middle arrangement, at high Rayleigh numbers, maximum and minimum rate of heat transfer was obtained by Cu-water and TiO2-water nanofluids respectively.

scholarly journals Mixed convection inside nanofluid filled rectangular enclosures with moving bottom wall

2011 ◽  
Vol 15 (3) ◽  
pp. 889-903 ◽  
Author(s):  
Mostafa Mahmoodi
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Mixed Convection ◽  
Richardson Number ◽  
Average Nusselt Number ◽  
Volume Fraction ◽  
Flow And Heat Transfer ◽  
Simpler Algorithm ◽  
Horizontal Wall

The mixed convection fluid flow and heat transfer in lid-driven rectangular enclosures filled with the Al2O3-water nanofluid is investigated numerically. The left and the right vertical walls as well as the top horizontal wall of the enclosure are maintained at a constant cold temperature Tc. The bottom horizontal wall of the enclosure, which moves from left to right, is kept at a constant hot temperature Th, with Th>Tc. The governing equations written in terms of the primitive variables are solved using the finite volume method and the SIMPLER algorithm. Using the developed code, a parametric study is performed and the effects of the Richardson number, the aspect ratio of the enclosure and the volume fraction of the nanoparticles on the fluid flow and heat transfer inside the enclosure are investigated. The results show that at low Richardson numbers, a primary counterclockwise vortex is formed inside the enclosure. More over it is found that for the range of the Richardson number considered, 10-1-101, the average Nusselt number of the hot wall, increases with increasing the volume fraction of the nanoparticles. Also it is observed that the average Nusselt number of the hot wall of tall enclosures is more that to that of the shallow enclosures.

Numerical investigation of fluid flow and heat transfer characteristics in novel circular wavy microchannel

2018 ◽  
Vol 233 (5) ◽  
pp. 954-966 ◽  
Author(s):  
Valaparla Ranjith Kumar ◽  
Karthik Balasubramanian ◽  
K Kiran Kumar ◽  
Nikhil Tiwari ◽  
Kanishk Bhatia
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Constant Heat Flux ◽  
Heat Transfer Characteristics ◽  
Number Range ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Centrifugal Instability ◽  
Transfer Behavior

In this study, the fluid flow and heat transfer behavior in a novel circular wavy microchannel design is numerically examined and compared with a sinusoidal wavy microchannel. The numerical studies were carried out in the Reynolds number range of 100–300 under a constant heat flux wall boundary condition. The sinusoidal profile has a continuously varying curvature, which peaks at the crests and troughs, and diminishes to naught at each section at the middle of adjacent crests and troughs. On the other hand, the circular profile has a curvature constant in magnitude (and alternating in direction). Heat transfer in wavy microchannels is enhanced by vortex flow induced by centrifugal instability, which in turn depends on the curvature of fluid channel profile. The sinusoidal wavy microchannel has a curvature continuously varying in a large range results in large fluctuations of Nusselt number, while the Nusselt number in the circular channel has smaller fluctuations. Hence, heat transfer performance of the circular wavy microchannel is higher than that of the sinusoidal wavy microchannel. Velocity vectors, velocity contours, and temperature contours are presented to aid the explanation of hydrodynamic and heat transfer characteristics of fluid flow in the novel circular wavy microchannels. The Nusselt number and pressure drop along the channel are also compared with the sinusoidal wavy microchannel using a performance factor.

scholarly journals Effect of baffle shape in heat transfer for jet impingement on a solid block

2018 ◽  
Vol 240 ◽  
pp. 01025
Author(s):  
Muthukannan Marimuthu ◽  
Uthayakumar ◽  
Rajesh Kanna P ◽  
Paweł Ocłoń ◽  
Jan Taler ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Jet Impingement ◽  
Reattachment Length ◽  
Heat Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Wide Range ◽  
Solid Block

The numerical solution solution is obtained for fluid flow and heat transfer in a confined impinging slot on a solid block with the presence of baffles. In order to consider the effect of baffle shape the rectangular and semi circular baffles are considered and for the effect for Reynolds number the Reynolds number is varied from 100 to 300 with the step of 50. The present study reveals the vital impact of Baffle shape and Reynolds number (Re) on the fluid flow and heat transfer characteristics over a wide range. It is finally added that the presence of baffle improves the Nusselt number. The Nusselt number increases with the increase of Reynolds number. The present study proved that, the primary peak of Nusselt number occurs nearer to the reattachment length. The secondary peak of Nusselt number occurs nearer to the baffle. It is observed that for semi circle baffle the velocity attains maximum one compared to rectangular baffle.

Numerical Study on Flow and Heat Transfer Characteristics of Jet Impingement

2011 ◽  
Author(s):  
Xinjun Wang ◽  
Rui Liu ◽  
Xiaowei Bai ◽  
Jinling Yao
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Average Nusselt Number ◽  
Jet Impingement ◽  
Target Surface ◽  
Heat Transfer Characteristics ◽  
Impingement Cooling ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer

A mathematical model used for studying jet impingement cooling characteristics is established, and the rationality of the calculation model and method is confirmed by the experimental data. The CFX software is used to numerically simulate the jet impingement cooling characteristics on a gas turbine blade. The effects of various parameters, such as the arrays of impinging nozzles, the jet Reynolds number, the jet-to-jet distance, the ratio of nozzle-to-surface spacing to jet diameter H/d, and the radius of curvature of the target surface, on the flow and heat transfer characteristics of a impingement cooling process are studied. The results indicate that the impingement jets can make complex vortex in the cooling channel, the flow boundary layer is extremely thin and highly turbulent. Underneath each impingement nozzle, there will appear a low temperature area and a peak of Nusselt number on the impingement target surface, the distribution of temperature and Nusselt number on the target surface are associated with arrangement of impingement nozzles. The average Nusselt number of the in-line arrangement nozzles is higher than that of the staggered arrangement ones. With the increasing of jet Reynolds number, the velocity impinging on the target surface and Nusselt number increase. However, heat transfer of impingement cooling on target surface is not sensitive to the jet nozzles distance; the velocity impinging on the target surface and Nusselt number decrease with the increasing of the H/d value. For the curved target surface cases, the average Nusselt number of the target surface and the effect of heat transfer decreased with the increasing of curvature radius R.

Numerical Investigation of Fully Developed Fluid Flow and Heat Transfer in Double-Trapezoidal Microchannels

2013 ◽  
Author(s):  
Mostafa Shojaeian ◽  
Ali Koşar
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Aspect Ratio ◽  
Heat Transfer Characteristics ◽  
Constant Wall Temperature ◽  
Base Angle ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Poiseuille Number

Fully developed fluid flow and heat transfer characteristics of double-trapezoidal microchannels with constant wall temperature are numerically investigated in the slip flow regime. The governing equations are solved together with the appropriate boundary conditions using finite volume method. The effect of rarefaction on Poiseuille number, Po, and Nusselt number, Nu, is studied for Knudsen numbers, Kn, varying from 0 to 0.1. The effects of base angle, B, and aspect ratio, A, on the fluid flow and the heat transfer characteristics are also examined. The results reveal that the rarefaction and the cross-section shapes have prominent effects on these characteristics of double-trapezoidal microchannels. According to the results, the Poiseuille number decreases with increasing Kn, while the values of the Nusselt number completely depend on the impacts of the rarefaction and the fluid-surface interaction. Po and Nu decrease with aspect ratio for A<1, while the effect of aspect ratio on Po and Nu becomes unclear for A>1. Moreover, an increase in the base angle has a positive effect on Po and Nu, however this increasing trend is less pronounced for B > 60 ° and A < 1.67.

Flow and Heat Transfer Characteristics of Single Jet Impinging on Dimpled Surface

2013 ◽  
Vol 135 (5) ◽  
Author(s):  
Yonghui Xie ◽  
Ping Li ◽  
Jibing Lan ◽  
Di Zhang
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Average Nusselt Number ◽  
Heat Transfer Process ◽  
Flow Structures ◽  
Relative Depth ◽  
Heat Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Baseline Case ◽  
Single Jet

Based on combined particle image velocimetry (PIV) and numerical simulation, the flow and heat transfer characteristics of a single jet impinging on a dimpled surface for Dj/D = 0.318, 0.5, 1.045; δ/D = 0.1, 0.2, 0.3; Rej = 5000, 10,000, 23,000, were investigated for the first time. The distance between jet nozzle and plate was fixed and equal to H/D = 2. The results show that the flow structures of the single jet impingement with dimpled target surface can be summarized into three typical conceptual flow structures. Particularly, the third flow structure in the form of a large toroidal vortex bound up with the dimple is the result of the centrifugal force of the flow deflection at the stagnation region and spherical centrifugal force of the deep dimple surface. The heat transfer area increases when the dimple relative depth increases. For the cases of Dj/D = 0.318 and 0.5, the area increasing dominate the heat transfer process, and the average Nusselt number increases with the increasing of dimple relative depth. For the cases with Dj/D = 1.045, the local Nusselt number reduction dominate the heat transfer process, the average Nusselt number decreases with the increasing of dimple relative depth. The average Nusselt number of the Dj/D = 0.318 and 0.5 cases is larger than the baseline case, while those of the Dj/D = 1.045 cases are smaller than the baseline case. Furthermore, the correlative expressions of the local Nusselt number, stagnation points Nusselt number and average Nusselt number are obtained.

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