An Experimental Study on Mixed Convection in a Horizontal Rectangular Channel Heated From a Side

2000 ◽  
Vol 122 (4) ◽  
pp. 701-707 ◽  
Author(s):  
C. Gau ◽  
Y. C. Jeng ◽  
C. G. Liu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Mixed Convection ◽  
Rectangular Channel ◽  
Side Wall ◽  
Heated Wall ◽  
Channel Cross Section ◽  
Parallel Plates ◽  
Nusselt Numbers ◽  
Buoyancy Parameter

Experiments are performed to study the mixed convection flow and heat transfer in a horizontal rectangular channel heated from a side. The channel is made of two vertical parallel plates with one of the plates heated uniformly and the opposite plate well insulated. The gap between the parallel plates is small and the height to gap ratio of the channel cross section is 6.67. Both flow visualization and the heat transfer along the heated wall are measured. The Reynolds number ranges from 317 to 2000, the buoyancy parameter, Gr/Re2, from 0 to 20000 and Pr of the air flow is 0.7. Flow structure inside the channel is visualized by injecting smoke at the inlet flowing along the heated side wall. The heated buoyant flow accumulates in the upper region of the channel, which grows in size as the buoyancy parameter increases. The accumulated flow is thermally stable and has a slower motion which can reduce the heat transfer enhancement by the buoyancy force. The effect of the Reynolds number and the buoyancy parameter on the heat transfer is presented and discussed. Comparisons of the Nusselt numbers with the case of the vertical channel flow and the prediction similar to the case of a horizontal flow through a heated vertical plate are also made. The normalized Nusselt numbers are found in proportion to the buoyancy parameter, correlations of the heat transfer data in terms of this parameter have been very successful. [S0022-1481(00)01404-3]

scholarly journals Thermal Performance Enhancement of the Mixed Convection between two Parallel Plates by using Triangular Ribs

2021 ◽  
Vol 26 (2) ◽  
pp. 11-30
Author(s):  
K.A. Jehhef ◽  
F.A. Badawy ◽  
A.A. Hussein
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Mixed Convection ◽  
Performance Enhancement ◽  
Stokes Equations ◽  
Channel Width ◽  
Heated Wall ◽  
Channel Height ◽  
Parallel Plates

Abstract This paper aims to investigate the mixed convection between two parallel plates of a vertical channel, in the presence of a triangular rib. The non-stationary Navier-Stokes equations were solved numerically in a two-dimensional formulation for the low Reynolds number for the laminar air flow regime. Six triangular ribs heat-generating elements were located equidistantly on the heated wall. The ratio of the ribs to the channel width is varied (h / H = 0.1, 0.2, 0.3 and 0.4) to study the effect of ribs height effects, the ratio of the channel width to the ribs height is fixed constant at (H / w = 2) and the ratio of the channel height to the ribs pitch is fixed at (W/p=10). The influence of the Reynolds number that ranged from 68 to 340 and the Grashof number that ranged from 6.6 ×103 to 2.6 ×104 as well as the Richardson number chosen (1.4, 0.7, 0.4 and 0.2) is studied. The numerical results are summarized and presented as the profile of the Nusselt number, the coefficient of friction, and the thermal enhancement factor. The contribution of forced and free convection to the total heat transfer is analyzed. Similar and distinctive features of the behavior of the local and averaged heat transfer with the variation of thermal gas dynamic and geometric parameters are investigated in this paper. The results showed that the Nusselt number and friction factor increased by using the attached triangular ribs, especially when using the downstream ribs. Also, the results revealed that the Nusselt number increased by increasing the ratio of the ribs to the channel width.

Spatially Resolved Heat Transfer and Friction Factors in a Rectangular Channel With 45-Deg Angled Crossed-Rib Turbulators

2003 ◽  
Vol 125 (3) ◽  
pp. 575-584 ◽  
Author(s):  
P. M. Ligrani ◽  
G. I. Mahmood
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Rectangular Channel ◽  
Test Surface ◽  
Spatially Resolved ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Smooth Channel ◽  
Rib Turbulators

Spatially resolved Nusselt numbers, spatially averaged Nusselt numbers, and friction factors are presented for a stationary channel with an aspect ratio of 4 and angled rib turbulators inclined at 45 deg with perpendicular orientations on two opposite surfaces. Results are given at different Reynolds numbers based on channel height from 10,000 to 83,700. The ratio of rib height to hydraulic diameter is .078, the rib pitch-to-height ratio is 10, and the blockage provided by the ribs is 25% of the channel cross-sectional area. Nusselt numbers are given both with and without three-dimensional conduction considered within the acrylic test surface. In both cases, spatially resolved local Nusselt numbers are highest on tops of the rib turbulators, with lower magnitudes on flat surfaces between the ribs, where regions of flow separation and shear layer reattachment have pronounced influences on local surface heat transfer behavior. The augmented local and spatially averaged Nusselt number ratios (rib turbulator Nusselt numbers normalized by values measured in a smooth channel) vary locally on the rib tops as Reynolds number increases. Nusselt number ratios decrease on the flat regions away from the ribs, especially at locations just downstream of the ribs, as Reynolds number increases. When adjusted to account for conduction along and within the test surface, Nusselt number ratios show different quantitative variations (with location along the test surface), compared to variations when no conduction is included. Changes include: (i) decreased local Nusselt number ratios along the central part of each rib top surface as heat transfer from the sides of each rib becomes larger, and (ii) Nusselt number ratio decreases near corners, where each rib joins the flat part of the test surface, especially on the downstream side of each rib. With no conduction along and within the test surface (and variable heat flux assumed into the air stream), globally-averaged Nusselt number ratios vary from 2.92 to 1.64 as Reynolds number increases from 10,000 to 83,700. Corresponding thermal performance parameters also decrease as Reynolds number increases over this range, with values in approximate agreement with data measured by other investigators in a square channel also with 45 deg oriented ribs.

Computer Simulation of Mixed Convection of Alumina-Deionized Water Nanofluid Over Four In-Line Electronic Chips Embedded in One Wall of a Vertical Rectangular Channel

2019 ◽  
Vol 12 (4) ◽  
Author(s):  
Nalla Ramu ◽  
P. S. Ghoshdastidar
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Mixed Convection ◽  
Transfer Coefficient ◽  
Base Fluid ◽  
Rectangular Channel ◽  
Working Fluid ◽  
Al2o3 Nanoparticles ◽  
Enhancement Factors

Abstract This paper presents a computational study of mixed convection cooling of four in-line electronic chips by alumina-deionized (DI) water nanofluid. The chips are flush-mounted in the substrate of one wall of a vertical rectangular channel. The working fluid enters from the bottom with uniform velocity and temperature and exits from the top after becoming fully developed. The nanofluid properties are obtained from the past experimental studies. The nanofluid performance is estimated by computing the enhancement factor which is the ratio of chips averaged heat transfer coefficient in nanofluid to that in base fluid. An exhaustive parametric study is performed to evaluate the dependence of nanoparticle volume fraction, diameter of Al2O3 nanoparticles in the range of 13–87.5 nm, Reynolds number, inlet velocity, chip heat flux, and mass flowrate on enhancement in heat transfer coefficient. It is found that nanofluids with smaller particle diameters have higher enhancement factors. It is also observed that enhancement factors are higher when the nanofluid Reynolds number is kept equal to that of the base fluid as compared with the cases of equal inlet velocities and equal mass flowrates. The linear variation in mean pressure along the channel is observed and is higher for smaller nanoparticle diameters.

Convective Heat Transfer From Heated Extended Surfaces With a Confined Slot Jet Impingement

2004 ◽  
Author(s):  
L. K. Liu ◽  
M. C. Wu ◽  
C. J. Fang ◽  
Y. H. Hung
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Reynolds Number ◽  
Mixed Convection ◽  
Average Nusselt Number ◽  
Jet Impingement ◽  
Separation Distance ◽  
Nusselt Numbers ◽  
Transfer Behavior ◽  
Extended Surfaces

A series of experimental investigations with stringent measurement methods on the studies related to mixed convection from the horizontally confined extended surfaces with a slot jet impingement have been successfully conducted. The relevant parameters influencing mixed convection performance due to jet impingement and buoyancy include the Grashof number, ratio of jet separation distance to nozzle width, ratio of extended surfaces height to nozzle width and jet Reynolds number. The range of these parameters studied are Grs = 3.77 × 105 – 1.84 × 106, H/W = 1–10, Hs/W = 0.74–3.40 and Re = 63–1383. In the study, the heat transfer behavior on the extended surfaces with confined slot jet impingement such as the temperature distribution, local and average Nusselt numbers on the extended surfaces has been systematically explored. The results manifest that the effect of steady-state Grashof number on heat transfer behavior such as stagnation, local and average Nusselt number is not significant; while the heat transfer performance increases with decreasing jet separation distance or with increasing extended surface height and jet Reynolds number. Besides, two new correlations of local and average Nusselt numbers in terms of H/W, Hs/W and Re are proposed for the cases of extended surfaces. A satisfactory agreement is achieved between the results predicted by these correlations and the experimental data. Finally, a complete composite correlation of steady-state average Nusselt number for mixed convection due to jet impingement and buoyancy is proposed. The comparison of the predictions evaluated by this correlation with all the present experimental data is made. The maximum and average deviations of the predictions from the experimental data are 7.46% and 2.87%, respectively.

Mixed Convective Heat Transfer From a Simulated Microchip to Liquid Flows in a Horizontal Rectangular Channel

1991 ◽  
Vol 113 (3) ◽  
pp. 309-312 ◽  
Author(s):  
Y. Chin ◽  
C. F. Ma ◽  
X. Q. Gu ◽  
L. Xu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rayleigh Number ◽  
Mixed Convection ◽  
Transfer Process ◽  
Rectangular Channel ◽  
Heat Transfer Process ◽  
Flow Directions ◽  
Liquid Flows ◽  
Hot Surface

Mixed convection from a small heater (5mm × 5mm) to liquid flows in a horizontal rectangular channel is investigated experimentally. The results of three cases in which the buoyancy is normal to the liquid flow directions — hot surface facing upward, facing downward and vertically attached to one wall of the channel — are presented. Correlations are also provided to predict the mixed convective effects in the range 100 < ReL < 4000. The results demonstrated that both the Reynolds number ReL and the modified Rayleigh number RaL* pronouncedly dominate the heat transfer process. In all of the above cases, heat transfer was enhanced over that of forced convection.

Convective Heat Transfer From a Stationary or Rotating MCM Disk With a Unconfined Round Jet Impingement

2005 ◽  
Author(s):  
Y. M. Kuo ◽  
C. J. Fang ◽  
M. C. Wu ◽  
C. H. Peng ◽  
Y. H. Hung
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Steady State ◽  
Mixed Convection ◽  
Jet Impingement ◽  
Disk Surface ◽  
Separation Distance ◽  
Heat Flux Distribution ◽  
Disk Rotation ◽  
Nusselt Numbers

A series of experimental investigations with stringent measurement methods on the studies related to fluid flow and transient mixed convection from a horizontally unconfined stationary or rotating ceramic-based MCM disk with unconfined jet impingement have been successfully conducted. The relevant parameters influencing fluid flow and heat transfer performance are (1) mixed convection due to jet impingement and buoyancy: steady-state Grashof number, jet Reynolds number, and ratio of jet separation distance to nozzle diameter; and (2) mixed convection due to jet impingement, disk rotation and buoyancy: steady-state Grashof number, jet Reynolds number (Rej), rotational Reynolds number (Rer), ratio of jet separation distance to nozzle diameter (H/d). The thermal behavior explored includes the transient temperature distribution on the MCM disk surface, transient heat flux distribution of input power, transient convective heat flux distribution of chips, and transient chip and average heat transfer characteristics on the MCM disk surface. Besides, two new correlations of transient stagnation and average Nusselt numbers in terms of Rej, H/d and t are presented for the cases of stationary MCM disk. For the cases of rotating MCM disk, a new empirical correlation to classify two regimes of heat transfer modes such as disk rotation mode and jet impingement mode is presented; and a complete composite correlation of steady-state average Nusselt number for mixed convection due to jet impingement, disk rotation and buoyancy is proposed. As compared with the steady-state results, if the transient chip and average heat transfer behaviors may be considered as a superposition of a series of quasi-steady states, the transient chip and average Nusselt numbers in all the present transient experiments can be properly predicted by the existing steady-state correlations when t > 6 min in the power-on transient period.

scholarly journals Effect of Inlet and Outlet Locations on Transverse Mixed Convection Inside a Vented Enclosure

1970 ◽  
Vol 36 ◽  
pp. 27-37 ◽  
Author(s):  
Sumon Saha ◽  
Md. Tofiqul Islam ◽  
Mohammad Ali ◽  
Md. Arif Hassan Mamun ◽  
M Quamrul Islam
Keyword(s):  
Heat Transfer ◽  
Finite Element Method ◽  
Reynolds Number ◽  
Finite Element ◽  
Mixed Convection ◽  
Vertical Wall ◽  
Flow Fields ◽  
Temperature Fields ◽  
Heated Wall ◽  
Element Method

Transverse mixed convection is studied numerically in a vented enclosure with constant heat flux from uniformly heated bottom wall. An external airflow enters the enclosure through an opening in one vertical wall and exits from another opening in the opposite wall. The two-dimensional mathematical model includes the system of four partial differential equations of continuity, linear momentum and energy, solved by the finite element method. Flow fields are investigated by numerical simulations for air flowing with a Reynolds number in the range 50 ≤ Re ≤ 1000, for Richardson numbers: 0 ≤ Ri ≤ 10. Four different locations of inlet and outlets are introduced to analyze the effect of heat transfer in terms of velocity and temperature fields within the enclosure. The computational results show that the location of inlet and outlets alters significantly the temperature distribution in the flow fields and the heat transfer across the heated wall of the cavities. Empirical correlation is developed for relations using Nusselt number, Reynolds number and Richardson number, based on the enclosure height.   Keywords: Mixed convection, finite element method, vented enclosure, Richardson number.Journal of Mechanical Engineering Vol.36 Dec. 2006 pp.27-37DOI = 10.3329/jme.v36i0.808

scholarly journals Heat Transfer Around Sharp 180 Degree Turns in Smooth Rectangular Channels

1985 ◽  
Author(s):  
D. E. Metzger ◽  
M. K. Sahm
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Forced Convection ◽  
Cross Section ◽  
Rectangular Cross Section ◽  
Side Wall ◽  
Bottom Wall ◽  
Channel Depth ◽  
Nusselt Numbers ◽  
Rectangular Channels

Measured Nusselt numbers are presented for forced convection within and around sharp 180 degree turns in smooth channels of rectangular cross section. Separately determined top wall, bottom wall, and side wall values are presented individually along with azimuthal averages. The geometry of the channels and connecting turn is characterized by parameters W*, the ratio of upstream and downstream channel widths; D*, the non-dimensional channel depth; and H*, the non-dimensional clearance at the tip of the turn. Results from nine combinations of these parameters are presented at several values of channel Reynolds number to illustrate the effect of turn geometry on the heat transfer distributions.

Spatially-Resolved Heat Transfer and Flow Structure in a Rectangular Channel With 45° Angled Rib Turbulators

2002 ◽  
Author(s):  
G. I. Mahmood ◽  
P. M. Ligrani ◽  
S. Y. Won
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Flow Structure ◽  
Channel Cross Section ◽  
Cross Sectional ◽  
Spatially Resolved ◽  
Nusselt Numbers ◽  
Smooth Channel ◽  
Rib Turbulators

Spatially-resolved Nusselt numbers and flow structure are presented for a stationary channel with an aspect ratio of 4 and angled rib turbulators inclined at 45° with perpendicular orientations on two opposite surfaces. The flow structure results include time-averaged distributions of streamwise velocity and total pressure, surveyed over flow cross-sectional planes, as well as flow visualization images and friction factors. Results are given at different Reynolds numbers based on channel height from 270 to 90,000. The ratio of rib height to hydraulic diameter is .078, the rib pitch-to-height ratio is 10, and the blockage provided by the ribs is 25 percent of the channel cross-sectional area. Spatially-resolved local Nusselt numbers are highest on tops of the rib turbulators, with lower magnitudes on flat surfaces between the ribs, where regions of flow separation and shear layer re-attachment have pronounced influences on local surface heat transfer behavior. Also important are intense, highly unsteady secondary flows and vortex pairs, which increase secondary advection and turbulent transport over the entire channel cross-section. The resulting augmented local and spatially-averaged Nusselt number ratios (rib turbulator Nusselt numbers normalized by values measured in a smooth channel) generally increase on the rib tops as Reynolds number increases. Nusselt number ratios decrease on the flat regions away from the ribs, especially at locations just downstream of the ribs, as Reynolds number increases. Globally-averaged Nusselt number ratios vary from 3.36 to 2.82 as Reynolds number increases from 10,000 to 90,000. Thermal performance parameters also decrease somewhat as Reynolds number increases over this range, with values in approximate agreement with, or slightly higher than 60° continuous rib data measured by other investigators in a square channel.

Heat Transfer Around Sharp 180-deg Turns in Smooth Rectangular Channels

1986 ◽  
Vol 108 (3) ◽  
pp. 500-506 ◽  
Author(s):  
D. E. Metzger ◽  
M. K. Sahm
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Forced Convection ◽  
Cross Section ◽  
Rectangular Cross Section ◽  
Side Wall ◽  
Bottom Wall ◽  
Channel Depth ◽  
Nusselt Numbers ◽  
Rectangular Channels

Measured Nusselt numbers are presented for forced convection within and around sharp 180-deg turns in smooth channels of rectangular cross section. Separately determined top wall, bottom wall, and side wall values are presented individually along with azimuthal averages. The geometry of the channels and connecting turn is characterized by the parameters W*, the ratio of upstream and downstream channel widths; D*, the nondimensional channel depth; and H*, the nondimensional clearance at the tip of the turn. Results from nine combinations of these parameters are presented at several values of channel Reynolds number to illustrate the effect of turn geometry on the heat transfer distributions.

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