The Effects of Nozzle Diameter on Impinging Jet Heat Transfer and Fluid Flow

2003 ◽  
Vol 126 (4) ◽  
pp. 554-557 ◽  
Author(s):  
Dae Hee Lee ◽  
Jeonghoon Song ◽  
Myeong Chan Jo
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Nozzle Diameter ◽  
Uniform Heat Flux ◽  
Intensity Level ◽  
Plate Surface ◽  
Heat Transfer Augmentation ◽  
Nusselt Numbers ◽  
The Mean ◽  
Mean Time

The effects of nozzle diameter on heat transfer and fluid flow are investigated for a round turbulent jet impinging on a flat plate surface. The flow at the nozzle exit has a fully developed velocity profile. A uniform heat flux boundary is created at the plate surface by using gold film Intrex, and liquid crystals are used to measure the plate surface temperature. The experiments are performed for the jet Reynolds number (Re) of 23,000, with a dimensionless distance between the nozzle and plate surface L/d ranging from 2 to 14 and a nozzle diameter (d) ranging from 1.36 to 3.40 cm. The results show that the local Nusselt numbers increase with the increasing nozzle diameter in the stagnation point region corresponding to 0⩽r/d⩽0.5. This may be attributed to an increase in the jet momentum and turbulence intensity level with the larger nozzle diameter, which results in the heat transfer augmentation. In the mean time, the effect of the nozzle diameter on the local Nusselt numbers is negligibly small at the wall jet region corresponding to r/d>0.5.

Numerical Investigation of Heat Transfer in Rectangular Microchannels Under H2 Boundary Condition During Developing and Fully Developed Laminar Flow

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
V. V. Dharaiya ◽  
S. G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Flux ◽  
Fluid Flow ◽  
Microfluidic Devices ◽  
Transport Processes ◽  
Uniform Heat Flux ◽  
Data Set ◽  
Nusselt Numbers ◽  
Aspect Ratios

Study of fluid flow characteristics at microscale is gaining importance with shrinking device sizes. Better understanding of fluid flow and heat transfer in microchannels will have important implications in electronic chip cooling, heat exchangers, MEMS, and microfluidic devices. Due to short lengths employed in microchannels, entrance header effects can be significant and need to be investigated. In this work, three dimensional model of microchannels, with aspect ratios (α = a/b) ranging from 0.1 to 10, are numerically simulated using CFD software tool fluent. Heat transfer effects in the entrance region of microchannel are presented by plotting average Nusselt number as a function of nondimensional axial length x*. The numerical simulations with both circumferential and axial uniform heat flux (H2) boundary conditions are validated for existing data set for four wall heat flux case. Large numerical data sets are generated in this work for rectangular cross-sectional microchannels with heating on three walls, two opposing walls, one wall, and two adjacent walls under H2 boundary condition. This information can provide better understanding and insight into the transport processes in the microchannels. Although the results are seen as relevant in microscale applications, they are applicable to any sized channels. Based on the numerical results obtained for the whole range, generalized correlations for Nusselt numbers as a function of channel aspect ratio are presented for all the cases. The predicted correlations for Nusselt numbers can be very useful resource for the design and optimization of microchannel heat sinks and other microfluidic devices.

Numerical Investigation on Thermal and Fluid Dynamic Behavior of Laminar Slot-Jet Impinging on a Surface at Uniform Heat Flux in a Confined Porous Medium in Local Thermal Non-Equilibrium Conditions

2014 ◽  
Author(s):  
Bernardo Buonomo ◽  
Oronzio Manca ◽  
Sergio Nardini ◽  
Guy Lauriat
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Porous Medium ◽  
Numerical Investigation ◽  
Forced Flow ◽  
Uniform Heat Flux ◽  
Nusselt Numbers ◽  
Uniform Heat ◽  
The Mean ◽  
Non Equilibrium

A numerical investigation on a single slot jet impinging in a porous parallel-plate channel containing an air-saturated high permeability porous medium is accomplished. The wall opposite the slot jet is partially heated at uniform heat flux and the buoyancy effects are taken into account. The fluid flow is assumed two dimensional, laminar and steady. The porous medium is modeled using the Brinkman–Forchheimer-extended Darcy model and the Boussinesq approximation. The local thermal non-equilibrium (LTNE) hypothesis is invoked. The results are discussed in terms of streamlines, fluid and solid phase temperature fields, wall temperature profiles and local and average Nusselt numbers. The porous medium allows a more significant heat transfer close to the end of the heated part of the plate. For low Peclet numbers, forced flow and natural convection are opposite and the mean Nusselt number shows a decrease in heat transfer, whereas they are aiding for high Peclet numbers. Porosity effects on the mean Nusselt numbers were found weak.

scholarly journals Laminar Forced Convective Heat Transfer and Fluid Flow in a Finned Cylindrical Annulus

2017 ◽  
Vol 2 (1) ◽  
Author(s):  
Isaac K Adegun ◽  
Olalekan A Olayemi ◽  
Temidayo S Jolayemi ◽  
Oladapo T Ogunbodede
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Energy Transport ◽  
Numerical Study ◽  
Bulk Temperature ◽  
Uniform Heat Flux ◽  
Heat Transfer Augmentation ◽  
Cylindrical Annulus ◽  
Flow Variables

The purpose of this paper is to numerically investigate the effects of some geometric parameters and flow variables on heat transfer augmentation in annuli with equi-spaced internal longitudinal fins along the external walls. A fully developed flow and a constant thermal boundary condition of uniform heat flux at the walls of the pipe were assumed. Continuity, momentum and energy transport equations were adopted for the solutions of the problem. A Q-BASIC code was written based on the finite difference scheme generated. Numerical experiments were conducted to ascertain the effects of Reynolds number Re, radius ratio, R.R, Prandtl number Pr, fin height H, and pipe inclination, on the rate of heat transfer and fluid flow. The results obtained show that for 50 ≤ Re ≤ 500, total Nusselt number NuT increases with increase in Re while for Re > 500, there was no significant increase in NuT. Nusselt number, average velocity and bulk temperature of the fluid increase with increasingin the range 0° ≤ ≤ 75° but for the range 75°≤  ≤ 90°  the effect is negligible. For R.R > 0.6, the heat transfer was observed to be almost independent of R; therefore for economic purposes, heat exchangers similar to the configuration studied should be run at a low pumping power. A numerical study was done to validate the program by test running it for the finless annuli for similar boundary conditions; the results obtained in the present work show the same trend as that of Kakac and Yucel.

INVESTIGATION ON HEAT TRANSFER ENHANCEMENT IN A CORRUGATED FIN-AND-TUBE COMPACT HEAT EXCHANGER

2016 ◽  
Vol 78 (10-2) ◽  
Author(s):  
Ahmadali Gholami ◽  
Mazlan A. Wahid ◽  
Hussein A. Mohammed ◽  
A. Saat ◽  
M. Y. M. Fairus ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Pressure Loss ◽  
Boundary Layer Separation ◽  
Performance Criteria ◽  
Recirculation Region ◽  
Moderate Pressure ◽  
Compact Heat Exchangers ◽  
Heat Transfer Augmentation

Heat transfer augmentation and pressure loss penalty in the fin-and-tube compact heat exchangers (FTCHEs) with the corrugated shape as a special form of the fin are numerically investigated to improve heat transfer performance criteria in low Reynolds numbers. The corrugated fin as the newly design of fin pattern is presented in this study. The influence of applying corrugated design adjustments on the thermal and hydraulic characteristics of air flow are analyzed on the in-line tube arrangements. The performance of air-side heat transfer and fluid flow is investigated by numerical simulation for Reynolds number ranging from Re = 400 to 800 based on the tube collar diameter, with the corresponding frontal air velocity ranging from 0.35 to 0.72 m/s. The outcomes of simulation revealed that the corrugated fin could significantly improve the heat transfer augmentation of the FTCHEs with a moderate pressure loss penalty. The computational results indicated that some eddies were developed behind the fluted domain of corrugated finwhich produce some disruptions to fluid flow and enhance heat transfer compared with plain fin. The corrugated form of fins could enhance the thermal mixing of the fluid, delay the boundary layer separation, and reduce the size of the wake and the recirculation region behind tubes compared with the conventional form of the fin at the range of Reynolds number used in this study. In addition, the results showed that the average Nusselt number for the FTCHE with corrugated fin increased by 7.05–10.0% over the baseline case and the corresponding pressure loss decreased by 5.0–6.2%.

Three-Dimensional Fluid Flow and Coupled Heat Transfer in Simplified Bipolar Plates

2007 ◽  
Author(s):  
Jianfei Wu ◽  
Jianhu Nie ◽  
Yitung Chen
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Solid Wall ◽  
Three Dimensional ◽  
Cathode Side ◽  
Uniform Heat Flux ◽  
Bipolar Plates ◽  
Coupled Heat Transfer ◽  
Temperature Distributions

Numerical simulations were performed for three-dimensional fluid flow and coupled heat transfer in simplified bipolar plates. The Reynolds number of inlet flow is varied from 100 to 900 on the anode side while the Reynolds number is maintained as a constant of 100 on the cathode side. The solid wall surfaces of the bipolar plates are assumed to be adiabatically insulated, except that the active areas of the channels are supplied with uniform heat flux. Results of velocity and temperature distributions for different Reynolds numbers are presented and discussed. It is shown that effects of flow pattern on temperature distributions in channels becomes negligible when the Reynolds number is as high as 900.

Enhancement of Heat Transfer in Miniaturized Channels Using Ferrohydrodynamic Convection

2003 ◽  
Author(s):  
Ranjan Ganguly ◽  
Swarnendu Sen ◽  
Ishwar K. Puri
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
External Magnetic Field ◽  
Rectangular Channel ◽  
Colloidal Dispersion ◽  
Electronic Cooling ◽  
Fluid Temperature ◽  
Heat Transfer Augmentation ◽  
Nusselt Numbers ◽  
The Magnetic Field

Heat transfer in miniaturized channels and slots in electronic cooling applications is restricted by relatively low convection due to flow limitations. The flow is generally laminar and heat transfer in these small geometries is usually conduction limited. We have proposed the use of ferrofluids as coolants in the presence of a nonuniform external magnetic field to enhance the heat transfer. A magnetic ferrofluid consists of a stable colloidal dispersion of subdomain magnetic nanoparticles in a liquid carrier that remain suspended due to their thermal Brownian energy. Under a varying external magnetic field (B), a ferrofluid experiences a local volumetric body force (M.∇)B. The magnetization M of the ferrofluid is coupled with the fluid temperature through its density and magnetic susceptibility. In our simulations, a strong magnetic field is considered to be applied by placing an edge pole adjacent to one of the walls of a rectangular channel. The channel is assumed to carry a pressure-driven ferrofluid flow. The resulting flowfield is predicted by numerically solving the coupled mass, momentum, energy, and Maxwell’s equations. A parametric study is performed to identify the influence of the magnetic field strength on the temperature distribution and the resulting heat transfer. A comparison based on the local and average Nusselt numbers shows that there is a significant heat transfer augmentation due to the magnetic field.

Heat transfer to pulsating turbulent flow in an abrupt pipe expansion

2003 ◽  
Vol 13 (3) ◽  
pp. 286-308 ◽  
Author(s):  
S.A.M. Said ◽  
M.A. Habib ◽  
M.O. Iqbal
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Prandtl Number ◽  
Turbulent Flow ◽  
Pulsation Frequency ◽  
Pipe Expansion ◽  
Cent Increase ◽  
The Mean ◽  
Mean Time

A numerical investigation aimed at understanding the flow and heat transfer characteristics of pulsating turbulent flow in an abrupt pipe expansion was carried out. The flow patterns are classified by four parameters; the Reynolds number, the Prandtl number, the abrupt expansion ratio and the pulsation frequency. The influence of these parameters on the flow was studied in the range 104<Re<5×104, 0.7<Pr<7.0, 0.2<d/D<0.6 and 5<f<35. It was found that the influence of pulsation on the mean time‐averaged Nusselt number is insignificant (around 10 per cent increase) for fluids having a Prandtl number less than unity. This effect is appreciable (around 30 per cent increase) for fluids having Prandtl number greater than unity. For all pulsation frequencies, the variation in the mean time‐averaged Nusselt number, maximum Nusselt number and its location with Reynolds number and diameter ratio exhibit similar characteristics to steady flows.

The Influence of Coolant Unsteadiness on Impingement Heat Transfer

2014 ◽  
Author(s):  
Victor J. Zimmer ◽  
James L. Rutledge ◽  
Chris Knieriem ◽  
Shichuan Ou
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Coolant Flow ◽  
Time Resolved ◽  
Average Mass ◽  
Flow Unsteadiness ◽  
Nusselt Numbers ◽  
Jet Cooling ◽  
The Mean ◽  
The Impact

Interest in impingement jet cooling and the associated convection phenomena has grown in the past few decades due in part to the desire for higher operating temperatures and reduced coolant flow in turbines. This study utilizes an array of 55 impingement jets to explore both steady and unsteady impingement flow conditions to evaluate the impact of the inherent unsteadiness present in engines compared to traditional steady experiments. Although unsteadiness occurs naturally in engines, intentional pulsation of coolant flow has also been proposed for flow control purposes, further underscoring the need for examination of the impact of pulsation on the heat transfer. Flow unsteadiness of varying amplitudes was induced at Strouhal numbers of magnitude 10−3 to 10−4. Infrared thermography was used to determine high spatial and temporal resolution Nusselt numbers. Time-resolved Nusselt number and mass flow characteristic waveforms were found to differ substantially as a function of the fluctuation amplitude relative to the mean. In some cases, transient coolant flow increases were associated with non-monotonic behavior in the time resolved Nusselt number. Although with certain configurations unsteady flow demonstrated time-averaged Nusselt numbers equivalent to steady flow with equivalent average mass flux, those with the greatest fluctuation in the amplitude of flow unsteadiness relative to the mean resulted in lower average Nusselt numbers.

Numerical Investigation of Heat Transfer Effects in Microchannels Under H2 Boundary Condition

2010 ◽  
Author(s):  
V. V. Dharaiya ◽  
R. R. Srivastava ◽  
S. G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Fluid Flow ◽  
Transport Processes ◽  
Uniform Heat Flux ◽  
Three Dimensional Model ◽  
Transfer Effects ◽  
Cross Sectional ◽  
Aspect Ratios ◽  
Heat Transfer Effects

Study of fluid flow characteristics at microscale level is gaining importance with shrinking device sizes. Better understanding of fluid flow and heat transfer in microchannels will have important implications in biomedical industry, MEMS, electronic chip cooling, heat exchangers, and microfluidic devices. Also, due to short lengths employed in microchannels, entrance header effects can be significant and needs to be investigated. In this work, three dimensional model of microchannels, with aspect ratios (α = a/b) ranging from 0.1 to 10, are numerically simulated using CFD software, FLUENT. Heat transfer effects in the entrance region of microchannel are presented by plotting average Nusselt number as a function of non-dimensional thermal entrance length x*. The numerical simulations with both circumferential and axial uniform heat flux (H2) boundary conditions were performed for four wall, three wall and two wall cases. Large numerical data sets, generated in this work for rectangular cross sectional microchannels for three walls and two walls H2 boundary condition, can provide better understanding and insight into the transport processes in the microchannel.

Applicability of Uniform Heat Flux Nusselt Number Correlations to Thermosyphon Heat Exchangers for Solar Water Heaters

1999 ◽  
Vol 121 (2) ◽  
pp. 85-90 ◽  
Author(s):  
S. Dahl ◽  
J. Davidson
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mixed Convection ◽  
Heat Exchangers ◽  
Convection Heat Transfer ◽  
Uniform Heat Flux ◽  
Convection Heat ◽  
Solar Water ◽  
Nusselt Numbers ◽  
Uniform Heat

Nusselt numbers are measured in three counterflow tube-in-shell heat exchangers with flow rates and temperatures representative of thermosyphon operation in solar water heating systems. Mixed convection heat transfer correlations for these tube-in-shell heat exchangers were previously developed in Dahl and Davidson (1998) from data obtained in carefully controlled experiments with uniform heat flux at the tube walls. The data presented in this paper confirm that the uniform heat flux correlations apply under morerealistic conditions. Water flows in the shell and 50 percent ethylene glycol circulates in the tubes. Actual Nusselt numbers are within 15 percent of the values predicted for a constant heat flux boundary condition. The data reconfirm the importance of mixed convection in determining heat transfer rates. Under most operating conditions, natural convection heat transfer accounts for more than half of the total heat transfer rate.

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