Mixed Convection in an Impinging Laminar Single Square Jet

2008 ◽  
Vol 131 (2) ◽  
Author(s):  
L. B. Y. Aldabbagh ◽  
A. A. Mohamad
Keyword(s):  
Reynolds Number ◽  
Nusselt Number ◽  
Richardson Number ◽  
Vortex Motion ◽  
Navier Stokes ◽  
Heated Plate ◽  
Calculation Results ◽  
Single Jet ◽  
Energy Equations ◽  
Target Spacing

The effect of Richardson number (Ri=Gr/Re2=Ra/Pr Re2) in a confined impinging laminar square jet was investigated numerically through the solution of Navier–Stokes and energy equations. The simulations were carried out for Richardson number between 0.05 and 8 and for jet Reynolds number between 50 and 300. The jet-to-target spacings were fixed to 0.25B, 0.5B, and 1.0B, respectively, where B is the jet width. The calculation results show that for the jet-to-target spacing of 0.25B, the flow structure of a square single jet impinging on a heated plate is not affected by the Richardson number. For such very small jet-to-target distances the jet is merely diverted in the transverse direction. The wall jet fills the whole gap between the plates with a very small vortex motion formed near the corners of the jet cross section close to the upper plate. In addition, the effect of the Richardson number on the variation in the local Nusselt number is found to be not significant. For higher jet-to-target spacing, the Nusselt number increased as the Richardson number increased for the same Re. In addition, the heat transfer rate increased as the jet Reynolds number increased for the same Richardson number.

Heat Transfer Enhancement by Imposed Pulsation in a Channel With Sudden Expansion

1999 ◽  
Author(s):  
E. Tandogan ◽  
N. K. Mitra
Keyword(s):  
Reynolds Number ◽  
Nusselt Number ◽  
Cross Section ◽  
Sudden Expansion ◽  
Navier Stokes ◽  
Transfer Enhancement ◽  
Channel Axis ◽  
Number Range ◽  
Field Symmetry ◽  
Energy Equations

Abstract A numerical investigation of laminar pulsating flows in a channel with sudden expansion in the cross section has been performed by solving two dimensional Navier-Stokes and energy equations for an incompressible fluid. A sinusoidal pulsation has been imposed on the axial velocity at the inlet. Results show that the flow field symmetry at the channel axis vanishes at even a Reynolds number of 100. The time averaged Nusselt number of pulsating flow increases sharply over the nonpulsating flow in the Reynolds number range of 400 and 500. The time averaged Nusselt number on the two walls can be different.

scholarly journals Unsteady Heat Transfer from an Equilateral Triangular Cylinder in the Unconfined Flow Regime

2011 ◽  
Vol 2011 ◽  
pp. 1-13 ◽  
Author(s):  
Amit Dhiman ◽  
Radhe Shyam
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Prandtl Number ◽  
Flow Regime ◽  
Cross Flow ◽  
Navier Stokes ◽  
Central Difference ◽  
Simple Method ◽  
Energy Equations

Effects of Reynolds number on the heat transfer characteristics of a long (heated) equilateral triangular cylinder are investigated for the range of conditions Re = 50–150 (in the steps of 10) and Prandtl number = 0.71 (air) in the unconfined unsteady cross-flow regime. In order to simulate the present situation, the computational grid is created by using commercial grid generator GAMBIT and the numerical computations are carried out by using FLUENT (6.3). The SIMPLE method is used to solve continuity, Navier-Stokes and energy equations along with the appropriate boundary conditions. The second order upwind scheme is used to discretize the convective terms, while the central difference scheme is used to discretize the diffusive terms in the governing equations. The present results are in an excellent agreement with the literature values. The temperature isotherms and temporal history of Nusselt number are presented in detail. The local as well as time-averaged Nusselt numbers are calculated. The time-averaged Nusselt number increases with increasing Reynolds number for the fixed value of the Prandtl number. Finally, the present numerical results are used to develop the simple heat transfer correlation for the range of conditions covered here.

Investigating Gas Turbine Internal Cooling Using Supercritical CO2 at High Reynolds Numbers for Direct Fired Cycle Applications

2021 ◽  
Author(s):  
Matthew Searle ◽  
Arnab Roy ◽  
James Black ◽  
Doug Straub ◽  
Sridharan Ramesh
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Gas Turbines ◽  
Cfd Simulation ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Process Conditions ◽  
Internal Cooling ◽  
Air Breathing

Abstract In this paper, experimental and numerical investigations of three variants of internal cooling configurations — dimples only, ribs only and ribs with dimples have been explored at process conditions (96°C and 207bar) with sCO2 as the coolant. The designs were chosen based on a review of advanced internal cooling features typically used for air-breathing gas turbines. The experimental study described in this paper utilizes additively manufactured square channels with the cooling features over a range of Reynolds number from 80,000 to 250,000. Nusselt number is calculated in the experiments utilizing the Wilson Plot method and three heat transfer characteristics — augmentation in Nusselt number, friction factor and overall Thermal Performance Factor (TPF) are reported. To explore the effect of surface roughness introduced due to additive manufacturing, two baseline channel flow cases are considered — a conventional smooth tube and an additively manufactured square tube. A companion computational fluid dynamics (CFD) simulation is also performed for the corresponding cooling configurations reported in the experiments using the Reynolds Averaged Navier Stokes (RANS) based turbulence model. Both experimental and computational results show increasing Nusselt number augmentation as higher Reynolds numbers are approached, whereas prior work on internal cooling of air-breathing gas turbines predict a decay in the heat transfer enhancement as Reynolds number increases. Comparing cooling features, it is observed that the “ribs only” and “ribs with dimples” configurations exhibit higher Nusselt number augmentation at all Reynolds numbers compared to the “dimples only” and the “no features” configurations. However, the frictional losses are almost an order of magnitude higher in presence of ribs.

scholarly journals Analysis of transient mixed convection in a horizontal channel partially heated from below

2021 ◽  
Vol 4 (8(112)) ◽  
pp. 16-22
Author(s):  
Mahmoud A. Mashkour
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Source ◽  
Local Nusselt Number ◽  
Richardson Number ◽  
Stokes Equations ◽  
Heat Convection ◽  
Horizontal Channel ◽  
Outlet Temperature

The heat convection phenomenon has been investigated numerically (mathematically) for a channel located horizontally and partially heated at a uniform heat flux with forced and free heat convection. The investigated horizontal channel with a fluid inlet and the enclosure was exposed to the heat source from the bottom while the channel upper side was kept with a constant temperature equal to fluid outlet temperature. Transient, laminar, incompressible and mixed convective flow is assumed within the channel. Therefore, the flow field is estimated using Navier Stokes equations, which involves the Boussinesq approximation. While the temperature field is calculated using the standard energy model, where, Re, Pr, Ri are Reynolds number, Prandtl number, and Richardson number, respectively. Reynolds number (Re) was changed during the test from 1 to 50 (1, 10, 25, and 50) for each case study, Richardson (Ri) number was changed during the test from 1 to 25 (1, 5, 10, 15, 20, and, 25). The average Nusselt number (Nuav) increases exponentially with the Reynold number for each Richardson number and the local Nusselt number (NuI) rises in the heating point. Then gradually stabilized until reaching the endpoint of the channel while the local Nusselt number increases with a decrease in the Reynolds number over there. In addition, the streamlines and isotherms patterns in case of the very low value of the Reynolds number indicate very low convective heat transfer with all values of Richardson number. Furthermore, near the heat source, the fluid flow rate rise increases the convection heat transfer that clarified the Nusselt number behavior with Reynolds number indicating that maximum Nu No. are 6, 12, 27 and 31 for Re No. 1, 10, 25 and 50, respectively

scholarly journals Modeling of natural convection of a concentrated solar power receiver absorber tube in interaction with neighbouring absorbers

2021 ◽  
pp. 53-61
Author(s):  
Olanrewaju Miracle Oyewola ◽  
Niyi Ezekiel Olukayode ◽  
Olusegun Olufemi Ajide
Keyword(s):  
Nusselt Number ◽  
Natural Convection ◽  
Average Nusselt Number ◽  
Solar Power ◽  
Renewable Energy Sources ◽  
Navier Stokes ◽  
Element Formulation ◽  
Concentrated Solar Power ◽  
Set Up ◽  
Energy Equations

Concentrated Solar Power (CSP) technology stands out among other renewable energy sources not only because of its ability to address current energy security and environmental challenges but because its energy can be stored for future use. To ensure optimum performance in this system, the heat losses need to be evaluated for better design. This work studies the natural convection in the receiver absorber tube of a CSP plant taking into consideration the influence of neighboring absorbers. A 2-Dimensional model was adopted in this study. Initially, a single absorber tube was considered, it was subjected to heat flux at the top wall, the bottom wall was insulated and a temperature differential was set up at the lateral walls. The dimensionless forms of Navier-Stokes and energy equations were solved using the finite element formulation of COMSOL Multiphysics software. The result obtained for a single absorber tube showed good agreement with existing research works. This validated model was then extended to multiple absorber tubes (two to six absorber tubes). On the basis of the study, there is an observed increase in the intensity and dominance of convective heat transfer with an increase in the number of absorber tubes. This is occasioned by an increase in the average surface temperature as well as average Nusselt number. For the Rayleigh number of 104, 105 and 106, the average Nusselt number increases with the number of absorber tubes by 13.87 %, 6.26 %, and 1.55 %, respectively. This increment suggests effect of thermal interactions among the neighboring absorber tubes

Effect of Driven Sidewalls on Mixed Convection in an Open Trapezoidal Cavity With a Channel

2020 ◽  
Vol 142 (8) ◽  
Author(s):  
Muneer A. Ismael ◽  
Ahmed Kadhim Hussein ◽  
Fateh Mebarek-Oudina ◽  
Lioua Kolsi
Keyword(s):  
Reynolds Number ◽  
Nusselt Number ◽  
Mixed Convection ◽  
Richardson Number ◽  
Average Nusselt Number ◽  
Airflow Velocity ◽  
Driven Cavity ◽  
Thermal Fields ◽  
Number Ratio ◽  
The Right

Abstract The mixed convection in an open trapezoidal lid-driven cavity connected with a channel is investigated in the present paper. Four different cases were considered depending on the movement of the cavity sidewalls. For case I, the left sidewall moves downward; for case II, the left sidewall moves downward and the right one moves upward; while for case III, only the right sidewall moves upward. A comparative case (case 0) is accounted when both sidewalls are assumed stationary. The base of the cavity is subjected to a localized heat source of constant temperature Th. The effects of Richardson number Ri and Reynolds number ratio Rer on the flow and thermal fields have been investigated. The results indicated that for cases I and II, the average Nusselt number increases with the increase of the Richardson number and Reynolds number ratio. Moreover, it was found that the maximum average Nusselt number occurs with case I. When the lid-driven speed is three times that of the inlet airflow velocity, the augmentations of the average Nusselt number compared with stationary walls are 163%, 158%, and 96% for cases I, II, and III, respectively.

Convective Heat Transfer in a Circular Annulus With Various Wall Heat Flux Distributions and Heat Generation

1985 ◽  
Vol 107 (2) ◽  
pp. 334-337 ◽  
Author(s):  
O. A. Arnas ◽  
M. A. Ebadian
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Heat Generation ◽  
Navier Stokes ◽  
Circular Pipes ◽  
Negative Effect ◽  
Energy Equations ◽  
Steady Laminar

Convective heat transfer for steady laminar flow between two concentric circular pipes with walls heated and/or cooled independently and subjected to uniform heat generation is presented in analytical closed form utilizing the linearized Navier-Stokes and energy equations. The flow field is hydrodynamically and thermally fully developed. The effect of heat generation is depicted in Fig. 1 where the ratio of the Nusselt number with heat generation to without heat generation is plotted against the radius ratio, the core size ω. It is seen that heat generation may have positive as well as negative effect on the Nusselt number.

Aggregate Intensification of Natural Convection Between Air and a Vertical Parallel-Plate Channel by Inserting an Auxiliary Plate at the Mouth and Appending Colinear Insulated Plates at the Exit

2000 ◽  
Author(s):  
Assunta Andreozzi ◽  
Oronzio Manca ◽  
Antonio Campo
Keyword(s):  
Nusselt Number ◽  
Parallel Plate ◽  
Navier Stokes ◽  
Working Fluid ◽  
Uniform Heat Flux ◽  
Heated Plate ◽  
Computational Domain ◽  
Plate Height ◽  
Pressure Profiles ◽  
Plate Channel

Abstract This paper addresses the examination of heat transfer in parallel-plate channels using a combination of two passive schemes: (1) the insertion of an auxiliary plate at the mouth and (2) the appendage of colinear insulated plates at the exit. The investigation is made by numerically solving the full elliptic Navier-Stokes and energy equation in a I-type computational domain. The channel is symmetrically heated by uniform heat flux. The working fluid is air. The results are reported in terms of induced mass flow rate and maximum wall temperatures. Further, the local Nusselt number, the mean Nusselt number and pressure profiles are presented. The analyzed Grashof numbers based on the heated plate height are 103 and 106.

Study of Heat Transfer Characteristics of a Single Jet Impinging on a Conical Surface

2020 ◽  
Author(s):  
Bo Su ◽  
Wei-jiang Xu ◽  
Zhi-ping Li ◽  
Tian-liang Zhou ◽  
Fei Lu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Stagnation Point ◽  
Target Surface ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Maximum Value ◽  
Conical Target ◽  
Single Jet

Abstract In this paper, the heat transfer performance of single jet impinging conical surface is investigated based on transient liquid crystal experiments. Because of different target surface structures, impingement heat transfer will have different heat transfer characteristics. In order to better understand the heat transfer mechanism of the impinging conical target surface, this paper studies the three jet Reynolds number (Re) ranged from 25000 to 70000, three the dimensionless nozzle-to-surface distance (H/D) from 0.75 to 6 on heat transfer characteristics. The liquid crystal thermal imaging technology is used in the experiment to obtain the heat transfer efficiency of jet heat transfer on the conical target surface. The research in this paper shows that the larger the jet Reynolds number, the larger the Nusselt number at the stagnation point. It is worth noting that the maximum Nusselt number is not necessarily obtained at the stagnation point. When Re = 70000 and H/D = 0.75, the maximum value of the Nusselt number is 1.24 times the stagnation point. The larger the Reynolds number, the smaller the impingement distance, and the more obvious the secondary maxima. At the same impingement distance, when the Reynolds number is larger, the position of the secondary maxima appears earlier. When Re = 25000, H/D = 3.5, 6 and Re = 45000, H/D = 6, the local Nusselt number monotonously decreases from the maximum value at the stagnation point along the flow, and it appears secondary maxima in other experimental conditions. Within the scope of this study, the overall heat transfer performance is better when the dimensionless distance between the jet hole and the target surface is 3.5.

Simulation of Solid Particles in Combined Conduction, Convection and Radiation Gas Flow over a Backward-Facing Step in a Duct

2011 ◽  
Vol 110-116 ◽  
pp. 5276-5282 ◽  
Author(s):  
Vahid Golkarfard ◽  
Seyyed Abdolreza Gandjalikhan Nassab ◽  
Amir Babak Ansari
Keyword(s):  
Reynolds Number ◽  
Gas Flow ◽  
Numerical Data ◽  
Solid Particles ◽  
Navier Stokes ◽  
Convection Flow ◽  
Backward Facing Step ◽  
Number Variation ◽  
Laminar Convection ◽  
Energy Equations

A numerical simulation procedure for studying deposition of aerosol particles in a laminar convection flow of radiating gas over a backward-facing step including the effect of thermal force is developed. In the gas flow, all of the heat transfer mechanisms consisting of conduction, convection and radiation take place simultaneously. Behavior of solid particles is studied numerically based on an Eulerian–Lagrangian method. Two dimensional Navier-Stokes and energy equations are solved using CFD techniques, while the radiating transfer equation (RTE) is solved by discrete ordinate method (DOM) for calculating radiative heat flux distribution. The objective of this research is to study the effect of Reynolds number variation and also radiation on thermophoretic deposition of particles. Numerical results show a decrease in deposition percent by increasing in Reynolds number and the radiation effect is negligible. The results are compared with the existing experimental and numerical data and good agreement is found.

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