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1

Numerical study on thermal performance of water flow in a twisted duct heat exchanger

Rashed Musaab K., Jehhef Kadhum Audaa, Badawy Faris Ali

International Journal of Applied Mechanics and Engineering

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2022

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Vol. 27, no. 2

199--216

EN

This paper presents a numerical study of heat transfer through a downstream annulus using water as the working fluid within the laminar flow region. The annulus consisted of an outer twisted square duct and an inner circular pipe. A three-dimensional formulation was used to solve the Navier-Stokes equations numerically for the laminar flow system with a low Reynolds number. Three parameters were used in the numerical simulation: the length of the twisted square [...] the inner diameter of the inner circular pipe [...] and 25 mm and the twist angle [...]. Numerical calculations were conducted on sixteen twisted square duct heat exchangers, with water flowing within a Reynolds number range of .220 1100− The results were illustrated as a profile of the thermal enhancement factor, the friction factor and the Nusselt number. The results show that the twisted outer duct of the heat exchanger can create a swirl flow along the length of the heat exchanger. It also caused a boundary layer separation-reattachment on the wall of the inner pipe. Moreover, an increase in the twist angle increased the Nusselt number by %,20 and the friction factor was also increased as the annular gap of the heat exchanger decreased.

2

Effect of aiding buoyancy on heat transfer from an isothermal square cylinder in power-law fluids

Mishra Pragya, Mishra Lubhani, Tiwari Anurag Kumar

Chemical and Process Engineering

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2022

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Vol. 43, nr 2

265–-270

EN

The aim of the present study was to explore the influence of aiding buoyancy on mixed convection heat transfer in power-law fluids from an isothermally heated unconfined square cylinder. Extensive numerical results on drag coefficient and surface averaged values of the Nusselt number are reported over a wide range of parameters i.e. Richardson number, 01 Ri 5, power-law index, 04 𝑛 18, Reynolds number, 01 Re 40, and Prandtl number, 1 Pr 100. Further, streamline profiles and isotherm contours are presented herein to provide an insight view of the detailed flow kinematics

3

Mixed convective flow with variable viscosity and variable thermal conductivity in a channel in the presence of first order chemical reaction with heat generation or absorption

Shobha K. C., Biradar Mahadev, Mallikarjun B Patil

Journal of Applied Mathematics and Computational Mechanics

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2021

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Vol. 20, nr 1

91--102

EN

A study has been made on the flow and heat transfer of a viscous fluid in a vertical channel with first order chemical reaction and heat generation or absorption assuming that the viscosity and thermal conductivity are dependent on the fluid temperature. The temperature of the walls is maintained constant. Under these assumptions, the governing balance equations of mass, momentum and energy are formulated. The dimensionless forms of the governing equations are coupled and non-linear, which cannot be solved analytically and therefore require the use of the Runge-Kutta fourth order along with shooting technique. Graphs for velocity and temperature under different values of parameters involved are plotted and discussed. The skin friction and Nusselt number on the channel walls are also computed and discussed. Furthermore, the investigation found that variable viscosity and variable thermal conductivity enhance the velocity and temperature of the flow.

4

Thermal performance enhancement of the mixed convection between two parallel plates by using triangular ribs

Jehhef K. A., Badawy F. A., Hussein A. A.

International Journal of Applied Mechanics and Engineering

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2021

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Vol. 26, no. 2

11--30

EN

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.

5

Mixed convective flow of unsteady hydromagnetic couple stress fluid through a vertical channel filled with porous medium

Makhalemele C. R., Rundora L., Adesanya S. O.

International Journal of Applied Mechanics and Engineering

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2020

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Vol. 25, no. 4

148--161

EN

In this paper, the mixed convective flow of an electrically conducting, viscous incompressible couple stress fluid through a vertical channel filled with a saturated porous medium has been investigated. The fluid is assumed to be driven by both buoyancy force and oscillatory pressure gradient parallel to the channel plates. A uniform magnetic field of strength 0B is imposed transverse to the channel boundaries. The temperature of the right channel plate is assumed to vary periodically, and the temperature difference between the plates is high enough to induce radiative heat transfer. Under these assumptions, the equations governing the two-dimensional couple stress fluid flow are formulated and exact solutions of the velocity and the temperature fields are obtained. The effects of radiation, Hall current, porous medium permeability and other various flow parameters on the flow and heat transfer are presented graphically and discussed extensively.

6

Mixed convection on MHD flow with thermal radiation, chemical reaction and viscous dissipation embedded in a porous medium

Zigta B.

International Journal of Applied Mechanics and Engineering

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2020

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Vol. 25, no. 1

219--235

EN

In this paper, a theoretical analysis has been made to study the effect of mixed convection MHD oscillatory Couette flow in a vertical parallel channel walls embedded in a porous medium in the presence of thermal radiation, chemical reaction and viscous dissipation. The channel walls are subjected to a constant suction velocity and free stream velocity is oscillating with time. The channel walls are embedded vertically in a porous medium. A magnetic field of uniform strength is applied normal to the vertical channel walls. The nonlinear and coupled partial differential equations are solved using multi parameter perturbation techniques. The effects of physical parameters, viz., the radiation absorption parameter, Prandtl number, Eckert number, dynamic viscosity, kinematic viscosity, permeability of porous medium, suction velocity, Schmidt number and chemical reaction parameter on flow variables viz., temperature, concentration and velocity profile have been studied. MATLAB code is used to analyze theoretical facts. The important results show that an increment in the radiation absorption parameter and permeability of porous medium results in an increment of the temperature profile. Moreover, an increment in the Prandtl number, Eckert number and dynamic viscosity results in a decrement of the temperature profile. An increment in suction velocity results in a decrement of the velocity profile. An increment in the Schmidt number, chemical reaction parameter and kinematic viscosity results in a decrement of the concentration profile.

7

Mixed convection in MHD flow and heat transfer rate near a stagnation-point on a non-linear vertical stretching sheet

Fenuga O. J., Hassan A. R., Olanrewaju P. O.

International Journal of Applied Mechanics and Engineering

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2020

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Vol. 25, no. 1

37--51

EN

This work investigates the mixed convection in a Magnetohydrodynamic (MHD) flow and heat transfer rate near a stagnation-point region over a nonlinear vertical stretching sheet. Using a similarity transformation, the governing equations are transformed into a system of ordinary differential equations which are solved numerically using the fourth order Runge-Kutta method with shooting technique. The influence of pertinent flow parameters on velocity, temperature, surface drag force and heat transfer rate are computed and analyzed. Graphical and tabular results are given to examine the nature of the problem. The heat transfer rate at the surface increases with the mixed convection.

8

MHD mixed convection in copper-water nanofluid filled lid-driven square cavity containing multiple adiabatic obstacles with discrete heating

Gorla R. S. R., Siddiqa S., Hasan A. A., Salah T., Rashad A. M.

International Journal of Applied Mechanics and Engineering

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2020

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Vol. 25, no. 2

57--74

EN

The objective of the present work is to investigate the influence of nanoparticles of copper within the base fluid (water) on magneto-hydrodynamic mixed-convection flow in a square cavity with internal generation. A control finite volume method and SIMPLER algorithm are used in the numerical calculations. The geometry is a lid-driven square cavity with four interior square adiabatic obstacles. A uniform heat source is located in a part of the left wall and a part of the right wall of the enclosure is maintained at cooler temperature while the remaining parts of the two walls are thermally insulated. Both the upper and bottom walls of the cavity are considered to be adiabatic. A comparison with previously published works shows a very good agreement. It is observed that the Richardson number, Ri, significantly alters the behavior of streamlines when increased from 0.1 to 100.0. Also, the heat source position parameter, D, significantly changes the pattern of isotherms and its strength shifted when D moves from 0.3 to 0.7.

9

Influence of heat generation/absorption on mixed convection flow behaviour in the presence of Lorentz forces in a vertical micro circular duct having time periodic boundary conditions: steady periodic regime

Aina B., Isa S.

International Journal of Applied Mechanics and Engineering

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2020

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Vol. 25, no. 4

1--21

EN

The problem of mixed convection flow of a heat generating/absorbing fluid in the presence existence of Lorentz forces in a vertical micro circular subjected to a periodic sinusoidal temperature change at the surface has been studied taking the first-order slip and jump effects into consideration. The research analysis is carried out by considering a fully developed parallel flow and steady periodic regime. The governing equations, together with the constraint equations which arise from the definition of mean velocity and temperature, are written in a dimensionless form and mapped into equations in the complex domain. One obtains two independent boundary value problems, which provide the mean value and the oscillating term of the velocity and temperature distributions. These boundary value problems are solved analytically. A parametric study of some of the physical parameters involved in the problem is conducted. The results of this research revealed that the magnetic field has a damping impact on the flow and results in decreases in fluid velocity for both air and water. Furthermore, the presence of the heat generation parameter is seen to enhance the temperature distribution and this is reflected as an increase in the magnitude of the oscillation dimensionless velocity, whereas in the presence of heat absorption a reversed trend occurs.

10

Effects of viscous dissipation and wall conduction on steady mixed convection Couette flow of heat generating / absorbing fluid

Ajibade A. O., Umar A. M.

International Journal of Applied Mechanics and Engineering

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2019

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Vol. 24, no. 4

12--35

EN

This article theoretically investigated mixed convection flow of heat generating/absorbing fluid in the presence of viscous dissipation and wall conduction effects. The flow is considered to be steady in a vertical channel with some boundary thickness. One of the plates is heated while the other is kept at ambient temperature. The governing flow equations were solved analytically using Homotopy Perturbation Method (HPM). The influences of the governing parameters were captured in graphs, tables and a table was constructed for validation of the work. It is worthwhile to stress that, both the velocity and temperature profiles decrease near the heated plate with an increase in boundary thickness (d) while the reverse cases were observed toward the cold plate. The velocity profile increases near the heated plate with increase in mixed convection parameter (Gre) and decreases towards the cold plate. Rate of heat transfer has been observed to decrease with increase in boundary plate thickness (d) while the critical value of (Gre) increases with growing boundary plate thickness. The study therefore established the importance of boundary plate thickness in mixed convection investigation.

11

Ferdows M., Liu D.

International Journal of Applied Mechanics and Engineering

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2017

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Vol. 22, no. 1

253--258

EN

The aim of this work is to study the mixed convection boundary layer flow from a horizontal surface embedded in a porous medium with exponential decaying internal heat generation (IHG). Boundary layer equations are reduced to two ordinary differential equations for the dimensionless stream function and temperature with two parameters: ε, the mixed convection parameter, and λ, the exponent of x. This problem is numerically solved with a system of parameters using built-in codes in Maple. The influences of these parameters on velocity and temperature profiles, and the Nusselt number, are thoroughly compared and discussed.

12

Mixed convective fully developed flow in a vertical channel in the presence of thermal radiation and viscous dissipation

Prasad K. V., Mallikarjun P., Vaidya H.

International Journal of Applied Mechanics and Engineering

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2017

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Vol. 22, no. 1

123--144

EN

The effect of thermal radiation and viscous dissipation on a combined free and forced convective flow in a vertical channel is investigated for a fully developed flow regime. Boussinesq and Roseseland approximations are considered in the modeling of the conduction radiation heat transfer with thermal boundary conditions (isothermal-thermal, isoflux-thermal, and isothermal-flux). The coupled nonlinear governing equations are also solved analytically using the Differential Transform Method (DTM) and regular perturbation method (PM). The results are analyzed graphically for various governing parameters such as the mixed convection parameter, radiation parameter, Brinkman number and perturbation parameter for equal and different wall temperatures. It is found that the viscous dissipation enhances the flow reversal in the case of a downward flow while it counters the flow in the case of an upward flow. A comparison of the Differential Transform Method (DTM) and regular perturbation method (PM) methods shows the versatility of the Differential Transform Method (DTM). The skin friction and the wall temperature gradient are presented for different values of the physical parameters and the salient features are analyzed.

13

Unsteady laminar mixed convection boundary layer flow near a vertical wedge due to oscillations in the free-stream and surface temperature

Roy N. C., Hossain A., Hussain S.

International Journal of Applied Mechanics and Engineering

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2016

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Vol. 21, no. 1

169--186

EN

The unsteady laminar boundary layer characteristics of mixed convection flow past a vertical wedge have been investigated numerically. The free-stream velocity and surface temperature are assumed to be oscillating in the magnitude but not in the direction of the oncoming flow velocity. The governing equations have been solved by two distinct methods, namely, the straightforward finite difference method for the entire frequency range, and the extended series solution for low frequency range and the asymptotic series expansion method for high frequency range. The results demonstrate the effects of the Richardson number, Ri, introduced to quantify the influence of mixed convection and the Prandtl number, Pr, on the amplitudes and phase angles of the skin friction and heat transfer. In addition, the effects of these parameters are examined in terms of the transient skin friction and heat transfer.

14

Effects of inclined magnetic field and Joule heating in mixed convective peristaltic transport of non-Newtonian fluids

Abbasi F. M., Hayat T., Alsaedi A.

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2015

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Vol. 63, nr 2

501--514

EN

This article describes the influence of an inclined magnetic field on the mixed convective peristaltic transport of fluid in an inclined channel. Two types of non-Newtonian fluids are considered. The problem formulation is presented for the Eyring-Prandtl and Sutterby fluids. Viscous dissipation and Joule heating in the heat transfer process are retained. The presence of a heat source in the energy equation is ensured. The resulting problems are solved by the perturbation method. The plots for different parameters of interest are given and discussed. Numerical values of a heat transfer rate are given and analyzed.

15

Exact solution of MHD mixed convection periodic flow in a rotating vertical channel with heat radiation

Singh K. D.

International Journal of Applied Mechanics and Engineering

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2013

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Vol. 18, no. 3

853--869

EN

Magnetohydrodynamic (MHD) mixed convection flow of a viscous, incompressible and electrically conducting fluid in a vertical channel is analyzed analytically. A magnetic field of uniform strength is applied perpendicular to the planes of the channel walls. The fluid is acted upon by a periodic variation of the pressure gradient in the vertically upward direction. The temperature of one of the plates is non-uniform and the temperature difference of the walls of the channel is high enough to induce heat transfer due to radiation. The fluid and the channel rotate in unison with an angular velocity about the axis normal to the plates of the channel. An exact analytical solution of the problem is obtained. Two cases of small and large rotation have been considered to assess the effects of different parameters involved in the flow problem. The velocity field, the amplitude and the phase angle of the shear stress are shown graphically and discussed in detail. During analysis it is found that the flow problem studied by Makinde and Mhone (2005) is incorrect physically and mathematically.

16

Buoyancy and Soret effect on unsteady MHD mixed convective slip flow in a permeable vertical plate

Rashi Kumar B., Sivaraj R.

International Journal of Applied Mechanics and Engineering

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2012

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Vol. 17, no. 1

179-190

EN

This paper is focused on the study of heat and mass transfer in the unsteady MHD mixed convective flow of a viscous incompressible fluid bounded by a permeable vertical plate subject to the influence of buoyancy, viscous dissipation, ohmic heating and the Soret effect embedded with slip condition at the boundary layer. In order to obtain a better insight into this problem, we make use of the perturbation method. The results for velocity, temperature, concentration, skin friction, the Nusselt number as well as the Sherwood number are examined analytically and the effects of various significant parameters entering into this problem are displayed graphically.

17

Mixed radiation-convection boundary layer flow of an opically dense fluid along a vertical flat plate in a non-Darcy porous medium

Takhar H. S., Beg O. A., Chamkha A. J., Filip D., Pop I.

International Journal of Applied Mechanics and Engineering

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2003

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Vol. 8, no 3

483-496

EN

The combined effects of thermal radiation flux, thermal conductivity, Reynolds number and non-Darcian (Forcheimmer drag and Brinkman boundary resistance) body forces on steady laminar boundary layer flow along a vertical surface in an idealized geological porous medium are investigated. The classical Rosseland one-dimensional diffusion approximation is implemented in the energy equation to avoid solving the general integro-differential equation for radiative transfer. Pseudo-similarity transformations are invoked and the resulting highly coupled and non-linear set of ordinary differential equations for momentum and energy equations are solved numerically using a well-tested and highly accurate shooting Runge-Kutta quadrature with a Merson-Gill algorithm. It is shown that the dimensionless velocity functions generally increase with rising radiation parameter and the Prandtl number, and the dimensionless temperature functions decrease as the non-Darcian body forces decrease. It is also shown that the dimensionless temperature functions rise in magnitude with rising radiation parameter and the Prandtl number but are depressed by lowered non-Darcian resistance parameter and rising Reynolds number. Generally radiation is seen to substantially boost the overall heat transfer.

18

Wizualizacja pola temperatury w obszarze konwekcji mieszanej

Fornalik E., Leiner W., Szmyd J., Kolenda Z.

Prace Naukowe Politechniki Warszawskiej. Konferencje

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2002

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T. 2, z. 22

417-424

PL

W prezentowanej pracy dokonano wizualizacji pola temperatury w obszarze konwekcji mieszanej. Przedstawiono stanowisko pomiarowe, warunki eksperymentu oraz metody badawcze wykorzystane podczas wizualizacji pola temperatury. Dokonano analizy wyników wizualizacji pola temperatury i porównano je z wynikami dotyczącymi pola prędkości.

EN

The visualisation of a temperature field in mixed convection by using the termochromic liquid crystals is presented in this paper. The experimental set-up, experimental conditions and applied methods were described. The images of temperature field were analised and compared to the results of velocity field.

19

Konwekcja mieszana przy opływie walca w warunkach hiperbarycznych

Stachel A.

Prace Naukowe Politechniki Warszawskiej. Konferencje

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2002

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T. 4, z. 22

1127-1134

PL

Praca stanowi eksperymentalną próbę opisu procesu wnikania ciepła na zewnętrznej ścianie grzanego walca, przy poprzecznym laminarnym opływie walca strumieniem powietrza, ze szczególnym uwzględnieniem obszaru konwekcji mieszanej, realizowaną w warunkach wysokich ciśnień. Warunki hiperbaryczne sprzyjają występowaniu konwekcji mieszanej i umożliwiają prowadzenie prac w szerokim zakresie zmienności liczby Grashoffa bez zmiany rodzaju używanego medium.

EN

The present work is an experimental attempt to understand the issue of mixed convection under hyperbaric conditions. Such conditions favour existence of mixed convection and enable conducting works in a wide range of Grashof number, without change of a working medium. The principal objective of the present work is to conduct investigations leading to a fuller explanation of heat transfer process on the external wall of a heated cylinder under conditions of laminar flow at transverse (level, upward and downward cases) of a flow around the cylinder.

20

MHD fully developed mixed convection flow with asymmetric heating of the wall

Ghosh S. K., Pop I., Nandi D. K.

International Journal of Applied Mechanics and Engineering

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2002

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Vol. 7, no 4

1211-1228

EN

Magnetohydrodynamic fully developed mixed convection flow of a viscous incompressible electrically conducting fluid confined to a vertical channel with asymmetric heating of the wall, is studied. It has been shown that a reversed flow occurs due to asymmetric heating of the wall when the magnitude of the buoyancy parameter Gr exceeds a certain threshold value. The limiting cases of the MHD free and forced convection flow are analysed. A qualitative discussion for the occurrence of a flow reversal is given in this paper. It is interesting to note that in the higher buoyancy the bulk temperature of the MHD flow exceeds the value 1 when rT < 1.