The Experts below are selected from a list of 10446 Experts worldwide ranked by ideXlab platform
Chaobin Dang - One of the best experts on this subject based on the ideXlab platform.
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the heat transfer of supercritical co2 in helically coiled tube trade off between curvature and Buoyancy effect
Energy, 2019Co-Authors: Shijie Zhang, Chao Liu, Xinxin Liu, Yadong Zhang, Chaobin DangAbstract:Supercritical CO2 Rankine cycle has great development potential as a power cycle for converting low-grade thermal energy into electricity. Better understanding of supercritical CO2 heat transfer in helically coiled tubes (HCTs) is required for design and operation of supercritical CO2 Rankine cycle power systems. In this work, the SST k∼ω model is employed. A new dimensionless Buoyancy parameter Ψ is proposed which denotes the ratio of gravitational Buoyancy Force to overall curvature effect. Furthermore, a flow regimes map is proposed based on the inclination angle of the dividing streamline between the two vortexes and Buoyancy parameter Ψ. The mixed convection region in HCT is decomposed into a gravitational Buoyancy Force dominated heat transfer region (B Region α>45°) and a curvature effect dominated heat transfer region (C Region α<45°). Subsequently, the effects of HCT geometry on heat transfer mechanisms are respectively investigated in B and C Region, which help us better understanding the relationship of the Buoyancy criterion and flow characteristics. The results indicate that the effects of coiled pitch and coiled diameter on heat transfer can be neglected in B Region. In C Region, the heat transfer is suppressed as coiled pitch increases and it will appear oscillation when torsion effect is strong enough. In addition, the heat transfer is enhanced with curvature increases but except for near the pseudo-critical region.
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The Buoyancy Force and flow acceleration effects of supercritical CO2 on the turbulent heat transfer characteristics in heated vertical helically coiled tube
International Journal of Heat and Mass Transfer, 2018Co-Authors: Shijie Zhang, Chao Liu, Yadong Zhang, Chaobin DangAbstract:Abstract Numerical simulations are performed to investigate the turbulent heat transfer characteristics of supercritical CO2 in heated vertical helically coiled tube, and primary focus is to analyze the mechanism of Buoyancy Force and flow acceleration on the heat transfer. The results show similar effect from Buoyancy Force and centrifugal Force, and both Forces induce a secondary flow in the cross section that improves the heat transfer efficiency. The Buoyancy parameter ϕ2 and flow acceleration parameter q+ are established with reasonably good validation against numerical results. On the basis of the two parameters, the Buoyancy factor Fb and the acceleration factor FAc are proposed to quantify Buoyancy and flow acceleration effect, respectively. Furthermore, a temperature difference correction factor Ft is introduced to consider variation of thermo-physical properties. A new semi-empirical heat transfer correlation is proposed for supercritical CO2 in function of Fb, FAc and Ft for the vertical helically coiled tube.
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numerical study of the effect of Buoyancy Force and centrifugal Force on heat transfer characteristics of supercritical co2 in helically coiled tube at various inclination angles
Applied Thermal Engineering, 2017Co-Authors: Xinxin Liu, Chao Liu, Wanjin Bai, Chaobin DangAbstract:The fully developed turbulent flow of supercritical CO2 in a heated helically coiled pipe is investigated by numerical simulation. The supercritical CO2 in the helically coiled tube is heated under constant heat flux with the inclination angles range from −90° to 90°. This work analyzes the effects of the heat flux, pressure, mass flux, flow direction, Buoyancy Force and centrifugal Force on the convection heat transfer characteristics of supercritical CO2. Results show that the non-uniformity of the circumferential heat transfer coefficients is more evident with the decrease of the incline angle. When the helically coiled tube is oriented vertically, the heat transfer coefficient firstly increases and then decreases, exhibiting a maximum near the pseudo-critical temperature. When the helically coiled tube is positioned at horizontal or inclined angles, the heat transfer coefficient (HTC) oscillates dramatically as a result of the fact that the Buoyancy Force becomes a dominant factor compared to the centrifugal Force.
Ioan Pop - One of the best experts on this subject based on the ideXlab platform.
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influence of Buoyancy Force on ag mgo water hybrid nanofluid flow in an inclined permeable stretching shrinking sheet
International Communications in Heat and Mass Transfer, 2021Co-Authors: Nur Syazana Anuar, Norfifah Bachok, Ioan PopAbstract:Abstract The present work explored the heat transfer and boundary layer flow of a hybrid nanofluid past an inclined stretching/shrinking sheet with suction and Buoyancy Force effects. Silver (Ag) and magnesium oxide (MgO) are considered as the hybrid nanoparticles and suspended in water to form Ag-MgO/water hybrid nanofluid. The partial differential equations (PDEs) are converted into a system of ordinary differential equations (ODEs) by employing appropriate similarity transformation. The simplified mathematical model is then solved numerically using the bvp4c solver in the MATLAB software. The effects of governing parameters, namely the inclination angle, suction, stretching/shrinking, Buoyancy or mixed convection and nanoparticle volume fraction parameters on the velocity and temperature profiles as well as skin friction coefficient and local Nusselt number are examined and presented graphically. The results are proven to have two solutions for both stretching and shrinking case, which consequently lead to the implementation of a stability analysis, hence confirming that only the first solution is stable. In addition, the local Nusselt number increases when the angle of inclination and suction parameters increase. The results also reveal that increasing values of Ag nanoparticle volume fraction in MgO/water nanofluid declines the local Nusselt number.
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boundary layer flow and heat transfer over an exponentially shrinking vertical sheet with suction
International Journal of Thermal Sciences, 2013Co-Authors: Azizah Mohd Rohni, Syakila Ahmad, Ahmad Izani Md Ismail, Ioan PopAbstract:Abstract In this paper, we investigate theoretically the problem of steady laminar two-dimensional boundary layer flow and heat transfer of an incompressible viscous fluid in the presence of Buoyancy Force over an exponentially shrinking vertical sheet with suction. The shrinking velocity and wall temperature are assumed to have specific exponential function forms. The governing equations are first transformed to similarity equations using an appropriate similarity transformation. The resulting equations were then solved numerically using shooting technique involving fourth-order Runge–Kutta method and Newton–Raphson method. The influence of mixed convection/Buoyancy parameter λ, suction parameter s and Prandtl number Pr on the flow and heat transfer characteristics is examined and discussed. Numerical results indicate that the presence of Buoyancy Force would contribute to the existence of triple solutions to the flow and heat transfer for particular value of pertinent parameters. It is different for the non-buoyant flow case i.e. when the Buoyancy Force is absent, the problem admits only dual solutions. Further, this study also reveals that the features of flow and heat transfer characteristics are significantly affected by Buoyancy parameter λ, suction parameter s and Prandtl number Pr.
G. Nath - One of the best experts on this subject based on the ideXlab platform.
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non darcy mixed convection in power law fluids along a non isothermal horizontal surface in a porous medium
International Journal of Engineering Science, 2004Co-Authors: M Kumari, G. NathAbstract:Abstract The non-similar non-Darcy mixed convection from a horizontal surface in a porous medium saturated with a power-law type non-Newtonian fluid has been studied. Non-similarity solutions have been obtained for the case of a variable surface temperature of the form T w ( x )= T ∞ ± Ax λ , λ ≠1/2. It has been found that for λ =1/2, self-similar solution exists. A single mixed convection parameter has been used which covers the entire regime of mixed convection from pure Forced convection to pure free convection limits. Both these limiting flows admit self-similar solutions. The partial differential equations governing the non-similar flow and the ordinary differential equations governing the self-similar flow have been solved numerically. The Buoyancy Force and the wall temperature have significant influence on the heat transfer and the velocity at the wall. For a fixed Buoyancy Force, the heat transfer and the velocity at the wall decrease with increasing non-Newtonian parameter, non-Darcy parameter and Peclet number.
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Unsteady free convection flow in the stagnation-point region of a rotating sphere
International Journal of Non-Linear Mechanics, 1998Co-Authors: Harmindar S. Takhar, Arezki Slaouti, Mahesh Kumari, G. NathAbstract:The unsteady free convection boundary-layer flow in the forward stagnation-point region of a sphere, which is rotating with time-dependent angular velocity in an ambient fluid, has been studied. Both constant wall temperature and constant heat flux conditions have been considered. The non-linear coupled parabolic partial differential equations governing the flow have been solved numerically using an implicit finite-difference scheme. The skin friction and the heat transfer are enhanced by the Buoyancy Force. The effect of the Buoyancy Force is found to be more pronounced for smaller Prandtl numbers than for larger Prandtl numbers. For a given Buoyancy Force, the heat transfer increases with an increase in Prandtl number, but the skin friction decreases.
Oluwole Daniel Makinde - One of the best experts on this subject based on the ideXlab platform.
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effects of thermal radiation and Buoyancy Force on transient hartmann flow in a channel with permeable walls
Latin American Applied Research - An international journal, 2021Co-Authors: Om Prakash Verma, Oluwole Daniel MakindeAbstract:The combined effects of thermal radiation, Buoyancy Force and variable heat source on an unsteady MHD flow of a conducting fluid through a porous walled channel is theoretically investigated. Base on some simplified assumptions, the model partial differential equations are obtained and tackled analytically using variable separable technique. Numerical solutions depicting the impact of various embedded thermophysical parameters on the fluid velocity and temperature profiles, skin friction and Nusselt number are displayed graphically and quantitatively discussed. An escalation in both skin friction and heat transfer rate is observed with a rise in fluid injection–suction at the channel walls.
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UNSTEADY MHD FLOW OF RADIATING CASSON FLUID THROUGH A PERMEABLE CHANNEL WITH SLIP, Buoyancy Force AND HEAT SOURCE
2020Co-Authors: Om Prakash Verma, Oluwole Daniel Makinde, R.l. MonalediAbstract:Analytical investigation is performed into an unsteady Magnetohrodynamics mixed convective Casson fluid flow and heat transfer characteristics with thermal radiation, wall slip, heat source and Buoyancy Force in a permeable vertical channel. The fluid is injected into the left wall of the channel and sucked out at right wall. The governing momentum and energy balance equations are achieved and tackled analytically. The effects of numerous thermophysical parameters on the temperature profiles, velocity, Nusselt number as well as skin friction are presented graphically and discussed qualitatively. The results show that a temporal decline in the pressure gradient causes both the temperature and fluid velocity to decrease. Moreover, the enhancement in heat transfer due to wall injection/suction also causes the skin friction to decrease.
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heat transfer to mhd oscillatory dusty fluid flow in a channel filled with a porous medium
Sadhana-academy Proceedings in Engineering Sciences, 2015Co-Authors: O M Prakash, Oluwole Daniel Makinde, Devendra Kumar, Y K DwivediAbstract:In this paper, we examine the combined effects of thermal radiation, Buoyancy Force and magnetic field on oscillatory flow of a conducting optically thin dusty fluid through a vertical channel filled with a saturated porous medium. The governing partial differential equations are obtained and solved analytically by variable separable method. Numerical results depicting the effects of various embedded parameters like radiation number, Hartmann number and Grashof number on dusty fluid velocity profiles, temperature profiles, Nusselt number and skin friction coefficient are presented graphically and discussed qualitatively.
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Buoyancy effects on mhd stagnation point flow and heat transfer of a nanofluid past a convectively heated stretching shrinking sheet
International Journal of Heat and Mass Transfer, 2013Co-Authors: Oluwole Daniel Makinde, W A Khan, Z H KhanAbstract:Abstract This paper analyzes the combined effects of Buoyancy Force, convective heating, Brownian motion, thermophoresis and magnetic field on stagnation point flow and heat transfer due to nanofluid flow towards a stretching sheet. The governing nonlinear partial differential equations are transformed into a system of coupled nonlinear ordinary differential equations using similarity transformations and then tackled numerically using the Runge–Kutta fourth order method with shooting technique. Numerical results are obtained for dimensionless velocity, temperature, nanoparticle volume fraction, as well as the skin friction, local Nusselt and Sherwood numbers. The results indicate that dual solutions exist for shrinking case. The effects of various controlling parameters on these quantities are investigated. It is found that both the skin friction coefficient and the local Sherwood number decrease while the local Nusselt number increases with increasing intensity of Buoyancy Force.
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Combined Effect of Buoyancy Force and Navier Slip on Entropy Generation in a Vertical Porous Channel
Entropy, 2012Co-Authors: Adetayo Samuel Eegunjobi, Oluwole Daniel MakindeAbstract:In this paper, we investigate the combined effects of Buoyancy Force and Navier slip on the entropy generation rate in a vertical porous channel with wall suction/injection. The nonlinear model problem is tackled numerically using Runge–Kutta–Fehlberg method with shooting technique. Both the velocity and temperature profiles are obtained and utilized to compute the entropy generation number. The effects of slip parameter, Brinkmann number, the Peclet number and suction/injection Reynolds number on the fluid velocity, temperature profile, Nusselt number, entropy generation rate and Bejan number are depicted graphically and discussed quantitatively.
Mei Yang - One of the best experts on this subject based on the ideXlab platform.
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numerical study of the characteristic influence of the helically coiled tube on the heat transfer of carbon dioxide
Applied Thermal Engineering, 2016Co-Authors: Mei YangAbstract:Abstract The cooling heat transfer of supercritical CO 2 is simulated numerically in the horizontal helically coiled tube using RNG k – e turbulence model. The parameters of the tube are: inner diameter of 4 mm, a length of 2000 mm, a pitch of 10 mm, radius of helically coiled tube of 20 mm, curvature of 0.1. It is found that the heat transfer coefficient fluctuates from top to bottom along the flow direction. On this basis, the effect of the pitch p , tube diameter of helically coiled tube d , radius of helically coiled tube R on the heat transfer coefficient ( h ) are studied. The results show that the h increases as the p , d , R increases and is insensitive when the p , d , R further increases to higher values. The change condition of the pressure is different with the p , d , R increasing. At the same time the contours show that the effect of the Buoyancy Force on h is weaker than that of the centrifugal Force. A quantitative analysis is carried on to study the effect of gravity based on the setting conditions and the results shows that the effect of gravity can be ignorable on the heat transfer coefficient. The change condition of Ri g is consistent with that of Gr / Re 2.7 in judging the scope of the Buoyancy Force. The change condition of Ri c / Ri g indicates that the gravitational Buoyancy Force is more important than the centrifugal Buoyancy Force on the heat transfer coefficient under the setting conditions.
