scholarly journals Heat Transfer Enhancement in Unsteady MHD Natural Convective Flow of CNTs Oldroyd-B Nanofluid under Ramped Wall Velocity and Ramped Wall Temperature

Entropy ◽  
2020 ◽  
Vol 22 (4) ◽  
pp. 401 ◽  
Author(s):  
Talha Anwar ◽  
Poom Kumam ◽  
Ilyas Khan ◽  
Wiboonsak Watthayu
Keyword(s):  
Heat Transfer ◽  
Carbon Nanotubes ◽  
Shear Stress ◽  
Differential Equations ◽  
Heat Transfer Enhancement ◽  
Wall Temperature ◽  
Convective Flow ◽  
Transfer Enhancement ◽  
Wall Condition ◽  
The Difference

This article analyzes heat transfer enhancement in incompressible time dependent magnetohydrodynamic (MHD) convective flow of Oldroyd-B nanofluid with carbon nanotubes (CNTs). Single wall carbon nanotubes (SWCNTs) and multi-wall carbon nanotubes (MWCNTs) are immersed in a base fluid named Sodium alginate. The flow is restricted to an infinite vertical plate saturated in a porous material incorporating the generalized Darcy’s law and heat suction/injection. The governing equations for momentum, shear stress and energy are modelled in the form of partial differential equations along with ramped wall temperature and ramped wall velocity boundary conditions. Laplace transformation is applied to convert principal partial differential equations to ordinary differential equations first and, later, complex multivalued functions of Laplace parameter are handled with numerical inversion to obtain the solutions in real time domain. Expression for Nusselt number is also obtained to clearly examine the difference in rate of heat transfer. A comparison for isothermal wall condition and ramped wall condition is also made to analyze the difference in both profiles. A graphical study is conducted to analyze how the fluid profiles are significantly affected by several pertinent parameters. Rate of heat transfer increases with increasing volume fraction of nanoparticle while shear stress reduces with elevation in retardation time. Moreover, flow gets accelerated with increase in Grashof number and Porosity parameter. For every parameter, a comparison between solutions of SWCNTs and MWCNTs is also presented.

Numerical Study of the Effects of Different Buoyancy Models on Supercritical Flow and Heat Transfer

2013 ◽  
Author(s):  
X. Y. Xu ◽  
T. Ma ◽  
M. Zeng ◽  
Q. W. Wang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Enhancement ◽  
Wall Temperature ◽  
Mass Flux ◽  
Wall Heat Flux ◽  
Turbulent Heat ◽  
Transfer Enhancement ◽  
Temperature Prediction ◽  
Flow And Heat Transfer

Due to the dramatic changes in physical properties, the flow and heat transfer in supercritical fluid are significantly affected by buoyancy effects, especially when the ratio of inlet mass flux and wall heat flux is relatively small. In this study, the heat transfer of supercritical water in uniformly heated vertical tube is numerically investigated with different buoyancy models which are based on different calculation methods of the turbulent heat flux. The applicabilities of these buoyancy models are analyzed both in heat transfer enhancement and deterioration conditions. The simulation results show that these buoyancy models make few differences and give good wall temperature prediction in heat transfer enhancement condition when the ratio of inlet mass flux and wall heat flux is very small. With the increase of wall heat flux, the accuracy of wall temperature prediction reduces, and the differences between these buoyancy models become larger. No buoyancy model can currently make accurate wall temperature prediction in deterioration condition in this study.

scholarly journals Experimental Investigation of Heat Transfer Enhancement by Pulsating Flow in a Minichannel

2021 ◽  
Vol 2116 (1) ◽  
pp. 012031
Author(s):  
P Kumavat ◽  
S M O’Shaughnessy
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Enhancement ◽  
Flow Rate ◽  
Wall Temperature ◽  
High Performance ◽  
Amplitude Ratio ◽  
Constant Heat Flux ◽  
Pulsating Flow ◽  
Transfer Enhancement

Abstract The increasing power density requirements of next generation high performance electronic devices has resulted in ever-increasing heat flux densities which necessitates the evolution of new liquid-based heat exchange technologies. Pulsating flow in single-phase cooling systems is viewed as a potential solution. In this study, an experimental analysis of thermally developed pulsating flow in a rectangular minichannel is conducted. The channel test setup involves a heated bottom section approximated as a constant heat flux boundary. Asymmetric sinusoidal pulsating flows with a fixed flow rate amplitude ratio of 0.9 and Womersley numbers (Wo) of 0.51 and 1.6 are investigated. The wall temperature profiles are recorded using infrared thermography. It is observed that the transverse wall temperature profile is influenced by the sudden velocity variations of such characteristic waveforms. A heat transfer enhancement of 6% was determined for asymmetric flow pulsations of Wo > 1 over the steady flow with a potential augmentation for higher flow rate amplitudes.

Heat Transfer in Liquid-Liquid Taylor Flow in a Mini-Scale Tube With Constant Wall Temperature

2015 ◽  
Author(s):  
W. M. Adrugi ◽  
Y. S. Muzychka ◽  
K. Pope
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Wall Temperature ◽  
Silicone Oil ◽  
Transfer Enhancement ◽  
Constant Wall Temperature ◽  
Flow Rates ◽  
Taylor Flow ◽  
Low Viscosity ◽  
Wide Range

In this paper, heat transfer enhancement using liquid-liquid Taylor flow is examined. The experiments are conducted in mini-scale tubes with constant wall temperature. The segmented flow is created using several fractions of low viscosity silicone oil (1 cSt) and water for a wide range of flow rates and segment lengths. The variety of liquids and flow rates change the Prandtl, Reynolds, and capillary numbers. The dimensionless mean wall flux and the dimensionless thermal flow length are used to analyze the experimental heat transfer data. The comparison shows the heat transfer rate for Taylor flow is higher than in single-phase flow. The heat transfer enhancement occurs due to internal circulation in the fluid segments.

Chaotic Heat Transfer in a Laminar Pulsating Flow With Constant Wall Temperature

2014 ◽  
Author(s):  
Mohammad Karami ◽  
Mojtaba Jarrahi ◽  
Zahra Habibi ◽  
Ebrahim Shirani ◽  
Hassan Peerhossaini
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Secondary Flow ◽  
Wall Temperature ◽  
Pulsating Flow ◽  
Mean Flow ◽  
Transfer Enhancement ◽  
Constant Wall Temperature ◽  
Homoclinic Connections

The correlation between heat transfer enhancement and secondary flow structures in laminar flows through a chaotic heat exchanger is discussed. The geometry consists of three bends; the angle between curvature planes of successive bends is 90°. Numerical simulations are performed for both steady and pulsating flows when the walls are subjected to a constant temperature. The temperature profiles and secondary flow patterns at the exit of bends are compared in order to characterize the flow. Simulations are carried out for the Reynolds numbers range 300≤Re≤800, velocity amplitude ratios (the ratio of the peak oscillatory velocity component to the mean flow velocity) 1≤β≤2.5, and wall temperatures 310 ≤ Tw(K) ≤ 360. The results show that in the steady flow, heat transfer enhancement occurs with increasing Reynolds number and wall temperature. However, heating homogenization becomes almost independent of Reynolds number when homoclinic connections exist in the flow. Moreover, at high values of wall temperature, heat transfer enhancement is greater than mixing improvement due to the presence of homoclinic connections. In the pulsating flow, Nusselt number improves with β, and β≥2 is a sufficient condition for heat transfer enhancement. The formation and development of homoclinic connections are correlated with the heating homogenization.

Heat Transfer in Liquid–Liquid Taylor Flow in Miniscale Curved Tubing for Constant Wall Temperature

2017 ◽  
Vol 139 (2) ◽  
Author(s):  
Wesam Adrugi ◽  
Yuri Muzychka ◽  
Kevin Pope
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Wall Temperature ◽  
Transfer Enhancement ◽  
Constant Wall Temperature ◽  
Constant Length ◽  
Transfer Rates ◽  
Taylor Flow ◽  
Low Viscosity ◽  
Copper Tubing

In this paper, heat transfer enhancement using liquid–liquid Taylor flow in miniscale curved tubing for isothermal boundary conditions is examined. Copper tubing with an inner tube diameter of D = 1.65 mm and different radii of curvature and lengths is used in the experiments. Taylor flow is created using water and low-viscosity silicone oils (0.65 cS, 1 cS, and 3 cS) to examine the effect of Prandtl number on heat transfer rates in curved tubing. A series of experiments are conducted using tubing with constant length and variable curvature as well as variable length and constant curvature. The experimental results are compared with models for liquid–liquid Taylor flow in straight tubing and single-phase flow in curved tubes. The results of the research highlight the effects of liquid–liquid Taylor flow in curved tubing. This research provides new insights into the effect of curvature on heat transfer enhancement for liquid–liquid Taylor flow in miniscale curved tubing, at a constant wall temperature.

Heat Transfer in Liquid-Liquid Taylor Flow in Mini-Scale Curved Tubing for Constant Wall Temperature

2016 ◽  
Author(s):  
W. M. Adrugi ◽  
Y. S. Muzychka ◽  
K. Pope
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Wall Temperature ◽  
Transfer Enhancement ◽  
Constant Wall Temperature ◽  
Constant Length ◽  
Transfer Rates ◽  
Taylor Flow ◽  
Low Viscosity ◽  
Copper Tubing

In this paper, heat transfer enhancement using liquid-liquid Taylor flow in mini scale curved tubing for isothermal boundary conditions is examined. The copper tubing has an inner tube diameter of Di = 1.65 mm with different radii of curvature and lengths. Taylor flow is created using water and low viscosity silicone oils (0.65 cSt, 1 cSt, 3 cSt) to examine the effect of Prandtl number on heat transfer rates in curved tubing. A series of experiments are conducted using tubing with constant length and variable curvature, as well as variable length and constant curvature. The experimental results are compared with models for liquid-liquid Taylor flow in straight tubing and single-phase flow in curved tubes. The results of the research develop a new model for liquid-liquid Taylor flow in curved tubing. This research provides new insights into the effect of curvature on heat transfer enhancement for liquid-liquid Taylor flow in mini scale curved tubing, at a constant wall temperature.

Numerical Study of EHD-Enhanced Forced Convection Using Two-Way Coupling

2003 ◽  
Vol 125 (4) ◽  
pp. 760-764 ◽  
Author(s):  
M. Huang ◽  
F. C. Lai
Keyword(s):  
Heat Transfer ◽  
Electric Field ◽  
Heat Transfer Enhancement ◽  
Forced Convection ◽  
Electric Fields ◽  
Numerical Solutions ◽  
Numerical Study ◽  
Transfer Enhancement ◽  
Wide Range ◽  
The Difference

Numerical results are presented for heat transfer enhancement using electric field in forced convection in a horizontal channel. The main objective of the present study is to verify the assumption that is commonly used in the numerical study of this kind of problem, which assumes that the electric field can modify the flow field but not vice versa (i.e., the so-called one-way coupling). To this end, numerical solutions are obtained for a wide range of governing parameters (V0=10, 12.5, 15 and 17.5 kV as well as ui=0.0759 to 1.2144 m/s) using both one-way and two-way couplings. The results obtained, in terms of the flow, temperature, and electric fields as well as the heat transfer enhancement, are thoroughly examined. Since the difference in the results obtained by two approaches is insignificant, it is concluded that the assumption of one-way coupling is valid for the problem considered.

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