Numerical Simulation of Natural Convection Heat Transfer of Nanofluid With Cu, MWCNT, and Al2O3 Nanoparticles in a Cavity With Different Aspect Ratios

2019 ◽  
Vol 11 (6) ◽  
Author(s):  
Hossein Goodarzi ◽  
Omid Ali Akbari ◽  
Mohammad Mohsen Sarafraz ◽  
Majid Mokhtari Karchegani ◽  
Mohammad Reza Safaei ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Al2o3 Nanoparticles ◽  
Natural Convection Heat Transfer ◽  
Conductive Heat ◽  
Convection Heat ◽  
Closed Cavity ◽  
Aspect Ratios ◽  
Hot Zone

Effect of the size of a closed cavity and different nanoparticles on natural convection heat transfer is investigated using the finite volume method. In the current numerical study, free convection of nanofluid with Cu, multi-walled carbon nanotubes, and Al2O3 nanoparticles is considered at Rayleigh numbers (Ra) of 10–100,000 inside a two-dimensional rectangular cavity with different aspect ratios. Results of this study show that in the presence of cooling fluid with low temperature and hot zone in the cavity, due to the temperature difference between the fluid and hot zone, heat transfer occurs. Heat transfer in the cavity is influenced by fluid circulation caused by natural convection heat transfer and conductive heat transfer mechanism.

Effect of Wall Heat Conduction on Natural Convection Heat Transfer in a Square Enclosure

1985 ◽  
Vol 107 (1) ◽  
pp. 139-146 ◽  
Author(s):  
D. M. Kim ◽  
R. Viskanta
Keyword(s):  
Heat Transfer ◽  
Heat Conduction ◽  
Natural Convection ◽  
Solid Wall ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Square Enclosure ◽  
Void Fractions ◽  
Aspect Ratios

This paper presents numerical and experimental results for buoyancy-induced flow in a two-dimensional, fluid-filled enclosure. Rectangular cavities formed by finite conductance walls of different void fractions and aspect ratios are considered. Parametric heat transfer calculations have been performed and results are presented and discussed. Local and average Nusselt numbers along the cavity walls are reported for a range of parameters of physical interest. The temperatures in the walls were measured with thermocouples, and the temperature distributions in the air-filled cavity were determined using a Mach-Zehnder interferometer. Good agreement has been obtained between the measured and the predicted temperatures in both the solid wall and in the fluid using the mathematical model. Wall heat conduction reduces the average temperature differences across the cavity, partially stabilizes the flow, and decreases natural convection heat transfer.

scholarly journals Heat Transfer Performance of Different Fluids During Natural Convection in Enclosures with Varying Aspect Ratios

2021 ◽  
Vol 287 ◽  
pp. 03010
Author(s):  
Rajashekhar Pendyala ◽  
Suhaib Umer Ilyas ◽  
Yean Sang Wong
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Heat Transfer Performance ◽  
Convection Heat Transfer ◽  
Heat Transfer Process ◽  
Natural Convection Heat Transfer ◽  
Transfer Performance ◽  
Convection Heat ◽  
Aspect Ratios

The heat transfer process takes place in numerous applications through the natural convection of fluids. Investigations of the natural convection heat transfer in enclosures have gained vital importance in the last decade for the improvement in thermal performance and design of the heating/cooling systems. Aspect ratios (AR=height/length) of the enclosures are one of the crucial factors during the natural convection heat transfer process. The investigated fluids consisting of air, water, engine oil, mercury, and glycerine have numerous engineering applications. Heat transfer and fluid flow characteristics are studied in 3-dimensional rectangular enclosures with varying aspect ratios (0.125 to 150) using computational fluid dynamics (CFD) simulations. Studies are carried out using the five different fluids having Prandtl number range 0.01 to 4500 in rectangular enclosures with the hot and cold surface with varying temperature difference 20K to 100K. The Nusselt number and heat transfer coefficients are estimated at all conditions to understand the dependency of ARs on the heat transfer performance of selected fluids. Temperature and velocity profiles are compared to study the flow pattern of different fluids during natural convection. The Nusselt number correlations are developed in terms of aspect ratio and Rayleigh number to signify the natural convection heat transfer performance.

Natural Convection Heat Transfer From Horizontal Rectangular Ducts

2006 ◽  
Vol 129 (9) ◽  
pp. 1195-1202 ◽  
Author(s):  
Mohamed E. Ali
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Aspect Ratios ◽  
Rayleigh Numbers

Experimental investigations have been reported on steady state natural convection from the outer surface of horizontal ducts in air. Five ducts have been used with aspect ratios (Γ=duct height/duct width) of 2, 1, and 0.5. The ducts are heated using internal constant heat flux heating elements. The temperatures along the surface and peripheral directions of the duct wall are measured. Longitudinal (circumference averaged) heat transfer coefficients along the side of each duct are obtained for laminar and transition regimes of natural convection heat transfer. Total overall averaged heat transfer coefficients are also obtained. Longitudinal (circumference averaged) Nusselt numbers are evaluated and correlated using the modified Rayleigh numbers for transition regime using the axial distance as a characteristic length. Furthermore, total overall averaged Nusselt numbers are correlated with the modified Rayleigh numbers, the aspect ratio, and area ratio for the laminar and transition regimes. The longitudinal or total averaged heat transfer coefficients are observed to decrease in the laminar region and to increase in the transition region. Laminar regimes are obtained only at very small heat fluxes, otherwise, transitions are observed.

Natural Convection and Sidewall Losses in Trapezoidal Groove Collectors

1981 ◽  
Vol 103 (2) ◽  
pp. 167-172
Author(s):  
L. Iyican ◽  
L. C. Witte ◽  
Y. Bayazitoglu
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Heat Losses ◽  
Natural Convection Heat Transfer ◽  
Conductive Heat ◽  
Convection Heat ◽  
Uniform Temperature ◽  
Number Range

Experimental data for heat transfer across air-filled inclined trapezoidal enclosures are reported for a Rayleigh number range of ∼2 × 103 to ∼5 × 107. The large side was cooled to uniform temperature while the opposing small side was electrically heated. The enclosures were completed by two aluminum sidewalls which simulated the reflective surfaces in moderately-concentrating solar collectors. The experiments show that conductive heat losses up the sidewalls can be very large even when the sidewalls are thermally insulated from the top and bottom surfaces. However, the conductivity of the sidewalls has only a small effect on convective heat transfer across the groove. Natural convection heat transfer in the groove can be correlated reasonably well by an equation of the form Nu = C Ra0.345.

Natural Convection Heat Transfer in Moderate Aspect Ratio Enclosures

1979 ◽  
Vol 101 (4) ◽  
pp. 655-659 ◽  
Author(s):  
B. A. Meyer ◽  
J. W. Mitchell ◽  
M. M. El-Wakil
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Aspect Ratio ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Aspect Ratios

Local and average heat transfer coefficients for natural convection between parallel plates separated by slats to create enclosures of moderate aspect ratio have been experimentally determined using an interferometric technique. The effects of Rayleigh number, tilt and slat angle, and aspect ratio on the Nusselt number have been determined. The Rayleigh number range tested was up to 7 × 104, and the aspect ratio (ratio of enclosure length to plate spacing) varied between 0.25 and 4. The angles of tilt of the enclosure with respect to the horizontal were 45, 60 and 90 deg. Slat angles of 45, 60, 90 and 135 deg were studied. The results obtained in a previous investigation [1] for aspect ratios of 9 to 36 are included to show continuity. The results indicate that the convective heat transfer is a strong function of the aspect ratio for aspect ratios less than 4. For aspect ratios in the range of 0.5 to 4, spacers between the plates increase, rather than decrease, natural convection heat transfer compared to that for long enclosures. Slat angles less than 90 deg (i.e., oriented downward) reduce convective heat transfer.

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