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Research Papers: Natural and Mixed Convection

# Natural Convection Heat Transfer From a Short or Long, Solid or Hollow Horizontal Cylinder Suspended in Air or Placed on Ground

[+] Author and Article Information
Swastik Acharya

Department of Mechanical Engineering,
Indian Institute of Technology Kharagpur,
BRH, A—513,
Kharagpur 721 302, India
e-mail: swastik.acharya8@gmail.com

Sukanta K Dash

Professor
Department of Mechanical Engineering,
Indian Institute of Technology Kharagpur,
Kharagpur 721 302, India
e-mail: sdash@mech.iitkgp.ernet.in

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received December 7, 2016; final manuscript received January 28, 2017; published online March 21, 2017. Assoc. Editor: Zhixiong Guo.

J. Heat Transfer 139(7), 072501 (Mar 21, 2017) (13 pages) Paper No: HT-16-1792; doi: 10.1115/1.4035919 History: Received December 07, 2016; Revised January 28, 2017

## Abstract

Numerical simulations have been conducted to study natural convection heat transfer from solid or hollow cylinders in the laminar range of Ra spanning from 104 to 108 for L/D in the range of $0.05≤(L/D)≤20$. Interesting flow structures around the thin hollow cylinder have been observed for small and large L/D. It has been found that the average Nu for solid or hollow horizontal cylinders in air is marginally higher than when they are on ground for the entire range of L/D and Ra limited up to 107. Up to a Ra of 107 Nu for a solid cylinder in air is higher than that of Nu for a hollow cylinder in air but when Ra exceeds 107 Nu for a hollow cylinder is marginally higher than that of the solid cylinder until an L/D of 0.2. When, L/D rises beyond 0.2 the situation reveres causing Nu for a solid cylinder to be again higher than that of the hollow cylinder when suspended in air. A solid cylinder on ground has higher Nu compared to that of a hollow cylinder on ground up to a Ra of 106. However, for higher Ra of 108 a hollow cylinder on ground has higher Nu compared to that of a solid cylinder on ground until an L/D of 5 and after that the situation reverses again.

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Topics: Cylinders

## Figures

Fig. 1

Flow vector around a (a) hollow and (b) solid isothermal cylinder on ground, L/D = 1, Ra = 10

Fig. 2

(a) A solid or thin hollow cylinder in air with the computational domain around it, (b) solid or the thin hollow cylinder lying on ground with its computational domain (aschematic representation)

Fig. 3

Influence of domain height on average Nu for a solid cylinder in air

Fig. 4

(a) Cell arrangement for hollow cylinder in air, (b) cross-sectional view, and (c) blown up view near the cylinder wall

Fig. 5

Average Nu for a hollow cylinder in air as a function of number of cells

Fig. 6

Average Nu for a solid cylinder in air, a comparison with experimental correlation

Fig. 7

(a) Average Nu for a solid cylinder in air or lying on ground as a function of L/D and (b) average Nu for a hollow cylinder in air or lying on ground as a function of L/D

Fig. 8

Temperature plume near a hollow cylinder on (a) ground and in (b) air, Ra = 108, L/D = 5

Fig. 9

Average Nu for a solid cylinder in air or ground when end faces are isothermal

Fig. 10

Comparison of Nu between a solid and hollow cylinder in air

Fig. 11

Comparison of Nu between a solid and hollow cylinder on ground

Fig. 12

Comparison of heat loss from the outer and inner surface of a hollow cylinder when placed in air

Fig. 13

Comparison of heat loss from the outer and inner surface of a hollow cylinder when placed on ground

Fig. 14

Velocity vector around a hollow cylinder placed on ground for Ra = 106, L/D (a) 0.5, (c) 1, and (e) 2

Fig. 15

Temperature plume around a hollow cylinder at Ra = 106 and L/D (a) 1, (b) 2, and (c) 5 when the cylinder is in air

Fig. 16

Temperature plume around a hollow cylinder at Ra = 106 and L/D (a) 1, (b) 2, and (c) 5 when the cylinder is on ground

Fig. 17

Thermal plume around a short solid cylinder in air (a)–(b) and ground (c)(d), Ra = 106

Fig. 18

velocity vector around a short solid cylinder in air (a)–(b) and ground (c)–(d), Ra = 106

Fig. 19

Thermal buoyant plume around a solid and hollow cylinder in air or ground

Fig. 20

A comparison of predicted Nu with that of the computed value for a solid cylinder in air

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