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Design of finned spherical enclosures and thermal performance evaluation under natural convection

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Abstract

Natural convection over spherical surfaces has been an important subject for numerical and experimental studies. Many applications like LED lights, optical systems, etc., housed inside the spherical enclosure, need fins on the spherical surfaces to cool the system naturally. One of the genuine usages of this research is the usage of normal convection to electronic circuits cooling. Many fascinating handy issues on regular convection heat exchange deal with the assortments of a complex shape. This present study discusses the thermal behaviour of rectangular fins of various heights and thicknesses on spherical surfaces. Fins on the spherical surface were simulated using computational fluid dynamics tool (Ansys—Fluent), the variation of Nusselt number for different fin configuration with Ra in the range of 1010 is studied. Simulation results were validated on a sector of a sphere with rectangular fins by measuring the temperature of various fin configurations. Here, the influence of fin thickness concerning the height of it is analysed at the different gap between fins is done and found that at particular fin spacing and height the thickness effects the heat transfer from the sphere. But by the current study, as thickness and spacing increase, the heat transfer rate decreases from the sphere, thus resulting in high temperature of the sphere. When heat flux over a 400 mm diameter free cooled hollow sphere varies from to 600 W/m2, the Raleigh number varies between 8.5 × 1009 and 3 × 1010, and the Nusselt number varies from 110 to 150. Hence, by the present study, it is observed that every time the heat transfer rate will not increase in increasing the fin thickness and it depends on the particular configuration as well as heat flux available at the source.

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Abbreviations

B :

Sphere surface (m)

Cp:

Specific heat (J Kg K−1)

D :

Diameter of the sphere (m)

Gr:

Grashof number

G :

Gravitational Pull (m s−2)

h :

Avg. heat transfer coefficient (W K m−2)

h c :

Convective heat transfer coefficient (W K m−2)

H :

Fin height (m)

k :

Thermal conductivity of air (W K m−1)

L :

Characteristic Length (m)

Nu:

Avg. Nusselt number

Pr:

Prandtl number

p :

Static pressure

Q conv :

Heat transfer due to convection (W)

Ra:

Raleigh Number

r :

Radial direction

S :

Spacing between the fins (m)

t :

Thickness of the fin (m)

T h,T H :

Hot wall temperature (K)

T c :

Cold wall temperature (K)

T :

Surface temperature (K)

T ∞ :

Bulk mean temperature (K)

T Atm :

Atmospheric temperature

u :

Velocity in x-direction (m s−1)

v :

Velocity in y-direction (m s−1)

μ :

Dynamic viscosity (Kg m s−1)

ν :

Kinematic viscosity (m2s−1)

β :

Volumetric expansion (K−1)

ρ :

Density of air (Kg m−3)

α :

Thermal diffusivity (m2s−1)

ΔT :

Temperature rise (K)

φ :

Azimuthal coordinate (degrees)

θ :

Angle over the sphere (degrees)

UQconv. :

Uncertainty of convective heat transfer (W)

Uhc :

Uncertainty of Convective heat transfer coefficient (W K m−2)

U(Nu)c :

Uncertainty of Convective Nusselt number

Uk:

Uncertainty of Thermal conductivity (W K m−1)

UTH :

Uncertainty of Hot wall temperature (K

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Authors and Affiliations

  1. SAMEER-Centre for Electromagnetics, Chennai, India

    Nainar Palani & Ganesan Dhanushkodi

  2. Department of Mechanical Engineering, SRM Institute of Science and Technology, Chennai, India

    Shaik Subhani & Rajendran Senthil Kumar

Authors
  1. Nainar Palani
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  2. Shaik Subhani
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  3. Rajendran Senthil Kumar
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  4. Ganesan Dhanushkodi
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Correspondence to Rajendran Senthil Kumar.

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Palani, N., Subhani, S., Kumar, R.S. et al. Design of finned spherical enclosures and thermal performance evaluation under natural convection. J Therm Anal Calorim 147, 3879–3888 (2022). https://doi.org/10.1007/s10973-021-10751-0

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  • DOI: https://doi.org/10.1007/s10973-021-10751-0

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