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Experimental and numerical study of natural convection in bottom-heated cylindrical cavity filled with molten salt nanofluids

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Abstract

This paper combines numerical and experimental to study the heat transfer by free convection for nanofluids of molten salt within a cavity with cylindrical shape which is heated at the bottom and releases heat at the top. The aim is to acquire the free convection laws for nanofluids of molten salt in a cylindrical cavity. It is found that after adding nanoparticles, the molten salts have lower viscosity, higher flow velocity and higher heat transfer rate, and therefore, the free convection heat transfer is enhanced. Meanwhile, nanofluids Nusselt number is larger than that of the molten salts at the same Rayleigh number. In addition, as the classical Garon’s equation cannot provide good predictions of free convection heat transfer for the nanofluids of molten salt, this paper establishes a free convection equation for the nanofluids of molten salt in a cylindrical cavity. This equation is able to predict with an error less than 20% the experimental results. Therefore, the findings can provide a basis for engineering applications of nanofluids and for designing optimal systems of heat stockpile with a single tank.

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Abbreviations

Nu :

Nusselt number

Ra :

Rayleigh number

Pr :

Prandtl number

d :

Diameter of cavity (m)

I :

Electric current (A)

U :

Voltage (V)

Q T :

Total heating power of heater (W)

Q R :

Radiative heat dissipation per unit time (W)

Q :

Heat flux of natural convection (W)

A :

Heating area (m2)

h :

Heat transfer coefficient (W m−2 K−1)

T wo :

Surface temperature of external wall of thermal insulation layer (K)

T a :

Ambient temperature (K)

T w :

Bottom temperature (K)

ΔT :

Temperature difference between bottom and top surface (K)

l :

Distance between bottom and top surface (m)

T c :

Top temperature (K)

T m :

Average temperature (K)

T :

Temperature (K)

ρ :

Density (kg m−3)

λ :

Thermal conductivity (W m−1 K−1)

T c :

Top temperature (K)

T f :

Qualitative temperature (K)

ρ c :

Density at Tc temperature (kg m−3)

g :

Acceleration caused by gravity (m s−2)

ρ f :

Density of base salt (kg m−3)

ρ nf :

Density of nanofluid (kg m−3)

(Cp)f :

Specific heat of base salt (J kg−1 K−1)

(Cp)nf :

Specific heat of nanofluid (J kg−1 K−1)

μ f :

Viscosity of base salt (Pa S)

μ nf :

Viscosity of nanofluid (Pa S)

λ f :

Thermal conductivity of base salt (W m−1 K−1)

λ nf :

Thermal conductivity of nanofluid (W m−1 K−1)

v f :

Velocity of base salt (m s−1)

v nf :

Velocity of nanofluid (m s−1)

ε :

Surface emissivity ε = 0.05

σ b :

Blackbody radiation constant σb = 5.67 × 10−8 (W m−2 K−4)

ν :

Kinematic viscosity (m2 s−1)

α :

Thermal diffusivity(m2 s−1)

β :

Coefficient of thermal volume expansion (K−1)

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Acknowledgements

This work was supported by the National Natural Science Foundation of China with Grant Number 51576006, the Qinghai Science and Technology Project with grant number 2017-GX-A3 and National Key Research and Development Program of China with Grant Number 2017YFB0903603.

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Authors and Affiliations

  1. Key Laboratory of Enhanced Heat Transfer and Energy Conservation, Ministry of Education of China, College of Environmental and Energy Engineering, Beijing University of Technology, Beijing, 100124, China

    Qiang Yu, Yuanwei Lu, Cancan Zhang & Yuting Wu

  2. Department of Energy Sciences, Lund University, P.O. Box 118, 22100, Lund, Sweden

    Bengt Sunden

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  1. Qiang Yu
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Correspondence to Yuanwei Lu.

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Yu, Q., Lu, Y., Zhang, C. et al. Experimental and numerical study of natural convection in bottom-heated cylindrical cavity filled with molten salt nanofluids. J Therm Anal Calorim 141, 1207–1219 (2020). https://doi.org/10.1007/s10973-019-09112-9

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