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Experimental and numerical investigation of temperature distribution and heat loss of molten salt tank foundation at different scales

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Abstract

The two-tank thermal energy storage system with a mixture of sodium nitrate and potassium nitrate is one of the most common ways in concentrated solar power plants. However, the unreasonable thermal performance of tank foundations such as excessive heat loss and overheating of concrete slab could result in local molten salt solidification and foundation settlement. This work proposes a novel foundation configuration with road base, light expanded clay aggregate, thermal clay blocks and fire bricks as insulation materials. The temperature distribution and heat loss of the tank foundations are studied at different scales through experimental and numerical methods. A laboratory foundation is set up to prove the feasibility of foundation materials, which is used in the thermal energy storage system of the 1 MWth pilot plant. According to the results, the pilot foundation has a reasonable temperature distribution. Moreover, the foundation configuration and materials are applied to an industrial molten salt tank foundation. The maximum temperature of external surface of the foundation drops from 162.6 °C to 37.3 °C, the maximum temperature of concrete slab decreases from 96.1 °C to 43.2 °C, and the heat loss of foundation reduces by 39.8%. The results indicate that the foundation with the proposed configuration and materials could enhance the thermal performance of the tank foundation and decrease the heat loss through the tank foundation. The proposed foundation is of great significance for guiding the construction of the thermal storage system of commercial concentrated solar power plants.

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Abbreviations

a ms :

molten salt absorptivity

\( {\dot{g}}_{us} \) :

irradiation on molten salt upper surface (W/m2)

\( {\dot{m}}_{in, ms} \) :

mass flow rate entering the control volume (kg/s)

\( {\dot{m}}_{out, ms} \) :

mass flow rate leaving the control volume (kg/s)

\( \dot{Q} \) :

total heat loss of molten salt (W)

\( {\dot{Q}}_b \) :

heat loss through tank bottom (W)

\( {\dot{Q}}_{\mathrm{d}w} \) :

heat loss through dry walls (W)

\( {\dot{Q}}_{so} \) :

heat loss to soil (W)

\( {\dot{Q}}_{us} \) :

heat loss through molten salt upper surface (W)

\( {\dot{Q}}_{ven} \) :

heat loss to ventilating system (W)

\( {\dot{Q}}_{ww} \) :

heat loss through wet vertical walls (W)

S b :

tank bottom area (m2)

S us :

area of molten salt upper surface (m2)

S ww :

wet vertical wall area (m2)

T b :

tank bottom temperature (°C)

T amb :

ambient temperature (°C)

T gu :

gas ullage temperature (°C)

T i :

insulation temperature (°C)

T ms :

molten salt temperature (°C)

T sky :

sky temperature (°C)

T so :

soil temperature (°C)

T ts :

tank shell temperature (°C)

T us :

upper surface molten salt temperature (°C)

T ww :

wet vertical wall temperature (°C)

α b :

superficial heat transfer coefficient at tank bottom (W/(m2·K))

α ext :

superficial heat transfer coefficient at external surface (W/(m2·K))

α us :

superficial heat transfer coefficient at molten salt upper surface (W/(m2·K))

α ww :

superficial heat transfer coefficient at wet vertical wall (W/(m2·K))

ε ms :

molten salt thermal emissivity.

λ i :

thermal conductivity of insulation (W/(m·K))

λ ts :

thermal conductivity of tank shell (W/(m·K))

σ :

Stefan-Boltzmann constant (W/(m2·K4))

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Acknowledgments

This work was supported by the National Science Fund for Distinguished Young Scholars (51825605).

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Authors and Affiliations

  1. State Key Laboratory of Clean Energy Utilization, Institute for Thermal Power Engineering, Zhejiang University, Hangzhou, 310027, China

    Hao Zhou, Hua Shi, Jiakai Zhang & Mingxi Zhou

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  1. Hao Zhou
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  2. Hua Shi
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Correspondence to Hao Zhou.

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Zhou, H., Shi, H., Zhang, J. et al. Experimental and numerical investigation of temperature distribution and heat loss of molten salt tank foundation at different scales. Heat Mass Transfer 56, 2859–2869 (2020). https://doi.org/10.1007/s00231-020-02905-x

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