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Entropy 2018, 20(8), 581; https://doi.org/10.3390/e20080581

Thermo-Fluid Characteristics of High Temperature Molten Salt Flowing in Single-Leaf Type Hollow Paddles

1
School of Energy and Power Engineering, Nanjing university of Science and Technology, Nanjing 210094, China
2
Shenzhen Douwin Technology Co., Ltd., Shenzhen 518116, China
3
Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla 666303, China
*
Author to whom correspondence should be addressed.
Received: 8 July 2018 / Revised: 2 August 2018 / Accepted: 5 August 2018 / Published: 7 August 2018
(This article belongs to the Special Issue Entropy Generation and Heat Transfer)
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Abstract

A single-leaf type paddle heat exchanger with molten salt as the working fluid is a proper option in high temperature heating processes of materials. In this paper, based on computational fluid dynamics (CFD) simulations, we present the thermo-fluid characteristics of high temperature molten salt flowing in single-leaf type hollow paddles in the view of both the first law and the second law of thermodynamics. The results show that the heat transfer rate of the hollow paddles is significantly greater than that of solid paddles. The penalty of the heat transfer enhancement is additional pressure drop and larger total irreversibility (i.e., total entropy generation rate). Increasing the volume of the fluid space helps to enhance the heat transfer, but there exists an upper limit. Hollow paddles are more favorable in heat transfer enhancement for designs with a larger height of the paddles, flow rate of molten salt and material-side heat transfer coefficient. The diameter of the flow holes influences the pressure drop strongly, but their position is not important for heat transfer in the studied range. Other measures of modifying the fluid flow and heat transfer like internal baffles, more flow holes or multiple channels for small fluid volume are further discussed. For few baffles, their effects are limited. More flow holes reduce the pressure drop obviously. For the hollow paddles with small fluid volume, it is possible to increase the heat transfer rate with more fluid channels. The trade-off among fluid flow, heat transfer and mechanical strength is necessary. The thermo-fluid characteristics revealed in this paper will provide guidance for practical designs. View Full-Text
Keywords: hollow paddle; molten salt; thermo-fluid; entropy generation rate; trade-off hollow paddle; molten salt; thermo-fluid; entropy generation rate; trade-off
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Rajeh, T.; Tu, P.; Lin, H.; Zhang, H. Thermo-Fluid Characteristics of High Temperature Molten Salt Flowing in Single-Leaf Type Hollow Paddles. Entropy 2018, 20, 581.

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