Heat Transfer Enhancement of Supercritical Nitrogen Flowing Downward in a Small Vertical Tube: Evaluation of System Para
- PDF / 4,667,812 Bytes
- 17 Pages / 595.22 x 842 pts (A4) Page_size
- 100 Downloads / 144 Views
https://doi.org/10.1007/s11630-020-1377-0
Article ID: 1003-2169(2020)00-0000-00
Heat Transfer Enhancement of Supercritical Nitrogen Flowing Downward in a Small Vertical Tube: Evaluation of System Parameter Effects ZHU Xiaojing1*, LYU Zhihao1, YU Xiao2, LI Qiang1, CAO Maoguo2, REN Yongxiang2 1. Key Laboratory of Ocean Energy Utilization and Energy Conservation of Ministry of Education, Dalian University of Technology, Dalian 116024, China 2. Shenyang Aeroengine Research Institute, Aero Engine Corporation of China, Shenyang 110015, China © Science Press, Institute of Engineering Thermophysics, CAS and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract: In this paper, the heat transfer enhancement (HTE) of supercritical nitrogen flowing downward in a vertical small tube (diameter 2 mm) is studied using the commercial software CFX of Ansys16.1, to provide theoretical guidance on the design of high-performance heat transfer systems. An effective numerical simulation method, which employs the SSG Reynolds stress model with enhanced wall treatment, is applied to study the heat transfer of supercritical nitrogen under typical working conditions. The objective is to evaluate the effect of the main parameters taking into account the buoyancy and flow acceleration effects. Simulation results are compared with results calculated from three well-known empirical correlations and the applicability of empirical correlation is discussed in detail. It is discovered that the Watts and Chou correlation accurately fits the simulation results of supercritical nitrogen and the Dittus-Boelter and Jackson correlations can only be used for high-pressure conditions. The HTE of supercritical nitrogen is closely related to the laminar sub-layer and buffer layer of a boundary layer. The buoyancy effect on the HTE should be considered at low mass flux conditions, and thermal acceleration can be completely ignored for the cases studied. The special HTE featured by the increment in heat transfer coefficient with increasing heat flux is discovered at low pressure, and simulation results proved that this HTE is caused by the combined actions of buoyancy as well as significant variations in specific heat and viscosity.
Keywords: supercritical nitrogen, heat transfer enhancement (THE), numerical simulation, vertically downward flow, system parameter evaluation
1. Introduction Supercritical fluids have unique thermodynamic properties compared with subcritical fluids; therefore, they have a wider range of applications, especially in the domains of energy production, environment protection, and green processes [1–3]. For example, supercritical water is being actively used in the new generation of nuclear power plants to improve efficiency, and Received: Apr 30, 2020
supercritical CO2 has been proven to exhibit more advantages in a supercritical Rankine cycle for low-grade thermal conversion [4]. The heat transfer performance of supercritical fluid is key for its application in industrial fields and has therefore garnered significant
Data Loading...
