Coupled Model of Heat and Mass Balance for Droplet Growth in Wet Steam Non-Equilibrium Homogeneous Condensation Flow

Xu Han,Zhi Wang,Zhonghe Han,Wei Zeng,Jiangbo Qian

doi:10.3390/en10122033

Abstract

Because of the complexity of wet steam two-phase condensation flow, many problems remain to be solved. The important part of condensation theory—the calculation of the water droplet growth model in the transition zone—is not ideal; thus, it is necessary to develop a water droplet growth model with full-scale range. On the basis of the heat and mass transfer equilibrium in droplet growth, a coupled model of heat and mass balance for droplet growth is proposed. To verify the accuracy of this model, the differences and applicable ranges of various models were analysed using the experimental data of Peters and Meyer and two widely used models. In the free molecular flow region, the heat and mass balance model coincides with the Young low-pressure correction model. In the transition region, the heat and mass balance model agrees well with the experimental values of Peters and Meyer. In the continuous flow region, the heat and mass balance model coincides with the Gyarmathy model. Therefore, the heat and mass balance model can be used to accurately describe the growth process of water droplets in the arbitrary range of Knudsen numbers.

Highlights

The development level of the electric power industry is an important index for measuring the modernisation degree of a country
Assuming that the condensation nucleus and vapour phase are in a metastable equilibrium state, r* = 1.1 × 10−9 m
Through growth rate in the the aforementioned full range of Knudsen number (Kn).analysis, Model 3 can correctly calculate the droplet temperature; in addition, in the free molecular flow region, it coincides with Model 2, which is widely used at present

Summary

Introduction

The development level of the electric power industry is an important index for measuring the modernisation degree of a country. The steam turbine, as a type of power generator, plays an important role in the safe and economical operation of power plants [1]. In 2016, thermal power and nuclear power generation capacity accounted for approximately 78% of China’s power generation capacity. Given China’s energy structure, power generation in the few decades will continue to rely on steam turbines. Spontaneous two-phase condensation flow in a steam turbine is very complex and involves many disciplines of computational fluid dynamics, multiphase flow, heat and mass transfer, statistical thermodynamics, and gas dynamics. The wet steam spontaneous condensation and droplet growth process occurs at the nanometre scale, and micro-droplet surface tension and mass transfer have always been difficult problems. The calculation of non-equilibrium condensation flow involves many

Methods

Results

Conclusion