Numerical investigation of turbulent two-phase flow in direct steam generation solar receiver

Abstract

Direct Steam Generation (DSG) technology is gaining significant attention in concentrated solar power (CSP) systems due to its potential to increase plant efficiency and environmental sustainability. However, DSG presents considerable challenges, particularly in horizontal receiver configurations under non-uniform heating, due to complex two-phase flow and heat transfer phenomena. The objective of this thesis is to investigate the thermal and hydrodynamic behavior of direct steam generation in a horizontal solar receiver, focusing on the effect of different operating parameters. The thesis comprises two major objectives: firstly, the development of advanced numerical models for simulating two-phase flow and validating the PROMES-CNRS novel DSG experimental setup. Secondly, a systematic parametric study analyzing the influence of key variables—including mass flow rate, tilt angle, and heat flux distribution—on flow regime transitions, vapor production, heat transfer partitioning, and wall temperature distributions. NEPTUNE-CFD and SYRTHES were used for this complex two-phase coupled simulation. Understanding the capability and identifying the limitations of NEPTUNE-CFD in accurately modeling these complex flow regimes is also an integral part of this work. The numerical results showed good agreement with the experimental data for most of the cases. NEPTUNE-CFD demonstrates the capability to capture the essential physics of DSG when the solar receiver is tilted. However, under stratified flow conditions, NEPTUNE-CFD was found to struggle with accurately modeling the steam convective heat flux, leading to higher errors at the vapor-rich top wall. The parametric study revealed that tilt angle promotes more uniform temperature fields and enhances vapor removal, while horizontal operation leads to stratified flow, higher top wall temperatures, and greater risk of thermal stress. Additionally, it is observed that the variation of mass flow rate significantly affects vapor production, flow regime development, and heat transfer performance. The findings provide valuable insights and practical guidance for the design and operation of reliable, efficient CSP plants employing DSG technology and highlights key modeling challenges to address in future research.

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