Study on Temperature Distribution Characteristics Downstream of Internal Leaking Steam Valves in Power Plants and CFD Simulation

Internal leakage in power plant valves is often concealed by piping and equipment casings, making it difficult to detect. Yet even small leaks can cause substantial energy losses, especially for steam valves. Current monitoring methods, mainly acoustic and temperature-based, are largely limited to qualitative detection. To address the issues of difficult detection and effective quantitative monitoring of internal leakage in power plant steam valves, a high-temperature and high-pressure test bench was built, and a corresponding numerical model was established to investigate the temperature field distribution downstream of the leaking valve. Experimental and numerical results demonstrate that temperature monitoring is highly sensitive to steam leakage. When leakage occurs, the positive Joule–Thomson effect causes the pipe wall temperature to drop sharply from the valve upstream to its outlet; the temperature then rises rapidly before declining further downstream, with the steady-state peak consistently occurring at 2.5–7.5 DN downstream. Valve leakage causes obvious temperature stratification and severe pressure drop. This process approximates isenthalpic throttling and involves steam phase change. The large pressure differential across the valve also generates high flow velocity and choked flow. In addition, steam pressure and moisture exert a notable influence on temperature distribution. The findings of this study provide a theoretical foundation for quantitative research on valve leakage.