PhD defence of Mr. Deepak Kumar Solanki at 10 AM in ME Auditorium.  His topic is 

Thermal Hydraulic Characteristics of Condensing and Evaporating flows

External Examiner:  Prof. K. Srinivasan - IIT Madras

Internal Examiner: Prof. Janani SM

Chairman: Prof. Narasimhan 

Supervisors: Prof. S.V. Prabhu and Prof. Arunkumar Sridharan

Abstract:

The current study is divided into two verticals: condensing flows (steam condensation in the presence of non-condensables) and evaporating flows (subcooled boiling). The condensing flow study focuses on improving containment safety, while the evaporating flow study aims to enhance plant capacity. In condensing flows, understanding the heat transfer coefficient is crucial for maintaining containment integrity during severe nuclear accidents and designing passive containment cooling systems (PCCS). Steam condensation in the presence of non-condensable gases (NCGs) plays a critical role in removing decay heat after accidents like LOCA and MSLB by cooling steam and reducing system pressure. PCCS enhances safety by using convection to condense steam on condenser tube surfaces. While many empirical correlations exist for condensation HTC considering operating parameters like system pressure, mass fraction and wall subcooling, fewer correlations address geometric factors such as tube diameter, length and orientation.
The study employs two approaches: forced coolant circulation in the condenser tube to analyze condensation HTC behavior in the presence of non-condensables and natural coolant circulation to demonstrate the proof of concept for sustaining a natural circulation loop. For forced coolant circulation, experiments are conducted to scrutinize condensation HTC in the presence of air as a NCG under conditions of 2–5.5 bar pressure, air-mass fractions of 0.28–0.7 and wall subcooling of 27–80°C. The impact of condenser tube diameter (48.2 mm, 32 mm, 22 mm and 16 mm) and inclination angles (90° and 68°) is also studied. Condensation HTC is found to be directly proportional to system pressure and inversely proportional to air-mass fraction, wall subcooling and diameter. Inclination angle positively affects HTC, while tube length shows weak dependency. A correlation for condensation HTC is proposed, with deviations within ±15% at a 95% confidence level.
In natural coolant circulation studies, experiments are performed for 48.2 mm diameter tubes under various initial air pressures. Insulation configurations, including insulating risers, downcomers, or both, are analyzed. Results indicate that a preheater reduces experimentation time to reach a steady state without affecting coolant flow rate. For a 48.2 mm tube and 800 W power, steady-state flow under natural circulation is 8–10 g/s.
Evaporating flow studies focus on the local HTC and pressure drop during subcooled boiling of water in horizontal smooth tubes, both with and without twisted tape (TT) inserts. Experiments under high heat and mass flux (HHHM) conditions consider tube diameters of 5.5 mm to 12 mm and operating parameters like mass flux (250–2000 kg/m²·s) and heat flux (up to 1837 kW/m²). Infrared thermography is employed to measure wall temperatures. Correlations for pressure drop ratio and two-phase HTC based on Jakob number, Boiling number and Prandtl number are developed. Twisted tape inserts enhance HTC at the cost of higher pressure drop penalties.