Two-phase natural circulation loop behaviour at atmospheric and subatmospheric conditions

Abstract

This paper aims to present the steady-state behaviour of two-phase natural circulation loop at atmospheric and sub-atmospheric conditions. One-dimensional numerical approach is adopted to evaluate various system parameters, with special emphasis on spatial variation of thermo-physical properties and flashing. Homogeneous equilibrium model is applied for two-phase flows. An in-house code is developed in MATLAB to solve numerical model iteratively. It is observed that consideration of spatial variation of thermo-physical properties can precisely predict the loop behaviour. The evaluated results are validated with the open literature and reasonably good agreement is observed. The heater inlet temperature, inlet pressure and heat flux are found to have significant influence on spatial variation of pressure, temperature and enthalpy. As system pressure decreases from atmospheric to sub-atmospheric (1–0.8 atm), it is observed that the sub-atmospheric loop gives a higher mass flow rate compared to atmospheric loop at lower heat fluxes. However, as the heat flux increases in the sub-atmospheric loop, the mass flow rate is reduced due to increased drag force in the loop.

Effect of heater and condenser orientations on fluid flow behaviour in a two-phase natural circulation loop

“…The authors earlier presented a numerical model to analyse the two phase NCL. 18 So, in the present work the same assumptions, governing equations and solution procedure is used. Figure 1 depicts the possible NCL configurations by varying the heater and condenser orientation either in horizontal or vertical direction.…”

Steady-state and nonlinear stability analysis for the feasibility of different fluids in a supercritical natural circulation loop

“…The NCL is a passive system in which the coolant flows due to the buoyancy effects caused by the density difference between the hot and cold limbs. It eliminates the requirement of a pump for the natural circulation systems (NCSs) [10][11][12] .…”

“…The analysis explained that if a supercritical water system follows a density wave instability, then Ledinegg excursive instability and pressure drop oscillations will not occur. Sudheer et al 10 considered a homogeneous equilibrium model for two-phase flows in NCL. They performed the steady-state analysis at atmospheric and subatmospheric conditions to evaluate the effect of operating pressure, heat flux, and heater inlet temperature for NCL.…”