Supercritical Pseudo-Boiling and its Relevance for Transcritical Injection

Abstract

In this paper, a new interpretation of cryogenic jet break-up in supercritical environments is introduced. It is firmly established that under these conditions a pure fluid will exhibit neither latent heat of vaporization nor surface tension. The jet undergoes a transition from a dense cryogenic fluid to an ideal gas as it mixes and blends with the surrounding warmer gas. Regarding the thermodynamic process, this transition is characterized by large changes in density and very small changes in temperature as energy is supplied. The state where density changes and the heat capacity are maximal is sometimes called 'pseudo-boiling' in the literature. However, no clear definition of this process is available, its very existence debated. In this paper, the first quantitative pseudo-boiling analysis is presented. It can be shown that pseudo-boiling exists along a line which effectively structures supercritical fluid states. An equation for this continuation of the coexistence line is given. Across this line, a continuous state transition can be identified. The temperature at pseudo-boiling replaces the critical temperature as relevant parameter at supercritical pressures. By introducing a suitable definition for a supercritical fluid boundary, supercritical jet break-up can be quantified thermodynamically. This suggests a novel, thermal, jet break-up mechanism. Experimental evidence from the literature is shown, further supported by CFD simulations. The pseudo-boiling effect is found to play a role for injection conditions of reduced pressures smaller than 3, and reduced temperatures lower than 1.2.

Comparison of energy-, pressure- and enthalpy-based approaches for modeling supercritical flows

“…This has been previously reported by Hickey et al [6], Terashima and Koshi [7], Kawai et al [8] and Schmitt et al [9]. In Reynolds Average Navier Stokes (RANS) simulations, gradients are diffused and well resolved which minimizes the problem [10,11,12,13,14,15,16,17]. In Direct Numerical Simulations (DNS), grid resolution is selected to resolve all scales, which also circumvents the issue.…”

Transcritical diffuse-interface hydrodynamics of propellants in high-pressure combustors of chemical propulsion systems

“…This temperature depends on pressure and is not too different from T c (e.g., T pb ∼ 130 K at 40 bar and T pb ∼ 150 K at 60 bar, both for N 2 , for which K). In particular, T pb corresponds approximately to the temperature where a second-order phase transition occurs, with the density, viscosity and thermal conductivity plunging as transition from a liquid-like to a gas-like state occurs, and with the specific heat at constant pressure displaying a characteristic finite-amplitude spike [69,70]. As the pressure becomes increasingly larger than P c , the distinction between liquid-like and gas-like supercritical behavior is increasingly more difficult to ascertain.…”

Analysis of heat transfer mechanism in supercritical fluids from the aspect of pool heating

“…From a theoretical perspective, the mechanisms for improved heat transfer and deteriorated heat transfer are still controversial. According to observations of bubble-like structures and flow noise such as subcritical boiling, some studies (Ackerman, 1970;Banuti and Hannemann, 2014;Nasuti and Pizzarelli, 2020;Xu et al, 2020) proposed a pseudo-boiling theory and likened the improved heat transfer to nuclear boiling, and the deteriorated heat transfer to film boiling. Another theory focused on the buoyancy and flow acceleration effects caused by changes in the properties (McEligot et al, 1970;Petukhov et al, 1972;Hiroaki et al, 1973;Liu et al, 2017;Xu et al, 2017).…”