Comparative study of turbulence model predictions of upward supercritical fluid flow in vertical rod bundle subchannels

Analysis of the Dynamic Characteristics of the Pump Valve System of an Ultra-High Pressure Liquid Hydrogen Reciprocating Pump

This paper developed a 3D physical model of the hydraulic end of a high-pressure liquid hydrogen reciprocating pump to research the dynamic characteristics of the pump valve system. Based on dynamic mesh technology, we analyzed the coupling characteristics of pump valve and plunger motion and spool force considering the leakage model, closure model of valve gap, and compressibility of liquid hydrogen. Further, we analyzed the effect of the spring stiffness and preload force on the laws of motion of the pump valve. Finally, a liquid hydrogen pressurization test was conducted to revise the simulation model and verify the accuracy of the simulation. The results of the simulation and test show that the simulation method in this paper can simulate the liquid hydrogen pressurization process more accurately and obtain the motion law of the suction and discharge valves. Both the suction and discharge valves have an opening hysteresis angle of about 40°, and there is a strong coupling relationship between the spool motion and the piston motion and forces. The greater the preload force of the suction valve, the more obvious the oscillation effect of the suction valve. As the preload of the discharge valve increases, the opening hysteresis angle of the discharge valve increases significantly and the closing hysteresis angle decreases. The results of the research can provide some useful reference for the design of pump valves of high-pressure liquid hydrogen reciprocating pumps.

Heat Transfer Limitations in Supercritical Water Gasification

Supercritical water gasification (SCWG) is a promising technology for the valorization of wet biomass with a high-water content, which has attracted increasing interest. Many experimental studies have been carried out using conventional heating equipment at lab scale, where researchers try to obtain insight into the process. However, heat transfer from the energy source to the fluid stream entering the reactor may be ineffective, so slow heating occurs that produces a series of undesirable reactions, especially char formation and tar formation. This paper reviews the limitations due to different factors affecting heat transfer, such as low Reynolds numbers or laminar flow regimes, unknown real fluid temperature as this is usually measured on the tubing surface, the strong change in physical properties of water from subcritical to supercritical that boosts a deterioration in heat transfer, and the insufficient mixing, among others. In addition, some troubleshooting and new perspectives in the design of efficient and effective devices are described and proposed to enhance heat transfer, which is an essential aspect in the experimental studies of SCWG to move it forward to a larger scale.