Calculation of heat transfer coefficients for explosive boiling of a liquid under conditions of low pressure

The paper discusses the problem of determining the temperature head for calculating the heat transfer coefficient during explosive boiling of a liquid on a smooth horizontal surface under conditions of low pressure. The task of the work is obtaining the method for determining the characteristic pressure for calculating the temperature of saturated vapors. As a result, it is found that the difference between the heat transfer coefficients calculated at the pressure specified at the beginning of the experiment and the pressure averaged over time differ on average by 5%.

A new method to determine the causes of deviation in cylinder pressure curves of motored reciprocating piston engines

Simulation calibration of modern engines to test bench measurements, mainly matching the indicated pressure curves in the combustion chamber, is a time consuming task that requires high user experience to manage a multitude of adjustment parameters. In the scope of this work an automated process for calibrating simulations at motored engine operating points is presented. This is achieved using characteristic pressure deviation curves, based on 1D simulations of a simplified base model. They incorporate the dimensionless deviation of the cylinder pressure originating from one parameter. A set of these curves is scaled and superposed to recreate the original pressure deviation between simulation and measurement. The scaling factor is used to quantify each parameter’s suggested adjustment value. This work presents the workflow of creating the characteristic pressure deviation curves, matching the deviation between measurement and simulation and determining the adjustment values. Further, the methodology is tested for interference of different parameters. A series of applications, ranging from 1D and 3D CFD simulation test cases to real world applications in different engines, concludes this work.

Experimental constraints on the ordinary chondrite shock darkening caused by asteroid collisions

Context. Shock-induced changes in ordinary chondrite meteorites related to impacts or planetary collisions are known to be capable of altering their optical properties. Thus, one can hypothesize that a significant portion of the ordinary chondrite material may be hidden within the observed dark C/X asteroid population. Aims. The exact pressure-temperature conditions of the shock-induced darkening are not well constrained. Thus, we experimentally investigate the gradual changes in the chondrite material optical properties as a function of the shock pressure. Methods. A spherical shock experiment with Chelyabinsk LL5 was performed in order to study the changes in its optical properties. The spherical shock experiment geometry allows for a gradual increase of shock pressure from ~15 GPa at a rim toward hundreds of gigapascals in the center. Results. Four distinct zones were observed with an increasing shock load. The optical changes are minimal up to ~50 GPa. In the region of ~50–60 GPa, shock darkening occurs due to the troilite melt infusion into silicates. This process abruptly ceases at pressures of ~60 GPa due to an onset of silicate melting. At pressures higher than ~150 GPa, recrystallization occurs and is associated with a second-stage shock darkening due to fine troilite-metal eutectic grains. The shock darkening affects the ultraviolet, visible, and near-infrared region while changes to the MIR spectrum are minimal. Conclusions. Shock darkening is caused by two distinct mechanisms with characteristic pressure regions, which are separated by an interval where the darkening ceases. This implies a reduced amount of shock-darkened material produced during the asteroid collisions.

Static and dynamic characteristics of proportional directional valve

This article deals with experimental measurement and numerical simulation of static and dynamic characteristics of the proportional directional valve. The characteristics of the proportional directional valve are measured on experimental equipment. At the static characteristic, pressure drop on the proportional directional valve, flow and oil temperature are measured on this equipment. The spool position is measured to determine of the dynamic characteristic of the proportional directional valve. Mathematical model of the proportional directional valve is created using Matlab SimScape Fluids software and is complemented by a mathematical model of the experimental equipment. The simulation results on the mathematical model are compared with the results of the experimental measurement.