Influence of Critical Flow Rates on Characteristics of Enforced and Shear Flows in Circular Convergent-Divergent Channels

Leonid A Savin,Alexey V Kornaev,Elena P Kornaeva

doi:10.1155/2017/8761375

Leonid A Savin, Alexey V Kornaev + Show 1 more

Open Access

https://doi.org/10.1155/2017/8761375

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Abstract

Analysis of the reasons of critical flow rate occurrence in hydraulic tracts of cryogenic machines has been carried out. Theoretical expressions have been derived to calculate critical velocities in a boiling multiphase medium. Applied to hybrid fluid-film bearings with throttles for lubricant supply, a mathematical model has been developed to calculate pressure distribution and hydrodynamic reaction forces of a lubricant considering the influence of steam content and critical flows in throttle devices. Numerical results of phase state and load capacity calculations of a hybrid fluid-film bearing under lubricant’s critical flow rates condition have been presented.

Highlights

One could note the tendency to widen the field of application of cryogenic and low-boiling liquids, for example, liquid O2, H2, methane, and noble gases, as fuel components and parts of technological machines and cooling systems
As for positive effects, it could be noted that there are a slight decrease of power losses due to friction and some (∼20%) increase of load capacity due to anticipatory boiling of lubricant in the unloaded area of a bearing which results in redistribution of pressure and change in the main reaction force vector’s direction of a fluid film
With the increase of temperature of the supplied lubricant the boiling process spreads across the whole radial gap and results in rapid decrease of load capacity (3-4) due to a general decrease of pressure in the film

Summary

Introduction

One could note the tendency to widen the field of application of cryogenic and low-boiling liquids, for example, liquid O2, H2, methane, and noble gases, as fuel components and parts of technological machines and cooling systems These materials have particular thermophysical properties, namely, low viscosity, compressibility in liquid state, and low boiling temperatures Tboil. Triple (critical) point K separates liquid and gas from some metastatic zones where no difference between phase properties can be observed [2] Under real conditions, these materials exist in liquid state under pressures of 1–50 MPa and are transported in special tanks. As for positive effects, it could be noted that there are a slight decrease of power losses due to friction and some (∼20%) increase of load capacity due to anticipatory boiling of lubricant in the unloaded area of a bearing which results in redistribution of pressure and change in the main reaction force vector’s direction of a fluid film. In a number of cases heat capacity, thermal conductivity, compressibility, and coefficient of expansion are of great significance in formation of load bearing fluid film

Mathematical Model

Test Rig

Bearing

Conclusion