Article Preview
TopIntroduction
Etsion et al. (1997) discussed the misalignment of a two-phase mechanical seal, which poses unique challenges due to variations in temperature profile and phase distribution in the working fluid. The thermohydrodynamic approach takes these variations into account by incorporating sophisticated mathematical models that describe the thermal and hydrodynamic behavior of the system. Iterative solutions allow the equations governing heat transfer and phase change to be solved simultaneously, providing an accurate representation of the boiling interface. It has been shown that, under certain operating conditions, particularly those characterized by a modified Sommerfeld number, it is possible to use several approximate solutions to calculate the boiling radius. The modified Sommerfeld number is a dimensional parameter that combines the effects of rotational speed, fluid viscosity, and applied load, thus influencing the characteristics of boiling and heat transfer in the packing.
A hydrodynamic journal bearing (Fig. 1) is a component that provides guidance during the rotation of rotating machines, such as turbines and reactors. This equipment is widely used due to its adequate load support, simplicity, and better damping characteristics when operating under very severe conditions, such as high rotational speeds and high radial loads (Pfeil et al., 2021). However, as the speed increases a portion of the oil will evaporate, adding a new phase to the flow. Therefore, it is essential to comprehend the impact of the multiphase flow.
Figure 1. (a) sketch of a hydrodynamic journal bearing and (b) cross-section of a hydrodynamic journal bearing
Numerous industries, including petrochemicals and nuclear technology, use gas–liquid two-phase flows (Ozbayoglu & Ozbayoglu, 2009). As a result of the close connection between the distribution phase and many essential design and engineering parameters such as pressure, mass transfer, and heat transfer, determining the distribution, or rather determining the patterns of two-phase flow, is one of the main issues in two-phase flow analysis (Ishii et al., 2004).
Experimental approaches have been employed for analysis due to the two-phase flow's complexity and issues with using computational methods to represent these flows. One of the main drawbacks of experimental approaches is that the flow maps they produce are typically accurate for only a narrow range of flow parameters, making it risky to generalize them to other circumstances (Galbiati & Andreini, 1992).
Currently, computational techniques are used in investigations of the lubrication performance of sliding bearings due to their high calculation efficiency and low cost. Although computational fluid dynamics (CFD) software is useful for handling complex issues, it typically needs to be verified by theoretical analysis and experimental results.
The flow in a lubricant film is supposed to be laminar in fundamental lubrication theory. However, in high-speed machinery, the flow of a lubricant coating is no longer laminar, but rather turbulent (Ghosh et al., 2017). Over the past decades, several researchers have created varied ideas to analyze the turbulent flow and its influence in various lubrication conditions.
Taylor (1973) presented a numerical study of the lubrication performance of inclined slider bearings operating in a turbulent environment. He incorporated the turbulent-flow condition into the pressure-regulating equation using two turbulent models, the Constantinescu model and the Ng–Pan model. The results show that load support is better when compared to laminar flow, but friction force is increased in the turbulent domain, which is a disadvantage. Furthermore, the two hypotheses produced similar results for a wide range of operating conditions.
Solghar and Gandjalikhan Nassab (2013) used a numerical method to examine the thermohydrodynamic (THD) characteristics of journal bearings with finite lengths. Using a CFD technique, they studied the three-dimensional THD characteristics of journal bearings with a single axial groove operating in a turbulent environment. Their findings demonstrate that, depending on the Reynolds number, the predicted performance of finite journal bearings operating in turbulent conditions might vary significantly.