A Steam Ejector Refrigeration System Powered by Engine Combustion Waste Heat: Part 2. Understanding the Nature of the Shock Wave Structure

Abstract

In general, engine fuel combustion generates 30% waste heat, which is disposed to the environment. The use of the steam ejector refrigeration to recycle the waste heat and transfer them to useful energy source could be an environmentally friendly solution to such an issue. The steam ejector is the main component of the ejector refrigeration system, which can operate at a low-temperature range. In this article, the internal shock wave structure of the ejector is comprehensively studied through the computation fluid dynamics (CFD) approach. The shock wave structure can be subdivided into two regions: firstly the pseudo-shock region consisting of shock train and co-velocity region; secondly the oblique-shock region composed of a single normal shock and a series of oblique shocks. The effect of the shock wave structure on both pumping performance and the critical back pressure were investigated. Numerical predictions indicated that the entrainment ratio is enhanced under two conditions including (i) a longer pseudo-shock region and (ii) when the normal shock wave occurs near the outlet. Furthermore, the system is stabilized as the back pressure and its disturbance is reduced. A critical range of the primary fluid pressure is investigated such that the pumping is effectively optimized.

CFD analysis of operating condition effects on optimum nozzle exit position of a supersonic ejector using the refrigerant R134a

“…This distance is sometimes presented in its nondimensional form with respect to the throat diameter. This factor has a highly significant effect on the ejector efficiency when the operating conditions are different from the on-design conditions [4][5][6][7]. The existence of at least an optimum NXP that maximizes the ejector performance was stated in different studies (Table 1).…”

A novel thermal management system for battery packs in hybrid electrical vehicles utilising waste heat recovery

“…It was found that when the nozzle exit position is fixed, the ejector's COP is positively related to the diameter of the constant section. Han et al studied the internal flow structure [28] and shock waves [29] inside a steam ejector powered by engine combustion waste heat. It was found that the internal flow structure, such as the pseudoshock region and normal shock position, can affect the entrainment ratio.…”

Optimum Efficiency of a Steam Ejector for Fire Suppression Based on the Variable Mixing Section Diameter

“…However, in the aspect of experimental study, the experimental study of the ejector is insufficient. Han et al reported the structure of the internal steam ejector flow [ 18 ] and shock wave [ 19 ] driven rejected combustion engine heat source. The research revealed the potential effect of the internal structure flow on the entrainment ratio (determined as the ratio between the suction and the motive nozzle mass flow rates), mainly the location of the normal shock and the pseudo-shock region.…”