Surface Temperature Effect on Convective Heat Transfer Coefficients for Jet Impingement Cooling of Electric Machines With Automatic Transmission Fluid

Abstract

In this study, the results of NREL’s continued work on experimental characterization of the thermal performance of free-surface jets of automatic transmission fluid impinged on a heated target surface are presented. The measured heat transfer coefficients are useful for understanding factors influencing performance of driveline fluid-based cooling systems for electric machines and help designers in developing high-performance, power-dense and reliable machines. Experiments were carried out for different fluid and target surface temperatures (50°C, 70°C, and 90°C for the fluid and 90°C, 100°C, 110°C, and 120°C for the target surface). Impinging jet velocities (0.5 m/s to 7.5 m/s) and the jet position on the target surface (center versus edge) were also varied. The impinging angle was kept at 90° relative to the target surface. It was found that higher target surface temperature increased heat transfer coefficients, namely, increasing surface temperature from 90°C to 120°C enhanced heat transfer coefficient values at higher impinged jet velocities (7.5 m/s) by up to 15%.

Experiment and Simulation Study on the Cooling Performance of Oil-Cooling PMSM with Hairpin Winding

“…In [28], the CHTC of oil-cooling on end winding was determined via an experiment. Due to the similar cooling process, it can be used as a reference to verify the correctness of the established model in this paper.…”

“…Due to the similar cooling process, it can be used as a reference to verify the correctness of the established model in this paper. Based on the experiment settings and boundary conditions shown in [28], we established a model and finished the simulation. The results show that the CFD results are in good agreement with the experimental results, as shown in Figure 4c.…”

“…Tcu is winding temperature is winding heat source. (c) Experiment[28] and CFD results at fluid temperature 50 °C at var inlet velocity values (jet on center, Tsurf = 90 °C).…”

Numerical Study of Oil Jet Cooling in Electric Traction Motors with Hairpin Windings

“…Jet impingement cooling is known to provide excellent heat extraction capabilities. For instance, oil jet cooling on a continuous surface is capable of achieving a heat transfer coefficient of 8000 W/m 2 k with a jet velocity of 7.5 m/s [15]. But, the hairpin end-windings have inherent air gaps and a complex geometry, which considerably decreases the ability of the impinging jet to wet the target surface.…”

An experimental study of local heat transfer using high Prandtl number liquid jets

“…Other studies have encountered this phenomenon using oil as working fluid. In their recent works on electric machine stator cooling, Kekelia et al [29] highlighted the influence of surface temperature, which could be linked to heating flux. They found a relative difference on mean Nusselt number as high as 15% between a 90°C and a 120°C imposed condition on the target.…”