This study experimentally investigates the combined impact of several parameters on the two-phase flow distribution in an evaporator header for an air/water mixture, in flow pattern similarity with a low Global Warming Potential refrigerant. The test were performed at isothermal conditions under the assumption that phase change is negligible in an evaporator header. The water and air flow rates were varied and three inlet qualities were targeted (x=0.04,0.1and0.25). Total mass fluxes G ranging from 42 kg/(sm²) to 513 kg/(sm²) were covered. The impact of the fluid properties on the flow patterns was preliminary and theoretically evaluated by means of flow maps for all pipe directions: horizontal, vertical upward and vertical downward. A rectangular header connected to eight parallel channels of internal diameter (I.D.) of 10 mm was used to mimic an evaporator. Four header and channels orientations were investigated. The inlet position and the diameter of the feeding tube (23 mm or 56 mm) could be changed as well as the channels intrusion inside the header height. A flow pattern breaking device, also called splashing grid, was also tested at the inlet of the header. A Design Of Experiment (DOE) technique was used to build an optimized test matrix ensuring that the impact of each parameter individually as well as their combinations could be assessed in a balanced manner and within a minimum amount of tests. Forty-eight tests were needed. The standard deviation of the water flow distribution among the channels is set as comparative variable. Based on the experimental results, a ranking of the most influential parameters was established. The study highlights that the orientation of the header and channels is the most significant parameter impacting the flow distribution, followed the tube inlet position. The combined influence of the inlet tube position and diameter, the tube intrusion and the presence/absence of the splashing grid is evaluated for each of the four orientations. Based on these conclusions, design rules were established for each header and channel orientation. The findings of this research represent a significant advancement in the field and can serve as a foundation for greatly improving flow distribution within evaporators, thereby enhancing their thermal performance.

In this study, an infrared system is developed for accurate measurements of surface temperature and heat transfer on fast moving targets. The system was designed for the Oxford Turbine Research Facility, a world-leading experimental facility delivering highly engine representative, scalable heat transfer results for aerospace research. Infrared thermography is employed to acquire temperature maps of high-pressure turbine blades, allowing assessment of surface thermal conditions including heat transfer coefficient, adiabatic wall temperature, Nusselt number, cooling effectiveness, and metal effectiveness. Achieving accurate infrared thermography measurements in rotating turbomachinery experimental conditions is arduous due to reflections from the surroundings, low emissivity of metallic parts, and motion blur resulting from high speed. To overcome these challenges, calibration procedures were developed against a traceable standard using a bespoke steady experimental facility. A method to determine the reflected temperature from surroundings was also validated. Correction for all measurement disturbances is demonstrated to within the accuracy of the primary measurement thermocouple. Finally, the developed calibration method was validated on a fast-moving rotating geometry demonstrating accurate correction for all measurement disturbances, without the need for an in situ calibration. A detailed uncertainty analysis for each calibration step is also presented.

This paper compares the indirect cooling method using a heatpipe and air-cooled circular fins with conventional cooling methods like forced air convection and forced water convection for cooling power electronics placed underground. A two-module dual active bridge power converter with reconfigurable outputs for electric vehicle charging is used for the thermal analysis. The comparison is based on specific constraints imposed by semiconductor switch surface area requirements and the maximum junction temperature limit. A detailed analysis is presented, and performance parameters like convective resistance, pressure drop, and mechanical pumping power of the cooling systems as the function of volume flow of working fluid are obtained. Commercially available cooling components like extruded fin heatsinks, cold plate, and heat exchanger are used for conventional cooling methods analysis. Whereas indirect cooling using heatpipes and air-cooled circular fins is designed by performing individual analysis on a heatpipe sizing, air-cooled circular fin design, and heatpipe integrated base plate. This work also highlights the equivalent thermal resistance model for each cooling system.