William Dwight Gerstler

Rotor End Losses in Multiphase Fractional-Slot Concentrated-Winding Permanent Magnet Synchronous Machines

Fractional-slot concentrated windings (FSCW) have been gaining a lot of interest in permanent magnet (PM) synchronous machines. This is due to the advantages they provide including shorter nonoverlapping end turns, higher efficiency, higher power density, higher slot fill factor, lower manufacturing cost, better flux-weakening capability resulting in wider constant power versus speed range, and fault tolerance. This paper focuses on eddy-current losses in the rotor clamping rings. Additionally, the loss in the nonmagnetic shaft with the option of i) metallic, ii) nonmetallic, and iii) metallic with shielding laminations clamping rings is analyzed. The study is based on finite element analysis (FEA). Desirable slot/pole combinations for different number of phases with both single- and double-layer windings are investigated. Experimental results for a three-phase 12 slot/10 pole design are presented to confirm that the losses in the rotor clamping rings can be very significant in case of FSCW machines and should not be overlooked during the design phase.

Rotor end losses in multi-phase fractional-slot concentrated-winding permanent magnet synchronous machines

Fractional-slot concentrated-windings (FSCW) have been gaining a lot of interest in Permanent Magnet (PM) synchronous machines. This is due to the advantages they provide including shorter non-overlapping end turns, higher efficiency, higher power density, higher slot fill factor, lower manufacturing cost, better flux-weakening capability resulting in wider constant power vs. speed range, and fault-tolerance. This paper focuses on eddy current losses in the rotor clamping rings. Losses in the non-magnetic shaft with the option of i) metallic, ii) nonmetallic, and iii) metallic with shielding laminations clamping rings are analyzed. The study is based on Finite Element Analysis (FEA). Desirable slot/pole combinations for different number of phases with both single- and double-layer windings are investigated. Experimental results for a 3-phase 12slot/10pole design will be presented to confirm that the losses in the rotor clamping rings can be very significant in case of FSCW and should not be overlooked during the design phase.

Scalable, low-cost, high performance IPM Motor for Hybrid Vehicles

Electric drive systems, which include electric machines and power electronics, are a key enabling technology for advanced vehicle propulsion systems that reduce the petroleum dependence of the ground transportation sector. To have significant effect, electric drive technologies must be economical in terms of cost, weight, and size while meeting performance and reliability expectations. This paper will provide an overview of the DoE/GE project to develop scalable, low-cost, high-performance next generation IPM traction motors for hybrid applications. The goal is to leap frog the state of the art and meet the FredomCar 2020 specifications. The paper will include the analytical and test results of the first proof-of-principle machine, analytical and preliminary test results for the second proof-of-principle machine as well as next steps.

Enhancement of natural convection using synthetic jets

Natural convection air-cooling is the method of choice for many low power electronics applications due to cost, availability, and reliability. However, its performance is very limited due to buoyancy dependent flow. Therefore, there is a need for further enhancement of natural convection. Enhanced natural convection will allow higher heat dissipation and still largely maintains the simplicity of passive cooling. This paper presents an experimental study on synthetic jet assisted heat transfer on a vertical hot finned plate. Synthetic jets generate pulsed airflow concurrent with buoyancy driven flow. Tests were conducted with a single jet to investigate the effect of jet placement on heat transfer enhancement, while multiple jets were tested to understand how thermal performance changes with the number of jets. As jet placement and the number of jets were varied, local temperature on the plate surface was measured. Comparing natural convection results with and without synthetic jet enhancement, local and average enhancements of heat transfer were quantified. It was found that the cooling enhancement increases with the number of jets, and is sensitive to jet placement. The results show that 3 times enhancement can be achieved with coefficient of performance of 47.

Introduction of an additively manufactured multi-furcating heat exchanger

Currently, additive manufacturing advancements are continuous and frequent. Heat transfer equipment, such as heat exchangers, are an exemplary application that benefits from additive manufacturing innovation. Attributes such as low weight and volume are attainable using additive designs. Additive also allows monolithic builds with no braze joints required. A novel geometry was conceptualized, built, tested, and compared to the test results from a conventionally manufactured heat exchanger. Both heat exchangers were designed to meet the same heat transfer and pressure drop specifications — those of a commercial fuel-cooled oil cooler. Results show the additive design has equivalent heat transfer to the conventional heat exchanger and meets the pressure drop specifications — while having 66% lower weight when built with the same material and 50% lower volume. Additionally, the additive build requires no braze joints thus is expected to have improved reliability compared to the conventional design. The additive heat exchanger design was successfully built, and passed vacuum leak tests, using four different materials: Aluminum, Titanium 6–4, Cobalt Chrome, and Inconel-718.

Heat Transfer Impact of Synthetic Jets for Air-Cooled Array of Fins

Free convection air cooling from a vertically placed heat sink is enhanced by upward concurrent pulsated air flow generated by mesoscale synthetic jets. The cooling enhancement is experimentally studied. An enhancement factor is introduced and defined as the ratio of convection heat transfer coefficients for jet-on (enhanced convection) to jet-off (natural convection) cooling conditions. To obtain the two coefficients, heat transfer by radiation is excluded. A high-resolution infrared (IR) camera is used to capture detailed local temperature distribution on the heat sink surface under both cooling conditions. Analysis is carried out to obtain local convection heat transfer coefficients based on measured local surface temperatures. The enhancement of convectional cooling by synthetic jets can be then quantified both locally and globally for the entire heat sink. Two categories of thermal tests are conducted. First, tests are conducted with a single jet to investigate the effects of jet placement and orifice size on cooling enhancement, while multiple jets are tested to understand how cooling performance changes with the number of jets. It is found that the cooling enhancement is considerably sensitive to jet placement. Jet flow directly blowing on fins provides more significant enhancement than blowing through the channel between fins. When using one jet, the enhancement ranges from 1.6 to 1.9 times. When multiple jets are used, the heat transfer enhancement increases from 3.3 times for using three jets to 4.8 times for using five jets. However, for practical thermal designs, increasing the number of jets increases the power consumption. Hence, a new parameter, “jet impact factor (JIF),” is defined to quantify the enhancement contribution per jet. JIF is found to change with the number of jets. For example, the four-jet configuration shows higher JIF due to higher contribution per jet than both three-jet and five-jet configurations.