Thiago Dutra

Thermal conductivity evaluation of fractional-slot concentrated winding machines

The use of Fractional-Slot Concentrated Windings (FSCW) in electrical machines allows more compact, efficient and reliable design with respect to machines equipped with distributed windings. However, an electromagnetic design linked to a thermal analysis of the electrical machine is mandatory to achieve the desired performance and to fulfill the requirements of efficiency and reliability. One of the most critical issues in thermal design of electrical machines is to assign fair values for the input parameters of the thermal simulation models, particularly those related to the stator winding insulation system. This paper deals with the assessment of the equivalent thermal conductivity of the insulation system of FSCW machines. For this purpose, three FSCW electrical machines for different applications were evaluated via an experimental method based on a dc thermal transient test. Whereas the investigated machines present different characteristics among themselves, different approaches were required to properly estimate the thermal conductivity.

Loop Heat Pipe: Design and Performance During Operation

Loop heat pipes (LHPs) have been extensively investigated and considered for the thermal control of satellites and other space equipments, but some geometric limitations, as well as the use of hazardous working fluids must be considered. Focusing on such concerns, a LHP was designed and built to accomplish certain requirements towards its future application in space missions. The designing procedure had to consider some limitations, such as a reduced scale capillary evaporator and the use of an alternative working fluid. Thus, an experimental LHP was built and tested for acetone as the working fluid to manage up to 70 W of heat transfer rate. The experimental results showed a good thermal management performance of the proposed LHP for the imposed limitations to its design. The proposed LHP presented to be a reliable thermal management device for applying in future space missions, especially when considering the use of a less hazardous working fluid.

Analysis of the Thermal Performance of a Loop Heat Pipe

Focusing on the concern of predicting the LHP thermal performance, this paper presents an experimental investigation of a LHP. The experimental performance of the LHP is analyzed, which used acetone as the working fluid, operating in a range of heat to be dissipated form 2 to 70 W. The LHP presented reliable operation during both startup and power cycles applied to it. The experimental results were then compared to a mathematical model, which was able to predict the LHP operation temperature. This comparison presented good agreement between the experimental and calculated results using the model. The results gathered from this experimental investigation are intended to be used in future LHP application in both ground and space projects.Copyright

Thermal Conductivity Evaluation of Fractional-Slot Concentrated-Winding Machines

The use of Fractional-Slot Concentrated Windings (FSCW) in electrical machines allows more compact, efficient and reliable design with respect to machines equipped with distributed windings. However, an electromagnetic design linked to a thermal analysis of the electrical machine is mandatory to achieve the desired performance and to fulfill the requirements of efficiency and reliability. One of the most critical issues in thermal design of electrical machines is to assign fair values for the input parameters of the thermal simulation models, particularly those related to the stator winding insulation system. This paper deals with the assessment of the equivalent thermal conductivity of the insulation system of FSCW machines. For this purpose, three FSCW electrical machines for different applications were evaluated via an experimental method based on a dc thermal transient test. Whereas the investigated machines present different characteristics among themselves, different approaches were required to properly estimate the thermal conductivity.

Winding Thermal Model for Short-Time Transient: Experimental Validation in Operative Conditions

This paper presents the validation of a first-order winding thermal model in machine operative conditions. The proposed model can be used in motor control strategies for the winding temperature prediction during transient overload, or vice versa, for the prediction of the maximum time duration of the overload maintaining the winding temperature within the limit imposed by the class of insulation. The thermal model has been validated using two different electrical machines. The first one is a 10-kW automotive starter-generator prototype for mini-hybrid powertrain equipped with distributed bar windings, while the second one is a 2.2 kW total enclosed fan cooled industrial induction motor equipped with conventional stranded wire windings. Depending on the application for both machines, a short-duty transient operation in overload conditions could be required. In particular, the automotive starter-generator must accomplish engine cranking and torque assistance during the vehicle acceleration and braking, while the industrial induction machine could operate in intermittent service in overload conditions when used in machine tool applications. As a consequence, an accurate stator winding temperature prediction is mandatory to fully exploit the machine performance. For both motors, the thermal model parameters have been evaluated by fast experimental approach, and, subsequently, the model has been validated during operative overload conditions.

Thermal parameters evaluation for stator fractional-slot concentrated winding machines

The aim of this paper is the determination of the thermal parameters and thermal coefficients for a fractional-slot concentrated winding machine. In previous papers, the authors presented a detailed analysis of the values obtained for machines equipped with distributed windings. Since the two winding topologies have a complete different realization, it has been mandatory to validate the approach proposed for distributed windings even in the case of concentrated windings. In this sense, the experimental tests and the model validation have been performed using a reduced-scale prototype of a generator properly designed for aircraft applications. The machine is equipped with single-layer fractional-slot concentrated windings and the coils are produced using Litz wire. The obtained results indicate that the proposed method to estimate the thermal parameters and coefficients for distributed winding machines can be used for this specific fractional-slot concentrated winding machine as well.

Thermal parameters evaluation of a fractional-slot concentrated winding machine for home appliance applications

Efficiency and reliability of electrical machines are considerably affected by their thermal performance, therefore, thermal simulation models have been developed to support the thermal design of electrical machines. However, the adoption of reasonable values to represent the input thermal parameters required in such simulations is as important as the modeling strategy itself. This paper deals with the determination of thermal parameters concerning a Fractional-Slot Concentrated Winding “FSCW” electrical machine properly designed for home appliance applications. Equivalent thermal resistance and capacitance of the winding insulation system composed by winding, impregnation, and coil support are evaluated. In addition, the equivalent thermal conductivity value has been assessed using a novel approach suitable for FSCW machines. A critical analysis of the obtained results has been conducted and it has shown that the equivalent thermal conductivity of the FSCW machine is up to two times higher than the values obtainable for conventional distributed winding machines.

Experimental validation in operative conditions of winding thermal model for short-time transient

This paper presents the validation of a first-order winding thermal model in machine operative conditions. The proposed model can be used in motor control strategies for the winding temperature prediction during transient overload or vice versa, for the prediction of the maximum time duration of the overload maintaining the winding temperature within the limit imposed by the class of insulation. The thermal model has been validated using two different electrical machines. The first one is a 10 kW automotive starter-generator prototype for mini-hybrid powertrain equipped with distributed bar windings, while the second one is a 2.2 kW total enclosed fan cooled industrial induction motor equipped with conventional stranded wire windings. To both machines it is mainly required a short-duty transient operation in overload conditions. In particular, the automotive starter-generator must accomplish the engine cranking and torque assistance during the vehicle acceleration and braking, while the considered industrial induction machine has to operate in intermittent service in overload conditions for machine tool applications. As a consequence, an accurate stator winding temperature prediction is mandatory to fully exploit the machine performance. For both motors, the thermal model parameters have been evaluated by fast experimental approach and subsequently, the model has been validated during operative overload conditions.

Theoretical and Experimental Analysis of the Superheating in Heat Pump Compressors

This paper presents an analysis of the effects of refrigerant superheating in a compressor operating in a heat pump system. In a conventional cooling system, refrigerant superheating inside the compressor is largely responsible for overall energy losses, increasing the compression specific work. Similarly, superheating increases the compression loss in a compressor operating in a heat pump system. However, superheating regards to the heating capacity of the system as well, since it affects the final temperature of compression and the inlet temperature of the condenser, therefore. Thus, the superheating analysis in compressors applied to heat pump purposes requires a more detailed treatment if compared to refrigeration applications, otherwise results may lead to mistaken interpretations. In this work, a new approach to identify and understand the superheating losses in compressors submitted to heat pump applications is proposed. Experimental results are presented in a compressor losses inventory and considerations are made on this way.

Numerical prediction of turbulent flow and heat transfer in the suction muffler of a small reciprocating compressor

The efficiency of reciprocating compressors adopted for household refrigeration is quite affected by gas superheating in the suction system. This paper reports a numerical analysis of turbulent flow through the suction muffler of a small reciprocating compressor with especial attention to the heat transfer process. The integration of the flow conservation equations (continuity, momentum and energy) is carried out via the finite volume method. A hermetic reciprocating compressor was instrumented with several sensors to measure heat flux at the muffler wall, as well as temperature and velocity transients undergone by the fluid flow in the suction chamber. Overall, the numerical results are seen to be in reasonable agreement with the measurements, allowing the description of complex phenomena due to pressure pulsation and heat transfer in the muffler.