Christopher Micallef

Improved Cooling in the End Region of a Strip-Wound Totally Enclosed Fan-Cooled Induction Electric Machine

Computational fluid-dynamics modeling has been used to investigate the cooling of the end region of a two-pole strip-wound totally enclosed fan-cooled induction motor. The modeling is validated by experimental measurements. The changes in airflow and heat transfer that each configuration gives are discussed, and recommendations are made of features that can be used to achieve lower convective thermal resistance in the end region.

Electrical machines for high speed applications with a wide constant-power region requirement

This paper discusses the issues associated with the design of high speed machines with a wide constant-power region requirement. Using described multi-physics design environments, which put equal weight on the electromagnetic, thermal and mechanical considerations, the suitability and power density achievable using Induction Machines (IM) and Permanent Magnet Synchronous Machines (PMSM) are compared.

Improvements in Air Flow in the End Region of a Large Totally Enclosed Fan Cooled Induction Motor

The power density of modern induction machines is constantly increasing due to industry demands and material costs. This gives rise to higher operating temperatures. This paper investigates how the cooling characteristics of the end region of totally enclosed fan cooled induction machines may be enhanced. With the aid of computational fluid dynamics techniques various features in the end region which need particular attention when designing such machines are highlighted. It turns out that computational fluid dynamics tools are indispensable for a proper design exercise

Mathematical Model of a Lithium-Bromide/Water Absorption Refrigeration System Equipped with an Adiabatic Absorber

The objective of this paper is to develop a mathematical model for thermodynamic analysis of an absorption refrigeration system equipped with an adiabatic absorber using a lithium-bromide/water (LiBr/water) pair as the working fluid. The working temperature of the generator, adiabatic absorber, condenser, evaporator, the cooling capacity of the system, and the ratio of the solution mass flow rate at the circulation pump to that at the solution pump are used as input data. The model evaluates the thermodynamic properties of all state points, the heat transfer in each component, the various mass flow rates, and the coefficient of performance (COP) of the cycle. The results are used to investigate the effect of key parameters on the overall performance of the system. For instance, increasing the generator temperatures and decreasing the adiabatic absorber temperatures can increase the COP of the cycle. The results of this mathematical model can be used for designing and sizing new LiBr/water absorption refrigeration systems equipped with an adiabatic absorber or for optimizing existing aforementioned systems.

Mathematical model of a vapour absorption refrigeration unit

By means of carefully devised assumptions, a simple linear model is presented for an absorption refrigeration unit employing either water-lithium bromide or ammonia-water refrigerant-absorbent pairs. Absorption systems are an alternative to vapour compression systems by being thermally activated. Such heat energy may come from the sun or even from hot exhaust gases from a particular engineering process. A thorough investigation of the optimal operating temperatures is necessary to ensure effective operation of the system. By means of this simulation, the system response to varying absorber, generator and condenser temperatures was analyzed. (Received in October 2009, accepted in March 2010. This paper was with the authors 1 month for 1 revision.)