Reciprocating compressors are usually adopted in low and medium refrigeration capacity applications. Since these compressors are designed to run without the necessity of periodical maintenance, all the components are arranged inside a sealed shell. However, some of the physical phenomena in compressors, such as the compression process, friction in bearings and electrical motor losses act as heat sources, bringing about the elevation of the compressor temperature distribution and affecting the compressor performance.
Thermal management of compressors consists of designing their components with respect to layout, shape and material, in order to attend requirements of efficiency and reliability. In particular, the reduction of the gas initial compression temperature increases the volumetric and isentropic efficiencies. On the other hand, the operating temperatures of the lubricant oil and electrical motor are limited by reliability issues.
For the last 30 years, POLO has been developing research on compressor thermal management. The activities are divided into two major lines: computational modeling and experimental developments.Thermal simulation models have been developed for the temperature prediction of components of positive displacement compressors (reciprocating, rolling piston and scroll). Theoretical results are validated with measurements obtained from the experimental activities, which require the instrumentation of compressors with thermocouples, anemometers and heat flux sensors. By combining theoretical and experimental lines of research, it is possible to analyze alternatives of compressor thermal management in a fast and reliable manner.
Currently, the main thermal management researches performed at POLO concern the electrical motor of reciprocating compressors. One of them consists on the development of a multiphysics simulation model, coupling specific models for the compression cycle, the heat transfer between components and the induction motor operation. The comprehensive model is an object oriented code written in C++ programming language and can be used for the purpose of integrated multidisciplinary design of compressors. By using this model, it is possible to evaluate the effect of constructive and operating parameters on the motor components temperatures and the compressor thermodynamic performance. Other activity currently performed at POLO is the analysis of thermal management solutions for the induction motor of a reciprocating compressor adopted to commercial refrigeration. To that extent, both theoretical analyses and measurements have been carried out.