A study of off-design performance improvement for a centrifugal refrigerant compressor

Abstract

This study numerically investigates the effects of changing vaned diffuser angles and vaneless diffuser widths of a twostage centrifugal refrigerant compressor on the reduction of surge flow rate and the improvement of part-load performance. The first stage has a low-solidity vaned diffuser, while the second stage has a vaneless diffuser. The analysis results show that adjusting the angle of low-solidity vaned diffuser in the first stage can lower the surge flow rate and keeps high efficiencies at low flow rates. The inlet guide vane of the first stage can also lower the surge flow rate; however, their simultaneous actuation cannot lower the surge flow rate further. Reducing the vaneless diffuser width of the second stage can lower the surge flow rate. Meanwhile, simultaneously adjusting the individual inlet guide vanes of the second stage can also effectively lower the surge flow rate. If the diffuser width of the first stage is reduced while the low-solidity vaned diffuser blade angle is fixed, the surge flow rate will be lowered obviously as the inlet guide vane is adjusted. However, reduction in diffuser width decreases the efficiency at low flow rate. Controlling the inlet guide vane and diffuser width well can lower the surge flow rate to 30% of the design flow.

Instability Phenomena in Centrifugal Compressors and Strategies to Extend the Operating Range: A Review

“…It has been observed that, at low mass flow rates, the de-swirler vane influences the upstream flow structure of the vaneless diffuser and return channel [46]. Hung [47] suggested that, in the case of a vaned diffuser, the vane angle must be increased to reduce the surge mass flow rate. The IGV can have a beneficial effect if not combined with the previous parameter, but the width reduction of the second vaned diffuser can also be beneficial.…”

A Comparative Study of the Oil-Free Centrifugal Water Chillers with the Flooded or Falling Film Evaporator—A Case Study

“…Yet, in subtropical or tropical zones, centrifugal chillers may work all year round. However, the full-load running period of the chiller is usually shorter than one month during a whole year operation, meaning that most of the time, chillers are in part-load operation [1]. Hence, for more effective characterization of a chiller in association with the part-load operation, implementation of integrated part-load value (IPLV) [2] is adopted as the design concept.…”

“…Hence, for more effective characterization of a chiller in association with the part-load operation, implementation of integrated part-load value (IPLV) [2] is adopted as the design concept. The IPLV is defined as follows IPLV = 0.01A + 0.42B + 0.45C + 0.12D (1) where A is the coefficient of performance (COP) at 100% load, B is the COP at 75% load, C is the COP at 50% load, and D is the COP at 25% load. From Equation (1), the proportions of 75% and 50% part-loads are much higher than full-load or 25% load.…”

“…The IPLV is defined as follows IPLV = 0.01A + 0.42B + 0.45C + 0.12D (1) where A is the coefficient of performance (COP) at 100% load, B is the COP at 75% load, C is the COP at 50% load, and D is the COP at 25% load. From Equation (1), the proportions of 75% and 50% part-loads are much higher than full-load or 25% load. For effective part-load operation as far as cooling of commercial buildings is concerned, variable speed chillers are increasingly used in central air-conditioning systems, as they can effectively reduce electricity consumption.…”

A zonal approach for estimating pressure ratio at compressor extreme off-design conditions

“…Compressor off-design conditions have been thoroughly studied experimentally and numerically. [5][6][7][8] However, less research has been devoted to the analysis of extreme off-design points outside the standard corrected maps. Experimentally, it is hard to measure extreme off-design conditions due to different reasons depending on the region of the map, although some authors have been able to characterize extended maps.…”