Fouling Of Axial Flow Compressors - Causes, Effects, Detection, And Control.

LecturePg. 55-76The fouling of axial flow compressors is a serious operating problem in gas turbines and in process axial flow compressors. Gas turbines are being increasingly used in cogeneration applications and with the large air mass flowrate (e. g., 633 lb/sec for a 80 MW gas turbine) foulants even in the ppm range can cause deposits on the blading, resulting in a severe performance decrement. This is a common operating problem experienced by almost all operators of gas turbines. The effect of compressor fouling is a drop in air flow and compressor isentropic efficiency, which then manifests itself as a drop in power output and thermal efficiency. In some cases, fouling can also result in s urge problems as its effect is to move the compressor surge line to the right, i. e., towards the operating line. The mechanisms are discussed for fouling, the aerodynamic and thermodynamic effects, types of foulants, detection methods, and control techniques. A brief discussion on turbine fouling is also made

Forced Rating Systems from Employee and Supervisor Perspectives

Many firms use forced rating systems in which supervisors must evaluate employees according to a predefined distribution. We develop new theory suggesting that forced ratings are less likely to enhance performance when supervisors assess subjective dimensions of employee performance (e.g., creativity), but can have some harmful side effects. In a laboratory experiment, employees work on a creative task, and supervisors rate their performance. We do not find any difference in the employees’ performance or effort in a creative task setting between forced and free ratings. We do however find that forced ratings create higher stress for employees (ex post stress scales and biomarkers). Higher stress in turn mitigates the positive effect of effort on creativity. Furthermore, we find that actual creativity explains less of supervisors’ ratings of employees’ performance under forced ratings. Instead, factors that are unrelated to actual creativity, such as eloquent writing and strategic gaming behavior, matter more. Results of an additional online experiment confirm that forced ratings work differently in tasks where performance needs to be evaluated subjectively compared to tasks where objective measures are available