This document is intended to assist engineers and operators in the use of the Centrifugal Compressor Performance computer program. This simple to use computer-based program utilizes the Microsoft Excel spread sheet program and contains embedded macros that quickly solve basic centrifugal compressor problems with a minimum of set-up time. This user’s Guide will explain the input parameters, output parameters and the methods used to solve basic compressor performance and operating problems. This guide will describe the program limitations and error checking capabilities. Example problems are given in both USC and SI units and are intended to help users understand how the computer program can be used to find a centrifugal compressor operating point, performance limitations and solutions to everyday engineering problems.
This computer program was prepared with two purposes in mind. The first was to help engineers who are new to the field of centrifugal compressors learn about basic performance fundamentals without having to solve problems using tedious and repetitive hand calculations. Nothing hinders the learning experience more than the time consuming need to write down equations, gather data and calculate a solution only to get the wrong answer because of a rudimentary arithmetic error. Even more frustrating is an incorrect answer may not be known until the procedure is checked or verified by others. The other purpose of this computer program is to assist engineers with understanding common control techniques and related performance limits of a machine. It is especially well suited to those trying to understand how changes in gas properties or operating conditions can affect a machine's performance.
The computer program only requires the user to input data from the compressor performance curve and rated design conditions. The user is given an opportunity to input performance data that deviate from the given design values. The program will calculate and display the compressor performance and effects caused by changing operating conditions, gas physical properties and the compressor's control. The results are displayed in both tabulated and graphic formats.
While this computer program may not be capable of solving all centrifugal compressor performance problems, it can teach users how to solve basic performance problems and simulate operating conditions. Keep in mind that the program is primarily for training purposes. It will give, however, the user a sense of how more complex vendor programs handle more comprehensive problems and give an understanding of reports that describe a machine’s performance.
Analysis of a centrifugal compressor’s performance is based on a variety of complex formulas and algorithms used by manufacturers to solve problems found in a wide variety of applications. For this reason their programs and performance reports can be difficult to understand and use. Many engineers and compressor operators who set out to learn the basics of centrifugal machines can gain the desired knowledge from this simplified program. Learning the basics of compressor performance curves, design and off-design parameters and operating conditions begins with a simple, conventional-type machine. The effects of gas physical properties and operating conditions can be found from this rudimentary configuration. More complex conditions can be analyzed by changing the operating conditions cause by four types of compressor control methods - suction, speed, discharge or recycle.
The Centrifugal Compressor Performance computer program is easy to use and provides quick solutions to basic operating and performance problems. Users of Microsoft Excel program will find it easy to install. Those with a basic knowledge of thermodynamics and compressor terminology will adapt to the input data requirements and find how easy it is to modify modify data and operating parameters for alternate solutions. Users will also find the results easy to understand.
The computer program utilizes five Excel worksheets to display input parameters, output parameters, control buttons and warning messages. The five worksheets are Menu, Comp-Data, Q-Disc Curve, Q-H Curve and Q-Power Curve which are described below. With little effort the user can adjust input parameters and determine a range of “off-design” operating conditions and compare them to the "design" operating conditions. It is also possible to analyze the effects of changing gas properties and operating parameters.
The Centrifugal Compressor Performance program has been prepared to help engineers learn about basic performance from the most common arrangement of a centrifugal compressor - multi-stage, single section, straight-through machine. This typically means the user has access to the manufacturer's performance curve, efficiency values, and corresponding design data. Complex issues related to the compressor's size, parasitic losses, acoustics, and impeller arrangement have not been included in the program. Their effects are dependent on a particular compressor manufacturer’s design and are therefore ignored. The interested reader can find more about these effects and other related compressor topics by reviewing the referenced literature.
The Menu worksheet lists notes that briefly describe the program’s features and the basis used to determine the performance results. It also allows users to choose the units of measure and the compressor's control method. See the attachments section for an illustration of the Menu worksheet.
The Menu worksheet allows users to select the two most common types of units. The two options are as follows:
1. United States Customary (USC) and 2. Systeme Internationale (SI).
It is recommended to select units of measure before proceeding with input of other parameters. The user can select the desired units pressing on the two command buttons shown below. The Menu worksheet will display either USC orSI as the selected units.
This worksheet is also used to select the control method that can be utilized to change the operating point. The four control methods are as follows:
1. Suction Control 2. Discharge Control 3. Speed Control 4. Recycle Control
It is recommended to select the desired control method before proceeding with input of other parameters. The user can select the desired control method by pressing one of the following command buttons.
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