Compressor model

The book Gas Turbine Performance by Walsh and Fletcher [10] has excellent treatment on turbomachineiy maps. An example of a compressor map is shown in Figure 8.10. This map fully defines the pressure-flow-efficiency-rotational speed relationship of the compressor. Employing the Beta-line or R-line method, maps can be digitized into tabular form as described by Walsh and Fletcher [10], The Betaline method is helpful to ensure numeric stability with such maps that would be otherwise problematic because of the near zero and infinite slope at the ends of the constant speed lines. Note that the compressor model can either be a flow element or a pressure element. That is, from speed and pressure it is possible to obtain flow and efficiency from the map, or from speed and flow it is possible to obtain pressure and efficiency from the map. The choice depends on what is more convenient, that is, what type of elements are modeled upstream and downstream. 

Centrifugal Compressor Constants and Characteristic Curves—Quantity Constant.—The quantity of gas delivered by a centrifugal compressor is proportional to UaDaha, or, quantity constant = UaDaha- Compressor Constant.— compressor model can be used with practically the same efficiency for various combinations of quantity and pressure such that K = Q/y/p where K is the compressor constant, Q and pe are the desired quantity and mean effective pressure, respectively. The compressor constant can be more conveniently written aaK = QN /pi. ... 

The general multistage compressor model may have several functions polytropic and isentropic compressor, positive displacement compressor, inter-cooler between stages, isentropic turbine. Single phase, as well as two- or three-phase calculations, is possible. 

Pump and tank model Compressor model Heat exchanger model Cooling tower model Boiler model Furnace model... 

Pump and tank model Compressor model Heat exchanger model Cooling-tower model Steam-generation model Furnace model Distillation model Reaction model Separation model Absorption and stripping model Combination of the preceding models... 

The basic equipment components found in a compressor model include ... 

Figure 17-6 shows the basic components of a compressor model. A variety of troubleshooting scenarios can be applied to this simple model. Variations depend on the instructor s experience and questions generated by the students. 

The compressor model and type, the loading, the gas being compressed, and other environmental conditions dictate the type and viscosity of the oil to be nsed. Most compressors are lubricated with petroleum oils however, there has been considerable interest in synthetic lubricants for compressor lubrication in recent years. 

XVI-8] TAKADA, S. et al.. Program for aerodynamic performance tests of helium gas compressor model of the gas turbine high temperature reactor (GTHTR300), Trans. At. Energy Soc., Japan, 2, No. 3 (2003), 291-300... 

Fisher, James E., Davis, Cliff B., and Weaver, Walter L., Idaho National Laboratory, RELAP5-3D Compressor Model , Proceedings of the Space Nuclear Conference 2005, San Diego, California, June 5-9,2005, Paper 1115... 

Chan et al. [25] modeled a part load operation of a solid oxide fuel cell-gas turbine hybrid power plant. This paper contains a centrifugal compressor model and axial turbine. The system generated 1.7 MW at 60% efficiency. The turbine inlet temperature was 1036°C at a pressure ratio of 3. This paper contains no detailed model description of an SOFC module and ejector. 

In RELAP5-3D, the compressor model is similar to the pump model. It performs the same function on a gas as the pump performs on fluids. It can be driven by a shaft or use the other capabilities available to a pump (speed table, motor torque table and/or the coastdown feature). The homologous head and torque curves required for a pump are replaced with compressor pressure ratio and efficiency appropriate for the compressor as a function of mass flow rate for up to 99 different shaft speeds. The compressor component consists of an inlet junction, a single volume and optionally an exit junction. Similar to TRACE, the turbine component in RELAP5-3D extracts momentum and energy. 

For the compressor component, compressor maps are input directly. Pressure ratio and efficiency are provided as functions of relative corrected mass flow rate (CFLO) and corrected shaft speed (CORSPD). The compressor maps are further described in Reference 12-8. The compressor model uses the default junction control flags except no choking model is applied. The compressor performance is entirely described by the compressor maps. It was judged that if the choking mode were used, choked flow might occur distorting the compressor performance. 

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