Wind Tunnel: Flow Around a Cylinder



Gas Turbine

Objectives:

Investigate and report on the operation of a gas turbine by determining the following:

• Plot points one through four, corresponding to the compressor inlet, combustor inlet, turbine inlet and turbine exit, on P-v and T-s diagrams for the maximum load (60 kW). Assume a reference entropy state such that s1 = s1o.

• Determine the isentropic efficiencies of the compressor and turbine at the maximum load of the engine.

• Determine the efficiency of an ideal Brayton cycle operating at the inlet conditions and pressure ratio of the gas turbine used in this experiment.

• Determine the rate of heat addition in the combustor, the mass flow rate of fuel and the cost per kW-hr to run the gas turbine at five different loads ranging from the minimum to maximum of the engine.

• Determine the thermal efficiency of the engine based on [pic] and [pic] at 5 loads.

Background:

The cogeneration system is equipped with a 79 kW gas turbine generator, a waste heat boiler, an absorption chiller and a variety of heat exchangers, pumps and related equipment (Figure 1).

The basic operation is as follows:

1. The gas turbine engine burns high pressure natural gas and generates up to 75 kW of electricity which is dissipated by an electric load bank on the roof of the building.

2. Exhaust gases from the gas turbine pass through a waste heat boiler which generates up to 1200 Ibs/hr of 25 PSIG saturated steam.

3. Much of the steam is condensed with the heat being rejected to the cooling tower outside the building.

4. A portion of the steam heats water which operates a 10 ton absorption chiller which chills water to about 45 F.

5. The chilled water cools 3750 CFM of air

The gas turbine engine and generator used in this experiment can be seen in Fig. 2. This engine has a single stage centrifugal compressor and a single stage radial flow turbine on the same shaft operating at about 60,000 RPM. The output shaft from the engine is connected to a gearbox which reduces the speed and transmits the power to a 480 V, 3 phase, 60 Hz generator. The output from the generator goes to an electric load bank, essentially an electric heater, on the roof of the building. The fuel for the engine is 100 PSIG natural gas which is metered outside the building (between Santa Clara Hall and the University Union). Various values are called by stroking the meter with a magnet at the location shown in Figure 3.

The value of interest for this experiment is the Instantaneous Gas Flow, which is the flow in thousands of cubic feet per hour at standard conditions. (Make sure the cover on the meter is kept closed at all times except when readings are actually being taken.)

Previous experiments indicate that the air flow to the engine is approximately 6700 Ibs/hr, regardless of the load on the engine. The load on the engine can be varied by switching on elements in the load bank in 5 kW increments; control switches for the load bank are located in a box on top of the turbine case. The flow of electricity is monitored by instrumentation on top of the turbine case as shown in Figure 4.

Approximately 2500 Ibs/hr of cooling air enter the turbine case through the grill shown at the lower left of Figure 1, go through the generator, pass over the engine and exit via a small fan at the rear of the turbine case. Previous experiments indicate virtually all of the cooling takes place in the generator. The exhaust gas temperature can be monitored by instrumentation on top of the turbine case and by a thermocouple in the boiler inlet.

VERY, VERY IMPORTANT!

EAR PROTECTION MUST BE WORN AT ALL TIMES WHEN THE TURBINE IS RUNNING; THE NOISE LEVELS ARE VERY HIGH AND CAN DO SERIOUS DAMAGE TO UNPROTECTED EARS.

References:

Pages 519-525 of Cengel and Boles, Thermodynamics, 6th Edition.

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