Rankine Cycler Lab (Updated 5/2/2008)

Rankine Cycler Lab

The RankineCycler is a steam turbine laboratory demonstration system made by Turbine Technologies, Ltd. and includes the components shown in the following diagram. Notice that it is an open system thus the water in the boiler is heated by the gas burner to form superheated steam which is expanded through a throttle valve and turbine/generator before being released to the atmosphere in the "cooling tower". The three monitoring stations shown record pressure and temperature at the boiler outlet (1) and the turbine inlet and outlet (2),(3). Furthermore we can monitor the gas fuel flow, current and voltage of the electric generator, and the average flow rate of the water out of the boiler (volume of water used over a specified time interval).

Because of the open circuit nature of this unit, we will use this lab exclusively in order to evaluate the performance of the steam throttle and turbine as well as demonstrate the usefulness of the enthalpy-entropy (h-s) diagram in evaluating these two components.

A photograph showing the major components of the RankineCycler follows. Normally an ideal throttle valve and steam turbine are insulated in order to prevent any heat loss from these two components. Notice on the photograph that this has not been done and one of the tasks of this lab will be an attempt to evaluate the effect of the heat loss on the performance of these components.

Consider the energy equation for a flow system applied to the steam throttle and turbine:

One of the purposes of this lab is to attempt to evaluate and justify the heat transfer and work output of these two components and to compare their performance to that of the ideal adiabatic throttle (constant enthalpy) and isentropic turbine on the h-s diagram presented below. Note that this diagram has been expanded to include the values of pressure and temperature relevant to the RankineCycler experiment.

For each of the 3 stations above we will use Steam Tables to determine the enthalpy h and entropy s in order to quantitatively evaluate the throttle and turbine energy values. The plot on the h-s diagram is mainly used in order to obtain a qualitative graphical evaluation of these components, and to check whether we have chosen a suitable set of data for the analysis.

Experimental Procedure

At least two persons are required to operate the RankineCycler experiment. One person to monitor and control the boiler pressure and the electric generator output, and the second person operating the computer for data recording as well as noting and timing the various events. Data will be continually recorded over about 10 minutes, and only one representative set of the data will be used for analysis. The detailed experimental procedure is presented in the document steamlab_procedure (92k pdf file). It includes the four stages of the experiment - preparation, startup, data recording, and shutdown, a summary of which is presented below.

1. Preparation

Visually inspect the RankineCycler and surrounding area to ensure that everything is ready for safe operation.
Fill the boiler with 6000mL of Reverse Osmosis (RO) or distilled water.
Connect the propane tank and power connections to the RankineCycler.
Connect the PC's power and USB cable for the data acquisition system (DAQ).

2. Startup

Turn on the PC and start the DAQ.
Turn on the RankineCycler and start the burner.
When the boiler pressure begins to increase perform the preheat/purge procedure.
Slowly open the steam admission valve and turn on the load switch.
Adjust the load rheostat and steam admission valve to maintain approximately 115psig boiler pressure, steady voltage and steady amperage as indicated on the DAQ display on the PC or the gauges on the RankineCycler.

3. Data Recording

When "steady state" is achieved, note the readings for time, amperage, voltage, and all pressures and temperatures.
Mark the water level on the sight glass with the upper bezel.
Stop data logging after recording data for about 10 minutes,
Mark the water level on the sight glass with the lower bezel.

4. Shutdown

Turn off the burner.
Close the gas valves.
Slowly bleed off the boiler pressure to 0 psig.
Turn off the RankineCycler main power.
Disconnect the propane tank and power connections to the RankineCycler.
Convert binary data to ASCII format and import the data to MS-EXCEL.
Measure water usage during steady state with the beaker and marked water levels

Evaluation and Analysis

Choose a "steady state" data set for analysis, convert all pressure measurements from psig to kPa absolute, and plot the two processes on the h-s diagram.
Plot the ideal throttle process (horizontal line) and isentropic turbine process (vertical line) and indicate the throttle heat loss and the actual turbine work output on the h-s diagram.
Using the Steam Tables determine the enthalpy and entropy at all three stations and compute the throttle heat loss as well as the specific work and isentropic efficiency of the turbine. You may find that using the Steam Tables requires double interpolation - this can be avoided by going directly to the NIST Chemistry WebBook where you can determine the enthalpy and entropy values directly for a specific temperature and pressure of the steam. Thus for example assume we wish to determine enthalpy and entropy at 500 kPa, 200°C.
- With water default fluid, choose units Celsius, MPa, and kJ/kg.
- Choose isobaric data type.
- Enter Pressure: 0.5 MPa, Tlow: 200°C, Thigh: 200°C, Incement: 0.
- View data as HTML, results will include - enthalpy = 2855.8 kJ/kg, entropy = 7.061 kJ/kg K
Determine the average mass flow rate of the steam and thus the turbine power output. Compare this value to the electric generator power output and determine the "generator efficiency".
Attempt to justify and discuss all these results, and in particular discuss the effect of heat loss from the turbine and the throttle. What could be done to improve the performance of these components?

Spring 2008 Lab

Due to the size of the ME328 class, this lab was run in the form of a demo over two sessions, Thursday 5/1/08 and Friday 5/2/08. On both test runs the lab results could not be used due to a faulty thermocouple at the turbine outlet (Station 3). In order to do the lab analysis and evaluation please use the test results from a previous test. These are available in the file: test4_30_08.xls (Microsoft Excel file). For this test we used 1150 mL water over 10 minutes.