Steam turbines are a common element of thermodynamics problems. By allowing water vapor to expand, the turbine generates energy for a power system. This instructable will teach you to find properties for an isentropic turbine. Isentropic simply means the system operates in ideal conditions and has no energy loss.
You will need:
- Some knowledge of thermodynamics and interpolation.
- A thermodynamics textbook with water properties data tables.
- A calculator with an interpolation function.
- Approximately 15 minutes of your time.
Step 1: Creating Your Table
Before you can begin filling your table, you must first create it. Simply create 2 vertical columns for State 1 (the entrance state) and State 2 (the exit state) with a minimum of four rows.
Step 2: Filling Your Table
Every thermodynamics problem you encounter will give you some data regarding the system. Record these values in your table. Additionally, write down the remaining properties you will need.
- For each problem, you may need pressure (P), enthalpy (h), entropy (s), and temperature (T)
Below is a list of metric units for the values:
- Pressure: Pascals
- Enthalpy: Kilojoules per kilogram
- Entropy: Kilojoules per kilogram Kelvin
- Temperature: Degrees celsius
The picture shown above is a correct table.
Step 3: Finding State 1 Properties
Now you will begin to record the remaining properties for both states. Since this problem involves a steam turbine, state one must be superheated to avoid mechanical failure. This helps you find your properties.
The first step is to complete the State one properties using the following steps.
- Locate your state one pressure value in the metric superheated tables in the thermodynamics textbook. The picture above shows the section you need.
- Identify which row lists properties for your given temperature.
- Record enthalpy and entropy values corresponding to your temperature.
The above picture shows completed state one.
Step 4: Finding State 2 Properties
Now you will find the remaining State 2 properties using the following steps.
- Locate your State 2 pressure in the metric superheated tables.
- Since this is an isentropic turbine, the entropy at state 2 is equal to the entropy at state 1. Find the two values closest to this entropy in the pressure block.
- Once you find entropy values higher and lower than the needed value, use an interpolation function to find the corresponding temperature and enthalpy.
The above table shows a completed state 2.
Step 5: Finishing Up
You have now completed your state table for this problem. This is necessary to complete before any additional analysis can continue, especially as problems escalate in intensity.
To dive deeper into working thermodynamics problems, check out the following links.