The Uconeer steam tables can be used to calculate the properties of the ice, water or steam when the temperature and pressure conditions are known. However, these steam tables are also able to search for the conditions that give rise to a particular value of the enthalpy, entropy or density of the ice, water or steam. This is useful when doing calculations involving flashing, compression or throttling.
The known temperature or pressure must be entered and the program will find the other parameters (i.e. pressure or temperature and quality) that give rise to the target water or steam property value. The operation of the search function is best illustrated with a couple of examples, as shown below.
A typical use case for the water and steam property search function would be to find the changed steam conditions after a pressure let-down station. For our example we assume that 40 bar gauge saturated steam at 97% quality is to be throttled down to 2 bar gauge. For practical purposes it can be assumed that the throttling device is adiabatic and the process is isenthalpic.
The first step is to determine the enthalpy of the 40 bar gauge steam before the let-down station. At the top of the window we select Saturation Pressure as the Data Available and enter the value of 40 bar gauge. (For this example the atmospheric pressure has been set to 101.325 kPa abs.) Next we click on the Wet Steam tab and enter the steam quality of 97.0 %. We note that the enthalpy of the wet steam is 2749.22 kJ/kg. All the calculated water and steam property values are shown below.
The next step is to click on the Steam Search tab and select Enthalpy as the Search Property. Note that the value for the enthalpy has defaulted to the correct value. On the second line we select Pressure as the steam property which is known downstream of the flash and enter the value of 2 bar gauge.
After clicking the Search button the program scans all possible values of its ice, water and steam properties and then shows that the steam will become superheated and the temperature will be 144.5°C. All the other relevant water or steam properties are shown as well in the screenshot below.
The second example looks at the case of flashing high temperature condensate into a flash vessel controlled at a lower pressure in order to generate secondary steam. It is assumed that condensate from a high pressure system arrives at the flash tank at a pressure of 18 bar absolute and a temperature of 205°C. The flash tank is controlled at 3 bar absolute. The object of the calculation is to determine what fraction of the condensate will flash to create 3 bar absolute secondary steam.
As in the previous example, it can be assumed that the entire flash vessel system is adiabatic and that enthalpy will remain constant. This is an ideal calculation for the Steam Search function because we can search for the conditions at the lower pressure after flashing where the enthalpy is the same as before.
The first step is therefore to calculate the enthalpy of the condensate at 18 bar abs and 205°C. These values are entered into the water and steam properties calculator and it is seen that the condensate is slightly sub-cooled (boiling point is 207.12°C) and the enthalpy is 208.995 kcal/kg.
In the same way as in Example 1 the next step is to click on the Steam Search tab and select Enthalpy as the water or steam property we want to search for. Note that the value for the enthalpy has defaulted to the correct value. On the second line we select Pressure as the known water or steam property and enter the value of 3 bar abs.
After clicking the Search button the program shows that the condensate will become saturated at 3 bar abs (133.5°C) and 14.49 % by mass will flash to steam. The program also displays the relevant water and steam properties at these conditions for the individual phases and the combined properties for the wet steam.