For instance, when a propane cylinder is charged, or steam escapes a pressure cooker, a clear b-state and a  f-state serve as the process anchors signaling a process . In addition, depending on the problem, an inlet or an exit port,  identified by the  i-state or  the e-state characterizes the mass transfer for the open system. As the state of the fluid in the cylinder changes, so does the inlet or exit states. A simplifying assumption, called the uniform flow process ,  treats the states at the inlet and exit as invariant during the process, which is quite reasonable for many practical problems. For instance, the state of propane in the supply line may not be affected during the charging of a cylinder as long as the supply comes from a large reservoir. When water boils inside a pressure cooker, the steam exiting through the valve is saturated vapor and its state does not change, as the pressure inside remains constant,  until the last drop of liquid vaporizes.

The open process daemons appear under the branch Daemons. Systems. Open. Process on the TEST-Map. 

In an Open Process  problem, partial information is given about the i- , e- , b- and f-States and the process variables . The task is to find the unknown variables using the balance equations and property relations for the given working fluid. 

While m , j and s at the  i- , e- , b- and f-States , and T_B (see Fig. 1) are all  State properties, the variables  m_i, m_e, Q, W and S_gen depend on the particular process the open system executes in taking the system from the b-State to the f-State . These variables, m_i, m_e, Q, W and S_gen , are the fingerprints of the open process and are called the open process variables .  The balance equations of Fig. 1 provide a bridge between the difficult-to-measure device variables and the easy-to-evaluate state properties of the anchor states,  b-state, f-state, i-state and e-state.
 

The global control panel remains unaffected. On the local control panel, there are four state selectors for the i- and e-states , and the b- and f-states . The default state of a port, State-Null , is equivalent to leaving a port plugged, i.e., no flow. For a charging problem leave the e-state plugged, while for a discharge problem have the i-state plugged.  The device is identified by a letter (just like a State is identified by a number), Device-A being the default device. 

The boundary temperature  T_B is given a default value of 25 deg-C, which can be overridden if necessary. For adiabatic devices, the value of T_B is inconsequential as can be inferred from the balance equations of Fig. 2. 
 

d. Solution Procedure: The solution procedure that is emphasized in example after example in the Archive, Slide Show and the Applications page is simple. (a) Evaluate the anchor states, the b- and f-states and the i- or e-state as best as possible. (b) On the Analysis panel, choose a device name (Device-A, for instance), and select from the calculated states the anchor states. (c) Enter the known device variables (for instance Q=0 for an adiabatic device). (d) Press the Enter key (or the Calculate button) and Super-Calculate to update all variables.

A detailed report, a spreadsheet friendly table of properties and a few lines of what is called the TEST-Codes are produced on the I/O panel. The TEST-Codes can be saved for later use. In a later session, the solution can be regenerated by pasting the TEST-Codes on the I/O panel and clicking the Load and Super-Calculate button. In the Archive you will find a library of TEST-Codes for many practical problems involving open processes..

You will find a number of open process examples on the Applications  page, Slide Show and the Archive . Try them all!