In the Approach section, we have discussed in details the six questions that need to be answered to completely classify a problem.  If there is  mass transfer across the boundary, the system is open . In a steady problem the snapshot of the system taken with the state camera (discussed in the States page) remains unchanged with time even though there the system exchanges heat , work and mass with its surroundings. 

For instance, when steam expands in a steady  turbine, the system image, a composite of all the different states (or colors in our camera analogy) at different locations, does not change with time. Steam, as it passes through the turbine, cools down dramatically from the inlet to the exit. However, at a given location, the state (or color) remains unchanged. The red hot inlet state always remains red hot. 

To characterize the mass transfer across the control surface of an open, steady single-flow device,  all that is required is to identify two unique states ,  the i- and e-state , at the inlet and exit ports (now you know why TEST identifies the initial state of a process as the b-State and not i-State ). In more complicated multi-flow devices, such as a heat exchanger or a mixing chamber, there can be more than one inlet or exit. 

The daemons for the single-flow, open, steady problems appear under the branch  Daemons. Systems. Open. SteadyState. Generic.SingleFlow   while the multi-flow daemons are sub-divided into two branches: Daemons...MultiFlowMixed and  Daemons...MultiFlowUnMixed .

Open and Steady systems can also be found under the Daemons. Systems. Open. SteadyState. Specific branch  in the Open Cycles, HVAC, Combustion  and GasDynamics chapters. They will be discussed in the corresponding chapters linked at the top of this Tutorial. However, in  all problems involving Open Steady Devices, be it a single flow through a nozzle or a sequence of devices forming a refrigeration cycle, a complete understanding of how to handle a single open device operating under steady state is essential.

In an open and steady  problem, partial information is given about the i- and e-States and the device variables . The task is to find the unknown variables using the balance equations and property relations for the given working fluid. 

The global control panel remains unaffected. On the local control panel, the i-State and the e-State selectors contain only those states which have been already calculated in the States panel. The default state of a port, State-Null, is equivalent to leaving a port plugged, i.e., no flow. 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 overriden if necessary. For adiabatic devices, the value of T_B is inconsequential as can be inferred from the balance equations of Fig. 1. 
 

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

Evaluation of states have been discussed in the State Daemon manual. In an open steady problem, the states can be evaluated to various degree of completeness. Consider the solution for a steady state nozzle, for instance. Suppose the inlet state is completely specified and only the exit pressure is supplied for an isentropic nozzle. In evaluating State-2 (the e-state), Vel2 must be made an unknown. The mass, energy and entropy equations produce mdot2=mdot1,  j2=j1 and s2=s1 respectively. Using '=mdot1' for mdot2,  '=j1' for j2, and '=s1' for s2, State-2 can be completely evaluated. The Device Panel, in this case, simply confirms the assumption as Qdot and Sdot_gen are calculated as zero once the anchor states, State-1 and State-2, are loaded as the i- and e- states.  Another way to obtain the same answer is to enter p2 and partially evaluate State-2. In the Device Panel, Qdot=0 and Sdot_gen=0 are specified. Super-Calculate  deduces the facts that mdot2=mdot1, j2=j1, and s2=s1 from the balance equations, post them into State-2, and completes its evaluation.

Although two exits, e1 and e2 are present, one of those can be left closed by leaving its state at its default value State-Null .  For that matter, by using only one inlet and one exit port, the daemon can be made to handle single-flow problems. 

As in a  single-flow daemon, you choose a device name, load the inlet states (i1 and i2 for a mixing problem) and the single exit state (e1 or e2), enter the device variables, which remain identical to the single-flow device variables, and Calculate. Most of the previous discussions on the single flow device  (sections c-f) apply equally well for this daemon. The TEST-Codes now contains an additional statement in the Analysis block indicating the mixing or non-mixing nature of the device as appropriate.

Examples: The companion Applications page provides at least one complete example to lead you step-by-step to the solution. To see what types of problems these daemons are capable of solving visit the Problems>Chapter-4 page.