Outlet Temperatures Mode¶
Overview¶
In Outlet Temperatures mode, the user specifies the desired outlet temperature for each stream. The MSHX verifies energy balance closure and calculates the resulting UA, MITA, and LMTD.
How It Works¶
All Temperatures Specified¶
When all outlet temperatures are provided:
- PT flash each stream at (P_inlet, T_outlet) to get outlet enthalpy
- Calculate heat duty: \(Q_i = \dot{m}_i \cdot (H_{\text{in}} - H_{\text{out}})\)
- Classify streams: \(Q > 0 \Rightarrow\) hot, \(Q < 0 \Rightarrow\) cold
- Verify energy balance: \(\sum Q_i + Q_{\text{leak}} \approx 0\)
Energy Balance
If the specified outlet temperatures don't satisfy energy balance (within 1%), the calculation will fail with an error. Adjust temperatures until the net heat is approximately zero.
One Temperature Auto-Solved¶
Leave one stream's outlet temperature as 0 (auto). The solver will:
- Calculate heat duties for all specified streams
- Solve the remaining stream by energy balance: \(Q_{\text{auto}} = -\sum Q_{\text{specified}} - Q_{\text{leak}}\)
- Perform a PH flash to find the auto stream's outlet temperature
This is the most common usage — specify \(N-1\) outlet temperatures and let the solver find the last one.
Configuration¶
Steps¶
- Select Outlet Temperatures from the Calculation Mode dropdown
- In the Specifications group, enter the desired outlet temperature for each connected port
- Leave at most one port with temperature = 0 for auto-solve
- Optionally enter pressure drops for each port
- Run the calculation
Results¶
After calculation, the following results are available:
| Result | Description |
|---|---|
| Outlet temperatures | All stream outlet temperatures (including auto-solved) |
| Total heat duty | Total heat transferred (W) |
| UA calculated | Resulting overall heat transfer coefficient-area product (W/K) |
| MITA calculated | Resulting minimum internal temperature approach (K) |
| Effective LMTD | Effective log-mean temperature difference (K) |
| Thermal efficiency | Fraction of maximum possible heat transfer |
| Composite curves | T-Q diagram with individual and composite curves |
Example¶
3-stream configuration with water at 10 atm:
| Port | Inlet T (°C) | Flow (kg/s) | Outlet T (°C) | Role |
|---|---|---|---|---|
| 1 | 90 | 1.0 | 50 | Hot |
| 2 | 20 | 0.5 | 60 | Cold |
| 3 | 25 | 0.8 | auto | Cold |
The solver determines Port 3's outlet temperature from energy balance.