The following types of heat exchanger models are available in Aspen HYSYS.

**1. Simple End Point Model**

The standard heat exchanger equation can be stated as:

There are two main assumptions of this model:

- The overall heat transfer coefficient is constant.
- Specific heats of both shell and tube side streams remain constant.

The Simple End Point Heat Exchanger model is based on the same equation as shown above.

This model can be used when:

- Heat curves for both Heat Exchanger sides as linear.
- There is no phase change
- Specific heat is relatively constant

**2. Simple Weighted Model**

When the assumptions of the Simple End Point Model are not valid then the Simple weighted model can be used instead.

This is an excellent model for:

- Non-linear heat curve problems
- The phase change of pure components in one or both Heat Exchanger sides.

In this model, the heating curves are broken into intervals (default intervals are 5) and energy balance is performed on each internal. The LMTD and overall heat transfer coefficient are calculated for each internal. Overall exchanger UA can be calculated by adding the UA of each interval.

Note: This model is available only for counter-current exchangers.

**3. Simple ****Steady-State**** Rating Model**

This model is the extension of the Simple End Point Model to incorporate the rating calculation of the heat exchanger. The assumption of this model is the same as the simple endpoint restated below:

- The overall heat transfer coefficient is constant.
- Specific heats of both shell and tube side streams remain constant.

Exchanger rating calculation can be performed if the detailed geometry is known. Due to the solver method incorporated into this rating model, the Steady State Rating model can perform calculations exceptionally faster than the Dynamic Rating model.

**4. Dynamic Rating Model**

There are three models available for the Dynamic Rating

- Basic
- Intermediate
- Detailed.

If two/three temperatures and overall transfer coefficient is available, then the exchanger can be rated with the Basic Model. If the zonal analysis and tube thermal inertia are required without providing the detailed geometry the intermediate model can rate the heat exchanger. In the detailed model, detailed geometry is required to rate the heat exchanger.

The Basic, Intermediate, and Detailed Dynamic Rating models share rating information with the Dynamics Heat Exchanger model. Any rating information entered using these models is observed in Dynamic mode. Once the Dynamic Rating model is selected, no further information is required on the Parameters page of the Design tab. You can choose the model on the Parameters page of the Rating tab.

**Read also**: Classification of Heat Exchangers

**5. Rigorous Shell and Tube Model**

This mode accesses the Aspen Exchanger Design and Rating (EDR) program and lets you set up a rigorous shell and tube exchanger model on the separate program tab page. Using this model also allows advanced analysis and error checking through the EDR-activated analysis environment. You must have prior knowledge of the Aspen Exchanger Design and Rating (EDR) to access this model.