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Step by step modeling of a heat pump

by Siemens Experimenter Siemens Experimenter on ‎07-12-2016 10:13 AM - edited

Purpose

In two phase flow systems, a heat pump is a device that transfers energy from a heat source to a destination called a "heat sink". Heat pumps are designed to move thermal energy opposite to the direction of spontaneous heat flow by absorbing heat from a cold area and releasing it to a warmer one. Reversible heat pump can also be used as a cooling system. 

The target of this demo is to illustrate the modeling of a heat pump and more generally a heat transfer loop. Each component will be modeled and optimized separately in LMS Imagine.Lab Amesim software. All components will then be connected together to obtain the whole heat pump system model, first with an open loop and ultimately by closing the loop (step by step methodology).

NB for LMS Amesim users: the step by step methodology is further detailed in the LMS Amesim two-phase flow demo “Heat pump configuration”. The demo’s thermodynamic cycle values are presented there.

 

Description

This demonstration example presents a basic heat pump technology. The final closed-loop model represents the whole system and permits the creation of the thermodynamic cycle.

The operating of the heat pump is synthesized in the picture below:

COMMUNITY_NCY_HEATPUMP_KB_picture1.png

 The simple P-H diagram of the heat pump is defined as follows:

COMMUNITY_NCY_HEATPUMP_KB_picture2.png

 According to this picture, the 4 transformations arising in the system will be modeled by focusing on the main components:

  • 1 ⇒ 2: Compressor
  • 2 ⇒ 3: Condenser
  • 3 ⇒ 4: Expansion device
  • 4 ⇒ 1: Evaporator

 

Compressor

The compressor increases the refrigerant temperature and pressure. At both suction and discharge, the fluid is in gaseous state (superheated gas). It is modeled as follows in LMS Amesim:

COMMUNITY_NCY_HEATPUMP_KB_picture3.png

                                                          LMS Amesim compressor model

 

Condenser

The superheated refrigerant transfers its latent heat to air (or any other cooling fluid) during condensation process. At the outlet, the refrigerant remains at the same pressure level but has changed phase from gas to liquid.

COMMUNITY_NCY_HEATPUMP_KB_picture4.png

                                                          LMS Amesim condenser model

With the new half heat exchanger components and the proper input parameters, the condenser could be modeled very quickly.

 

Expansion device

The refrigerant pressure (and thus temperature) is strongly reduced through an isenthalpic transformation.

COMMUNITY_NCY_HEATPUMP_KB_picture5.png

                                                          LMS Amesim expansion device model

 

Evaporator

The cold refrigerant then absorbs heat from the air (or any other media) during evaporation process. At the outlet, the refrigerant pressure is almost unchanged but its state changed from liquid to gas.

 

COMMUNITY_NCY_HEATPUMP_KB_picture6.png

                                                          LMS Amesim evaporator model

With the new half heat exchanger component and the proper input parameters, the evaporator could be modeled very quickly.

 

  • Creation of an open-loop heat pump

As presented above, the four major components are built separately. They should be connected together step by step in order to get an open loop heat pump as follows:

COMMUNITY_NCY_HEATPUMP_KB_picture7.png

  • Creation of a closed-loop heat pump

Once the open-loop model is created, signal connections should be replaced by direct connection. This should be done step by step. The final result is the following sketch:

COMMUNITY_NCY_HEATPUMP_KB_picture8.png

Note that before making the last connection, the calculated charge of fluid should be re-used to ensure a proper initialization of the closed-loop model. The heat pump P-H diagram is consistent with the expected cycle:

COMMUNITY_NCY_HEATPUMP_KB_picture9.png

 

Conclusion

As illustrated in this article, to create a two-phase flow heat transfer loop in LMS Amesim, these rules must be followed:

  • Determine cycle physical parameters
  • Create the associated PH diagram and split it into simple stages
  • Create and set one LMS Amesim sketch per stage
  • Connect components together in open loop
  • Then close the loop

From such a very functional model, each component could then be refined and new components could be added using the presented methodology. Each component could be sized and validated separately before being connected to the heat transfer loop.

 

Visit our website to have more information on two-phase flow simulation.

 

NB for LMS Amesim users: for more information, please refer to LMS Amesim demo “Heat pump configuration”.

 

 

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