Parent Category: Industries

Simulation of Polyurethane - foaming fridge

 
The simulation of the polyurethane(PU) foaming in a fridge can be performed with our CFD simulation software NOGRID points.  By using polyurethane foams a good thermal isolation can be achieved. The most efficient way to produce a thermal isolation of a refrigerator is the injection of PU directly into the hollow wall. The foaming takes place in the cavity and fills it completely.
NOGRID points can help to understand the flow inside the cavity. It can show the entrapment of air, the density distribution of the isolation material and the pressure of the PU foam acting on the cavity. NOGRID unites abilities to handle free surface flow and moving parts in the domain and allows the simulation of any conceivable refrigerator geometry and operation modes such as
  • polyurethane (PU) injection by one or more inlets,
  • moving parts and inlets,
  • free definable PU properties by equations or curves and
  • large refrigerator geometries with small gaps or cutouts.
NOGRID's particular strengths are the rapid preprocessing (no grid needs to be generated) and the outstandingly short computation time even for complicated cavities with very small ducts.



Three possible types of production

The left example shows a refrigerator where the PU is injected using two inlets at the lower side. The foaming process starts when the PU enters the cavity, the filling is done after two seconds. In the middle example the fluid is injected by a pipe which moves outwards during the filling process. In the right example the simulation starts with PU liquid inside an open cavity. The cavity closes and presses the foaming liquid into the refrigerator wall.

PU injection in a fridge by two fixed inlets PU injection by a moving pipe PU distribution in a fridge by a closing cavity
Figure 1: Simulation of PU foaming in a fridge - injection by two fixed inlets (left), injection by a moving pipe (middle) and PU distribution by a closing cavity; computed with NOGRID points
Click on the animations to see high quality videos.


Identification air entrapment

Air entrapment increases the heat conductivity of the thermal isolation and must be avoided. CFD simulations can reveal critical positions. In our simulation the cooling cutouts on the lower left side of the refrigerator are at risk for an entrapment, see figure 2. The PU enters the gaps from both sides, resulting in an entrapment of air. A solution would be ventilation holes or different inlet positions.

Velocity field and free surface flow near cooling cutouts in a fridge

Figure 2: Velocity field and free surface flow near cooling cutouts, computed with NOGRID points
The simulation shows that this position is at risk for an air entrapment.