A good thermal isolation can be achieved by using polyurethane (PU) foams. 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.
The meshless CFD simulation software 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
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 fill 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.
Figure 1: PU injection by two fixed inlets (left), injection by a moving pipe (middle) and PU distribution by a closing cavity. 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.
Figure 2: Velocity field and free surface flow near cooling cutouts. The simulation shows that this position is at risk for an air entrapment.
Did you know,
that numerical simulation is not only used to understand processes or to optimize a process,
but also to control the process development in terms of quality (Two-man rule)?
Did you know,
that numerical simulation helps to give your project a structure and to establish a very useful documentation system?
Did you know,
that numerical simulation helps to train your employees and to increase the knowledge about your procedures and processes?