Dishwasher Simulation in PreonLab

February 10, 2022
Saba Golshaahi Sumesaraayi and Max Flamm

The possibility of quickly testing and analyzing different design variants has become of very high importance in the industry, including the white goods sector. This has made simulation a key. Particle-based CFD methods have already found their way into the workflow of engineering teams within this sector. As a leading particle-based CFD software, PreonLab offers high-fidelity flow simulations while being much quicker than the conventional methods, especially when it comes to pre-processing and computation. In this article, examples of how PreonLab can be used for the design and analysis of a dishwasher are demonstrated.

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Introduction

Who hasn’t wondered as a child: “What actually happens in a dishwasher?”
As we grew up and started understanding the physics and mechanisms behind it, this black box lost a bit of its magic. However, it still is a complex task to design one of such useful kitchen appliances. Thus, we decided to have a look inside our very own dishwasher in our office!

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Vid. 1: How the inside of our own dishwasher in the office looks during the operation.

Using a camera inside the dishwasher is one way to go. However, if you are the engineer who is designing a dishwasher or analysing its performance, you want to know more about the details and are interested in quickly testing and analysing various design variants.

With the help of simulation methods (an important one of which being CFD), the design process of a dishwasher becomes easier and less expensive. This is the main reason why dishwasher manufacturers (and in general, the white goods sector) face a growing need for using high-fidelity simulation tools.

When it comes to simulating fluid flows in a dishwasher, the grid-based simulation methods are extremely demanding from both pre-processing and computational time perspectives. This makes the gridless CFD methods, more specifically said smoothed particle hydrodynamics (SPH) used in PreonLab, of high benefit and a reason why it has found its way to the white goods sector.

Simulation and Post-processing

Depending on what the design/analysis engineers are looking for by performing CFD simulations, the simulation can look differently. They might be interested in improving the water distribution through optimizing the shapes as well as the directions of the spray nozzles. For doing so, it might not be necessary at the beginning to include the dishware in the simulation. Moreover, simulating for only a single full rotation of the spray arm might suffice for this purpose. One strategy could be to place some planes properly positioned in the tub connected to PreonLab’s wetting sensors in order to observe how well they get wet for a number of design variants to improve the design probably in an iterative manner. An example of how such simulations could look like in PreonLab is depicted below.

Fig. 1: Optimizing the positioning and the orientations of the nozzles with the help of wetting sensors.

Simulations including the dishware could also be performed in order to test and potentially optimize the initial design of the jets in a more realistic case for multiple scenarios depending on the size and the form of the dishware. Such simulations could also help the engineers to come up with best practices for designing the baskets, which to a great extent dictate how the dishware should be arranged as well as where each category of dishware are to be placed. Moreover, best practices for arranging the dishware can be concluded and introduced to the users. In the video below, you can see how such simulations could look like in PreonLab:

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Vid. 2: Simulation of a dishwasher in PreonLab.

An example problem to be addressed could be finding a solution for what you might already have experienced after the dishwashing process is finished; formation of water puddles on top of some dishware, esp. the cups as can be seen in the figure below:

Fig. 2: Simulation of the formation of water puddles on top of cups in PreonLab. 

PreonLab sensors could also be of great help when it comes to optimizing and analysis of the flow as well as its interaction with the solid parts (mainly the dishware). Wetting sensors are capable of measuring the time each point of a solid has been in contact with a fluid (called wetting time in PreonLab). In the figure below, the distribution of wetting time for the dishware is demonstrated.

Fig. 3: Wetting sensors showing the distribution of wetting time for the dishware.

Moreover, force sensors can be used for measuring the shear stress applied by water to the dishware. This can be one of the decisive metrics regarding the washing efficiency. The figure below shows the distribution of the maximum shear viscosity on the surface of the dishware.

Fig. 4: Force sensors showing the distribution of shear force for the dishware.

One further step would be to include the dirt in the simulation. This can be achieved by performing multiphase simulations in PreonLab. Let’s assume ketchup sauce is to be modeled in the simulation. Since ketchup is not a Newtonian fluid, a more complicated model is needed to be used for it when compared to that of water. In PreonLab, for such fluids the Herschel–Bulkley fluid model is used. Since there are several ketchup types each having its own properties, it is up to the user whether or not to go for values coming from their own precise experiments (if available) or to go with some values coming from a reference. In the video below, values used for the ketchup properties have been taken from an online reference.

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Vid. 3: Simulation of a dishwasher including the physical dirt removal.

Note that the effects of detergents and in general, the solubility of the dirt in water can not be taken into account at the moment in PreonLab.

In addition to the flow dynamics aspect, the thermodynamics aspect of the washing process can also be of high importance for the engineers. Conjugate Heat Transfer (CHT) is possible to be modeled in PreonLab. In the video below, 60°C water jets hit the dishware initially having a temperature of 20°C which results in the evolution of the cup temperature as shown.

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Vid. 4: Simulation of hot water jets warming up a cup during the washing process using Conjugate Heat Transfer in PreonLab.

PreonLab is also very strong when it comes to photo-realistic renderings. This has been proven to be of benefit for demonstration and presentation purposes in order to make the results more insightful and of stronger impact. There are some material presets available for both solids and fluids in PreonLab which make the setup for such renderings easier. Glass, steel, rubber and water are some of the presets relevant for the dishwasher simulation. Moreover, a textured surface material makes it possible to project a texture onto a given mesh, as is the case for the knife handle in the figure below.

Fig. 5: Photo-realistic rendering of solid materials in PreonLab.

Conclusion

In a nutshell, with the help of PreonLab, it is possible to optimize, speed up and reduce the cost of the design process of white goods, more specifically said dishwashers, in diverse aspects. What is shown here is just the tip of the iceberg!

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