Engineers at Nestlé’s Product Technology Centre in York, UK (PTC York), work, among other things, on the research and development of three different products — a chocolate depositor for making candy bars, a wafer baking plate and an extruder, used to cook and sort cereals at the same time. At PTC York, which is home to the research and development of Nestlé’s confectionery products, engineers rely on multiphysics simulation to optimise and streamline the production process.
Candy bars, such as Kit Kat®, Aero®, Crunch, and solid milk chocolate bars are produced using a chocolate depositor that fills a mould with molten chocolate. Chocolate enters the depositor via an arm at the top and exits into a mould through each of the nozzle tips.
“Ensuring that the amount of chocolate in every bar is consistent means that the flow rate and pressure of the chocolate exiting each nozzle must be the same,” says William Pickles, Process Engineer, Nestlé. “Not only do we need to make sure that each chocolate bar is the same weight for cost effectiveness and standardisation, but we are also committed to guaranteeing that the calorie information on the package is correct as well. This allows us to deliver products with exact nutritional content that fit in with our customers’ balanced diets,” he adds further. In order to achieve this standardisation, the uniformity in flow and pressure between each nozzle tip
must be precise to within a narrow margin.
To achieve this consistency, Nestlé uses a combination of modeling and simulation tools. The chocolate depositor was first designed using SOLIDWORKS® software and the geometry was then imported into the COMSOL Multiphysics® simulation software for analysis. Simulation was used to perform fluid flow optimisation, test mechanical stress, and analyse the thermal properties for a particular geometry.
As per Pickles, every chocolate manufacturer has its own special recipe that produces chocolate with unique characteristics. “We were able to fully model the non- Newtonian behaviour of Nestlé’s signature chocolate by setting up a simulation where an experimental curve relating the shear rate to the shear stress of the fluid was imported into the software. This way, we were sure that we were modeling chocolate with the same fluid properties as the real product.”
Using simulation, the team identified areas of high and low flow rates and determined the differences in flow between each of the depositor needles. Numerical probes in the flow channels and at the tips of the nozzles were used to analyse conditions at certain locations of the geometry.
“By optimising the depositor design, we were able to achieve a flow rate through each of the nozzles that is consistent to within a tenth of a percent of the desired value,” adds Pickles.
Simulation saves crunch
What would a Kit Kat® be without the well known snap of the wafer baked inside? When baking a wafer, uneven heating can cause different moisture concentrations within the wafer, ruining its crunchy texture or even causing it to spontaneously snap.
The wafer baking process at Nestlé uses two baking plates that compress the batter between them. During baking, the plates are passed above a series of about 40 flames. “We are using simulation to optimise the baking plate design by looking at the flow of hot air below and around the plates to ensure that we have an even temperature profile across the plates’ surfaces,” describes Pickles. “Our aim for this study is to correct burner power and orientations to give the best wafer, while simultaneously reducing the amount of fuel we use.” The flames underneath the baking plates were modeled as jets of hot air, where heating proceeds via convection.
“We were able to validate our model against baking plates used in experiments, and we found our simulation results were in very good agreement,” opines Pickles. The results also show how warmer spots occur due to increased heat conduction through the bolts holding the baking plates together. The next step will be to optimise this design to distribute the heat as evenly as possible across the top of the plate and minimise temperature peaks.
Cooking while extruding
Cereals such as Cheerios®, Trix®, Nesquik®, and many others are made at Nestlé using an extruder. “The hightemperature extruder used at Nestlé to make certain types of cereals works by forcing dough through a die. The pressure and friction created during this process causes the dough to cook through viscous heating. Extruders are common because they are a compact and cost-effective way of manufacturing products,” avers Pickles.
He further adds, “For our design, we needed to make sure that the viscometer housing could withstand the high pressure within the device.” In the original extruder design, the pressure was too high for the viscometer housing to withstand. “We redesigned the housing, which helped to reduce the pressure. We were then able to make sure that the die design didn’t exceed the yield stress so that the viscometer could safely be housed inside it,” he vouches. Additionally, simulation was used to check that the displacement of the extruder was consistent, as varying displacement of the device would cause the cereal being produced to have uneven shapes and sizes.
Towards healthier products
At Nestlé, simulation is a big part of the design process, from producing chocolates to wafers to cereals and everything in between. Concludes Pickles, “We are confident in the results obtained from our simulations, and we know that they can be trusted to help us produce the best and safest designs possible. This in turn allows us to consistently deliver tastier and healthier products.” ☐ Courtesy: Comsol