Advanced simulations are already commonly used in industry and other industries. However, Siemens experts have tried to use proven Siemens FLOED technology to find out exactly how hot air flows in a charcoal boiler grill and achieve optimal conditions for summer grilling. Almost every one of us prepares meat or vegetables on the grill in the summer.
How to become a perfect grill master
Masters in grilling take a long time to become experts, for a very simple reason – each grill has unique properties such as shape, material, etc. The performance and behavior of the grill can change even the type of coal used.
Siemens experts have focused on the extremely popular model of grill, which is called the cauldron. At the bottom it has ventilation holes for variable air flow, at the top for hot air leakage. The coal is located near the lower vents.
A factor that is very important for achieving perfectly grilled food is the even distribution of heat, which is necessary for even baking. Grill masters have their tricks and procedures, some even keep them secret and would never share them voluntarily. Here, however, airflow simulation (CFD) and Simcenter FLOEFD can help, which can reveal the performance of the kettle grill in detail.
Grill parameters (Fig. 1)
- Top lid – The lid is usually made of steel and painted. It has a plastic handle for safe lifting.
- Lower kettle – This part has a similar construction as the upper lid. It has flanges for placing a charcoal grate and a barbecue grate.
- Ash catcher – Some grills hold ash when the lower ventilation handle is moved back and forth.
- Bottom vents – Allow cold air to enter so as to provide enough air to burn coal.
- Coal grate – Usually located directly above the lower vents.
- Cooking rack – It is located above the charcoal grill.
- Upper vents – This is where the hot air leaves the grill. These are gases that are produced by burning coal.
- Temperature probe – Usually used to assess how hot the grill is.
At first glance, several observations can be made: The temperature probe is located at the very top of the grill. There may be a temperature difference inside the grill that cannot be detected by the probe. Some parts of the grill may be warmer or colder than where the probe is located. The location of the lower and upper vents can affect the performance of the grill. Other factors that cause variability in grill performance are:
- amount of grilled food
- food location
- quantity and location of charcoal
Grilovací experiment – simulace výpočetní dynamiky tekutin
For the study, we assume an even distribution of charcoal on the grate, this basic rule is taken very seriously by the grill masters. We will be the first to determine the burning temperature of charcoal. Here we start from an article by Abhishek Vanaparti from Auburn University, where he describes two types of coal – fast-burning and slow-burning. The temperature is measured when the charcoal turns gray, which is when most people consider it ready for grilling. We also assume that charcoal maintains the temperature throughout our experiment.
Another assumption concerns the type of grilled food. Meat consists of different types of tissues and fibers, which complicates the characterization of this part. The choice of density, temperature and thermal conductivity values of the simulation used corresponds to the characteristics of the chicken. Special attention is paid to the emissivity value of metal components of the boiler grill. The color of the upper and lower cauldrons is considered black. It is assumed that all metal parts are made of steel.
The grill is located in an open environment at an ambient temperature of about 15.5 ° C. Heat conduction in solids, radiation and gravity are also taken into account. Thermal radiation played a large role in the study, because a significant amount of heat leaves the charcoal in this form. The analysis itself is divided into two steps: heating the grill and own grilling.
What technology has told us about barbecue
Looking at the flow trajectories (see Figure 2), we see that cold air enters from below and circulates in the area of the coal grate. Another large recirculation zone is under the upper lid of the grill, which ensures an even temperature distribution inside the grill.
The figure below (see figure 3) shows the center of the grill when all the vents are closed. The temperature distribution is relatively uniform. We also see several hot spots that are about 7 ° C warmer than the area near the chicken. This difference could be important if the food was grilled for a long time.
Figure 4 shows a section made at one of the ventilation openings. We can clearly see that the heat distribution in this part is not very uniform. This is due to several factors – the lower vents are located directly under several pieces of coal and above all, the upper vent and the lower vent are aligned, so the air enters the lower vent and leaves the upper without circulating inside. That’s why we have a big hot spot near the coal leading to the top hole. The left side of this picture shows the hot air coming out of the grill, while the right side is still circulating.
Temperature distribution on the outer surface of the grill
Another simulation (Figure 5) shows that the temperature distribution on the outer surface is not uniform. Hot air exits through the upper vents (see Figure 5 bubble 1) and this area clearly shows a higher temperature. The bottom and top vents are covered, so the temperature around them is lower than elsewhere. This can be caused by insufficient recirculation or heat dissipation by the metal handle (see Fig. 5 bubble 2). The condition of the other side of the grill where the probe is located is shown in Figure 6 and it can be seen that the temperature of this lower part of the grill is much more uniform.
Does the temperature probe on the lid provide reliable information on the grill function?
The temperature probe is usually placed on the lid and is generally assumed to show the average temperature inside the grill. However, the simulation shows (see Figure 7) that the probe shows a temperature of 143 ° C, but the temperature at the top of the grill where the food is grilled can be anywhere between 204 – 210 ° C. This is more than 37 ° C difference between the measured and the actual temperature.
Next steps and summary
CFD simulations helped to understand what was actually going on inside our grill. The results of the simulation provided valuable information without the need to perform physical tests or consume unbaked or burnt chicken. In fact, these simulations provide a much more detailed analysis of the grill’s operation than can be achieved by physical testing.
With Simcenter FLOEFD, engineers could even analyze the design of individual grill models and design new ones with better performance and functionality, directly through their CAD system. A number of parameters can be adjusted, such as geometry or constraint adjustments, in addition to parameters such as temperature in given areas, flow velocities in key areas, etc. Simulation using advanced Siemens systems experiences.
Some conclusions and recommendations for masters of the kettle grill
The temperature distribution inside the boiler is relatively uniform, but there are hot spots with a difference higher than 4.4 ° C. An even temperature distribution is required in all parts of the grill. This problem can be caused by placing the lower and upper vents in the cover. Better placement of vents would lead to improvement.
There was an uneven temperature distribution on the outer surface of the bottom of the grill, which can be caused by hot air leaks or metal accessories. Here, the real reason for the inequality needs to be revealed by a deeper analysis.
The temperature probe shows a temperature more than 37.7 ° C lower than some areas of the grill. It would be useful to carry out more studies and simulations and identify a correction factor that would resolve the discrepancy. A possible solution would be to use more temperature probes to get a better idea of the temperature distribution inside the grill.
Source: Aktuality – 2D a 3D CAD Design Software by www.cad.cz.
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