Induction cooking becomes widely used in our kitchens (Figure 1 [1]). it is gaining more popularity all over the world thanks to several advantages such as high efficiency, safety, cleanliness, etc. [2], [3].The main drawback of the induction cookware is the use of specific vessels made of ferromagnetic materials like iron and stainless steel [2].
The physical principle of induction cooking consists of passing a high frequency current into stranded coil located under an electric conductor pan. The high frequency magnetic fieldsgenerated by the coil will induce eddy currentsinside the pan which causethe heat by Joule effect phenomenon. Almost the induced currents are concentrated in a small thickness of the pan called the skin depth due to the skin effect phenomenon. Figure 1 illustrates the working principle [4].
To keep the efficiency in a high level, the eddy loss in the used pan should be increased the highest possible by using optimal material properties. Electrical resistivity and relative permeabilityplay an important role in thermal power of induction cooking system [5]. The purpose of this article is to find the optimal material properties and the thickness of an induction cookware pot allowing to get the highest possible thermal power.
This article will treat the simulation of an induction cooker. A coupled electro-thermal analysis inside EMS for SOLIDWORKS will be used for this purpose. Eddy losses, winding losses and temperature predicted results will be computed.
The simulated system is composed from a pan and an aluminum ring, a ferrite core and a thermal insulation made of glass [5]. The pan contains water as the heated material. The simulated model geometry is shown in Figure 3 while the 3D CAD model built inside SOLIDWORKS is shown in Figure 4. The dimensions , and are respectively 98.5 mm, 135.5 mm and 168.3 mm.
Two copper wound coils are defined for this analysis. Each coil has 10 turns conducting 24A rms at the frequency of 23.4 kHz.
Induction cooking problems are analyzed using the AC Magnetic module of EMS inside SOLIDWORKS.It solves linear and nonlinear electromagnetic equations in frequency domain with the capability to be coupled to steady state and transient thermal, structural, motion and external circuit without exporting and importing any kind of results. It helps to analyze eddy current problems, wireless power transfer, induction heating process and NDT applications, etc.
In the first section (scenarios 1 and 2), the AC Magnetic module of EMS was used for the calculation of the eddy losses generated by the induced current in the pan when there is a time varying magnetic flux. The simulation was established using different material properties. In the second section, a thermal analysis was performed to compare temperature evolution for two different generic materials. An AC Magnetic study coupled to transient thermal analysis is needed. Finally, in the last section, thickness of the pan bottom was varied. The eddy loss versus the pan thickness is plotted. For this purpose, a parameterized AC Magnetic simulation was resorted to.
Scenario 1: Varying the relative permeability and keepingthe electrical resistivity constant
The electrical resistivity is maintained fixed at and the relative permeability ranges from 100 to 1500. The eddy losses computed by EMS for each case is plotted in Figure 5.The thermal loss (Eddy loss) keeps increasing with the relative permeability until reaching a maximum at then it drops down as can be interpreted from the figure below.
Scenario 2: Varying the electrical resistivity and keeping the relative permeability constant
In this scenario the relative permeability is maintained invariable at the value of while the electrical resistivity is varied from to .The thermal power versus the electrical resistivity is shown in Figure 6. The eddy loss increases from 1.5 kW at to reach 1.8kW at , then it decreases to 1.1kW at .
From the previous analyses, a generic material with an electrical resistivity of and a relative permeability of gives an optimal thermal power which is about 1.8kW .
Electromagnetic thermal analysis of an induction cooker with different pots material:
Based on the previous analyses two generic materials are selected. This analysis will show the impact of the eddy loss on the temperature evolution of each material case.Table 1 resumes the properties and the resultant thermal power of each material. AC Magnetic module coupled to transient thermal is used to analyze the temperature response of the induction cooking system. Due the rotational symmetry of the induction cooking system, only small portion (1/48) of the model is simulated to save the computation time. Figures 7(a) and 7(b) show the temperature distrubition of the pan after 2 minutes. The curve in Figure 8 illustrates the temperature rising versus time of each pan. As a conclusion from these figures, The pan made of generic material 1 is heated faster and higher than the second pan made of generic material 2. It correponds of the pan with higher resistivity and less permeability.
Generic material 1 | Generic material 2 | |
Relative permeability | 400 | 1500 |
Electrical resistivity | 2e-6 | 9.7e-7 |
Thermal conductivity | 80 | 80 |
Specific Heat | 444 | 444 |
Mass Density | 7860 | 7860 |
Generated thermal power | 1801.198 W | 1384.8 W |
Electromagnetic thermal analysis of an induction cooker with different potThickness :EMS ensures optimization analysis through parameterized study. Both geometrical and simulation parameters could be optimized using this feature. In the current example, the bottom thickness of the pot will be varied. Eddy loss at each thickness is captured and plotted in Figure 10. The Figure below shows that the eddy loss in the pot gets higher from 1 mm thickness and becomes almost constant from 1.5 mm. This behavior is mainly depending on the skin effect phenomenon. Figure 11 illustrates an animation of the eddy loss density versus the pan thickness.
In induction cooking system, the eddy loss inside the pan, which is converted into a heat by Joule Effect phenomenon, depends on several parameters such as the material properties (electrical resistivity, relative permeability), frequency, thickness of the pan, etc. EMS was used to study and analyze different scenarios and cases of an induction cooker pan. Material properties and the thickness of the used pan were varied. Eddy loss and temperature results were computed and plotted for several study cases as a function of the different variables. The eddy loss reaches high values for higher electrical resistivity and lower relative permeability.With greater thickness the power loss continues to increase until it becomes constant. Using these material properties and specific thickness in the induction pan will allow to have an optimal power thermal.
EMS helps to study and optimize the material used in the induction pan to keep a high efficiency.
[1]:https://www.consumerreports.org/electric-induction-ranges/pros-and-cons-of-induction-cooktops-and-ranges/
[2]:https://www.nytimes.com/2010/04/07/dining/07induction.html
[3]:http://www.nicecook.in/facts-about-induction-cookers/induction-cooker-pros-and-cons
[4]:http://garnisoldanella.com/induction-cooktop-frequency/induction-cooktop-frequency-how-does-an-induction-cooktop-work-its-cooking-mechanism-4-burner-gas-cooktop/
[5]:Li Qiu, XiboWen, Hongshen Liand Tiegang Li.Study on effect of material property on thermal power in induction cooker system with finite element method. International Journal of Applied Electromagnetics and Mechanics, vol. 46, no. 1, pp. 35-42, 2014
[6]:DaigoYonetsu and Yasushi Yamamoto. Estimation Method for Heating Efficiency of Induction Heating Cooker by Finite Element Analysis.The Journal of the Institute of Electrical Installation Engineers of Japan,2014 Volume 34 Issue 5 Pages 339-345