Can a non-rotating microwave oven still heat food evenly?

The microwave oven, a convenient tool in the family kitchen, has long been associated with the image of a rotating turntable. Imagine pressing the start button, accompanied by soft yellow light, the food slowly turns on the glass turntable until the familiar "ding" sound is heard, and the hot food can be served on the table.

A microwave oven that can "spin"

But as time goes by, the design of microwave ovens has also evolved. Modern microwave ovens not only incorporate many advanced features, but some models even abandon the traditional turntable and leave only a smooth bottom. This design reduces the restrictions on the size of the heating container, is easier to clean, and significantly improves the user experience.

However, facing a microwave oven without a turntable, people can't help but ask: Can it still heat food effectively? Between a microwave oven with a turntable and one without a turntable, which one is a better choice?

Why a turntable?

To understand the role of the turntable, you first need to understand how microwave ovens work. Microwave ovens heat food by generating microwaves, which are electromagnetic waves with a frequency of around 2.45 GHz. These electromagnetic waves are generated by a magnetron, which forms a changing electromagnetic field inside the microwave oven. Polar molecules in the food (such as water molecules) react to the electromagnetic field, rotating, vibrating, and colliding with each other, generating heat in the process. This inside-out heating method is different from traditional heat conduction methods, allowing microwave ovens to heat food quickly in a short period of time.

Microwave oven heating food principle

However, microwaves are not evenly distributed in the microwave cavity. As microwaves propagate through the cavity, they create peaks and troughs, forming a phenomenon called "standing waves." Standing waves cause microwave energy to be concentrated in certain locations and weaker in other locations, resulting in uneven heating of different parts of the food. This is why, if nothing is done, food heated in a microwave oven can sometimes be overheated in some places and still cold in others.

Schematic diagram of standing waves

The turntable is designed to address this problem. When the food is placed on the turntable and rotates, different parts of the food are exposed to the high energy area and low energy area of ​​the microwave in turn, thus achieving a more uniform heating effect. It can be said that the existence of the turntable is an important optimization in the design of the microwave oven, so that we don't have to manually flip or stir the food when using the microwave oven.

Is there any other way?

While a turntable is an important tool for evenly heating food in a microwave oven, it is not the only solution. In fact, advances in microwave technology have led to some modern microwave ovens no longer relying on a turntable, but instead achieving even heating of food through other means. Technologies such as "plate heating technology" or "stirrer technology" can distribute microwaves more evenly inside the microwave oven, thus eliminating the need for a turntable.

Flatbed Technology is an important innovation that replaces the turntable design. This technology distributes microwave energy evenly throughout the heating chamber through the clever use of reflectors and distributors, ensuring that food is evenly heated without a turntable. Thanks to this innovation, microwave ovens not only reduce mechanical components, thereby reducing maintenance costs and the risk of failure, but also significantly improve the efficiency of internal space utilization. This means that users can now easily heat larger or differently shaped containers and enjoy a more flexible and convenient cooking experience.

A flat microwave oven

Stirrer technology achieves dynamic distribution of microwaves by installing specially designed metal "blades". Although these blades do not move the food itself, their rotation can continuously change the reflection path of microwaves inside the microwave oven. This dynamic change effectively disrupts the fixed standing wave pattern that may have been formed, making the energy distribution during the heating process more uniform .

These metal blades are called "mode stirrers". They are usually hidden under the glass or ceramic bottom plate of the microwave oven, or covered by a plastic cover, and are not easy to be noticed in daily use. Although these plastic covers are opaque in appearance, they are transparent to microwaves and will not hinder the function of the stirrer. In addition, in some microwave ovens, the design of the stirrer and turntable coexisting is also adopted, which provides a double guarantee of heating uniformity.

The metal fan blades in the microwave oven are responsible for stirring the electromagnetic waves

Turntable and stirrer heating

Is there any difference in the effects of the two?

Both turntables and stirrers are auxiliary tools used to improve the uniformity of heating in microwave ovens, but there are some differences in their working principles and effects.

The turntable uses a simple rotating motion to keep the food moving in the microwave, so that it receives microwave radiation from different directions. This method is simple and effective, but it may not completely solve the problem of uneven heating, especially when heating large or irregularly shaped foods.

Agitators use more complex mechanical motions to tumble and stir food in the microwave, resulting in more comprehensive heating. This approach may provide more even heating in some cases, but it may also increase the complexity and cost of the microwave due to the addition of mechanical parts.

In addition to the design factors of the microwave oven, the uniformity of microwave heating is also significantly affected by the composition and form of the food itself , which is a problem that is difficult to completely overcome even through technological innovation. For example, under the same microwave power, there are significant differences in the ability of water and fat in food to absorb and convert heat. In the process of heating meat products, we often observe that the fat part will become boiling hot faster, because the specific heat capacity of fat is much lower than that of water. Although fat is not as efficient as water in absorbing microwave energy, it only requires less energy to achieve a significant increase in temperature.

From this point of view, the turntable is an effective design for microwave ovens to heat food evenly, but it is not the only solution. With the continuous advancement of microwave oven technology, the application of new technologies such as stirrers and flat plate heating has enabled microwave ovens to achieve efficient and uniform heating without relying on turntables. Although these new technologies have their own advantages and disadvantages, their common goal is to improve the heating quality of microwave ovens and meet the diverse needs of consumers.

References

[1]Geedipalli SSR, Rakesh V, Datta A K. Modeling the heating uniformity contributed by a rotating turntable in microwave ovens[J]. Journal of food engineering, 2007, 82(3): 359-368.

[2]Harold S H. Design considerations for microwave oven cavities, IEEE Xplore[J]. IEEE Transactions on Industry Applications, 1970, 1: 74-80.

[3]https://mp.weixin.qq.com/s/dh1N7_cGafQNwGKo2RhHLg

[4]https://mp.weixin.qq.com/s/mbQXoFMapY6KsmssxjD6iQ

[5]https://mp.weixin.qq.com/s/v_kbEexyOXUC9Kv9NJSIKA

[6]https://mp.weixin.qq.com/s/7eKxu66KgykPe8d1Fwj4sw

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Source丨Popular Science of Physical Science (ID: lxcp_cstam)

Editor: He Tong

Proofread by Xu Lailinlin