A sealed thermos flask weeps mysterious sound of its inner story
When bringing a sealed thermos flask close to the ear, users often hear a sound coming out like a draft. People may wonder why such a sound is there, others could think that the flask is broken. Let's take a look at the inner mechanism of a thermos flask to it produces such a sound.
If the vacuum flask is properly sealed, where the wind could come from, one may ask. In fact, this is just normal acoustic resonance, which occurs with all containers.
Sound waves come from changes in the air density, between stages of being dilute and dense, and they propagate from the source of the sound to all directions at a certain speed. The number of dilute-dense transitions per second is called the frequency. The distance between two adjacent dense or dilute parts is called the wavelength. The higher the frequency of the sound, or the shorter the wavelength, the higher the audible tone.
In general, sound is caused by vibrating objects. For example, when beating a drum, because the drum surface vibrates up and down, a sound is emitted in the air. Different objects vibrate at different frequencies.
If there are two objects that emit sound with the same frequency and are located close to each other, when one object is allowed to speak, the other can also speak. This phenomenon is called resonance.
Interestingly, almost the air (or column of air) in any container can resonate with vocal objects. If a sonic object is placed close to the mouth of a container and the frequency or wavelength of the sound source matches the natural frequency or wavelength of the column of air, the column of air will resonate immediately (i.e. it oscillates) and make the sound a lot louder.
Researchers say that as long as the wavelength is four times, ¾ or ⅘ the length of the column of air, after it is passed into the container, it will cause resonance.
The inner height of a thermos is usually about 30 cm. From that, it can be calculated that, when the sounds with wavelengths of 120 cm, 40 cm, or 24 cm etc.are transmitted into the thermos, they can cause resonance.
We are surrounded by all kinds of sounds big and small. They can simultaneously resonate with the column of air in the thermos, creating a humming sound that we will hear when we put our ears to it. Because the air column is short, the wavelengths of the resonant sounds are also short. Therefore, the sound coming from a small bottle will be sharper than those from a thermos.
If the sealed thermos flask has damages, making the air column incomplete, the resonant sound will also be changed. That's why people often listen to the noise to check if the water bottle is broken.
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One of Rang Dong's double-walled thermos flasks export destinations is China, which used to sell similar products across the border to Vietnam, a strong evidence of Chinese users' confidence in the household item.
Thermos flask has been a popular item to keep our hot or cold drink. Manufacturers have stepped up in broadening user's convenience by turning the lid into a cup. If you have ever wondered if it was safe to drink from this lid, the answer rests with the material and design of the thermos flask with cup. Let’s find out more about it in this article.
Rang Dong thermos has gained its reputation in northern Vietnam decades ago, right from the 1960s when it was first produced because there was no electric or gas stove at the time, not to mention super-speed kettles, while it was cold for three to four months during winter. It may not be an exaggeration when we say the traditional thermos flask was the most essential consumer product at that time. Today Rang Dong's reputation stands firm at home and the company has also been expanding its penetration in overseas markets.
Many people have been using thermos flask as the device conveniently keeps hot and cold drinks/soups for many hours. It becomes quite handy when we need to go out for shopping, going to work or school, or camping. The thermos flask’s heat retention is in place thanks to its special structure.