How does a vacuum flask work？Vacuum flask:principles,materials, and applications

In daily life, we often use vacuum flask to drink water, make tea or coffee. But have you ever thought about the working principle of a vacuum flask? This article will introduce the definition and working principle of vacuum flask, explore their practical applications, and summarize the precautions to be taken when using vacuum flasks.

1.Definition of vacuum flask

A vacuum flask is a cylindrical container manufactured based on the principle of the Dewar flask, used to maintain a constant internal water or beverage temperature for a certain period of time, making it convenient for people to drink.
A vacuum bottle is composed of an inner liner, an insulation layer, and an outer shell. The inner liner is used to store liquids and is usually made of double-layer glass or stainless steel. The function of the insulation layer is to reduce heat conduction and maintain a constant temperature inside the bottle for a certain period of time. The outer shell is generally made of stainless steel or plastic material to protect the inner liner.

2.The transfer mode of heat

Before learning how a vacuum flask works, we need to understand how heat is transferred.

Heat has the property of transferring from objects with high temperatures to objects with low temperatures, and there are three ways in which it can be transferred. They are conduction, convection, and radiation.

Heat conduction refers to the transfer of heat through the molecules inside a material. This transfer method is very common in solids and liquids, for example, when heating the bottom of a stainless steel kettle, the handle of the kettle will become hot.

Thermal convection is the transfer of heat through the flow of gas or liquid. For example, after turning on the heater, due to the flow of air in the room, the overall temperature inside the room will rise.

Thermal radiation is electromagnetic radiation generated due to the temperature of the object itself, which can transfer heat. Its frequency and intensity are related to the temperature of the object.A representative example is sunlight.

3.The working principle of a vacuum flask

The above introduces three ways of heat transfer, and the structure of the vacuum flask is to block these three ways of heat transfer as much as possible.

(1)Vacuum layer insulation: Extract the air between the inner liner and the outer shell to form a vacuum layer. Due to the absence of air molecules in the vacuum layer, heat cannot be transferred through conduction and convection, ensuring a slow temperature change inside the bottle.

(2)Foam insulation: The insulation layer of the insulation cup adopts foam insulation material, which has many small bubbles. The air inside the bubbles plays a role in insulation, thereby reducing the occurrence of heat transfer.

(3)Reflective thermal radiation: The inner and outer shells of vacuum flasks are usually made of metal materials, which can reflect thermal radiation and reduce the transfer of thermal radiation.

(4)Slow down convection: The insulation layer of the vacuum flask adopts vacuum insulation material and foam insulation material, which can form two independent temperature zones for the water inside the cup and the air outside the cup, thereby slowing down the occurrence of convection. As convection is a way of heat transfer, slowing down
convection can also reduce the occurrence of heat transfer.

(5)Excellent sealing mechanism: Due to the easy contact between the mouth of the vacuum flask and air, heat transfer occurs. Therefore, ensuring sealing at the connection between the lid and the bottle mouth is crucial for maintaining internal constant temperature.Vacuum flask manufacturers will use various sealing technologies, such as rubber pads or silicone sealing rings, to ensure sealing performance.

4. Factors affecting thermal insulation effect

(1) Materials: Different materials have different thermal conductivity and radiation coefficients, so choosing different materials will affect the insulation effect of the insulation cup. Generally speaking, vacuum insulation materials and foam insulation materials have better insulation effects.

(2) Craftsmanship: Different manufacturing techniques can also affect the insulation effect of the insulated cup. For example, the thickness of the vacuum layer, the size and distribution of bubbles can all affect the insulation effect. Generally speaking, the thicker the vacuum layer and the smaller and more uniform the bubbles, the better the insulation effect.

(3) Environmental temperature: The temperature of the environment can also affect the insulation effect of the insulated cup. At lower ambient temperatures, the insulation time of the insulated cup will be longer. On the contrary, at higher ambient temperatures, the insulation time of the insulated cup will be shorter.

(1) Inner liner material: usually made of food grade stainless steel, ceramics and other materials, which have excellent corrosion resistance and high temperature resistance, and will not affect human health.

(2) Shell material: usually made of plastic, metal, etc., which has excellent durability and anti drop performance.

(3) Insulation layer materials: Vacuum insulation materials, foam insulation materials, etc. are usually used, which have excellent insulation performance.

6.Vacuum flask manufacturing process

(1) Inner liner production: Processing food grade stainless steel, ceramics and other materials into the shape of the inner liner and polishing treatment.

(2) Shell making: Processing plastic, metal and other materials into the shape of the shell.

(3) Insulation layer production: Vacuum insulation materials, foam insulation materials, etc. are processed into the shape of insulation layers and pasted between the inner liner and outer shell.

(4) Assembly: Assemble the inner liner, outer shell, and insulation layer together and seal them.

(5) Inspection: Conduct quality inspection and performance testing on the pre made insulation cup to ensure that the product meets the standards.

7.Application scenarios of vacuum flask

(1) Applications in daily life

Tea making: Many people like to use vacuum flasks to make tea, which can maintain the temperature and aroma of the tea, making the taste better. When brewing tea, it is important to avoid soaking the tea leaves in hot water for a long time to avoid affecting the quality and taste of the tea leaves. Generally speaking, the time for using a thermos to brew tea should not exceed 2-3 hours.

Drinking water: During winter or outdoor activities, using a thermos to drink water can maintain the water temperature and avoid discomfort caused by drinking cold water. When drinking water, be careful not to pour too much hot water into the insulated cup to avoid burns or spillage. Generally speaking, the temperature for drinking water from a thermos should not exceed 60 ℃.

(2) Applications in the medical field

Cold and hot compress: In some physical therapies, cold and hot compress is needed to alleviate pain or promote recovery. Vacuum bottles can be used to hold hot or cold water, providing continuous temperature treatment.

Drug storage: Some drugs need to be stored at specific temperatures to maintain their effectiveness. Medical institutions can use thermoses to store these drugs, ensuring that they can maintain a stable temperature when needed.

Operating room use: During the surgical process, it is sometimes necessary to use a specific temperature of liquid or medication. A thermos can provide these liquids or medications in the operating room and maintain their temperature stability throughout the entire surgical process.

Patient dietary insulation: For patients who require special diets or diets with specific temperatures, thermos bottles can be used to keep food warm, ensuring that it can maintain an appropriate temperature when needed.

(3) Applications in the laboratory

Reagent storage: Many chemical reagents are highly sensitive to temperature and humidity. By placing the reagent bottle in a thermos, temperature fluctuations can be reduced, which helps maintain the stability and activity of the reagent.

Liquid storage and reaction: It is often necessary to store or conduct liquid reactions at specific temperatures in the laboratory. A thermos can be used as a temporary container to ensure that the liquid maintains the desired temperature.

Liquid nitrogen storage: Some laboratories need to store biological samples or compounds in liquid nitrogen. Vacuum flasks can be used to store a small amount of liquid nitrogen and maintain its low-temperature state to ensure the preservation and preservation of the sample.

8.Precautions for using vacuum flask.

Avoid scalding: When adding boiling water to the pot, it should not be too full, as there is a risk of overflow and scalding. The thermos pot is a high vacuum insulation product with a longer insulation time. When drinking hot drinks, it is important to avoid burns and it is best to pour them into other containers until the temperature is suitable before drinking.

Avoid deformation: Avoid any form of direct heating or placing it in a high temperature area to avoid causing deformation of the product and affecting its use.

Avoid bacterial growth: To minimize bacterial growth, it is best not to store milk or other food in a vacuum flask.

Avoid filling liquids that are prone to high pressure: High vacuum insulation products should avoid filling liquids that are prone to high pressure, such as dry ice and carbonated beverages, as well as strong acid and alkali liquids to prevent corrosion of the inner walls of the container.

Cleaning: Before using the insulated cup, it is necessary to clean it. You can use neutral detergent and a soft cloth to wipe the inner and outer shells to remove dust and odors. Be careful not to use overly irritating cleaning agents or hard brushes during cleaning to avoid damaging the inner and outer shells of the vacuum flasks.

Storage and maintenance: When not in use, the insulated cup should be stored in a dry, ventilated, and away from direct sunlight to avoid moisture or deformation. When using a thermos, attention should be paid to maintenance to avoid collision, dropping, or pressure, so as not to affect the service life and insulation effect of the thermos. If there are problems such as water leakage or decreased insulation effect in the insulation cup, it needs to be repaired or replaced in a timely manner.