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How Thermo-flask can keep heat for a longer period of time? Everything You’ve Ever Wanted to Know About Vacuum Flask In 10 Simple Steps


The article demonstrates the scientific explanation behind this thermo-flask bottle. Three different modes of heat transfer such as conduction, conviction and radiation transfer. For users’ interest, the best use of thermo flasks is also incorporated.


Today the thermo-flask bottle (Vacuum flask or thermos or Dewar flask, Dewar Bottle) became one of our household’s most important material. Nearly all of them occasionally or regularly use thermo flasks depending on their requirements. It is a big question why the water in the thermo flask bottle will remain warm for longer periods. The school kids from 12 to 16 years of age and sometimes beyond this age limit raised the question more often. This means, every household needs flasks that become essential.

Scientific reason behind the long term heat retention of the thermo-flasks:

The scientific fact behind this thermo flask bottle gives me great pleasure to explain. Three ways of heat loss by water are applicable. The way they are:

1. Conduction 

2. Convection 

3. Radiation

The theory states that, if we minimise these three heat transmission modes, the temperature of the water can be maintained for a longer period. Let us talk about how this occurs in thermo-flask construction.

Conduction is the first way to lose the heat. The thermo-flask consists of glass that is the good insulator in room temperature and perfect conductor when heated to a high temperature. Thus, in this method conduction process cannot escapes heat. The second step is convection, which is used by air media to transfer heat to the environment. Therefore, t he flask is made of two glass walls and then create vacuum in between the two walls. So in between the walls of the bottle there is no air. Hence, vacuum generation limits the transfer of heat.

Thus, due to convection, no heat transfer occurs. Radiation is the third and last way to transmit heat. In the form of radiation, heat can be lost. The wall of the flask is coated with silver to prevent the loss of heat via radiation to reduce this form of heat loss. At last, a ll three methods of heat transfer are finally limited. This means it’s not possible to loss heat inside the bottle in order to keep the water warm.

We can use a basic equation to understand how a thermos still allows the heat flow equation to look at:

The thermos are designed to keep warm or cold without assistance so we can take no heat transfer. The thermo-lid and the container provide the sources of heat flow out.

Next, the heat flow from the container sides is zero when the best thermal material are used, because reflective vacuum may not pass through heat.

It shows that the only heat flow is through the lid if the thermo-flask is perfectly insulated. The signs of heat flow depend on whether the thermos contain a warm and cool substance, either negative or positive.

History of Thermo-Flasks 

However, thermos are used in labs and experiments not only to maintain the warmth of your coffee but also for conducting experiments. If you have a laboratory that uses a Dewar (i.e., a double walled flask of metal or silvered glass with vacuum in between them) you tell us a ‘thermos’. The use of thermo-flasks began in 1892 by Sir James Dewar. The real name is dewar, but the name of dewar is taken over from the general public by Thermos, the first commercial producer of dewars. In experiments, scientists use dewars to maintain experiments at constant temperatures. Dewars are also used in industries to hold liquified gases or flash freezing. Any time a low temperature is desired, a dewar is used.

Uses of thermos flask:

From hot liquids to cold fruit juices, you can enjoy food and drink when you’re away from home with a thermos. Here are a few great ideas to start with.

• Flask is primarily used in the clinic. If a family member receives tea, coffee, milk, or hot water, then he or she needs a flask.

• Flask is extremely useful to maintain infant hot milk. It was a problem in late hours with heating milk.

• For the making of juice or cold drink we use flask to store ice cubes or cold water.

• Children who are preparing for examinations often notice that they want to keep few cups of tea in the bottle late in the night to drink.

• To get from one place to another is very easy.

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