Question

What is Dewar flask?

Answer 1

Hint:To explain what a Dewar flask is first we will discuss its formation, its purpose and where it is used (both industrial and domestic).
We will give a briefing about the material of which it is made up of.

Let’s start explaining.

Complete step by step solution:
Dewar flask or vacuum flask is an insulating storage vessel which strengthens the time over which its contents remain hotter or cooler than the surroundings. It consists of two flasks one inside the other the space between the two flasks is made complete vacuum so that no contact remains with the surroundings either conduction or convection.

Heat transfer by thermal radiation can be reduced or minimized by making the surface which is facing the gap of the flask as silver but if the surroundings of the flask are very hot then it causes a problem therefore , the flask must hold the contents below the boiling point of water.

Vacuum flasks are usually made up of metal, borosilicate glass, foam or plastic.

Latest improvements done to the vacuum flask include the vapour cooled radiation shield and the vapour cooled neck, both the improvements help to reduce evaporation from the flask.

Note:
Vacuum flasks are used for domestic purposes like storing hot and cold beverages ,used in industries and laboratories to hold liquefied gases for flash freezing ,sample preparation and other processes where maintaining an extreme low temperature is required. MRI machines use double vacuum flasks, having two vacuum sections. The inner section contains helium and the outer section contains nitrogen, in this manner we can limit the loss of precious helium.