Explain how vacuum flasks construction minimize heat exchange with the surrounding?
there is no conductive or convective heat transfer...only radiative
the partial movement is visible , the flask feels cold.
Vacuum flasks, also known as thermos flasks, are constructed in a way that minimizes heat exchange with the surroundings. Here is a step-by-step explanation of their construction and how it helps in minimizing heat exchange:
1. Inner Container: The innermost part of the vacuum flask is typically made of glass or stainless steel. This container holds the liquid or food that you want to keep hot or cold.
2. Vacuum Layer: Surrounding the inner container, there is a vacuum layer. This layer is created by removing the air between the inner and outer containers, creating a vacuum. The vacuum acts as an excellent thermal insulator, preventing heat transfer through conduction and convection.
3. Reflective Coating: To further reduce heat exchange, the inner surface of the outer container is coated with a reflective material, often a thin layer of metal. This coating reflects back some of the heat radiation that tries to escape, keeping the contents of the flask at the desired temperature.
4. Outer Container: The outer container is typically made of metal or plastic and serves as an extra layer of insulation. It prevents any heat loss that may occur due to the temperature difference between the contents of the flask and the outside environment.
5. Stopper or Lid: The flask is equipped with a stopper or lid, which is often made of plastic or rubber. This stopper creates an airtight seal, preventing air from entering the flask and compromising the vacuum insulation.
By incorporating these construction elements, vacuum flasks effectively minimize heat exchange with the surroundings. The vacuum layer restricts heat transfer through conduction and convection, while the reflective coating and outer container prevent heat radiation and conduction respectively. This insulation, combined with the airtight seal, helps to maintain the temperature of the contents for longer periods of time.
A vacuum flask, also known as a thermos or a Dewar flask, is specifically designed to minimize heat exchange with the surrounding environment. The construction of a vacuum flask involves several key elements that contribute to its excellent thermal insulation:
1. Double Wall Structure: A vacuum flask consists of two walls, an inner and an outer wall, which are separated by a vacuum or very low-pressure space. This creates a barrier that prevents heat transfer through conduction and convection between the contents of the flask and the surrounding environment.
2. Inner Reflective Coating: The inner wall of a vacuum flask is often coated with a reflective material, such as silver or aluminum. This reflective coating helps to minimize heat transfer through radiation by reflecting the thermal radiation back towards the contents of the flask.
3. Insulating Material: The space between the two walls of a vacuum flask is typically filled with insulating material, such as foam or glass fibers. This insulating material further reduces heat transfer through conduction and helps maintain the temperature of the contents.
4. Tight Lid or Stopper: The lid or stopper of a vacuum flask is designed to create an airtight seal, preventing the exchange of air between the inside and outside of the flask. This minimizes heat transfer through convection, as there is no circulation of air inside the flask that can carry away heat.
By combining these features, a vacuum flask effectively reduces heat exchange with the surrounding environment, allowing hot liquids to stay hot for an extended period and cold liquids to stay cold.