9. Radiation Heat Transfer from a Thermos Bottle

Heat transfer in a thermos bottle mainly involves radiation and to a much lesser extent conduction and convection. Dewar invented the thermos bottle at the beginning of the twentieth century which is simply a stainless steel inner bottle covered by another stainless steel outer bottle which are separated by vacuum. The outer wall of the inner bottle and the inner wall of the outer bottle are coated with silver in order to minimize radiation heat transfer between the fluid inside the thermos bottle and the outside environment. See Figure 9-1. Two silver coated walls facing each other reflect electromagnetic waves between themselves in the infrared region and minimize radiation heat transfer from the medium inside the inner bottle to the outside environment or vice versa. There is some heat loss, i.e. less than 2.58% of total heat loss in the present example, due to conduction and convection from the lid of the thermos bottle where a small portion of the inner surface of the stainless steel inner bottle contacts the lid.