Question

Q1. Cassowaries have a distinctive helmet-like structure on their heads called a casque. The casque consists of a layer of keratin (the material that hair and nails are made of) that sheathes a twin-layer bony structure containing many blood vessels and surrounding a large air pocket. The purpose of the casque is unclear, but one proposed purpose is that t acts as a thermal window, i.e. a part of the body where heat is easily exchanged with the surroundings. (a) Based on the structure of the caque, explain why it would make a good thermal window. (b) Cassowaries are large birds with dark feathers that live in tropical environments. Why would having a structure to act as a thermal window be beneficial for cassowaries? (e) A scientist measures the rate of heat loss from a cassowary's casque to be 1.91 W when the temperature of the surrounds is 15°C. The casque surface has area of 0.038 m2 and emissivity of 0.96 If the primary method of heat loss is radiation, what is the temperature of the surface of the casque?

Answer 1

a. Thermal window is a kind of window that has two panes of glass separated by an insulating gas which reduces the heat exchange between interior and surroundings.

In case of cassowaries, the air pocket below sheath serves as an insulating gas and thus acts as a thermal window.

b. In case of thermal window, whenever the ambient temperature is lower(winter temperatures), it minimizes/prevents the heat loss arising due to heat exchange between internal conditions and external environment.

In the same way casque protects cassowarries from heat loss during the cold conditions.

c. $Heat loss due to radiation (W)= \sigma A\varepsilon (T_i^4 - T_s^4)$

Ti denotes internal temperature, Ts denotes surrounding temperature

Upon solving 297.21 K = $24^{0} C$