In analyzing the performance of a thermal system, the
engineer must be able to identify the relevant heat
transfer processes. Only then can the system behavior
be properly quantified. For the following systems identify
the pertinent processes, designating them by appropriately
labeled arrows on a sketch of the system. Answer additional
questions that appear in the problem statement.
(a) Identify the heat transfer processes that determine
the temperature of an asphalt pavement on a summer
day. Write an energy balance for the surface of
the pavement.
(b) Microwave radiation is known to be transmitted by
plastics, glass, and ceramics, but to be absorbed by
materials having polar molecules such as water.
Water molecules exposed to microwave radiation
align and reverse alignment with the microwave radiation
at frequencies up to 109 s1, causing heat to
be generated. Contrast cooking in a microwave oven with cooking in a conventional radiant or convection
oven. In each case what is the physical
mechanism responsible for heating the food?
Which oven has the greater energy utilization efficiency?
Why? Microwave heating is being considered
for drying clothes. How would operation of a
microwave clothes dryer differ from a conventional
dryer? Which is likely to have the greater energy
utilization efficiency and why?