Why a nonshallow lake does not freeze completely even in an

Why a non-shallow lake does not freeze completely even in an extreme winter? Explain the heat transfer to and from a road pavement in winter, in North Texas, over a 24-hour period with the day being bright, sunny, and cold and the night being windy and chilly. What is the wind chill factor? How can a person in Alaska experience frostbite on a bright sunny day? What is the inherent difference between the application of conservation of energy over a time interval and an instant of time. It is recommended that a fin must increase heat transfer rate by at least 100% to justify its use. Explain.

Solution

a) As ice is lighter than water it floats on the water surface thus ice at the surface creates a blanket that insulates the underlying water from the cold air. The underlying earth is warmer, so the water reaches a stable temperature somewhere between the temperature of the ground beneath the lake and the air temperature.

b) Specific heat of the material of the road pavement is larger (1 in SI units) than that of air (0.73 in SI units). Hence accordingly the heat gets stored in the pavement material. Now during the whole day as the temperature fluctuates, the heat flows in and out accordingly decided by the temperature difference. The rest can be figured out easily.

c) Wind chill factor is basically a measure of the total heat loss from temperature, relative humidity, wind, skin evaporation,to a person adjusted to an equivalent temperature only on a still, dry day.
If a person stands still with no wind, the body heats up the air around, so it doesn\'t feel as cold. A parked car will just cool down to the air temperature and stay there. We try and maintain a body temperature. With wind the air next to the skin gets close to the air temperature and the amount of water changes how fast heat is removed.

d) Energy conservation for a given instant of time tells about the relation between various flows of the system. It is generally expressed in the continuity equation and relates the change in energy density to the energy current in an infintesimal volume.

Whereas while talking in terms of conservation over a time period, one generally talks about the conservation of various quantites.

e) i didn\'t get what do you mean by a fin.