14.6 Convection

The movement of icebergs is another example of convection accompanied by a phase change. Suppose an iceberg drifts from Greenland into warmer Atlantic waters. Heat is removed from the warm ocean water when the ice melts and heat is released to the land mass when the iceberg forms on Greenland.

Explain why using a fan in the summer feels refreshing!

Under which two conditions would convection in a fluid be greatest?

1. The gravitational acceleration is large, and the fluid density varies greatly for a given temperature change.
2. The gravitational acceleration is small, and the fluid density varies greatly for a given temperature change.
3. The gravitational acceleration is large, and the fluid density varies slightly for a given temperature change.
4. …

At what wind speed does $- \text{10}º \text{C}$ air cause the same chill factor as still air at $- \text{29}º \text{C}$?

The “steam” above a freshly made cup of instant coffee is really water vapor droplets condensing after evaporating from the hot coffee. What is the final temperature of 250 g of hot coffee initially at $\text{90} . \text{0}º\text{C}$ if 2.00 g evaporates from it? The coffee is in a Styrofoam cup, so other methods of heat transfer can be neglected.

On a hot dry day, evaporation from a lake has just enough heat transfer to balance the $1 . \text{00} \textrm{ }\text{kW}/\text{m}^{2}$ of incoming heat from the Sun. What mass of water evaporates in 1.00 h from each square meter? Explicitly show how you follow the steps in the Problem-Solving Strategies for the Effects of Heat Transfer.

A person inhales and exhales 2.00 L of $\text{37} . \text{0}º\text{C}$ air, evaporating $4 . \text{00} \times \text{10}^{- 2} \textrm{ }\text{g}$ of water from the lungs and breathing passages with each breath.

(a) How much heat transfer occurs due to evaporation in each breath?

(b) What is the rate of heat transfer in watts if the person is breathing at a moderate rate of 18.0 breaths per minute?

(c) If the inhaled air had a temperature of $\text{20} . 0º \text{C}$, what is the rate of heat transfer for w…