Engineering for Industrial Designers and Inventors

Chapter 7. Heat Transfer

We know all about heat transfer. Everyone has touched that hot pot and had our neurons awoken—ouch! We pay a lot of money to heat and cool buildings and houses. We buy fashionable coats to keep us warm and hats to keep the sun out of our eyes and off our heads (yes, and to keep us warm too!). We have touched sun-soaked objects and been sadly startled at how hot they were. We are fearful of boiling grease and hissing steam. We watch dogs pant and have no idea how small birds can survive frigid cold. We are happiest at a certain temperature and humidity but the world around us often wants us to be much hotter or colder.

In products and systems, heat is often created by friction and has to be removed. If you pull and squeeze a kneaded eraser you will be surprised how much heat builds up. Hopefully you have never touched a brake rotor after you park your car—the frictional heat produced by braking a car is enormous. Moreover, materials and our bodies behave differently when hot or cold. Studying heat transfer tells us why water evaporates at room temperature, why shiny seat belt buckles get so hot, why dogs pant, and why the SR 71 Blackbird airplane is painted black. It is for all of these reasons that the behavior of heat is important for a designer.

What Is Heat?

Heat is the movement of molecules—the faster molecules vibrate, the higher the measured temperature. The second law of thermodynamics tells us that this vibration energy wants to be shared; that ...