From Thermal-FluidsPedia

Revision as of 23:41, 28 June 2010 by Administrator (Talk | contribs)
Jump to: navigation, search

Conduction Conduction is the transfer of heat from molecule to molecule through Table 5-2. Thermal Conductivities of Selected Materials, W/m.K (values at 20ºC, unless otherwise stated) Good Conductors Average conductors Poor conductors (good insulators) Diamond 2,000 Ice (0ºC) 2.20 Brick, insulating 0.150 Silver 429 Concrete 1.70 Asbestos 0.090 Copper 400 Soil 1.50 Fiberglass 0.040 Aluminum 220 Glass 1.00 Glass wool 0.040 Iron 80 Water 0.60 Styrofoam 0.033 Lead 35 Epoxy 0.59 Air (dry) 0.026 Stainless steel 14 Body fat 0.20 Silica aerogel 0.004 Granite 3 Snow 0.16 Vacuum 0 89 Chapter 5 - Thermal Energy a substance. If a steel bar is temporarily heated at one end, its molecules become agitated and move faster than neighboring molecules. When fast-moving molecules collide with slower molecules, energy is transferred from faster to slower molecules. The chain reaction moves along the bar until its temperature is uniform. While conduction does take place in gases and liquids, its effects are most pronounced in solids. The closer the molecules are packed, the easier conduction is. Heat transfer via conduction increases in materials with a greater heat conductivity and larger temperature gradients. Question: Why do animals living in freezing climates often burrow into the snow to sleep? Answer: In addition to furs and thick skin, air spaces in the snow help animals protect themselves in such harsh weather. Snow, a poor conductor, slows the loss of body heat. In freezing weather, an igloo would provide a warmer shelter than would a wooden shack because the snow and ice of the igloo are better insulators than wood. Question: How do gloves protect our hands in the cold? Answer: The temperature difference between hands (37°C) and outdoor air (say 0°C) is the same whether we wear gloves or not. However, with gloves heat follows a path of greater resistance, and the rate of heat loss from our hands reduces.


Further Reading

External Links