Conduction Contents Basic Concept Example Whiteboards Conduction Heat
Conduction Contents: • Basic Concept • Example • Whiteboards
Conduction Heat transfer by contact Random wiggling Hot to cold Flow rate T, A, material, 1/thickness Simulation Insulation prevents conduction Down/Synthetics Thickness Demo – Ice Melter blocks. Heat sinks
Conduction ΔQ/ k A l T 1 T 2 t = Heat flow rate in J/s or Watts = Thermal Conductivity (Wm-1 o. C-1) = Area (m 2) = Thickness of insulation (m) = High temperature (o. C) = Low Temperature (o. C)
Example #1 – A 100. W light bulb can maintain a temperature of 15. 0 o. C in a well head enclosure when it is -28. 0 o. C outside. The enclosure is a box is 1. 20 m wide x 1. 20 m long x 0. 950 tall insulated by 12. 0 cm of insulation. What is thermal conductivity of the insulation? (ignore the heat that goes into the ground) A = 1. 2 x 1. 2 + 4 x 1. 2 x. 95 = 6. 00 m 2 100 = k(6. 00 m 2)(43 o. C)/0. 12 k = 0. 0465 W/m/o. C
Conduction 1 -3
What is the heat flow rate through a 2. 4 m x 1. 2 m window that is a single pane when the air next to the glass is at 12. 0 o. C and the air outside is at 3. 4 o. C? The glass is 4. 0 mm thick, and has a thermal conductivity of 0. 84 W/m/o. C. Q/t = (0. 84)(1. 2 x 2. 4)(12 -3. 4)/(0. 00400) = 5201. 28 W 5200 W
What is the temperature difference between the inside and the outside of a wall if it is insulated by 8. 94 cm of fiberglass insulation (k = 0. 048 W/m/o. C) is 2. 4 m tall by 3. 7 m wide and heat is flowing through it at a rate of 140 J/s? 140 = (0. 048)(2. 4 x 3. 7)(ΔT)/(0. 0894) ΔT = 29. 3637387387 o. C 29 o. C
A glass (k = 0. 84 J/m/o. C) beaker is 1. 4 mm thick, contains 175 grams of ice (L = 3. 33 E 5 J/kg) in an ice bath (at 0 o. C of course), has a surface area of 0. 025 m 2 exposed to a well stirred water bath maintained at 20. 0 o. C. What time will it take the ice to all melt? (Assume it has a perfectly insulating lid) (0. 175)*3. 33 E 5/t = (0. 84)(0. 025)(20)/(0. 0014) t = 194. 25 s 190 s
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