Possible Swain journals for first Article Summary. Scientific American (e.g. Sept. 2006) Nature (e.g. Nov. 2001) Science (access through Swain library web page, they no longer have paper copies) Science News Physics Today The Physics Teacher Bulletin of the Atomic Scientists Summary will be graded on how well it covers the essential thrust of the article itself as well as on the quality of your writing. Look at syllabus on ONCOURSE for the “article” link that describes in more detail what the assignment entails.

Swain Hall West- 2nd Floor Swain Hall Library http://www.libraries.iub.edu/index.php?pageId=92

Phase transitions in water

Passive Solar House

Specific Heats Temperature Scales: Ice (near 0oC) 2090 J/kg.K=2090 J/kg.Co Water (near 0oC) 4186 J/kg.K=1.00 cal/kg.Co Aluminum 900 J/kg.K Copper 387 J/kg.K Temperature Scales: 0oC = 273.15 K ice melts at this temp 100oC = 373.15 K water boils at this temp O K absolute zero, the coldest temperature possible. Note that 1Co = 1 K. The Celsius degree and the Kelvin are the same size! The only difference in the scales is the position of the origin, hence the two scales are equivalent for talking about temperature DIFFERENCES, but not for talking about actual temperatures.

Power=(Q/Dt) = kA(TH – TC)/L Thermal Conduction Power=(Q/Dt) = kA(TH – TC)/L k: thermal conductivity (depends on the material, not on the geometry). Units? http://sol.sci.uop.edu/~jfalward/heattransfer/heattransfer.html

Some thermal conductivities Diamond >1000 W/m.K Aluminum ~225 W/m.K Stainless steel 14 W/m.K Window glass 1 W/m.K Fiberglass insulation 0.048 W/m.K Polyurathane foam 0.024 W/m.K Air (still, dry) 0.026 W/m.K

Some thermal conductivities Diamond >1000 W/m.K Aluminum ~225 W/m.K Stainless steel 14 W/m.K Window glass 1 W/m.K Fiberglass insulation 0.048 W/m.K Polyurathane foam 0.024 W/m.K Air (still, dry) 0.026 W/m.K Question: Look at fiberglass vs. air (still dry). Why do you put fiberglass insulation in your attic if still air is a better insulator than fiberglass?

Why replace a thin layer of air (k=0 Why replace a thin layer of air (k=0.026) near the floor of your attic with fiberglass (k=0.048)? Toutside Tc

Heat Transfer through a window Conduction is NOT the only means of heat transfer!!! There is also: CONVECTION When a fluid (gas or liquid) flows, it transfers heat much more effectively than when it is still.

Convection in your attic It’s efficient at bringing the T of the attic floor to the T of the outside. Insulation allows the attic floor to be at a much lower (or higher) T than the house ceiling Toutside Ta Tc

One way to use Solar Heat in a home You can use of convection to your advantage, if you’re clever!

The Electromagnetic Spectrum

Radiative Heat Transfer Wavelength Power = esAT4 Effect of increasing temperature: more power, shorter wavelengths lpeak T= 2898 mm.K

Basic Heat Engine Efficiency = h = W/QH = (QH-QC)/QH

OTEC Tsurf = 25 C Tdeep = 5 C

Second Law of Thermodynamics The entropy (disorder) of the universe may never decrease. If we let S denote entropy, then the change in the entropy of an object associated with an exchange of heat, Q, at ABSOLUTE temperature, T, is given by: DS = Q/T

Carnot (reversible) Heat Engine The entropy change of the universe in an operation of a heat engine is given by: DS = QC/TC - QH/TH Since this cannot be negative, the best you can do is have DS = 0, in which case: QC/TC = QH/TH

Carnot Heat Engine (cont.) For a Carnot cycle then we can rewrite the efficiency in terms of the ABSOLUTE temperatures of the two reservoirs (note the symbols := or =: denotes a definition for the quantity next to the colon): h= 1 - QC/QH = 1 - TC/TH =: hCarnot

Chapter 5 Home Energy Cons. Thermal Resistance: Q/Dt = kADT/L =: ADT/R R:= L/k This is useful because it folds in both the material property (k) and the thickness of the insulating layer (L), AND if you combine layers, then the thermal resistances (R) simply add, as shown on the next slide.

R-value for a typical wall See table 5.2 in H&K for typical values of building materials