Possible Swain journals for first Article Summary.

• 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.

• 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

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• 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.

Thermal Conduction

Power=(Q/t) = 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 insulationin your attic if still air is a better insulator than fiberglass?

Why replace a thin layer of air (k=0.026) near the floor of your attic

with fiberglass (k=0.048)?

Tc

Toutside

Heat Transfer through a windowConduction is NOT the onlymeans 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 atticIt’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

Ta

Tc

Toutside

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 TransferWavelength

Effect of increasing temperature:more power, shorter wavelengths

peak T= 2898 m.K

Power =AT4

Basic Heat Engine

Efficiency = = 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:

S = Q/T

Carnot (reversible) Heat Engine

• The entropy change of the universe in an operation of a heat engine is given by:

S = QC/TC - QH/TH

• Since this cannot be negative, the best you can do is have S = 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):=QC/QH=TC/TH =: Carnot

Chapter 5 Home Energy Cons.

• Thermal Resistance:Q/t = kAT/L =: AT/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