Tenta teori

Question 1

What is the difference between the lower heating value (LHV) and the higher heating value (HHV)? And when are they used?

Answer 1

Both: the amount of heat released when the fuel is combusted and the products of combustion are cooled to the initial temperature of the fuel and air mixture
HHV: and the water vapor in the combustion products is condensed to a liquid.

HHV: used to measure the total energy content of a fuel, because it includes the energy contained in the water vapor produced during combustion.
LHV: used to calculate the efficiency of a fuel in practical situations

Question 2

Plancks law and greenhouse effect

Answer 2

As the concentration of greenhouse gases in the atmosphere increases, more infrared radiation is absorbed and re-emitted, which leads to a warming of the Earth’s temperature. This is because the increased concentration of greenhouse gases increases the amount of energy that is absorbed and re-emitted by the gases, and this energy is proportional to the frequency of the radiation according to Planck’s law.

Increasing concentration of greenhouse gases in atmosphere =>
More radiation is absorbed and re-emitted (increases the amount of energy that is absorbed and re-emitted by the gases) =>
heats the Earth’s temperature (this energy is proportional to the frequency of the radiation according to Planck’s law)

Question 3

Q_loss

Answer 3

delta T/resistans

Question 4

egenskaper solcell

Answer 4

Lid: short wavelengths from sun => High transmissivity for short wavelengths
Low transmissivity for long wavelengths.
Tubes: short wavelengths from sun => High absorptivity for short wavelengths
Low emissivity for long wavelengths (se s745)

Question 5

Incident heat/light

Answer 5

Infallande värme/ljus

Question 6

Hur stor area har en halvsfär?

Answer 6

2πr^2

Question 7

Hur stor area har en disk?

Answer 7

π*r^2

Question 8

What are flue gas losses? Name a few ways the solid fuel can make an impact?

Answer 8

The amount of heat that is lost through the flue or chimney when a fuel is burned.
Increased by for example increased moisture and increased ash (water and ash content “steals” heat)
Decreased by increased heating value (more heat goes to heating up)