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:yuck:

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- Thread starter Pudulax1
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:yuck:

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russ_watters

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But, in order to understand the principle of heat pumps, you can imagine a very poor heat pump filled with a near ideal gas as helium at atmospheric pressure. The process in the compressor is mostly

In actual heat pumps the gas used is not helium, but a gas that can be liquefied at room temperature and high pressure, as Freon, NH3, or other hydrocarbons. This allows using the heat of vaporization in the cooling cycle.

The formula for ideal gases is, written in the physical version:

[tex]PV=N{3\over 2}kT[/tex]

N is the number of molecules (not moles) and k the Boltzman constant. When the gas is formed by polyatomic molecules, the formula changes to:

[tex]PV=N{n\over 2}kT[/tex]

where n is the number of degrees of freedom of the molecule.

Furthermore, when the pressure is high (far more than a few bars) the gas formula must be corrected to take into account the volume of the molecules themselves. In actual heat pumps, this is not necessary.

In an adiabatic process the quantity conserved is the product [tex]PV^\gamma[/tex] where [tex]\gamma[/tex] is the adiabatic coefficient of the gas. It is 1.67 for monatomic gases, 1.40 for diatomic gases and less for polyatomic gases.

When a mass of gas passes adiabatically from a state 1 to a state 2 we write:

[tex]P_1V_1^\gamma= P_2V_2^\gamma[/tex]

[tex]P_1V_1= N{n\over 2}kT_1[/tex]

[tex]P_2V_2= N{n\over 2}kT_2[/tex]

If you know [tex]P_1[/tex], [tex]V_1[/tex], [tex]T_1[/tex] and [tex]P_2[/tex]or [tex]V_2[/tex], you can compute [tex]T_2[/tex]

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