Refrigeration and cryogenics Zakad Kriogeniki i Technologii Gazowych

Refrigeration and cryogenics Zakład Kriogeniki i Technologii Gazowych Dr hab. inż. Maciej Chorowski, prof. PWr

Methods of lowering the temperature Isentropic expansion n Joule-Thomson expansion n Free expansion – gas exhaust n

Gas isentropic expansion with external work

Gas isentropic expansion with external work Drop of the gas temperature: Entropy is a function of pressure and temperature S= S(p, T) Total differential must be equal to zero: Differential effect of isentropic expansion ms shows the change in temperature with respect to the change of pressure:

Gas isentropic expansion with external work We know from thermodynamics We get where: b is coefficient of cubical expansion

Gas isentropic expansion with external work For the ideal gas: After integration

Piston expander

Cryogenic turboexpander

Isenthalpic – Joule-Thomson - expansion n n When gas, vapour or liquid expands adiabatically in an open system without doing any external work, and there is no increment in velocity on the system reference surface, the process is referred to as throttle expansion. In practice, this process is implemented by installing in the gas stream some hydraulic resistance such as throttling valve, gate, calibrated orifice, capillary, and so on.

Isenthalpic – Joule-Thomson - expansion

Isenthalpic – Joule-Thomson - expansion Temperature drop in Isenthalpic – Joule-Thomson - expansion Enthalpy is a function of pressure and temperature: h= h(p, T) Total differential must be equal to zero: Differential throttling effect μh:

Isenthalpic – Joule-Thomson - expansion

Isenthalpic – Joule-Thomson - expansion Gas Maximal inversion temperature, K eksperyment z równania van der Walsa Argon 765 ----- Azot 604 837 Hel – 3 39 ----- Hel – 4 46 34, 3 Neon 230 ----- Powietrze 650 895 Metan 953 ----- Tlen 771 1090 204, 6 223 Wodór

Free expansion (exhaust)

Free expansion (exhaust) 1. 2. 3. 4. Adiabatic process Non equilibrium process – gas pressure and external pressure are not the same Constant external pressure (pf= const. ) External work against pressure pf

Free expansion (exhaust) Final gas temperature: I Law of Thermodynamics where: u 0, uf – initial and final gas internal energy v 0, vf – initial and final gas volume

Free expansion (exhaust) For ideal gas: We get:

Comparison of the processes for air

Cryogenic gas refrigerators

Heat exchangers Recuperative Regenerative

Comparison of coolers

Refrigerators with recuperative heat exchangers Joule – Thomson refrigerators

Examples of miniature Joule-Thomson refrigerator

Claude refrigerators

Stirling coolers

Stirling cooler

Stirling cooler In Stirling refrigerator a cycle consists of two isotherms and two isobars Stirling cycle is realized in four steps : 1. Step 1 -2: Isothermal gas compression in warm chamber 2. Step 2 -3: Isochoric gas cooling in regenerator 3. Step 3 -4: Isothermal gas expansion with external work 4. Step 4 -1: Isochoric gas heating in regenerator

Stirling split cooler

Stirling cooler with linear motor

Efficiency of Stirling cooler filled with ideal gas Work of isothermal compression Work of isothermal expansion Heat of isothermal expansion

Stirling cooler configuration:

Stirling cooler used for air liquefact -ion

Stirling cooler used for air liquefaction

Two stage Stirling refrigerator

Gifforda – Mc. Mahon cooler

Gifforda – Mc. Mahon cooler Four steps of Mc. Mahon cycle: 1. Filling. 2. Gas displacement 3. Free exhaust of the gas 4. Discharge of cold chamber Efficiency of Mc. Mahon cooler:

Mc. Mahon refrigerator

Combination of Mc. Mahon and J-T cooler, 250 m. W at 2, 5 K

Pulse tube – free exhaust

Scheme of pulse tube cooler

Development of pulse tube coolers Gifford, 1963, rather curiosity that efficient cooler Kittel, Radebaugh, 1983 orifice pulse tube Dr. Zhu et. al. , 1994, multiply by-pass pulse tube

Comparison of Stirling and orifice pulse tube cooler

Pulse tube cooler for 77 K applications Weight: 2. 4 kg Dimensions (l x w x h): 11. 4 x 22 cm Capacity: 2. 5 W @ 65 K Ultimate low temperature: 35 K Input power 2 k. W

Pulse tube

Two stage pulse tube

Pulse tube configuration

Adiabatic demagnetization of paramagnetic

Paramagnetic salts

Magnetic coolers

Magnetic cooler

Magnetic cooler with moving paramagnetic

Three stage magnetic cooler with magnetic regenerator Ceramic magnetic regenerator material Gd 2 O 2 S with an average diameter of 0. 35 mm for G-M and pulse tube cryocoolers.

Cooler efficiency at 80 K

„Family” of cryocoolers