Please enable JavaScript.
Coggle requires JavaScript to display documents.
Magnetic Refrigeration (MR) - Coggle Diagram
Magnetic Refrigeration (MR)
Definition
MR is an emerging technology based on Magneto Caloric Effect (MCE)
MCE is caused due to varying magnetic entropy of magnetic materials in varying magnetic field
MCE concept is used because in traditional vapor compression refrigeration (VCR)
High cost of electricity to operator compressor
The refrigerant gas is costing
High cost of compressor
The refrigerant gas toxic and flamable
Principle of MCE
A
heating
or
cooling
of Magneto Caloric Material when it is
magnetized
and
demagnetized
respectively where pressure has no influence
Focus on the 2nd Law of Thermodynamics because it is related to
energy
and
entropy
Entropy is the degree of randomness
High randomness
High energy
High disorder
and vice versa
Magnetic Entropy f(H,T)
Thermal Entropy f(T)
Theory of Magneto Caloric Effect
1) Adiabatic Magnetization (H is high)
Q=0 -> Stotal = CONSTANT
H (magnetic filed) is high, Sm (magnetic entropy) is reduced to compensate it high St (thermal entropy)
Temperture of material increases because :
Electron spin within material are forced to align with magnetic field.
Thus magnetic field does not work at higher order state.
Q=0, by the first law of thermodynamic internal energy increase, temperature increases (Eint;inc , T;inc).
It's magnetic entropy (Sm) reduced and thermal entropy (St) in vibrational lattice increases to compensate total entropy (Stotal).
2) Adiabatic Demagnetization (H is low)
Q=0 -> Stotal = CONSTANT
H is low, Sm increased to compensate it low St
Temperature of the material decreases because :
The electron spin returns to original alignment (no push factor) as St decreased (vibration of molecule decreases)
Sm is increased and St is decreased to compensate Stotal.
Using the concept of Refrigeration Cycle
1) Adiabatic Magnetization
2) Isomagnetic Cooling
3) Adiabatic Demagnetization
4) Isomagnetic Heating
Necessary part of Magnetic Refrigerator
Hot heat excanger
Heat transfer fluid
Glycol water
Ethanol water
Cold heat exchnager
Motor, pump & valve
Magnet
Power supply
Magneto Caloric material
Properties of Magneto Caloric Materials
Show increase in Magneto Caloric effect (Tadiabatic increase)
Low in specific heat - ratio of the quantity of heat required to raise temperature of a body degree.
High thermal conductivity - generate from non electricity to electricity lead to the thermal conductivity.
non toxic - environmental friendly
Resistance to corrosion - bcs it will reduce the quality of refrigeration.
High electrical resistance - high power.
Low manufacturing cost.
Low environmental impact.
Example of material
Gadolinium and some alloys
Advatages
Disadvantages
Initial cost of refrigerator is high (due to Gadolinium)
Safety cooling and less environmental effect
Low pressure operation
Low cost
No refrigerant
Achieving very low temperature nearly 4 Kelvin
No compressor
Highly reversable
Limitation
Idea of magneto caloric material still in research process
Magnetic fridge usage still in research
Application
Cryogenic engine
Magnetic air conditioner in building and houses