It is known that the electron motion generates a magnetic field. The constant motion of the electron in the orbit of the atom can be called a single source of the magnetic field.
It is also known that the permanent magnet can be replaced by an electromagnet, which is connected to a constant electric current source. The motion of electrons in the coil creates a similar magnetic field.
Therefore, the permanent magnet may be called as a natural source of the magnetic field. It can be called as a battery of the magnetic field. However, using the electric current of battery like a motion of electrons and using coil it can induce a controlled magnetic field, or create a heat energy, which could be converted into mechanical work. Unfortunately, this type of conversion cannot be produced without extra mechanical work with constant magnetic field of permanent magnet (a battery of magnetic field ).
However, the battery of magnetic field can produce a special thing – polarization of magnetic spins. This polarization of magnetic spins of particles from external magnetic field can distort entropy (change of heat capacity) of substance. During this polarization process of magnetic spins of particles, the magnetic part of the entropy of substance is reduced. Based on the second law of thermodynamics, the entropy of a closed system remains constant or increases. Therefore, the other part of entropy will be increased i.e. the temperature of a substance will be increases. Conversely, during the demagnetization process of substance, the magnetic part of the entropy increases and the temperature of the material falls. This is called the magnetocaloric effect. This magnetocaloric effect works for ferromagnetic and paramagnetic materials. In this particular case the paramagnetic is a ferromagnetic material with temperature more than Curie point.
Based on this, possible build a kind of virtual demon of Maxwell, which is based on the redistribution of entropy of the substance.
This distortion of entropy (change of heat capacity) also allow to have virtual locations with different temperature. In case with magnetocaloric effect the different temperature virtual locations is exists when observed object is present in this location.
Heat-engine Carnot works on temperature difference. However, not necessary to heat something to make a temperature difference. The magnetic field can change heat capacity of substance and this action will change the substance temperature. Enough to have a difference of intensity of magnetic field. It could be called as Entropy Engine.
Since the observed object can take a different temperature on different virtual locations, therefore possible make simple heat engine.
The equivalent of Entropy Engine
On this diagram of equivalent of Entropy Engine, the heat engine has two locations with temperature T1 and T2. A thermal conductor attached to the location with temperature T2 and heats a gas which will increase its internal energy. This increase of internal energy will make a gas expansion into cylinder and a thermal conductor will detached from a hot location and will be connected to a location with cold temperature T1. Cooling the gas from temperature T2 to T1 will reduce the internal energy. This will reduce a pressure of gas inside the cylinder and will connect the thermal conductor with hot location again.
The entropy machine contains a permanent magnet, a paramagnetic element which connected with piston and cylinder with gas. All system is experiencing a gravity force. At initial time, based on magnetocaloric effect the permanent magnet will increase temperature of paramagnetic from T1 to T2. The paramagnetic element will heat a gas which will increase its internal energy. This increase of internal energy will make a gas expansion into cylinder and the piston will remove paramagnetic element from magnetic field of the permanent magnet. The temperature of the paramagnetic element will be decreased and it will start cool down the gas from temperature T2 to T1. This will reduce the gas internal energy and it will reduce a pressure of gas inside the cylinder. The piston will move into initial position and it will return the paramagnetic element into magnetic field of the permanent magnet again.
A polycrystalline Ni-Mn-Ga and a Gadolinium alloy have temperature Curie close to normal temperature 325K and 293K. The Neodymium magnet has 1.4T strength of the magnetic field. This allow to build a real Entropy Engine.
This is example of “drinking bird” toy, which was modified for Entropy Engine model.
The paramagnetic element increase own temperature inside magnetic field of permanent magnet. This will heat a low point boiling liquid and it will start expand process. When liquid expand enough then “bird” will be overturned and this will remove paramagnetic element from magnetic field of permanent magnet.
Now. At this time, the paramagnetic element will cool the liquid. It will be compressed back to normal volume and “bird” will return back to initial position.
The “drinking bird” toy works on temperature difference about 2K.
In case to use Gadolinium alloy it would be possible in temperature above than its own Curie temperature 293K (20C). Based on this graph of magnetocaloric effect for Gadolinium alloy, it has temperature difference more than 2K.
The neodymium permanent magnet grade N52 can provide the magnetic field’s strength 1.4Tesla.
The temperature difference should be enough to work this model in temperature range 295K~320K.
More critical model for short temperature range.
This model will induced oscillation in temperature range around Curie point. At initial bi-stable position these elements have temperature a little less than Curie temperature and the paramagnetic elements are become to ferromagnetic elements. When one of ferromagnetic element will be close to permanent magnet then it will be inside high intensity magnetic field. This magnetic filed changes the heat capacity property of this element and it increases its own temperature. Since the initial temperature was close to Curie point and changes of heat capacity then the element will heat up more than this Curie point. After this moment, in phase transition the ferromagnetic element will be as paramagnetic element. Also, the vaporization of low boiling liquid will displace liquid into different position and will change the mass balance. At this point, when paramagnetic element will get a bigger heat capacity without high intensity magnetic field and will cool back to initial temperature and will compress liquid, the another ferromagnetic element will heat to high temperature more than Curie point at position close to permanent magnet. During time when second element will lose ferromagnetic property and vaporization will displace liquid in second tube then the first element will take back its own ferromagnetic property and liquid will be compressed in first tube. At this time the first element will be attracted by permanent magnet again.