Osm Physics by Ashish

Regenerative Cooling, Adiabatic Expansion and Adiabatic Demagnetisation Definition: The cooling produced by reducing the magnetic field acting on a thermally isolated paramagnetic substance is called cooling by adiabatic demagnetisation . Principle A suitable paramagnetic salt, such as gadolinium sulphate, is placed in a thermally insulated glass tube. The tube is connected to a helium chamber and a vacuum system. The cooling assembly is surrounded by liquid helium. Additional cryogenic shielding may be used to minimize heat transfer from the surroundings. The sample is placed between the poles of a strong electromagnet. A magnetic field is therefore applied to the paramagnetic salt. The temperature can be determined from the magnetic susceptibility ...

Regenerative Cooling, Adiabatic Expansion and Adiabatic Demagnetisation Definition: The cooling produced when a compressed gas expands under adiabatic conditions is called cooling by adiabatic expansion . Adiabatic Relation For a reversible adiabatic expansion of an ideal gas, \[ PV^\gamma=\text{constant} \] where \[ \gamma=\frac{C_P}{C_V} \] Using the ideal-gas equation, the temperature-pressure relation becomes \[ TP^{(1-\gamma)/\gamma}=\text{constant} \] Therefore, between two states, \[ \boxed{ \frac{T_2}{T_1} = \left( \frac{P_2}{P_1} \right)^{(\gamma-1)/\gamma} } \] Hence, ...

Regenerative Cooling, Adiabatic Expansion and Adiabatic Demagnetisation Definition: Regenerative cooling is a continuous cooling process in which the cold gas produced by expansion is used to precool the incoming high-pressure gas before it undergoes further expansion. Principle of Regenerative Cooling In regenerative cooling, a portion of the gas that has already undergone Joule–Thomson expansion is passed through a heat exchanger in thermal contact with the incoming high-pressure gas. The returning cold gas cools the incoming gas before it reaches the throttle valve. The precooled gas then undergoes another Joule–Thomson expansion and becomes still colder. The process is repeated continuously. With each cycle, the temperature of the incoming gas decreases furth...

When a real gas is allowed to flow adiabatically through a porous plug from a region of high pressure to a region of low pressure, its temperature may change. This phenomenon is known as the Joule–Thomson effect , and the process is called Joule–Thomson expansion or throttling . Porous Plug Experiment The apparatus used in the Joule–Thomson porous-plug experiment is shown schematically in Fig. Consider a gas flowing through a thermally insulated tube containing a porous plug P . Two weightless and frictionless pistons X and Y are fitted on the two sides of the plug. The entire system is thermally insulated; hence, no heat is exchanged with the surroundings. Initially, let the gas occupy chamber A , having ...

The second law of thermodynamics states that the entropy of an isolated system never decreases; it either stays the same (in reversible processes) or increases (in irreversible processes). It places fundamental limits on the direction of natural processes and on the efficiency of heat engines and refrigerators. Two classical equivalent formulations are the the Kelvin–Planck (Kelvin) and Clausius statement statement. (i) Kelvin–Planck Statement It is not possible to design an engine which works in a cyclic process and converts all the heat extracted from a heat source into work so that the working substance may remain unaffected. In other words, for the continuous production of work, a heat sink is necessary along with the heat source. According to the original statement given by Ke...

A Carnot cycle is a cyclic process consisting of four reversible processes performed in a definite sequence, namely two isothermal processes and two adiabatic processes. Main Parts of a Carnot Engine (i) Heat Source The heat source is a reservoir of effectively infinite heat capacity maintained at a high temperature \(T_1\) K. Its temperature remains constant even when heat is supplied to the working substance. Its upper surface is perfectly conducting. (ii) Mechanical Arrangement and Working Substance A hollow cylinder is used whose walls are perfectly insulating and whose base is perfectly conducting. A frictionless piston made of insulating material is fitted inside the cylinder. An ideal gas is used as the working substance. (iii) Heat Sink The heat sink is a reservoir of effectively infinite heat capacity maintained at a lower temperature \(T_2...

``` Heat Engine, Carnot Cycle and Efficiency of Carnot Engine Heat Engine A heat engine is a device that converts a part of the heat supplied to it into useful mechanical work. A heat engine must contain the following three essential parts: Heat source Mechanical arrangement and working substance Heat sink (i) Heat Source A heat source is a heat reservoir maintained at a high temperature. It has a very large, ideally infinite, heat capacity so that its temperature remains constant even when a large amount of heat is continuously extracted from it. (ii) Mechanical Arrangement and Working Substance To convert heat into mechanical work, a hollow cylinder fitted with a movable piston is used as the mechanical arrangement. The working substance is placed inside the cylinder. The working substance absorbs heat from the heat source and expands, t...