What is Joule Thomson Effect in simple words?
The Joule-Thomson effect, also known as the Kelvin–Joule effect or the Joule-Kelvin effect, is the change in temperature of a fluid when it moves from a high-pressure to a low-pressure zone.
The Joule-Kelvin effect is best explained, in accordance with the thermodynamic principle, by assuming a separate gas packet inserted in the opposite flow direction to cause restriction. For the gas packet to pass through, the upstream gas must exert force to push the packet through. The work is equal to the packet’s volume multiplied by the upstream pressure.
As the packet traverses the restriction, it must create space by dislodging a substantial amount of the downstream gas. It entails carrying out the amount of labour that is equal to the product of packet volume and downstream pressure.
Due to the varying effects of compressibility, the quantity of work performed upstream and downstream for actual gases is not equal. Since depressurization is considered an adiabatic process, it demonstrates that no gas exchanges work or heat with its surroundings; hence, any change in internal energy must adhere to the first rule of thermodynamics.
As gas molecules are in random motion, they are subject to repulsive and attraction forces (Van der Waals forces). When the gas pressure is decreased, i.e. when the average distance between molecules increases, the attractive forces become dominant for many gases at room temperature, resulting in an increase in potential energy.
At room temperature, the majority of actual gases necessitate more labour due to the effects of compressibility.
This suggests that the internal energy of gas reduces as it travels through a limitation.
In general, the temperature of many real gases falls when the pressure decreases, but this is not true for all gases and conditions. The lack of change in enthalpy is evidenced by the fact that decompression is an isenthalpic process. Depending on how the internal energy changes to hold the enthalpy constant, the temperature of any gas may fall or increase.
Implementations of the Joule Thomson Effect
The cooling generated by the Joule-Thomson expansion has made it a very valuable refrigeration technology.
In the Linde technique used in the petrochemical sector to liquefy gases, this phenomenon is utilised.
It is also employed in a number of cryogenic applications. For instance, to produce liquid nitrogen, oxygen, and argon.
Even helium can be liquefied employing this mechanism.
What is the principle underlying the Joule Thomson effect?
The transport of heat is the underlying principle of the Joule Thomson effect. Moreover, under standard temperature and pressure, all genuine gases undergo expansion, and this phenomenon is utilised in the process of liquifying gases. Hydrogen and helium are exceptions to this rule.
Frequently Asked Questions – FAQ
How cooling is produced in the Joule Thomson effect?
As gas molecules travel farther apart, work is required to overcome their long-distance attraction. This results in cooling. Hydrogen and helium will only cool upon expansion if their beginning temperatures are extremely low, due to the unusually weak long-range forces in these gases.
Which gases are used in the Joule-Thomson effect?
At a pressure of one atmosphere, Thomson inversion temperatures are extremely low (e.g., around 45 K, 228 °C for helium). Thus, when expanded with constant enthalpy at average room temperatures, helium and hydrogen warm.
In the Joule Thomson effect, what is the inversion temperature?
The inversion temperature in the Joule-Thomson effect is the temperature at which the sign of the coefficient reverses.
Why is the Joule-Thomson coefficient important?
The Joule-Thomson coefficient is an important feature of a specific gas. These coefficients are significant for two reasons:
- intermolecular interaction
- liquefaction of gases.
For an ideal gas, what is the Joule Thomson coefficient?
As the enthalpy of an ideal gas is dependent on its temperature, the Joule Thomson coefficient is equal to zero.
What is the highest possible inversion temperature?
The greatest inversion temperature for hydrogen is 200 Kelvin, whereas the maximum inversion temperature for helium is 24 Kelvin.
Is the Joule expansion adiabatic?
In Joule-Thomson expansion in steady flow through a porous plug or resistive valve, the process is adiabatic, but only for substances whose equation of state is such that specific volume is precisely proportional to temperature at constant pressure (like an ideal gas).
Why doesn’t Joule Thomson apply to hydrogen gas?
Joule Thomson can be applied to hydrogen gas, but only at lower temperatures. This is because their behaviour approaches that of an ideal gas at higher temperatures.
Joule Thomson Effect video lecture
Also Watch -> Liquefaction of gases