[Physics Class Notes] on Joule-Thomson Effect Pdf for Exam

The Joule-Thomson Effect illustrates the change in temperature of a fluid when it is forced to flow through an insulated valve from a high-pressure region towards a region with low pressure. The Joule-Thomson Effect is often termed the Joule Kelvin or Kelvin Joule effect. According to their theory, change in pressure in the valve can cause changes in the temperature of the fluid.

 

For quite some time, James Prescott Joule and William Thomson – both British Physicists – worked in a coordinated effort, directing investigations intended to dissect and propel Thermodynamics. In 1852, the specialists made an especially outstanding disclosure. They observed that a temperature change can happen in gas because of an abrupt tension change over a valve. Known as the Joule-Thomson Effect (or now and then the Thomson- Joule effect), this peculiarity has demonstrated to be significant in the headway of refrigeration frameworks just as liquefiers, climate control systems, and hotness siphons. It is additionally the effect that is liable for a tire valve getting cold when you let out the air from a bike tire.

Joule-Thomson’s impact delineates the adjustment of temperature of a fluid when it is compelled to move through a protected valve from a high-pressure district towards a locale with low pressure. Joule-Thomson’s effect is regularly called the Joule Kelvin or Kelvin Joule impact. As indicated by their hypothesis, a change in tension in the valve can cause changes in the temperature of the fluid.

Most gasses at typical temperatures are somewhat cooled at choking, except for hydrogen and helium. The inner cooling happens on the grounds that hotness is changed over to work that is applied to defeat intermolecular powers. Ideal gas relations dismiss any intermolecular powers and accordingly pass up the Joule-Thomson Effect. Thus, depending just on ideal gas law presumptions when doing stream estimations with computational apparatuses can be dangerous.

Joule-Thomson Experiment

Refer to the image shown above that helps understand the effect of Joule-Thomson law quickly. To illustrate this, a gas packet is placed opposite to the flow of direction in a Joule-Thomson valve. As a result, it faces restriction, and the upstream gas will need to perform work to help it move. This work done is equivalent to the multiplication of upstream pressure and volume of a packet. 

W1 = VPacket1 x P1

Further, the fluid packet has to perform certain work to make a place for itself by displacing some amount of downstream gas. This work done can be expressed as 

W2 = VPacket2 x P2

However, this work performed upstream and work performed downstream is not equal because of various effects of compressibility. This internal energy of fluid follows the 1st law of Thermodynamics. And the adiabatic process does not allow this system to lose any heat or work. 

From the above theories, we can conclude that 

U2 – U1 = W1 – W2

For cases where the fluid pressure is lowered, there is a rise in aggregate distance between molecules. As a result, the increased attractive forces also cause an increase in potential energy. 

Further, it is seen that real gasses need to work more downstream to make a place for the packets than they need to work upstream. 

Therefore, the following equation can be written  

P1 x V1 < P2 x V2

It also illustrates a decrease in potential energy as the fluid goes through restriction. Most real gasses show a reduction in temperature with a decrease in pressure. However, that does not hold true for every condition or gas. To conclude, the temperature of this fluid varies with varying potential energy, given the enthalpy of the gas remains unchanged.

Joule-Thomson Coefficient

It can be defined as the change in temperature of the fluid with the varying pressure in order to keep its enthalpy constant. It can be expressed as follows 

μJT = (∂T / ∂P) H

Joule-Thomson Expansion

The coefficient is to be derived using the law of Thermodynamics and will be written as, 

μ = (∂T / ∂P)H  (∂T / ∂P)T (∂P / ∂T)H (∂T / ∂H)P

= -1 (∂H / ∂P)T 

= − (∂H / ∂T)P (∂T/ ∂P)H  (∂H / ∂P)T 

= – CP μ

Further, 

(∂H / ∂P)T = [v~ − T (∂v / ∂T)P

μ= RT2 PCP (∂Z / ∂T) P μ

= (∂T / ∂P)H

= 1/CP [T. (∂v / ∂T)P−v]

=−1/ CP (∂H / ∂P)T

= RT2 / PCP (∂Z / ∂T)P

Mentioned above is the expansion, which will help you calculate the Joule-Thomson coefficient for real gas step by step. Learn the steps carefully to understand the derivation procedure. 

Inversion temperature is the fluid’s temperature at which there is no change in pressure even with decrease in temperature. 

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What is the Process of Joule-Thomson Effect?

The temperature change relating to the Joule-Thomson Effect can happen when a streaming gas goes through a strain controller, which goes about as a choking gadget, valve, or permeable fitting. Here, a temperature cha
nge isn’t really attractive. To adjust any Joule – Thomson-related temperature changes, a warming or cooling component can be utilized. For situations where the fluid strain is brought down, there is an ascent in total distance between atoms. Therefore, the expanded appealing powers additionally cause an increment in expected energy. Further, it is seen that genuine gasses need to work all the more downstream to make a spot for the parcels than they need to work upstream. It likewise shows a lessening in possible energy as the fluid goes through limitations. Most genuine gasses show a decrease in temperature with a diminishing in pressure. Notwithstanding, that doesn’t remain constant for each condition or gas. To finish up, the temperature of this fluid changes with fluctuating likely energy, given the enthalpy of the gas stays unaltered.