Throttling process and its application

Throttling process and its application

1. GOVERNMENT ENGINEERING COLLEGE Subject: CHEMICAL ENGINEERING THERMODYNAMIC (2140502) Topic: Throttling and Joule-Thompson Coefficient and its Applications

2. 1 Bhadja Anand C. 160190105006 2 Davra Dharmik G. 160190105016 3 Moradiya Milan L. 160190105043 4 Pandav Mukund G. 160190105049 5 Papaniya Hitesh L. 160190105051 Submitted By:

3. Throttling & The Joule-Thomson Experiment Throttling process involves the passage of a higher pressure fluid through a narrow constriction. The effect is the reduction in pressure and increase in volume This process is adiabatic as no heat flows from and to the system, but it is not reversible. It is not an isentropic process The entropy of the fluid actually increases Such a process occurs in a flow through a porous plug, a partially closed valve and a very narrow orifice.

4. In this experiment gas is forced through a porous plug and is called a throttling process • In an actual experiment, there are no pistons and there is a continuous flow of gas • A pump is used to maintain the pressure difference between the two sides of the porous plug • In this experiment, as pressures are kept constant work is done

5. The pump maintains the pressures and In the experiment , and are set and is measured Consider a series of experiments in which and are constant ( constant) and the pumping speed is changed to change and hence Since the final enthalpy does not change, we get points of constant enthalpy  

6. Work Done The overall change in internal energy of the gas is For Adiabatic Expansion is 0 But Enthalpy is H = U + PV Hence, in a Throttling process, enthalpy is conserved.  

7. Since = 0 and = 0, the equation reduces to dH = 0. This is therefore an ISOENTHALPIC expansion and the experiment measures directly the change in temperature of a gas with pressure at constant enthalpy which is called the Joule-Thomson coefficient ( μ ). For expansion, P is negative and therefore a positive value for μ corresponds to cooling on expansion and vice versa.  

8. The gas which is initially at a state represented by the point P as shown in fig., is undergoing Joule-Thompson Expansion. It will experience the rise in temperature till the point Q is reached, and thereafter the temperature decreases with further decreases in pressure. T he slope i s the isenthalpy is equal to the Joule-Thompson coefficient as per the relation. It is positive only in the region where pressure is less than that of Q and is Zero at point Q, where the isenthalpy exhibits a maximum. A smooth curve is placed through the points yielding an isenthalpic curve

9.   < 0 temperature increases = 0 temperature remains constant > 0 temperature decreases  

10. This also tells us that we cannot just use any gas at any set of pressures to make a refrigerator, for example - At a given pressure, some gases may be cooling (m > 0) but others may be heating (m < 0) The proper choice of refrigerant will depend on both the physical properties, esp. the Joule-Thompson coefficient as well as the mechanical capacity of the equipment being used. Thus , we cannot just exchange our ozone-depleting freon in our car's air conditioner with any other coolant unless the two gases behave similarly in the pressure - temperature ranges of the mechanical device, i.e., they must have the same sign of m at the pressures the equipment is capable of producing. Generally , to use a more environmentally friendly coolant, we need to replace the old equipment with new equipment that will operate in the temperature range needed to make m positive The sign of the Joule–Thomson coefficient, μ, depends on the conditions The temperature corresponding to the boundary at a given pressure is the ‘inversion temperature’ of the gas at that pressure

11. Application Of throttling process The throttling process is commonly used for the following purposes : For determining the condition of steam (dryness fraction) For controlling the speed of the turbine Used in refrigeration plants Liquefaction of gases. In the Linde technique as a standard process in the petrochemical industry I n many cryogenic  applications.

12. Liquefaction

13. Simple refrigeration cycle

14. Natural Gas Liquefaction process

15. Hampson-Linde process

16. Controlling the speed of turbine by throttling

17. References Beattie, J. A. and Bridgeman, O. C., J. Amer. Chem. Soc., 49 , 1665 (1927 ). Taylor , H. S. and Glasstone , S. (eds.), "A Treatise on Physical Chemistry ", vol . II, 187 ff. van Nostrand, Princeton, N.J. (1951 ). Atkins, P.W. "Physical Chemistry", 5 th ed., (Freeman, 1994), pp 104-108 . “A Textbook of Chemical Engineering Thermodynamics.” K.V. Narayanan PHI Learning, 6 th ed., pp 127,150, 214. J.H. Noggle , "Physical Chemistry", 3rd ed., Harper Collins, 1996 pp 104ff. R.G . Mortimer "Physical Chemistry ", Benjamin/Cummings , Redwood City, Calif ., 1993, pp 70-73.