Joule expansion

Varesi J, Majumdar A (1998) Scanning joule expansion microscopy at nanometer scales. Appl Phys Lett 72 37-39... 

For gases, this may be positive or negative, depending on conditions. Note that it is zero for an ideal gas. It applies directly to the Joule expansion, an adiabatic expansion of gas confined in a portion of a container to fill the entire container. 

Fig. 8.2. Schematic cartoons illustrating various types of adiabatic volume changes. In each case the points on the PV diagram correspond to those in Figure 8.1. (a) Reversible, Isentropic. (b) Joule Expansion, (c) Joule-Thompson Expansion.

Consider the following cycle using 1 mol of an ideal gas, initially at 25 °C and 1 atm pressure. Step 1. Isothermal expansion against zero pressure to double the volume (Joule expansion). 

A closed insulated vessel having rigid walls is divided into two compartments by a membrane. One compartment is loaded with a fluid at state 1 the other compartment is evacuated. The membrane ruptures, allowing the fluid to fill the vessel. Show that the final state of the fluid (2) must have U2 = but 2 > Si, regardless of the nature of the fluid. (This process is called a Joule expansion.)... 

Reactions between gases in static systems require only simple reaction vessels in conventional calorimeters. The gases can be introduced into the vessel by simple Joule expansion, when account has to be taken of the energy of the expansion process, or they may be contained in a two-compartment glass reaction vessel and separated by a break-seal, a technique employed by Gunn for the chlorination of B2CI4 using a heat-flow calorimeter suitable for the study of processes of an hour s duration. ... 

The effect is named after the British physicists James Prescott Joule and William Thomson, the U Baron Kelvin who discovered it in 1852 following earlier work by Joule on Joule expansion, where gas undergoes free expansion in a vacuum. 

Dehydration may also be accompHshed by expansion refrigeration which utilizes the Joule-Thompson effect. This technique is normally used when the prime objective is hydrocarbon recovery. 

Expansion from high to low pressures at room temperature cools most gases. Hydrogen is an exception in that it heats upon expansion at room temperature. Only below the inversion temperature, which is a function of pressure, does hydrogen cool upon expansion. Values of the Joule-Thorns on expansion coefficients for hydrogen have been tabulated up to 253 MPa (36,700 psi) (48), and the Joule-Thorns on inversion curve for i7n -hydrogen has been determined (49,50). 

To reduce the work of compression in this cycle a two-stage or dualpressure process may be usedwhereby the pressure is reduced by two successive isenthalpic expansions. Since the isothermal work of compression is approximately proportional to the logarithm of the pressure ratio, and the Joule-Tnomson cooling is roughly proportional to... 

Expanders The primary function of cryogenic expansion equipment is the reduction of the temperature of the gas being expanded to provide needed refrigeration. The expansion of a fluid to produce refrigeration may be carried out in two distinct ways (1) in an expander where mechanical work is produced, and (2) in a Joule-Thomson valve where no work is produced. 

Hydroearbon dew point eontrol is aehieved by eooling the gas. There are three eooling alternatives free expansion or Joule-Thomson expansion, external refrigeration, and using a turboexpander. Joule-Thomson expansion does not always produee the needed refrigeration over the life of the plant and, henee, is not eonsidered as a viable... 

Option 1 Initial Installation—Joule-Thomson Expansion... 

Physical characteristics Molecular weight Vapour density Specific gravity Melting point Boiling point Solubility/miscibility with water Viscosity Particle size size distribution Eoaming/emulsification characteristics Critical temperature/pressure Expansion coefficient Surface tension Joule-Thompson effect Caking properties... 

We next consider the application of the exergy flux equation to a closed cycle plant based on the Joule-Brayton (JB) cycle (see Fig. 1.4), but with irreversible compression and expansion processes—an irreversible Joule-Brayton (IJB) cycle. The T,.s diagram is as shown in Fig. 2.6. 

Figure 9-3 shows a typical cryogenic plant where the gas is cooled to -100°F to -150°F by expansion through a turbine or Joule-Thompson (J-T) valve. In this example liquids are separated from the iniei gas at 100 F and 1,000 psig. It is then dehydrated to less than I ppm water vapor to assure that hydrates will not form at the low temperatures encountered in the plant. Typically, a mole sieve dehydrator is used. 

A Mollier Diagram is useful for the expansion of a specific gas/vapor or multicomponent vapor fluid. See Figure 12-91 for comparison of (1) constant enthalpy (Joule-Thompson effect), isenthalpic, and (2) isentropic (constant entropy), which provides the colder temperature. Note that the expander indicated on the figure is somewhere between isenthalpic and isentropic or polytropic. See Figure 12-92. ... 

The Joule-Kelvin effect may also be calculated from van der Waals equation. For an expansion from i to r2 at constant temperature, let the change of intrinsic energy be 112 — iii = Amt. 

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