3b-scientific Critical Point Apparatus User Manual

3B SCIENTIFIC® PHYSICS 1 Critical Point Apparatus 1002670 Instruction sheet 02/13 MH/JS 5171819221220 218762391112131516 143 4 1 Vernier

10 10. Degassing the hydraulic fluid Owing to the inevitable diffusion of the test gas through the conical seal, the pressure in the measur-ing cell

11 • In order to connect the vacuum pump, take a vacuum hose with 6 mm internal diameter and connect it via a stopcock or preferably via a three-way

12 11.2 Examine threaded bush. The threaded bush in the frame is subject to slow but constant wear, and therefore the axial play must be checked once

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2 2. Safety instructions When used properly, the operation of the critical point apparatus is not dangerous, since both the experimenter and the equi

3 5. Technical data Sulphur hexafluoride: Critical temperature: 318.6 K (45.5°C) Critical pressure: 3.76 MPa (37.6 bar) Critical volume: 197.4 cm3

4 the corresponding pressures p0 and p1 of the trapped air, we get: 1100spsp ⋅=⋅ (2) Substituting sss Δ+=10and rearranging gives: sppps Δ⋅−=0101 (3)

5 ϑ⋅−⋅++=ϑCpCssspe 0 (9) By substituting in equation 4, we get: ()000=⋅−ϑ+ϑ⋅ϑ⋅β−⋅β++⋅ϑRnApssppe (10) If we take several readings at various temperatur

6 the pipe (more precisely, on the ratio of the pipe length to the volume of the measuring cell). In the process, care should be taken that the quanti

7 • Open the flush valve slightly till the pressure has dropped to almost 0 bar. • Shut the flush valve. Filling with test gas: • After at least fo

8 the water bath and the measuring cell must attain the desired temperature first. 8.5 Determining the mass of gas: Blow the gas out of the measurin

9 0012345246 81012V / ml g-1p / MPa Fig. 5: p-V diagram of SF6, measured with the critical point apparatus: Readings taken at 10°C (), 20°C ( ), 30