aspects of flow for current, flow rate is directly … info/electron spectroscopies...pumps pumps...
TRANSCRIPT
![Page 1: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/1.jpg)
Vacuum technology
Aspects of flow
For current, flow rate is directly proportional to potential difference and inversely proportional to resistance.
I = V/R or I = 'V/R
For a fluid flow, Q = (P1-P2)/R or 'P/R
Using reciprocal of resistance, called conductance, we have, Q = C (P1-P2)
![Page 2: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/2.jpg)
There are two kinds of flow, volumetric flow and mass flow
Volume flow rate, S = vAv – the average bulk velocity, A the cross sectional areaS = V/t, V is the volume and t is the time.Mass flow rate is S x density.G = UvA or UV/tMass flow rate is measured in units of throughput, such as torr.L/sThroughput = volume flow rate x pressureThroughput is equivalent to power.Torr.L/s o (g/cm2)cm3/s o g.cm/s o J/s o W
It works out that, 1W = 7.5 torr.L/s
![Page 3: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/3.jpg)
![Page 4: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/4.jpg)
Types of low1. Laminar: Occurs when the ratio of mass flow to viscosity (Reynolds number) is low for a given diameter.This happens when Reynolds number is approximately
below 2000.Q ~ P12-P22
2. Above 3000, flow becomes turbulentQ ~ (P12-P22)0.53. Choked flow occurs when there is a flow restriction
between two pressure regions. Assume an orifice and the pressure difference between the two sections, such as 2:1. Assume that the pressure in the inlet chamber is constant. The flow relation is, Q ~ P1
4. Molecular flow: When pressure reduces, MFP becomes larger than the dimensions of the duct, collisions occur between the walls of the vessel. Q~P1-P2
There are also other flows such as surface diffusion, permeation and diffusion of one gas through another.
![Page 5: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/5.jpg)
![Page 6: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/6.jpg)
Different kinds of flow patters
![Page 7: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/7.jpg)
Number of molecules striking unit area from all sides,n = [3.5 x 1022 P]/(MT)0.5 per cm2 per sTo convert this to volume that strikes per unit area we need to divide by number density.S = n/N = 3640 (T/M)0.5 cm3/s . cm2
For air at RT, this gives, 3640(295/28.7) =11.6 L/s.cm2
![Page 8: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/8.jpg)
Flow through an orificeAssume the flow through an orifice as shown below.Pressure in the top chamber is constant and it is very small or near zero below.The flow through orifice is, A x 11.6 L/s., A is the area in sq. cm.
Molecules come to the orifice from all angles, but the flowcan be represented in termsof a velocity. 11.6 L/cm2.s = 11,600 cm3/cm2.s = 116 m/s
![Page 9: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/9.jpg)
Conductance
C = Q/(P1-P2) = pvA/'pP is the pressure, v is the velocity, A cross sectionalarea and 'p is the pressure difference.
Pumping speed
In the case of an orifice, this can be given as, S = C = Q/P as P2 is much smaller than P1.
For constant pumping speed, S = Vln(P1/P2)/(t1-t2)
V is the volume of the chamber, P1 and p2 are two pressure points and t1 and t2 are times at which these pressure points occurred.
![Page 10: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/10.jpg)
How to measure pumping speed?S = Q/P-Po, P is the pressure when gas is leaked and Po is the ultimate pressure.
![Page 11: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/11.jpg)
Pumps
There is no single pump for UHV technology. Various pumps are used to take the system from atmosphere to UHV
![Page 12: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/12.jpg)
Time for pumping
This is a difficult parameter to calculate or predict in view ofseveral aspects such as out gassing (virtual leak). When one disregards outgassing, -Vdp/dt = SpT = (V/S)ln(Po/Pf)
This is valid only in the high pressure region, above 10 torrand above this rage many factors, such as permeation, outgassing, etc. become important.
![Page 13: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/13.jpg)
Typical vacuum system
![Page 14: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/14.jpg)
Virtual leaks
There are several possibilities of such leaks in every vacuum system.
An example,
![Page 15: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/15.jpg)
Typical vacuum system and process of evacuation
![Page 16: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/16.jpg)
Process of evacuation
Initial pumping Crossover region
![Page 17: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/17.jpg)
Coarse vacuum pumps
Rotary pumpsMechanical diagrams
![Page 18: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/18.jpg)
Double stage pump
![Page 19: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/19.jpg)
Pumping speed
![Page 20: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/20.jpg)
Diffusion (vapour jet) pumps
![Page 21: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/21.jpg)
Vapour streams
![Page 22: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/22.jpg)
Diffstack pump
![Page 23: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/23.jpg)
Variation of pumping speed
![Page 24: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/24.jpg)
UHV Chamber
![Page 25: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/25.jpg)
![Page 26: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/26.jpg)
![Page 27: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/27.jpg)
Back streaming
![Page 28: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/28.jpg)
Turbomolecular Pumps
![Page 29: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/29.jpg)
![Page 30: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/30.jpg)
![Page 31: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/31.jpg)
![Page 32: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/32.jpg)
![Page 33: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/33.jpg)
Why a turbo is better?
![Page 34: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/34.jpg)
Cryo Pumps
![Page 35: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/35.jpg)
Getter Pumps
![Page 36: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/36.jpg)
Ion Pumps
![Page 37: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/37.jpg)
UHV Instrumentation
Flanges
![Page 38: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/38.jpg)
Valves
![Page 39: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/39.jpg)
UHV fittings
Feedthroughs, view ports, gas admittance valves
![Page 40: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/40.jpg)
Pressure measurement, mechanical
![Page 41: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/41.jpg)
Capacitance
![Page 42: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/42.jpg)
![Page 43: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/43.jpg)
![Page 44: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/44.jpg)
![Page 45: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/45.jpg)
![Page 46: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/46.jpg)
![Page 47: Aspects of flow For current, flow rate is directly … Info/Electron Spectroscopies...Pumps pumps are used to take the system from atmosphere to UHV pumping This is a difficult parameter](https://reader034.vdocuments.us/reader034/viewer/2022042216/5ebe10260dcf553321002c7a/html5/thumbnails/47.jpg)
A chamber contains all these, in addition to your experiment!