Wake Frequency
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Temperature Measurement Technical Data Sheet
TD-TM/WFPA
Wake Frequency Problems
Graphs The graphs here show the maximum lengths possible for a given process velocity for a variety of popular thermowell designs. All graphs assume the thermowell material to be 316 Stainless Steel, at an operating temperature of 20ºC. For different materials and process temperatures, a correction factor must be applied, as determined from the graph shown overleaf. These graphs are intended for guidance only, and if in doubt, a formal calculation should be completed. Please contact our sales department for further details, and for specific calculations which are not catered for here. Note that the Thermocouple Instruments Ltd software package for solving wake frequency problems, WFCalc, is available for purchase. Please refer to data sheet TM-SW/WFCA.
Example What is the maximum length of a 20 mm diameter parallel profile thermowell, with 6.2 mm bore, in Monel -1 400, given that the fluid velocity is 6 ms and the operating temperature is 300ºC? From the graph, the maximum length of the thermowell is 400 mm. The correction factor, from the graph overleaf is 0.94. The actual maximum length is given by Lma x= 400 ´ 0 . 94 = 376 mm
Thermowell Length (mm)
750 725 700 675 650 625 600 575 550 525 500 475 450 425 400 375 350 325 300 275 250 225 200 175 150 125 100
½” NB sch 40 Pipe 11 mm OD x 7 mm ID
2
4
6
8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 Fluid Velocity (m/s)
Solid Drilled Thermowells - Parallel Profile Thermowell Length (mm)
When fluid flows past a thermowell inserted into a pipe or duct, vorticies form at both sides of the well. These vorticies detach, first from one side, and then from the other. This phenomenon is known as the Von Karmann effect. The frequency of shedding of these vortices is a function of the diameter of the thermowell, the fluid velocity and, to a lesser extent, the Reynolds number. The vortex shedding subjects the thermowell to a periodic transverse force. As the vortex shedding frequency approaches the natural frequency of the thermowell, the thermowell will oscillate, and is liable to snap off. (The natural frequency of the thermowell is a function of its shape and material of manufacture.) The Von Karmann effect must be taken into account when designing thermowells of sufficient strength to withstand service conditions, and generally thermowells are chosen such that the shedding frequency is always less than or equal to 80% of the natural frequency.
Fabricated Thermowells - Parallel Profile
700 675 650 625 600 575 550 525 500 475 450 425 400 375 350 325 300 275 250 225 200 175 150 125
20 mm OD x 6.2 mm ID 16 mm OD x 6.2 mm ID
2
4
6
8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 Fluid Velocity (m/s)
Solid Drilled Thermowells - Tapered Profile Thermowell Length (mm)
Theory
775 750 725 700 675 650 625 600 575 550 525 500 475 450 425 400 375 350 325 300 275 250 225 200 175 150 125 2
26 mm x 20 mm x 6.2 mm 20 mm x 16 mm x 6.2 mm
4
6
8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 Fluid Velocity (m/s)
Technical Data Sheet TD-TM/WFPA
550 525 500 475 450 425 400 375 350 325 300 275 250 225 200 175 150 125 100 75 50
17.5 mm x 13.5 mm x 6.6 mm
2
4
6
DIN 43761 Thermowells- Tapered Profile Thermowell Length (mm)
Thermowell Length (mm)
UOP 6-105-3 Thermowells - Tapered Profile
Wake Frequency Problems
8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
800 775 750 725 700 675 650 625 600 575 550 525 500 475 450 425 400 375 350 325 300 275 250 225 200 175 150 125
30 mm x 16 mm x 9 mm 24 mm x 12.5 mm x 7 mm
2
4
6
8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 Fluid Velocity (m/s)
‘Vanstone’ Type Thermowells - Parallel Profile
BP 2006/2007 Thermowells - Tapered Profile
Thermowell Length (mm)
Thermowell Length (mm)
Fluid Velocity (m/s)
750 725 700 675 650 625 600 575 550 525 500 475 450 425 400 375 350 325 300 275 250 225 200 175 150 125 100
22 mm OD x 9.5 mm ID 18 mm OD x 5 mm ID 12 mm OD x 6.2 mm ID
2
4
6
8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 Fluid Velocity (m/s)
2
4
6
8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
Material and Temperature Correction Factors
25.4 mm x 19 mm x 6.6 mm
Correction Factor
Thermowell Length (mm)
mm xx 25 25mm mmxx13.2 13.2mm 26.5 mm mm mm x 18 mm x 6.2 mm 26.5
Fluid Velocity (m/s)
Esso FSI 776 - Tapered Profile
1.04 1.03
CH
1.02 1.01
RO
MIU
MS
TE
EL
2¼
Cr-
3C
1.00 INC
0.99
ON
0.98 0.97 0.96
TI
HAS
N TA
0.95
r
EL
TEL
625
LOY
C27
IU
6
M
0.94 NE
0.91 0.90
2
4
6
8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 Fluid Velocity (m/s)
Thermocouple Instruments Limited
Pentwyn, Cardiff, CF23 7XJ, UK Tel: (+44) 029 20 734121 Fax: (+44) 029 20 734040 Internet: http://www.thermocouple.co.uk E-mail: [email protected]
-50 0
HA
00
ST
0.92
L4
ST
MO
0.93
6 31
750 725 700 675 650 625 600 575 550 525 500 475 450 425 400 375 350 325 300 275 250 225 200 175 150
800 775 750 725 700 675 650 625 600 575 550 525 500 475 450 425 400 375 350 325 300 275 250 225 200 175 150
ST
EL
LO
Y
B3
50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 9501000
Process Temperature (ºC)
All Rights Reserved. © Copyright 1999 Thermocouple Instruments Ltd.
TD-TM/WFPA
Wake Frequency Problems
Graphs The graphs here show the maximum lengths possible for a given process velocity for a variety of popular thermowell designs. All graphs assume the thermowell material to be 316 Stainless Steel, at an operating temperature of 20ºC. For different materials and process temperatures, a correction factor must be applied, as determined from the graph shown overleaf. These graphs are intended for guidance only, and if in doubt, a formal calculation should be completed. Please contact our sales department for further details, and for specific calculations which are not catered for here. Note that the Thermocouple Instruments Ltd software package for solving wake frequency problems, WFCalc, is available for purchase. Please refer to data sheet TM-SW/WFCA.
Example What is the maximum length of a 20 mm diameter parallel profile thermowell, with 6.2 mm bore, in Monel -1 400, given that the fluid velocity is 6 ms and the operating temperature is 300ºC? From the graph, the maximum length of the thermowell is 400 mm. The correction factor, from the graph overleaf is 0.94. The actual maximum length is given by Lma x= 400 ´ 0 . 94 = 376 mm
Thermowell Length (mm)
750 725 700 675 650 625 600 575 550 525 500 475 450 425 400 375 350 325 300 275 250 225 200 175 150 125 100
½” NB sch 40 Pipe 11 mm OD x 7 mm ID
2
4
6
8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 Fluid Velocity (m/s)
Solid Drilled Thermowells - Parallel Profile Thermowell Length (mm)
When fluid flows past a thermowell inserted into a pipe or duct, vorticies form at both sides of the well. These vorticies detach, first from one side, and then from the other. This phenomenon is known as the Von Karmann effect. The frequency of shedding of these vortices is a function of the diameter of the thermowell, the fluid velocity and, to a lesser extent, the Reynolds number. The vortex shedding subjects the thermowell to a periodic transverse force. As the vortex shedding frequency approaches the natural frequency of the thermowell, the thermowell will oscillate, and is liable to snap off. (The natural frequency of the thermowell is a function of its shape and material of manufacture.) The Von Karmann effect must be taken into account when designing thermowells of sufficient strength to withstand service conditions, and generally thermowells are chosen such that the shedding frequency is always less than or equal to 80% of the natural frequency.
Fabricated Thermowells - Parallel Profile
700 675 650 625 600 575 550 525 500 475 450 425 400 375 350 325 300 275 250 225 200 175 150 125
20 mm OD x 6.2 mm ID 16 mm OD x 6.2 mm ID
2
4
6
8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 Fluid Velocity (m/s)
Solid Drilled Thermowells - Tapered Profile Thermowell Length (mm)
Theory
775 750 725 700 675 650 625 600 575 550 525 500 475 450 425 400 375 350 325 300 275 250 225 200 175 150 125 2
26 mm x 20 mm x 6.2 mm 20 mm x 16 mm x 6.2 mm
4
6
8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 Fluid Velocity (m/s)
Technical Data Sheet TD-TM/WFPA
550 525 500 475 450 425 400 375 350 325 300 275 250 225 200 175 150 125 100 75 50
17.5 mm x 13.5 mm x 6.6 mm
2
4
6
DIN 43761 Thermowells- Tapered Profile Thermowell Length (mm)
Thermowell Length (mm)
UOP 6-105-3 Thermowells - Tapered Profile
Wake Frequency Problems
8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
800 775 750 725 700 675 650 625 600 575 550 525 500 475 450 425 400 375 350 325 300 275 250 225 200 175 150 125
30 mm x 16 mm x 9 mm 24 mm x 12.5 mm x 7 mm
2
4
6
8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 Fluid Velocity (m/s)
‘Vanstone’ Type Thermowells - Parallel Profile
BP 2006/2007 Thermowells - Tapered Profile
Thermowell Length (mm)
Thermowell Length (mm)
Fluid Velocity (m/s)
750 725 700 675 650 625 600 575 550 525 500 475 450 425 400 375 350 325 300 275 250 225 200 175 150 125 100
22 mm OD x 9.5 mm ID 18 mm OD x 5 mm ID 12 mm OD x 6.2 mm ID
2
4
6
8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 Fluid Velocity (m/s)
2
4
6
8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
Material and Temperature Correction Factors
25.4 mm x 19 mm x 6.6 mm
Correction Factor
Thermowell Length (mm)
mm xx 25 25mm mmxx13.2 13.2mm 26.5 mm mm mm x 18 mm x 6.2 mm 26.5
Fluid Velocity (m/s)
Esso FSI 776 - Tapered Profile
1.04 1.03
CH
1.02 1.01
RO
MIU
MS
TE
EL
2¼
Cr-
3C
1.00 INC
0.99
ON
0.98 0.97 0.96
TI
HAS
N TA
0.95
r
EL
TEL
625
LOY
C27
IU
6
M
0.94 NE
0.91 0.90
2
4
6
8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 Fluid Velocity (m/s)
Thermocouple Instruments Limited
Pentwyn, Cardiff, CF23 7XJ, UK Tel: (+44) 029 20 734121 Fax: (+44) 029 20 734040 Internet: http://www.thermocouple.co.uk E-mail: [email protected]
-50 0
HA
00
ST
0.92
L4
ST
MO
0.93
6 31
750 725 700 675 650 625 600 575 550 525 500 475 450 425 400 375 350 325 300 275 250 225 200 175 150
800 775 750 725 700 675 650 625 600 575 550 525 500 475 450 425 400 375 350 325 300 275 250 225 200 175 150
ST
EL
LO
Y
B3
50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 9501000
Process Temperature (ºC)
All Rights Reserved. © Copyright 1999 Thermocouple Instruments Ltd.
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