FATIGUE RESISTANT THERMOWELL AND METHODS
TECHNICAL FIELD
[0001] The embodiments of the subject matter disclosed herein generally relate to
thermocouples and thermowells, and more particularly to fatigue resistant thermocouple
thermowell combinations.
BACKGROUND
[0002] Thermocouples are devices which are used for measuring temperatures based
upon an electrical measurement. Thermocouples have a wide use in a variety of industries
and environments today. Due to the various industries and environments in which
thermocouples are used, various forms of thermocouples can be found. A generic
thermocouple is now described with respect to Figure 1.
[0003] Figure 1 shows a thermocouple 100 which includes electrical junctions 102 and
104, a housing 106 and a probe (also known as a stinger) 108. A tip 110 of the probe 108 is
typically placed near a point at which a temperature value is to be measured. A measuring
device (not shown) is usually connected to the electrical junctions 102 and 104 for reading a
voltage. From this voltage measurement, the temperature value at the tip 110 of the probe
108 is ascertained. Depending upon the use environment of the thermocouple 100, it is
sometimes desirable to provide the thermocouple 100 with protection from the environment
in which the temperature is to be measured. The protective piece used can be a thermowell.
[0004] A generic thermowell 200 is now described with respect to Figure 2. Thermowell
200 can be mounted to or inserted into a housing 208 of a device to protect thermocouple 100
while still allowing the thermocouple 100 access to the desired location for obtaining an
accurate temperature measurement. Thermowell 200 can include a cap piece 202 which
mates with and seals off (if needed) the housing 208. The thermowell 200 also includes a
body 204 and a cavity 206 in which the probe section 108 of the thermocouple 100 can be
inserted.
[0005] Thermocouples 100 and thermowells 200 are generally off the shelf components,
often for use with one another, used in various temperature obtaining applications. However,
in some cases, these off the shelf components are not able to withstand environmental
conditions for which obtaining the temperature is desired. For example, the probe 108 can
experience mechanical failure at its base if it undergoes enough motion caused by, for
example, vibration of the housing 208. In other words, a mechanical connection between the
thermocouple 100 and the thermowell 200 makes a portion of the thermocouple 100 to
vibrate at a same frequency as the housing 208 while another portion, e.g., 110, of the
thermocouple 100, which is free to move, exerts continuous stress on the fixed portion, thus
resulting in fractures of the thermocouple 100.
[0006] Accordingly, systems and methods for using thermocouples with thermowells
under various operating conditions are desirable.
SUMMARY
[0007] According to an exemplary embodiment there is a thermocouple system which
includes: a thermowell configured to enter a structure through which a medium flows; an
elongated probe provided partially inside the thermowell and configured to measure a
temperature; at least one o-ring disposed around the elongated probe at a first end, the o-ring
being configured to dampen a vibration for the elongated probe by contacting the
thermowell; and an elastomer disposed around the elongated probe section at a second end,
the elastomer being configured to dampen the vibration for the elongated probe by contacting
the thermowell.
[0008] According to another exemplary embodiment there is a compressor which
includes: a thermowell configured to enter a wall of the compressor along which a medium
flows; an elongated probe provided and configured to measure a temperature; at least one oring
disposed around the elongated probe at a first end, the o-ring being configured to
dampen a vibration for the elongated probe by contacting the thermowell; and an elastomer
disposed around the elongated probe section at a second end, the elastomer being configured
to dampen the vibration for the elongated probe by contacting the thermowell; an intake
section being configured to receive the medium; a shaft and rotor assembly configured to
rotate and initiate compression of the medium received from the intake section; and an outlet
section being configured to discharge the medium.
[0009] According to still another exemplary embodiment there is a method for
dampening vibrations of a thermocouple system. The method includes: providing an
elastomer in a housing piece, where the elastomer surrounds a first end of an elongated probe
section of the thermocouple system, and where the elongated probe section is configured to
measure a temperature; disposing at least one o-ring around a second end of the elongated
probe section of the thermocouple system; disposing a dampening fluid within a housing of a
thermowell in which the elongated probe section is provided; and inserting the elongated
probe section of the thermocouple into the thermowell. The elastomer, the at least one o-ring
and the dampening fluid reduce vibrations of the thermocouple.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The accompanying drawings illustrate exemplary embodiments, wherein:
[0011] Figure 1 depicts a traditional thermocouple;
[0012] Figure 2 illustrates a traditional thermowell;
[0013] Figure 3 shows an oil free screw compressor according to exemplary
embodiments;
[0014] Figure 4 illustrates a thermocouple system according to exemplary embodiments;
[0015] Figure 5 shows another thermocouple system according to exemplary
embodiments;
[0016] Figures 6-8 shows thermowells according to exemplary embodiments; and
[0017] Figure 9 is a flowchart for a method for dampening vibrations according to
exemplary embodiments.
DETAILED DESCRIPTION
[0018] The following detailed description of the exemplary embodiments refers to the
accompanying drawings. The same reference numbers in different drawings identify the
same or similar elements. Additionally, the drawings are not necessarily drawn to scale.
Also, the following detailed description does not limit the invention. Instead, the scope of
the invention is defined by the appended claims.
[0019] Reference throughout the specification to "one embodiment" or "an embodiment"
means that a particular feature, structure, or characteristic described in connection with an
embodiment is included in at least one embodiment of the subject matter disclosed. Thus,
the appearance of the phrases "in one embodiment" or "in an embodiment" in various places
throughout the specification is not necessarily referring to the same embodiment. Further,
the particular features, structures or characteristics may be combined in any suitable manner
in one or more embodiments.
[0020] As described in the Background section, thermocouples can be used with
thermowells to obtain temperature measurements in various environments in which a
thermocouple is not used by itself. However, in some environments, these off the shelf
components fail, e.g., mechanical fracture of the thermocouple probe. Therefore, according
to exemplary embodiments, systems and methods for preventing failure of the thermocouple
system, i.e., a thermocouple used with a thermowell, in difficult environments are desirable
and obtainable as discussed next. One example of a difficult environment in which a
thermocouple thermowell combination has been known to fail, is an environment which has a
high dynamic pressure, e.g., 300 +/- 50 psi (20.68 +/- 3.45 bar). Alternatively, other high
dynamic pressure ranges, e.g., +/- 500 psi (+/- 34.5 bar), can be used. The pressure range can
depend upon operating conditions. This high dynamic pressure can cause vibrations and
have a structural resonance which may be at a frequency that allows additional vibration for a
thermocouple system which in turn causes mechanical failure of the thermocouple.
[0021] According to exemplary embodiments, an oil free screw compressor 300, as
shown in Figure 3, can exhibit a high dynamic pressure. The oil free screw compressor 300
includes an air gas intake section 302 for channeling air (or other medium) to a compression
chamber 304 and a motor driver 306 attached to a shaft 308. The compression chamber 304
also includes screws 314, one of which is attached to the shaft 308 for initiating compression.
Additionally, a pressurized air gas exhaust section 310 allows exit of pressurized air gas from
the compression chamber and a thermocouple system 312 for measuring a temperature.
Arrows 316 show the direction of air gas travel. Reference sign "X" 318 represents a spot
where mechanical failure occurs if a traditional thermocouple in a thermowell were used in
this type system with a high dynamic pressure, i.e., the thermocouple 100 tended to
mechanically fail at the junction with the cap piece 106 to the probe section 108 which
approximately corresponds to the piercing of the thermowell 200 into the pressurized gas
exhaust section 310 (using a traditional thermocouple 100 and a traditional thermowell 200).
Additionally, thermocouples 100 and thermowells 200 can fail at any connection point as
well as the thermocouple probe section 108.
[0022] According to exemplary embodiments, thermocouple systems 312 which survive
in high dynamic pressure environments are described below with respect to Figures 4 and 5.
Also, while an oil free screw compressor 300 is shown in Figure 3, other compressors (and
other devices) which have a high dynamic pressure, e.g., positive displacement compressors
and reciprocating compressors, can be used in these exemplary embodiments. Additionally,
other components can be included in the oil free screw compressor 300 but are not shown
here for simplification.
[0023] According to an exemplary embodiment, the thermocouple system 312 as shown
in Figure 4 can be used in high dynamic pressure environments. The thermocouple system
312 includes a thermocouple 402 and a thermowell 404. The thermocouple 402 includes an
elongated probe section 406 and electrical junctions 408 and 410. The thermowell 404 is
mounted to the pressurized air exhaust 310 and includes a solid shell (or housing) 412 which
has an inner wall 414, a cavity 416, a cap section 426 and a stem section 428. An o-ring 418
may be disposed on the elongated probe section 406 such that the o-ring has contact with the
inner wall 414, however the contact is loose enough such that fluid, if placed in the cavity
416, may pass, i.e., the o-ring 418 does not provide a fluid seal between the elongated probe
section 406 and the inner wall 414. The o-ring 418 is located generally near a tip 420 of the
elongated probe 406 but may be placed in other locations in alternative exemplary
embodiments. An elastomer 422 may be displaced around the elongated probe section 406
and contacts the cap section 426. Additionally, a dampening fluid 424 may be disposed in
the cavity 416. The stem section 428 may have a length between 10.16 cm and 53.35 cm and
an inner diameter between 0.635 cm and 1.27 cm, however other sizes may be used
depending upon the thermocouple 402 and the environment as desired.
[0024] As described above, operation of the compressors 300 can cause vibration. This
vibration allows for motion in a thermocouple/thermowell which can lead to mechanical
failure, e.g., a snapping of the probe section or thermowell. The vibration may be caused by
the high dynamic pressure/acoustical resonance within the system or by a structural
resonance which, when in a frequency range of the thermocouple system 312, increases the
vibration of the thermocouple 402 or thermowell assembly 404. The exemplary
thermocouple system 312 shown in Figure 4 is less likely to fail in the high dynamic pressure
environments of the compressor 300. This exemplary thermocouple system 312 includes the
use of the o-ring 418 and the elastomer 422 which reduce vibration by being in contact with
the elongated probe section 406 and other structural elements. The elastomer 422 is
displaced tightly enough around the elongated probe section to dampen vibration, but not so
tightly as to directly transmit the structural resonance of the compressor 300 to the elongated
probe section 406. In other words, the elastomer 422 may alter or provide dampening to a
frequency transmitted from the compressor to the thermocouple 402.
[0025] The addition of the o-ring 418 and the elastomer 422 to the probe section 406
additionally changes the frequency of the thermocouple 402 such that the frequency of the
thermocouple 402 is outside the range of frequencies generated by the compressor 300 which
would induce additional vibrational motion. The addition of the o-ring 418 and the elastomer
422 can also provide damping such that if the probe section 406 was still at a resonant
frequency the excitation of the frequency would be reduced. Additionally, the dampening
fluid 424 may be added to further reduce vibrations. For example, the dampening fluid 424
may fill up to one half of the volume of the cavity of the stem section 428 of the thermowell
404. This dampening fluid 424 may be an oil with a high thermoconductivity and a flash
point greater than the expected operating temperatures, e.g., having a flash point greater than
176.7° C. However, other quantities and types of dampening fluid 424 may be used.
[0026] According to another exemplary embodiment, another thermocouple system 500
is shown in Figure 5 and can be used in high dynamic pressure environments. The
thermocouple system 500 includes a thermocouple 502 and a thermowell 504. The
thermocouple 502 includes an elongated probe section 506, electrical junctions 508 and 510,
a cap section 512 and a dampening section 514. The cap section 512 is used for attaching the
thermocouple 502, e.g., via threads, to the thermowell 504. While this attaches the
thermocouple 502 to the thermowell 504 in an exemplary embodiment the probe section 506
is not in direct contact with the thermowell 504. The dampening section 514 includes an
elastomer 524 which is disposed around the elongated probe section 506 and contacts both
the elongated probe section 506 and the dampening section 514. The thermowell 504 is
mounted to a structure where a temperature of a media is to be measured, e.g., the
pressurized exhaust section 310 of the compressor 300, and includes a solid shell (or
housing) 516 which has an inner wall 518, a cavity 520 and a mounting section 522. O-rings
526, 528, 530 and 532 are disposed on the elongated probe section 506 such that the o-rings
526, 528, 530 and 532 may have contact with the inner wall 518 especially if the elongated
probe section 506 experiences slight movement. However, if contact exists, the contact is
loose enough such that fluid, if placed in the cavity 520 may pass, i.e., the o-rings 526, 528,
530 and 532 do not provide a fluid seal between the elongated probe section 506 and the
inner wall 518. The o-rings 526, 528, 530 and 532 are spaced along the elongated probe
section to prevent excess motion of the elongated probe section 506 that would result in
mechanical failure of the elongated probe section 506. While four o-rings 526, 528, 530 and
532 are shown in Figure 5, more or fewer may be used. This exemplary thermocouple
system 500 reduces vibrations and alters the frequency of the thermocouple 502 in a manner
similar to that as described above for the thermocouple system 312 as shown in Figure 4.
[0027] According to exemplary embodiments, various types of thermowells can be used
in the exemplary thermocouple systems described above as shown in Figures 6-8. According
to one exemplary embodiment, as shown in Figure 6, a flanged thermowell 602 can be used.
The flanged thermowell 602 includes a flanged section 604 for mating with and sealing off a
surface associated with, e.g., the pressurized air exhaust section 310, through which a
housing section 606 passes. According to another exemplary embodiment, a threaded
thermowell 702 includes a cap section 708 and a threaded section 704 for mating with and
sealing off a surface associated with, e.g., the pressurized air exhaust section 310, through
which a housing section 706 passes. According to yet another exemplary embodiment, a
weld-in thermowell 802 includes a cap section 804 and a housing 806. The weld-in
thermowell 802 is welded to the location where a temperature is to be measured, and attached
via welding which also seals the pierced surface.
[0028] Utilizing the above-described exemplary systems according to exemplary
embodiments, a method for dampening vibrations is shown in the flowchart of Figure 9. A
method for dampening vibrations in a thermocouple system includes: at step 902 providing
an elastomer in a housing piece, wherein the elastomer surrounds a first end of an elongated
probe section of the thermocouple system, and wherein the elongated probe section is
configured to measure a temperature; at step 904 disposing at least one o-ring around a
second end of the elongated probe section of the thermocouple system; at step 906 disposing
a dampening fluid within a housing of a thermowell in which the probe is provided; and at
step 908 inserting the elongated probe section of the thermocouple into the thermowell,
where the elastomer, the at least one o-ring and the dampening fluid reduce vibrations of the
thermocouple.
[0029] The above-described exemplary embodiments are intended to be illustrative in all
respects, rather than restrictive, of the present invention. Thus the present invention is
capable of many variations in detailed implementation that can be derived from the
description contained herein by a person skilled in the art. All such variations and
modifications are considered to be within the scope and spirit of the present invention as
defined by the following claims. No element, act, or instruction used in the description of the
present application should be construed as critical or essential to the invention unless
explicitly described as such. Also, as used herein, the article "a" is intended to include one or
more items.
[0030] This written description uses examples of the subject matter disclosed to enable
any person skilled in the art to practice the same, including making and using any devices or
systems and performing any incorporated methods. The patentable scope of the subject
matter is defined by the claims, and may include other examples that occur to those skilled in
the art. Such other examples are intended to be within the scope of the claims.

WHAT IS CLAIMED IS:
1. A thermocouple system, comprising:
a thermowell configured to enter a structure through which a medium flows;
an elongated probe provided partially inside the thermowell and configured to measure a
temperature;
at least one o-ring disposed around the elongated probe at a first end, the o-ring being
configured to dampen a vibration for the elongated probe by contacting the thermowell; and
an elastomer disposed around the elongated probe section at a second end, the elastomer
being configured to dampen the vibration for the elongated probe by contacting the
thermowell.
2. The thermocouple system of claim 1, wherein the thermowell is selected from a group
comprising flanged thermowells, weld-in thermowells and threaded thermowells.
3. The thermocouple system of claim 1, further comprising:
a second o-ring provided away from the first end.
4. The thermocouple system of claim 1, further comprising:
a dampening fluid disposed in the thermowell and configured to pass the at least one oririg.
5. The thermocouple system of claim 1, the thermowell further comprising:
a housing which includes a stem section which is in contact with the medium, the stem
section having a length in a range of 10. 16 - 53.35 cm, and an inner diameter in a range of
0.635 - 1.27 cm.
6. The thermocouple system of claim 5, wherein an amount of a dampening fluid disposed
inside of the stem section fills approximately one half of a volume within the stem section
after the probe has been inserted into said housing.
7. The thermocouple system of claim 6, wherein the dampening fluid is a thermoconductive
oil with a flash point over 176.7° C.
8. The thermocouple system of claim 1, further comprising:
a cap section configured to connect the elongated probe to the thermowell via the
elastomer so that a vibrational frequency of the thermocouple is different from a resonating
frequency of the structure.
9. A compressor comprising:
a thermowell configured to enter a wall of the compressor along which a medium flows;
an elongated probe provided and configured to measure a temperature;
at least one o-ring disposed around the elongated probe at a first end, the o-ring being
configured to dampen a vibration for the elongated probe by contacting the thermowell; and
an elastomer disposed around the elongated probe section at a second end, the elastomer
being configured to dampen the vibration for the elongated probe by contacting the
thermowell;
an intake section being configured to receive the medium;
a shaft and rotor assembly configured to rotate and initiate compression of the medium
received from the intake section; and
an outlet section being configured to discharge the compressed medium.
10. The compressor of claim 9, wherein the thermowell is selected from a group comprising
flanged thermowells, weld-in thermowells and threaded thermowells.
11. The compressor of claim 9, further comprising:
a second o-ring provided away from the first end.
12. The compressor of claim 9, the thermowell further comprising:
a housing which includes a stem section which is in contact with the medium, the stem
section having a length in a range of 10. 16 - 53.34 cm, and an inner diameter in a range of
0.635 - 1.27 cm.
13. The compressor of claim 12, wherein an amount of a dampening fluid disposed inside of
said stem section fills approximately one half of a volume within said stem section after the
probe has been inserted into said housing, wherein the dampening fluid is configured to pass
the at least one o-ring.
14. The compressor of claim 13, wherein the dampening fluid is a thermoconductive oil with
a flash point over 350° F.
15. The compressor of claim 9, further comprising:
a cap section configured to connect the elongated probe to the thermowell via the
elastomer so that a vibrational frequency of the thermocouple is different from a resonating
frequency of the structure.
16. A method for dampening vibrations of a thermocouple system, the method comprising:
providing an elastomer in a housing piece, wherein the elastomer surrounds a first end of
an elongated probe section of the thermocouple system, and wherein the elongated probe
section is configured to measure a temperature of a medium contacting the thermocouple
system;
disposing at least one o-ring around a second end of the elongated probe section of the
thermocouple system;
disposing a dampening fluid within a housing of a thermowell in which the elongated
probe section is provided; and
inserting the elongated probe section of the thermocouple into the thermowell, wherein
the elastomer, the at least one o-ring and the dampening fluid reduce vibrations of the
thermocouple.
17. The method of claim 16, further comprising:
selecting the thermowell from a group comprising flanged thermowells, weld-in
thermowells and threaded thermowells.
18. The method of claim 16, further comprising:
providing a second o-ring on the elongated probe section away from the first o-ring.
19. The method of claim 16, wherein the housing section includes a stem section which is in
contact with the medium, the stem section having a length in a range of 10.16 - 53.34 cm,
and an inner diameter in a range of 0.635 - 1.27 cm.
20. The method of claim 16, further comprising:
altering a frequency of the thermocouple system such that the frequency of the
thermocouple is a different from a resonating frequency of a structure to which the
thermowell is attached.