The present invention generally relates to systems and methods for heating tubing. The invention particularly relates to heating devices configured to provide heat to small-diameter tubing products.
Various applications use flexible polymeric tubing to convey fluids. In certain applications, such tubing may or must be heated for the purpose of heating a fluid (liquid or gas) being conducted through the tubing. One approach for heating flexible polymeric tubing involves surrounding the tubing with a tape or cable comprising an encased electrical wire that produces heat when an electrical current is conducted through the wire. Another approach involves the use of an electrically resistive wire, for example, formed of NICHROME® (60Ni-24Fe-16Cr-0.1C), that is directly wrapped on the tubing. However, such methods may be impractical or ill-suited if the polymeric tubing has a particularly small diameter and/or the tape or cable interferes with the desired flexibility of the tubing. As nonlimiting examples, equipment used in low volume processes or analysis techniques, including but not limited to microfluidics, mass spectrometry (e.g., electrospray ionization (ESI)), liquid chromatography (LC), continuous flow chemical reactors, and atmospheric sampling equipment, often use small-diameter flexible tubes (for example, PTFE tubes with diameters of about 0.0625 inch (about 1.6 mm) or about 0.03125 inch (about 0.8 mm) that ideally remain flexible while installed.
In view of the above, it can be appreciated that there is an ongoing desire for systems and methods for heating tubing, including but not limited to small-diameter flexible tubing.
The present invention provides devices and methods suitable for heating tubing, and particularly small-diameter flexible tubing.
According to one aspect of the invention, a heating device is provided that includes a tubular body having a passage therethrough, at least an inner layer surrounding the passage, and an outer layer surrounding the inner layer. The inner layer is electrically resistive and the outer layer is electrically insulating, and the passage is sized and configured to receive therethrough a tubing. The heating device further includes electrical contacts located at oppositely-disposed ends of the tubular body. The contacts are configured to functionally couple with a power source to provide an electrical current to the inner layer, such that applying an electrical current to the inner layer increases the temperature of the inner layer.
According to other aspects of the invention, methods are provided for using and fabricating a heating device of a type described above.
Technical effects of devices and methods as described above preferably include the capability of heating and/or regulating the temperature of small-diameter tubing that has been placed within the passage of the device.
Other aspects and advantages of this invention will be further appreciated from the following detailed description.
The present disclosure provides systems, devices, and methods suitable for heating lengths of tubing, and particularly flexible, small-diameter tubing.
The device 10 defines an internal passage 18 in which the tubing 20 of
In use, the device 10 is heated by Joule heating by applying an electrical current to the inner layer 14 to generate heat, which in turn can be used to regulate the temperature of the tubing 20 to an elevated temperature above ambient.
The temperature sensor 40, for example, a thermocouple (e.g., Type-J), resistance temperature detector (RTD), or thermistor, is preferably attached to the fiber sleeve 32 at a suitable location along the length of the fiber sleeve 32 between the two collars 34, preferably approximately midway along the length of the fiber sleeve 32. To electrically isolate the temperature sensor 40 from the fiber sleeve 32, an insulator may be provided between the temperature sensor 40 and sleeve 32. For example,
In
Alternatively, in some cases the heating device 10 may be manufactured as or become an integral component of the tubing 20. For example, the tubing 20 could be inserted and routed through the internal passage 18 of the inner layer 14 in place of a forming wire 46, and thereafter used as a form that prevents the inner layer 14 from collapsing as the sheath 48 is installed onto the inner layer 14 to form the outer layer 16. In these cases, the heating device 10 is formed around the tubing 20 and as such is an integral component of the tubing 20, and therefore cannot be removed or is difficult to remove from the tubing 20 without damaging the device 10 and/or tubing 20. However, a preferred aspect of the invention is to provide a heating device 10 that enables the device 10 or tubing 20 to be readily removed and replaced without damage to either, in which case the heating device 10 is fabricated using the forming wire 46 (or other suitably sized and shaped forming tool) and is not an integral component of the tubing 20.
During use of the heating device 10, an electric current is applied to the contact leads 38 from the power source 22 (
Given a desired temperature and a predetermined constant electrical resistance per length of the inner layer 14, for example, ohms per inch, the compliance or maximum voltage can be determined for a given application. For example, a 0.25 inch (about 6.4 mm) diameter braided carbon fiber sleeve commercially available from Rock West Composites (Part number BR-C-025) has an average resistance of 0.17 ohms per inch. Therefore, to maintain a temperature of about 110° C. in this fiber sleeve, a current of approximately 2.0 amperes is required to flow through the sleeve. If the braided carbon fiber sleeve length is 10 inches (25.4 cm), the total resistance is 1.7 ohms. Using ohms law, the compliance voltage of the power supply is a minimum of about 3.40 volts (1.7 ohms×2.0 amps). The compliance voltage would increase as the braided carbon fiber sleeve length (and resistance) increases. The same calculation may be used if multiple heating devices 10 are connected in series. Since resistance per unit length is a constant, multiple heating devices 10 of various different lengths can be connected in series and operated at a constant current to achieve the same temperature.
Table 1 below discloses temperatures obtained at various constant currents for the 0.25 inch (6.4 mm) diameter braided carbon fiber sleeve noted above, and Table 2 discloses maximum operating parameters for the braided carbon fiber sleeve (corresponding to the inner layer 14 of the device 10) having a heat-shrinkable rubber sheath thereon (corresponding to the outer layer 16 of the device 10).
One nonlimiting application for heating devices of the type disclosed herein includes regulating the temperature of flexible polymeric tubing used in low volume processes or analysis techniques, including but not limited to microfluidics, mass spectrometry (e.g., electrospray ionization (ESI)), liquid chromatography (LC), continuous flow chemical reactors, and atmospheric sampling equipment. In such applications, it may be necessary or desirable to heat a flexible polymeric tubing to maintain compound solubility, increase reaction rates, decrease fluid viscosity, etc., of a fluid flowing through the tubing. One particular example is 0.0625 inch (1.6 mm) and 0.03125 inch (0.8 mm) tubing formed of polyetheretherketone (PEEK) or tetrafluoroethylene (TFE), which are commonly used in liquid chromatography applications. In investigations leading to the present invention, a heating device 10 constructed with the 0.25 inch (6.4 mm) diameter braided carbon fiber sleeve noted above was fabricated to have a passage 18 of sufficient diameter to accommodate a 1.6 mm tubing. During construction, a 12-gauge (2 mm diameter) solid wire was used as the forming wire 46 during the step of shrinking a heat-shrinkable sheath 48 to ensure that an adequate diameter was maintained for the passage 18 within the heating device 10.
While the invention has been described in terms of a specific or particular embodiment and investigations, it should be apparent that alternatives could be adopted by one skilled in the art. For example, the system 12, heating device 10, and their components could differ in appearance and construction from the embodiment described herein and shown in the drawings, functions of certain components of the heating device 10 and system 12 could be performed by components of different construction but capable of a similar (though not necessarily equivalent) function, process parameters such as temperatures and durations could be modified, and appropriate materials could be substituted for those noted. Accordingly, it should be understood that the invention is not necessarily limited to any embodiment described herein or illustrated in the drawings. It should also be understood that the phraseology and terminology employed above are for the purpose of describing the disclosed embodiment and investigations, and do not necessarily serve as limitations to the scope of the invention. Therefore, the scope of the invention is to be limited only by the following claims.
This application claims the benefit of U.S. Provisional Application No. 62/451,128, filed Jan. 27, 2017, the contents of which are incorporated herein by reference.
This invention was made with government support under Contract No. W911NF-16-2-0020 awarded by the Defense Advanced Research Projects Agency (DARPA). The government has certain rights in the invention.
Filing Document | Filing Date | Country | Kind |
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PCT/US2018/014649 | 1/22/2018 | WO |
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WO2018/140344 | 8/2/2018 | WO | A |
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Number | Date | Country | |
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20200196393 A1 | Jun 2020 | US |
Number | Date | Country | |
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62451128 | Jan 2017 | US |