JP5305437B2 - Orifice temperature control heater - Google Patents

Description

  The present invention relates to an orifice type temperature adjusting heater for adjusting a fluid to a predetermined temperature.

  Conventionally, a heat exchanger type heater such as a shell and tube has been used as a heater for heating a fluid (gas or liquid) (for example, Patent Document 1). In this type of heater, as shown in FIG. 1, a bundle of a large number of tube-type sheath heaters 1 is housed in a cylindrical body (hereinafter also referred to as a shell) 2, and a baffle plate 3 is illustrated in the shell 2. As shown in FIG. In this type of heater, as shown in the figure, the fluid flows in a direction substantially perpendicular to the sheath heater 1.

  In the shell and tube type heater as described above, the sheath heater 1 is adopted as the heater element, so that not only the fluid in the shell 2 can be directly heated but also a relatively large heat transfer area can be obtained. Due to its characteristics, it has been widely used as a large capacity heater. In addition, because of the simple structure of the sheath heater 1 and the shell 2, it is also an advantage that it can be manufactured relatively easily instead of the heat transfer area.

  However, in the shell and tube type heater as described above, the flow between the baffle plates 3 is not uniform, and there is a stagnation region as a flow, and therefore, heat transfer is locally deteriorated. For this reason, it is necessary to perform a design that fully considers that point at the time of designing. Further, since the volume of the shell 2 becomes large, it is necessary to take a large installation space and maintenance space, and the cost of material costs such as a shell and a large-diameter flange increases due to the increase in size. was there.

  On the other hand, in the High-Strength Proton Accelerator Research Facility (J-PARC), which is a state-of-the-art scientific research facility using a proton accelerator constructed in cooperation with the Japan Atomic Energy Agency (JAEA) and the High Energy Accelerator Research Organization (KEK) In order to realize a wide variety of neutron utilization experiments, technological development related to cryogenic hydrogen circulation system to cool fast neutrons generated in spallation reaction to cold neutrons by cryogenic hydrogen under supercritical pressure has been promoted .

  In the cryogenic hydrogen circulation system, pressure control with respect to fluctuations in pulse heat load in the kW order at the time of proton beam incidence and stop was an important technical issue. This is because the 1.5 MPa, 20 K supercritical pressure hydrogen supplied and circulated in the cryogenic hydrogen circulation system has an incompressible property, so even a slight temperature rise in the hydrogen loop is very large. This is because it causes a pressure increase.

  Therefore, in the cryogenic hydrogen circulation system as described above, hydrogen is heated by a heater to compensate for a change in the thermal load due to the proton beam, and the volume of the hydrogen circulation system is varied by an accumulator according to pressure fluctuations. Pressure control has been performed.

  The accumulator has a bellows structure with a variable volume in a hydrogen circulation loop, and the inside of the bellows is filled with helium gas having compressibility even at a cryogenic hydrogen temperature. That is, the accumulator has a structure in which a compressible region partitioned by a bellows is provided in supercritical pressure hydrogen that is in a single phase state. Even when a large pressure fluctuation is given to the hydrogen circulation system, the pressure fluctuation in the hydrogen circulation system can be reduced by the expansion and contraction of the bellows.

Also, in this system, when the proton beam is stopped, in order to realize control in the low temperature hydrogen region that compensates for a large thermal load fluctuation of 4 kW, which corresponds to the proton beam thermal load, in the low-temperature hydrogen region, the response is large and uniform. Development of a heater capable of capacity heating was indispensable. Furthermore, since this system is a low temperature system, the heater had to be installed in a vacuum insulated container. Therefore, downsizing as much as possible was an important issue in heater development.
Japanese Patent Application Laid-Open No. 8-193395

  The present invention has been made in view of the circumstances as described above, and it is an object of the present invention to provide a temperature adjusting heater that can heat a circulating fluid with high response, uniformly large capacity, and can be downsized.

  Another object of the present invention is to provide a temperature adjusting heater suitable for use in a heater for heating circulating hydrogen in the cryogenic hydrogen circulation system as described above.

According to the present invention, in order to solve the above-described problem, first, a cryogenic temperature having a fluid inlet portion on one end side, a fluid outlet portion on the other end side, and containing helium, hydrogen, or nitrogen inside. A cylindrical body through which liquid fluid flows, and a plurality of sheath heaters arranged in parallel in the axial direction of the cylindrical body and directly heating the cryogenic liquid fluid, and a plurality of openings through which the plurality of sheath heaters are inserted are provided. A plurality of baffle plates arranged at a predetermined interval in the axial direction of the cylindrical body, the cryogenic liquid fluid passes through an orifice formed by a clearance formed by an opening of the baffle plate and a sheath heater, and the cryogenic liquid fluid parallel to flow and the sheath heater, set so that the surface heat flux of the sheath heater element is below a predetermined value for heating the cryogenic liquid fluid to a predetermined temperature, to ensure the airtightness orifice It is possible to provide a temperature adjusting heater.

  According to a second aspect of the present invention, there is provided an orifice type temperature adjusting heater according to the first invention, wherein the sheath tube of the sheath heater is fixed to the upper flange by welding.

  According to a third aspect of the present invention, in the first or second aspect of the invention, the bottom end baffle plate is provided with an anti-rest fitting having a plurality of flanges for anti-sheathing of the sheath heater. A heater for temperature control can be provided.

  According to a fourth aspect of the invention, in the first to third inventions, the fluid inlet portion is provided at the lower end, and the fluid outlet portion is provided on the side of the cylindrical body near the upper end. A mold temperature control heater can be provided.

  Further, fifthly, in any one of the first to fourth inventions, there can be provided an orifice type temperature adjusting heater characterized in that the sheath heater electrode portion is provided outside the cylindrical body.

  According to the present invention, by providing an orifice having a clearance formed by the opening of the baffle plate and the sheath heater in the fluid flow region, the flow velocity of the fluid is locally increased and formed on the heater surface. Therefore, the heat transfer can be promoted, and the fluid can be heated uniformly by the stirring effect.

  Further, according to the present invention, since the sheath heater has a very simple structure in which a plurality of baffle plates provided with openings are passed, it can be very downsized compared to a conventional shell and tube heater. In addition, large-capacity heating can be performed and manufacturing costs can be reduced.

  In addition, the orifice type temperature control heater of the present invention can be installed without being limited by space due to its miniaturization, and is suitable for, for example, a heater installed in an adiabatic vacuum container of a cryogenic helium refrigerator.

  In the present invention, since the sheath heater is employed as the heater element, the fluid can be directly heated and the fluid can be uniformly heated by the orifice effect. Therefore, the temperature response is good and the temperature can be adjusted to an arbitrary temperature.

  Furthermore, since the orifice type temperature control heater of the present invention can maintain an airtight structure and can be used under high pressure conditions ranging from a high temperature to a very low temperature region, it can be used as a target device of the high pressure gas safety law. Is possible.

  Hereinafter, embodiments of an orifice type temperature adjusting heater according to the present invention will be described in detail.

  FIG. 2 is a perspective view showing an internal structure of an orifice type temperature adjusting heater (hereinafter also referred to as a temperature adjusting heater or heater) according to the present embodiment, and shows a state where the heater container is cut in half. FIG. 3 is a cross-sectional view of a baffle portion of the temperature adjusting heater. Here, a case where the temperature adjustment heater is applied to the heat compensation heater in the cryogenic hydrogen circulation system will be described as an example.

  In the temperature adjusting heater of this embodiment, a plurality of (20 in this example) sheath heaters 12 are arranged in parallel in the axial direction of the shell 11 in a long cylindrical body (shell) 11. The lower end of the shell 11 is closed by a bottom wall 14 except for the fluid inlet portion 13, an upper flange 15 is provided at the upper end, and a fluid outlet portion 16 is provided on the side wall of the shell 11 slightly below the upper flange 15. Is provided. A plurality of disk-shaped baffle plates 18 having a plurality of circular openings 17 are arranged at a required interval in the axial direction of the shell 11, and a plurality of sheath heaters 12 are inserted through the plurality of openings 17 of the baffle plate 18. ing. As shown in FIG. 3, the opening 17 of the baffle plate 18 and the sheath heater 12 form a clearance. This clearance is referred to as an orifice (throttle mechanism) 19 in this specification. The shell 11, the sheath tube of the sheath heater 12, the bottom wall 14, and the upper flange 15 are made of the same material stainless steel.

  The sheath tube of the sheath heater 12 and the upper flange 15 are fixed by welding, and the terminal box 20 having an electrode portion at the upper end of the sheath heater 12 is disposed above the upper flange 15 so as not to contact the fluid portion. . Further, as shown in FIG. 4, the lowermost baffle portion has three points as shown in FIG. 4 to secure the clearance between the opening 17 provided in the baffle plate 18 and the sheath heater 12 with a predetermined width and to prevent the sheath heater from swinging. A contact type saddle brace 21 is provided. Further, another opening is provided in the baffle plate 18, and a baffle support rod 22 is fitted into this opening, and is fastened and fixed with a nut at the lowermost baffle portion. The baffle support rod 22 is fitted with a circular pipe (pipe having a larger inner diameter than the support rod) having the same length as the baffle interval so that the baffle interval can be adjusted arbitrarily. Furthermore, the temperature adjusting heater of the present embodiment is airtight.

  The sheath heater 12 employed in the present embodiment is one in which a nichrome wire is arranged as a heater wire in a sheath tube, and in the same manner as the sheath heater used in the above-described conventional shell and tube heater, Since it can be heated directly, it has excellent responsiveness. A uniform flow distribution is formed in the shell 11 by flowing the fluid in parallel to the sheath heaters 12 arranged in the shell 11. Further, in the region from the fluid outlet portion 16 to the upper flange portion 15, the heater element of the sheath heater 12 is a non-heated portion so that the thermal fluid can be prevented from staying in this region.

  In the temperature adjusting heater having the above-described configuration, the supercritical pressure hydrogen that is the target fluid flows from the fluid inlet portion 13 below the shell 11 and flows in parallel to the sheath heater 12, and the side surface of the shell 11 near the upper flange 15. Out of the fluid outlet portion 16. In the shell 11, when the supercritical pressure hydrogen passes through the baffle portion, the temperature boundary layer that is locally throttled by the orifice 19, the flow velocity is increased, and has been formed on the heater surface until then is developed. Since it is initialized once by 19, heat transfer is improved and large capacity heating is possible. Therefore, the surface heat flux (heat amount per unit area) of the sheath heater can be designed to be large, the number of heater elements can be reduced, and the size can be reduced. Further, since the temperature distribution in the radial direction of the shell 11 can be reduced by the stirring effect by the orifice 19, the fluid can be heated uniformly.

  Next, a specific design example of the orifice type temperature control heater will be described. This design example is designed based on a simulation described later.

  In the cryogenic hydrogen circulation system to which the orifice type temperature control heater of this embodiment is applied, as described above, 1.5 MPa, 20 K supercritical pressure hydrogen is forcibly circulated to form a closed cycle. ing. Since a large pressure fluctuation is given as the proton beam enters and stops, volume control by an accumulator and heat compensation by a hydrogen heater (this temperature adjusting heater) are performed.

As shown in FIG. 5, as the temperature dependence of the density of supercritical pressure hydrogen of 1.5 MPa, the decreasing tendency of the density increases at 28 K or more, and the change near the pseudocritical temperature (33 K) is very large. When supercritical pressure hydrogen is heated by a heater, if the temperature near the heater surface is near the pseudocritical temperature, such a rapid change in density may cause flow instability. Therefore, the maximum surface temperature was set to 28K or less as a heater design condition. Therefore, as an initial stage of design, using the Dittus-Boelter equation, which is a correlation equation of forced convection heat transfer generally used in non-boiling regions, supercritical pressure hydrogen (R 160 g / s) Forced convection heat transfer in 1.5 MPa, 20K) was evaluated. The result is shown in FIG. A region indicated by diagonal lines in FIG. 6 is the surface heat flux of the heater element for satisfying the design condition of the surface temperature of 28K or less. Therefore, the heater for the hydrogen circulation system was set so that the surface heat flux of the heater element was 5 × 10 ³ W / m ² or less when the heat input was 5 kW. Also, the pressure loss in the cryogenic hydrogen circulation system and the characteristics of the circulation pump are taken into consideration, and the allowable pressure loss generated in the heater vessel is set to 1 kPa or less.

  The shell 11 uses a stainless steel circular tube having an inner diameter of 133 mm (outer diameter of 139.8 mm) and a total length of 1600 mm. The inlet and outlet piping of the fluid inlet 13 and the fluid outlet 16 to the heater are the same size as the main piping of the circulation loop. It was set to 32A (inner diameter 38.7 mm).

The sheath tube 12 is made of stainless steel with an outer diameter of 12 mm and a length of 1340 mm so that the heater element surface heat flux is 5 × 10 ³ W / m ² or less. As shown in FIG.

  The sheath heater electrode portion is structured not to be in direct contact with the fluid portion. This is because an explosion-proof measure against hydrogen which is a flammable fluid and maintenance of an airtight structure conforming to the High Pressure Gas Safety Law are necessary for use under a high pressure condition of 1.5 MPa.

  A stainless steel baffle plate 18 having a diameter of 130 mm and having 20 openings 17 having a diameter of 16 mm larger than the diameter of the heater having a diameter of 12 mm was arranged at intervals of 100 mm in the length direction of the sheath heater.

  The sheath heater 12 having a heater diameter of φ12 mm was inserted into the φ17 mm opening 17 of the baffle plate 18 to form an orifice 19 having a clearance of 2 mm in width.

  The heater element portion and the shell 11 have a flange structure in consideration of maintainability. However, in order to ensure hermeticity in a low temperature region, an aluminum metal O-ring seal was adopted as a sealing material.

  In order to support the baffle plate 18, a stainless steel baffle support rod 22 (φ8 mm / M6) in which three screws were cut from the upper flange 15 was installed. By inserting a circular pipe (6A pipe having a larger inner diameter than the baffle support rod 22) having the same length as the baffle interval into the baffle support rod 22, the baffle interval can be arbitrarily adjusted, and a nut is provided at the lowermost baffle portion. Tightened and fixed with. Further, in order to ensure the clearance between the opening 17 provided in the baffle plate 18 and the sheath heater 11, a stainless steel touch-resisting bracket 21 having a three-point contact type hook is provided at the lowermost baffle portion.

  Since the heater for temperature adjustment of this embodiment is applied to a low temperature system, it is installed in an adiabatic vacuum vessel. Therefore, as a countermeasure against discharge of the terminal box 20, the terminal box 20 was filled with resin.

  In order to avoid contact between the sheath heater 12 and the baffle plate 18 and contact between the shell 11 and the baffle plate 18 and excessive clearance in consideration of heat shrinkage of the material, all the members are the same as described above. Made of material.

  Here, an example of the design procedure of the temperature adjusting heater will be described. Here, the case where the fluid is a general liquid and gas is taken as an example.

(1) Determine the fluid, pressure (P), and temperature (T _in ).

(2) If it is liquid, determine the saturation temperature (T _sat ) at the operating pressure.

(3) In the case of liquid, the subcool degree ΔT _L (= T _in −T _sat ) or the difference between the heater heating upper limit temperature T _H and the operating temperature (T _H −T _in ) is the smallest surface of the heater. The temperature rise. In the case of gas, it becomes only the latter.

(4) Determine the amount of heat input required. Q (W)
(5) Determine the surface area of the heater. S (m ² )
(6) Heater surface heat flux q (W / m ² ) is calculated from Q / S.

  (7) The flow velocity is obtained from the circulation flow rate (if known) and the cross-sectional area of the heater shell (cylindrical cylinder), and Re (Reynolds number) is evaluated. The physical property values may be those under the operating temperature and pressure conditions.

(8) Temperature rise using the formula is a general forced convection heat transfer indication type _{Dittus-Boleter:} evaluated (T _w heater surface temperature), so as not temperature above set in the above (3), Increase the flow rate or decrease the heater surface heat flux (that is, increase the heater surface area or decrease the heat input per sheathed heater). However, this is a mean temperature T _w, to approximate the local surface temperature of the heater for the heater length direction as shown in FIG. 7 by using the inlet temperature T _in. Using this extrapolation line, the baffle interval l _buff is determined from the allowable maximum temperature rise (a).
(9) About the opening diameter of the baffle: 1) Determine the opening diameter appropriately. 2) Obtain the flow velocity when passing through the orifice (by the effective orifice cross-sectional area to the shell cross-sectional area ratio).
* Effective orifice cross-sectional area is the area of clearance between the opening diameter and the sheath heater diameter. 3) From Bernoulli's theorem, the pressure drop is evaluated locally at the orifice. This is because cavitation occurs when the pressure at the orifice portion is equal to or lower than the saturation pressure at the operating temperature. As shown in 4) and 3), when the pressure is below the saturation pressure, measures are taken to increase the opening diameter.

  Next, the characteristics of the orifice type temperature control heater of the above design example were evaluated by simulation. For the evaluation, a general-purpose thermal fluid analysis program STAR-CD was used.

  The present inventors have used liquid nitrogen, which is the same low-temperature fluid as hydrogen, in a simple shape (circular tube) and forced convection under a wide range of pressure, temperature, and flow rate conditions from subcooled state to supercritical pressure. A lot of experimental data was obtained by measuring heat transfer. Furthermore, in order to grasp the forced convection heat flow phenomenon of liquid nitrogen, numerical analysis was performed under the same conditions as the acquired experimental data, and the validity of the analysis code was verified. Using the turbulence model and parameters, the temperature distribution in the orifice heater at the design heat load of 5 kW was obtained by numerical analysis, and the optimum shape of the orifice heater for the cryogenic hydrogen circulation system was determined. .

  FIG. 8 shows the inside of the temperature adjustment heater when supercritical pressure hydrogen of 20 K and 1.5 MPa is introduced at a flow rate of 1.87 m / s corresponding to the rated flow rate of 160 g / s from the fluid inlet 13. The flow velocity distribution at is shown.

  When passing through the baffle plate 18, the flow velocity locally increases by the orifice 19 provided in the baffle plate 18 and reaches about 1 m / s. After passing through the orifice 19, the flow rate gradually decreases due to the influence of fluid spreading. At a point 5 mm away from the baffle plate 18, it becomes 0.7 m / s, and at the intermediate portion between the baffle plate 18 and the baffle plate 18, it decreases to 0.2 m / s, which is the shell cross-section average flow velocity. Thus, it was found that almost the same flow velocity distribution was repeatedly formed between the baffle plates 18 as predicted at the time of design.

  FIG. 9 shows the pressure distribution at this time. FIG. 9 shows the amount of increase when the fluid outlet 16 is at a reference pressure of 1.5 MPa. The pressure loss in the heater container of the temperature adjusting heater is about 640 Pa. In addition, the pressure loss that occurs when the flow path contracts from the heater container to the fluid outlet 16 is about 300 Pa, which is half of the pressure loss that occurs in the heater container. It was confirmed that the condition was 1 kPa or less.

  FIG. 10 shows the temperature distribution at the time of 5 kW heat load. Although the temperature boundary layer has developed in the length direction of the sheath heater 12, since the flow path is locally narrowed in the baffle portion, the superheated liquid in the temperature boundary layer and the mainstream fluid outside the temperature boundary layer The temperature boundary layer is temporarily initialized. After passing through the baffle, a temperature boundary layer develops again in the vicinity of the surface of the sheath heater, but the next baffle is stirred again. As a result, as shown in FIG. 11, in the baffle portion, each sheath heater surface temperature falls to the mainstream temperature at that point, and the temperature is highest at the baffle-baffle intermediate portion, but the temperature rise is Compared to the baffle part, it can be suppressed to about 3K. At the time of rating, when 20 K supercritical pressure hydrogen flowed in, the maximum temperature in the temperature adjusting heater was 26.6 K, and it was confirmed that the design conditions were sufficiently satisfied. It was confirmed by analysis that the fluid in the shell 11 can be heated uniformly by the stirring effect between the outside of the temperature boundary layer and the bulk liquid. It was also confirmed that the heat fluid did not stay as designed by making the sheath heater 12 a non-heated part in the space from the fluid outlet 16 to the upper flange 15.

  As mentioned above, although this invention was demonstrated based on one Embodiment, it cannot be overemphasized that it is not limited to the said embodiment, A various deformation | transformation and a change are possible.

  Moreover, this invention is applied to the various uses illustrated below other than said cryogenic hydrogen circulation system.

  The present invention is a large-capacity heater for temperature control of large helium refrigerators and liquefiers, large-capacity heaters for temperature control of hydrogen liquefaction equipment, low-temperature hydrogen circulation equipment, electric boilers, hot water heating, reactors, etc. It can be used for general fluid (gas / liquid) heaters such as capacity heaters, air heaters (for drying), and temperature control heaters for chemical production lines.

It is explanatory drawing of the conventional shell and tube type heater. It is a perspective view which shows the internal structure of the heater for orifice type temperature control which concerns on embodiment of this invention, and shows the state by which the heater container was cut in half. It is sectional drawing in the baffle part of the said orifice type temperature control heater. It is a top view of the metal fitting for steadying of a sheath heater. It is a graph which shows the temperature dependence of the density of 1.5 MPa supercritical pressure hydrogen. It is explanatory drawing of the design conditions of a heater element. It is explanatory drawing for determining a baffle space | interval in the design of the heater for orifice type temperature control. It is a figure which shows the flow-velocity distribution at the time of making supercritical pressure hydrogen flow in into the heater container of the said orifice type temperature control heater. It is a figure which shows the pressure distribution at the time of making supercritical pressure hydrogen flow in into the heater container of the said orifice type temperature control heater. It is a figure which shows the temperature distribution of the supercritical pressure hydrogen which flows through the inside of the heater container of the said orifice type temperature control heater with a heat load of 5 kW. It is a figure which shows the surface temperature distribution of each sheath heater (at the time of a thermal load of 5 kW).

Explanation of symbols

11 Cylindrical body (shell)
12 Sheath heater 13 Fluid inlet 14 Bottom wall 15 Upper flange 16 Fluid outlet 17 Opening 18 Baffle plate 19 Orifice (throttle mechanism)
20 Terminal box 21 Sheath heater steady rest bracket 22 Baffle support rod

Claims (5)

A cylinder barrel having a fluid inlet portion on one end side, a fluid outlet portion on the other end side, and a cryogenic liquid fluid made of helium, hydrogen or nitrogen flowing through the inside;
A plurality of sheath heaters arranged in parallel in the axial direction of the cylindrical body and directly heating the cryogenic liquid fluid ;
A plurality of baffle plates provided with a plurality of openings through which a plurality of sheath heaters are inserted are arranged at a required interval in the axial direction of the cylindrical body,
The cryogenic liquid fluid passes through the orifice formed by the clearance formed by the opening of the baffle plate and the sheath heater, the cryogenic liquid fluid flows in parallel with the sheath heater, and the surface heat flux of the sheath heater element is a constant value. An orifice type temperature control heater that ensures airtightness by heating the cryogenic liquid fluid to a predetermined temperature by setting so as to be as follows .   The orifice type temperature adjusting heater according to claim 1, wherein the sheath tube of the sheath heater is fixed to the upper flange by welding.   The orifice type temperature adjusting heater according to claim 1 or 2, wherein the bottom end baffle plate is provided with an anti-rest fitting having a plurality of flanges for anti-sheathing of the sheath heater.   The orifice type temperature adjusting heater according to any one of claims 1 to 3, wherein a fluid inlet portion is provided at a lower end and a fluid outlet portion is provided on a side surface of a cylindrical body near the upper end.   The orifice type temperature adjusting heater according to any one of claims 1 to 4, wherein a sheath heater electrode portion is provided outside the cylindrical body.