JP2014052153A - Solar heat collection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solar heat collection device which can suppress heat loss with a relatively simple constitution, facilitates maintenance and can reduce expenses such as a manufacturing cost.SOLUTION: A heat collecting pipe 12 for causing heat medium to flow through an internal part is arranged in a vacuum transparent pipe 11. A pair of first reflection plates 13 are disposed along the heat collecting pipe 12 in the vacuum transparent pipe 11. Respective first reflection plates 13 extend in an involute curve shape right and left symmetrically from the heat collecting pipe 12, in a cross-section vertical to the length direction of the heat collecting pipe 12. A pair of second reflection plates 14 assume a composite parabolic surface shape and are respectively connected to opening edges A,D of the respective first reflection plates 13 in the vacuum transparent pipe 11. Solar light made incident from a part between respective incident edges B, C of the respective second reflection plates 14 hits the heat collecting pipe 12 directly or after at least one time being reflected by the respective first reflection plates 13 or the respective second reflection plates 14.

Description

  The present invention relates to a solar heat collecting apparatus.

  As a conventional solar heat collecting device, a solar collector is provided with a solar tracking mechanism (see, for example, Patent Document 1), or a compound parabolic condenser (CPC) type reflecting mirror. (For example, see Patent Document 2).

  The present inventors have developed an involute reflector that can efficiently reflect light emitted from a cylindrical radiation source and obtain a uniform and isotropic radiation surface at the opening ( For example, see Patent Document 3), this involute reflector has been developed to emit light from a light source, and has never been used to collect light.

JP 2010-286200 A Japanese Patent No. 3958032 Japanese Patent No. 3205809

  In the solar heat collecting apparatus having the solar tracking mechanism as described in Patent Document 1, high light collection efficiency can be obtained. However, since the solar tracking mechanism has a complicated configuration, there is a problem that manufacturing cost and installation cost increase. It was. In addition, there is a problem that maintenance becomes difficult and maintenance costs increase. In the solar heat collecting apparatus using the composite parabolic concentrating reflector as described in Patent Document 2, the condensing range by the composite parabolic concentrating reflector is flat, and the planar heat collecting surface is Since heat loss from both the front and back surfaces to the surrounding air and heat loss due to convection and heat radiation occur, there is a problem that the heat collection efficiency decreases. In Patent Document 2, a fine composite paraboloidal concentrating mirror is used to suppress heat loss. However, in this case, an advanced processing technique is required, resulting in an increase in manufacturing cost. It was.

  The present invention has been made by paying attention to such problems, and it is possible to suppress heat loss with a relatively simple configuration, easy maintenance, and reduction of manufacturing costs and other costs. The object is to provide a device.

  A solar heat collecting apparatus according to the present invention includes a vacuum transparent tube that can be evacuated inside, a heat collection tube that is disposed inside the vacuum transparent tube and allows a heat medium to flow inside, and the vacuum transparent tube A pair of first reflectors that extend in an involute curve shape symmetrically from the heat collection tube within a cross section perpendicular to the length direction of the heat collection tube, and provided in the inside of the heat collection tube. A pair of second reflectors each having a compound paraboloid shape connected to an opening edge of each first reflector opposite to the heat collecting tube inside the vacuum transparent tube; Sunlight incident from between the incident edges of the second reflector opposite to the first reflectors is reflected directly or at least once by each first reflector or each second reflector to collect the light. It is configured to hit the heat tube.

  In the solar heat collecting apparatus according to the present invention, each second reflecting plate has a composite parabolic shape, so that each second of the sunlight incident from between the incident edges of each second reflecting plate. The light striking the reflecting plate can be reflected one or more times and applied to each first reflecting plate or heat collecting tube. Moreover, since each 1st reflecting plate is comprised so that it may each extend in an involute curve shape symmetrically from the heat collecting tube within the cross section perpendicular | vertical with respect to the length direction of a heat collecting tube, the light which hits each 1st reflecting plate Can be collected in a heat collecting tube. As described above, in the solar heat collecting apparatus according to the present invention, the sunlight incident from between the incident edges of each second reflector is directly or once or more in each first reflector or each second reflector. It is configured to reflect and hit the heat collecting tube, has high light collection efficiency, and has an excellent heat collecting effect.

  The solar heat collecting apparatus according to the present invention optimizes the size of each first reflecting plate and each second reflecting plate, the light receiving opening angle and the mounting angle of the incident edge of each second reflecting plate according to the installation area. It can be designed and can be focused without being affected by seasonal variations. For this reason, the complicated structure like a solar tracking mechanism is unnecessary, and it can raise condensing efficiency with a comparatively simple structure. In addition, maintenance is facilitated, and costs such as manufacturing costs can be reduced.

  In the solar heat collecting apparatus according to the present invention, since the heat collecting tube, each first reflecting plate, and each second reflecting plate are installed inside the vacuum transparent tube, the inside of the vacuum transparent tube is evacuated. Thus, it is possible to prevent heat loss due to heat transfer from the heat collecting tubes, the first reflecting plates, and the second reflecting plates to the surrounding air. Since heat loss due to heat transfer, which accounts for a large proportion of heat loss, is eliminated, heat loss is caused by heat transfer between the vacuum transparent tube and the ambient air, the heat collecting tube, each first reflector, and each second reflector. It can be limited to the radiation. Further, by reducing the diameter of the heat collecting tube, the radiation loss from the heat collecting tube can be reduced. Since each first reflector has an involute curve shape, the contact area between each first reflector and the heat collecting tube can be reduced, and the heat conduction loss from the heat collecting tube to each first reflector is also minimized. Can be limited. Thus, the solar heat collecting apparatus according to the present invention can suppress heat loss with a relatively simple configuration.

  In the solar heat collecting apparatus according to the present invention, since the heat collecting tubes, the first reflecting plates, and the second reflecting plates are covered with the vacuum transparent tubes, dust and dust can be prevented from adhering to them. It is possible to prevent a failure due to dust or the like. Further, dust and dirt can be removed by simply wiping the outside of the vacuum transparent tube, and maintenance such as cleaning is easy. By manufacturing this heat collecting tube, the vacuum transparent tube enclosing each first reflecting plate and each second reflecting plate as one unit, the required number of units and arrangement can be configured according to the size of the installation place. , Can reduce the cost.

  In the solar heat collecting apparatus according to the present invention, each first reflecting plate can be designed according to the installation area, and does not have to be symmetrical like a conventional CPC type reflecting mirror. Further, the solar heat collecting apparatus according to the present invention includes each first reflecting plate and each second reflecting plate in order to suppress heat loss on the back side of each first reflecting plate and each second reflecting plate inside the vacuum transparent tube. A heat insulating material may be provided on the back side. The vacuum transparent tube is made of glass, for example.

  In the solar heat collecting apparatus according to the present invention, for example, water, oil, chlorofluorocarbon alternative, fluorinate, supercritical carbon dioxide, or the like can be used as a heat medium flowing inside the heat collecting tube. When water is used, after passing through the heat collecting tube, it can be used directly as hot water, or can be used as steam in a factory such as a laundry factory or a food factory. When oil or supercritical carbon dioxide is used, it can be used as a heat source for a steam generator or the like after passing through the heat collecting tube. Although the utilization efficiency of heat is reduced, a steam turbine can be connected and used for power generation. Moreover, since the diameter of the heat collecting tube can be reduced, a high-pressure fluid can be used as the heat medium flowing inside.

  The solar heat collecting apparatus according to the present invention uses an involute reflector, which has been used only for light emission, for the first time for collecting light. The solar heat collecting apparatus according to the present invention uses each of the composite parabolic second reflectors capable of condensing in a plane having a predetermined width and light incident on the plane having a predetermined width as a heat collecting tube. By combining the involute-shaped first reflectors that can be collected, it is possible to obtain dramatically higher light collection efficiency that cannot be obtained by using each of them alone. Moreover, the heat loss from the back side of the plane which arises with the conventional planar heat collecting device can be made zero by combining each 1st reflecting plate and each 2nd reflecting plate. That is, in the conventional planar heat collecting device, the portion where heat loss occurs is on both the front and back surfaces of the plane, whereas in the solar heat collecting device according to the present invention, only the surface of the heat collecting tube is used. The area where this occurs is about half. For this reason, the solar heat collecting apparatus which concerns on this invention can suppress heat loss significantly compared with the conventional planar heat collecting apparatus.

  In the solar heat collecting apparatus according to the present invention, the heat collecting tube has a cylindrical shape, and each of the first reflectors has a cross-section perpendicular to the length direction of the heat collecting tube, and the outer circumferential circle of the heat collecting tube. Light that extends from one point to the left and right, and is formed so that a straight line that connects each opening edge is substantially in contact with the one point on the opposite side of the outer circumference of the heat collecting tube. However, each of the second reflecting plates is attached so as to be widened toward each incident end edge, and is reflected between each incident end edge. It is preferable that the sunlight incident on the first reflecting plate is collected between the opening edges of the first reflecting plates. In this case, almost all of the sunlight incident between the incident edges of each second reflecting plate can be applied to the heat collecting tube, and in particular, the light collecting efficiency is high and has a very excellent heat collecting effect. .

  The solar heat collecting apparatus according to the present invention has two sets of heat collectors composed of the heat collecting tubes, the first reflecting plates, and the second reflecting plates, and each of the heat collecting devices is a vacuum transparent tube. The openings may be arranged inside each other with the direction of the opening between the incident end edges aligned. In this case, the internal space of the vacuum transparent tube can be used efficiently, and the utilization rate of sunlight relative to the installation area can be increased.

  According to the present invention, it is possible to provide a solar heat collecting apparatus that can suppress heat loss with a relatively simple configuration, can be easily maintained, and can reduce costs such as manufacturing costs.

It is sectional drawing which shows the solar heat collecting device of embodiment of this invention. It is sectional drawing which shows (a) each 2nd reflecting plate for demonstrating the design method of the solar heat collecting apparatus shown in FIG. 1, (b) It is sectional drawing which shows an installation state. It is a graph which shows the optical efficiency and thermal efficiency of the solar heat collecting apparatus shown in FIG. It is a graph which shows the relationship between the temperature of the heat collecting tube of the solar heat collecting apparatus shown in FIG. 1, and thermal efficiency. It is (a) sectional drawing and (b) perspective view which show the modification which has two sets of heat collectors of the solar heat collecting device of embodiment of this invention. It is a perspective view which shows the use condition of the solar heat collecting device shown in FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 6 show a solar heat collecting apparatus according to an embodiment of the present invention.
As shown in FIG. 1, the solar heat collecting apparatus 10 includes a vacuum transparent tube 11, a heat collecting tube 12, a pair of first reflecting plates 13, and a pair of second reflecting plates 14.

The vacuum transparent tube 11 is made of glass and has a cylindrical shape. The vacuum transparent tube 11 is configured to be able to maintain a vacuum state by extracting the air inside.
The heat collecting tube 12 has a cylindrical shape and is configured to allow a heat medium such as water or oil to flow inside. The heat collecting tube 12 is arranged along the length direction of the vacuum transparent tube 11 so as to pass through the inside of the vacuum transparent tube 11.

  Each first reflecting plate 13 is provided inside the vacuum transparent tube 11 along the heat collecting tube 12. Each first reflecting plate 13 is formed in a cross section perpendicular to the length direction of the heat collecting tube 12 so as to extend symmetrically from one point E on the outer circumference of the heat collecting tube 12 in an involute curve shape. . Each first reflecting plate 13 is formed such that a straight line connecting the opening edges A and D on the opposite side of the heat collecting tube 12 is substantially in contact with one point E of the outer circumference of the heat collecting tube 12. . Further, each first reflecting plate 13 is formed such that the length of the straight line connecting the opening edges A and D is the same as the circumference of the heat collecting tube 12. Thereby, each 1st reflecting plate 13 is comprised so that the light which entered between each opening edge A and D may be reflected by the 1st reflecting plate 13 directly or hits the heat collecting tube 12. FIG.

  Each second reflecting plate 14 is connected to the opening edges A and D of each first reflecting plate 13 inside the vacuum transparent tube 11. Each of the second reflecting plates 14 is composed of a compound paraboloidal concentrating (CPC) type reflecting mirror, and is attached so that the distance between the second reflecting plates 14 increases toward the incident edges B and C on the opposite side to the first reflecting plate 13. ing. Each of the second reflecting plates 14 is configured such that sunlight incident between the incident edges B and C is condensed between the opening edges A and D of the first reflecting plates 13. Thus, in the solar heat collecting apparatus 10, at least one of the sunlight incident between the incident edges B and C of each second reflecting plate 14 is directly or at each first reflecting plate 13 or each second reflecting plate 14. It is configured to be reflected once and hit the heat collecting tube 12.

Specifically, the solar heat collecting apparatus 10 is designed as follows. Here, the design is performed on the assumption that it is used in Sendai City (latitude 38.254162 °, longitude 140.891403 °). As shown in FIG. 2, the solar altitude of Sendai in the summer solstice is 74.4664 °, and the solar altitude of the winter solstice is 28.0169 °. The optimum opening angle θ _i of the plate 14 in the south-central time is 23.22 °, and the elevation angle is 51.24 °.

  Next, assuming that the diameter of the heat collecting tube 12 is 15 mm, the length a ′ of the straight line connecting the opening edges A and D of the first reflecting plates 13 is 47.1 mm. Moreover, since each 2nd reflecting plate 14 consists of a CPC type | mold reflecting mirror, the parameter of each 2nd reflecting plate 14 can be calculated by the following (1)-(4) formula.

  From the formulas (1) to (4), the focal length f of each second reflector 14 is 65.7 mm, the distance a between the opening edges A and D is 119.5 mm, the length L is 388.3 mm, CPC type The theoretical maximum condensing rate C of each second reflecting plate 14 that is a reflecting mirror is 2.54.

Next, the optical efficiency of the solar heat collecting apparatus 10 designed in this way is calculated. Here, the optical efficiency indicates the ratio of the light reaching the heat collecting tube 12 in the sunlight incident on the solar heat collecting apparatus 10. The sunlight is attenuated when passing through the glass vacuum transparent tube 11, and part of the sunlight is absorbed when reflected by each first reflector 13 or each second reflector 14. Optical efficiency is important in evaluating the light condensing performance. It is assumed that the transmittance of the glass of the vacuum transparent tube 11 with respect to sunlight is 0.95, the absorption rate of the heat collecting tube 12 is 0.90, and the reflectivity of each of the first reflector 13 and each second reflector 14 is 0.90. FIG. 3 shows the optical efficiency of the solar heat collecting apparatus 10 when it is done. As shown in FIG. 3, when the incident angle of sunlight is 23.2 ° or less of the opening angle θ _i , the optical efficiency is about 70%, and a high optical efficiency is obtained regardless of the incident angle. .

Next, the thermal efficiency of the solar heat collecting apparatus 10 is calculated. Here, the thermal efficiency represents the proportion of energy absorbed into the heat collecting tube 12 in the incident solar energy. Since the solar heat collecting apparatus 10 keeps the inside of the glass vacuum transparent tube 11 in a vacuum, heat loss from the heat collecting tube 12 to the environment occurs only by heat radiation (radiation). Therefore, the thermal efficiency η _thermal can be calculated by the following equation using the optical efficiency η _opt .

Here, the second term on the right side of equation (5) represents the heat loss due to radiation, ε is the emissivity of 0.90, σ is the Stefan-Boltzmann constant, q _in is the solar constant, and C is the concentration ratio. The opening area of the solar heat collecting device 10 is divided by the surface area of the heat collecting tube 12. T _amb is the ambient temperature, here 20 ° C. Further, T _a is a temperature of the heat collecting pipe 12, assuming that make hot water solar heat collector 10, was 100 ° C..

  The calculation result of the thermal efficiency using the equation (5) is shown in FIG. As shown in FIG. 3, when the solar heat collecting apparatus 10 is operated to make hot water of 100 ° C., it can be confirmed that heat can be collected with a thermal efficiency of about 50%. Further, as shown in the equation (5), the remaining 50% is a loss due to radiation, and by improving the radiation characteristics of the heat collecting tube 12, the thermal efficiency can be greatly improved. In the calculation in FIG. 3, the emissivity ε of the heat collecting tube 12 is set to 0.9. This is the case where iron that is completely oxidized is used as the heat collecting tube 12, or the surface is painted with black paint. It is assumed that is used.

  FIG. 4 shows the relationship between the temperature of the heat collecting tube 12 and the thermal efficiency. As shown in FIG. 4, it can be confirmed that when the solar heat collecting apparatus 10 is operated at a low temperature, the thermal efficiency is increased. On the other hand, it can be seen that when operated at a high temperature, the rate of heat loss due to radiation increases and the thermal efficiency decreases. Moreover, as shown in FIG. 4, the solar collector 10 in this example has a maximum temperature of 180 ° C.

Next, the operation will be described.
In the solar heat collecting apparatus 10, each second reflecting plate 14 has a compound parabolic shape, and each of the second reflecting plates 14 out of sunlight incident between the incident edges B and C of each second reflecting plate 14. The light hitting the two reflecting plates 14 can be reflected once or a plurality of times and applied to each first reflecting plate 13 or the heat collecting tube 12. In addition, each first reflecting plate 13 is configured to extend in an involute curve shape symmetrically from the heat collecting tube 12 in a cross section perpendicular to the length direction of the heat collecting tube 12, and thus each first reflecting plate 13. Light hitting the plate 13 can be collected in the heat collecting tube 12. As described above, in the solar heat collecting apparatus 10, the sunlight incident between the incident end edges B and C of each second reflecting plate 14 is directly or each first reflecting plate 13 or each second reflecting plate 14. It is configured to reflect at least once and hit the heat collecting tube 12, has high light collection efficiency, and has an excellent heat collecting effect.

  The solar heat collecting apparatus 10 has a size of each first reflecting plate 13 and each second reflecting plate 14, a light receiving opening angle and an attachment angle of the incident edges B and C of each second reflecting plate 14 according to the installation area. Can be designed optimally, and can be condensed while being fixed regardless of seasonal variations. For this reason, the complicated structure like a solar tracking mechanism is unnecessary, and it can raise condensing efficiency with a comparatively simple structure. In addition, maintenance is facilitated, and costs such as manufacturing costs can be reduced.

  Moreover, since the solar heat collecting apparatus 10 has the heat collection tube 12, each 1st reflecting plate 13, and each 2nd reflecting plate 14 installed in the inside of the vacuum transparent tube 11, the inside of the vacuum transparent tube 11 is evacuated. By doing so, it is possible to prevent heat loss due to heat transfer from the heat collecting tubes 12, the first reflecting plates 13 and the second reflecting plates 14 to the ambient air. Since heat loss due to heat transfer that occupies a large proportion of heat loss is eliminated, heat loss is reduced between heat transfer between the vacuum transparent tube 11 and ambient air, and the heat collecting tube 12, each first reflector 13 and each heat loss. It can be limited to radiation from the second reflector 14. Further, by reducing the diameter of the heat collecting tube 12, the radiation loss from the heat collecting tube 12 can be reduced. Since each first reflecting plate 13 has an involute curve shape, the contact area between each first reflecting plate 13 and the heat collecting tube 12 can be reduced, and from the heat collecting tube 12 to each first reflecting plate 13. Thermal conduction losses can also be minimized. Thus, the solar heat collecting apparatus 10 can suppress heat loss with a relatively simple configuration.

  In the solar heat collecting apparatus 10, since the heat collecting tube 12, each first reflecting plate 13, and each second reflecting plate 14 are covered with the vacuum transparent tube 11, dust and dust can be prevented from adhering to them. Failure due to dust or dust can be prevented. In addition, dust and dirt can be removed simply by wiping the outside of the vacuum transparent tube 11, and maintenance such as cleaning is easy. By manufacturing the heat collecting tube 12, the first reflector 13 and the vacuum transparent tube 11 enclosing the second reflector 14 as a unit, the required number of units, arrangement, etc. are configured according to the size of the installation location. Can reduce costs.

  In addition, the solar heat collecting apparatus 10 has each 1st reflecting plate 13 and each 2nd reflection in order to suppress the heat loss of the back side of each 1st reflecting plate 13 and each 2nd reflecting plate 14 inside the vacuum transparent tube 11. FIG. A heat insulating material may be provided on the back side of the plate 14.

  As shown in FIG. 5, the solar heat collecting apparatus 10 includes two sets of heat collectors 20 each including a heat collecting tube 12, each first reflecting plate 13, and each second reflecting plate 14. The heater 20 may be arranged inside the vacuum transparent tube 11 with the direction of the opening between the incident edges B and C aligned. In this case, the internal space of the vacuum transparent tube 11 can be used efficiently, and the utilization factor of sunlight with respect to the installation area can be increased. For example, when there is only one set of the heat collector 20 shown in FIG. 1, the ratio of the opening between the incident edges B and C is small with respect to the diameter of the vacuum transparent tube 11, and the sunlight that has reached the vacuum transparent tube 11 Only about 50% of the light enters from the opening between the incident edges B and C. On the other hand, when two sets of the heat collector 20 shown in FIG. 6 are provided, about 80% of the sunlight reaching the vacuum transparent tube 11 can be collected in the heat collection tube 12. Further, as shown in FIG. 5 (b), by folding one heat collecting tube 12 inside the vacuum transparent tube 11, it can be used for each heat collector 20. At this time, since the heat collecting tube 20 can be disposed inside the vacuum transparent tube 11 from only one end surface of the vacuum transparent tube 11, the other end surface can be sealed. For this reason, while being able to make the sealing process of the vacuum transparent tube 11 easy, a heat loss part can be decreased.

  The solar heat collecting apparatus 10 can use, for example, water, oil, supercritical carbon dioxide, or the like as a heat medium flowing inside the heat collecting tube 12. FIG. 6 shows an example of use when a refrigerant such as alternative chlorofluorocarbon is used as the heat medium. In the usage example shown in FIG. 6, the solar heat collecting device 10 shown in FIG. 5 is used, and the refrigerant is circulated between the heat collecting pipe 12, the turbine 52, and the condenser 53 by the pump 51. Has been. That is, the refrigerant heated through the heat collecting pipe 12 is converted to superheated steam and rotates the turbine 52. Thereby, it is possible to generate power with the generator 54 connected to the turbine 52. Further, the superheated steam that has passed through the turbine 52 is returned to the liquid by the condenser 53 and then circulated again to the heat collecting pipe 12.

  Since the solar heat collecting apparatus according to the present invention is easy to maintain, it is suitable for installation not only in the roofs of Japanese houses and factories, but also in areas with abundant solar radiation, especially in the center of Eurasia and Africa. ing. Further, when combined with a heat medium circulation device, for example, when water is used as the heat medium, it can be used as a water heater capable of supplying hot water of about 100 ° C., depending on the operating pressure. In addition, when a heat medium other than water, such as supercritical carbon dioxide or oil, is used as the heat medium, the heat pressure can be adjusted to about 150 ° C. by adjusting the operating pressure, and superheated steam can be generated. . For this reason, this steam can be used in a factory or used for power generation.

DESCRIPTION OF SYMBOLS 10 Solar collector 11 Vacuum transparent tube 12 Heat collection tube 13 1st reflector A, D Opening edge 14 2nd reflector B, C Incident edge

Claims (3)

A vacuum transparent tube that can be evacuated inside,
A heat collecting tube disposed inside the vacuum transparent tube for flowing a heat medium therein;
A pair of firsts provided in the vacuum transparent tube along the heat collecting tube and extending symmetrically from the heat collecting tube in an involute curve shape in a cross section perpendicular to the length direction of the heat collecting tube. A reflector,
A pair of second reflectors each having a compound paraboloid shape connected to an opening edge of each first reflector opposite to the heat collecting tube inside the vacuum transparent tube;
Sunlight incident from between the incident edges of the second reflecting plates opposite to the first reflecting plates is reflected directly or at least once by each first reflecting plate or each second reflecting plate, and A solar heat collecting apparatus, characterized by being configured to hit a heat collecting tube. The heat collecting tube has a cylindrical shape,
Each of the first reflectors extends left and right from one point of the outer circumference of the heat collecting tube in a cross section perpendicular to the length direction of the heat collecting tube, and a straight line connecting each opening edge is the heat collecting tube. The outer circumferential circle is formed so as to be substantially in contact with the one point opposite to the one point, and is configured such that light incident between each opening edge is reflected directly or by each first reflecting plate and hits the heat collecting tube. ,
Each of the second reflectors is attached so that the distance between the second reflectors increases toward each incident edge, and sunlight incident from between each incident edge gathers between the opening edges of each first reflector. The solar heat collecting apparatus according to claim 1, wherein the solar heat collecting apparatus is configured as follows. Two sets of heat collectors composed of the heat collecting tubes, the first reflecting plates, and the second reflecting plates,
3. The solar heat collector according to claim 1, wherein the heat collectors are arranged in the vacuum transparent tube so that the openings between the incident end edges are aligned.