JP5876601B1 - Steam heating device - Google Patents

Abstract

A steam heating apparatus for heating corrosive steam having corrosivity at high temperature is provided. A steam heating device has a flow path through which corrosive steam v flows from an inlet to an outlet, and a steam heating member 70 that raises the temperature of the corrosive steam while the corrosive steam flows through the flow path. And a heating unit 74 that heats the steam heating member, and a temperature control unit that controls the temperature of the steam heating member heated by the heating unit. [Selection] Figure 1

Description

  The present invention relates to a steam heating apparatus that heats corrosive steam.

  As a heat exchanger for heating a fluid, one using graphite is disclosed (see Patent Document 1). Moreover, what uses the carbon tube which has corrosion resistance with respect to a sulfuric acid is disclosed as a gas gas heat exchanger in a wet desulfurization apparatus (refer patent document 2).

  By the way, for example, a chalcopyrite type compound semiconductor has a higher photoelectric conversion efficiency than a crystalline or amorphous silicon (Si) -based semiconductor, and thus is promising as a solar cell that converts sunlight into electric energy. Yes. As a method for producing a chalcopyrite type compound semiconductor, for example, a selenization method in which a film is formed by heat treatment in an atmosphere of selenium vapor corrosive at high temperatures has been studied.

JP 09-77991 A Japanese Patent Application Laid-Open No. 09-14871

The heat exchange assembly of Patent Document 1 has a configuration in which the joint surface between the graphite and the silicon carbide tube is sealed with a fluorine polymer coating so that inorganic acids and organic solvents such as battery acid (H ₂ SO ₄ ) and acetone can be treated. Is disclosed. Moreover, the gas-gas heat exchanger of patent document 2 is a low temperature which alternately repeats that the heat medium (circulation water) flows from the left side to the right side and flows from the right side to the left side in a plurality of straight carbon tubes arranged horizontally. Disclosed is cooling the exhaust gas to a temperature suitable for wet desulfurization by contacting the heat transfer section.

  However, none of the prior art heat exchangers heat corrosive steam that is corrosive at high temperatures, such as selenium vapor. And the inventor of this application is not aware of the existence of a steam heating apparatus that heats corrosive steam such as selenium steam.

  Therefore, the technical problem to be solved by the present invention is to provide a steam heating apparatus for heating corrosive steam having corrosive properties at high temperatures.

  In order to solve the above technical problem, according to the present invention, the following steam heating apparatus is provided.

That is, the steam heating device according to the present invention is
A steam heating member comprising a block body, and a plurality of axially extending flow paths are formed inside the block body, and the temperature of the corrosive steam is increased while the corrosive steam flows through the flow path. A steam heating member;
A heating section for heating the steam heating member;
A temperature control unit for controlling the temperature of the steam heating member heated by the heating unit;
The steam heating member is accommodated in an airtight state under an atmospheric pressure or a reduced pressure, and has a flange portion on the inlet side and a flange portion on the outlet side at each of the inlet end portion and the outlet end portion, the casing including the inlet Each of the flange portion on the side and the flange portion on the outlet side includes a casing attached to the attachment plate on the inlet side and the attachment plate on the outlet side via packing .

In the present invention, the temperature of the corrosive steam can be increased while the corrosive steam flows through the plurality of flow paths formed inside the block body of the steam heating member. Therefore, it is not necessary to produce corrosive steam that is more corrosive at high temperatures, and it is not necessary to configure the vaporizer to withstand high-temperature corrosive steam, thereby reducing costs. Furthermore, the casing that houses the steam heating member in an airtight state can prevent leakage of corrosive steam flowing through the flow path in the steam heating member and can be maintained at an arbitrary pressure including decompression.

  The steam heating member is preferably made of a material having corrosion resistance against corrosive steam having corrosivity at high temperatures. In this way, the replacement frequency of the steam heating member is reduced, and the cost can be reduced.

  The corrosive vapor is preferably selenium vapor or sulfur vapor, and the vapor heating member is preferably made of carbon. In this way, selenium vapor or sulfur vapor that is corrosive at high temperatures can be heated. In addition, since the carbon steam heating member stores the heat generated in the heating section, the temperature inside the steam heating member is unlikely to decrease, and less power is required for heating.

  The steam heating member connects the steam heating body having a forward flow path from the inlet side to the outlet side and a return flow path from the outlet side to the inlet side, and connects the forward flow path and the return flow path on the outlet side. It is preferable to include an outlet side steam heating end portion having an outlet side communication channel. In this way, since the reciprocating flow path returning to the inlet side is provided, the steam heating member can be made compact.

  The steam heating member connects the steam heating body having a forward flow path from the inlet side to the outlet side and a return flow path from the outlet side to the inlet side, and connects the forward flow path and the return flow path on the outlet side. It is preferable to include an outlet-side steam heating end portion having an outlet-side communication channel, and an inlet-side steam heating end portion having an inlet-side communication channel that connects the forward channel and the return channel on the inlet side. In this way, since the flow path that reciprocates at least once from the inlet side toward the outlet side is provided, the steam heating member can be made compact while increasing the total length of the flow path and increasing the heat exchange area. it can.

  The numbers of the forward flow path, the return flow path, the outlet side communication flow path, and the inlet side communication flow path formed in the steam heating member are h, i, j, and k, and the desired number of forward flow paths. Is n (natural number), h = n, i = n-1 (when the outlet is downstream) or n (when the outlet is upstream), j = n-1 (when the outlet is downstream) Alternatively, it is preferable that n (when the outlet is on the upstream side) or k = n−1 is satisfied. In this way, since the steam heating member includes a flow path that reciprocates n times or n times and a half times between the inlet side and the outlet side, the steam heating member increases the total length of the flow path and increases the heat exchange area. The heating member can be made compact.

  It is preferable that the steam heating member further includes an additive gas channel configured to introduce the additive gas from the outlet side and to merge the additive gas at the inlet side of the forward channel. If it does in this way, while a steam heating member becomes compact, additive gas can be heated effectively.

  It is preferable that the steam heating member has a cylindrical shape. In this way, since the flow paths are arranged on the circumference and are integrated in a three-dimensional manner, it is more compact than a thin plate-shaped rectangular parallelepiped-shaped steam heating member (shown in FIG. 9), and the steam heating member Since the outer surface area becomes smaller and it is difficult to dissipate heat, the heating efficiency is improved.

  It is preferable to further include a casing that houses the steam heating member in an airtight state under atmospheric pressure or reduced pressure, and has a flange portion on the inlet side and a flange portion on the outlet side at each of the inlet end portion and the outlet end portion. If it does in this way, leakage of corrosive vapor which flows through a channel in a steam heating member can be prevented, and it can hold at arbitrary pressures including decompression.

  In the steam heating apparatus according to the present invention, the temperature of the corrosive steam is increased while flowing through the flow path of the steam heating member, whereby the steaming apparatus that generates corrosive steam that is more corrosive at a high temperature is prevented from being corroded at high temperature. This eliminates the need for a structure that can withstand chemical vapor, thereby reducing costs.

It is sectional drawing which looked at the steam heating apparatus from the upper surface. It is sectional drawing which looked at the steam heating apparatus from the side. FIG. 3 is a cross-sectional view taken along the line III-III in FIG. 2. It is IV-IV arrow sectional drawing of FIG. 2 explaining typically when the steam heating apparatus is seen from the entrance side to the exit side. It is a VV arrow sectional view of Drawing 2 explaining typically when a steam heating device is looked at an entrance side from an exit side. It is a figure explaining typically when the vapor | steam heating apparatus which concerns on a modification is seen from the entrance side to the exit side, Comprising: IV-IV arrow view when the vapor | steam heating apparatus shown in FIG. 2 is replaced with the said modification It is sectional drawing. It is a figure which illustrates when the steam heating apparatus which concerns on a modification is seen from the exit side to the inlet side, Comprising: The VV arrow view when the steam heating apparatus shown in FIG. 2 is replaced with the said modification It is sectional drawing. It is a figure which illustrates typically the steam heating device concerning the further modification. (A) is a plan view and (B) is a side view.

  A steam heating apparatus 7 according to an embodiment will be described in detail with reference to FIGS.

  The steam heating device 7 is a device for heating corrosive steam having corrosivity at high temperature (hereinafter referred to as corrosive steam v) generated by vaporizing a liquid material in the vaporizer 5 described later. For example, it is an apparatus for heating a corrosive vapor v such as selenium (Se) vapor or sulfur (S) vapor. The corrosive vapor v such as selenium (Se) vapor or sulfur (S) vapor is used, for example, when producing a chalcopyrite type compound semiconductor. Chalcopyrite compound semiconductors have higher photoelectric conversion efficiency than crystalline or amorphous silicon (Si) -based semiconductors, and therefore are being studied for use as solar cells that convert sunlight into electrical energy.

Among the compound semiconductors (Ag, Cu) (Al, In, Ga) (S, Se) ₂ having a chalcopyrite structure, in particular, copper (Cu) is used as a group I source, indium (In) and gallium (Ga) as a group III source. ), And a so-called CIGS compound semiconductor using sulfur (S) and selenium (Se) as a group VI material, a Cu (In, Ga) (S, Se) ₂ compound semiconductor is ideal for light absorption of solar cells. A band gap can be realized, and a CIS thin film solar cell using such a CIGS compound semiconductor has high photoelectric conversion efficiency.

  In order to form a CIS-based thin film, there is a method in which the component elements copper, indium, and selenium are simultaneously deposited as sources. Furthermore, a selenization method is used in which a laminated film in which copper and indium are individually formed is heat-treated in a hydrogen selenide or selenium vapor atmosphere to form a selenide film.

  Of the selenization methods, the method using hydrogen selenide is difficult to handle because the hydrogen selenide is toxic, and it is necessary to spend a large amount of safety measures on the gas supply system and exhaust system. Become. On the other hand, among the selenization methods, the method using selenium vapor is significantly improved in safety, but it is said that the photoelectric conversion efficiency is inferior to the method using hydrogen selenide. Since selenium vapor is easily bonded to form a large molecular aggregate, the poor diffusivity of copper and indium into the film is considered to be one of the causes of reducing photoelectric conversion efficiency. It has been.

  In the vaporization apparatus 5 for vaporizing liquid selenium or the like, it seems that the formation of a huge molecular aggregate is less likely to occur by increasing the heating temperature of liquid selenium. However, if the heating temperature of the vaporizer 5 is increased, the vapor pressure increases, so the amount of selenium vaporization increases, and the opportunity for the selenium vapors to associate and combine with each other increases, thereby suppressing the formation of huge molecular aggregates. It is difficult to do. Moreover, in order to raise heating temperature, since it is necessary to make the heating part and heat insulation part in the vaporization apparatus 5 respond | correspond to high temperature, there exists a problem that the enlargement and cost increase of the vaporization apparatus 5 are caused.

  Therefore, it has been studied that the selenium vapor generated in the vaporizer 5 is further heated to decompose (crack) the selenium vapor that has become a large molecular aggregate into a small size for reforming. The steam heating device 7 can be used for the application, for example.

  The steam heating device 7 will be described in detail below. FIG. 1 is a cross-sectional view of the steam heating device 7 as viewed from above, and FIG. 2 is a cross-sectional view of the steam heating device 7 as viewed from the side.

  The steam heating member 70 has a steam heating main body portion 71, an inlet side steam heating end portion 72, an outlet side steam heating end portion 73, and a temperature control portion, and has corrosion resistance against the corrosive steam v. It is made of carbon material. The steam heating main body 71 is a cylindrical block body and has a plurality of flow paths extending in the axial direction. The steam heating main body 71 can be formed in a thin plate-shaped rectangular parallelepiped shape as shown in FIG. 8, but the columnar steam heating main body 71 is thinner than a thin plate-shaped rectangular parallelepiped shape. In addition to being compact, since the outer surface area of the steam heating member 70 is reduced and it is difficult to dissipate heat, the heating efficiency of the steam heating main body 71 is increased. The inlet side steam heating end portion 72 is a disk-like block body, and is disposed in contact with the inlet side of the steam heating main body portion 71. The inlet-side steam heating end portion 72 has a groove-shaped connecting flow path for connecting the flow path of the steam heating main body portion 71 on the side facing the inlet side end face of the steam heating main body portion 71. The outlet side steam heating end portion 73 is a disk-shaped block body, and is disposed in contact with the outlet side of the steam heating main body portion 71. The outlet-side steam heating end 73 has a groove-shaped communication channel for communicating the channel of the steam heating main body 71 on the side facing the outlet side end surface of the steam heating main body 71. The steam heating member 70 is accommodated in the cylindrical tubular portion 78A of the casing 78 in an airtight state under atmospheric pressure or reduced pressure via the heat insulating materials 83 and 84. The casing 78 is made of a heat and corrosion resistant material (for example, quartz glass or heat and corrosion resistant stainless steel). The casing 78 has a flange portion 78B on the inlet side at the inlet end portion and a flange portion 78B on the outlet side at the outlet end portion.

  A heating unit 74 made of a ceramic fiber heater is disposed on the outer periphery of the casing 78. In the space surrounded by the flange portion 78B on the inlet side and the flange portion 78B on the outlet side in the casing 78, the outer periphery of the heating portion 74, the inlet side end portion, and the outlet side end portion so as to surround the heating portion 74, respectively. A heat insulating material 75 is provided. The temperature of the heating unit 74 is measured by a thermocouple 85.

  A packing 79 is interposed between the outlet side surface of the inlet side mounting plate 88 and the flange portion 78B of the casing 78, and between the inlet side surface of the outlet side mounting plate 88 and the flange portion 78B of the casing 78. With the packing 79 interposed therebetween, the mounting plate 88 on the inlet side and the mounting plate 88 on the outlet side are fixed with a plurality of long bolts 89 so that the inside of the system can withstand vacuum. An inlet pipe 81 is inserted into a mounting hole of the inlet-side mounting plate 88, and an end of the inlet pipe 81 is connected to a connection hole of the inlet-side steam heating end 72. An outlet pipe 82 is inserted into the mounting hole of the outlet-side mounting plate 88, and an end of the outlet pipe 82 is connected to a connection hole of the outlet-side steam heating end 73. Further, carbon pipes are inserted inside the inlet pipe 81 and the outlet pipe 82 for corrosion resistance.

  Further, as shown in FIG. 1, an additive gas introduction pipe 87 is connected to the additive gas flow path 71G. As shown in FIG. 2, a thermocouple 85 for measuring the temperature of the steam heating member 70 is inserted into the thermocouple insertion hole 85A. The temperature of the steam heating member 70 heated by the heating unit 74 is controlled by a temperature control unit (not shown), and the temperature of the steam heating member 70 is controlled to be 500 ° C. to 600 ° C., for example.

  Next, the flow path in the steam heating member 70 will be described with reference to FIGS.

  3 is a cross-sectional view taken along arrow III-III in FIG. 4 is a schematic cross-sectional view when the steam heating main body 71 is viewed in the direction of the outlet-side steam heating end 73 at the position IV-IV in FIG. FIG. 5 is a schematic cross-sectional view of the steam heating main body 71 viewed in the direction of the inlet-side steam heating end 72 at the position VV in FIG.

  In FIG. 3, the first forward flow path 71A is at the center of the steam heating main body 71, and the first return flow path 71B and the second forward flow path 71C are obliquely above the first forward flow path 71A. A second return flow path 71D is disposed obliquely below the path 71A, and a third forward flow path 71E is disposed below the first forward flow path 71A. Each of the first return flow path 71B, the second forward flow path 71C, the second return flow path 71D, and the third forward flow path 71E is centered on the first forward flow path 71A of the columnar steam heating main body 71. It is arranged on a substantially circumference and is located in the vicinity of the heating unit 74 that surrounds the outer periphery of the steam heating main body 71. A thermocouple insertion hole 85A is disposed above the first forward flow path 71A, and an additive gas flow path 71G is disposed beside the first forward flow path 71A. The first forward flow path 71A communicates with the inlet flow path 81A of the inlet pipe 81, and the third forward flow path 71E communicates with the outlet flow path 82A of the outlet pipe 82.

  In FIG. 4, the outlet-side steam heating end 73 includes a first outlet-side communication channel 73A that connects the first forward channel 71A and the first return channel 71B, and a second forward channel 71C and a second channel. A second outlet side communication channel 73B connecting the return channel 71D is formed in a groove shape. In FIG. 5, the inlet-side steam heating end portion 72 includes a first inlet-side communication channel 72A, a first return channel 71B, and a second forward channel that connect the first forward channel 71A and the additive gas channel 71G. A second inlet-side connecting flow path 72B that connects 71C and a third inlet-side connecting flow path 72C that connects the second return flow path 71D and the third forward flow path 71E are formed in a groove shape. 1 and 2, the left side is the upstream side in the gas flow direction and the flow path inlet is located, and the right side is the downstream side in the gas flow direction and the flow path outlet is located.

  3 to 5, the corrosive vapor v from the inlet channel 81A of the inlet pipe 81 merges with the additive gas from the additive gas channel 71G and the first inlet side communication channel 72A. After that, it flows through the first forward flow path 71A toward the outlet side. The corrosive vapor v flows toward the inlet side through the first return channel 71B via the first outlet side communication channel 73A, and then flows through the second forward channel 71C via the second inlet side communication channel 72B. Flows toward the exit side. The corrosive vapor v flows through the second return channel 71D toward the inlet side via the second outlet side communication channel 73B, and then flows through the third forward channel 71E via the third inlet side communication channel 72C. Flows toward the exit side. The corrosive vapor v from the third forward flow path 71E flows through the outlet flow path 82A of the outlet pipe 82.

  In the steam heating member 70 shown in FIGS. 3 to 5, a flow path reciprocating twice in the axial direction in the steam heating main body 71 is formed by the first forward flow path 71A, the first return flow path 71B, and the like. ing. Therefore, according to the steam heating member 70, the entire length of the flow path in the steam heating member 70 is lengthened, and since all the flow paths are arranged in the vicinity of the heating unit 74, the corrosive vapor v is sufficiently heated. The steam heating member 70 can be made compact.

  A steam heating device 7 according to a modification will be described with reference to FIGS. The modification is different from the above-described embodiment in the configuration of the flow path in the steam heating member 70. 6 and 7 are substantially the same as the cross-sectional positions in FIGS. 4 and 5, respectively.

  In FIG. 6, the outlet side steam heating end portion 73 is formed with a fourth outlet side communication channel 73D that connects the first forward channel 71A and the third return channel 71F in a groove shape. In FIG. 7, the inlet-side steam heating end portion 72 is formed with a first inlet-side communication channel 72A that connects the first forward channel 71A and the additive gas channel 71G in a groove shape.

  6 and 7, the corrosive vapor v from the inlet channel 81A of the inlet pipe 81 merges with the additive gas from the additive gas channel 71G and the first inlet side communication channel 72A. After that, it flows through the first forward flow path 71A toward the outlet side. The corrosive vapor v flows in the third return channel 71F toward the inlet side via the fourth outlet side communication channel 73D. And the corrosive vapor | steam v from the 3rd return flow path 71F flows through the exit flow path 82A of the exit pipe | tube 82 provided in the inlet side. Accordingly, in the steam heating device 7 of FIGS. 1 and 2, the left side of the figure is the upstream side in the gas flow direction, and both the inlet and the outlet of the flow path are located upstream in the gas flow direction.

  6 and 7, the corrosive vapor v from the inlet channel 81A of the inlet pipe 81 merges with the additive gas from the additive gas channel 71G and the first inlet side communication channel 72A. After that, it flows through the first forward flow path 71A toward the outlet side. The corrosive vapor v flows in the third return channel 71F toward the inlet side via the fourth outlet side communication channel 73D. And the corrosive vapor | steam v from the 3rd return flow path 71F flows through the exit flow path 82A of the exit pipe | tube 82 provided in the inlet side.

  In the steam heating member 70 shown in FIGS. 6 and 7, a flow path reciprocating once in the axial direction in the steam heating main body 71 is formed by the first forward flow path 71A and the third return flow path 71F. . Therefore, it is possible to make the steam heating member 70 compact while sufficiently heating the corrosive steam v by increasing the overall length of the flow path in the steam heating member 70.

In the embodiment and the modification described above, specific examples of the flow path in the steam heating member 70 have been described. That is, h, i, j, and k are the numbers of the forward flow path, the return flow path, the outlet side communication flow path, and the inlet side communication flow path formed in the steam heating member 70, and the desired forward flow paths. When the number of is n (natural number),
h = n,
i = n-1 (when the outlet is downstream) or n (when the outlet is upstream),
j = n-1 (when the outlet is downstream) or n (when the outlet is upstream),
The relationship k = n−1 is satisfied.

  In the above-described embodiment, since the desired number n of the forward flow paths is 3 and the outlet is on the downstream side in the gas flow direction, h = 3, i = 2, j = 2, and k = 2. In the above-described modification, since the desired number n of the forward flow paths is 1 and the outlet is on the upstream side in the gas flow direction, h = 1, i = 1, j = 1, and k = 0. Become.

  In order to facilitate understanding of the present invention, the description has been made using specific configurations and numbers, but the present invention is not limited to the specific configurations and numbers of the above-described embodiments, Various modifications that can be considered without departing from the scope of the claims can be included. For example, in the embodiment and the modification described above, the steam heating main body 71 is a cylindrical block body and has a plurality of channels extending in the axial direction therein, but has a channel inside. A configuration in which a plurality of circular tubes are bundled can also be used. Moreover, although the steam heating member 70 illustrated that it was made from carbon, according to the kind of corrosive vapor | steam v, the appropriate material which has corrosion resistance with respect to the corrosive vapor | steam v in high temperature can be used. In addition, the steam heating member 70 is not limited to a cylindrical shape, and may have another shape (for example, a thin plate-like rectangular parallelepiped shape as shown in FIG. 8).

  Although the steam heating apparatus 7 used when manufacturing a solar cell among compound semiconductors was illustrated, the steam heating apparatus 7 is not limited to the said use. Needless to say, the steam heating device 7 can be used for semiconductors other than solar cells, and further, for example, can be used for forming a vapor deposition plating layer on a steel plate. Moreover, although the metal selenium (Se) vapor | steam or the nonmetallic sulfur (S) vapor | steam was illustrated as the corrosive vapor | steam v, it can apply also to other corrosive vapor | steam.

7 Steam heating device 70 Steam heating member 71 Steam heating body 71A First forward flow path 71B First return flow path 71C Second forward flow path 71D Second return flow path 71E Third forward flow path 71F Third return flow path 71G Addition gas channel 72 Inlet side steam heating end 72A First inlet side communication channel 72B Second inlet side communication channel 72C Third inlet side communication channel 73 Outlet side steam heating end 73A First outlet side communication channel 73B Second outlet side communication flow path 73D Fourth outlet side communication flow path 74 Heating section 75 Heat insulating material 78 Casing 78A Tubular section 78B Flange section 79 Packing 81 Inlet pipe 81A Inlet flow path 82 Outlet pipe 82A Outlet flow paths 83, 84 Material 85 Thermocouple 85A Thermocouple insertion hole 87 Additive gas introduction pipe 88 Mounting plate 89 Long bolt v Corrosive steam

Claims (3)

A steam heating member comprising a block body, wherein a plurality of axially extending flow paths are formed inside the block body, and the temperature of the corrosive steam is controlled while the corrosive steam flows through the flow path. A steam heating member to be raised;
A heating unit for heating the steam heating member;
A temperature control unit for controlling the temperature of the steam heating member heated by the heating unit;
The steam heating member is accommodated in an airtight state under an atmospheric pressure or a reduced pressure, and has a flange portion on the inlet side and a flange portion on the outlet side at each of the inlet end portion and the outlet end portion, the casing including the inlet And a casing attached to an inlet side mounting plate and an outlet side mounting plate via packing, respectively . Oite to claim 1,
The steam heating member has a cylindrical shape, and the steam heating member is
A steam heating body having a forward flow path from the inlet side to the outlet side, and a return flow path from the outlet side to the inlet side;
An outlet-side steam heating end portion having an outlet-side connecting flow path connecting the forward flow path and the return flow path on the outlet side;
It is formed in the steam heating member to heat the additive gas introduced from the outlet side steam heating end, and communicates with a first inlet side communication channel formed in a groove shape at the inlet side steam heating end. And an additive gas flow path for joining the additive gas and the corrosive steam . Oite to claim 1,
The steam heating member has a cylindrical shape, and the steam heating member is
A steam heating body having a forward flow path from the inlet side to the outlet side, and a return flow path from the outlet side to the inlet side;
An outlet-side steam heating end portion having an outlet-side connecting flow path connecting the forward flow path and the return flow path on the outlet side;
An inlet-side steam heating end portion having an inlet-side connecting flow path connecting the forward flow path and the return flow path on the inlet side;
Communicating with a first inlet side communication channel formed in the steam heating member to heat the additive gas introduced from the outlet side steam heating end and formed in a groove shape at the inlet side steam heating end And an additive gas flow path for joining the additive gas and the corrosive steam .

Images