Steam injector

Abstract: A steam injector is comprising: a casing provided with a steam intake port and a water supply port; a steam nozzle disposed inside the casing and communicated with the steam intake port for introducing steam into the casing; a water nozzle disposed inside the casing and communicated with the water supply port for introducing water into the casing; a steam-water mixing nozzle disposed inside the casing and on a downstream side of the steam nozzle and the water nozzle; a steamk jetting nozzle disposed inside the casing so as to extend axially therein and have a front end facing the steam-water mixing nozzle; a diffuser disposed inside the casing and on a downstream side of the steam jetting nozzle, said diffuser being provided with a throat portion and a discharged port formed to the casing on a downstream side of the diffuser, and is characterized by said water nozzle being disposed inside said steam jetting nozzle, said water nozzle having front end with respect to a flow of water, said front end being formed so as to reduce a hydraulic equivalent diameter.

Description: BACKGROUND OF THE INVENTION The present invention relates to a steam injector for jetting highly pressurized water adapted to a boiler water supply particularly utilized for a water supply system in an emergency core cooling system such as light water reactor. A steam injector is generally utilized for a water supply system in a steam locomotive or a boiler of one type in which a steam is flown in its central region or another type in which a water is flown in its central region. First, with reference to Fig. 17, one type of the steam injector in which the steam is flown in its central region will be described. Namely, a steam injector shown in Fig. 17 has a casing 302 provided with a steam intake port 301, and a steam jetting nozzle 304 provided with a needle valve 303. The front, righthand as viewed, end of the steam jetting nozzle 304 is positioned naer a water suction port 305. A steam-water mixing nozzle 306 and a pressure increasing diffuser 307 are arranged on a downstream side of the steam jetting nozzle 304, which are communicated with a discharge port 309 through a check valve 308. The steam-water mixing nozzle 306 is provided with a throat portion 310 to which an overflow discharge port 312 communicating with an overflow water duct 311 is opened, which is otherwise closed in accordance with an operation. In the steam injector of the structure described above, when the needle valve 303 is drawn out from the steam jetting nozzle 304 by the operation of a handle 313 connected to one end, lefthand end as viewed, of the needle valve 303 and the steam taken into from the steam intake port 301 is hence jetted from the steam jetting nozzle 304, the pressure at the water suction port 305 is made negative by the condensation of the steam to a value below an atmospheric pressure and the water is sucked from a tank or the like. The steam is flown, while being condensed by a low-temperature water (less than 70°C) sucked from the water suction port 305, into the steam-water mixing nozzle 306 and then constitutes a downstream water flow at the throat portion 310. Namely, because an enthalpy η g of the steam is higher than an enthalpy η l of a saturated water by an amount corresponding to latent heat of evaporation, the latent heat evaporation is converted into a kinetic energy to thereby form a high velocity water flow. When this high velocity water flow passes the diffuser 307, the pressure is increased by an amount of ΔP shown in the following equation in accordance with a hydrodynamic theory. ΔP = (1/2) ρ W U t 2 (ρ W = water density; U t = flow velocity of high velocity water flow passing the throat portion) According to this equation, a discharge pressure higher than the steam supply pressure can be obtained by the steam injector. When the pressure on the outlet side of the diffuser 307 is sufficiently increased, the check valve 308 is automatically opened to thereby jet the pressurized water through the discharge port 309. However, in the steam injector of the structure described above, only the discharge pressure of about 7kg/cm 2 G could be obtained, and such discharge pressure is a value which can merely be utilized for a boiler of a steam locomotive. It is considered that the cause of such limited low pressure increase resides in the fact that the longitudinal, i.e. axial, sectional area of the steam jetting nozzle 304 is made small or narrow towards the front end thereof. Various attempts and studies have been carried out for increasing the discharge pressure utilized for the steam injector for an emergency core cooling system. Fig. 18 also shows a conventional example provided on the basis of these various attempts and studies. The steam injector shown in Fig. 18 has substantially the identical structure to that of Fig. 17, but it is not provided with a needle valve such as that 303 in Fig. 17. Namely, the steam injector has a structure as a diffuser having gradually increased inner diameter towards the downstrem side of the steam to thereby obtain a supersonic steam flow. A second nozzle is further located at the discharge side of the steam-water mixing nozzle 306 and the overflow discharge port 312 is formed on the upstream side of the throat portion 310. According to the steam injector of this structure, it is possible to obtain the discharge pressure of the amount about six or more times of the steam injector shown in Fig. 17. As described above, in the steam injector, the steam is mixed with the low-temperature water to thereby condense the steam, the thus released latent heat of evaporation is converted into the kinetic energy and then into the pressure energy to obtain highly pressurized water. Accordingly, for the operation of the steam injector, it is necessary for the water to be supplied to have a temperature being sufficiently low to the extent capable of condensing the steam, and usually, the water has a temperature lower by about more than 70°C than the steam saturation temperature. For example, when the steam injector is operated in the atmospheric pressure, it is necessary to use the water having a temperature of less than 30°C because of the steam saturation temperature of 100°C. As is apparent from the structures of the steam injectors and the operational principles, it is desired to exist large temperature difference bewteen the steam and the water at a time of being contacted to each other. However, in the described conventional structures, the heat of the steam is transferred to the water through the wall of the steam injection nozzle, so that the temperature of the water is made high in comparison with the water temperature of the the water supply time, thus the temperature difference being made small. Furthermore, since the heat of the steam in the steam jetting nozzle is released, a portion of the steam is condensed, thus reducing its volume, resulting in the lowering of the flow velocity of the steam. According to these reasons, the efficiency of the steam injector is itself reduced, and in an adverse case, the steam injector may be stopped in its operation. Furthermore, in the steam injector which is not incorporated with the needle valve, there is provided a problem of causing pulsation of the discharge pressure variable in a short period. In the case of application of the steam injector to a nuclear power plant, the osccillation caused by the pressure pulsation may adversely affect on the steam injector itself and the other equipments or lines, and therefore, it is required to reduce such pressure pulsation for ensuring a stable operation of the nuclear power plant. Since the pressure pulsation of the steam injecter is caused by the fact of the steam being not stably condensed, it is necessary for the reduction of the pressure pulsation to facilitate the condensation of the steam and to carry out continuous reaction. In order to achieve this purpose, it is considered to be effective to increase contacting area between the steam and the water. The contacting area between the steam and the water may be determined by the hydraulic equivalent diameter of the front end of the water nozzle. The hydraulic equivalent diameter corresponds to a value obtained by dividing the cross sectional area of the water nozzle port by the wetted perimeter length, and the contacting area can be increased by making small this value. However, since the the cross sectional area is determined by the capacity of the steam injector, in the conventional round-type nozzle in which the wetted perimeter length naturally corresponds to the peripheral length of the water nozzle port, the cross sectional area is also naturally determined. Accordingly, it may be said that the increasing of the contacting area between the steam flow and the water flow has a restricted limit. Figs. 19 and 20 further show other examples of the steam injectors of the prior art each in which the water is flown through the central region of the steam injector. Fig. 19 represents a horizontal type one and Fig. 20 represents a vertical type one, but both the steam injectors have basically similar structures to each other. That is, in the steam injector shown in Fig. 20, a water nozzle 316 is incorporated in a body 315 connected to the casing 302 and a needle valve 303 is inserted into the water nozzle 316, wherein the pressure of the steam is increased together with a steam from an adjacent steam suction port by a steam-water mixing nozle 306 disposed on the downstream side of the water nozzle 316. The steam injector shown in Fig. 20 has substantially the same structure as that of Fig. 19 but it is not provided with the needle valve. In a case where the conventional steam injectors are utlized as emergency water supply systems, the operation condition and the pressure are deemed as variable factors in balance to conditions on the water supply side, so that it is necessary for the injector side to reach a rated pressure as soon as possible and to keep a stable operation for a long time. Furthermore, it is desired to control the startup characteristic from the operation free from a complicated control system. Moreover, in the case of the steam injector being utilized as a fluid driving source, it is necessary for the steam injector to keep stable jetting condition. In the conventional structure of the steam injector, there is a case in which the jetting condition of the steam injector reaches the rated power in a certain time interval just after the operation of the steam injector and the jetting pressure lowers as the time passes thereafter. This is considered to be based on the deformation between the steam nozzle and the mixing nozzle due to temperature variation and pressure variation on the periods of the waiting condition and the operating condition. Accordingly, suppression of such deformation will result in the improvement of the operational characteristics. Although the adjustments of the flow rate and the pressure may be treated with the location of the needle valve, the performance of the steam injector is significantly affected by the positional relationship between the steam nozzle and the steam-water mixing nozzle and it is hence necessary to keep this positional relationship most suitable. However, in the conventional steam injectors, the operating temperatures are different from each other at the starting time at a normal temperature and at the operating time at a high temperature. This temperature difference results in the change of the positional relationship, which adversely affects on the originally expected performance. Furthermore, in the conventional steam injectors each in which the needle valve is provided, and the needle valve is shifted to adjust and change the flow area of the water supply nozzle to attain the optimum dischrge power, the flow areas of the steam is rapidly contracted at the steam jetting nozzle portion, thereby causing the supersonic steam flow. For this reason, there may cause a wear, due to the supersonic steam flow, to the outer wall surface of the water supply nozzle forming the steam jetting nozzle portion and the inner wall surface of the casing of the steam injector, and furthermore, there is caused an errosion at an area of the wall surface of the throat portion positioned downstream side of the steam jetting nozzle portion by the high velocity water flow, thus causing the wear to this portion. As described, when the wear to the respective wall portions progresses, the flow area itself changes, and hence, the balance of the flow rates of the water and the steam changes gradually, resulting in the degradation of the performance of the steam injector. With respect to the steam-water mixing nozzle, it becomes difficult to ensure a stable condensation of the steam. These problems are also made significant for the water supply device of an emergency core cooling system of a power plant, for example, which requires high reliability and performance. A steam injector according to the preamble of the appended claim 1 is known from US 4,569,635. The front end of the water nozzle of this known steam injector is formed with multiple openings or by an annular opening, whereby the hydraulic equivalent diameter of the front end of the water nozzle is reduced. By this reduction of the hydraulic equivalent diameter the condensation of the steam is facilitated, whereby the discharge water flow can be stabilized and a pressure pulsation can be reduced, as mentioned before. It is an object of the invention to provide a steam injector with further improved operating performance, especially improved operating stability and safety. A solution of this object is achieved by a steam injection according to appended claim 1. By forming the front end of the water nozzle in a star shape configuration the hydraulic equivalent diameter is very effectively reduced and the condensation of the steam is facilitated. This results in a further improved operating performance, especially an improved operating stability and safety. Appended subclaims are directed towards advantageous embodiments of the inventive steam injector. Claims 2 to 5 are directed towards an embodiment, by which the performance of the steam injection is further improved by providing means for controlling thermal extensions to keep constant the relative positional relationships between the different nozzles. Subclaims 6 to 10 are directed towards embodiments of the inventive steam injector which has a further improved performance by providing a wear resisting structure of relevant components. By features of subclaim 11 the performance of the steam injector is further improved. The further natures and features of the present invention will be more clarified by the following description made with reference of the accompanied drawings. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: Fig. 1 shows a longitudinal section of a first embodiment of a steam injector; Fig. 2 is a longitudinal section of a main portion, in an enlarged scale, of the steam injector of Fig. 1; Fig. 3 and Fig. 4 are views similar to that of Fig. 2, but are related to second and third embodiments of a steam injector; Fig. 5 shows an elevational section of an fourth embodiment of a steam injector according to the present invention; Fig. 6A is an illustrated section of a water nozzle of the steam injector of Fig. 5, and Fig. 6B is a section taken along the line IXXB-IXXB of Fig. 6A; Fig. 7A and 7B are views similar to those of Fig. 6A and 6B, but are related to a modification of the embodiment of Fig. 6A and 6B; Fig. 8 is a graph showing characteristic features of the water nozzles of the present invention of Fig. 6 in comparison with a conventional technique; Fig. 9 shows an elevational section of a fifth embodiment of a steam injector according to the present invention; Fig. 10 is an elevational view of a main portion, in an enlarged scale, of the steam injector of Fig. 9; Fig. 11 is an elevational section similar to that of Fig. 9, but is related to a sixth embodiment; Fig. 12 to 16 are longitudinal sections of a main portion, in enlarged scales, of a steam injector of a seventh embodiment of the present invention; and Fig. 17 to 20 are elevational and longitudinal sectional views of steam injectors according to the prior art. A first embodiment of a steam injector will be described hereunder with reference to Figs. 1 and 2, which is similar in a type to the steam injector of Fig. 17 in which a needle valve is incorporated, and the main differnce resides in the location of the steam jetting nozzle wall having a hollow portion or structure 115. Referring to Figs. 1 and 2 a steam injector has a casing 102 having a steam intake port 101 and a steam jetting nozzle 104 incorporated with a needle valve 103 is disposed in the casing 102. A water suction port 105 is formed near the steam jetting nozzle 104, and a steam-water mixing nozzle 106 is arranged on the downstream side, righthand side as viewed, of the water suction port 105. A discharge port 108 is further provided for the casing 102 on further downstream side of the steam-water mixing nozzle 106 through a diffuser 107 disposed for increasing a pressure of the steam. An overflow discharge port 112 is opened to a throat portion 109 of the diffuser 107. The steam jetting nozzle 104 is provided with a hollow wall portion 115 as a closed space structure so as to provide a so-called double wall structure. In the steam injector of the structure described above, when the steam is supplied into the casing 102 through the steam intake port 101 and the needle valve 103 is withdrawn from the steam jetting nozzle 104 by the operation of a handle 113, the steam is jetted from the steam jetting nozzle 104, condensed by a low-temperature water sucked from the water suction port 105 and then flown into the steam-water mixing nozzle 106, thus forming a high velocity flow at the throat portion 110. In this embodiment, a hollow portion or structure 115 is formed to the wall structure of the steam jetting nozzle 104. According to this structure, the heat transfer, through the wall structure of the nozzle, between the steam passing the steam jetting nozzle 104 and the water sucked from the water suction port 105 is substantially suppressed, thus significantly maintaining the temperature difference between the steam and the water both being mixed in the steam-water mixing nozzle 106. According to this embodiment, since the heat is substantially not transferred from the steam to the water, the steam is not condensed in the steam jetting nozzle 104 and the flow velocity of the steam can be suitably maintained, thus reducing an excessive amount of the steam supply. Moreover, the temperature increasing of the supply water before the mixing with the steam can be prevented, the temperature difference at the mixing time can be properly maintained. Accordingly, the water temperature is not lowered unnecessarily, and the condensation of the steam in the steam-water mixing nozzle can be ensured, thus maintaining the stable operation of the steam injector. Second and third embodiments of the steam injectors will be further described hereunder with reference to Figs. 3 and 4 , which are similar to Fig. 1 and in which like reference numerals are added to portions or elements corresponding to those of the first embodiment. In the second embodiment of Fig. 3 , a wall structure member 116 is disposed on the outer surface of the steam jetting nozzle 104, and in the third embodiment of Fig. 4, a wall structure member 117 is disposed on the inner surface of the steam jetting nozzle 104. In a modified embodiment, these wall structure members 116 and 117 may be both provided for the steam jetting nozzle 104. It is desired to completely close the space by these wall structure members 116 and 117, but a slight gap may be allowed. For this purpose, it is desired to construct the wall structure members 116 and 117 with a material having a superior heat insulation property such as ceramics. According to the second and third embodiments, substantially the same functions and effects can be expected when the completely heat transfer preventing condition is established, but in the case of the presence of the slight gap, the heat transfer between the steam and the water can be reduced in comparison with the metal material. Furthermore, the wall structure of the steam jetting nozzle 104 may be made likely to that of the conventional structure without providing any means such as hollow structure or wall structure members, but is formed of ceramics, which has coefficient of thermal conductivity remarkably smaller than that of a metal material to thereby attain heat insulation effect. According to the described embodiments, the wall structure of the steam jetting nozzle, which is usually formed of a metal material generally having high coefficient of thermal conductivity, is formed to have a hollow portion which is made vaccum or in which a low-pressure gas is filled up for preventing the heat transfer, or the wall structure may be formed as a honeycomb structure, whereby the heat transfer can be prevented or limited. Accordingly, the temperature increasing in the steam jetting nozzle can be preferably prevented before the condensation of the steam therein, whereby the temperature difference at the mixing time can be maintained largely, thus providing a steam injector having high performance and reliability. An fourth embodiment of the steam injector according to the present invention will be further described with reference to Figs. 5 and 6, in which a needle valve is not incorporated and in which like reference numerals are added to members or portions corresponding to those of Figs. 1 and 2 In Fig. 5 , a vertically arranged steam injector is illustrated, but this embodiment may be adapted for a horizontally arranged steam injector. Referring to Fig. 5 , the casing 102 is provided with the steam intake port 101, the water suction port 105 and an overflow discharge pipe 111, and within the casing 102 are disposed the steam jetting nozzle 104 and a star-shape water nozzle 118. The steam-water mixing nozzle 106 is disposed on the dischrge side of the steam jetting nozzle 104 and the water nozzle 118, and the diffuser 107 provided with the throat portion 110 is also arranged on the discharge side of the steam-water jetting nozzle 106. An overflow discharge port 112 is provided on the downstream side of the steam-water mixing nozzle 106. The overflow discharge port 112 and the overflow discharge pipe 111 are communicated with each other. The inventive star-shape water nozzle 118 is shown in Figs. 6A and 6B and has a front, lefthand as viewed, end formed in a star shape in a plan view. According to such star-shape structure of the water nozzle 118, a hydraulic equivalent diameter is made small, and an area contacting the steam is increased because the surface of the water jet from the star-shape water nozzle 118 is bubbled, thus facilitating the condensation of the steam. Accordingly, the pressure pulsation of the steam can be reduced by the location of the star-shape water nozzle 118. Fig. 7 shows a modified embodiment of Fig. 6, in which a multiple hole type water nozzle 119 is provided in place of the star-shape water nozzle 118 of Fig. 6 , and the multiple hole type water nozzle 119 is formed by forming a plurality, four in the illustrated embodiment, holes 121 by sectioning the front end of a conventional conical round type water nozzle by a sectioning member 120. The other structure of the steam injector of Fig. 7 is substantially the same as that of Figs. 5 and 6 . According to this modified embodiment, the hydraulic equivalent diameter is reduced, and accordingly, an area contacting the steam is increased because the water jetted from the holes 121 of the water nozzle 119 are divided into four fine water jets, thus facilitating the condensation. The pressure pulsation can be also reduced by arranging this multiple hole type water nozzle 119 to a portion at which a conventional water nozzle is arranged. Fig. 8 shows a graph in which is shown experimental results in the usages of the star-shape water nozzle and the multiple hole type water nozzle in which the hydraulic equivalent diameter is reduced in comparison with the conventional conical round type water nozzle. Referring to Fig. 8, the vertical axis represents a pressure pulsation (kg/cm 2 ) and the horizontal axis represents a hydraulic equivalent diameter (mm). As can be seen from this graph, the pressure pulsation can be significantly reduced to about half degree by forming the front end of the water nozzle so as to provide a star-shape or multiple hole structure. In Fig. 8, letters a, b and c are values of 7.6mm, 9.5mm and 16.2mm, respectively, thus confirming the effectiveness of the present invention. In another aspect of the present invention, a fifth embodiment of the steam injector is shown in Figs. 9 and 10. As can be seen from Fig. 9 the steam injector of this embodiment is of a type similar to that of Fig. 19, but arranged vertically, and duplicated explanation of portions is now omitted as far as it is not concerned with the present embodiment. Referring to Figs. 9 and 10, in general, in an illustrated steam injector, a casing 203 is composed of an upper casing half 203a and a lower casing half 203b, and a steam intake port 201 and a water supply port 202 is formed to the lower casing 203b. The casing halves 203a and 203b are unitarily joined by means of bolt and nut assemblies 203c and 203d. The steam intake port 201 is formed to a flanged portion 201a which is fastened to the lower casing 203b through a pipe 201b. The water supply port 202 is formed to a attaching flanged portion 202a which is fastened to the lower casing 203b. In the upper casing 203a, a valve shaft 204a for supporting a needle valve 204 is fastened by means of bolts 204b. The needle valve 204 is connected to the water nozzle adjsuting handle 214. A shaft seal 204c is disposed on the side surface of the needle valve 204 and the shaft seal 204c is pressed by a seal press cap 204d, which is fastened to the top portion of the upper casing 203a. A holder 216 is also mounted to the lower portion of the water nozzle adjusting handle 214, and the holder 216 is fastened to the top portion of the upper casing 203a by means of bolts 217 and also connected at its one end to a support rod 218. The front end of the support rod 218 is connected to the upper casing 203 through a pin 219. The steam supply nozzle 205 is fastened to the innser surface of the lower casing 203b by means of bolts 205a. The description of such constructions may be selectively applied to the embodiments described hereinbefore as illustrated in the respective figures. Further referring to Figs. 9 and 10, the needle valve 204 is disposed in the water supply nozzle 204. The steam jetting nozzle 206 is formed between the water supply nozzle 205 and the casing 203, and a steam-water mixing nozzle 207, a throat portion 208 and a diffuser 209 are disposed on the downstream side of the steam-water mixing nozzle 206. According to the pressent invention, in the steam injector of the structure described above, to the wall of the casing 203 forming the water supply nozzle 205 and the steam jetting nozzle 206 and to the surfaces of the steam-water mixing nozzle 207, the throat portion 208 and the diffuser 209 are formed wear resisting walls 211 formed of a wear resisting material such as ceramics, CRA (cobalt replaced alloy) or CFA (cobalt free alloy), and the water supply nozzle 205 is also formed of the wear resisting material of the kind described above. According to the structure described above, although the steam supplied from the steam intake port 201 becomes supersonic flow on passing the steam jetting nozzle 206, the wearing by this supersonic flow can be suppressed or prevented since the water supply nozzle 205 is formed of the wear resisting material and the wear resisting wall structure 211 is adapted for the necessary portions in the casing 203. Thereafter, the water flow passing the steam-water mixing nozzle 207 becomes high velocity water flow at the throat portion 208 and errosion will be hence caused at these portions, but the wear resisting walls 211 are formed on the inside of these steam-water mixing nozzle 207, the throat portion 208 and the diffuser 209, whereby the wearing due to such errosion cuased by the high velocity water flow can be preferably suppressed. The steam injector having such wear resisting structure can be hence applied to a water supply device in an emeregency core cooling system in a nuclear power plant requiring high reliability and high performance. Fig. 11 represents a sixth embodiment of the steam injector in which like reference numerals are added to portions or members corresponding to those shown in Fig. 9. In the embodiment of Fig. 11 there is provided a handle assembly 213 for adjusting the steam nozzle, which operates to vertically, i.e. axially, shift the water supply nozzle 215 to thereby control the steam flow area inside the casing 203. This steam nozzle adjusting handle assembly 213 is mounted to the upper casing 203a through a sheat plate 220 by means of bolt and nut assembly 203c and 203d. Namely, this embodiment provides the steam injector in which the water supply nozzle 205 provided with the needle valve 204 is arranged to the lower casing 203b having the steam intake port 201, the steam jetting nozzle 206 is defined between the water supply nozzle 215 and the casing 203, and steam-water mixing nozzle 207, the throat portion 208 and the diffuser 209 are disposed on the downstream side of the steam jetting nozzle 206, and in such steam injector, the wear resisting wall structures are formed, of the wear resisting material such as ceramics, CRA or CFA, to the wall surfaces of the water supply nozzle 215 and the casing 203 forming the steam jetting nozzle 206 and also formed on the side of the steam-water mixing nozzle 207, the throat portion 208 and the diffuser 209. The water supply nozzle 205 is also formed of the described wear resisting material. A fin 212 is mounted to the steam jetting nozzle 206 for forming swivelling flow of the steam so as to prevent the water from contacting the wall surface at the steam-water mixing nozzzle portion 207. Although the steam constitutes a supersonic flow at a time when the steam fed from the steam intake port 201 passes the steam jetting nozzle 206, the wearing due to the supersonic flow of the seam can be prevented because the providion of the wear resisting wall structure of the water supply nozzle 205 and the casing 203. Furthermore, the steam constitutes a high velocity water flow at the throat portion 208 through the steam-water mixing nozzle 206, and in these portions, errosions are caused, but the wear resisting wall structures 211 are formed to the inside portions contacting the water flow of the steam-water mixing nozzle 207, the throat portion 208 and the diffuser 209, thus preventing the wearing due to the errosion caused by the high velocity water flow. Moreover, the steam passing the steam jetting nozzle 206 through the steam intake port 201 constitutes a swivelling flow at the steam-water nozzle 207 by the location of the fin 212, and the water fed from the water supply port 202 through the water supply nozzle 205 is also swivelled by the influence of such steam swivelling flow and mixed with the steam at the central portion thereof, thus obtaining the stable latent heat of the steam. According to this sixth embodiment, the reliability of the steam injector can be enhanced by effectively preventing the wearing and the performance thereof can be also improved by the swivelling flow of the steam, whereby the steam injector can be applied to a water supply unit of an emergency core cooling system of a nuclear reactor, for example, which requires high reliability with high performance. A seventh embodiment of the steam injector according to the present invention will be described hereunder with reference to Figs. 12 to 16, which show structures or portions of the steam injector necessary for this embodiment and in which other portions or structures which substantially correspond to those of the former embodiments are omitted. Namely, in this seventh embodiment, the steam injector is provided with a control rib 429 at a portion, in which the steam flow likely stays, on the outside of the steam jetting nozzle 404 and the inside of the steam-water mixing nozzle 406. Referring to Fig. 13, on the operation start of the steam injector, a low-temperature supply water 431 flows in the steam jetting nozzle 404, and the supply water flow 431 is converted into the high-pressure steam flow due to the condensation of the low-pressure steam flow 430 inside the steam-water mixing nozzle 406. The converted steam flow is thereafter discharged downstream side. The steam flow is accelerated during the passing through the most narrow area A between the steam jetting nozzle 404 and the steam-water mixing nozzle 406 and then blasted as a supersonic high-temperature steam flow. In this operation, as shown in Fig. 14, a gap is initially formed between the steam jetting nozzle 404 and the steam-water mixing nozzle 406 for maintaining the optimum operating condition. However, the flow passage is narrowed as shown by a letter B by the thermal expansion or deformation of the steam-water nozzle due to the temperature and pressure changes of the steam-water mixing nozzle 406 in response to the operation progress, thus changing the steam discharge amount. In order to prevent such phenomenon of deformation, the control rib 429 is arranged to the steam-water mixing nozzle 406 in this fourth embodiment as shown in Figs. 15 and 16 . Namely, when the temperature is changed after the operation start, the control rib 429 is first thermally expanded and deformed as shown by reference numeral 433 in Fig. 16 to thereby ensure the necessary flow area and to suppress the power change due to the deformation of the steam-water mixing nozzle 406. In an alternation of this seventh embodiment, it may be possible to construct the steam injector body so as to be initially provided with the features of the control rib 429 and namely, there may be provided a body having a rigidity property for absorbing by itself the temperature and pressure changes of the steam-water mixing nozzle 406 during the operating period. Accordingly, it may be possible to construct the body to expand the gap between the steam jetting nozzle 404 and the steam-water mixing nozzle 406 in response to the operation progress of the steam injector, whereby the steam discharging performance can be controlled accordingly to improve the rapid startup. It is therefore necessary to form the control rib 429 with a material having a thermal expansion coefficient larger than that of a material of the nozzle portions. Four this purpose, it is desired to form the control rib of a material such as ferrite series low thermal expansion alloy or ceramics. In a modification, a springy structure may be adopted. In a case where it is desired to change the flow rate with time delay, it may be possible to utilize a high heat capacitance structure, for example, to utilize a closed loop coolant. According to this seventh embodiment, it is made possible to constantly maintain the flow passage between the steam jetting nozzle 404 and the steam-water mixing nozzle 406 during a stable operation period after the operation start of the steam injector and also possible to adjust the power output and the operating conditions. These advantages or merits can be achieved by the movable structure of the steam jetting nozzle in this fourth embodiment. Accordingly, the deformation of the steam-water nozzle during the operation can be prevented without utilizing a complicated structure of the steam injector and the stable operation can be also achieved with superior operational performance. This results in the improvement of the reliability of a machinery or system utilizing the steam injector according to the present invention. It is to be noted that the present invention is not limited to the described preferred embodiments and changes or modifications may be made without departing from the scopes of the present invention. For example, the control rib 429 shown in Fig. 12 may be applied to the other embodiment or the hollow wall structure or wall structure member of Figs. 2 and 3 may be applied to the other embodiments.

Claims: A steam injector comprising: a casing (102; 203) provided with a steam intake port (101; 201) and a water supply port (105; 202); a steam nozzle disposed inside the casing and communicated with the steam intake port for introducing steam into the casing; a water nozzle (118; 119) disposed inside the casing and communicated with the water supply port for introducing water into the casing; a steam-water mixing nozzle (106; 207) disposed inside the casing and on a downstream side of the steam nozzle and the water nozzle; a steam jetting nozzle (104; 206) disposed inside the casing so as to extend axially therein and have a front end facing the steam-water mixing nozzle; a diffuser (107; 209) disposed inside the casing and on a downstream side of the steam jetting nozzle, said diffuser being provided with a throat portion (110; 208); and a discharge port formed to the casing on a downstream side of said diffuser, wherein said water nozzle (118, 119) being disposed inside said steam jetting nozzle (104), said water nozzle (118) having front end with respect to a flow of water, said front end being formed so as to reduce a hydraulic equivalent diameter by increasing a surface area of the flow of water contacting the steam characterized in that said front end of the water nozzle (118) is formed in a star shape in a plan view so as to further increase the surface area contacting the steam. A steam injector according to claim 1, characterized by means (29) for controlling thermal extensions of the steam jetting nozzle (404) and the steam-water mixing nozzle (406) to keep constant relative positional relationship between these nozzles. A steam injector according to claim 2, characterized in that said control means is a control rib (429) integrally formed to the steam-water jetting nozzle, said control rib is formed of a material having a thermal expansion coefficient larger than that of the steam-water nozzle. A steam injector according to claim 3, characterized in that said control rib (429) is formed of a ferrite series low thermal expansion alloy. A steam injector according to claim 4, characterized in that said control rib (429) is formed of a ceramics material. A steam injector according to any of claims 1 to 5, characterized in that a wear resisting structure is formed to outer surfaces of said steam-water nozzle (207) and said diffuser (209). A steam injector according to claim 6, characterized in that said wear resisting structure is a wall structure formed of a wear resisting material. A steam injector according to claim 7, characterized in that said wear resisting material is a ceramics. A steam injector according to claim 8, characterized in that said wear resisting material is a cobalt free alloy or cobalt replaced alloy. A steam injector according to claim 6, characterized in that said water nozzle (204) is formed of a wear resisting material. A steam injector according to claim 6, characterized in that a fin means (212) is provided for the water nozzle for causing a swivelling flow of the steam in the steam-water mixing nozzle (207).

Inventors: MIYANO HIROSHI, NARABAYASHI TADASHI, TAKAHASHI HIDEAKI, TANAKA NOBUHIKO, YAMADA KATSUMI, YASUDA MAKOTO, MIYANO, HIROSHI, NARABAYASHI, TADASHI, TAKAHASHI, HIDEAKI, TANAKA, NOBUHIKO, YAMADA, KATSUMI, YASUDA, MAKOTO
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1992
Main classification: F04F5
IPC codes: F04F5