DE1526996A1 - Process for operating a heat exchanger and carrying out the same - Google Patents

Description

Oberhausen, January 12, 1966 serial no. 1398 ZZ / Ew.

PATENT APPLICATION

Method of operating a heat exchanger and its implementation

The invention relates to a method for operating a with the primary cooling medium of a reactor, in particular Pressurized water reactor, charged heat exchanger operating at low mass flow, and an embodiment of the same.

The mass flow is to be understood as the amount of medium that passes through a specific plane in a given time Area flows. It is generally believed that high mass flow numbers-at Forced circulation heat exchangers are required to maintain the quality at which the bubble evaporation ceases to enlarge and increase the heat transfer coefficient for film evaporation at and above the bubble evaporation limit.

The limit of bubble evaporation in a forced flow heat exchanger is of particular importance because

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they create a sharp dividing line between the high heat transfer coefficients draws that usually occur in vesicle evaporation, and the relatively low V / poor transition figures, resulting from film evaporation. Bubble evaporation is due to the formation and release of vapor bubbles on the heat-transferring side of the Y / arm transition area marked, whereby the liquid still wets the side, while with aer film evaporation the heat-transferring side with a liampffilm is occupied. To heat from the transmitting side to the liquid to transfer, a temperature gradient is required. In certain operating conditions, the size of this gradient mainly depends depends on whether there is bubble or film evaporation.

During the evaporation of the bubbles, the dissolve on the heat transfer surface The vapor bubbles that form quickly move and move with the liquid, the resulting disquiet of the mixture an excellent heat transfer coefficient results in β During film evaporation, a vapor film forms over it the heat transfer surface, so that steam generation does not take place on the heat transfer surface, but at the interface between liquid and vapor · The film of vapor causes the liquid cannot wet the surface and the resulting heat transfer coefficients are low. The steam film namely acts as an insulating layer which decelerates the speed with the heat from the heat-receiving surface

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is transferred to the liquid. Lie temperature of the heat-absorbing The area is therefore higher than in the case of bottle evaporation under the same ... air flow conditions, and the point at which the ■ Bubble evaporation turns into film evaporation, is used as a limit the vesicle evaporation. It can be seen that while local overheating in the tubes oei bubble evaporation does not take place in the Viarmeüber ^ angsbereich Problem of tube overheating in the film boiling area depending on the heat flow and given flow of air within the V / heat transition area is.

In order to achieve maximum efficiency in a V / heat exchanger It is important to achieve the liläsohenverdampi'ung in one possible 'Maintain a wide range. So far, the general line has been that one is forced to cure I / heat exchanger in a relatively high mass flow area have to work. i) It seemed as if od. -r. with iem the mass flow the Biäachenverdampfun ^ s limit would decrease further. Leary examinations have shown that there is a point both; the vaporizing of vapors in another The sinking of the lilast flow begins to rise.

The construction of a heat exchanger operated in the Z'.vangdurohiauf depends on a number of factors such as: 3. Speed, iilassenfiuj, heat flow, pressure and structure of the container. So far it has been assumed that high Lassen flows are required

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thus the necessary high bubble evaporation limit in this heat exchanger and also the maximum cooling effect the heat exchange surfaces in the film evaporation area to avoid local overheating is achieved. When it it became apparent that forced run operation in a relatively low!, flow range is possible, was recognized, that such low mass flow ratios are advantageously used in forced flow heat exchangers can that aroeiten in connection with nuclear reactors, in particular pressurized water reactors. The primary coolant outlet temperatures from solji.en xieo.ctors are relatively low. That Coolant is pressurized to evaporate in the heater and consequently it is circulated at high pressures but at fairly low temperatures.

The invention is based on the object of a method create after a heat exchanger operated in forced flow can work in the bubble evaporation area using low flow rates, as well as a heat exchanger to carry out this procedure "

This object on which the invention is based is achieved in that the medium to be evaporated is mixed with part of the already evaporated medium when it enters the heat exchanger, the medium to be evaporated flowing downward in a case chamber and up to the saturation temperature

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is heated and then in the riser chamber with immediately incipient evaporation in countercurrent to the primary medium flows upwards to complete evaporation, where the greatest Part of the steam is discharged to the consumer via the superheater and the smaller part is mixed back into the incoming medium »This ensures that the heat exchanger works at low mass flows in the bubble evaporation area.

Further features of the invention emerge in connection with the following description. The drawing shows an embodiment of a heat exchanger according to the invention which is suitable for carrying out the method according to the invention. It shows:
Fig. 1 shows a vertical section through a heat exchanger according to the invention

FIG. 2 shows a section along the line I-I in FIG. 1 5 shows a section along the line II-II.

As can be seen from FIG. 1, there is the heat exchanger 1 from a vertical cylindrical pressure vessel 2, which is closed at its ends with the lids 3 and 4. In the upper part of the container 2, the tube plate 5 is arranged, which in connection with the cover 3 forms the inlet chamber 6 forms for the primary cooling medium, while the arranged in the lower part of the container 2 Hohrplatte 7 in connection with the Cover 4 forms the outlet chamber 6 a. A bundle of straight tubes 8 extends vertically between the tube plates 5 and 7.

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These tubes 8 are each at a certain distance from one another Surrounded by the .Pipe plates 5 and 7 held casing 9, so that a falling chamber 10 and a rising chamber 11 is created · Through the openings 12, these two chambers are connected to one another. The upper end of the drop chamber 10 is closed by the ring plate 13 » Within the riser chamber 11 several tube guide plates H are arranged at the same distance from one another.

In the upper part of the dough chamber 11, i. h, above the openings 12,

steering walls 15 »16 and 17 (see Fig. 1, 2 and 3) are arranged, to achieve a tortuous flow of the secondary medium over the it-tubes. This part of the riser chamber serves as a superheater 18. The steam outlet nozzles are located approximately in the middle of the superheater 19 in the return container wall.

At the upper end of the fall chamber 10, the inlets 20 for the medium to be evaporated are arranged, which extend through the wall of the Container 2 up to the collector 21 extend. The collector 21 owns a plurality of small openings 22 in its lower

During operation, this flows, for example, from a pressurized water reactor incoming primary cooling medium through the nozzle 25 into the inlet chamber 6. From here it passes through the pipes 8 to Outlet chamber 6 a, from which the primary coolant leaves the steam generator through the nozzle 24.

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The medium to be evaporated b ^ w. the secondary medium flows through the entries 20 to the collector 21. Distributed from this collector the secondary cooling medium, which has a temperature the somewhat below the saturation temperature corresponding to the Operating pressure of the secondary system is evenly in the upper Part of the falling chamber 10. At the same time, steam escapes from the rising chamber 11 through the openings 12 into the fall chamber. The steam condenses as a result of a small drop in pressure, creating a suction, the steam from the interior of the Steigkaainer 11 in the Falling chamber 10 sucks in, and while flowing downwards, the steam releases its latent heat of vaporization to the secondary medium, so that aas Mixture comes essentially to Süttigung temperature. Of the Fall chamber 10 flows the Sekunaärinedium into the oteigka: .. n: er 11 and, since it essentially has the saturation; unstemyeratur, begins its vaporization instantly. The ecological medium flies upwards the head around and there will be a vaporization of bubbles as it flows through in countercurrent and in indirect exchange of heat with the Maintain primary medium in the pipes. The small amount and the temperature of the secondary medium, which flows within the falling chamber, are dimensioned correspondingly to a natural one Circulation of the secondary medium in the upward flow around the tube around to ensure.

When the secondary medium flows up through the riser chamber 11, is steam of saturated steam quality in the space from the lower tube plate 7 to the openings 12 of the envelope 9 of the riser chamber generated. Most of the steam flows in from here

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a winding path corresponding to the steering walls 15 »16 and 17 over the doorway, whereby it is overheated. The superheated steam ¹ then leaves the heat exchanger through the outlet nozzle 19, so there is only a cross countercurrent with high secondary medium velocity in the superheater part 18, while in the larger lower part of the heat exchanger there is a pure counterflow with a low secondary medium velocity. In addition to a low pump output for the secondary medium, the arrangement of the guide walls results in a significant reduction in the heat exchanger surface due to the use of twice the heat transfer coefficients in some areas.

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Claims (4)

Oberhausen, January 12, 1966 serial no. 1398 ZZ / Ew. PATENT CLAIMS 1V Procedure for operating a with the primary cooling medium a reactor, in particular a Liruckwasserreaktor, charged heat exchanger, which works at low mass flow, characterized in that the medium to be evaporated upon entry into the heat exchanger with part of the already evaporated medium is mixed. 2. The method according to claim 1, characterized in that the medium to be evaporated in a fall chamber (10) downwards flows and is heated to saturation temperature and then in the riser chamber (11) with immediately onset Evaporation in countercurrent to the primary medium flows upwards until complete evaporation, where the greatest Part of the steam is discharged to the consumer via the superheater (18) and the smaller part is returned to the incoming Medium is admixed. 3. Heat exchanger for performing the method according to claim 1 and 2, daduroh that in the envelope (9) of the riser chamber (11) at the level of the inlet (20) for the Secondary medium openings (12) are provided. BATH ORIGINAL 90988 3 / 06ΑΛ _ ₂ - Jb 4. Heat exchanger according to claim 3 »characterized in that in the superheater part (18) of the riser chamber (11), pipe walls (15 »16 and 17) are arranged for the secondary medium. 90988 3/06 / »4 ORIGINAL INSPECTED