JPS60202289A - Liquid film downcoming type vertical heat exchanger - Google Patents

Abstract

PURPOSE:To control the boiling state of liquid film in a heat transfer pipe at its upper part and consequently prevent the liquid film from separating by a structure wherein a heat transfer buffering body is interposed onto the outer surface of the heat transfer pipe at its upper part. CONSTITUTION:A heat transfer buffering body is located onto the outer peripheral surface of the heat transfer pipe at its upper region so as to suppress the heat flow in the direction of pipe wall thickness in said region. The heat transfer buffering body 1 is made of metallic fibers 1'. The heat transfer buffering body 1 contacts with high temperature condensate, resulting in holding liquid water among the fibers due to the surface tension of the water. Concretely, because the condensate generates on the outer peripheral surface of the fibering body 1 due to the condensing heat transfer of steam having saturation temperature and shifts itself in the direction of the thickness of the buffering body 1 by diffusion, the state of coexistence of fiber and water is realized in the buffering body 1 during usage, resulting in enabling to have the thermal conductivity of the buffering body 1 determined by the coefficients of thermal conductivities and the ratio of volumes of the fiber and the water.

Description

[Detailed description of the invention] [Technical field of the present invention] The present invention relates to a vertical liquid film descending heat exchanger.

[Background technology]

The liquid film descending type (also called the wet wall type) vertical heat exchanger is a type of heat exchanger that belongs to the shell-and-tube type multi-tube type heat exchanger. This is a type of heat exchanger that allows all water vapor to exist at saturation temperature. A liquid film of a certain thickness of the liquid to be heated is formed on the inner wall surface of the heat transfer tube, and the liquid is allowed to descend by the gravity of the liquid, and the outer surface of the heat transfer tube is brought into full contact with water vapor at a saturated temperature to reduce condensation and heat transfer. Heats the liquid inside the tube. Naturally, the saturated temperature steam on the outer surface of the heat exchanger tube is maintained at a constant pressure, so unless the tube is immersed in condensed water, the steam temperature and heat transfer coefficient on the outer surface of the heat exchanger tube will be constant values in the tube length direction.

On the other hand, the temperature of the liquid (liquid film) inside the heat transfer tube increases due to heating, and an action occurs that tries to shift the liquid temperature, pressure, liquid composition, and gas composition to a vapor-liquid equilibrium state, and from non-equilibrium to equilibrium. Boiling and evaporation occur as migration transients. By taking this evaporated substance out of the heat exchanger, the pressure inside the tube and the vapor pressure of the evaporated substance are maintained at a constant value, and the tube ′
Constant boiling and evaporation of the internal liquid.

This liquid enters from the top of the heat transfer tube and is discharged from the bottom.
The composition of the liquid in the heat transfer tube differs widely between the upper and lower parts, and in the lower part, the concentration of the liquid increases as a result of substances with high vapor pressure moving to the gas phase side, and boiling gradually decreases. From another perspective, it can be said that boiling decreases due to the increase in boiling point. The water vapor temperature (pressure) on the outside of the heat exchanger tube of the kerosene liquid film descending type heat exchanger is set to the conditions necessary to obtain the desired liquid concentration at the lower end of the heat exchanger tube.

However, the composition and temperature of the liquid in the tube above the heat transfer tube, and the composition of the gas phase in the tube, are of course significantly different from the equilibrium conditions, and the boiling state changes depending on the degree of non-equilibrium.

[Object of the present invention]

An object of the present invention is to provide a liquid film descending type vertical heat exchanger whose performance is completely improved by fully controlling the boiling state of the liquid film inside the tube of the upper blade of the heat transfer tube.

[Configuration of the present invention]

As a means for achieving the above object, the present invention includes a heat transfer buffer interposed on the outer surface of a certain length of the upper part of the heat transfer tube. That is, the present invention provides a liquid film descending type vertical heat exchanger characterized in that a heat transfer buffer made of fibrous materials laminated in a cylindrical shape is interposed on the outer surface of a certain length of the upper part of the heat transfer tube. be.

In a vertical liquid film descending heat exchanger, when concentrating a liquid whose boiling point increases due to an increase in the concentration of a desired substance in the liquid, the temperature difference between the inside and outside of the tube in the upper region of the heat transfer tube is large, resulting in strong nucleate boiling. (Depending on the liquid composition, film boiling may occur), which may cause liquid film peeling. As an example, the heat transfer coefficient of the inner and outer surfaces of the tube is 10.000 kca'l/m"hU, the tube thickness is 5 mg,
Thermal conductivity of pipe materials! i 0 kca'l/m, hjc, the heat transmission coefficient is 5 x 10' when the temperature difference between the inside and outside of the tube is 80C
kcal/m"h, and this condition is in the strong nucleate boiling region from the diagram of pure water in Figure 1. (Pure water is rarely handled industrially, but it is presented as an example.) , 1st
The figure is an example of a boiling curve of water at atmospheric pressure, 'I'w-
T8 is the temperature difference between the metal temperature of the heat transfer surface and the saturated water temperature. Further, in FIG. 1, A and B are convective heat transfer regions, B and D are nucleate boiling heat transfer regions, and E and G are film boiling heat transfer regions. (Source: "Heat Transfer Engineering" by Hideo Uchida, Shokado Publishing, published in 1970, p. 251) By the way, as is well known, in the heat transfer tubes of industrial heat exchangers, the liquid inside the tubes is Liquid film peeling should occur due to the action of Na due to multiple factors such as viscosity, density, liquid film thickness, and the above-mentioned liquid film boiling, but in the present invention, a heat transfer buffer is provided on the outer surface of the tube in the upper region of the heat transfer tube. By adjusting the boiling strength of the liquid film in the tube, separation of the liquid film can be prevented.

Hereinafter, the present invention will be explained in detail based on FIGS. 2(A), 2(B), 5, and 4.

The heat transfer buffer of the present invention is positioned on the outer circumferential surface of the tube in the upper region of the heat transfer tube to suppress heat transfer in the tube thickness direction in the upper region, and the full cross-sectional view of its structure is shown in FIG. ),
As shown in (B). Figure 2 (7!) shows the heat transfer buffer 1 made of metal fibers 1', and Figure 2 (B) shows the heat transfer buffer 1 made of a composite material using metal fibers 1' and organic fibers 1' at the same time. These are all specific examples of the heat transfer buffer according to the present invention.

The heat transfer buffer 1 in the present invention is in contact with high temperature condensed water,
Liquid water exists between the fibers due to the surface tension of the water. In other words, in this buffer body 1, condensed water is generated on the outer peripheral surface by condensation heat transfer of water vapor at saturated temperature, and this water moves in the thickness direction of the buffer body 1 by diffusion, so that fibers and water do not mix during use. They coexist, and the thermal conductivity becomes a value determined by the thermal conductivity and volume ratio of fiber and water. Further, the thickness, fiber diameter, inter-fiber distance, and fiber material of the buffer body 1 can be arbitrarily determined depending on the intended use.

In addition, when creating a composite material structure that uses both metal fibers such as stainless steel and organic fibers such as cotton at the same time [Figure 2 Italy]
] or a structure using these alone [FIG. 2(A)], both are effective in the present invention.

To explain the effectiveness of the heat transfer buffer in the present invention based on FIG. 3, the heat transfer buffer 1 in FIG.
The wire (105@@φ is made of gold and assembled and formed so that the volume ratio of the metal wire and condensed water is α3. In Fig. 3, 20 is the metal tube wall, and 21 is the liquid film. Yes. 5th
In the figure, the thickness of the metal tube is 5 m+, and the thickness of the heat transfer buffer is 4 mm. The average heat conduction of this heat transfer buffer 1 is λ= a 5 kcal/m, h, c for water, and λ = 15 kcal/m for 5US304 wire.
, h, 'C, [α5X0.7)+(1
5Xα3) = 4.85 kcal/m, h, 'c.

Using one heat transfer buffer shown in FIG. The heat transfer coefficient when the temperature difference between the saturated temperature steam and the outside saturated temperature steam is 80° C. is as shown in Table 1, and as is clear from Table 1, the effectiveness of the present invention is recognized.

Table 1 Note that by applying the present invention, the heat transfer efficiency as a heat exchanger decreases compared to the conventional structure, but this can be improved by increasing the length of the heat transfer tubes or increasing the number of tubes. Heat transfer f can be easily ensured.

Further, the thickness of the heat transfer buffer of the present invention can also be varied in the longitudinal direction of the pipe. Of course, if the heat transfer buffer of the present invention is not needed in the lower region of the tube, there is no need to attach it.

FIG. 4 is a longitudinal cross-sectional view of a liquid film descending type vertical heat exchanger which is an embodiment of the present invention. A heat transfer buffer is provided. This heat exchanger is composed of an upper cover 2, a tube plate (base part) 5, a shell 4, a tube plate (lower part) 5, and a lower cover 6''. The heat is introduced into the exchanger, passes through the heat exchanger tube 8 with a heat transfer buffer 1 interposed therebetween, passes through the heat exchanger tube 8 without this buffer, is heated by heat medium vapor, and is taken out from the liquid outlet nozzle 9.On the other hand, the heat The medium vapor is supplied from the heat medium inlet nozzle 10 and is discharged from the drain outlet nozzle 11 as a condensed liquid of the heat medium.

In addition, in FIG. 4, 12 is a gas outlet nozzle,
15 is a baffle.

Although the present invention has been described in detail above, the present invention is not limited to any of the materials, dimensions, composition, temperature, and pressure of the heat exchanger tubes, the composition, temperature, and pressure of the liquid inside the tubes, and the type, pressure, and temperature of the heat medium outside the tubes. do not have. Further, the present invention can be applied not only as a countermeasure against liquid film peeling, but also as a countermeasure against severe corrosion of heat exchanger tubes due to a large heat transmission coefficient.

[Effects of the present invention]

As described in detail above, the present invention has a heat transfer buffer interposed on the upper outer surface of the heat exchanger tube, so that the boiling state of the liquid film in the upper tube of the heat exchanger tube can be controlled. As a result, the effect of preventing liquid film peeling is produced.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a boiling curve of water at atmospheric pressure, and FIG. 2 shows a specific example of the heat transfer buffer according to the present invention. FIG. 4 is a longitudinal cross-sectional view of a descending liquid film type vertical heat exchanger according to an embodiment of the present invention. 1.Heat transfer buffer 1'..Metal fiber 1'..Organic fiber 2..Top cover 5..Tube plate (upper part) 4..Body 5..Tube sheet (lower part) 6..Lower cover 7m・Liquid inlet nozzle 8・・Heat transfer tube 9・・Liquid outlet nozzle 10・・Heating medium inlet 11@・Drain outlet nozzle 12@・Gas outlet nozzle 15・・Baffle 20・・Metal tube wall 21・・Liquid membrane reagent Number of people 1) Meifuku agent Ryo Hagiwara - Tw-Ts (deg) Figure 4

Claims (1)

[Claims] A liquid film descending vertical heat exchanger characterized in that a heat transfer buffer made of cylindrically laminated fibrous materials is interposed on the outer surface of a certain length of the upper part of a heat transfer tube.