JPS60162198A - Liquid-filled type heat exchanger - Google Patents

Abstract

PURPOSE:To contrive an improvement in a heat transmission coefficient, by a method wherein the external surface of a heat transfer tube is provided with a porous layer and as for the inner surface of the same, this side of a flowing direction of a fluid in the tube is provided with a rising surface and the opposite side of the rising surface is provided with an annular portrusion in the circumferential direction having a gentle slop. CONSTITUTION:The external surface of a heat transfer tube 10 of a liquid-filled type heat exchanger to be used for low heat head for generation due to temperature variations of sea water is provided with a porous layer 11 through flame spray coating of metallic particles. An inner wall surface of the heat transfer tube 10 is provided with an annular protrusion 12 which is extending in a prulurality of circumferential directions at intervals in the longitudinal direction of the tube. The annular protrusion 12 is constituted with a rising surface 12a rising at right angles with the longitudinal direction of the tube on this side of a flowing direction of a fluid in the inside of the heat transfer tube 10 and a gentle slope 12b descending toward the front of the flowing direction of the fluid from the upper end of the rising surface 12a. As for the rising surface, a height (e) of 0.2-0.7mm. is favorable and as to a ratio p/c of a pitch (p) of the rising surface to the height (e) of the rising surface, 20-80 is good. As for a flame- spraying metal for providing the porous layer on the external surface of the heat transfer tube, copper and a copper alloy are good for the quality of the material and 325-200 meshes are desirable for its grain size.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a flooded heat exchanger that heats a fluid to be heated outside a heat exchanger tube by a heating fluid flowing inside the heat exchanger tube. For example, the present invention relates to a flooded heat exchanger used in a low thermal drop power generation plant that generates electricity using low thermal drop energy such as seawater temperature difference.

[Technical background of the invention and its problems] Figure 1 is a schematic diagram of an ocean temperature difference power generation plant that uses temperature differences in seawater to generate electricity. The working fluid is heated and evaporated in the evaporator 1 by relatively high-temperature seawater at the surface of the ocean, and is introduced into the steam turbine 3 through the steam control valve, where it performs expansion work to drive the steam turbine 3 and generate steam. −(
2) The steam turbine 3 turns the generator V and generates ￥IL
Do the following. On the other hand, the steam discharged from the steam turbine 3 is condensed into relatively low-temperature seawater in the deep ocean in a condenser, and the condensed water is temporarily stored in a tank B.
The circulating pump 7 returns the water to the evaporator l.

Here, the amount of evaporation from the evaporator 1 is always kept constant, and the driving force of the steam turbine 3 is adjusted in response to load fluctuations of the generator V by opening and closing the engine valve r. This will allow you to respond accordingly.

However, in such a power generation plant, the temperature difference between the high and low heat sources is small, so the net efficiency of the transmission is low, on the order of several inches, and the heat load on the heat exchanger per unit power output is extremely large.
The manufacturing cost and installation space of the heat exchanger will be extremely large. On the other hand, low boiling point media such as chlorofluorocarbons have heat transfer characteristics that are about an order of magnitude worse than water, which is a conventional working fluid.

Therefore, in order to achieve higher performance and more compact heat exchangers, it is necessary to improve the heat transfer performance on the working fluid side, which defines the heat transfer coefficient.

In heat transfer tubes for evaporators, it is already known that the outer surface of the tube is subjected to machining, powder metallurgy, deposition of metal fibers, etc. in order to promote boiling heat transfer.

However, with this method, it is difficult to uniformly and economically form an uneven surface over a wide range of treated surfaces while suppressing thermal resistance with the tube wall.

Therefore, a heat exchanger tube for an evaporator has been proposed in which a copper sprayed layer is formed by flame spraying copper powder on the outer surface of the tube body to have excellent boiling heat transfer performance (JP-A-Sho, ?7-1 Review 67
issue). However, even if the heat transfer tubes described above are applied to heat exchangers used as evaporators in low heat drop power generation plants to improve the heat transfer performance on the working fluid side, the heat transfer performance on the seawater side in the tubes is low. Since the heat transfer coefficient of the evaporator is determined by the heat transfer performance of the seawater side in the tube, there is a problem that the effect cannot always be fully demonstrated.

For this reason, in order to achieve higher performance and more compact evaporators, it is also necessary to improve the heat transfer performance (3) on the seawater side of the pipe. By the way, as a method to improve the heat transfer coefficient inside the tube, conventionally, a threaded plate,
Inserting spiral blades to rotate the mainstream, inserting disks or rings at regular intervals in the flow path to disturb the mainstream, or providing protrusions on the heat transfer surface to disturb the boundary layer. A method is being taken.

However, in the case where a turbulence promoter such as the above-mentioned torsion plate is provided, the heat transfer coefficient is improved, but on the other hand, the pressure loss increases more than the proportion of the improvement in the heat transfer coefficient. However,
Using a turbulence promoter as described above in the evaporator of the power plant has problems such as the possibility that the equipment cost and power cost of the seawater circulation pump will increase more than the benefit obtained by improving the heat transfer coefficient. is.

[Purpose of the invention]

In view of these points, it is an object of the present invention to provide a flooded heat exchanger in which the heat transfer efficiency of the heat transfer tubes is sufficiently increased without any particular increase in power costs.

[Summary of the invention]

The present invention provides a flooded heat exchanger in which a fluid to be heated outside the heat transfer tube is heated (≠) by a heating fluid flowing inside the heat transfer tube, in which a porous layer is provided on the outer surface of the heat transfer tube. At the same time, a plurality of annular protrusions extending in the circumferential direction are formed on the inner surface of the tube, which are made up of an upright surface on the front side in the flow direction of the fluid in the pipe and an inclined surface that gently descends from the upper end of the upright surface along the flow direction of the fluid. It is characterized by this.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 2 to 6.

FIG. 2 is a longitudinal sectional view of a heat exchanger tube in the flooded heat exchanger of the present invention, and the outer surface of the heat exchanger tube 10 has a porous layer formed by flame spraying metal powder particles. It is provided. Further, a plurality of annular protrusions /2 extending in the circumferential direction are formed on the inner wall surface of the heat exchanger tube IO at intervals in the tube longitudinal direction. As shown in FIG. 3, the annular protrusion 7.2 has an upright surface /Ja whose front side in the flow direction of the fluid flowing inside the heat exchanger tube IO stands up at right angles to the longitudinal direction of the tube, and this upright surface. /, 2a, and a gentle slope descending from the upper end of 2a toward the front in the fluid flow direction shown by the arrow.

By the way, as mentioned above, the factors related to the boiling performance of heat exchanger tubes with a porous layer provided on the outer surface are the type of metal to be sprayed, the size of the sprayed powder particles, the thickness of the sprayed layer, etc. As the sprayed metal, in order to reduce the M resistance of the sprayed coating and layer, it is desirable to use a phase with high thermal conductivity such as copper or copper alloy. That is, the higher the thermal conductivity, the lower the thermal resistance in the sprayed coating layer, so the higher the tube wall temperature υ, the more effective the porous layer will be.

On the other hand, it is desirable to use thermal spray powder particles with a particle size coarser than 3.25 mesh and finer than 200 mesh. In other words, if the particle size is less than 3.25 mesh, the spread from the spray nozzle will not be large and the spraying efficiency will be likely to deteriorate.On the other hand, if the particle size is coarser than 200 mesh, the unmelted particles on the surface of the heat transfer tube will be reduced. This makes it difficult to form a welding material with sufficient adhesion strength. FIG. As the temperature rises, the heat transfer coefficient increases.

On the other hand, in order to obtain the characteristic values of the heat exchanger tube provided with the annular protrusions, the pressure loss and heat transfer coefficient were measured, and the results of the measurements showed that the difference between the heat exchanger tube and the smooth tube with constant pressure loss The characteristic values are shown in Figure 3. In this case, the pressure loss can be reduced by changing the flow rate in the pipe to OJ~ti, oI'/8, and the heat transfer coefficient can be calculated by keeping the flow rate constant (approximately 2.θ) and changing the heat load. Obtained.

In Fig. 2, the abscissa axis represents the interval P between the annular protrusions and the specific gravity of their upright surface height δθ, and the ordinate axis represents the pump power (pressure loss) and heat load under constant constraint conditions. The ratio between the heat transfer coefficient α' of the heat transfer tube of the present invention and the heat transfer coefficient α8 of the smooth tube in and. This is a diagram taken from .

As is clear from the figure, the direction of the arrow in Figure 3 (forward direction)
When a body is placed under the flow, as the height θ of the upright surface increases, the ratio of the heat transfer coefficient increases. gradually increases, reaching a maximum value of 7.4t-7 when the height e of the upright surface is o and smO. Furthermore, when the height of the upright surface becomes thicker α', the ratio x1 of the heat transfer coefficient decreases on the contrary.

On the other hand, when the fluid flows in the direction opposite to the arrow (reverse direction), the above a'/a as shown by the dotted line. Others will be small. Therefore, the upright surface should be on the front side in the fluid flow direction, and the height θ of the upright surface should be:
From a practical standpoint, O9.2 to 0.7 is preferable, and 0.3 to 0.7.
In addition, heat exchanger tubes with too large protrusions tend to have dirt attached to the vicinity of the base of the protrusions, which is difficult to remove, increases the dirt coefficient, and reduces the heat transfer coefficient. Therefore, there is no point in trying to promote heat transfer inside the tube. For this reason, the shape of the inner surface of the heat exchanger tube must be such that it can fully demonstrate the effect of sponge ball cleaning or brush cleaning, and from this point of view as well, the height of the upright surface elj: 0.
71 JL or less is preferable.

Furthermore, the ratio p/1 of the pitch p of the upright surface to the upright surface θ
0, as V6 increases, the ratio of heat transfer coefficients a′
/a8 gradually increases and reaches its maximum value when 1IsO.

Then, as the crane grows larger, it gradually decreases. Therefore, &- is preferably 3 to Sθ, more preferably 30 to 60.

FIG. 6 is a diagram showing the relationship between the heat transmission coefficient and the sprayed layer thickness of the heat exchanger tube according to the present invention, and is a diagram showing the results of a test conducted using Freon as the working fluid. Therefore, the heat transmission coefficient increases as the sprayed layer becomes thicker, but the rate of increase gradually decreases, and when the sprayed layer is 100 μm or more, the heat transmission coefficient becomes a constant value. Therefore, the thickness of the thermal spray layer applied to the outer surface of the heat exchanger tube having the above-mentioned annular protrusion on the inner surface is 100 to 100. When the thickness is 200 μm, the heat exchanger according to the present invention is most efficient.

In addition, as for the manufacturing method of the above-mentioned heat exchanger tube, firstly, a strip-shaped strip is rolled and then plastically worked into the optimal protrusion shape described above. After forming a pipe so that the formed protrusions are on the inside, the joints along the longitudinal direction are welded to produce a pipe having protrusions on the inner surface and a smooth outer surface. Then,
In order to increase the adhesion strength of the thermal spray layer, as a pretreatment for thermal spraying, the outer surface of the heat transfer tube is treated with alumina grid, and then copper or copper alloy powder with a particle size of 200 to 3.25 mesh is applied to 100 to 200 μm. A porous layer is formed by flame spraying on the outer surface of the heat transfer tube to a thickness of .

〔Effect of the invention〕

As explained above, in the present invention, a porous layer is provided on the outer surface of the heat transfer tube, and a raised surface is provided on the surface of the porous layer on the front side in the flow direction of the fluid in the tube, and a surface is formed from the upper end of the raised surface along the fluid flow direction. By forming a plurality of circumferentially extending annular protrusions consisting of gently descending slopes, it is possible to improve the heat transfer performance on both the inside and outside of the heat exchanger tube and to suppress the pressure loss of the fluid flowing inside the heat exchanger tube. The efficiency of the heat exchanger can be further improved, and when used in a power generation plant or the like that utilizes low heat drop energy, the heat energy can be fully utilized without being particularly large.

[Brief explanation of drawings]

Figure 1 is a schematic system diagram of an ocean temperature difference power generation plant, Figure 2 is a longitudinal cross-sectional view of a heat exchanger tube in the heat exchanger of the present invention, Figure 3 is an enlarged perspective view showing the inner surface of the heat exchanger tube, and Figure 1 is a copper A diagram showing the influence of the sprayed layer thickness on boiling heat transfer of a thermal sprayed tube. Figure 5 is a diagram showing changes in the heat transfer coefficient with respect to the height and pitch of the annular protrusion. Figure 6 is a diagram showing the influence of the sprayed layer thickness on the boiling heat transfer of the thermal sprayed tube. FIG. 3 is a diagram showing the relationship between the thermal transmittance coefficient and the sprayed layer thickness. 10... Heat exchanger tube, //... Porous layer, /2... Annular projection, /Ua... Upright surface, /B... Inclined surface. Dispatch agent boar crotch erasure 486 thin jN4 special (pm) l fi5mon ξ 6th; Minami eyebrow thickness A! (ILm)

Claims (1)

[Claims] 1. In a flooded heat exchanger that heats a fluid to be heated outside the heat exchanger tube by a heating fluid flowing inside the heat exchanger tube, a porous layer is provided on the outer surface of the heat exchanger tube. At the same time, a plurality of annular protrusions extending in the circumferential direction are formed on the inner surface of the tube, consisting of an upright surface on the front side in the flow direction of the fluid in the pipe and an inclined surface that gently descends from the upper end of the upright surface along the fluid flow direction. A flooded heat exchanger characterized by: A patent characterized in that the porous layer is formed on the outer surface of the heat transfer tube by flame spraying copper or copper alloy powder with a particle size of 0 to 326 mesh to a thickness of 100 to 200 μm. A flooded heat exchanger according to claim 1 JJ. 3. The height of the annular protrusion is 0.3~o, sm, the height of the annular protrusion (
1) The flooded heat exchanger according to claim 1, characterized in that the pitch between the s.