SU1698614A1 - High-temperature heat exchange pipe - Google Patents

Abstract

The invention relates to a power system and can be used in power plants with high-temperature coolant. The purpose of the invention is to increase the operational reliability and reduce the size. The heat exchange pipe 1 contains a fixed bed of balls 2 of the same diameter, placed between the permeable plates 3 and 4. The diameter of the balls 2 is 0.15-0.25 of the internal diameter of the pipe. 2 or

Description

The invention relates to a power system and can be used in transport power plants, mainly with high-temperature coolant.

Known heat exchange tubes with heat exchange intensifiers made in the form of a fixed dense filling of balls.

During operation, the coolant flows between the particles of the filling parallel to the walls. The intensity of heat removal from the pipe surface increases due to an increase in the velocity of the coolant near the pipe wall, on the one hand, and due to the heat conduction between the wall and the backfill of the balls, on the other hand. The efficiency of heat exchanging tubes with agar filling ensures the expediency of their use in compact transport heat exchangers.

In the well-known pipe pipe, the diameters of the balls of the backfill are less than the diameter of the pipe D so that the backfill can be considered as a quasi-homogeneous system (d / D). However, the thermo-hydraulic efficiency of such backfill is low. The table shows the relations of the Reynolds analogy factors (g a / A P, a is the heat transfer coefficient from the wall of the heat exchange pipe; D P is the pressure drop at the inlet and outlet of the pipe for various values of d / D related to the Reynolds r0 analogy factor d / d.

From the table it can be seen that the heat-hydraulic efficiency of the heat exchange tubes increases with an increase in the d / D ratio. Moreover, when d / D 0:15 with a decrease in d / D, the heat transfer coefficient from the pipe wall to the coolant drops. In balls located near the wall, a temperature gradient is observed, which, at high temperature pressures, generates large thermal stresses that can cause the balls to collapse and, consequently, the loss of efficiency of the heat exchanger tube. All this reduces the efficiency and reliability of the known heat exchange pipe.

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A heat exchange tube containing a charge of balls whose diameter is slightly larger than the radius of the tube (d / D Ј 0.5).

During operation, the coolant flows between the balls parallel to the pipe wall. The balls turbulent the flow of coolant, displace it to the pipe wall, thereby increasing the intensity of heat removal from the pipe surface. Increasing the d / D value to 0.5 or more permits an increase in the thermal-hydraulic efficiency of the ball fill (see table). However, when moving along a heat exchange tube of a high-temperature heat carrier, the balls are in the region of high temperature gradients causing thermal stresses that can cause the balls to collapse and the heat exchange tube to lose its functionality. In addition, at d / D of 0.15 with an increase in the value of d / D, the heat transfer coefficient from the pipe wall to the coolant decreases, which leads to the need to increase the length of the pipe for a given diameter and heat flux. These features reduce the reliability and increase the dimensions of the well-known heat exchange tube.

The aim of the invention is to increase the reliability of operation and compactness of the heat exchange pipe by choosing the optimal ratio between the diameters of the pipe and the backfill balls.

This goal is achieved by the fact that in a heat exchange pipe of diameter D containing a fixed bed of balls of the same diameter d placed between permeable plates (grids), according to the invention, the diameter of the ball of backfill is determined from the ratio d / D 0.2 ± ± 0.05.

In such a heat exchange tube, the coolant washes the balls, turbulence, is displaced by the balls to the wall and moves near it with greater speed than in the center of the pipe, due to an increase in the local difference of the ball backfill. All this causes an increase in the intensity of heat removal from the pipe surface. When moving in a high-temperature heat transfer pipe, it is advisable to use ceramic or steel balls, for which the dependence of the dimensionless heat transfer coefficient aa / Oo (O index, as above, refers to backfill with d / D - 0) on the ratio d / D obtained by The basis of the experiments is shown in FIG. 2a From FIG. 2a, it can be seen that the maximum heat output is reached at d / D = 0.15. The magnitude of the temperature gradient is reached in a tube filled with balls

inversely proportional to the effective thermal conductivity coefficient Aeff. Based on the experimental data for steel and ceramic balls placed in a pipe,

The dependence of the dimensionless value of the effective thermal conductivity Deff / Aeff0 on the ratio d / D was found. This relationship is shown in FIG. 26. Of FIG. 26 that the maximum value of the effective thermal conductivity coefficient is reached at d / D 0.2. The value of a Def describes the ratio of the thermal resistance of a layer of balls to the thermal resistance of the wall

zone. Based on the data already presented, the dependence of a / Aeff on d / D is obtained. It is shown in FIG. 2c. From FIG. 2c that the ratio and // eff is minimal at d / D 0.2 ± 0.05. The greatest heat removal in this

This is achieved with the lowest temperature gradient in the ball bed. With a fixed diameter of the heat pipe and heat flux, the length of the pipe can be reduced by almost 30%, and the temperature gradient

in ball fill more than b times. At d / D values of 0.15, the thermal conductivity of the ball fill decreases sharply, and at d / D 0.25, the heat transfer coefficient of the pipe wall decreases, which reduces reliability and increases the dimensions of the high-temperature heat exchange pipe.

Thus, based on the known experimental data, a new previously unknown relationship between the diameter

the heat pipe and the diameters of the balls poured into it, which allows to obtain a new property: to increase the heat removal from the surface of the high-temperature pipe with a simultaneous temperature gradient and,

consequently, thermal stresses in ball filling.

FIG. 1 shows a longitudinal section of a heat exchanger tube with ball filling.

The heat exchange tube 1 contains a fixed bed of ball elements 2, placed between the permeable plates (grids) 3, 4.

During the work the heat carrier through a grid 3

enters the heat exchange tube 1, flows around the spherical elements 2, provides the required heat removal from the walls of the tube 1 and is removed through the mesh 4 from the heat exchange tube.

The proposed solution in comparison with the prototype allows to reduce the temperature gradient and thermal stresses in the ball bed, the dimensions

heat exchange pipe by increasing the effective thermal conductivity of the filling of the balls and the heat transfer coefficient on the pipe wall by choosing the optimal ratio of the diameters of the pipe and the balls and thus making the high-temperature heat-exchange pipe compact and more reliable in operation.

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Claims (1)

Claims of Invention A high-temperature heat exchange tube comprising a fixed bed of balls of the same diameter, placed between permeable plates, which means that, in order to increase operational reliability and reduce the size, the balls of the backfill ball are 0.15 to 0.25 of internal diameter pipes. Ъ ЕТ N Н Jj H HJS /, s. . S. S-V // I LJ  I Q, Z About 0.1 Oft 0.5 0.4. fig..Ј d / j)