Double-pipe heat exchanger

FIELD: heating.

SUBSTANCE: double-pipe heat exchanger, in the internal pipe and in inter-pipe space of which screw inserts are installed. Inner space of the internal pipe and inter-pipe space between internal and external pipes represent screw cavities formed with walls of pipes and screw inserts. Screw inserts are installed so that an internal screw insert is connected mainly by welding or soldering to inner surface of the internal pipe. Screw insert in inter-pipe space is connected in the same manner to outer surface of the internal pipe and to inner surface of the external pipe. Materials of the internal pipe, screw inserts and points of joints of screw inserts with walls of the internal pipe shall have minimum thermal resistance. Flows of liquid or gaseous media in the internal pipe and in inter-pipe space flow along helical spirals.

EFFECT: invention allows shortening the length of double-pipe heat exchangers up to ten times and more and reducing the weight and overall dimensions of a heat exchanger.

2 dwg

 

The claimed invention relates to heat exchange apparatus and can be used in various industries, agriculture and communal farms.

Known heat exchangers of the type "pipe in pipe", consisting of two pipes, one of which, of smaller diameter, is placed inside another larger diameter annular gap, called the annular space. The inner tube is pumped media (liquid or gaseous) for example, a higher temperature (hot), and the annular space environment with a lower temperature (cold). Thus the wall of the inner tube is heated and transfers heat to the cold environment, which thus temperature increases. The direction of heat transfer may be such as described above, or in the opposite direction depending on the ratio of the temperatures in the inner tube and in the annular space.

The efficiency of heat transfer, in addition, depends on the degree of turbulence in the flow and viscosity of the media, the efficiency increases with increasing turbulence and reduce the viscosity.

If for specific environments to take the same initial temperature and therefore viscosity, and the diameters of the pipes, the only way to increase the efficiency of heat transfer between them will increase turbulence, Kataragama smooth pipes can only be achieved by increasing the speed of the media.

Improving the efficiency of heat transfer can reduce the required heat transfer area, to reduce the length of the heat exchanger, other dimensions and mass. But higher speed environments in pipes requires increasing the capacity of the pumps, which pump these fluids. If we consider that increasing the turbulence is proportional to the speed environment and the required capacity of the pump to the square of velocity, it is obvious that the increase of velocity environments has a certain limit, after which further increase in speed becomes unprofitable.

Therefore, strive to increase the turbulization due to installation in the inner tube and in the annular space of different types turbulized elements.

For example, the known heat exchangers "pipe in pipe", in which the inner tube is wound wire having different steps of winding and configuration.

The drawback of such heat exchangers is a slight increase in turbulence with the growth of hydraulic resistance.

Also known heat exchangers, the inner tube which is installed, for example, by welding, spiral ribs, the height of which is almost equal to the distance from the inner pipe to the outer. Such ribs largely increase the turbulence in the annular space compared to the winding wire in Addition they increase the area of thermal contact between the wall of the inner tube with the environment annulus, i.e. increase the efficiency of heat transfer.

The drawbacks of such heat exchangers are the following:

- not the whole environment in the annular cavity engages in a helical movement is part of it flows through the annular gap between the spiral ribs and the outer pipe;

- increase the fluid velocity, turbulence occurs only at a few percent, at least several tens of percent, since the elevation angle of helical ribs small, and with increasing elevation angle of the hydraulic resistance increases much faster growth of turbulence and increasing the amount of medium begins to flow through the annular gap;

- the heat transfer from the environment into the inner tube to its wall remains relatively low, as it determines the efficiency of heat transfer in General.

A known heat exchanger "pipe in pipe" patent # SU 1222207. In the heat exchanger inside the inner pipe installed turbulent insert in the form of a twisted coil line strip of sheet metal with the turbulent petals along its longitudinal edges. This insertion causes a twisting spiral line, significantly increases the turbulization of the environment in the inner pipe and the heat transfer from the environment to the wall.

The specified heat exchanger is adopted for the prototype.

However, he is pursuing the disadvantages:

- not all of the medium in the inner tube engages in a helical movement (only approximately 20-30%), which does not allow to reach the highest possible level of turbulence in the environment;

- large contact thermal resistance of the turbulent insert with the inner surface of the pipe (the turbulent insert touches the inner surface of the pipe only at certain points, and, by a simple pressing of it due to elastic forces. But such pressure is not quite securely and at any time may weaken i.e. thermal resistance of the contact area will increase and may become unacceptably large).

- large contact thermal resistance deprives the turbulent insert its essential function is to transfer heat from it to the wall of the inner tube due to the heat, (which is equivalent to increase the heat exchange surface of the inner pipe).

The aim of the present invention is more significant increase in the coefficient of heat transfer is not by tens of percent, and several times that, in turn, will allow the same time to reduce the length of the heat exchanger and, therefore, also in times to reduce its dimensions and weight, although to a lesser extent than the decrease in length.

Proposed by the present invention a heat exchanger tube in tube" differs from the prototype in that the internal issue is ransta inner pipe and the annulus between the inner and outer tubes are helical cavity, formed by the walls of pipes and screw inserts that are installed inside the inner tube and the inside of the annulus so that the internal screw insert is connected, particularly by means of welding or soldering, to the inner surface of the inner pipe, and screw the insert in the annular space is connected in the same manner with the outer surface of the inner pipe and the inner surface of the outer pipe, and the material of the inner pipe, screw inserts and joints screw inserts with the inner wall of the pipe must have a minimum thermal resistance.

The device proposed heat exchanger is shown schematically in figure 1 and figure 2.

Figure 1 shows a longitudinal section of the heat exchanger, figure 2 - cross section.

Figure 1: 1 - inner tube; 2 - outer tube; 3 - screw inserted into the inner tube; 4 - screw insert in the annular space; 5 - screw cavity in the inner pipe; 6 - screw cavity in the annular space; B - input medium in the inner tube; the output environment of the inner tube; D - input environment annulus; D - output environment of the annulus.

Figure 2: E - screw motion of the medium in the inner tube; W - helical flow in the annular space.

Has a heat exchanger as follows: in intova the cavity POS.1 comes hot environment and immediately acquires a helical movement, for example, clockwise. When moving environment washes the surface of the screw insert 3 and the inner surface of the pipe position 1 and transmits them warm. At the same time heat to the inner surface of the pipe item 1 is transferred by conduction through the screw insertion 3.

The efficiency of heat transfer from the fluid in the pipe position 1 to its wall in a first approximation proportional to the criterion of Reynolds (Re), and that, in turn, is proportional to the fluid velocity relative to the wall ceteris paribus. If the internal pipe set screw insert, the velocity of the medium inside it will be equal to the speed thereof at the entrance to the tube (i.e. in the direction of arrow B, figure 1) and the environment path is equal to the length taken of the pipe segment.

When installed, the insert, and when her step screw surface is equal to, for example, the inner diameter of the pipe POS.1 environment path relative to the wall is increased to 3.14 times. But to the whole environment, coming into the screw cavity POS.1 managed to pass this section of the pipe, the speed should increase also in 3.14 times. Proportionately increases the Reynolds criterion and, therefore, also proportional to and the heat transfer coefficient.

Thus, the coefficient of heat transfer from the fluid to the wall increases at least 3.14 times. In fact, the increase will be more, since when is the valuation were not taken into account two significant factors, to increase the heat transfer coefficient:

a) turbulization of the boundary layer at the inner wall of the pipe;

b) the heat transfer to the inner wall due to the heat coil insert.

To assess the degree of influence of these factors on the heat transfer coefficient increase is not exactly possible, but roughly this is 40-80%.

But, even without these two factors, the increase in heat transfer coefficient is very impressive. Moreover, it may increase several times. This should only reduce step screw insertion into the inner tube. For example, decreasing this step three times, about the same time will increase accordingly the velocity of the medium relative to the inner wall of the inner pipe, the Reynolds criterion and the overall heat transfer coefficient.

A similar pattern is observed in the annular space. I.e. with the set screw insert, depending on the internal diameter of the outer pipe and the pitch of the helical insert it increases the heat transfer coefficient from the wall of the inner pipe to the outside environment about the same time and from the environment in the inner pipe to the wall.

The use of the invention allows to intensify the heat transfer due to both improve hydrodynamic flow patterns and increase laptop is of waist environment, and due to the factor of the development of heat-exchange surface. This entails reducing the required length of the heat exchangers type "pipe" to ten or more times and a corresponding reduction in the mass and dimensions of the heat exchangers.

The heat exchanger pipe, the inner pipe and the annular space which has a screw insert, characterized in that the inner space of the inner pipe and the annulus between the inner and outer tubes are helical cavity formed by the walls of pipes and screw inserts installed in such a way that the inner coil insert is connected, particularly by means of welding or soldering, to the inner surface of the inner pipe, screw the insert in the annular space is connected in the same manner with the outer surface of the inner pipe and the inner surface of the outer pipe, and the material of the inner pipe, screw inserts and seats joints screw inserts with the inner wall of the pipe must have a minimum thermal resistance, the flow of fluids (liquid or gaseous) in the inner tube and in the annular space flow along the helical spirals.



 

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