RU2033592C1 - Heat-exchange element - Google Patents

Abstract

FIELD: heat-exchange apparatus. SUBSTANCE: double-pipe heat exchange element has outer pipe 2 blanked off at the end and inner pipe 1. Lateral surfaces of pipes 1 and 2 have hemispherical dimples; dimples made on outer pipe 2 are shifted relative to dimples made on inner pipe 1 which are provided with through holes in their center. EFFECT: enhanced efficiency. 2 cl, 6 dwg

Description

 The invention relates to heat engineering and can be used in heat exchangers of various industries.

 Known heat exchangers of the “bayonet” type (Handbook of heat exchangers vol. 2, translation from English under the editorship of OG Martynenko and other Energoatomizdat, 1987, p. 279, Fig. 11; US patent N 4106556, cl. F 28 F 9/10, 11/28/07; ed. St. USSR N 569170, class F 28 F 7/12, 06/25/79, in which Field tubes (Mitenkov F.I. et al. Design of heat exchangers of nuclear power plants. M. Energoatomizdat, 1988, p. 70, Fig. 3.1. 3.2.). The Field tube is a recuperative heat exchange element containing two coaxially mounted tubes separated by an annular channel. The outer tube is plugged at one end, and the channel of the inner tube is connected to the annular channel. During operation, one coolant washes the outer surface of the outer tube, and the other moves in the channel of the inner tube and in the annular annular space.

 Various methods are used to intensify heat transfer in such elements: finning the surface of the inner tube, swirling the flow in the annular channel, jet washing off the heat exchange surface (ed. St. USSR N 1118843, class F 28 D 7/12, 10.15.84; ed. . USSR N 1657922, class F 28 D 7/12, 06.23.91). The intensification of heat transfer causes a significant increase in the hydraulic resistance of the internal cavity of the Field tube, which reduces the energy efficiency of the heat exchange element.

 One of the promising directions for increasing the efficiency of heat transfer surfaces is the application of a regular system of spherical holes to the surface (Belenky M.Y. et al. An experimental study of the thermal and hydraulic characteristics of heat transfer surfaces formed by spherical holes. Thermophysics of High Temperatures, Volume 29, N 6, 1991 p. 1142-1147), the improvement of which was carried out in heat transfer methods (ed. St. USSR N 1481586, class F 28 F 13/06, 05/23/89; ed. St. USSR N 1657930, class F 28 F 13 / 06, 23.06.91) intended for intensive heat removal at high thermal loads and to ensure uniformity of the temperature field of the heat transfer surface.

 The closest in technical essence to the invention is a device (ed. St. USSR N 1043426, class F 28 D 7/12, 05/05/82), containing two coaxially located tubes separated by an annular channel, the outer of which is plugged from the end, and the inside is perforated. In such a heat-exchange element, one medium washes the outer surface of the outer pipe, and the other enters the inner part of the inner pipe and is directed through the perforation holes in the form of a beam of jets towards the muffled end of the outer pipe and into the annular annular gap. In this heat-exchange element, high heat transfer coefficients are achieved due to turbulence of the near-wall flow upon impact of transverse jets on the heat exchange surface.

 However, in such a device, significant turbulence of the near-wall zone of the flow takes place only near the muffled end of the outer pipe, where the coolant jets, perpendicular to the heat exchange surface, are practically not affected by the negative effect of the exhaust flow, on the rest of the greater part of the intensive heat exchange surface, they are much lower due to the drift removal by the spent heat flow, moving along the annular channel, especially in the exit zone, where the kinetic energy of the drift flow is high (Perri PP Heat Trasf er by Convection From a Hot Gas Iet to a plane surface. Proc. Inst. Mechan. Eng. t. 168, N 30, 1954, p. 778, Table 1).

 The aim of the invention is the intensification of heat transfer.

где S₁₁ поперечный шаг лунок на внутренней трубе;
S₁₂ то же на наружной трубе;
D_1н внешний диаметр внутренней трубы;
D_2н внешний диаметр наружной трубы.The goal is achieved by the fact that in a heat exchange element containing two coaxially arranged pipes separated by an annular channel, the external of which is blanked from the end, and the internal is perforated, hemispherical holes are staggered on the outer lateral surfaces of both pipes with the formation on their inner surfaces corresponding hemispherical protrusions while the holes of the perforation of the inner pipe are located in the center of the holes. The longitudinal steps of the holes on the outer pipe are equal to the corresponding steps of the holes on the inner pipe, the axial lines of the longitudinal rows of the holes of the outer and inner pipes are located in the same radial plane of the element, while the holes of one transverse row made on the outer pipe are offset in the direction of the blanked end relative to the corresponding transverse a number of holes of the inner tube half the diameter of the hole, the height of the hemispherical protrusion is less than the width of the annular channel, and the transverse step of the holes on the outer tube is determined from the relation
S ₁₂ S

where S _{11 is the} transverse step of the holes on the inner tube;
S _{12 is} the same on the outer pipe;
D _{1N the} outer diameter of the inner pipe;
D _2N outer diameter of the outer pipe.

 The proposed design not only increases the heat transfer coefficients during external washing of the outer surface of the tube formed by hemispherical holes (see Belenky I.Ya. et al. 1145, Fig. 3), as well as when the flow moves in an annular channel and a tube with hemispherical protrusions (see Migai V.K. Modeling of heat exchange equipment. L. Energoatomizdat, 1987, p. 1979, Fig. 5.15; Kuznetsov EF Intensification of heat transfer in the channels of gas heaters of gas turbines. Heavy Engineering, 1991, N 6, p. 9 , Fig. 2), but also hemispherical protrusions, location which is consistent with the placement of holes on the outer surface of the inner pipe, protect the jets flowing from the holes in the holes from the drift flow of the spent medium both by shielding them near the wall of the outer pipe and by accelerating the flow directed to the hole and participating in the formation of tornado structures that contribute to stability flowing jets. Reducing the negative influence of the drift flow and enhancing the re-supply of the cooler to the wall of the outer pipe in the form of toroidal vortices (see Kikonadze I.K. et al. DAN SSSR, 1986, vol. 291, No. 6, p. 1315) contribute to the intensification of heat transfer, which is a new property inherent in the proposed technical solution. Therefore, the claimed technical solution meets the criterion of "significant differences".

 In FIG. 1 shows a heat exchange element, a longitudinal section; in FIG. 2 and 3 show sections A-A and BB in FIG. 1; in FIG. 4 shows a scan of a portion of a heat exchange element with a conditional image of an outer pipe; in FIG. 5 hole of the inner tube; in FIG. 6 element of the annular channel.

В предлагаемом техническом решении один теплоноситель (стрелка 13, фиг. 6) омывает внешнюю поверхность наружной трубы 2, а другой (стрелка 14) движется по каналу внутренней трубы 1 в сторону заглушенного торца 4 с путевым расходом через отверстия 9, расположенные в лунках 5, и в виде множества струй (стрелка 15) направляются радиально на внутреннюю стенку наружной трубы. Другая часть потока второго теплоносителя (стрелка 16) поступает в кольцевой канал 3 со стороны торца 4 и движется в нем, омывая полусферические выступы 8, экранирующие струи 15 вблизи стенки трубы 2, лунки 5, боковые поверхности труб 1, 2, взаимодействуя со струями, вытекающими из отверстия 9 в лунках 5, частично закручивается вокруг струй, ослабляя влияние на них сносящего потока, после чего снова вместе со струями подается на внутреннюю стенку наружной трубы.The heat exchange element contains two coaxially mounted pipes 1 and 2, separated by an annular channel 3, the outer 2 of which are plugged from the end 4, and the inner 1 is perforated. On the outer side surfaces of both pipes, staggered hemispherical holes 5 and 6 are formed with the formation of corresponding hemispherical protrusions 7 and 8 on their inner surfaces, with holes 9 of the perforation of the inner pipe 1 located in the center of the holes 5. Longitudinal steps S _{22 of the} holes 6 on the outer pipe 2 are equal to the corresponding steps S _{21 of the} holes 5 on the inner pipe, the axial lines 10 and 11 of the longitudinal rows of the holes of the outer and inner pipes are located in the same radial plane 12 of the element, while the holes 6 are one transverse of a row made on the outer pipe 2 are offset in the direction of the blanked end 4 relative to the corresponding transverse row of holes 5 of the inner pipe by half the diameter of the hole, the height h _{in the} hemispherical protrusion 8 is less than the width δ _{to the} annular channel 3, and the transverse step of the holes 6 on the outer pipe determined from the relation
S ₁₂ S

In the proposed technical solution, one coolant (arrow 13, Fig. 6) washes the outer surface of the outer pipe 2, and the other (arrow 14) moves along the channel of the inner pipe 1 towards the muffled end 4 with the flow rate through openings 9 located in the holes 5, and in the form of a plurality of jets (arrow 15) are directed radially onto the inner wall of the outer pipe. Another part of the flow of the second coolant (arrow 16) enters the annular channel 3 from the side of the end 4 and moves in it, washing hemispherical protrusions 8, shielding jets 15 near the wall of the pipe 2, holes 5, the side surfaces of the pipes 1, 2, interacting with the jets, arising from the hole 9 in the holes 5, partially twists around the jets, weakening the influence of the drift flow on them, then again, together with the jets, it is fed to the inner wall of the outer pipe.

 The use of the invention allows to intensify heat transfer on the outer surface of the outer pipe, on the inner surface of the inner pipe, as well as in the annular channel between the pipes of the heat exchange element due to turbulence of the flow with hemispherical protrusions on the outer pipe, and due to the weakening of the negative effect of the drift flow on the heat transfer of impact jets with by shielding them with protrusions and enhancing the formation of twisted vortex structures around them (jets). In addition, the proposed technical solution provides a re-direction of part of the medium to the heat exchange surface, thereby more fully utilizing its storage capacity.

Claims (2)

 1. HEAT EXCHANGE ELEMENT containing two coaxially arranged pipes separated by an annular channel, the outer of which is plugged from the end, and the inside is perforated, characterized in that, in order to intensify heat transfer, hemispherical staggered holes are made on the outer side surfaces of both pipes with the formation on their inner surfaces of the corresponding hemispherical protrusions, while the holes of the perforations of the inner pipe are located in the center of the mentioned holes. 2. The element according to claim 1, characterized in that the steps of the longitudinal rows of holes on the outer surface are equal to the corresponding steps of the holes on the inner surface, the axial lines of the longitudinal rows of the holes of the outer and inner pipes are located in the same radial plane of the element, while the holes of one transverse row, made on the outer pipe, offset in the direction of the muffled end relative to the corresponding transverse row of holes of the inner pipe by half the diameter of the hole, the height of the hemispherical protrusion is less than the width of the annular channel a, a transverse hole pitch on the outer surface of the tube is determined from the relationship

where S _{1 1} and S _{1 2 are the} transverse step of the holes on the inner and outer pipe, respectively;
D _{1 n} and D _{2 n the} outer diameter of the inner and outer pipes, respectively.

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