RU2196281C2 - Vertical-tube condenser with film condensation of steam inside tubes - Google Patents

Abstract

FIELD: refrigerating engineering. SUBSTANCE: condenser has shell with lids, top and bottom tube plates with vertical tubes secured in them. Each tube accommodates condensate tapping members. Each mentioned member is made in the form of central rod mounting at least seven bushings. At least three U-shaped condensate-tapping chutes with condensate-tapping holes at bushing surfaces are fixed at angle β to minimum four bushings. V-shaped condensate accumulating chutes are attached to upper edge of these chutes. Inclination angle α of sides along front edge relative to vertical axis of tube and uplift angle β of U-shaped chute are determined. At least three stay rods carrying supporting plates on their ends are secured to at least three remaining bushings. EFFECT: reduced power requirement for steam delivery to condenser due to tapping condensate from tube wall. 3 cl, 6 dwg

Description

 The invention relates to refrigeration, in particular to vertical-tube condensers with steam condensation inside the pipes, and can also be used in the chemical, oil and gas, dairy, brewing, fermentation, canning and other industries where the vaporization of the working fluid is carried out.

 Known vertical-tube condensers (analogue) with condensation of steam inside the pipes (see 1. Halperin NI. The main processes and apparatuses of chemical technology, - M.: Chemistry, 1981, s.326) containing a housing, inside of which there are tube gratings with vertical pipes fixed in them, nozzles for supplying steam and for removing condensed liquid, nozzles for supplying and removing coolant.

 The disadvantages of the known condensers include the formation of a condensate film on the internal heat exchange surface of the vertical pipe, the thickness of which continuously increases from top to bottom, while increasing the film thickness significantly reduces the overall heat transfer coefficient of the pipes due to the increasing role of the thermal resistance of the film / cm. 2. Theoretical foundations of refrigeration. Heat and Mass Transfer / Ed. E.I. Guiko. - M .: Agropromizdat, 1986, p. 171 /.

 It is known the use of pipes with inner ribs in the form of pressed cores or twisted tapes placed inside the pipe, with a different shape of the tape (see, for example: 3. Heat exchangers, automation devices and tests of refrigeration machines: Reference / Edited by A.V. Bykov M.: Light and food industry, 1984. 4. "Intensification of heat transfer in evaporators of refrigeration machines / Edited by A. A. Gogolin. -M.: Light and food industry. 1982). The disadvantages of such fins the difficulty in ensuring the regularity of the ribs along con- cern pipe abutment density of the edges to the inner surface of the tube and retraction of the film organization working medium fluid (ZHRT) of the surface area of the tube.

 It is known to manufacture pipes with inner ribs (see US Pat. Nos. 5,184,674 and 5,383,329), in which the inner ribs are made in the form of a spiral or gear fin. The disadvantages of such fins include the complexity in the technology of their manufacture, the need to weld plates - pipe blanks.

 Known pipe heat exchanger with internal ribs (see ed. St. 443243 USSR), in which the ribs are made in the form of half rings placed along the length of the pipe in a checkerboard pattern. The disadvantages of such fins include the complexity in the technology of their manufacture and ensuring the regularity of the placement of ribs along the length of the pipe.

 Known placement in the inner cavity of the vertical pipe of the condenser condensate hoods (prototype) / see 5. Isachenko V.P. Heat transfer during condensation, - M .: Energy, 1977, p. 72 /. The condensate drains are installed sequentially inside the pipe and adjoin its surface, as a result of which condensate is removed from this surface. On the surface below the condensate hoods, a condensate film forms again. Thus, the average heat transfer coefficient increases, since the average (along the pipe height) film thickness decreases and, therefore, the thermal resistance of the condensate film decreases.

The disadvantages of the known element of a vertical pipe condenser - a vertical pipe with condensate hoods, include the following:
- caps create additional hydraulic resistance to the flow of steam of the working fluid, as they cover the entire inner perimeter of the pipe. As a result of this, the pressure P _{n of} injecting the steam of the working fluid increases by ΔP _hydr , which, in turn, leads to additional energy costs for driving the supercharger of the steam of the working fluid, due to an increase in the compression ratio P _n / P _sun , where P _sun is the pressure absorption of steam of the working fluid;
- the resulting liquid fuel liquid flow is diverted at a small distance from the condensation surface area, as a result of which it is not excluded that the flow of the working fluid (LR) of the withdrawn liquid working fluid (LR) is located on lower sections of the condensation surface area, which leads to an additional thickening of the condensate film and its increase thermal resistance and, consequently, to reduce the overall heat transfer coefficient of the pipes.

 Thus, the thermal performance of existing vertical pipe condensers is limited by the intensity of condensation of the vapor of the working fluid (refrigerant) inside the vertical pipes, with film condensation of a liquid working fluid (refrigerant), due to the inefficient removal of the resulting condensate film from the pipe surface. In addition, with an increase in the height of the heat exchange tubes and an increase in the heat load, a significant increase in the thickness of the condensate film relative to the vertical axis occurs, as a result of which the heat sink intensity sharply decreases on the inner surface of the pipe, due to a decrease in the average heat transfer coefficient through the heat exchange surface.

 The objective of the present invention is to reduce the thermal resistance of the layer of the condensate film, to reduce the hydraulic resistance to the vapor-liquid flow, due to the removal of condensate from the pipe wall and, consequently, to improve the external technical characteristics of the condenser in terms of power consumption for the steam supply to the condenser.

This object is achieved by the fact that in the inventive vertical-tube condenser with film condensation of steam inside the pipes, comprising a housing with caps, upper and lower tube sheets, vertical pipes fixed to them with condensate-removing elements installed inside each vertical heat-exchange pipe, cooling medium inlets and a pair of a working fluid and pipes for draining the cooling medium and a liquid working fluid (condensate), the condensate drainage element is made in the form of a central rod, on which at least seven bushings are attached, and at least three U-shaped gutters for condensate drainage with holes at the surface of the bushings are rigidly fixed to at least four bushings at an angle β, and V-shaped condensation gutters are attached to the outer edge of these gutters, which made with an angle α of the inclination of the sides along the front edge, with respect to the vertical axis of the pipe, along the arc of a circle φ no more than 90 ^o , with a radius of the outer side of the V-shaped edge equal to the inner radius R _ext , with at least three remaining bushings not fixed less than three spacer rods, at the ends of which support plates are fixed.

The angle β of lifting the U-shaped trough is from 30 to 45 ^o , and the angle α of the sides of the V-shaped trough along the front edge, relative to the vertical axis of the pipe, is from 20 to 30 ^o .

при условии 0<Δ<1, где

- относительное уменьшение средней толщины пленки конденсата при установке конденсатоотводящего элемента,

Н - длина теплообменной поверхности,

- средняя толщина пленки конденсата при установке конденсатоотводящего элемента,

- средняя толщина пленки конденсата без установки конденсатоотводящего элемента, λ_пл - коэффициент теплопроводности пленки конденсата, α₂ - коэффициент теплоотдачи от конденсирующегося пара к пленке конденсата, при этом V-образные желоба соответствующих втулок перекрывают в плане внутреннюю образующую трубы.The bushings with thrust rods are installed in the upper, middle and lower sections of the pipe, and the bushings with U- and V-shaped grooves fixed to them are located with respect to each other and the tube sheets at a distance h determined from the expression

under the condition 0 <Δ <1, where

- a relative decrease in the average thickness of the condensate film when installing a condensate drain element,

N is the length of the heat exchange surface,

- the average thickness of the condensate film when installing the condensate drain element,

is the average thickness of the condensate film without installing a condensate drainage element, λ _pl is the heat conductivity coefficient of the condensate film, α ₂ is the heat transfer coefficient from the condensing steam to the condensate film, while the V-shaped grooves of the corresponding bushings overlap in plan the inner pipe generatrix.

 The equipment of each heat exchanger pipe of a vertical-tube condenser with film condensation of the working fluid steam inside the pipes by a condensate drainage element made in the form of a central rod, on which at least four bushings with U- and V-shaped channels are fixed, are located relative to each other and to the tube sheets at a distance h, which ensures a decrease in hydraulic resistance to the vapor-liquid flow, due to the fact that the V-shaped grooves do not cover at the same level the entire inner perimeter of the pipe, since us on different levels and overlap in terms of forming the inner tube, which provides easy access to the steam condensation heat released from the film surface. A more efficient drainage of condensate, in which there is no return of the liquid liquid to be discharged by the steam of the working fluid to lower sections of the condensation surface area, is achieved by drainage of condensate from the heat exchange surface with the help of U- and V-shaped condensate drains to the center of the pipe and then the rod in the center of the pipe until the ZhRT exits the heat transfer pipe. Free steam access to the heat exchange surface freed from the condensate film and a reduction in the thermal resistance of the condensate film not removed from the pipe surface intensifies the heat transfer process from the side of the condensing steam and increases the average value of the heat transfer coefficient during condensation.

The fastening of the U- and V-shaped drainage gutters is carried out in such a way that the angle β of the rise of the U-shaped gutter is from 30 to 45 ^o , and the angle α of inclination of the sides of the V-shaped gutter along the front edge, relative to the vertical axis of the pipe, is from 20 to 30 ^o , which provides the most efficient drainage of condensate from the heat exchange surface to the Central rod, for subsequent removal of condensate from the apparatus.

при условии 0<Δ<1, где

- относительное уменьшение средней толщины пленки конденсата при установке конденсатоотводящего элемента,

Н - длина теплообменной поверхности,

- средняя толщина пленки конденсата при установке конденсатоотводящего элемента,

- средняя толщина пленки конденсата без установки конденсатоотводящего элемента, λ_пл - коэффициент теплопроводности пленки конденсата, α₂ - коэффициент теплоотдачи от конденсирующегося пара к пленке конденсата, при этом V-образные желоба соответствующих втулок перекрывают в плане внутреннюю образующую трубы, выведенному согласно нижеследующих рассуждений и преобразований.The bushings with thrust rods are installed in the upper, middle and lower sections of the pipe, which ensures the centering of the central rod in the pipe and ensures that the V-shaped grooves are attached to collect the condensate to the inner heat-exchange surface of the vertical pipes, and the bushings with U- and V-shaped fixed to them the grooves are located relative to each other and to the tube sheets at a distance h, determined from the expression

under the condition 0 <Δ <1, where

- a relative decrease in the average thickness of the condensate film when installing a condensate drain element,

N is the length of the heat exchange surface,

- the average thickness of the condensate film when installing the condensate drain element,

is the average thickness of the condensate film without installing a condensate drainage element, λ _pl is the heat conductivity coefficient of the condensate film, α ₂ is the heat transfer coefficient from the condensing steam to the condensate film, while the V-shaped grooves of the corresponding sleeves overlap in plan the internal pipe generatrix derived according to the following reasoning and transformations.

Steam having a temperature t _n condenses on a vertical wall of height H, the temperature of which t _c <t _n / cm. FIG. 6 /. The condensate film moves in the x-axis direction.

где α₁, α₂ - коэффициент теплоотдачи соответственно от стенки к хладоносителю и от пара к пленке конденсата, Вт/(м²•К);
δ_ст, δ_пл.i - толщина стенки и пленки конденсата, при х=х_i, м;
λ_ст, λ_пл - коэффициент теплопроводности стенки и пленки конденсата, Вт/(м•К).The heat transfer coefficient k _n from the condensing steam to the coolant in cross section x located at an arbitrary distance x _i from the initial portion of the heat exchange surface of the pipe, i.e. when x = x _i is equal to:

where α ₁ , α ₂ - heat transfer coefficient, respectively, from the wall to the coolant and from steam to the condensate film, W / (m ² • K);
δ _article , δ _{square i} — wall and film thickness of the condensate, at x = x _i , m;
λ _st , λ _pl - coefficient of thermal conductivity of the wall and the condensate film, W / (m • K).

The precipitated condensate flows down the wall in the form of a continuous film, the thickness of which increases as it moves from top to bottom and reaches a maximum value of δ $\genfrac{}{}{0ex}{}{\text{max}}{\text{pl}}$ .

является обратной коэффициенту теплоотдачи α от пара к стенке, то есть

Преобразовав выражение (2), получим, что коэффициент теплоотдачи от пара к стенке, при х=х_i равен:

Преобразуем выражение (3) и, принимая отношение 1/α₂ равным А, получаем:

Преобразуя (4) с учетом того, что теплопроводность пленки λ_пл конденсата не изменяется по х, и обозначив произведение λ_пл•A через В, получим выражение для нахождения коэффициента теплоотдачи от пара к стенке, при х=х_i, в следующем виде:

Толщина пленки конденсата δ_пл.i в выражении (5) при х=х_i, по /5, с.46/, определяется по зависимости:

где r - удельная теплота парообразования, кДж/кг;
g - ускорение свободного падения, м/с²;
ρ_ж - плотность конденсата, кг/м³;
λ_ж - коэффициент теплопроводности конденсата, Вт/(м•К);
μ_ж - коэффициент динамической вязкости конденсата, Па•с.In the expression (1), the value

is the inverse heat transfer coefficient α from steam to the wall, i.e.

Transforming the expression (2), we obtain that the heat transfer coefficient from steam to the wall, at x = x _i is:

We transform expression (3) and, taking the ratio 1 / α ₂ equal to A, we get:

Transforming (4) Given that the thermal conductivity of the film λ _mp condensate does not change with respect to x, and letting the product of λ _mp • A by B, we obtain the expression for finding the coefficient of heat transfer from the steam to a wall, at x = x _i, as follows:

The thickness of the condensate film δ _{square i} in the expression (5) at x = x _i , according to / 5, p. 46 /, is determined by the dependence:

where r is the specific heat of vaporization, kJ / kg;
g is the acceleration of gravity, m / s ² ;
ρ _W - the density of the condensate, kg / m ³ ;
λ _W - thermal conductivity of the condensate, W / (m • K);
μ _W - coefficient of dynamic viscosity of the condensate, Pa • s.

через С, получим:

Средний коэффициент теплоотдачи при конденсации пара на стенке, при х=Н, и с учетом выражений (5) и (7) определится по /5, с.46/ как:

Толщина пленки конденсата достигает своего максимального значения δ $\genfrac{}{}{0ex}{}{\text{max}}{\text{пл}}$ , при х= Н, и тогда средний коэффициент теплоотдачи при конденсации пара на стенке при х в интервале (0; Н) равен:

где

- средняя толщина пленки конденсата при х в интервале (0; Н).Denoting in (6) the expression

through C, we get:

The average heat transfer coefficient during steam condensation on the wall, at x = H, and taking into account expressions (5) and (7) will be determined by / 5, p. 46 / as:

The condensate film thickness reaches its maximum value δ $\genfrac{}{}{0ex}{}{\text{max}}{\text{pl}}$ , at x = H, and then the average heat transfer coefficient for steam condensation on the wall at x in the interval (0; H) is equal to:

Where

- the average thickness of the condensate film at x in the range (0; H).

где

- средняя толщина пленки конденсата при х в интервале (0; h).Similarly to the above, the average heat transfer coefficient from steam to the wall at x in the interval (0; h) when installing the bushings 11 with V- and U-shaped grooves at a distance h between themselves and the tube sheets is:

Where

is the average thickness of the condensate film at x in the interval (0; h).

Поскольку, по /5, с.72/ существует зависимость:

то приравнивая левые части выражений (11) и (12), получаем выражение (13).Thus, the relative increase in the heat transfer coefficient from steam to the wall, when installing the bushings 11 with V- and U-shaped grooves of the condensate drain element at a distance h between themselves and the tube sheets in a vertical pipe, will be:

Since, according to / 5, p. 72 / there is a dependence:

then equating the left parts of expressions (11) and (12), we obtain expression (13).

Поделив правую часть выражения (13) на

и обозначив частное

через Δ, а частное

через D, получим:

В зависимости от принимаемой при расчетах протяженности теплопередающей поверхности труб Н, задавшись отношением 0<Δ<1 при условии

определяется расстояние h между втулками 11 конденсатоотводящего элемента.

Dividing the right side of expression (13) by

and denoting the quotient

through Δ, and the quotient

through D, we get:

Depending on the length of the heat transfer surface of the pipes N taken in the calculations, setting the ratio 0 <Δ <1 under the condition

the distance h between the bushings 11 of the condensate drain element is determined.

 In FIG. 1 shows a General view of a vertical-tube condenser with condensation of the vapor of the working fluid inside the vertical pipes; in FIG. 2 - general view of the layout of the condensate drain element inside the pipe (place C); in FIG. 3 - the layout of the condensate drain element in the cross section of the pipe (section aa); in FIG. 4 - layout of the lock of the condensate drain element in the cross section of the pipe (section BB); in FIG. 5 - a sleeve with V- and U-shaped gutters fixed on it, used to collect and drain condensate (in a perspective view); in FIG. 6 is a diagram of film condensation on a vertical wall.

 A vertical-tube condenser with a film condensation of steam inside the pipes (see Fig. 1) contains a housing 1, tube sheets 2 and 3, vertical pipes 4 fixed therein, nozzles for supplying 5 and exhaust 6 of the cooling medium and nozzles for supplying steam to the working fluid 7 and drainage of liquid working fluid (condensate) 8.

 Inside each vertical heat exchanger pipe there is placed (see Fig. 2-5) a condensate drainage element for removing the condensate film, containing a central rod 9, on which the bushings 11 and 12 are fixed with clamps 10 (for example, screws).

To the sleeves 11 (see Fig. 2, 3, 5) at an angle β, U-shaped grooves 13 are rigidly fixed, with holes 14 at the surface of the sleeves 11. The angle β of lifting the groove 13 is from 30 to 45 ^o .

At least three V-shaped grooves 15 are attached to the outer edge of the grooves 13, which are made with an angle α of inclination of the sides along the front edge with respect to the vertical axis of the pipe, along a circular arc φ of not more than 90 ^o , with a radius of the outer side of the V-shaped edge, equal to the inner radius R _corolla tube 4. The angle α of inclination of the parties V-shaped trough along the leading edge, with respect to the vertical axis of the pipe is 20 to 30 ^o. To the bushings 12 (see Fig. 2, 4), at least three spacer rods 16 are fixed on the thread, at the ends of which support plates 17 are fixed.

 By the leading edge of the gutter, we mean exactly the surface of the V-shaped gutter, which, when the condensate drain element is installed inside the vertical pipe, adjoins the internal heat exchange surface of this pipe.

The inventive vertical-tube condenser with film vapor condensation inside the pipes (see Fig. 1-5) works as follows:
At least three bushings 12 are mounted on the central shaft 9 in such a way as to fix the central shaft 9 strictly along the vertical axis of the pipe 4 in its upper, middle and lower sections.

при условии 0<Δ<1, где

- относительное уменьшение средней толщины пленки конденсата при установке конденсатоотводящего элемента,

Н - длина теплообменной поверхности,

- средняя толщина пленки конденсата при установке конденсатоотводящего элемента,

- средняя толщина пленки конденсата без установки конденсатоотводящего элемента, λ_пл - коэффициент теплопроводности пленки конденсата, α₂ - коэффициент теплоотдачи от конденсирующегося пара к пленке конденсата, при этом V-образные желоба соответствующих втулок перекрывают в плане внутреннюю образующую трубы.At least four bushings 11 are mounted on the central rod 9 so that the bushings 11 are located in relation to each other and to the tube sheets at a distance h determined from the expression

under the condition 0 <Δ <1, where

- a relative decrease in the average thickness of the condensate film when installing a condensate drain element,

N is the length of the heat exchange surface,

- the average thickness of the condensate film when installing the condensate drain element,

is the average thickness of the condensate film without installing a condensate drainage element, λ _pl is the heat conductivity coefficient of the condensate film, α ₂ is the heat transfer coefficient from the condensing steam to the condensate film, while the V-shaped grooves of the corresponding bushings overlap in plan the inner pipe generatrix.

 After the above placement on the central shaft 9 of the bushings 11 and 12, the latter are fixed on the central shaft 9 with brackets 10.

 With the removed caps 18 and 19 of the condenser, each pipe 4 is installed along the vertical axis of the central rod 9, and spacer rods 16 are fixed inside the pipe 4. After that, the covers 18 and 19 are mounted and fixed to the housing 1. Through the pipe 5, they are fed and through the pipe 6 coolant is removed. Through the pipe 7, a stream of steam of the working fluid is supplied to the pipes, and the steam condenses on the inner heat exchange surface of the pipes 4.

 In the process of condensation of the working fluid on the inner heat exchange surface of the pipes 4, a condensate film is formed, the thickness of which δ increases in the direction from top to bottom. The resulting condensate film is discharged from the internal heat exchange surface of the pipes 4 into V-shaped grooves 15, from where it passes through the U-shaped grooves 13 to the holes 14 at the surface of the sleeves 11 and is merged through the holes 14 along the central shaft 9 to the lower tube sheet 3. The liquid working fluid through the pipe 8 is removed from the capacitor for appropriate use. The work cycle is ending.

Thus, the claimed, in comparison with the known, provides:
- intermediate condensate drain from the internal heat exchange surface of the vertical pipe, which helps to reduce the average thickness of the condensate film;
- free steam access to the heat exchange surface freed from the condensate film and a reduction in the thermal resistance of the condensate film not removed from the pipe surface leads to an intensification of the heat transfer process from the side of the condensing steam and increases the average value of the heat transfer coefficient during condensation;
- free steam access to the heat exchange surface freed from the condensate film and condensate drain along the guide in the center of the pipe reduces the hydraulic resistance of the vapor-liquid flow and improves the external technical characteristics of the condenser in terms of power consumption for the steam supply to the condenser.

Claims (3)

1. A vertical-tube condenser with film vapor condensation inside the pipes, comprising a housing with caps, upper and lower tube sheets, vertical pipes fixed to them with condensate-discharge elements installed inside each vertical heat-exchange pipe, coolant and steam inlets, and exhaust pipes cooling medium and liquid working fluid (condensate), characterized in that the condensate drain element is made in the form of a central rod on which at least seven bushings are fixed, p At least three U-shaped grooves are rigidly fixed to at least four bushings at an angle β to drain condensate with holes at the surface of the sleeves, and V-shaped condensation grooves are attached to the outer edge of these grooves, which are made with an angle α of the sides along the leading edge with respect to the vertical axis of the pipe along the arc of a circle φ no more than 90 ^o , with a radius of the outer side of the V-shaped edge equal to the inner radius R _ext. pipe, with at least three remaining bushings fixed at least three spacer rods, at the ends of which are fixed base plates. 2. The vertical tube condenser according to claim 1, characterized in that the angle β of the rise of the U-shaped trough is from 30 to 45 ^o , and the angle of inclination α of the sides of the V-shaped trough along the front edge with respect to the vertical axis of the pipe is from 20 up to 30 ^o . 3. The vertical-tube capacitor according to claim 1, characterized in that the bushings with thrust rods are installed in the upper, middle and lower sections of the pipe, and the bushings with U- and V-shaped grooves fixed to them are located relative to each other and to the tube lattices at a distance h determined from the expression

under the condition 0 <Δ <1,
where Δ = δ $\genfrac{}{}{0ex}{}{\text{-h}}{\text{pl}}$ / δ $\genfrac{}{}{0ex}{}{\text{-H}}{\text{pl}}$ - a relative decrease in the average thickness of the condensate film when installing the condensate drain element;
D = λ _pl / (α ₂ × δ $\genfrac{}{}{0ex}{}{\text{-H}}{\text{pl}}$ );
H is the length of the heat exchange surface;
δ $\genfrac{}{}{0ex}{}{\text{-h}}{\text{pl}}$ - the average thickness of the condensate film when installing the condensate drain element;
δ $\genfrac{}{}{0ex}{}{\text{-H}}{\text{pl}}$ - the average thickness of the condensate film without installing a condensate drainage element;
λ _PL - thermal conductivity of the condensate film;
α ₂ - heat transfer coefficient from condensing steam to the condensate film,
in this case, the V-shaped grooves of the respective bushings overlap in plan the inner pipe generatrix.

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