RU2039335C1 - Heat exchanging pipe - Google Patents

Abstract

FIELD: heat exchanging engineering. SUBSTANCE: heat exchanging pipe has ring turbulizers-grooves 1 and answered ring turbulizers- projections 2 of smooth profile. The turbulizers are made up as two arcs: first streamwise arc 3 and second streamwise arc 4 which are conjugated at the top 5 of projection 2. The arcs have smooth parts 6 between the turbulizers. The radius of the first arc 3 is differ from the radius of the second arc 4. The optimal range of the radii is presented in the invention description. EFFECT: improved design. 2 dwg

Description

 The invention relates to heat exchange devices and can be used in heat exchange equipment used in energy, construction, chemistry, cryogenic technology and other sectors of the economy.

 Known heat exchange pipe with annular turbulators grooves on the outer surface and the corresponding protrusions on the inner surface, in which the protrusions have a height 1.25-2.5 times less than the depth of the grooves [1] Such pipes in most ranges of Reynolds numbers, relative values steps and heights of the protrusion, the increase in hydraulic resistance outstrips the increase in heat transfer by a significant amount due to the relatively pointed shape of the transverse profile of the turbulator, which reduces its effectiveness.

 The closest in technical essence and the achieved result to the proposed one is a heat exchange pipe with grooves and corresponding protrusions on the outer and inner surfaces placed with a given step along the pipe and separated by smooth sections, each groove (protrusion) connected to the corresponding smooth section by a straight line segment. located to the longitudinal axis of the pipe with a slope of at least 2: 1 at the outer groove and no more than 1: 2 at the inner groove [2] However, an attempt to improve its shape only with the help of mentation magnitude bias line protrusion peaks compound with a smooth pipe section without influence turbulator pitch and their depth is insufficient.

 When a turbulent rectangular protrusion flows around the stream, two generally asymmetric vortex zones are formed in front of and behind it, depending on the shape of the protrusion and its size, three regions: three-dimensional, characterized by the presence of one or more vortices with axes perpendicular to the side walls, two-dimensional with the presence of a two-dimensional vortex and a three-dimensional non-stationary region. At the upper boundary of the three-dimensional zone, there is a maximum generation of turbulence; here, turbulent shear stress reaches large values. The energy costs of the flow to overcome the hydraulic resistance of the ledge are spent on maintaining the vortex zones and, as a result, on increasing the turbulence of the flow.

 With a smooth protrusion shape, the intensity of turbulence generation is higher, and the size of the vortex zones is much smaller, which reduces hydraulic losses at the same level of turbulence in the near-wall region. Moreover, with a certain smoothness of the profile of the protrusions in front of and after them, two-dimensional vortices may not form, and the generation of turbulence is determined mainly by a system of three-dimensional vortices, which are formed when the flow incident on the protrusion is turned. With this flow structure, significantly less energy is required.

 In the known construction, a certain smoothness is achieved only when the flow runs onto the turbulator, after which there is a deep hollow with a vortex zone, more significant than even in the heat exchange tube design described above according to [1] In this zone, in addition to undesirable two-dimensional vortices, a lone vortex can also be formed into two depressions, which, as already indicated, leads to an inexpedient (inadequate) increase in hydraulic resistance.

 The purpose of the invention is to increase the efficiency of the heat transfer pipe by reducing its hydraulic (aerodynamic) resistance.

R₂/D 0,25 (1 d/D)(1+A₂ ²) с интервалом значений
_для

_{2,0 +}

где D внутренний диаметр трубы в месте между турбулизаторами-выступами;
d внутренний диаметр трубы в месте расположения турбулизатора;
t шаг турбулизаторов.In a heat-exchange pipe with annular turbulators-grooves on the outside and corresponding annular turbulators-protrusions inside, this goal is achieved by the fact that the transverse profile of the turbulizer-protrusion formed during a longitudinal section of the pipe is made up of two circular arcs conjugated at the top point (top) of the protrusion-turbulator moreover, the front arc with respect to the moving flow is made with a radius R ₁ , and the far one with a radius R ₂ , and the interval of optimal values of the radii is determined from the dependencies
R ₁ / D 0.25 (1-d / D) (1 + A ₁ ² ) with an interval of values for A ₁ = 1 +

R ₂ / D 0.25 (1 d / D) (1 + A ₂ ² ) with an interval of values
_for

_{2.0 +}

where D is the inner diameter of the pipe in place between the turbulence protrusions;
d the inner diameter of the pipe at the location of the turbulator;
t step turbulators.

 Performed according to the above law, the profile of the turbulator is much smoother than in the prototype and analogue. Separation zones formed with this form of profile before and after the turbulizer consist mainly of only three-dimensional vortices, which determine the increased generation of turbulence at the upper boundary of the vortex zones. In this case, two-dimensional vortices that increase the hydraulic resistance, but have little effect on heat transfer, are practically absent.

Учитывая, что высота выступа равна полуразности значений диаметров трубы в месте выступа d и на гладком участке D, можно записать
h

0,5D

1-

Тогда предыдущее выражение преобразовывается к виду
A

(а)
Возводя в квадрат обе части полученного уравнения и решив его относительно R, получают
R 0,25 · D

1-

A² + 1

(b) или в относительных величинах

0,25

1-

A² + 1

(c)
В пределе в трубе с кольцевыми турбулизаторами
l_макс 0,5t, где t шаг турбулизаторов, т.е.The length l of the semi-chord of any of the two circular arcs forming the protrusion profile can be expressed in terms of the radius of the circle R and the height of the protrusion-turbulator h (according to the Pythagorean theorem):
l

Given that the height of the protrusion is equal to the half-difference of the pipe diameters in the place of the protrusion d and on the smooth section D, we can write
h

0,5D

1-

Then the previous expression is converted to
A

(a)
By squaring both sides of the resulting equation and solving it with respect to R, we get
R 0.25 D

1-

A ² + 1

(b) or in relative terms

0.25

1-

A ² + 1

(c)
In the limit in a pipe with annular turbulators
l _max 0,5t, where t is the step of the turbulators, i.e.

Тогда R_макс можно определить из выражения

0,25

1-

+ 1

Минимальное значение R определяется конструктивно-технологическими возможностями:
R_minr_н+δ где δ- толщина стенки трубы.A _max =

Then R _max can be determined from the expression

0.25

1-

+ 1

The minimum value of R is determined by the design and technological capabilities:
R _min r _n + δ where δ is the pipe wall thickness.

Given that r _n ≈0.5δ,
R _min 0.5δ + δ = 1.5δ
A smoother protrusion is possible only at R> R _min .

The range of optimal values of R ₁ and R ₂ is between R _min and R _max and is determined on the basis of studying the results of studying the flow structure behind protrusions with profiles of different smoothness.

As shown by studies and analysis, the optimal range of values of R ₁ and R ₂ lie within the claimed expressions.

 In FIG. 1 shows a section of a heat exchanger pipe, a longitudinal section; in FIG. 2 a, b the results of comparative studies of the aerodynamic and hydraulic drag of pipes with annular turbulators, made according to the invention and currently used in practice.

 The heat exchange tube has annular turbulators-grooves 1 and their corresponding annular turbulators, protrusions 2 of a smooth profile, consisting of two circular arcs: the first along the flow 3 and the second along the flow 4, conjugated at the upper point (top) 5 of the protrusion 2, as well as smooth sections 6 between the turbulators.

In FIG. 1 R ₁ and R _{2 are the} radii of the arcs of circles, respectively, of the first along the stream 3 and the second along the stream 4, l of the hemichord of the circular arc (for the arc of the first along the flow ll ₁ , for the second along the flow ll ₂ ), h height of the turbulence protrusion at the junction point of the arcs; d the diameter of the pipe in place of the turbulator; D the diameter of the pipe in place of a smooth section; δ is the pipe wall thickness; r is the radius of the arc of the circle forming the turbulizer-groove (respectively, the arcs of the turbulizer-protrusions r ₁ and r ₂ ).

 The pipe works as follows.

When the heat carrier moves inside the heat exchanger pipe, i.e. across the turbulizer-protrusions 2, the flow of liquid (gas) first washes the upstream part of the profile of the turbulator 3, made in the form of a circular arc of radius R ₁ , and then passes through the upper point (top) 5 of the protrusion 2 and washes the back part of the profile of the turbulator 4, made in the form of an arc of a circle of radius R ₂ . Moreover, due to a certain (smooth) configuration of the protrusion profile corresponding to the claimed optimal range of values of R ₁ and R ₂ , separation zones are formed in front of and after the turbulator, in which there are no visible two-dimensional vortices. When the incident flow turns onto a smoothly defined protrusion, a system of three-dimensional vortices arises (it is possible to form a system of three-dimensional vortices in combination with a small vortex behind the protrusion), which determines the increased generation of turbulence at the upper boundary of the vortex zone. The absence of two-dimensional vortices reduces the hydraulic (aerodynamic) resistance inside the heat exchange tube, since the additional energy of the averaged flow is spent only on maintaining the specified system of vortices. At the same time, the intensification of heat transfer (an increase in the heat transfer coefficient) can outstrip the increase in hydraulic (aerodynamic) resistance.

 As follows from FIG. 2, the hydraulic and aerodynamic drag in the pipes, the profile of the turbulators, in which, according to the claimed recommendations (A 2.1--7.41), both in air and in water is 25-35% lower than in pipes with a profile of turbulators , the characteristics of which are outside the claimed limits (A1.79-2.0). In this case, the heat transfer coefficient remains virtually unchanged.

 Thus, the use of a pipe with a turbulator profile, made according to the proposed law, can significantly increase its efficiency by reducing hydraulic resistance.

Claims (1)

HEAT EXCHANGE PIPE with annular turbulators-grooves of an asymmetric transverse profile and their corresponding annular turbulizer-protrusions on the inner surface, moreover, the said profile is formed by two sections conjugated at an extreme point, one of which is made in the form of an arc of a curve line and is located first along the coolant, characterized in that, in order to increase the efficiency of the heat transfer pipe by reducing hydraulic resistance, sections of the profile of the turbulator-protrusion in made in the form of arcs of circles of different radius, and the interval of optimal values of the values of the radii is determined from the following relationships:

where D is the inner diameter of the pipe in the area between the protrusions;
d minimum internal diameter of the pipe in the region of the extreme point of the protrusion profile;
t step turbulators.

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