RU186831U1 - FIRE BOILER - Google Patents

Abstract

A fire tube boiler is proposed that contains a furnace with periodically arranged protrusions of a smooth configuration (corrugation) made in the form of an ellipse with a cross-section with a corrugation efficiency coefficient k: k = F / F = 1.19, F is the actual area of the corrugated surface; F is the normal area the efficiency of the furnace η is determined by the formula: η = Q / Q, where Q is the heat used to heat the cold liquid Q = Q + Q, Q is the heat transferred by convection Q = αΔTS, where ΔT = T-T: T is the gas temperature in firebox; T- temperature of the furnace wall; Q- heat transferred and radiation determined by the probabilistic Monte Carlo method; Q is the amount of heat released during the combustion of the fuel, which is determined by the volume composition,%, and the known calorific value of the components (lower calorific value). The useful model relates to the power system and can be used in heating systems and hot water supply, including in household appliances, as well as a heater for liquids and gases. The calculated data confirm that an increase in the efficiency η is achieved through the use of protrusions of a smooth configuration (corrugation), due to the height of the protrusions h = 40 mm and the coefficient of corrugation efficiency k = 1.19. With these values, the efficiency is 9.5% higher than that of a furnace with an ellipse cross-sectional shape and 4% higher than that of a furnace with a cross-sectional shape of an ellipse with a finned surface inside the furnace. 5 ill.

Description

The utility model relates to a power system and can be used in heating and hot water supply systems, including household appliances, as well as a heater for liquids and gases.

A fire tube boiler is known, comprising a burner with a firebox, a reversing chamber, and a bundle of convection tubes in a water supply housing. (See “Handbook of heat exchangers: In 2 vols. T 2 / Transl. From English under the editorship of OG Martynenko et al. - M .: Energoatomizdat, 1987. - 352 p.).

The disadvantages of this boiler is its low efficiency, due to the low heat transfer coefficient in the furnace.

The closest to the claimed utility model in terms of technical nature and the effect achieved is a fire tube boiler, which contains a cylindrical body with a cooling chamber for exhaust gases, a heat chamber with a furnace coaxial with it, having an ellipse with transverse fins in the cross section in the cross section, with finning coefficient ϕ = 1, 32. Smoke tubes are placed around the flame chamber. The supply and removal of water to the housing is carried out by means of nozzles, and its heating is carried out using a burner fixed in the front of the housing (Patent RU 151351 publ. 07.08.2014).

The disadvantages of the known boiler are associated with an increase in the coefficient of hydraulic resistance, since in a number of special cases the pressure drop that can be used to pump the coolant is significantly higher than the possible hydraulic losses in this device for any structurally feasible flow turbulence. In non-circular fire chambers, the flow structure during the transition and turbulent flow changes not only normal to the wall, but also along the perimeter of the channel, and therefore, along with the turbulent flow in the flow core and near the wall in wide parts of the channel, there can be zones with weak turbulence or even with a laminar flow.

Therefore, when developing methods for intensifying heat transfer in such channels, it is necessary not only to look for ways of additional turbulization of the near-wall region in wide parts of the channel, but specific ways for turbulization of the flow in the corner zones. The hydrodynamic structure of the turbulent flow and the distribution of heat flux densities or temperature fields will allow us to identify areas in which an increase in the intensity of turbulent pulsations has the greatest effect on the intensification of heat transfer. The turbulent thermal conductivity in them is small in comparison with its values in the flow core, and the heat flux density is close to the maximum.

A study of the structure of the turbulent flow and the heat transfer mechanism in it showed that large-scale pulsations directed from the flow core to the wall as a result of the interaction of the flow core with the wall play an important role in heat transfer. In this case, large masses of coolant are transferred from the flow core to the wall and vice versa, the number of emissions from the wall increases, stimulating the generation of turbulence.

Corrugation of the inner surface has been widely used in heat exchangers [Kalinin E.K., Dreitser G.A., Kopp I.Z., Myakochin A.S. Effective heat transfer surfaces. - M .: Energoatomizdat, 1988 .-- 408 p. (p. 26, 63)], and the use of this intensifier in boiler furnaces has been little studied.

The main disadvantage of the above-described boilers of the same purpose is the low efficiency of the furnace η, due to the low heat transfer coefficient in the furnace.

The technical problem to be solved in the proposed device is to create a boiler design with improved thermal properties and a decrease in hydraulic resistance in order to obtain the highest efficiency of the furnace as a result of creating

This technical result is achieved by the fact that in a fire-tube boiler containing a water supply body, in the cavity of which a coaxial fire chamber is placed, having an ellipse in cross section with a burner installed in it, the fire chamber communicates with a convective tube bundle according to the proposed technical solution, the inner surface of the fire chamber is made corrugated with the formation of folds over a fixed distance with a coefficient of corrugation efficiency

k _G = F _G / F _H = 1.19,

where F _G - the actual area of the corrugated surface;

F _H - normal smooth surface area

The essence of the technical solution is illustrated by drawings, where:

in FIG. 1. Schematically shows a longitudinal section of the proposed fire tube boiler;

in FIG. 2. Schematically shows a cross section of the proposed fire tube boiler;

in FIG. 3. A plot of the relationships between the amount of heat transferred from the gas to the wall due to molecular heat conduction, convection and radiation, corrugated Q _corrugation to a smooth Q _{ellipse of} the furnace surface versus the fillet radius, which shows the section with the maximum _corrugation / Q _ellipse ;

in FIG. Fig. 4. Graph of dependences of the ratios of the amount of heat transferred from gas to the wall due to molecular thermal conductivity, convection, and radiation of the corrugated Q _corrugation to a smooth Q _{ellipse of} the furnace surface on the frequency of arrangement of turbulators t / h, which shows the section with maximum Q _corrugation / Q _ellipse at a constant coefficient of corrugation efficiency k _G , and at a constant height of the corrugation h;

in FIG. Fig. 5. Graph of the dependences of the ratios of the efficiency of the corrugated n _corrugation to the smooth n _{ellipse of} the furnace surface on the frequency of arrangement of turbulators t / h, which shows the section with the maximum η _corrugation / η _ellipse at a constant coefficient of corrugation efficiency k _G , and at a constant corrugation height h .

The fire tube tube contains a housing 1 filled with liquid, a burner 2 with a furnace 3 having an ellipse cross-sectional shape, the inner surface of the furnace is corrugated to form folds at a fixed distance with a corrugation efficiency coefficient k _G , a reversing chamber 4, and a bundle of convection tubes 5 (FIG. . one).

The boiler works as follows:

In the furnace 3 from the burner 2 direct the flow of flame. Combustion processes occur in the furnace. Next, the flow of combustion products enters the reversing chamber 4 and then into the convective bundle of pipes 5. A part of the heat of combustion and the heat of the exhaust gases is transmitted through the corrugated wall of the furnace to the heat carrier in the housing 1.

A turbulence model with two equations is used to describe turbulent flows of reacting gases. This turbulence model is called k-ε (Mikhailov, A.G. Numerical modeling of heat and mass transfer processes during combustion of gaseous fuel in the furnace volume / A.G. Mikhailov, P.A. Batrakov, S.V. Terebilov. - Natural and Technical Sciences . - 2011 - No. 5 (55). - P. 354-358), where k is the turbulent kinetic energy, ε is the dispersion value of the kinetic energy.

An effective method of turbulization of the parietal layer is the creation of separation zones near the wall. Periodically located protrusions of a smooth configuration provide for the generation of turbulent vortices that propagate along the wall and weakly diffuse into the flow core. This turbulization of the near-wall layer is achieved with the smallest hydraulic losses, since with the smooth shape of the protrusion either only a system of three-dimensional helical vortices is formed, or the same system, supplemented by a small unstable two-dimensional vortex behind the protrusion. Hydraulic losses due to the formation of such a system and energy dissipation in it are much smaller than in vortex structures in rectangular ones, with a rather close generation of excess turbulence. The height of the protrusions should be commensurate with the height of the wall layer, in which the bulk of the thermal resistance between the flow and the wall is concentrated. The distance between the protrusions should not be too small or too large. With frequent arrangement of turbulizers (t / h <5), the turbulent pulsations arising behind them do not have time to fade noticeably on the way to the next turbulizer and will diffuse into the flow core, increasing the intensity of turbulent pulsations. This results in large hydraulic losses. With a sufficiently large distance between the turbulators (t / h≥5), turbulent pulsations that additionally arise in the vortex zone or during their periodic destruction are transmitted by the main stream closer to the wall. This allows one to achieve significant intensification of heat transfer at the cost of minimal hydraulic losses. If the distance between the turbulators is too large (t / h> 100), the additional turbulence that arises behind them has time to fade noticeably at a certain distance from them, and the rest of the channel section to the next turbulizer differs little in structure from the smooth channel.

As the analysis of a mathematical experiment showed, when considering this technical problem with a given shape and height of the turbulators, the maximum increase in heat transfer and hydraulic resistance is achieved at t / h in the range from 4.5 to 6.5, while the maximum hydraulic resistance strongly depends on the shape of the turbulators related three-dimensional and non-stationary vortex structures.

Thus, to reproduce a given effect of heat transfer intensification, the surface must have geometry with reproducible parameters of turbulators (height, placement step, geometric shape).

Here is the calculation of the coefficient of corrugation

The corrugation efficiency coefficient k _{G is} calculated according to the formula [Kalinin E.K., Dreitser G.A., Kopp I.Z., Myakochin A.S. Effective heat transfer surfaces. - M .: Energoatomizdat, 1988 .-- 408 p. (p. 26, 63):

k _G = F _G / F _H = 1.19, where

F _G - the actual area of the corrugated surface;

F _H - normal smooth surface area.

F _r = π⋅d _Er ⋅ (L-δ⋅n) + π⋅d _Э ⋅ (L-δ _р ⋅n) + n⋅π⋅ (d _Er ² -d _Э ² ) / 2,

F _H = π⋅d _Э ⋅L, where

The equivalent diameter of the cross section of the furnace in the form of an ellipse is calculated by the formula:

d _e = 1.55⋅S ^0.625 / P ^0.2 , where

S is the cross-sectional area of the furnace in the form of an ellipse;

P is the perimeter of the cross section of the furnace in the form of an ellipse.

S = π⋅a⋅b,

P = 2⋅π ((a ² + b ² ) / 2) ^1/2 ,

where π = 3.1415 rad

a - semimajor axis;

b - minor axis.

a = a _D - inner major axis of the corrugated pipe,

b = b _D is the inner minor axis of the corrugated pipe;

d _EP is the equivalent diameter of the fold,

where a = a _d is the semi-major axis along the height of the fold (Fig. 2.),

b = b _d - minor axis along the height of the fold;

n = τ / 2 is the number of folds;

δ _p - the thickness of the fold (δ _p = 4⋅π⋅А + τ / 2),

τ is the corrugation pitch, A is the fillet radius (Fig. 1));

L is the length of the furnace,

With the following geometric characteristics

L = 1000 mm

b_D=410 мм,

b _D = 410 mm

b _d = 330 mm

t = 200 mm

h = 40 mm

A = 10 mm:

we obtain k _Г = F _Г / F _H = 1,19.

The efficiency of the furnace η is determined by the formula:

η = Q ₁ / Q _calculation ,

where Q ₁ is the heat used to heat the cold liquid

Q ₁ = Q _C + Q _R ,

Q _C - heat transmitted by convection

Q _C = αΔTS, where

ΔT = T ₁ -T ₂ :

T ₁ - gas temperature in the furnace;

T ₂ - the temperature of the wall of the furnace;

Q _R is the heat transmitted by the radiation, determined by the probabilistic Monte Carlo method;

Q _calc - the amount of heat released during the combustion of fuel, which is determined by the volume composition,%, and the known calorific value of the components (lower calorific value).

In this way:

b_D=440 мм,

b_d=330 мм, t=250 мм, h=55 мм, А=10 мм).In comparison with the patent (RU 151351 publ. 07.08.2014) if the coefficient of corrugation efficiency remains unchanged k _Г ≈1.32 maximum values of Q _corrugation / Q _ellipse = 1.17 (Fig. 5), η _corrugation / η _ellipse = 1,075 (Fig. 6) are achieved at a frequency of arrangement of turbulators t / h = 4,5 (L = 1000 mm,

b _D = 440 mm

b _d = 330 mm, t = 250 mm, h = 55 mm, A = 10 mm).

b_D=410 мм,

b_d=330 мм, t=200 мм, h=40 мм, А=10 мм).In a specific example, with a constant protrusion height h = 40 mm, the maximum values of Q _corrugation / Q _ellipse = 1,115 (Fig. 5), η _corrugation / η _ellipse = 1,093 (Fig. 6) are achieved with a corrugation efficiency coefficient k _Г = 1,19 , and the location frequency of the turbulators t / h = 5 (L = 1000 mm,

b _D = 410 mm

b _d = 330 mm, t = 200 mm, h = 40 mm, A = 10 mm).

Consequently, the calculated data confirm that the boiler, in which the inner surface of the furnace is corrugated with the formation of folds at a fixed distance with the coefficient of corrugation efficiency k _Г = F _Г / F _H = 1.19, leads to an increase in efficiency by 9.5% than for a furnace with a cross-sectional shape of an ellipse and 4% than that of a firebox with a cross-sectional shape of an ellipse with a ribbed surface on the inside.

Claims (4)

A fire tube boiler containing a water supply body, in the cavity of which a coaxial fire chamber is placed, having an ellipse in cross section, and a burner is installed in it, characterized in that the inner surface of the fire chamber is corrugated to form folds over a fixed distance with a corrugation efficiency coefficient k _Г = F _Г / F _Н = 1,19, where F _G - the actual area of the corrugated surface; F _N - normal smooth surface area.

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