RU2511859C1 - Heat exchanger pipe - Google Patents

Abstract

FIELD: power industry.

SUBSTANCE: in a heat exchanger pipe, smooth pipe sections and ledges form a channel, where ledges feature additional heat exchanger intensifier in the form of discreet slots perpendicular to flow, and the channel matches geometry relations: l₂=(90-100)h; l₁=(90-100)h; l'/l₁=0.05; h/D=0.03, where l₂ is slot length, mm; l₁ is ledge length, mm; l' is length of ledge section between shallow slots, mm; h is ledge height, mm; D is inner diameter of heat exchanger pipe, mm.

EFFECT: enhanced power efficiency due to reduced flow friction.

4 dwg, 1 tbl

Description

The present invention relates to the field of energy and can be used in transport, in chemical technology and other industries.

; Re=3·10³-2·10⁴, где $$\overline{t}=t/h$$

- относительный шаг выступов, Re - число Рейнольдса.Known heat exchange pipe [Gortyshov Yu.F., Olimpiev V.V., Abdrakhmanov A.R. Calculation of turbulent heat transfer and resistance in channels with transverse annular grooves. // Izv. universities. Aircraft technology. 1997. No3. S.56-68], the channel of which is made with narrow annular grooves on the inner surface of the pipe (channel "1"). In this channel, the interaction of the flow and the wall and the essence of the mechanism of heat transfer (heat transfer intensification) is completely determined by heat transfer and friction in the wall inner boundary layers (IPN) 1 and 2, the turbulence of which is provided by the recirculation zone (RE). The perfection of the ITO mechanism lies in the fact that the RE in the channel is located in the groove, which reduces the size of the RE. The experiments with annular grooves were carried out only for the outer surface of the pipes in the annular flow of the heat exchanger (TA), in a limited range of characteristic parameters - $$\overline{t}\le \mathrm{twenty}$$

; Re = 3 · 10 ³ -2 · 10 ⁴ , where $$\overline{t}=t/h$$

is the relative step of the protrusions, Re is the Reynolds number.

The closest analogue to the claimed invention is a heat transfer pipe [Leontyev A.I., Olympiev V.V. The effect of heat transfer intensifiers on the thermohydraulic properties of channels (review). // Thermophysics of high temperatures. 2007. No. 6. S.925-953], the channel of which is made with protrusions and grooves (channel "2"). In channel "2", narrow protrusions on the inner surface of the pipe (l <t, where l is the length of the groove, t is the length of a typical section of the channel with the protrusion and groove) serve as heat transfer intensifier (IT). The idea of the flow scheme is as follows. After each protrusion, РЗ1 is formed, on the surface of which and further beyond the attachment point x _k ≈6h, where h is the height of the protrusion, a turbulent inner boundary layer - IPN1 (thickness δ) develops. Under RP1, a returnable IPN2 is formed (Small P32 is not taken into account). The channel section with step t is typical (repeating). The thermohydrodynamic interaction of the flow with the wall is completely determined by the transfer processes inside VPS1 and 2. The main contribution to the intensification of heat transfer is made by the factors of increased heat transfer in the connection zone and low thermal resistance of the thin renewed turbulized VPS1 behind the connection point. The main purpose of the tear-off recirculation region of the flow - РЗ1 - is the production of additional turbulence, the impact of which on the renewed IPN1 stimulates the heat exchange process near the wall (Flow separation, PS renewal and the formation of РЗ1 are the result of the protrusion).

A disadvantage of the known heat exchange tubes is high hydraulic resistance and low efficiency.

The task to which the invention is directed is to increase energy efficiency by reducing hydraulic resistance.

The technical result is achieved by the fact that in the heat exchange pipe, according to the claimed invention, the channel is formed by smooth sections of the pipe and protrusions, while the protrusions are made with an additional heat transfer intensifier in the form of discrete grooves transverse to the stream, and the channel is made with geometric ratios

l ₂ = (90-100) h; l ₁ = (90-100) h; l '/ l ₁ = 0.05; h / D = 0.03,

 Where

l ₂ - the length of the groove, mm,

l ₁ - the length of the protrusion, mm

l'- the length of the section of the protrusion between the shallow grooves, mm,

h is the height of the protrusion, mm

D is the inner diameter of the heat exchanger pipe, mm

The invention is illustrated by drawings and a table, in which Fig. 1 shows the channel of the proposed heat exchange pipe (channel "3"), Figs. 2, 3, 4, Table 1 show the results of calculations of efficiency (heat transfer rate, coefficient of hydraulic resistance, relative energy coefficient) of channels "7", "2" and "3".

Thus, to achieve a technical result, the claimed design of a heat exchange pipe is proposed, the channel of which (channel "3") is a sequence of wide grooves l ₂ = (90-100) h and wide protrusions l ₁ = (90-100) h, on the protrusions of which as additional IT, discrete transverse to the flow grooves 4 (one or several) are used. The flow model (and the ITT mechanism) in channel 3 is based on thin (updated) internal boundary layers - VPS1, VPS2 and VPS3, which are turbulized (under the influence of external turbulence) by vortex disturbances from the recirculation zone РЗ1 formed behind the backward step at the inlet of the flow into the groove (l ₂ ), and perturbations arising on a straight ledge when the flow flows onto the protrusion (P32) and groove 4. For h / D <0.05, VPS1 and VPS3 quickly rebuild to the state of a “standard” turbulent PS (TPS) on a smooth the wall [Leontiev A.I., Olim iev VV The effect of heat transfer intensifiers on the thermohydraulic properties of channels (review) // TVT. 2007. No. 6. S.925-953]. With the thickness ratios of the corresponding boundary layers and the near-wall flow in the channel, it can be considered as a flow on a flat wall, and to calculate the IPN, use the model of the boundary layer on the plate. The channel 3 calculation model proposed in this paper, built on the basis of the UPU concepts, is similar to those formed during IT flow that were used in [V. Olimpiev Calculation of heat transfer and hydraulic resistance of a turbulent flow in discrete rough channels. // Izv. universities. Aircraft technology. 1991. No4. S.69-72. Olimpiev V.V. Analysis of the calculation results by the model of the internal boundary layers of heat transfer and resistance of pipes with transverse annular protrusions. // Izv. universities. Aircraft technology. 1995. No3. S.103-106].

The calculation of channel "3" is constructed as follows. The local heat transfer coefficients for IPN1 in the interval from x _to l ₂ are calculated by the ratio

where the Nusselt number Nu _x = α _x / λ; x is the current coordinate; λ is the coefficient of thermal conductivity of the coolant (liquid); Re _x = wx / v; w is the average flow rate of the fluid in the channel; ν is the kinematic coefficient of viscosity of the liquid; T _w , T _f - wall and flow temperatures.

Then, the correction α _hist , α _x is introduced, taking into account the influence of external Tu turbulence on heat transfer in IPN1 [A. Zhukauskas Convective transfer in heat exchangers. M .: Science. 1982]

, $$n_{\mathrm{one}}=3.71\cdot {10}^{-3}T{u}_{\max }^{1.41}$$

,

where α _hist is the true value of the coefficient of local heat transfer; Tu is the local value of the degree of turbulence; Tu _max = 10% (or 0.1) [Olimpiev V.V. Calculation of heat transfer and hydraulic resistance of a turbulent flow in discrete rough channels // Izv. universities. Aircraft technology. 1991. No4. S.69-72. Olimpiev V.V. Analysis of the calculation results by the model of the internal boundary layers of heat transfer and resistance of pipes with transverse annular protrusions // Izv. universities. Aircraft technology. 1995. No3. S.103-106.], Tu _max - the maximum value of Tu.

Local drag coefficient and shear stress τ _{wx of} friction for IPN1 are calculated by the formulas

$$\frac{c_{fx}}{2}=\frac{0.029}{{\mathrm{Re}}_x^{0.2}};\left(\text{3}\right)$$

where ρ is the density of the coolant.

The calculation for IPN3 (on segments l ') is carried out similarly to IPN1.

The local heat transfer coefficients for WWS2 (along the length of RE1 - L) are calculated using the universal function for the backward step α _x2 / α _xk = f (x / x _k ) [Fundamentals of heat transfer in aeronautical and space-rocket technology. / Under the total. ed. BC Avduevsky et al. M.: Mechanical Engineering. 1992.], where it is calculated by the formula (1) with x = x _k . Friction for UPU2 is calculated similarly.

Averaging the local parameters VPS1, VPS2, and VPS3 allows one to obtain the average values of the heat transfer coefficient α and the tangential friction stress τ _w in the region t (and in the entire channel).

The total pressure loss in this section can be calculated by the formula

where Δp _mp = R _mp / (πD ^2/4) - pressure losses due to friction, R _mp = πDtτ _w - frictional force; Δp _p and Δp _c are local pressure losses due to sudden expansion and narrowing of the channel when flowing around the groove l ₂ (determined by [Idelchik I.E. Handbook of hydraulic resistances. M .: Mechanical Engineering. 1992]). The resistance coefficient ξ in the region t (and in the entire channel) is calculated from the Darcy formula

The calculations were carried out for the same conditions as in [Gortyshov Yu.F., Olimpiev VV, Popov I.A. Efficiency of industrially promising heat transfer intensifiers // Izv. RAS. Energy 2002. No3. S.102-118]. The relative height of the protrusion was adopted from that recommended in [Effective heat transfer surfaces / E.K. Kalinin, G.A. Dreitzer, I.Z. Kopp, A.S. Myakochin. M .: Energoatomizdat, 1998.] range, and the Reynolds number was 10 ⁴ -10 ⁶ . Multivariate calculations were carried out with various combinations of IT geometric parameters for channels of all types. When calculating the channel "3", the parameter l '/ l ₁ varied within 0-1.

As a criterion for channel efficiency and the optimal choice of IT size, as in the works [Leontiev A.I., Olympiev V.V. The effect of heat transfer intensifiers on the thermohydraulic properties of channels (review) // TVT. 2007. No. 6. S.925-953. Rudy M.P. et all. Developments in Enhanceed Heat Transfer Technology from a Petroleum Industry Perspective in 2012 // Proceedings of the ASME 2012 Heat Transfer Conference. July 8-12, 2012, Puerto Rico.] Served as a relative energy coefficient

,

,

where Nu _hl and ξ _hl are the Nusselt number and the coefficient of friction resistance for a smooth channel.

When comparing options for a channel of one type (for each Reynolds number), the indicator of the highest channel efficiency and optimal IT sizes was the maximum value of the relative energy coefficient, for which all calculation materials are given.

, при этом $${\overline{Nu}}_3$$

превышает $${\overline{Nu}}_2$$

примерно на 28%. Относительная теплоотдача не зависит от числа $$\mathrm{Re}\left(\overline{Nu}\ne f\left(\mathrm{Re}\right)\right)$$

, т.к. характер функций Nu=f(Re") идентичный для гладкого канала и каналов «1;2;3». Модели всех каналов объективно отражают их свойства: при повышенных числах Re и $$\overline{h}=const$$

нарастание сопротивления обгоняет увеличение теплоотдачи $$\overline{\xi }>\overline{Nu}$$

, табл.1.Some calculation results for all channels are given in table 1 and figure 2-4. In a detailed assessment, it can be noted that $${\overline{Nu}}_3>{\overline{Nu}}_2>{\overline{Nu}}_{\mathrm{one}}$$

, wherein $${\overline{Nu}}_3$$

exceeds $${\overline{Nu}}_2$$

about 28%. The relative heat transfer is independent of the number $$\mathrm{Re}\left(\overline{Nu}\ne f\left(\mathrm{Re}\right)\right)$$

because the nature of the functions Nu = f (Re ") is identical for a smooth channel and channels"1;2; 3 ". The models of all channels objectively reflect their properties: at higher Re and $$\overline{h}=const$$

the increase in resistance overtakes the increase in heat transfer $$\overline{\xi }>\overline{Nu}$$

Table 1.

, фиг.3. На всем диапазоне чисел Re сопротивление канала «3» заметно ниже величины $${\overline{\xi }}_2$$

(до 43%), фиг.3, что, вероятно, связано с меньшим количеством РЗ на единицу длины в канале «3». Улучшенная теплоотдача и пониженное сопротивление привели к повышенной эффективности канала «3» по сравнению с др., табл.1, фиг.4.Dimensional coefficients ξ for all channels are self-similar with respect to the number Re-ξ / (Re), which is typical of discrete and sandy-granular roughness Nikuradze in the full manifestation of roughness. The calculations confirmed the assumption made in this work - the resistance of channel “1” turned out to be slightly less $${\overline{\xi }}_3$$

figure 3. Over the entire range of Re numbers, the resistance of the channel “3” is noticeably lower than $${\overline{\xi }}_2$$

(up to 43%), figure 3, which is probably due to a smaller number of RE per unit length in the channel "3". Improved heat transfer and reduced resistance led to increased efficiency of the channel "3" in comparison with others, table 1, figure 4.

In equal conditions, the efficiency of the channel "3" is higher than the indicator of the highly effective channel "2" tested by practice, Fig.4.

Table 1 Efficiency and optimal channel sizes Channel 1 (t / h = 100) Re 10,000 250000 500,000 750,000 1,000,000 Nu / Nu _Ch 1,406 1,406 1,406 1,406 1,406 ξ / ξ _ch 0.948 2.12 2,521 2.79 2,998

1.483 0.663 0.558 0.504 0.469 Channel 2 (t / h = 100) Re 10,000 250000 500,000 750,000 1,000,000 Nu / Nu _Ch 1,414 1,414 1,414 1,414 1,414 ξ / ξ _ch 2,093 3,465 3,914 4,211 4.44

0.676 0.408 0.361 0.336 0.319 Channel 3 (l '/ l ₁ = 0.05) Re 10,000 250000 500,000 750,000 1,000,000 Nu / Nu _Ch 1,953 1,953 1,953 1,953 1,953 ξ / ξ _ch 1.94 2,642 2,853 2.99 3,094

1.007 0.739 0.685 0.653 0.631

Claims (1)

A heat exchange pipe, the channel of which is made with grooves and protrusions, characterized in that the channel is formed by smooth sections of the pipe and protrusions, while the protrusions are made with an additional heat transfer intensifier in the form of discrete grooves transverse to the flow, the channel being made with geometric ratios
l ₂ = (90-100) h; l ₁ = (90-100) h; l '/ l ₁ = 0.05; h / D = 0.03,
Where
l ₂ - the length of the groove, mm,
l ₁ - the length of the protrusion, mm
l 'is the length of the section of the protrusion between the shallow grooves, mm,
h is the height of the protrusion, mm
D is the inner diameter of the heat exchanger pipe, mm

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