JPS6029593A - Construction of single-phase flow heat-transfer pipe - Google Patents

Abstract

PURPOSE:To enhance a heat transfer accelerating effect, by providing the inside surface of a single-phase flow heat-transmitting pipe with spiral grooves. CONSTITUTION:Ribs 5 are provided on the inside surface of the single-phase flow heat-transmitting pipe 1 at a set angle theta1 against the flow direction F, namely, the axial direction and at a pitch P, whereby primary grooves 2 with a depth e1 are provided. Secondary grooves 3' are cut in a spiral form in the ribs 5 in the manner of intersecting the ribs 5, at a set angle theta2 against the flow direction F and with a depth e2 from the upper surface of the ribs 5. Accordingly, the heat-transfer performance for a single-phase flow can be enhanced.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] This invention relates to the structure of a heat exchanger tube used in a heat exchanger such as an air conditioner or a refrigerator. This invention relates to a single-phase flow heat exchanger tube structure having primary grooves that intersect each other at predetermined angles with respect to the primary grooves, and secondary grooves formed in the primary grooves.

[Background of the invention]

As is well known, heat exchangers such as air conditioners and refrigerators are equipped with heat exchange tubes, and the inner structure of these tubes is generally designed to allow a single-phase flow of liquid or gas to flow through them, including straight tubes. However, it is known that a special structure is formed on the inner surface of the heat transfer tube to provide a function of improving thermal conductivity compared to the straight and smooth tube.

For example, heat transfer tubes in which three-dimensional grooves are formed in an intersecting manner on the inner surface of the tube are known, and a so-called cross rifle evaporation tube is known as an attempt to improve the critical heat flux as a measure to prevent burnout in boilers with high heat loads. , as a reference, Transactions of the Japan Society of Mechanical Engineers, Vol. 39, No. 32, pp. 1268 to 127.
It is described over 7 pages, and as a patent document, there is JP-A-54-116765.

By the way, the first one is shown in the patent document.

As shown in FIGS. 2 and 3, a spiral primary groove 2 having a set angle 01 with respect to the axial direction and a secondary groove 3 having a set angle θ are intersected and formed on the inner surface of the heat exchanger tube 1. The mutual pitch of these grooves 2 and secondary grooves 3 is mathematically very fine and is in the range of 0.15 to 1.5 pitches, and as a result -
A large number of minute protrusions 4, 4, . . . are formed between the notched groove 2 and the secondary groove 3.

By doing so, boiling and condensing heat transfer performance can be improved.

However, if a heat transfer tube having a structure related to boiling and condensation heat transfer is simply used as a single-phase flow heat transfer tube, the following problems occur.

That is, when the above-mentioned heat transfer tube is used as a heat transfer tube for single-phase flow without phase change, the flowing fluid flows through the projections 4.4 and 4.4.
... and as a result, a vortex is formed near the inner wall surface, and when the boundary between the vortex and the mainstream of the flow approaches the wall surface, the streamlines stagnate at the rear of the protrusion 4, forming a newly opened dead zone, and the heat exchanger tube It has the disadvantage of significantly reducing heat transfer performance.

Furthermore, if a nuclide heat transfer tube is used as a single-phase flow heat transfer tube in a temporary structure, the pitch between the primary grooves 2 and the secondary grooves 3 is extremely small as shown in the figure, so the forming process requires an extremely large number of man-hours, resulting in high costs. Disadvantages: Another disadvantage is that accuracy control is extremely careful.

By the way, as a result of theoretical analysis and experimental observation, the inventors analyzed the above-mentioned improvements in boiling and condensation heat transfer performance and inhibition conditions for single-phase flow in the structure of the conventional heat transfer tube, and found that In the stagnation region, the heat transfer coefficient locally increases significantly at the reattachment point of the next protrusion; It was also found that the range of optimum values differs depending on the heat transfer mode of condensation and that of single-phase flow.

[Purpose of the invention]

The purpose of this invention is to solve the problems of the inner wall structure of heat transfer tubes based on the above-mentioned prior art, and to solve the problems of the inner wall structure of heat transfer tubes based on the above-mentioned conventional technology. By determining the numerical range of the shape, the present invention aims to provide an excellent single-phase flow heat exchanger tube structure that is useful for heat exchange applications in the energy industry.

[Summary of the invention]

In accordance with the above-mentioned object, the present invention is summarized as follows: In order to solve the above-mentioned problems, primary grooves are formed spirally in the axial direction on the inner surface of a single-phase flow heat exchanger tube at an angle of 0° to 0°. 30" through the lip, and furthermore, the pitch of the notch groove is 2 to 5 m, and the lip forming the notch groove is formed with a secondary groove in a spiral shape at an angle of 0° to -30°. A technical measure has been taken in which the grooves are cross-formed at a set angle and the depth of these grooves is formed to a predetermined value to maximize the effect of promoting heat transfer.

Embodiment Next, an embodiment of the present invention will be explained below based on the drawings from FIG. 4 onwards. The same parts as in FIGS. 1 to 3 will be described using the same reference numerals.

In the basic embodiment shown in FIG.
The primary grooves 2.2... are carved with a depth el by forming the lips 5,... with a pitch p at a set angle θl with respect to the flow direction F, that is, with respect to the axial direction. It is being set up.

Similarly, the upper EIJ blades 5, 5... are crossed at a set angle θ3 with respect to the flow direction F, that is, with respect to the axial direction, and the depth C! Secondary groove 3/
, 3/... are similarly engraved and formed in a spiral shape.

Similarly, regarding the set angles θ weight and θ snow, if they are on the right side and in the same direction with respect to the axial direction, they are expressed as +, and when they are on the left side, they are expressed as -.

Therefore, in the basic embodiment shown in FIG. 4, the set angle θ1 is + and the active set angle 011 is -.

Therefore, in the embodiment shown in FIG. 5, where the set angle 011 and θ3 are on the same side with respect to the flow direction F, the streamline of the single-phase flow flowing along the primary groove 2 For secondary groove 3
It can be seen that the streamlines flowing in from ' are mixed smoothly and flow through without causing any disturbance.

On the other hand, in the embodiment shown in FIG. 6, the set angle θl
is on the + side with respect to the flow direction F, while the set angle θ3
There is a reed on one side, so that the streamline from the secondary groove 3/ is a delicate vortex line 7 formed by the protrusion 6 formed on the lip 5 with respect to the streamline from the primary groove 2. was recognized.

As will be explained in detail later, these vortex lines 7 actually promote heat transfer between the single-phase flow and the heat exchanger tube 1, and play a major role in producing a high-performance single-phase flow heat exchanger tube 1. This is what happens.

The above description is mainly based on the results obtained by creating a model suitable for observation and conducting experiments.Next, the numerical measurement results obtained from these and the theoretical background will be described.

The results of measuring the pressure loss and heat transfer coefficient of various single-phase flow heat transfer tubes 1 in accordance with the above-mentioned embodiments are shown in the graph of FIG. 7. In the graph of FIG. This is data obtained by fixing the setting angle θl of the secondary pitch 3 and investigating the influence of the setting angle θ2 of the secondary pitch 3.
-d/v, u: average flow velocity in the pipe (m/s), d
: Pipe inner diameter (z), C: Fluid kinematic viscosity coefficient (W?/8))
The vertical axis is the dimensionless heat transfer coefficient Nu/Pr (=α
d/λ10.4 pr, α: heat transfer coefficient (W/ll?・K), λ: heat transfer coefficient of fluid (W/ltt”・K), Pr: Prandtl number of fluid), and resistance of pipe line The coefficient f is shown.

Although it is not shown in Figure 7 to avoid being cautious, we conducted an experiment on a smooth tube without any grooves on the inner surface of the tube, and found that the heat transfer coefficient was not shown in the figure to avoid being cautious. D 1 t tus Boetter
Equation (7), Nu=0.023Re"pr"' (graph A
), and the resistance coefficient of the pipeline is in good agreement with prand.
tl formula 1/V'T=2.0 tog (Rev'7
″)-O,S (graph B).

The contents of the symbols 69 and 69 in FIG. 7 are as shown in the following table.

By the way, looking at the results of the data shown in FIG. 7, it can be seen that as the setting angle θ2 of the secondary groove 3' decreases, the resistance coefficient of the heat transfer coefficient also increases.

However, the success or failure of the heat transfer performance cannot be directly determined from the results shown in FIG. 7 alone.

Therefore, in the literature whose contents are generally known regarding heat transfer coefficient and resistance coefficient (for example, R, LWebb
and E, R, G, Eckert “Applic
ation of low 5 surfaces to
: [(eat Exchanger]) esign
International Journal of
Heatand Mass 'l'transfer,
■Al, 15, P1647-P1658) Regarding the heat transfer coefficient and resistance coefficient given by -
Single-phase flow heat exchanger tube 1 with grooves 2 and secondary grooves 3' formed
The most common method for evaluation is to calculate the ratio between the smooth tube and the smooth tube that has not undergone any such processing.

These values are 1 for smooth pipes, and as the heat transfer performance improves, the values increase. Therefore, the data shown in Figure 7 above is calculated by adjusting the water velocity to 2.5.
FIG. 8 shows the results summarized for the case of Re=4×10' corresponding to m/S.

In addition, in FIG. 8, C is a two-dimensional lip tube (a=30°,
p=2w, e=0.3mm). (However, to Re=4 It is clearly seen that the performance has improved significantly.

Therefore, when comparing and examining the observation results of the model experiment of the basic embodiment shown in Fig. 5.6 and the results shown in Fig. 8, it is found that the setting angle 01 is 30', and the setting angle θ The goose is 15°
The result is that the condition of 0, θ and θ1 is met, and as in the model experiment shown in FIG. It mixes smoothly and flows through without creating a vortex.

On the other hand, if 01 is 30@ and 03 is -30', then the 6th
Corresponding to the model experiment shown in the figure, it has been observed that the streamline passing through the secondary pitch 3' forms a delicate line 7 at the protrusion 6, causing disturbance.

As shown in FIG. 8, the heat transfer performance in that part is shown to be extremely good.

Therefore, as far as promoting heat transfer in single-phase flow is concerned, it can be seen that a single-phase flow in which both lines 7 above occur to some extent improves heat transfer performance. It is fully predicted that only the pressure drop in the pipeline where the heat transfer is applied will increase, and that there will be no increase in heat transfer.

Incidentally, although the setting angle θ2 of the secondary groove 3' shown in FIG. It is difficult to carve the line grooves 2 and 3' by rolling due to the constraints (11) on the machining of the lip 5 and groove 31.
Therefore, from this point of view as well, the critical angle is ±30@.

On the other hand, when θ==00, drawing can be performed along the axial direction, but generally speaking, it is easiest to produce a groove with θ=0 by drawing.

Therefore, from the point of view of actual heat transfer performance and manufacturing process, the optimal setting angle range for θ2 is θ°~
It turns out that it is -30@.

In principle, the partial groove 2 and the secondary groove 3/ can be considered symmetrical, so the setting angle θ! About'4b
It can be set to 0° to 30@.

Next, regarding heat transfer performance, some groove 2
There is a groove depth el of , and a groove depth el of the secondary groove 3',
When we investigated the cases where the two are equal and the cases where they are different based on various experiments, we found that there is virtually no difference.

However, in the case of el=9, that is, in the case of a two-dimensional ribbed tube, 83 is a finite value as shown in Figure 8 (12) However, the heat transfer performance of the three-dimensional ribbed tube is better. It turns out that the performance is good.

Also, for the range e, Re = 4 for a two-dimensional ribbed tube.
As shown in FIG. 9 in the case of X10', the lip height is 0.
Since results with peak values in the range of 2 to 0.5 m have been obtained, the distance of the inner wall surface 9 is 0.2 to 0.5 m.
It can be considered that the effect of promoting heat transfer is best provided by providing disturbance to the passing fluid within the range of , and this value can also be extended to the secondary groove 3'. .

Therefore, the optimal value for el and e2 is 0.2~
It turns out that 0.5 m is the best.

Next, regarding the pitch p of the partial groove 2 and the secondary groove 31,
As shown in the figure, it has been found that a straightness around p = 4 m is best for three-dimensional ribbed pipes.

In addition, in Fig. 1θ, D is a three-dimensional rib (01=30°
, e1=0.5 kaku, θ2=0°+"2:=0.3 kaku), and E is a two-dimensional rib (θ=30'.

e20.3 questions).

(13) Also, I'te=4×104.

Although shown for reference, a two-dimensional ribbed pipe without secondary grooves 3' also shows good values.

By the way, according to theory, quantitatively, the distance of the reattachment point that brings the protrusion 6 of the lip 5 into the stagnation area of the protrusion 6 is approximately 10 times the height of the lip. As for the size to prevent the formation of a stagnation region, the lip height is set in the range of <0.2~o, sm as described above, and a value of about 10 times the value of 9, that is, 2w~51
The range of 0I is the range in which no stagnation region is formed, and this is the range indicated by hatching in FIG.

Therefore, the optimum pitch range for the groove 2 is 2 to 5 m+
I understand that it is good to be ranked 11.

〔Effect of the invention〕

As described above, according to the present invention, it is basically possible to improve the heat transfer performance of the single-phase flow passing through the inside of the single-phase flow heat transfer tube, and an excellent effect of improving the thermal efficiency is achieved (14).

Also, set the setting angle of the -th groove to 0. By setting the angle to 30'', it is extremely easy to process the spiral groove between the lip and the primary groove, and the excellent effect of increasing precision control is achieved.

Moreover, since it is easy to manufacture, the product yield is high and an excellent effect leading to cost reduction is achieved.

By forming a secondary groove on the lip intersecting the secondary groove, the density of the protrusions formed on the rib becomes coarse, and therefore, unlike boiling and condensing heat transfer cells, The heat transfer tube can be made suitable for single-phase flow, and the heat transfer performance associated with the passage of the single-phase flow can be maximized.

[Brief explanation of the drawing]

Fig. 1 is a partial cross-sectional view explaining a boiling and condensing heat exchanger tube based on the prior art, Fig. 2 is an enlarged perspective view of a portion of Fig. 1, Fig. 3 is a cross-sectional view of Fig. 1, and Fig. 4 and the following are figures according to the present invention. FIG. 4 is a partial perspective view of one embodiment, FIG. 5 is a partially enlarged perspective view of another embodiment, and FIG. 6 is a partially enlarged perspective view of another embodiment. ) Figure 7 is a graph showing the experimental data, Figure 8 is a graph explaining the relationship between the setting angle of the secondary groove and heat transfer performance, Figure 9 is a graph showing the relationship between lip height and heat transfer performance, Figure 10 is a graph explanatory diagram of the relationship between lip, pitch, and heat transfer performance. 1...Heat exchange tube, 2...-Secondary groove, 3'...Secondary groove,
4747 width, 5...rep, θ1. θ2... Setting angle. Agent Patent Attorney Akio Takahashi (16) Akira 1 Figure 3 Tomi 4 Figure ■ 5 Figure 3' 100 Figure ￥: J 7 Figure Reino 1 Shizu@Mata Shakue Calendar 8 Figure 15' ρ −3θ' 2 Oomizo f)/AA θ?

Claims (1)

[Claims] 1. In a single-phase flow heat exchanger tube structure in which at least one spiral groove is formed through ribs at a set angle in the axial direction on the inner surface of the heat exchanger tube, the primary groove forming the groove is formed at a set angle. 1. A single-phase flow heat exchanger tube structure characterized in that a secondary groove is provided at an angle of 0° to 30°, and a secondary groove is further provided to intersect the rib forming the secondary groove. 2. The single-phase flow heat exchanger tube structure according to the patent scope 1, characterized in that the pitch of the -order grooves is formed in the range of 2 to 5a+.