JPH05141890A - Heat transfer tube with inner surface groove - Google Patents

Abstract

PURPOSE:To obtain a high fin heat transfer tube which has high performance and is coped with a small size and high performance of a heat exchanger and a noncleaning step without reducing productivity. CONSTITUTION:A heat transfer tube with an inner surface groove has a continuous and spiral groove on an inner surface of the tube in such a manner that each groove has a crest curved part and an oblique straight part connected smoothly to the curved part and the straight part and a bottom straight part of the groove are smoothly continued by a curve having a radius R of curvature for satisfying the relationship of 1.5<=h/R<=4 (h: the depth of the groove). The minimum radius Di of the tube and the depth h of the groove satisfy the relationship of 0.03<=Di s 0.04, and an angle a formed between the straight parts of both sides at the section perpendicular to the fin tube falls in a range of 35 degrees <= alpha <= 50 degrees.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat transfer tube with an inner groove,
More specifically, the present invention relates to an improvement of an inner surface spiral grooved heat transfer tube suitable for use in a heat exchanger such as an air conditioner or a refrigerator in which the fluid in the tube changes phase.

[0002]

2. Description of the Related Art Generally, in a heat transfer tube with an inner groove, grooves are continuously and spirally provided on the inner surface of the tube, and the fin portion has a triangular shape, a trapezoidal shape, a semicircular shape, or the like. For example,
Japanese Patent Laid-Open No. 62-142995 discloses an inner grooved tube having a trapezoidal fin portion, which has a minimum inner diameter Di, a fin height h, a groove helix angle γ, a fin crest angle α, and a groove sectional area s. Proposed a heat transfer tube having h / Di, γ, α, and s / h as parameters in a range where the heat transfer performance in the tube is optimum.

[0003]

By the way, the shape of the fin portion and the shape of the groove portion are closely related to the heat transfer performance, the fin workability and the weight of the heat transfer tube.

That is, regarding the heat transfer performance, the inner surface area is increased, the liquid holding and wetting area is increased by the capillary phenomenon, the turbulent flow effect, the effect of thinning the liquid film on the protrusion, and the swirling by giving a spiral angle. The effect of generating a force and increasing the wetted area, etc. are affected. It is known that the form of liquid flow in a two-phase flow in a pipe varies depending on the dryness. For example, when evaporating the liquid in the pipe, the performance of the pipe with internal groove is fully exhibited when the inner surface of the pipe is sufficiently wet with the liquid during the transition from the annular wave flow to the annular flow. There is. In this case, the groove is covered with the liquid film, and evaporation is promoted in the thin portion of the liquid film. In the case of condensation, the condensed liquid flows along the grooves and flows to the lower part. However, the better the discharging action is, the thinner the liquid film formed on the heat transfer surface is, and the heat transfer performance is improved. Regarding the weight of the heat transfer tube, the smaller the fin area, the smaller the wall thickness at the same bottom.However, in general, in the slim fin shape, the smaller the peak angle and the higher the fin height, the greater the groove formability. Known to be bad.

In recent years, the need for miniaturization and high performance of heat exchangers has promoted higher performance of heat transfer tubes, and improvements are being made to areas where processing is difficult. For example, in order to improve the heat transfer performance of the inner grooved tube, the shape has been improved by increasing the fin height and increasing the inner surface area, but in the shape where the fin crest angle is large and the fin tip curvature is large. , The higher the fin, the smaller the bottom of the groove,
The liquid discharging effect is hindered. Also, if the weight of the heat transfer tube increases, there is a problem that the weight of the heat exchanger increases and the cost increases, and if the fin crest angle is made small and slim to solve this problem, the metal flow is poor and There is a problem that the fins are not formed. Specifically, the groove of the grooved tool becomes narrower and deeper, and a larger pressing force is required to fill the material compared to the conventional shape, but increasing the pressing force also increases the drawing load, The flow is not in the groove direction but in the pipe axis direction, and as a result,
It is not possible to obtain a sufficient shape.

Further, from the recent viewpoint of environmental protection, there is a tendency to abolish the cleaning of the heat exchanger with CFCs and organic solvents. Therefore, it is required to reduce the oil remaining on the inner surface of the pipe, which causes the viscosity of the groove forming oil to be lowered. This further deteriorates the moldability and stable workability of the fin (change in shape in the longitudinal direction of the pipe).

Under such circumstances, the above-mentioned conventional heat transfer tube with internal groove has a trapezoidal or semi-circular fin shape, which cannot be sufficiently dealt with.

The present invention has been made in order to meet the demands for miniaturization and high performance of the above heat exchanger, abolishment of cleaning, etc., and its purpose is to provide a high fin high performance which can be manufactured without lowering productivity. To provide a heat transfer tube.

[0009]

As a result of intensive studies to solve these problems, the present inventor has found that, even in the case of a slim fin shape, the gap between the groove bottom and the linear portion of the sloped surface of the fin is reduced. It was found that the metal flow at the time of deformation can be improved and the liquid film thickness at the groove bottom can be reduced to improve the heat transfer performance by providing an appropriate curvature to the present invention. is there.

That is, according to the present invention, a groove is formed continuously and spirally on the inner surface of the pipe, each groove has a mountain peak curve portion and a slope straight line portion smoothly connected to the peak peak portion, and the slope straight line portion and the groove bottom straight line portion are formed. The curve has a radius of curvature R that satisfies the relationship of 1.5 ≦ h / R ≦ 4 (h: groove depth) and is smoothly continuous, and the minimum radius Di and the groove depth h of the inner grooved heat transfer tube are 0. An inner surface groove satisfying the relation of 03 ≦ h / Di ≦ 0.04, and an angle α formed by the inclined straight portions on both sides in a cross section perpendicular to the fin tube axis is in the range of 35 ° ≦ α ≦ 50 °. The main point is the attached heat transfer tube.

The present invention will be described in more detail below.

[0012]

[Action]

The inner surface grooved heat transfer tube of the present invention has continuous and spiral grooves on the inner surface of the tube, and each groove has a mountain peak curve portion and a sloped straight line portion smoothly connected to the peaked straight line portion and the sloped straight line portion and the groove. An inner spiral grooved tube whose bottom straight portion is smoothly continuous with a curve having a radius of curvature R, and its cross section perpendicular to the tube axis generally has a shape as shown in FIG.

Here, the curve of the summit means that the summit is not a straight line. The slope linear portion includes not only the case where the slope is linear, but also the case where the slope is substantially linear. The groove bottom linear portion is a portion that connects the R portions of adjacent mountains, and is a portion that is parallel to the outer peripheral surface (always having a certain curvature) of the pipe, and is microscopically linear. Since it can be said, it is called a straight line portion.

However, in the present invention, it is necessary that the heat transfer tube with the inner surface groove has a shape and size which satisfy the following conditions.

H / Di: The ratio of the minimum radius Di of the grooved pipe to the groove depth h. If h / Di is less than 0.03, sufficient heat transfer performance can be obtained in miniaturization and high performance of the heat exchanger. Absent. on the other hand,
If it exceeds 0.04, the moldability is poor even if a curvature is provided at the bottom of the groove, it becomes difficult to process, and the performance is saturated,
Not enough effect. In the shape with improved groove formability, it is possible to form a slim fin even with a high fin having h / Di of 0.03 or more, but 0.032 or more is required to improve heat transfer performance. preferable.

Α: If the angle (peak angle) α formed by the sloped straight portions on both sides in a cross section perpendicular to the fin tube axis is less than 35 °, moldability is difficult and a high fin shape cannot be obtained, resulting in high performance. Can't get On the other hand, if the angle exceeds 50 °, the fin cross-sectional area is large and the weight is large. In addition, the cross-sectional area of the groove becomes small, and the liquid discharging property deteriorates.

H / R: Ratio of the groove depth h to the radius of curvature R of the curve. When h / R is less than 1.5, the curvature R is large, the cross-sectional area of the groove is reduced, and the weight of the heat transfer tube is increased. .. On the other hand, when it exceeds 4, the cross-sectional shape of the groove becomes trapezoidal and the effect of curvature (improvement of groove formability and shape stability) cannot be sufficiently obtained.

The twist angle γ of the groove is not particularly limited, but if it is small, the effect of turbulence and the effect of scraping up the groove cannot be obtained. On the contrary, if it is too large, the pressure loss becomes large, resulting in sufficient performance. Therefore, it is usually in the range of 10 ° to 30 °, and 18 ° is preferable in terms of the balance of condensation and evaporation performance.

Next, examples of the present invention will be described.

[0021]

[Example] With an outer diameter of about 7 mmφ,

[Table 1] as well as

[Table 2] The heat transfer tube with inner groove having various specifications shown in Fig. 3 was manufactured, and the heat transfer performance and formability were investigated.

The performance test was conducted using the apparatus shown in FIG. The test section was a water-cooled countercurrent double-tube heat exchanger having a total length of 5000 mm, and the test tube was supported so that it was located at the center of the double tube and at the center of the outer tube. Outer tube has outer diameter of 12.69m
mφ, inner diameter 11.49mmφ, plate thickness 0.60mmt, length 50
The one of 00 mmL was used. Freon (R-22) in the test tube
The water was allowed to flow countercurrently to the annular portion for heat exchange. In the evaporation test, the water temperature was adjusted so that the refrigerant was completely evaporated and a predetermined degree of superheat was reached. Also in the condensation test, the water temperature was adjusted so that the refrigerant was completely condensed and a predetermined degree of supercooling was achieved.

Table 3 shows the performance test conditions. Based on the measurement result,

[Equation 1] The overall heat transfer coefficient (ko) was calculated by. Where Q: heat transfer
(kcal / h), Ao: test tube outer surface area (m ² ), ΔTm: logarithmic mean temperature difference (° C), where ΔTm is To: inlet water temperature
(° C), T ₂ : outlet water temperature (° C), ts: evaporation temperature or condensation temperature
(° C)

[Equation 2] It is represented by.

The film heat transfer coefficient inside and outside the tube is W
It was calculated by illson-Plot. Water-side film heat transfer coefficient (ho)
Is

[Equation 3] Was assumed. Here, Co: a factor resulting from the shape of the outer surface of the test tube, k: hydrothermal conductivity, De: equivalent diameter (≡di-D
o), di: outer tube inner diameter, Do: test tube outer diameter, Re: ≡ Deu /
ν (u: water flow rate, ν: water viscosity), Pr: ≡ Cpμ / k,
μ: water viscosity, μw: viscosity at water pipe wall temperature.

The moldability is

[Table 4] It evaluated by the standard shown in.

The test results are shown in Tables 1 and 2. All of the examples of the present invention are high-fin high-performance heat transfer tubes and have good groove formability. The test results for some test tubes are summarized in FIGS. 3 and 4, the performance ratio is shown as a relative ratio with the conventional example (marked by ▲) as 1. Note that FIG. 5 shows the relationship between the crest angle and the tube weight (unit weight ratio) with the crest angle (α) of 40 degrees as a reference. If the crest angle is too large, the tube weight becomes heavy and the cost increases.

The formability of the grooves shown in Tables 1 and 2 is summarized by the relationship between h / Di and h / R.

[Table 5] Shown in. Within the scope of the present invention, it has good moldability, but h
When both / Di and h / R are large, moldability tends to be slightly difficult.

[0028]

As described in detail above, according to the present invention,
It is possible to provide a high-fin high-performance heat transfer tube corresponding to a heat exchanger having a smaller size and higher performance and a cleaning-less process without lowering productivity.

[Brief description of drawings]

FIG. 1 is a cross-sectional view perpendicular to a tube axis of a heat transfer tube with an inner groove according to the present invention.

FIG. 2 is a diagram schematically showing a heat transfer performance test device.

FIG. 3 is a diagram showing a relationship between h / Di and an evaporation performance ratio.

FIG. 4 is a diagram showing a relationship between h / Di and a condensation performance ratio.

FIG. 5 is a diagram showing a relationship between a peak angle α and a unit weight ratio.

[Explanation of symbols]

 P Dynamic strain pressure detector PD Dynamic strain differential force detector T Pt Temperature sensor

[Table 3]

Claims (1)

[Claims] 1. A continuous and spiral groove is formed on the inner surface of the pipe, and each groove has a crest curve portion and a slope straight line portion smoothly connected to the peak peak portion, and the slope straight line portion and the groove bottom straight line portion are 1.5 ≦. h / R ≦ 4
The curve has a radius of curvature R that satisfies the relationship of (h: groove depth) and is smoothly continuous, and the minimum radius Di and the groove depth h of the inner surface heat transfer tube with groove are 0.03 ≦ h / Di ≦ 0.04. And the angle α formed by the inclined straight portions on both sides in the cross section perpendicular to the fin tube axis is in the range of 35 ° ≦ α ≦ 50 °.