Heat exchanging tube with spiral groove

Abstract

The present invention relates to a heat transfer tube with spiral groove, comprising a stainless steel tube body with inward convex spiral groove on surface, wherein the stainless steel tube body possesses unequal height and width in the cross sectional view. In the EGR (Exhaust Gas Recirculation) cooling system for automotive engine, such kind of spiral groove tube with the unequal height and width in the cross-section acting as the heat transfer tube for the cooler make the cooler gain higher heat transfer effect, and it is hard to make dirt deposited inside or outside the tube, which greatly improves the emissions performance for automotive engine, and satisfies higher requirement of environmental protection.

Description

CROSS-REFERENCE TO RELATED APPLICATION [0001]This application claims priority benefit of Chinese patent application No. 200610057223.7 filed on Mar. 9, 2006, the contents of which is hereby incorporated by reference in its entirety.FIELD OF THE INVENTION [0002]The present invention relates to a heat transfer tube with spiral groove, in particular a heat transfer tube with spiral groove applied in the EGR (Exhaust Gas recirculation) cooling system for automotive engine, and its cross-section has unequal height and width.DESCRIPTION OF RELATED ART[0003]The EGR cooling technique is an effective and reliable technique to decrease nitrogen oxides (NOx) emissions of diesel engine. The theory is: decreasing the temperature of the exhaust gas by the cooler, and then returning the gas to the engine combustor in order to decrease the temperature of the combustor so as to reduce nitrogen oxides' generation and emissions. Among them, the cooler is the key element in the EGR system, and the heat...

AI Technical Summary

Benefits of technology

[0005]The present invention aims to provide a heat transfer tube with higher thermal efficiency for improving the situation that the current heat transfer tube with spiral groove in circular sectional shape cannot meet the future requirement for environmental protection in heat transfer efficiency, such tube can greatly improve the thermal efficiency while the volume of the cooler does not vary.

[0007]In the above-mentioned solution, the sectional shape of said stainless steel tube body can be rectangle, and adjacent two sides are connected by arc transition; the sectional shape of the stainless steel tube body can also be consists of two relative short sides and two relative long sides, wherein the short sides appear as outward convex arcs and the long sides can be straight lines or outward convex arcs; the sectional shape of said stainless steel tube body can also be ellipse. It should be noted that in order to be better described, the sectional shape of said stainless steel tube body presents as the standard shape under the assumption that there is no spiral groove in the tube. The sectional shape of the heat transfer tube in the present invention is the combination of said sectional shape of the stainless steel tube and the sectional shape of said spiral groove. Said spiral groove can be set to be multiple, and each groove can be set continuously or intermitted; the sectional shape of the spiral groove can be “U” shape or “V” shape, which is of benefit to the generation of small size surface; the spiral lift angle β of the groove is designed between 20 and 75 degrees; the depth D of the groove is no less than 0.4mm, which can make the full developed turbulence generate in the tube; at the same time, in order to ensure the tube being economical and practical, and to simplify the manufacturing difficulty, all the acute angles of the section are designed to be arc R transition, in which the surface between said groove and said stainless steel tube body is also connected by arc transition so as to make all the surfaces sufficiently exchange heat very well and completely eliminate dead corner during heat exchanging.

[0008]When the exhaust gas passes through such kind of heat transfer tube, it can go through the spiral convex part, then the boundary layer of partial wall surface separates and forms vortex backward the spiral convex. Such separation of the boundary layer and generation of vortex make heat transition improved. And the spiral convex can trigger the exhaust gas operate spiral movement, which results in complicated secondary swirl flow (is also called as secondary flow) is generated in the exhaust gas, enlarging the turbulence scale of the exhaust gas, particularly enlarging the disturbance to the boundary layer nearby wall area, accelerating mixing of the fluid in the boundary layer and the core area, which makes heat convection improved; the secondary flow also has the effect to make the sectional speed distribute more even. Especially the design of the flat oval section such as the foregoing four sections like rectangle and ellipse makes the thickness of the boundary layer become thinner greatly by the combined cooperation of the secondary flow and the centrifugal force generated by spiral movement, and meanwhile reduces the critical Renault. In other words, the conversion from laminar flow into turbulence generates ahead of time, and violent turbulence makes dirt severely scoured within the tube. As a result, fouling of the spiral heat transfer tube with such kind of flat oval sectional shape like the foregoing rectangle, ellipse and other two shapes becomes difficult, which is of benefit to heat convection.

[0010]As shown in FIG. 1, when the flow areas are the same, comparing with the heat transfer coefficient of the tube with spiral groove in circular sectional shape, the heat transfer coefficient of the tube with spiral groove in flat oval sectional shape is greatly increased.

[0012]Therefore, it can be shown that the cooler manufactured according to the present invention can obtain greater cooling effect when the volume keeps the same, which greatly improves the index of automotive gas emissions performance, and satisfies higher requirement of environmental protection.

Problems solved by technology

In other words, the conversion from laminar flow into turbulence generates ahead of time, and violent turbulence makes dirt severely scoured within the tube.

As a result, fouling of the spiral heat transfer tube with such kind of flat oval sectional shape like the foregoing rectangle, ellipse and other two shapes becomes difficult, which is of benefit to heat convection.

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