Fin-and-tube type heat exchanger, and its return bend pipe

Abstract

Provided is a fin-and-tube type heat exchanger using a return bend pipe capable of improving the evaporation performance of the heat exchanger still better. This heat exchanger comprises a hair pin unit having a multiplicity of hair pin pipes arranged in parallel, a return bend unit having a multiplicity of such return bend pipes arranged in parallel as are jointed to the individual hair pin pipe end portions of the hair pin portions, and a fin portion having a multiplicity of fins arranged in parallel at a constant spacing on the outer surfaces of the hair pin pipes. The pipe insides are fed with a coolant. The heat exchanger has first grooves formed in the inner faces of the return bend pipes. The groove pitch ratio (P1 / P2) between a first groove pitch (P1), as taken in the section normal to the pipe axis, of the first grooves, and a second groove pitch (P2), as taken in the section normal to the pipe axis, of second grooves of a helical shape formed in the pipe inner faces of the hair pin pipes satisfies 0.65 to 2.2. At the same time, the groove sectional area ratio (S1 / S2) between a first groove sectional area (S1) per groove, as taken in the section normal to the pipe axis, of the first grooves and a second groove sectional area (S2) per groove, as taken in the section normal to the pipe axis, of the second grooves satisfies 0.3 to 3.6.

Description

technical field [0001] The invention relates to a finned tube heat exchanger and a U-shaped elbow tube connected with its return bend tube. In heat exchangers such as air-conditioning equipment, especially the finned tube heat exchanger, Freon refrigerant flows inside the tube For refrigerants such as natural refrigerants, a plurality of fins made of aluminum or the like are arranged in parallel on the outside of the tube. Background technique [0002] Currently, Patent Document 1 or Patent Document 2 proposes a finned tube heat exchanger in which a smooth tube with a smooth inner surface is used as a U-shaped elbow tube and a tube with a grooved inner surface is used as a hairpin tube. In addition, in Patent Document 1, the U-shaped elbow pipe is described as a U-shaped elbow pipe, and the return-bent pipe is described as an electric welded steel pipe. In Patent Document 2, the U-shaped elbow pipe is described as a U-shaped elbow, Return bends are recorded as heat pipes. ...

AI Technical Summary

Problems solved by technology

However, since the inner surface of the U-shaped elbow tube is smooth, it is difficult to maintain the swirling flow on the outlet side, and at the bend of the U-shaped elbow tube, water droplets (refrigerant liquid film) are sprayed, and the liquid film unstable flow

Therefore, there is a problem that after flowing into the return bend pipe of the next stage, the refrigerant is wasted in order to give the refrigerant a swirling flow again for a while, and in this region, the flow of the refrigerant is unstable, and a thick liquid film of the refrigerant is also formed. part, therefore, the thermal conductivity inside the tube tends to decrease, and sufficient evaporation performance cannot be obtained

Therefore, since the pressure loss of the refrigerant circulating inside the heat exchanger increases, the flow rate of the refrigerant decreases. Therefore, on the contrary, there is a problem that the heat transfer performance of the heat exchanger, especially the evaporation performance is significantly reduced.

[0011] Furthermore, as in Patent Document 3, when the pipe wall thickness is increased in consideration of the reduction in strength caused by the groove formation of the U-shaped elbow pipe, the inner surface of the joint portion of the U-shaped elbow pipe and the return bend pipe will produce a blockage of cooling. The step of the refrigerant circulation, so the pressure loss of the refrigerant is easy to increase

[0012] In addition, in the heat exchanger of Patent Document 4, the groove lead angle formed by the grooves formed in the U-shaped elbow pipe and the return bend pipe and the pipe axis is limited to a predetermined angle, but the groove pitch and groove cut-off angle have not been completed. Therefore, turbulence is generated in the refrigerant liquid film in the tube, and the refrigerant liquid film in the straight pipe part of the return bend is not uniform, and sometimes a part with a thick refrigerant liquid film is generated

As a result, there is a problem that sufficient evaporation performance cannot be obtained

After the refrigerant liquid film remains, the result is that the remaining part becomes excessively dry, the effective heat transfer area decreases, and the evaporation performance decreases.

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