JPH0222606Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an absorber having a heat transfer tube with excellent heat transfer performance.

Absorbers used in absorption chillers, concentration difference engines, etc., that is, heat exchangers that release heat in the process of absorbing refrigerant gas into an absorbent, are - Because lithium bromide (LiBr) systems have been widely used, the internal pressure is low and the specific volume of the refrigerant gas is large.
Therefore, many shell-and-tube type and shell-and-coil type heat exchangers are used in the area where the absorption action is performed on the shell side, and the so-called extra-tube absorption type in which the inside of the heat transfer tube is used as a passage for cooling water. Ta.

In recent years, fluorocarbon absorption systems have been put into practical use. For example, in the case of the fluorocarbon refrigerant R22-tetraethylene glycol dimethyl ether (TEGDME), the specific volume of the refrigerant becomes small when the internal system pressure of the absorber is 5 to 6 Kg/cm ² G. Since then, it has become possible to air-cool the absorber, and from this technical background, as the in-tube absorption method becomes possible to adopt, a heat exchanger tube for in-tube absorption is required to have high absorption heat transfer performance.

However, at present, copper bare tubes are considered to be the best heat transfer tubes, but they have a heat transfer performance limit determined by the material, tube thickness, etc., and high values cannot be expected. In order to increase the contact area with the absorber, it is necessary to increase the diameter and number of the heat transfer tubes, which poses practical problems such as the absorber becoming large.

The present invention was developed by focusing on the above-mentioned situation, and by making it possible to increase the absorption heat transfer coefficient per unit length of the intra-tube absorption heat transfer tube itself from a structural standpoint, the heat exchanger The purpose of this invention is to promote the general use of compact absorbers.

To this end, the present invention has developed an in-tube absorption heat transfer tube for use in this type of absorber, in which micro-irregularities formed by alternating repetitions of helical micro-grooves and helical micro-ridges that have a helical angle with respect to the tube generatrix exist on the inner surface of the tube. The pipe has a structure in which the inner and outer surfaces of the tube have spiral folds having a twist angle larger than the twist angle in the same twist direction as the micro-asperities, and the provision of the micro-asperities reduces the flow of the liquid phase. As a result of promoting the mixing action, the concentration gradient is reduced, the gas-liquid contact area is increased, and the absorption efficiency is improved.
Furthermore, the formation of the pleats further activates the mixing action of the absorbent liquid, thus achieving the intended purpose.

Hereinafter, the contents of one embodiment of the present invention will be explained with reference to the accompanying drawings.

Figures 1 and 2 are piping system diagrams for an absorption chiller and a concentration difference engine. and a refrigerant piping system that is equipped with a condenser 5, an expansion valve 6, and an evaporator 7 and connects the gas phase part of the generator 2 and the inlet side of the absorber 1. On the other hand, the engine has a solution piping system formed in the same manner as the refrigerator shown in FIG. It consists of a refrigerant piping system.

For detailed structural examples and operating modes of these devices, see Japanese Patent Application Laid-Open Nos. 146207-1982 and 1983-146207.
The explanation is omitted as it is well known from Publication No. 28818, etc., but it is formed so that cold heat and power can be generated by a refrigerant/absorption system that is an R22-TEGDME system, and the absorber 1 is an air-cooled A heat exchanger is used.

The absorber 1 has heat transfer tubes disposed horizontally, and the absorbent and refrigerant gas within the tubes are absorbed into each other at the horizontally disposed portions.

It should be noted that the present invention is not limited to an air-cooled system, and may of course be a double-tube system in which the absorption action is performed within the inner tube.

Therefore, the heat exchanger tube 9 used in the absorber 1
The structure of the heat transfer tube 9 is schematically shown by partially cutting it in FIGS. 3 and 4, and the inner surface has a helix angle α with respect to the generatrix of the heat transfer tube 9 (line on the tube wall parallel to the tube axis). It has micro-asperities 10 formed by alternating repetition of micro-grooves and spiral micro-ridges, and has a twist angle β and twist pitch larger than the twist angle α in the same twist direction as the micro-asperities 10. This is an inner/outer surface-processed tube that has spiral pleats 11 on both the inner and outer surfaces of the tube.

The absorption function of heat transfer tubes subjected to such processing will be explained based on FIGS. 5 and 6 in comparison with the case of condensation. In the case of absorption, a laminar flow is produced in contact with the inner surface of the heat transfer tube The absorbing liquid that forms (R22+
The gas-liquid interface _L1 , which is the boundary between the TEGDME) and the refrigerant gas layer in contact with it, has a high liquid temperature and high refrigerant concentration, making it difficult to absorb it in a slowly flowing liquid laminar flow state. .

Note that at the heat transfer surface interface _L2 where the absorbing liquid and the heat transfer tube 9 are in contact, the liquid temperature is lower and the refrigerant concentration is lower than that at the gas-liquid interface _L1 .

On the other hand, in the case of condensation, there is only a temperature gradient in the condensed liquid phase because the condensed liquid is a single component; if the gas-liquid interface temperature is lower than the saturated gas temperature, condensation will occur; Even in a state of slow liquid laminar flow, condensation does not become difficult.

From the above points, in the case of absorption, the concentration gradient of the absorption liquid should be eliminated by reducing the temperature gradient in the absorption liquid phase, and the gas-liquid interface
Reducing the refrigerant concentration in L ₁ is key to promoting absorption, and therefore active stirring within the liquid laminar flow should be ensured.

Therefore, by forming minute irregularities 10 on the inner surface of the tube, mixing and stirring using liquid flow can be performed effectively, resulting in almost no concentration (temperature) gradient and also increasing the gas-liquid contact area. It is possible to achieve a comprehensive improvement in absorption efficiency.

Furthermore, since the liquid laminar flow in this case is given a swirling force by the spiral grooves and ridges having a twist angle, it is dispersed along the inner surface of the heat exchanger tube 9, and the contact area with the refrigerant gas is further increased and mixed. The effect is doubled.

The generation of the above-mentioned winding force is not only due to the minute irregularities 10 but also becomes even greater due to the formation of the pleated surface 11, and furthermore, since the twisting direction of the pleated surface 11 matches the twisting direction of the minute unevenness 10,
If this is in the opposite direction, the winding force formed by the minute irregularities 10 is applied to the flowing object, giving a winding force in the opposite direction, which is inconvenient, resulting in a large increase in passage resistance. Such problems do not occur at all, and the mixing of the absorption liquid can be further promoted.

The present inventor has calculated the heat transfer (kca/m ² h°C) during the absorption action between an inner-treated tube of the present invention having the same diameter and a conventional bare tube without any inner surface treatment. After several experiments to compare,
The advantage of the inner surface treatment was demonstrated when it was found that the former inner surface treatment tube was about 50% better, and was found to be particularly effective in absorbers.

The present invention has the above-mentioned structure and function, and by providing the heat transfer tube surface with minute irregularities 10 having helical pitches and a helical fold surface 11, the absorption liquid can be actively mixed and stirred. As a result, the absorption heat transfer coefficient within the tube can be greatly improved.

In addition, since the pleated surface 11 has a large twist angle in the same twist direction as the minute unevenness 10, the turning force applied by the minute unevenness 10 is further increased, the contact area is increased, and the turning flow is On the other hand, it has the effect of promoting smooth flow without creating distribution resistance.

[Brief explanation of the drawing]

Figures 1 and 2 are piping system diagrams of each device according to an embodiment of the absorber of the present invention, and Figures 3 and 4 are partially cutaway perspective views of heat exchanger tubes used in an example of the absorber of the present invention. FIG. 5 is an explanatory diagram of the dynamics during absorption by the heat exchanger tube, and FIG. 6 is an explanatory diagram of the condensation dynamics for comparison. 1...Absorber, 10...Minute unevenness, 11...Fold surface.

Claims (1)

[Scope of utility model registration request] In absorption refrigerators, engines that utilize concentration differences, etc., heat transfer tubes that cause an absorption action in which refrigerant gas is absorbed by an absorbent inside the tubes have a torsion angle α with respect to the tube generatrix.
The inner surface of the tube has minute irregularities 10 formed by alternating repetition of spiral microgrooves and spiral microridges, and has a twist angle β larger than the twist angle α in the same twisting direction as the minute irregularities 10. An absorber characterized by having spiral folded surfaces 11 on both the inside and outside of the tube.