JPS5937435B2 - laminated heat exchanger - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a laminated heat exchanger used in low temperature systems such as air separation equipment, helium refrigerators, and liquefiers, and requires a compact heat exchanger with extremely small bulk. It is suitable for installation in a limited space.

One of the requirements for heat exchangers applied to low temperature systems is
The key is how compact it can be made, that is, how large the heat transfer area per unit volume can be.

Making the heat exchanger more compact not only has the advantage of making the heat exchanger itself cheaper, but also has the ripple effect of making the entire system, including the equipment that houses the heat exchanger, more compact and cheaper. The economic impact is significant.

The demand for compact heat exchangers is
This is especially true for small-sized helium refrigerators, and many researchers and engineers are attempting to apply stacked exchangers that have a large heat transfer area per unit volume.

1 and 2 show a conventional laminated heat exchanger. Reference numeral 1 denotes a laminated body in which heat exchanger plates 2 and spacers 3 are alternately bonded and arranged, and headers 4 are provided at both ends of the laminated body 1, respectively. 4A are arranged to constitute a laminated heat exchanger.

As the heat transfer plate 2, a perforated plate or screen made of aluminum or copper, which has good thermal conductivity, is generally used.

On the other hand, the spacer 3 has holes for forming a high temperature flow path 5 and a low temperature flow path 6 for the fluid flowing through the heat exchanger, so that the fluid flows as shown by the arrows in the figure.

This spacer 3 prevents heat transfer in the longitudinal direction (laminated direction) in the heat exchanger and improves heat exchange efficiency.
Materials with low thermal conductivity are commonly used, such as neoprene, plastic, and resin-impregnated paper.

In this way, when a metal material is used for the heat exchanger plate 2 and a non-metallic material is used for the spacer 3, bonding and fixing is generally used as a method for joining the two.

2. When conventional laminated heat exchangers were applied to low-temperature systems, there were the following problems.

Usually, heat exchangers applied to air separation equipment and helium refrigerators are used at extremely low temperatures, so each time the equipment is stopped and started, the temperature changes repeatedly from room temperature to extremely low temperatures (thermal cycle). receive.

When subjected to a thermal cycle, distortion occurs in the adhesive layer due to the difference in thermal expansion coefficients between the heat exchanger plate 2 and the spacer 3.

If the strain on the adhesive layer becomes too large or the accumulation of strain exceeds a permissible limit, the adhesive layer will peel off and fluid leakage will occur.

As a means to prevent this, a method of tightening metal bolts between the headers 4 and 4A has been used.

According to this method, peeling of the adhesive layer can be prevented to some extent, but since the coefficient of thermal expansion of the plastic spacer is significantly larger than that of metal bolts, it is possible to prevent the peeling of the adhesive layer from room temperature (300°K) to helium temperature (4.5°K). When the temperature drops, a large difference occurs in the amount of thermal contraction between the two, and a laminate with a large amount of shrinkage is subjected to a tensile action, causing separation between the heat exchanger plate and the spacer.

Additionally, when using metal bolts, because the bolts have good thermal conductivity, the amount of heat transferred from the high-temperature end to the low-temperature end through the bolts cannot be ignored, and this causes the problem of reducing the efficiency of the heat exchanger. was there.

An object of the present invention is to provide a laminated heat exchanger that does not cause distortion in the adhesive layer and does not cause peeling of the adhesive layer even when subjected to thermal cycles.

The laminated heat exchanger of the present invention is constructed by alternately stacking spacers made of a material with a relatively low coefficient of thermal conductivity and heat transfer plates formed of metal perforated plates or screens with a relatively high coefficient of thermal conductivity. At least two holes are formed in the laminate to form a high-temperature fluid passage and a low-temperature fluid passage, and bolts are formed between the heat sinks disposed at both ends of the laminate. The bolt is made of a material that has low thermal conductivity and has a coefficient of thermal expansion that is approximately the same as that of the laminate.

Hereinafter, one embodiment of the laminated heat exchanger of the present invention will be described with reference to FIGS. 3 to 6.

8 and 8A are headers, each with four brackets) 7 are fixed, and 9 is passed through the bracket 7 part and is attached to the header 8.
It is a bolt that clamps the laminate 1 between ゜8A, and the nut 1
It is fixed at 0.

The structure of the laminate 1 is the same as the conventional one shown in FIGS. 1 and 2, in which the heat transfer plate 2 is made of a metal with high thermal conductivity, and the spacer 3 is made of a non-metallic material with low thermal conductivity, such as neoprene or plastic. etc. are used.

The arrows indicate the respective flow directions of the high-temperature fluid, and 11 is the hole in the flow path.

Now, as shown in Figure 5, the thickness of the heat transfer plate 2! , the temperature T at which the entire heat exchanger is uniform, where the thickness of the spacer 3 is δ.

The amount of thermal contraction ΔL when the temperature is cooled to a linear temperature gradient of T1 at the high temperature end and T2 at the low temperature end is approximated as shown in equation (1).

,,,1. ,. However, α: Coefficient of thermal expansion of heat exchanger plate α2 Coefficient of thermal expansion of spacer Assuming that the temperature becomes a linear temperature gradient such that the high temperature end is T1 and the low temperature end is T2, the amount of thermal contraction ΔL' at that time is approximated by the following equation (2).

However, L: Initial distance between headers α: Coefficient of thermal expansion of bolt If ΔL and ΔL' are made equal in equations (1) and (2), thermal strain in the longitudinal direction of the adhesive layer can be eliminated. be done.

Calculating α from this results in the following.

That is, if the material of the bolt 9 is selected so as to satisfy equation (3), the thermal strain in the laminate can be reduced to almost zero.

Thermal expansion coefficient α7 of heat exchanger plate 2 and thermal expansion coefficient α of spacer 3
2, generally there is a relationship of α, <α2.

Therefore, one way to make the amount of thermal deformation of the bolt 9 and the amount of thermal deformation of the laminate 1 almost the same is to make the bolt 9 and the spacer 3 from the same material and embed a metal core wire therein. It is.

FIG. 6 shows this bolt, and the base material 15 of the bolt 9 is not limited to single-component plastic, but is made of polymeric materials including those containing glass fibers, those containing carbon fibers, and metals. The bolt 9 is made of a plurality of materials in which a core wire 16 of a flexible material is embedded, and the coefficient of thermal expansion of the bolt 9 is selected to be approximately the same as that of the laminate 1.

Reference numeral 14 denotes a threaded portion for threaded connection with the nut 10.

Since the laminated heat exchange device of this embodiment is configured in this way, the amount of thermal deformation of the bolts and the amount of thermal deformation of the laminate are approximately equal, so that the adhesive layer between the heat exchanger plate and the spacer prevents thermal strain. Therefore, the occurrence of peeling can be prevented.

In the above embodiment, the core wire is buried inside the bolt material, but instead of burying the core wire, the bolt material is made so that its coefficient of thermal expansion is smaller than that of the spacer 3 ( The same effect can be obtained even if the formula 3) is satisfied.

As described above, the laminated heat exchanger of the present invention has the effect of preventing peeling of the adhesive layer without causing distortion in the adhesive layer even when subjected to thermal cycles.

[Brief explanation of the drawing]

Fig. 1 is a front view of a conventional laminated heat exchanger, Fig. 2 is a plan view of the joint surface between the spacer and the heat exchanger plate in the direction of the ■-■ arrow in Fig. A front view of an embodiment of a laminated heat exchanger, Fig. 4 is a plan view of Fig. 3, and Fig. 5 is a plan view of Fig. 4.
FIG. 6 is an enlarged sectional view of the bolt shown in FIG. 3. 1... Laminated body, 2... Heat exchanger plate, 3...
...Spacer, 4.4A, 8,8A...Header, 9...Bolt, 10...Nut.

Claims (1)

[Claims] 1. Spacers made of a material with a relatively low coefficient of thermal conductivity and heat transfer plates formed of a metal porous plate or screen with a relatively high coefficient of thermal conductivity are alternately stacked to form a single spacer. The laminate is formed with at least two holes for forming a high-temperature fluid passage and a low-temperature fluid passage in the laminate, and headers arranged at both ends of the laminate are fixed by bolts. A laminated heat exchanger according to the present invention, wherein the bolt is made of a material having low thermal conductivity and a coefficient of thermal expansion substantially equal to that of the laminated body. 2. The laminated heat exchanger according to claim 1, wherein the bolt is formed from a composite material having approximately the same amount of thermal deformation as the laminated body made of a polymer material in which a metal core wire is embedded.