JP2008185297A - Heat exchanger for hot water supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the performance of a heat exchanger by regulating the flow velocity of a refrigerant upstream and downstream in a refrigerant passage. <P>SOLUTION: The heat exchanger for hot water supply comprises a core tube 1 forming a water passage, and small-diameter tubes 2 joined to the outer periphery of the core tube 1 to form passages for a carbon dioxide gas refrigerant. Tubes are arranged such that the mass velocity of the carbon dioxide gas refrigerant passing through the passages in the small-diameter tubes 2 is higher on the outlet side than the inlet side. Performance is thereby improved considerably in the same refrigerant tubing length (i.e. the tubing length of the small-diameter tubes), and sharp weight reduction can be attained to obtain the same capacity. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a heat exchanger for hot water supply, and more particularly to a heat exchanger for hot water supply that uses carbon dioxide gas as a refrigerant.

  As a heat exchanger for hot water supply, a heat exchanger configured by spirally winding a thin tube forming a refrigerant (for example, carbon dioxide gas) passage around an outer periphery of a core tube forming a water passage (that is, a snake heat exchanger). Conventionally well known (see Patent Document 1).

  By the way, since the heat exchanger for hot water supply which boils hot water with cheap nighttime electric power is used in a transient manner, the flow rate of water is very small. Under such conditions, the water pipe length is as long as about 10 m in order to boil water at 9 ° C. → 90 ° C. (winter conditions) and 17 ° C. → 65 ° C. (summer conditions). As shown in FIG. 9, the hot water supply heat exchanger for exchanging heat with water is configured by winding a thin tube 2 around a core tube 1 forming a water passage with a two-pass pipe. In this case, the inside diameter of the narrow tube 2 is the same diameter from the inlet side to the outlet side. Reference numeral 3 is a shunt, and 4 is a junction.

Japanese Patent Application Laid-Open No. 2002-364989.

  However, when carbon dioxide is used as a refrigerant in a supercritical state, as shown in FIG. 10, there is a temperature drop due to heat dissipation even at the same pressure. Further, when the pressure is reduced due to the pressure loss of the piping, especially in the vicinity of 40 ° C. to 60 ° C., the enthalpy difference is reduced even at the same refrigerant temperature, and the ability as a heat exchanger is reduced. In this case, in order to obtain the capacity, it is necessary to lengthen the heat transfer tube (that is, the narrow tube) or improve the performance, but in that case, the pressure loss further increases, and in the case of the equivalent capacity, it becomes longer. When the number of passes is increased, the pressure loss is reduced. However, in this case, the heat transfer performance in the pipe is lowered, so that the performance improvement is small when viewed in total. That is, if the number of passes is large (that is, the refrigerant circulation amount is small as a whole), the pressure loss is small and a temperature difference can be obtained, but the heat flow rate is also small, so the capacity is small. On the other hand, if the number of passes is small (that is, the refrigerant circulation amount is large as a whole), the pressure loss becomes large and the temperature difference is small, so that the capacity becomes small even if the heat transmissivity is large.

By the way, as a feature of supercritical carbon dioxide,
(1) When the temperature is as low as about 20 ° C., the change in enthalpy is small even when the pressure is somewhat reduced (see P1 → P2 in FIG. 10). Therefore, even if the pressure loss is increased, the performance is improved if the heat transfer performance is increased.
(2) In the vicinity of a temperature of 40 ° C. to 60 ° C., the enthalpy changes greatly even with a slight pressure change (see P1 ′ → P2 ′ in FIG. 10). Accordingly, the performance is improved by using the temperature difference by reducing the pressure loss, rather than increasing the performance by adding pressure loss.

  This invention is made | formed in view of said point, and aims at improving the performance of a heat exchanger by adjusting the flow velocity of a refrigerant | coolant by the upstream and downstream in a refrigerant path.

  In the present invention, as a first means for solving the above-mentioned problems, it comprises a core tube 1 that forms a water passage, and a narrow tube 2 that is joined to the outer periphery of the core tube 1 and forms a passage for carbon dioxide refrigerant. The hot water supply heat exchanger has a piping configuration in which the mass velocity of the carbon dioxide refrigerant flowing through the passage in the narrow tube 2 is larger on the outlet side than on the inlet side.

  By configuring as described above, the mass velocity of the carbon dioxide refrigerant flowing through the narrow tube 2 becomes larger on the outlet side than on the inlet side. Therefore, in the same refrigerant pipe length (that is, the pipe length of the narrow pipe), the performance is greatly improved, and in order to obtain the same capability, a significant weight reduction can be achieved.

  In the present invention, as a second means for solving the above-described problem, in the hot water supply heat exchanger provided with the first means, the number of passes of the thin tubes 2 is changed from the refrigerant inlet side to the refrigerant outlet side. In such a configuration, the mass velocity of the carbon dioxide refrigerant can be increased from the inlet side to the outlet side only by optimizing the number of passes of the narrow tube 2, and the cost can be reduced. Thus, the performance of the heat exchanger can be improved.

  In the present invention, as a third means for solving the above-mentioned problems, in the hot water supply heat exchanger provided with the first or second means, the inner diameter of the narrow tube 2 is changed from the refrigerant outlet side to the refrigerant inlet side. It can also be set so that the side becomes smaller. In such a configuration, the mass velocity of the carbon dioxide refrigerant can be increased from the inlet side to the outlet side only by optimizing the inner diameter of the thin tube 2, and the low The performance of the heat exchanger can be improved at a low cost.

  According to the first means of the present invention, in the heat exchanger for hot water supply comprising the core tube 1 forming the water passage and the narrow tube 2 joined to the outer periphery of the core tube 1 to form the carbon dioxide refrigerant passage. Since the pipe configuration is such that the mass velocity of the carbon dioxide refrigerant flowing through the passage in the narrow tube 2 is larger on the outlet side than on the inlet side, performance is greatly improved with the same refrigerant pipe length (that is, the pipe length of the narrow tube) In order to obtain the same ability, there is an effect that significant weight reduction can be achieved.

  As in the second means of the present invention, in the hot water supply heat exchanger provided with the first means, the number of passes of the narrow tube 2 is set so that the refrigerant outlet side is smaller than the refrigerant inlet side. In such a configuration, the mass velocity of the carbon dioxide refrigerant can be increased from the inlet side to the outlet side only by optimizing the number of passes of the narrow tube 2, and the performance of the heat exchanger can be improved at low cost. Can be planned.

  As in the third means of the present invention, in the hot water supply heat exchanger provided with the first or second means, the inner diameter of the narrow tube 2 is made smaller on the refrigerant inlet side than on the refrigerant outlet side. In such a configuration, the mass velocity of the carbon dioxide refrigerant can be increased from the inlet side to the outlet side simply by optimizing the inner diameter of the narrow tube 2, and the performance of the heat exchanger can be improved at low cost. Can be achieved.

  The preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

First Embodiment As shown in FIG. 1, the heat exchanger for hot water supply includes a core tube 1 that forms a water passage, and a thin tube that is joined to the outer periphery of the core tube 1 to form a passage for carbon dioxide gas refrigerant. The thin tube 2 is spirally wound around the outer periphery of the core tube 1 in four passes on the inlet side (that is, the first half portion) of the core tube 1, and the outlet side of the core tube 1 (i.e., the first half portion). In the second half part), the outer periphery of the core tube 1 is spirally wound in two passes. In the case of the present embodiment, the inner diameter of the narrow tube 2a on the inlet side (ie, the first half portion) that is four passes and the inner diameter of the narrow tube 2b on the outlet side (ie, the second half portion) that is two passes are the same diameter. Yes. Reference numeral 3 is a shunt, and 4 is a junction.

  By configuring as described above, the mass velocity of the carbon dioxide refrigerant flowing through the narrow tube 2 becomes larger on the outlet side than on the inlet side. Therefore, in the same refrigerant pipe length (that is, the pipe length of the narrow pipe), the performance is greatly improved, and in order to obtain the same capability, a significant weight reduction can be achieved.

  Here, as an example, the water pipe length is 9m, the number of passes is changed from 4.5m + 4.5m from 4 passes to 2 passes (thin solid line shown), all 2 passes (dotted line shown), and all 4 passes 2 to 5 show the results of examining changes in refrigerant pressure, refrigerant temperature, heat transmissivity, and water temperature (shown in bold solid lines). 6 shows an enthalpy-pressure characteristic diagram of the carbon dioxide refrigerant, and FIG. 7 shows an enlarged view of the main part in FIG.

  According to the above result, the pressure loss in the second pass is large and the temperature drop is fast. Further, when the length of the same refrigerant temperature is measured, the position is 3.5 m in 2 passes, and the position is 4.5 m in 4 passes or 4 passes → 2 passes. Therefore, even if the heat transmissivity from 0 to 3.5 m is large in two passes (see FIG. 4), the capacity is small because the refrigerant temperature is low and the temperature difference is small.

  The 4 → 2 pass has a large heat transmissivity on the water inlet side (9 → 4.5 m 2 pass portion), so the water side temperature rises even at the same refrigerant temperature as the 4 pass (see FIG. 5). On the outlet side (4.5 → 0 m), the heat flow rate is equivalent to 4 passes (see FIG. 4), but the water temperature has already risen, so the capacity finally increases.

Second Embodiment FIG. 8 shows a heat exchanger for hot water supply according to a second embodiment of the present invention.

  In this case, the hot water supply heat exchanger has the same structure as that disclosed in the section of the prior art (that is, the entire narrow tube 2 has two paths), but the narrow tube 2a on the inlet side (that is, the first half). The inner diameter of the narrow tube 2b on the outlet side (that is, the latter half) is made smaller than the inner diameter of the tube. For example, if the inner diameter of the thin tube 2a is 5 mm, the inner diameter of the thin tube 2b is 4 mm. Reference numeral 5 denotes a pipe connecting member.

  By configuring as described above, the mass velocity of the carbon dioxide refrigerant flowing through the narrow tube 2 becomes larger on the outlet side than on the inlet side. Therefore, in the same refrigerant pipe length (that is, the pipe length of the narrow pipe), the performance is greatly improved, and in order to obtain the same capability, a significant weight reduction can be achieved.

Third Embodiment In this case, the heat exchanger for hot water supply has the same structure as that disclosed in the first embodiment (see FIG. 1) (that is, the first half of the thin tube 2 has four passes and the second half has However, the inner diameter of the narrow tube 2b on the outlet side (that is, the second half portion) is smaller than the inner diameter of the narrow tube 2a on the inlet side (that is, the first half portion). For example, if the inner diameter of the thin tube 2a is 5 mm, the inner diameter of the thin tube 2b is 4 mm.

  By configuring as described above, the mass velocity of the carbon dioxide refrigerant flowing through the narrow tube 2 is further increased on the outlet side than on the inlet side. Therefore, in the same refrigerant pipe length (that is, the pipe length of the narrow pipe), the performance is greatly improved, and in order to obtain the same capability, a significant weight reduction can be achieved. Other configurations and operational effects are the same as those in the first embodiment, and thus description thereof is omitted.

  In each of the above embodiments, the thin tube is spirally wound around the outer periphery of the core tube has been described. However, the present invention can also be applied to a thin tube that is aligned along the axis of the outer periphery of the core tube. It is.

  The invention of the present application is not limited to the above-described embodiments, and it goes without saying that the design can be changed as appropriate without departing from the scope of the invention.

It is a perspective view which shows the principal part of the heat exchanger for hot water supply concerning 1st Embodiment of this invention. Changes in the refrigerant pressure for the hot water supply heat exchanger according to the first embodiment of the present invention (thin solid line shown), all in the case of two passes (dotted line shown), and in the case of all four passes (thick solid line shown). FIG. Changes in refrigerant temperature for the heat exchanger for hot water supply according to the first embodiment of the present invention (shown by thin solid line), and in the case of all two passes (shown by dotted lines) and in the case of all four passes (shown by thick solid lines). FIG. Changes in the heat transmissibility for the hot water supply heat exchanger according to the first embodiment of the present invention (shown by a thin solid line) and all cases of two passes (shown by dotted lines) and all four passes (shown by thick solid lines) FIG. Changes in water temperature for the hot water supply heat exchanger according to the first embodiment of the present invention (shown by thin solid line), and in the case of all 2 passes (shown by dotted lines) and in the case of all 4 passes (shown by thick solid lines) FIG. The enthalpy pressure characteristic figure in a carbon dioxide refrigerant is shown. It is a principal part enlarged view in FIG. It is a perspective view which shows the principal part of the heat exchanger for hot water supply concerning 2nd Embodiment of this invention. It is a perspective view which shows the principal part of the conventional heat exchanger for hot water supply. It is an enthalpy pressure characteristic figure in a carbon dioxide refrigerant.

Explanation of symbols

1 is the core tube 2 is the narrow tube 2a is the first half 2b is the second half

Claims (3)

A heat exchanger for hot water supply comprising a core tube (1) that forms a water passage and a thin tube (2) that is joined to the outer periphery of the core tube (1) to form a passage for a carbon dioxide gas refrigerant. (2) A heat exchanger for hot water supply characterized by having a piping configuration in which the mass velocity of the carbon dioxide refrigerant flowing through the inner passage is larger on the outlet side than on the inlet side. The hot water supply heat exchanger according to claim 1, wherein the number of passes of the narrow tube (2) is set to be smaller on the refrigerant outlet side than on the refrigerant inlet side. The hot water supply heat exchanger according to any one of claims 1 and 2, wherein an inner diameter of the narrow tube (2) is set to be smaller on a refrigerant inlet side than on a refrigerant outlet side.

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