JP2006242553A - Heat transfer tube, heat exchanger for supplying hot water, and heat pump water heater - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat transfer tube capable of keeping high heat exchanging characteristic by preventing accumulation of scale in use for a long period. <P>SOLUTION: This heat transfer tube has a height h from an inner face of the tube, of 0.005d-0.19d with respect to an inner diameter d of the tube, and comprises a plurality of spiral fins respectively held by grooves formed in the axial direction of the tube at distances a of 0.4 mm or more. Further a radius of curvature α of a connecting portion Fr of the fin formed on the inner face of the tube and the groove formed between the fins adjacent to each other, is 0.03-0.5 mm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a heat transfer tube used in a heat exchanger, and more particularly to a heat transfer tube used in a heat exchanger for a heat pump water heater that distributes hot water in the tube.

  Various heat transfer devices have been developed to reduce carbon dioxide emissions from the viewpoint of global environmental conservation. Hot water heaters for producing hot water were often manufactured by heating with city gas or oil-based fuel, but heat pump water heaters for producing hot water by forming a heat cycle by circulating refrigerant in a compressor driven by electric power The performance of the vessel is increasing. In heat pump water heaters, carbon dioxide is often used instead of chlorofluorocarbon as a refrigerant, which contributes to chlorofluorocarbon removal.

  Such a heat pump water heater is generally formed by a system as described below. That is, the high-temperature and high-pressure refrigerant in the compressor is sent to a heat exchanger called a gas cooler, and hot water used for hot water supply is produced by exchanging heat with tap water. The refrigerant whose temperature has been reduced by the gas cooler is reduced in pressure by the expansion valve, is vaporized by the outside air in the evaporator installed outside the room, and is again increased in temperature and pressure by the compressor.

There is an example of improving the performance of a gas cooler by adding fins on the inner wall surface of a pipe for improving the heat transfer coefficient of fluid (for example, Patent Document 1).
JP 2003-156291 A

  However, in the heat exchanger described in Patent Document 1, since the tap water is heated, calcium and silica contained in the tap water are precipitated (generally referred to as scale) and easily adhere to the inner wall surface of the pipe. The problem is that clogging is likely to occur in the tube. In particular, when fins are added to the inner surface of the pipe, the deposits are accumulated between adjacent fins, and the effect of improving the heat transfer coefficient due to the addition of fins deteriorates over time.

  In view of such a problem, the present invention has been made, and provides a heat transfer tube capable of maintaining good heat exchange characteristics because scale deposition hardly occurs during a long-term use process.

  The first aspect of the heat transfer tube according to the present invention has a height h from the inner surface of the tube of 0.005d to 0.19d with respect to the inner diameter d of the tube, and is 0.4 mm formed in the axial direction of the tube. A heat transfer tube comprising a plurality of helical fins sandwiched between grooves having the distance a.

  In the second aspect of the heat transfer tube according to the present invention, the curvature radius α of the connection portion Fr between the fin formed on the inner surface of the tube and the groove formed between the fin and the adjacent fin is 0.03 to 0.03. It is a heat transfer tube characterized by being 0.5 mm.

  In the third aspect of the heat transfer tube according to the present invention, the connection portion Fr between the fin formed on the inner surface of the tube and the groove formed between the fin and the adjacent fin forms at least another surface. It is a heat transfer tube characterized by doing.

  A fourth aspect of the heat transfer tube according to the present invention is a heat transfer tube characterized in that the heat transfer tube is made of copper or a copper alloy.

  The 1st aspect of the heat exchanger which concerns on this invention is a heat exchanger using the heat exchanger tube mentioned above.

  The 1st aspect of the heat pump water heater which concerns on this invention is a heat pump water heater using the heat exchanger mentioned above.

  The heat exchanger according to the present invention can provide a heat transfer tube that can maintain good heat exchange characteristics because scale deposition is unlikely to occur during a long-term use process for a heat transfer tube used in a heat pump or the like.

  Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 1 to 9.

  FIG. 1 is a schematic view of an embodiment showing a heat transfer tube according to the present invention. Fig.1 (a) is a top view of a heat exchanger tube. FIG.1 (b) is a longitudinal cross-sectional view of arrow x of a heat exchanger tube. FIG.1 (c) is a cross-sectional view of the heat exchanger tube of the arrow y. FIG.1 (d) is a diagonal sectional view of the heat exchanger tube of the arrow z.

  In the heat transfer tube of the present invention, the height (or groove depth) h of the fin 2 shown in FIG. 1C is 0.005d to 0.19d with respect to the tube inner diameter d. This is because if the height h is smaller than 0.005d, the heat transfer performance by the spiral fins or grooves is inferior. Conversely, even if the height h is greater than 0.19d, not only the improvement in heat transfer performance is saturated, but also scale deposition tends to occur in the surface groove formed between the fins in the pipe. This is because it becomes. Preferably it is 0.01d-0.13d.

In the heat transfer tube of the present invention, the distance a between adjacent grooves in the axial direction of the tube shown in FIG. This is because if the distance a is less than 0.4 mm, scale is likely to be deposited on the surface groove in the pipe. The distance a is preferably 0.5 to 1.8 mm.

  Further, the characteristics of the fins of the heat transfer tube of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected to the structure similar to each part of the heat exchanger tube shown by FIG. 1, and the description is abbreviate | omitted.

  FIG. 2 is a cross-sectional view schematically showing one aspect of the shape of the fin. Here, as shown in FIG. 2, the case where the fins 2 and the connecting portions Fr formed on the inner surface of the pipe are curved surfaces is classified as curved surface bonding. The curvature radius α of the connecting portion Fr between the fin 2 formed on the inner surface of the pipe by curved surface bonding and the adjacent fin 2 and the groove formed therebetween is set to 0.03 to 0.5 mm. If the radius of curvature α is less than 0.03 mm, scales are likely to be deposited at the connecting portion Fr of the curved surface joint. On the other hand, if the curvature radius α exceeds 0.5 mm, a material is unnecessarily required, resulting in an increase in unit length pipe weight. Preferably, the curvature radius α is 0.03 to 0.4 mm.

  FIG. 3 is a cross-sectional view schematically showing another aspect of the shape of the fin. Further, here, as an alternative to curved surface joining in the heat transfer tube of the present invention, as shown in FIG. 3, another surface (taper) is formed at the fin 2 on the inner surface of the tube and the connecting portion Fr of the tube. Are classified as chamfered joints. That is, the fin 2 and the inner surface of the tube are formed so as to form a part of a polygon. This chamfering makes it difficult for scale to be deposited at the boundary between the fin 2 and the groove. In addition, b shown in FIG. 3 shows the height of the surface of chamfering joining, and c shows the width | variety of the surface of chamfering joining.

  The material of the heat transfer tube of the present invention is not particularly limited as long as it has thermal conductivity, but a metal having excellent thermal conductivity is preferable. More preferably, it is copper or a copper alloy.

  The heat transfer tube of the present invention is used in a heat exchanger, and in particular, in a heat pump water heater that uses carbon dioxide as a refrigerant and exchanges heat with tap water.

Example 1
Below, the heat exchanger concerning the present invention is explained in detail using an example.
FIG. 4 is a table showing the characteristics of the heat transfer tubes and the evaluation results based on the characteristics. Phosphorous deoxidized copper was used as the material for the heat transfer tube, the outer diameter D was 9.52 mm, the inner diameter d was 7.92 mm, the tube length was 2.5 m, and the tube thickness t was 0.8 mm. In this state, the number of grooves, fin height h, groove distance a, curvature α of connecting portion Fr, and torsion angle θ were changed under various conditions, and the heat transfer tubes were evaluated.

  FIG. 5 is a schematic diagram showing a method for evaluating the heat transfer performance of the heat transfer tube according to the present invention. As shown in FIG. 5, the heat transfer performance of the heat transfer tube 1 was evaluated using a double tube heat exchanger. As the inner pipe of the double pipe type heat transfer pipe, the heat transfer pipe 1 of the present invention example and the comparative example is used, and low-temperature water with a water temperature of 30 degrees is flowed in the direction of arrow 3 shown in FIG. did. As the outer tube 4, a stainless steel tube having an outer diameter of 16 mm and a wall thickness of 1 mm was used, and high-temperature water having a water temperature of 60 degrees was flowed at a flow rate of 3 liters / minute in the direction of arrow 5 shown in FIG.

  First, in order to examine the evaluation of the heat transfer performance, the exchange heat quantity Q1 of water was measured under the experimental conditions shown in FIG. The exchange heat quantity Q1 immediately before the scale has the same outer diameter as that of the heat transfer pipe 1 of the present invention and the comparative example, and the exchange heat quantity Q1 of a smooth tube having no fins or grooves on the inner surface of the pipe is 100 (Comparative Example 7). In comparison with Comparative Example 7, the exchange heat quantities Q1 of Invention Examples 1 to 19 and Comparative Examples 1 to 6 were shown.

  Next, in order to examine the influence of the heat transfer performance due to the scale adhesion to the inner surface of the heat transfer tube 1, the scale adhesion acceleration test shown below was performed.

  Tap water heated to 80 ° C. by adding calcium chloride and sodium metasilicate so that the calcium hardness is 200 mg / liter and the ionic silica is 100 mg / liter inside the heat transfer tube 1 of the present invention example and the comparative example. Was passed for 270 days at a flow rate of 2 liters / minute. The test water was replaced with a new solution every 15 days.

  Further, in the same manner as in Example 1, the exchange heat amount of the heat transfer tubes 1 of the present invention example and the comparative example is measured at 90 days, 180 days, and 270 days from the start of water flow, and the deterioration of the exchange heat amount due to before and after the scale adheres. evaluated. The exchange heat amounts on the 90th, 180th, and 270th from the start of water flow were defined as Q2, Q3, and Q4. Further, after the test was completed (after 270 days), the heat transfer tube 1 was cut and the state of scale accumulation on the inner surface of the tube was visually confirmed. The case where there was almost no accumulation was marked as ◯, the case where slight accumulation was observed was marked as Δ, and the case where accumulation was significant was marked as x. The shape and evaluation result of the heat transfer tube 1 are shown in FIG.

  As can be seen from FIG. 4, the heat transfer tube 1 of the present invention is less likely to deposit on the scale, so that there is almost no deterioration in the amount of exchange heat, so that good heat exchange characteristics are maintained. On the other hand, since the h / d was smaller than 0.005 in the comparative example 1, the heat transfer performance was inferior to the example of the present invention. Moreover, since the comparative example 2 was joining (direct joining) by which the taper and the curved surface were not formed in the fin 2 of the inner surface of a pipe, and the connection part Fr of a pipe, the scale adhered and the fall of heat transfer performance was large. In Comparative Examples 3 and 4, since h / d was larger than 0.19, the scale adhered and the heat transfer performance was greatly reduced. In Comparative Examples 5 and 6, since the groove distance a was smaller than 0.4 mm, the scale adhered and the heat transfer performance was greatly reduced. Since Comparative Example 7 was a smooth tube, the amount of exchange heat was inferior to that of the present invention.

(Example 2)
Next, as in Example 1, the heat transfer tube 1 having an outer diameter D of 12.7 mm, an inner diameter d of 11.1 mm, and a wall thickness t of 0.8 mm was evaluated using the evaluation method shown in FIG. Other conditions are the same as in the first embodiment. The shape of the heat transfer tube and the evaluation results are shown in FIG.

  FIG. 6 is a table showing the characteristics of the heat transfer tube of the second embodiment and the evaluation results based on the characteristics. As is apparent from FIG. 6, the heat transfer tube 1 of the present invention is less likely to be scale-deposited, so that there is almost no deterioration of the exchange heat quantity, so that good heat exchange characteristics are maintained. On the other hand, Comparative Example 8 had a heat transfer performance worse than that of the present invention because h / d was smaller than 0.005. In Comparative Example 9, since h / d was larger than 0.19, the scale adhered and the heat transfer performance deteriorated. Since Comparative Example 10 is a smooth tube, the amount of exchange heat is lower than that of the present invention.

(Example 3)
Furthermore, the water temperature at the inlet of the heat transfer tube of the present invention example 15 having an outer diameter D of 9.52 mm and a wall thickness t of 0.8 mm and the comparative example 7 shown in FIG. The amount of exchange heat was measured using the evaluation method shown in FIG. 5 at a temperature of 10 ° C. and a water flow rate of 6 to 9 liters / minute (flow rate of about 2 to 3 m / sec). The result is shown in FIG.

  FIG. 7 is a table showing the characteristics of the heat transfer tube of the third embodiment and the evaluation results based on the characteristics. As can be seen from FIG. 7, the heat transfer tube of the present invention can obtain high heat transfer performance even when the water flow rate is increased. This indicates that the heat transfer tube according to the present invention is not limited to only a water heater, but can be used effectively as a heat transfer tube for cooling various high-temperature media.

Example 4
FIG. 8 is a plan view showing an example of a heat exchanger provided with the heat transfer tube of the present invention. As shown in FIG. 8, the heat exchanger 13 according to the present invention has a structure in which a pipe 6 through which a refrigerant such as carbon dioxide flows is sandwiched between heat transfer pipes 1 through which water flows, and both are bonded by a bonding material. Thus, the heat radiated from the tube 6 is transferred to the heat transfer tube 1 without being released to the atmosphere, and heat exchange with the heat transfer tube 1 is performed efficiently.

  While the refrigerant flows into the pipe 2 along the arrow 9 shown in FIG. 8, the water flows out of the heat transfer pipe 1 along the arrow 10 shown in FIG. Therefore, the refrigerant and water flowing inside the pipe are configured to face each other.

  Further, the heat exchanger of the present invention will be described in detail with reference to the aa cross-sectional view shown in FIG. 8. A range surrounded by the heat transfer tube 1, the tube 6, and the joint portion 7 is formed as the gap portion 8. Therefore, even if there is a hole in the tube wall of the heat transfer tube 1 or the tube 6 due to corrosion, the refrigerant or water flows out to the gap portion 8 and the leakage is detected before the corrosion to other tubes proceeds. be able to.

  In order to increase the contact area between the heat transfer tube 1 and the tube 6 and to secure a gap for leakage detection, it is desirable that the number of the tubes 6 be two or three. If it is going to ensure, the contact area of the heat exchanger tube 1 and the tube 6 will decrease, and a heat transfer characteristic will fall. By adopting these configurations, high performance of the heat exchanger can be achieved, and the heat exchanger itself can be miniaturized.

(Example 5)
An example in which the heat transfer tube of the present invention is used in a heat pump water heater will be described.
FIG. 9 is a system flow diagram of the heat pump water heater. The heat pump water heater of the present embodiment includes an outdoor unit 11 and a hot water tank 20.

The outdoor unit 11 includes a compressor 12, a heat exchanger 13 called a gas cooler, an expansion valve 14, and an evaporator 15, and is configured by a primary refrigerant circuit in which these are sequentially connected by a refrigerant pipe 16. In this refrigerant circuit, carbon dioxide having a low critical temperature is used as a refrigerant. On the other hand, a circuit including a heat exchanger 13, a circulation pump 18, and a hot water supply tank 20 and sequentially connected by a pipe 19 is referred to as a secondary refrigerant circuit. Therefore, the refrigerant pipe 16 and the pipe 19 are connected to the heat exchanger 13.

The compressor 12 sucks the refrigerant evaporated by the evaporator 15 through an accumulator (not shown) and performs a compression action to a critical pressure or higher. An accumulator may not be provided. The heat exchanger 13 exchanges heat between carbon dioxide and water as refrigerant discharged from the compressor 12. During normal operation, the refrigerant is pressurized to a critical pressure or higher by the compressor 12, so that it is not condensed even by heat radiation from the heat exchanger 13, and is in a gas state.

The expansion valve 14 depressurizes the refrigerant flowing out of the heat exchanger 13 according to the degree of opening of the valve, and is controlled by a control device (not shown). The evaporator 15 evaporates the refrigerant decompressed by the expansion valve 14. A fan 17 is provided to absorb heat from the atmosphere for the refrigerant. Using these members, the carbon dioxide refrigerant flows in the refrigerant pipe 16 in accordance with the arrows shown in FIG.

In the secondary refrigerant circuit, the circulation pump 18 leads water that flows from the outside through the hot water tank 20 to the heat exchanger 13. Further, the hot water heated to about 90 ° C. by the heat exchanger 13 is led out to the hot water tank 20. Accordingly, the circulation pump 18 circulates water in the secondary refrigerant circuit as indicated by an arrow. The circulation pump 18 controls the circulation amount by a control device (not shown).

As described above, by using carbon dioxide refrigerant in the primary refrigerant circuit, tap water flowing from the outside is made high temperature water on the secondary refrigerant circuit side, and the high temperature water is stored in the hot water supply tank 20 and necessary. Sometimes hot water is supplied.

  Furthermore, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention.

  According to the present invention, the heat transfer tube used in a heat pump or the like is less likely to cause scale deposition in a long-term use process, and therefore, it is possible to provide a heat transfer tube that can maintain good heat exchange characteristics, and has industrial applicability. high.

FIG. 1 is a schematic view of an embodiment showing a heat transfer tube according to the present invention. FIG. 2 is a cross-sectional view schematically showing one aspect of the shape of the fin. FIG. 3 is a cross-sectional view schematically showing another aspect of the shape of the fin. FIG. 4 is a table showing the characteristics of the heat transfer tube of the first embodiment and the evaluation results based on the characteristics. FIG. 5 is a schematic diagram of a method for evaluating the heat transfer performance of a heat transfer tube according to the present invention. FIG. 6 is a table showing the characteristics of the heat transfer tube of the second embodiment and the evaluation results based on the characteristics. FIG. 7 is a table showing characteristics of heat transfer tubes and evaluation results based on the characteristics. FIG. 8 is a plan view showing an example of a heat exchanger provided with the heat transfer tube of the present invention. FIG. 9 is a system flow diagram of the heat pump water heater.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heat transfer pipe 2 Fin 3 Low temperature water 4 Outer pipe 5 High temperature water 6 Pipe 7 Joint part 8 Crevice part 9 Refrigerant 10 Water 11 Outdoor unit 12 Compressor 13 Heat exchanger 14 Expansion valve 15 Evaporator 16 Refrigerant pipe 17 Fan 18 Circulation pump 19 Piping 20 Hot water tank D Outer diameter d Inner diameter t Wall thickness α Curvature radius Fr Connection part h Fin height a Groove distance b Surface height c Surface width θ Twist angle

Claims (6)

  The height h from the inner surface of the tube is 0.005d to 0.19d with respect to the inner diameter d of the tube, and is sandwiched by grooves having a distance a of 0.4 mm or more formed in the axial direction of the tube. A heat transfer tube comprising a plurality of spiral fins.   The curvature radius α of the connecting portion Fr between the fin formed on the inner surface of the tube and the groove formed between the fin and the adjacent fin is 0.03 to 0.5 mm. Item 2. The heat transfer tube according to Item 1.   The connection part Fr of the fin formed in the inner surface of a pipe | tube and the groove | channel formed between the said fin and the adjacent fin forms at least one more step | surface. Heat transfer tube.   The heat transfer tube according to any one of claims 1 to 3, wherein the heat transfer tube is made of copper or a copper alloy.   The heat exchanger using the heat exchanger tube of any one of Claim 1 to 4.   A heat pump water heater using the heat exchanger according to claim 5.

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