JP5792434B2 - Surface treatment copper pipe and heat pump water heater - Google Patents

Description

  The present invention relates to a copper tube used in a heat exchanger such as a water heater and a heat pump water heater using the copper tube, and more particularly to one that can suppress adhesion of scale.

In recent years, the natural refrigerant heat pump water heater known by the nickname of Ecocute (registered trademark) uses a hot water storage type, which uses cheap midnight power, and therefore has a lower running cost than a conventional combustion type water heater, and is far superior to alternative CFCs. In addition, since carbon dioxide (CO ₂ ) having a small global warming potential is used as a refrigerant (heat medium), it has features such as a low environmental load, and is widely used for business use and home use.

Generally, in a heat exchanger used for a hot water heater or the like, heating is performed while water is circulated inside a pipe. The groundwater and clean water, which are the actual water flowing inside the pipe, contain a small amount of calcium ions (Ca ²⁺ ) and bicarbonate ions (HCO ₃ ⁻ ), so the water is heated by the heat exchanger. It is known that calcium carbonate (CaCO ₃ ) is generated by the reaction of the following formula, and this calcium carbonate adheres to the inner wall of the tube as a scale. As a material for the tube, copper or a copper alloy is suitable in terms of excellent heat conduction, but Cu ₂ O existing as an oxide film of copper or a copper alloy is positively charged. There is a problem that the calcium carbonate that is easily attached.
Ca ²⁺ + 2HCO ₃ ⁻ → Ca (HCO ₃ ) ₂ → CO ₂ + H ₂ O + CaCO ₃

  In addition, this reaction proceeds as the temperature increases. In particular, the natural refrigerant heat pump water heater has a hot water temperature of about 90 ° C., which is higher than the temperature of about 60 ° C. of a combustion-type water heater due to the need for hot water storage in a tank, and an environment in which calcium carbonate is more easily generated. Yes. If the scale adheres to the pipes with a long-term use of the heat exchanger, the pressure loss may increase or the pipes may be blocked. For this reason, at present, pipes with a design that prioritizes securing the flow path by adopting a pipe having a larger diameter than the heat exchange efficiency are employed.

  For example, Patent Document 1 discloses a heat pump water heater in which the diameter of a pipe in an outlet portion through which high-temperature water that easily adheres to a scale flows is increased. Patent Document 2 discloses a heat exchanger for hot water supply that uses a corrugated tube having a spiral protrusion formed on the inner surface to crush the scale attached by stirring the water flow and improve the heat exchange efficiency. Has been. Patent Document 3 discloses a heat exchanger that includes a spiral wire made of a shape memory alloy in a pipe, and the wire slides inside the pipe to peel off the attached scale when the water temperature rises. .

JP-A-2005-77062 JP 2008-249163 A JP 2006-266514 A

  However, since all of the conventional heat exchangers are characterized by the shape of the piping, etc., the degree of freedom in designing the heat exchanger is small, and for example, there is a risk of hindering the downsizing and weight reduction of the heat exchanger.

  This invention is made | formed in view of the said situation, The objective is to provide the copper pipe to which scale does not adhere easily irrespective of a flow-path shape, and a heat pump water heater using the same.

In order to solve the above problems, a surface-treated copper tube according to the present invention includes a base material made of copper or a copper alloy, and a film made of polyphosphate formed on at least one surface of the base material. , to the surface of the film has been formed side, calcium carbonate characterized by being prevented from being deposited as scale.

  The polyphosphate constituting the film is preferably at least one selected from iron polyphosphate, cobalt polyphosphate, nickel polyphosphate, tin polyphosphate, zinc polyphosphate, and magnesium polyphosphate.

  Thus, by covering with a film made of polyphosphate, polyphosphate ions are generated in water, and further, by applying a salt with a predetermined metal, these metal ions are generated. Inhibits the growth of calcium carbonate and suppresses scale formation. Moreover, since such an effect | action is obtained by the membrane | film | coat which can be easily coat | covered on a copper pipe, the moldability for setting it as a pipe | tube can be maintained.

  Moreover, the heat pump water heater according to the present invention is characterized in that the surface-treated copper pipe is used in a heat transfer portion that circulates using water as a medium, with the surface on which the film is formed in contact with the water. To do.

  In this way, by applying a surface-treated copper pipe that does not easily adhere to the scale to the piping of a heat pump water heater that circulates water, particularly hot tap water that is likely to produce calcium carbonate, there is little pressure loss and the pipe is blocked. Can be made difficult to occur.

  According to the surface-treated copper pipe according to the present invention, the pipe of the heat exchanger that circulates water such as tap water as a medium can be obtained. Since it is difficult to adhere, it is not necessary to enlarge the diameter of the cross section of the flow path, and the heat exchange efficiency is not reduced. In addition, there is a high degree of versatility because there is a degree of freedom in pipe shape and piping design. And according to the heat pump water heater which concerns on this invention, continuous operation time can be lengthened and a maintenance can be made easy, and since there are few restrictions on piping shape, size reduction etc. are easy.

It is a fragmentary sectional view for explaining typically the composition of a surface treatment copper pipe concerning one embodiment of the present invention, and a scale adhesion control effect. It is a schematic diagram for demonstrating the structure of the heat pump water heater which concerns on one Embodiment of this invention.

  Hereinafter, the surface-treated copper pipe and the heat pump water heater using the same according to the present invention will be described in detail.

[Surface treatment copper tube]
The surface-treated copper pipe according to the present invention is applied to a heat exchanger, in particular, a pipe for circulating water of a heat pump water heater (see FIG. 2) described later, and has a shape corresponding to a use such as a smooth pipe, an inner grooved pipe, and the like. Although it is set as a dimension, it is not specifically limited, Furthermore, it is not limited to a tubular shape, For example, plate shape may be sufficient. As shown in FIG. 1, a surface-treated copper tube 1 according to an embodiment of the present invention uses a tube formed of copper or a copper alloy (hereinafter referred to as a copper tube) as a base material 11, and at least contacts with water. And a film 12 made of polyphosphate formed on the surface, that is, the inner surface. Hereinafter, each element which comprises this surface treatment copper pipe is demonstrated.

(Copper tube)
The copper tube (base material) 11 is made of copper or a copper alloy, and is preferably phosphorous deoxidized copper (for example, C1220) defined in JISH3300. By using phosphorous-deoxidized copper, the strength is improved and a film 12 described later is easily formed on the surface of the copper tube (base material) 1. The shape of the copper tube 11 is in accordance with the surface-treated copper tube 1.

(Film)
The coating 12 covers the inner surface of the copper tube 11, particularly when the surface-treated copper tube 1 is a pipe through which water flows, and is made of polyphosphate. As the polyphosphate that forms the coating 12 of the copper tube 11, metal salts of Fe, Co, Ni, Sn, Zn, and Mg are preferable. Examples of the polyphosphate include salts of linear condensed polyphosphoric acid such as tripolyphosphoric acid H ₅ P ₃ O ₁₀ and salts of cyclophosphoric acid such as cyclotetraphosphoric acid (HPO ₃ ) ₄ . The polyphosphate existing as the coating 12 of the surface-treated copper tube 1 is an ion of these various polyphosphates, such as P ₃ O ₁₀ ⁵⁻ (tripolyphosphate), P ₄ O ₁₃ ⁶⁻ (tetra Polyphosphoric acid), elution as [PO ₃ ⁻ ] _n (hexametaphosphoric acid) (indicated as [PO ₃ ⁻ ] _{n in} FIG. 1), and metal ions Me (Fe ²⁺ , Co ²⁺ , Ni) eluted from the coating 12 as well. ²⁺ , Sn ²⁺ , Zn ²⁺ , Mg ^2+, etc.) and adsorbed on the crystal growth surface of calcium carbonate CaCO ₃ formed on the inner surface of the surface-treated copper tube 1, so that the growth of calcium carbonate Can be prevented and scaling can be prevented.

  Although the thickness of the film 12 is not particularly defined, 10 nm to 10 μm is preferable. When the film 12 is thin, the life of the scale-adhesion suppressing effect of the surface-treated copper tube 1 is shortened. On the other hand, when the thickness is excessively thick, workability such as bending of the surface-treated copper pipe 1 is deteriorated, and when applied to a heat pump water heater, the thermal expansion / expansion of the base material (copper pipe) 11 due to the thermal cycle of operation and stoppage. There is a possibility that the film 12 cannot follow the shrinkage and the film 12 is cracked or peeled off.

(Method for manufacturing surface-treated copper tube)
Below, an example of the manufacturing method of the surface treatment copper pipe which concerns on this invention is shown.
The copper tube 11 used as a base material can apply what was manufactured by the well-known method. First, the raw electrolytic copper is dissolved under the charcoal coating. After the copper is dissolved, a copper alloy containing about 15% by mass of P is added for deoxidation, and the components are adjusted. A billet of a predetermined dimension is produced. Next, the billet is subjected to a homogenization heat treatment for improving segregation as required, and then formed into an extruded element tube by hot extrusion. The extruded element tube is rolled into a rolled element tube, and a drawn tube (element tube) having a predetermined size is manufactured by drawing. The drawing tube is used as it is or after further drawing to obtain a smooth tube. Alternatively, after drawing (intermediate annealing) the drawn tube, a grooved rolling process is performed to obtain an internally grooved tube. The obtained smooth tube or the internally grooved tube is annealed to obtain the copper tube 11.

Next, the surface (inner surface) of the copper tube 11 is coated with a coating 12 made of polyphosphate to form a surface-treated copper tube 1. As an example of the method, polyphosphate which elutes as polyphosphate ions in water, such as sodium tripolyphosphate (Na ₅ P ₃ O ₁₀ ), and metal which elutes to metal ions which are combined with the polyphosphate ions and deposited. A method of immersing the copper tube 11 in a mixed solution with a salt, for example, iron (III) chloride (FeCl ₃ ) can be mentioned. The thickness of the film 12 is adjusted by the concentration of the solution, the immersion time, and the like. Further, the coating 12 can be formed only on the inner surface by masking the outer side of the copper tube 11 and immersing it in the mixed solution, or filling or circulating the mixed solution inside the copper tube 11.

[Heat pump water heater]
The heat pump water heater according to the present invention uses the surface-treated copper pipe according to the present invention as a pipe for transferring heat to the water while circulating the water. The heat pump water heater 10 in accordance with an embodiment of the present invention, carbon dioxide (CO ₂₎ and water are natural refrigerant heat pump water heater for heat exchange as a heat medium, as shown in FIG. 2, CO ₂ as a heat exchanger A pipe that circulates water and hot water between the heat pump unit 2 including the heat transfer unit 21 that heats the water and the hot water storage tank 3 that stores the water supplied to the heat transfer unit 21 and the heated water (hot water). Connect and prepare. And changes in the state of the heat medium CO ₂ in the heat pump unit 2, heating of the water is as by known natural refrigerant heat pump water heater. That is, CO ₂ compressed by the compressor 24 to become a high-temperature / high-pressure fluid is supplied to the heat transfer section 21. In the heat transfer section 21, water (cold water) supplied from the hot water storage tank 3 by the pump P at a predetermined flow rate is heated by the CO ₂ and flows out as hot water while flowing inside the surface-treated copper pipe 1. Then go back to the hot water storage tank 3. On the other hand, the CO ₂ cooled with water is expanded by the expansion valve 22, absorbs the atmospheric heat (atmospheric heat) taken in by the fan in the evaporator 23, and is sent to the compressor 24 again.

In the heat transfer section 21, the surface-treated copper pipe 1, which is a pipe for water, is a small-sized heat pump unit 2 that is disposed close to the outside by, for example, spirally winding a pipe for CO ₂ . In order to make it easier, the U-shape is repeatedly bent. In such a heat transfer section 21, the circulating water exchanges heat with CO ₂ through the surface-treated copper pipe 1 and the CO ₂ pipe outside thereof. Alternatively, it may be a double pipe in which a small diameter CO ₂ pipe is arranged inside the surface-treated copper pipe 1 (water pipe). In heat transfer section 21 having such a configuration, the water in circulation CO ₂ and heat exchanger via a pipe for CO _2, CO ₂ flowing inside the pipe for CO ₂ in other words, through the pipe It exchanges heat with its external water. In this case, the CO ₂ pipe is a surface-treated copper pipe according to the present invention in which the coating 12 is formed on the outer surface because water directly contacts the outside. Other specifications are not particularly stipulated, and the surface-treated copper pipe according to the present invention is used according to the application of the heat pump water heater.

  As described above, according to the surface-treated copper pipe according to the present invention, pipes of heat exchangers that circulate water such as tap water, particularly high-temperature water of about 90 ° C., regardless of flow path shape or flow rate. As the piping of the heat transfer section of the heat pump water heater to be circulated, piping that is difficult to adhere to the scale is obtained. Therefore, since the pipe is not reduced in diameter or clogged as an internally grooved pipe, not only the continuous operation time is lengthened, but also the heat exchange by increasing the contact area to the pipe wall per water flow rate. A heat pump water heater with improved efficiency can be obtained.

  As mentioned above, although the form for implementing this invention has been described, the Example which confirmed the effect of this invention is demonstrated concretely compared with the comparative example which does not satisfy | fill the requirements of this invention below. It should be noted that the present invention is not limited by this embodiment, and can be implemented with appropriate modifications within the scope of the claims, all of which are included in the technical scope of the present invention. The

(Sample preparation)
The sample material was produced by the following steps.
As a copper tube as a base material, a smooth tube having an outer diameter of 9.52 mm and a wall thickness of 0.8 mm made of phosphorous deoxidized copper (P: 0.015% by mass) is applied, and this is cut into a length of 50 mm, After washing with a degreasing agent (Surf Cleaner 53: manufactured by Nippon Paint Co., Ltd.), it was air-dried at room temperature. This copper tube is immersed in a surface treatment solution consisting of a mixed aqueous solution of sodium polyphosphate (Na _{n + 2} P _n O _{3n + 1} ) and metal salt (chloride) shown in Table 1 to form a film on the surface. Then, it was washed with ion exchange water and air-dried at room temperature. Specimen No. For No. 4, the film thickness was measured by GD-OES (Glow Discharge Emission Analysis), and the film thickness was about 100 nm. In addition, the copper pipe which does not form a film | membrane (only washing | cleaning by a degreasing agent) was made into the comparative example (test material No. 7).

(Scale adhesion evaluation)
As an evaluation of the surface-treated copper tube, scale adhesion was evaluated by the method described in JP-A-2009-75080. As a scale adhesion test solution, a mixed aqueous solution (Ca: 354 ppm) of sodium hydrogen carbonate NaHCO ₃ : 1.5 g / L, calcium chloride CaCl ₂ .2H ₂ O: 1.3 g / L was prepared at 20 ° C. (sodium hydrogen carbonate , Calcium chloride: a special grade reagent manufactured by Wako Pure Chemical Industries, Ltd.).

  One end of the test material whose mass was measured was connected to the tube on the suction side of the tube pump, and the outer surface of the test material was covered with Teflon (registered trademark) tape. This specimen and the tube on the discharge side of the tube pump were immersed in 100 mL of a test solution placed in a beaker. Then, one cycle is completed when the temperature is raised from room temperature (20 ° C.) to 90 ° C. while circulating the test solution in the test material (surface-treated copper tube) at a flow rate of 1 L / min by a tube pump. The inside of the beaker was replaced with a new test solution (20 ° C.), and the circulation and temperature increase were repeated in the same manner. Note that it took about 8 minutes to raise the temperature of the test solution to 90 ° C. in one cycle.

  The test was performed for 10 cycles and 20 cycles for each specification of the test material. After the test in each cycle, the sample material was removed from the tape and tube, allowed to stand in the room and air-dried, and then the mass was measured. And from the difference with the mass measured before the test, the amount of scale adhesion per unit area of the tube inner surface of the test material is calculated and shown in Table 1.

(Evaluation results)
As shown in Table 1, the test material No. 1 to 6 are surface-treated copper tubes according to the present invention in which a film made of a polyphosphate of each metal is formed by surface treatment with a mixed aqueous solution of sodium polyphosphate and a metal salt. Compared with the copper pipe (test material No. 7) which is not equipped with the scale, the amount of scale adhesion was small, and the scale adhesion suppression effect was obtained.

10 Heat pump water heater 1 Surface treatment copper tube 11 Copper tube (base material)
12 Film 21 Heat transfer section

Claims (3)

A substrate made of copper or a copper alloy, comprising: a film comprising polyphosphate salts formed on at least one surface of the substrate, wherein the the film is formed the side surface, deposition of calcium carbonate as scale A surface-treated copper tube characterized in that it is suppressed.   2. The surface-treated copper according to claim 1, wherein the coating is made of at least one selected from iron polyphosphate, cobalt polyphosphate, nickel polyphosphate, tin polyphosphate, zinc polyphosphate, and magnesium polyphosphate. tube.   The surface-treated copper pipe according to claim 1 or 2 is used in a heat transfer portion that circulates water as a medium, with the surface on the side on which the film is formed in contact with the water. Heat pump water heater.

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