JP6294709B2 - Heat transfer tube with inner groove for evaporator - Google Patents

Description

  The present invention relates to an inner grooved heat transfer tube for an evaporator of a heat exchanger, and more particularly to an inner grooved heat transfer tube for an evaporator that uses carbon dioxide containing refrigeration oil as a refrigerant.

  Conventionally, in a heat exchanger using a carbon dioxide refrigerant, an internally grooved tube in which a groove is formed on the inner surface of a copper or copper alloy heat transfer tube is used, and the heat transfer tube and the refrigerant are formed by the inner surface groove of the heat transfer tube. The contact area is increased and the heat transfer performance is improved.

  However, the carbon dioxide refrigerant flowing through the heat transfer tube contains refrigeration oil that is a lubricant for the compressor. For this reason, if the groove is simply formed on the inner surface of the heat transfer tube, the refrigerating machine oil may stay on the inner surface of the tube.

  By the way, the fin-and-tube heat exchanger is manufactured as follows. That is, a plurality of metal plate-like members (hereinafter referred to as outer fins) are arranged apart from each other, a common through hole is provided in the plurality of outer fins, and the heat transfer tube is passed through the through hole. Thereafter, the expansion tube is inserted into the heat transfer tube, the tube inner surface is mechanically expanded by the expansion tube, and the heat transfer tube and the outer fin are brought into close contact with each other.

  For this reason, when the heat transfer tube is mechanically expanded, the fins formed between adjacent grooves inside the heat transfer tube are crushed or fall down, and the heat transfer performance is improved when the fin-and-tube heat exchanger is assembled. May decrease.

  On the other hand, by defining the specifications of the heat transfer tubes and fins, an internally grooved heat transfer tube that suppresses the accumulation of refrigeration oil and the occurrence of fin crushing and fin collapse during expansion of the heat transfer tubes has been proposed. (For example, refer to Patent Document 1).

JP 2009-228929 A

  Incidentally, there is a demand for reducing the manufacturing cost by changing the constituent material from copper to aluminum or an aluminum alloy in an evaporator inner surface grooved heat transfer tube using carbon dioxide containing refrigeration oil as a refrigerant.

  However, for the following reasons, simply changing the constituent material of the internally grooved heat transfer tube described in Patent Document 1 to aluminum or an aluminum alloy deteriorates the heat transfer performance.

  That is, since aluminum has a material strength of only about ½ that of copper, it is necessary to increase the thickness of the heat transfer tube. On the other hand, when the thickness of the heat transfer tube is increased, it is necessary to apply a large load to the heat transfer tube in order to expand the heat transfer tube to the same size as the conventional one. For this reason, when the heat transfer tube is mechanically expanded, the load applied to the apex of the fins is increased, and the fins are easily crushed.

  On the other hand, it is conceivable to increase the width of the fin (the length in the circumferential direction of the heat transfer tube) to suppress the collapse of the fin. However, when the width dimension of the fin is increased, the groove area or the width dimension of the groove is decreased, so that the refrigerating machine oil is liable to stay in the heat transfer tube and the heat transfer performance is deteriorated.

  In view of the above points, an object of the present invention is to improve heat transfer performance in an internally grooved heat transfer tube for an evaporator made of aluminum or aluminum alloy that uses carbon dioxide containing refrigerating machine oil as a refrigerant.

In order to achieve the above object, according to the first aspect of the present invention, in an internally grooved heat transfer tube for an evaporator of a heat exchanger that uses carbon dioxide containing refrigeration oil as a refrigerant, the heat transfer tube is made of aluminum or an aluminum alloy. A heat pipe (1) is provided, and a plurality of grooves (11) extending in a direction parallel to or inclined with respect to the tube axis of the heat transfer pipe (1) are formed on the inner surface of the heat transfer pipe (1). 11), a plurality of fins (12) are formed. The outer diameter of the heat transfer tube (1) is D (unit: mm), the number of grooves (11) is N, and the number of fins (12) When the height is H (unit: mm) and the width of the fin (12) is W2 (unit: mm), the outer diameter of the pipe and the number of grooves (11) satisfy the relationship of 4 ≦ N / D ≦ 9. And the height of the fin (12) and the width of the fin (12) are 0. ≦ H / W2 satisfies the relation of ≦ 1.7, the heat transfer tube (1) is characterized in that it is formed by drawing or extruding.

  According to this, the heat transfer performance can be improved by satisfying the relationship of 4 ≦ N / D ≦ 9 for the tube outer diameter and the number of grooves (11). In addition, when the ratio (H / W2) between the height of the fin (12) and the width of the fin (12) is reduced, the refrigeration oil is likely to stay in the groove (11), and thus the heat transfer performance is drastically reduced. To do. On the other hand, when the ratio (H / W2) between the height of the fin (12) and the width of the fin (12) is increased, the fin (12) falls when the heat transfer tube (1) is expanded by a tube expander or the like. , Heat transfer performance decreases. For this reason, heat transfer performance can be improved by making the height of the fin (12) and the width of the fin (12) satisfy the relationship of 0.5 ≦ H / W2 ≦ 1.7.

  In addition, the code | symbol in the bracket | parenthesis of each means described in this column and the claim shows the correspondence with the specific means as described in embodiment mentioned later.

It is a schematic perspective view which shows the fin and tube type heat exchanger in embodiment of this invention. It is a pipe axis orthogonal sectional view of an inner surface grooved heat exchanger tube concerning an embodiment of the present invention. It is a longitudinal cross-sectional view containing the tube axis | shaft of the heat transfer tube with an inner surface groove | channel which concerns on embodiment of this invention. It is the IV section enlarged view of FIG. The relationship between the ratio N / D of the number of grooves N and the tube outer diameter D and the fin width W2 is shown for the internally grooved heat transfer tube made of aluminum or aluminum alloy and the internally grooved heat transfer tube made of copper or copper alloy. FIG. The relationship between the ratio N / D of the number N of grooves and the tube outer diameter D and the groove width W1 is shown for an internally grooved heat transfer tube made of aluminum or an aluminum alloy and an internally grooved heat transfer tube made of copper or a copper alloy. FIG. Relationship between the ratio N / D of the number of grooves N and the tube outer diameter D and the heat transfer coefficient improvement ratio for the internally grooved heat transfer tube made of aluminum or aluminum alloy and the internally grooved heat transfer tube made of copper or copper alloy FIG. It is a schematic diagram which shows the fin shape before and behind the pipe expansion by the pipe expander of the inner surface grooved heat transfer tube in the embodiment of the present invention. FIG. 5 is a characteristic diagram showing the relationship between the ratio N / D of the number of grooves N and the tube outer diameter D and the fin width W2 for the internally grooved heat transfer tube according to the embodiment of the present invention and the internally grooved heat transfer tube according to the comparative example. is there. FIG. 5 is a characteristic diagram showing the relationship between the ratio N / D of the number of grooves N and the tube outer diameter D and the groove width W1 for the internally grooved heat transfer tube according to the embodiment of the present invention and the internally grooved heat transfer tube according to the comparative example. is there. It is a schematic diagram which shows the fin shape before and behind the pipe expansion by the pipe expander of the inner surface grooved heat transfer pipe in the comparative example. When the oil separator is provided in the refrigeration cycle, the inner surface grooved heat transfer tube according to the embodiment of the present invention, the inner surface grooved heat transfer tube according to the comparative example, and the inner surface grooved heat transfer tube configured by copper or copper alloy, It is a characteristic view which shows the relationship between ratio N / D of the number N of grooves, and pipe outer diameter D, and a heat transfer rate improvement ratio. In the case where the oil separator is not provided in the refrigeration cycle, the inner surface grooved heat transfer tube according to the embodiment of the present invention, the inner surface grooved heat transfer tube according to the comparative example, and the inner surface grooved heat transfer tube configured by copper or copper alloy, the groove It is a characteristic view which shows the relationship between ratio N / D of number N and pipe outer diameter D, and a heat transfer rate improvement ratio. It is a characteristic view which shows the relationship between ratio H / W2 of fin height H and fin width W2, and a heat transfer rate improvement ratio. It is a characteristic view showing the relationship between the ratio H / σ of the fin height H and the tensile strength σ of the aluminum or aluminum alloy that is the constituent material of the heat transfer tube 1 and the heat transfer coefficient improvement ratio. It is a characteristic view which shows the relationship between lead angle (theta) and a heat transfer rate improvement ratio. It is a characteristic view which shows the relationship between lead angle (theta) and the pressure loss increase ratio of a refrigerant | coolant. It is a characteristic view which shows the relationship between lead angle (theta) and heat exchange performance ratio.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The internally grooved heat transfer tube according to this embodiment is applied to a fin-and-tube heat exchanger that performs heat exchange between a carbon dioxide refrigerant containing refrigeration oil for a refrigeration cycle and air.

  As shown in FIG. 1, the fin-and-tube heat exchanger includes an internally grooved heat transfer tube 1 (hereinafter referred to as a heat transfer tube 1), a plate fin 2, a U vent tube 3 and a header 4.

  The heat transfer tube 1 is a tube through which a refrigerant flows, and is bent into a hairpin shape (substantially U shape). In the present embodiment, the heat transfer tube 1 is made of aluminum or an aluminum alloy. The plate fin 2 is a heat transfer promotion member that increases the heat transfer area between the air and the heat transfer tube 1 and promotes heat exchange between the air and the refrigerant, and is formed in a plate shape (plate shape). The U vent pipe 3 is formed in a U shape and connects the ends of the plurality of heat transfer tubes 1. The header 4 distributes or collects the refrigerant with respect to the heat transfer tube 1.

  The fin-and-tube heat exchanger of this embodiment is manufactured as follows. First, after forming a tube by drawing, the heat transfer tube 1 having a groove formed on the inner surface of the tube is formed by rolling the inner surface of the tube.

  Next, a through hole through which the heat transfer tube 1 is inserted is formed in the plate fin 2. And after arrange | positioning the several plate fin 2 at equal intervals, the heat exchanger tube 1 is penetrated to a through-hole. In this state, a tube expander is inserted into the heat transfer tube 1, and the tube inner surface is mechanically expanded by the tube expander to bring the heat transfer tube 1 and the plate fin 2 into close contact with each other. Thereafter, the U vent pipe 3 and the header 4 are brazed to the heat transfer pipe 1. As a result, a fin-and-tube heat exchanger having a coolant channel formed therein is completed as shown in FIG.

  Then, the detailed structure of the heat exchanger tube 1 of this embodiment is demonstrated. Hereinafter, unless otherwise specified, “heat transfer tube 1” means the heat transfer tube 1 before expansion.

  As shown in FIGS. 2 and 3, a plurality of grooves 11 are spirally formed on the inner surface of the heat transfer tube 1. The groove 11 extends in a direction inclined with respect to the tube axis of the heat transfer tube 1. In addition, fins 12 that spirally extend as protrusions between the spiral grooves 11 are formed on the inner surface of the heat transfer tube 1. By forming the grooves 11 and the fins 12 on the tube inner surface of the heat transfer tube 1, the contact area between the tube inner surface and the refrigerant is increased, and the heat transfer performance is improved.

  As shown in FIG. 2, the outer diameter (tube outer diameter) of the heat transfer tube 1 is D (unit: mm). As shown in FIG. 3, the lead angle with respect to the tube axis direction of the groove 11, that is, the angle (twist angle) formed by the straight line L parallel to the tube axis direction on the tube inner surface of the heat transfer tube 1 and the direction in which the groove 11 extends is θ ( Unit: °).

  As shown in FIG. 4, in the tube axis orthogonal cross section of the heat transfer tube 1, the bottom wall thickness is t, and the fin height, that is, the groove depth is H (unit: mm). In the cross section perpendicular to the tube axis of the heat transfer tube 1, the width of the bottom surface of the groove 11 (groove width), that is, the length in the circumferential direction of the heat transfer tube 1 at the bottom surface of the groove 11 is defined as W1 (unit: mm). In the cross section orthogonal to the tube axis of the heat transfer tube 1, the width of the root portion of the fin 12 (fin width), that is, the circumferential length of the heat transfer tube 1 at the root portion of the fin 12 is W2 (unit: mm). Let N be the number of grooves 11 (number of grooves) of one heat transfer tube 1.

  Here, the relationship between the ratio N / D between the number of grooves N and the tube outer diameter D and the fin width W2 is shown in FIG. 5, and the ratio N / D between the number of grooves N and the tube outer diameter D and the groove width W1 The relationship is shown in FIG. FIG. 7 shows the relationship between the ratio N / D between the number N of grooves and the pipe outer diameter D and the heat transfer coefficient improvement ratio.

  The vertical axis | shaft of FIG. 7 has shown the improvement ratio of the heat transfer rate with respect to the fin and tube type heat exchanger which made the heat exchanger tube 1 the smooth tube which does not have the groove | channel 11 and the fin 12 in the tube inner surface. In addition, the vertical axis | shaft of FIGS. 12-16 mentioned later has also shown the improvement ratio of the heat exchange rate similar to the vertical axis | shaft of FIG. 5 to 7, the solid line indicates the case where the heat transfer tube 1 is made of aluminum or an aluminum alloy (hereinafter referred to as an Al grooved tube), and the broken line indicates the case where the heat transfer tube 1 is formed of copper or a copper alloy (hereinafter referred to as “the aluminum grooved tube”). , Referred to as a Cu grooved tube).

  Since the tensile strength of the constituent material of the Al grooved tube is lower than that of the Cu grooved tube, the bottom wall thickness t of the heat transfer tube 1 is increased. Therefore, in the Al grooved tube, as shown in FIG. 5, the fin width W2 when the number of grooves N is the same is larger than that of the Cu grooved tube, and as shown in FIG. The groove width W1 when made the same is smaller than the Cu grooved tube. As a result, in the Al grooved tube, the refrigerating machine oil is likely to stay in the groove 11, and as shown in FIG.

  By the way, the conventional heat transfer tube 1 uses copper or a copper alloy as a constituent material, and in order to prevent the fin 12 from being crushed by the expansion of the heat transfer tube 1 by the expansion tube, ensure a fin width W2 of a certain level or more. Yes.

  On the other hand, the heat transfer tube 1 of the present embodiment uses aluminum or an aluminum alloy as a constituent material, and, as shown in FIG. 8, in order to ensure a groove width W1 ′ after the tube expansion to a certain level or more, The fin width W2 is set smaller than the conventional one. Therefore, the present inventor examined the optimum specifications of the fin height H and the number of grooves N in anticipation of the fin crush after the pipe expansion.

  For the heat transfer tube 1 according to this embodiment and the heat transfer tube 1 according to the comparative example, the relationship between the ratio N / D of the number of grooves N and the tube outer diameter D and the fin width W2 is shown in FIG. FIG. 10 shows the relationship between the ratio N / D with the outer diameter D and the groove width W1. 9 and 10, the solid line indicates the heat transfer tube 1 according to the present embodiment, and the alternate long and short dash line indicates the heat transfer tube 1 according to the comparative example.

  The heat transfer tube 1 according to the comparative example has a fin width of a certain level or more in order to prevent the fin 12 from being crushed by the heat transfer tube 1 having a conventional shape as shown in FIG. The heat transfer tube 1 that secures W2 is made of aluminum or an aluminum alloy.

  The heat transfer tube 1 according to the present embodiment has a fin width W2 that is smaller than that of the heat transfer tube 1 according to the comparative example when the number of grooves N is the same as shown in FIG. 9, and the number of grooves N is as shown in FIG. The groove width W1 when it is the same is larger than the heat transfer tube 1 according to the comparative example.

  Subsequently, for the heat transfer tube 1 according to the present embodiment, the heat transfer tube 1 of the comparative example, and the Cu grooved tube as the conventional technology, the ratio N / D of the number N of grooves and the tube outer diameter D and the heat transfer coefficient improvement ratio The relationship is shown in FIG. 12 and FIG. FIG. 12 shows a case where the refrigeration cycle is provided with an oil separator (not shown) for separating the compressor lubrication oil mixed in the refrigerant from the refrigerant (oil rate is less than 1%). FIG. 13 shows a case where an oil separator is not provided in the refrigeration cycle (oil rate is 1 to 5%).

  12 and 13, the solid line indicates the heat transfer tube 1 according to the present embodiment, the alternate long and short dash line indicates the heat transfer tube 1 according to the comparative example, and the broken line indicates a Cu grooved tube. 12 and 13, as the heat transfer tube 1 according to the present embodiment, the number of grooves N and the tube in the case where the fin height H is changed in four steps between 0.15 mm and 0.3 mm. The relationship between the ratio N / D with the outer diameter D and the heat transfer coefficient improvement ratio is shown.

  As shown in FIG. 12, in the case where an oil separator is provided in the refrigeration cycle, the conventional Cu grooved tube improves the heat transfer coefficient up to about 2.1 times the heat transfer coefficient of the smooth tube. be able to. On the other hand, in the heat transfer tube 1 of the comparative example, that is, the heat transfer tube having the same shape as the Cu grooved tube is made of aluminum or an aluminum alloy, the heat transfer is only up to about 1.3 times the heat transfer coefficient of the smooth tube. The rate cannot be improved.

  On the other hand, in the heat transfer tube 1 of the present embodiment, the heat transfer rate can be improved up to about 2.1 times the heat transfer rate of the smooth tube, similarly to the conventional Cu grooved tube. Specifically, by setting the ratio N / D between the number of grooves N and the tube outer diameter D to be in the range of 4 to 9, the heat transfer coefficient of about 1.7 times the heat transfer coefficient of the smooth tube is secured. can do.

  In addition, as shown in FIG. 13, when the oil separator is not provided in the refrigeration cycle, the heat transfer coefficient can be increased up to about 1.9 times the heat transfer coefficient of the smooth tube in the conventional Cu grooved tube. Can be improved. On the other hand, in the heat transfer tube 1 of the comparative example, that is, the heat transfer tube having the same shape as the Cu grooved tube is made of aluminum or an aluminum alloy, the heat transfer is only up to about 1.3 times the heat transfer coefficient of the smooth tube. The rate cannot be improved.

  On the other hand, in the heat transfer tube 1 of the present embodiment, the heat transfer coefficient can be improved up to about 1.9 times the heat transfer coefficient of the smooth tube, similarly to the Cu grooved tube which is the prior art. Specifically, by setting the ratio N / D between the number of grooves N and the pipe outer diameter D to be in the range of 4 to 7.5, the heat transfer coefficient is about 1.7 times the heat transfer coefficient of the smooth tube. Can be secured.

  Next, FIG. 14 shows the relationship between the ratio H / W2 between the fin height H and the fin width W2 and the heat transfer coefficient improvement ratio. As shown in FIG. 14, when the ratio H / W2 between the fin height H and the fin width W2 is reduced, the refrigerating machine oil is liable to stay in the groove 11, and thereby the heat transfer performance is drastically reduced. On the other hand, when the ratio H / W2 between the fin height H and the fin width W2 is increased, fin collapse occurs in which the fin 12 collapses when the heat transfer tube 1 is expanded by the expander, and heat transfer performance is reduced. For this reason, heat transfer performance can be improved by making ratio H / W2 of fin height H and fin width W2 into the range of 0.5 or more and 1.7 or less.

  Next, FIG. 15 shows the relationship between the ratio H / σ between the fin height H and the tensile strength σ of aluminum or aluminum alloy which is a constituent material of the heat transfer tube 1 and the heat transfer coefficient improvement ratio. In the present embodiment, the tensile strength σ of the constituent material of the heat transfer tube 1 is set to 95 MPa or more.

  As shown in FIG. 15, when the ratio H / σ between the fin height H and the tensile strength σ becomes small, the effect of stirring the refrigerant by the fins 12 becomes small, so that the heat transfer performance sharply decreases. On the other hand, when the ratio H / σ between the fin height H and the tensile strength σ is increased, the fin collapse occurs in which the fin 12 falls when the heat transfer tube 1 is expanded by the tube expander, and the heat transfer performance is deteriorated.

  For this reason, the heat transfer performance can be improved by setting the ratio H / σ of the fin height H to the tensile strength σ in the range of 0.0014 or more and 0.004 or less. In particular, when the ratio N / D between the number of grooves N where the heat transfer performance is highest and the pipe outer diameter D is 7, the ratio H / σ between the fin height H and the tensile strength σ is 0.002 or more, 0 Heat transfer performance can be improved by setting it as the range below 0.004.

  Subsequently, FIG. 16 shows the relationship between the lead angle θ and the heat transfer coefficient improvement ratio, and FIG. 17 shows the relationship between the lead angle θ and the pressure loss increase ratio of the refrigerant. FIG. 18 shows the relationship. The vertical axis | shaft of FIG. 17 has shown the raise ratio of the pressure loss of the refrigerant | coolant with respect to the fin and tube type heat exchanger which used the heat exchanger tube 1 as the smooth tube. Further, the performance ratio of the heat exchanger shown on the vertical axis in FIG. 18 is a value of the heat exchange performance in which the heat exchange performance of the fin-and-tube heat exchanger having the heat transfer tube 1 as a smooth tube is represented as 1.

  As shown in FIG. 16, when the lead angle θ is smaller than 10 °, the refrigerant flow in the heat transfer tube 1 becomes closer to a straight line from the spiral shape, so that it is dried out in the high thirst degree region and the heat transfer coefficient is lowered. To do. On the other hand, as shown in FIG. 17, the pressure loss of the refrigerant increases as the lead angle θ increases.

  For this reason, heat exchange performance can be improved as shown in FIG. 18 by making lead angle (theta) into the range of 10 degrees or more and 40 degrees or less. Specifically, the heat exchange performance can be improved up to 1.05 times that of the smooth tube.

(Other embodiments)
The present invention is not limited to the above-described embodiment, and can be variously modified as follows without departing from the spirit of the present invention.

  (1) Although the said embodiment demonstrated the example which formed the groove | channel 11 so that it might extend in the direction inclined with respect to the tube axis | shaft of the heat exchanger tube 1, it does not restrict to this but the groove | channel 11 is the tube axis | shaft of the heat exchanger tube 1. You may form so that it may extend in parallel.

(2) In the above-described embodiment, the heat transfer tube 1 is formed by drawing the tube by drawing and then rolling the inner surface of the tube. However, the method for manufacturing the heat transfer tube 1 is described below. It is not limited to. For example, the heat transfer tube 1, but it may also be formed by extrusion molding.

1 Heat Transfer Tube with Internal Groove 11 Groove 12 Fin

Claims (5)

An internal grooved heat transfer tube for an evaporator of a heat exchanger that uses carbon dioxide containing refrigeration oil as a refrigerant,
A heat transfer tube (1) made of aluminum or aluminum alloy;
A plurality of grooves (11) extending in a direction parallel to or inclined with respect to the tube axis of the heat transfer tube (1) are formed on the inner surface of the heat transfer tube (1),
A plurality of fins (12) are formed between the adjacent grooves (11),
The tube outer diameter of the heat transfer tube (1) is D (unit: mm), the number of the grooves (11) is N, the height of the fin (12) is H (unit: mm), and the fin (12) When the width is W2 (unit: mm), the outer diameter of the tube and the number of the grooves (11) satisfy the relationship of 4 ≦ N / D ≦ 9, and the height of the fin (12) And the width of the fin (12) satisfies the relationship of 0.5 ≦ H / W2 ≦ 1.7 ,
The heat transfer tube (1) is an internally grooved heat transfer tube for an evaporator, wherein the heat transfer tube (1) is formed by drawing or extrusion .   The tube outer diameter and the number of grooves (11) satisfy the relationship of 4 ≦ N / D ≦ 7.5, and the height of the fin (12) and the width of the fin (12) are The internal grooved heat transfer tube for an evaporator according to claim 1, wherein a relationship of 0.5 ≦ H / W2 ≦ 1.7 is satisfied.   A lead angle (θ) that is an angle formed by a straight line parallel to the tube axis direction on the inner surface of the heat transfer tube (1) and a direction in which the groove (11) extends is 10 ° or more and 40 ° or less. An internally grooved heat transfer tube for an evaporator according to claim 1 or 2.   When the tensile strength of aluminum or aluminum alloy as the constituent material of the heat transfer tube (1) is σ (unit: MPa), the height of the fin (12) and the tensile strength of the constituent material are 0.0014 ≦ 4. The evaporator inner grooved heat transfer tube according to claim 1, wherein a relationship of H / σ ≦ 0.004 is satisfied. 5.   5. The inner groove for an evaporator according to claim 4, wherein the height of the fin (12) and the tensile strength of the constituent material satisfy a relationship of 0.002 ≦ H / σ ≦ 0.004. Heat transfer tube.

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