JP2516966B2 - Heat exchanger with fins - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat exchanger with fins which is used for air conditioning, refrigeration, etc. and transfers heat between a refrigerant and a fluid such as air.

2. Description of the Related Art In recent years, the prevalence of heat pump air conditioners has been increasing. This is because during cooling operation, the indoor heat exchanger is used as an evaporator and the outdoor heat exchanger is used as a condenser, and during heating operation. Conversely, the indoor heat exchanger is used as a condenser and the outdoor heat exchanger is used as an evaporator. Conventionally, this type of heat exchanger with fins is composed of fins 1 arranged in parallel at regular intervals and a heat transfer tube 2 inserted at a right angle to the fins 1 as shown in FIG. Flows between the fins 1 and exchanges heat with the refrigerant 4 flowing inside the heat transfer tube 2. Further, in such a heat exchanger with fins, a device for reducing the thermal resistance on the air side is made in order to achieve miniaturization and high performance.

The problem to be solved by the invention is that when such a heat exchanger with fins is used as an outdoor heat exchanger of an air conditioner and heating operation is performed, it functions as an evaporator, which reduces the outside air temperature. , When the surface temperature of the fin 1 or the heat transfer tube 2 becomes 0 ° c or less,
Frost occurs as shown in FIG. That is, the frost layer 5 is formed from a portion having a good heat transfer coefficient, that is, a portion having a low surface temperature. Speaking from the inside of the heat transfer tube 2, a region where the dryness of the refrigerant is relatively high (for example, in the case of CFC R-22, the dryness is 0.5 ≦ χ ≦
0.9) Heat transfer tube, near the heat exchanger outlet where refrigerant evaporation pressure and evaporation temperature decrease due to pressure loss inside the tube, and from the outside of heat transfer tube 2, frost is formed from the fins on the upstream side of the air flow where the boundary layer leading edge effect is large. Begins. Therefore, in the case of the heat exchanger with fins as shown in FIG. 5, frost is intensively generated near the fin tip region 6 near the refrigerant outlet.

When the frost formation progresses in this way, the region 6 is first blocked, and the wind speed between the fins 1 in the other regions is increased. Immediately the frost layer 5 closes the frost layer 5, so that the air is blown between the fins 1. As a result, the heat exchange capacity decreases, and therefore the heating operation must be frequently interrupted to perform the defrosting operation, which has a problem of impairing comfort during heating.

Therefore, in view of the above problems, the present invention provides uniform fins on the front surface of the finned heat exchanger to provide the fin 1
The purpose is to extend the time until the space is closed by frost 5 and maintain comfort during heating for a long time.

Means for Solving the Problems Technical means of the present invention for solving the above problems are arranged in parallel, fins through which an air flow flows, and the fins inserted at right angles and horizontally to the fins. And a heat transfer tube in which a fluid flows in a plurality of stages arranged in a direction perpendicular to the air flow direction. The fin pitch of the fins is changed to two or more in the direction perpendicular to the air flow, and at the inlet side of the fluid in the heat transfer tube. The fin pitch on the outlet side is made larger than that of the fin pitch.

Operation The effects of this technical means are as follows.

That is, as described above, the fin pitch of the fins is changed to two or more in the direction perpendicular to the air flow, and the fin pitch on the outlet side is made larger than the fin pitch on the inlet side of the fluid in the heat transfer tube. Speaking of the fin side, if the fin length in the airflow direction is constant: when the fins are installed densely, the air flow between the fins becomes closer to a rectangular shape than when the fins are installed sparsely. As shown in FIG. 3, the air-side heat transfer coefficient α ₀
Has a high value. On the other hand, speaking of the inside of the heat transfer tube,
According to the experience based on the experiments by the inventors, the relationship between the dryness χ of the fluid in the tube and the evaporative heat transfer coefficient αi is from about middle dryness to high dryness (dryness 0.5
≦ χ ≦ 0.9) It is known that the evaporation heat transfer coefficient is high.

Therefore, a fin portion having a relatively high air-side heat transfer coefficient α ₀ is combined with a heat transfer tube portion having a relatively low inner tube evaporation heat transfer coefficient α i, and a fin portion having a relatively low air-side heat transfer coefficient α ₀ is used. By combining with the heat transfer tube portion having a relatively high heat transfer coefficient αi in the tube air side, a substantially uniform heat transfer rate can be obtained as a whole of the finned heat exchanger. As a result, frost is not partially blocked during the heating operation, frost is evenly formed on the front surface of the heat exchanger with fins, and the time until the fins are blocked by frost can be extended. Comfort can be maintained for a long time.

Example Hereinafter, an example of the present invention will be described with reference to FIGS. 1 and 2.

FIG. 1 is a perspective view of a heat exchanger with fins according to an embodiment of the present invention, and FIG. 2 is a front view of the same. Fins 10a and 10b are arranged in parallel, and 11a and 11b are heat transfer tubes that are horizontally inserted through the fins 10a and 10b, and are arranged in a plurality of stages in a direction perpendicular to the air flow. Inside the heat transfer tubes 11a, 11b, the refrigerant 12 is flowing from the lower stage to the upper stage, and the heat of the refrigerant is
The heat transfer tubes 11a, 11b and the fins 10a, 10b are sequentially transferred. On the other hand, when the airflow 13 passes between the fins 10a and 10b, the refrigerant 1
The heat transferred from 2 is indirectly exchanged via the surface in contact with the air flow 13.

Then, the refrigerant 12 inflow side, that is, the fin pitch P1 on the lower side is reduced and the fins 10a are densely installed, and the outflow side of the refrigerant 12, that is, the fin pitch P2 on the upper side is increased and the fins 10b are sparsely arranged. It is installed. That is, P1 <P2.

 Next, the operation of the configuration of this embodiment will be described.

As described above, the inflow side of the refrigerant 12 (low-dryness area of the refrigerant)
Around the heat transfer tube 11a, the fin pitch P1 is reduced and the fins 10a are densely installed, and the fin pitch P2 is increased around the heat transfer tube 11b on the outflow side of the refrigerant 12 (high dryness range of the refrigerant) to increase the sparseness. Speaking from the outside of the heat transfer tube, the fin length is in the air flow direction because the fins 10b are installed.
The air-side heat transfer coefficient α ₀ has a higher value when the fins 10a are densely arranged than when the fins 10a are densely arranged because the flow path of the air flow 13 between the fins 10a becomes closer to a rectangular shape. On the other hand, from the inside of the heat transfer tube, the dryness x of the refrigerant and the evaporation heat transfer rate αi
According to the experience based on the experiments by the inventors, the evaporation heat transfer coefficient αi is high from the middle dryness range to the high dryness range (dryness 0.5 ≦ χ ≦ 0.9).

Therefore, the fin 10a having a relatively high heat transfer coefficient α ₀ on the air side is relatively high.
Section is combined with the heat transfer tube 11a having a relatively low inner tube evaporation heat transfer coefficient αi, and the fin 10b having a relatively low air-side heat transfer coefficient α ₀ and the relatively high heat transfer coefficient αi in the tube have a relatively high heat transfer coefficient αi. By combining with the heat pipe 11b, a substantially uniform heat transfer rate can be obtained in the finned heat exchanger as a whole. However,
In this case, since it is affected by the fin pitches P1 and P2, it is desirable that 1 <P2 / P1 <1.5 in order to obtain a uniform heat transfer rate. As a result, during heating operation, frost does not block partly quickly, frost is evenly formed on the front surface of the finned heat exchanger, and the time until fins 10a and 10b are blocked by frost can be extended. , It is possible to maintain comfort during heating for a long time.

EFFECTS OF THE INVENTION As described above, according to the present invention, the fins that are arranged in parallel with each other and the air flow flows between them, and the fins are vertically and horizontally inserted through the fins and are arranged in a plurality of stages in the vertical direction with respect to the air flow. A heat transfer tube through which the fluid flows, and in the direction perpendicular to the air flow, the fin pitch of the fins is changed to two or more, and the fin pitch on the outlet side of the fin in the heat transfer tube is higher than that on the inlet side. By increasing the value of, the heat exchange rate with fins can be substantially uniform as a whole. As a result, frost is not partially blocked during the heating operation, frost is evenly formed on the front surface of the heat exchanger with fins, and the time until the fins are blocked by frost can be extended. Comfort can be maintained for a long time.

[Brief description of drawings]

FIG. 1 is a perspective view of a heat exchanger with fins according to an embodiment of the present invention, FIG. 2 is a front view thereof, and FIG. 3 is a diagram showing the relationship between fin pitch and air side heat transfer coefficient in the present invention. FIG. 4 is a diagram showing the relationship between the dryness of the refrigerant and the evaporation heat transfer coefficient inside the pipe in the present invention, FIG. 5 is a perspective view of a finned heat exchanger showing a conventional example, and FIG. 6 is a sectional view of the same when frosting. Is. 10a, 10b ... Fins, 11a, 11b ... Heat transfer tubes, 12 ... Refrigerant,
13 …… Air flow, P1, P2 …… Fin pitch.

Claims (1)

(57) [Claims] 1. A heat transfer tube in which fins are arranged in parallel and through which air flows, and through which fins are inserted at right angles and horizontally and arranged in a plurality of stages in a direction perpendicular to the air to flow the fluid inside. The fin pitch of the fins is changed to two or more in the direction perpendicular to the air flow, and the fin pitch of the fins on the outlet side is made larger than the fin pitch on the inlet side of the fluid in the heat transfer tube. Heat exchanger with fins.