JPH0455691A - Pin fin heat exchanger - Google Patents

Abstract

PURPOSE:To expand the temperature range of heat exchange, improve a heat exchanging capacity remarkably and permit the miniaturization of a ventilating fan for a heat exchanger having the same size by a method wherein the heights of the tip ends of pin fins are formed so as to be lowered sequentially as the position is approached to the receiving side of airstream. CONSTITUTION:The rate of the length of the vertical part 6a of a pin fin 6 to the length of the bent part 6b of the same is designed so as to be changed gradually and the bent part 6b is longer than the vertical part 6a in the pin fin 6A of the upstream side of airstream A. On the other hand, the vertical part 6a is designed so as to be longer than the bent part 6b as the position of the pin fin is approached to the pin fins 6B, 6C of the downstream side of air conditioning airstream A. The airstream A hits the pin fin heat exchanger 1 from one side whereby the airstream A passes easily while being guided by a passage B between the pin fin groups 60, 61 and increasing the flow speed thereof. Accordingly, new air-conditioning airstream A prevails over the whole area of the upstream side and the downstream side of the pin fins 6 whereby the bent parts 6b of the pin fins 6 are contacted with the new airstream A at the upstream side while and at least one part of the vertical parts 6a of the same are contacted with the same airstream A in the downstream side and heat exchanging can be made effectively by the whole of the pin fins 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention (Industrial Application Field) This invention relates to a pin fin heat exchanger used as a heat exchanger for air conditioning, industrial use, vehicle use, etc.

(Prior art) As a conventional pin fin heat exchanger, for example, the one shown in Fig. 6 (
Those shown in a) and (b) are known.

This FIG. 6 is constructed as an evaporator of an air conditioner for an automobile, for example. As shown in the figure (a), the pin fin heat exchanger 1 has manifolds 3 and 4 communicating with pipes 5 such as refrigerant C on the left and right sides, and a plurality of heat transfer parts are arranged between these manifolds 3 and 4. book heat transfer tube 2
are connected at both ends and placed at equal intervals. The heat transfer tube 2 has a cylindrical shape with a rectangular cross section, for example, as shown in FIG. 2(b), and a large number of pin fins 6 are vertically attached to the upper and lower heat transfer surfaces 2a and 2b. The pin fins 6 are all linear and have the same length, and are provided by welding the base or by cutting out the surface of the heat transfer surface 2a or the like.

(Problem to be Solved by the Invention) However, in the conventional pin fin heat exchanger 1, all the lengths of the pin fins 6 are equal, and heat is transferred at right angles to the airflow A of the air conditioned air. Since it is fixed to the tube 2, the flow of the airflow A is obstructed, and ventilation resistance is large. In addition, since the airflow A that has already exchanged heat hits the pin fins 6 near the downstream of the conditioned air A, the amount of heat exchanged is smaller than that at the upstream airflow receiving side, and for these reasons, there is a limit to the overall heat exchange capacity. There is.

Therefore, an object of the present invention is to provide a pin fin heat exchanger that can improve heat exchange capability.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems, the present invention provides a plurality of heat transfer parts arranged in parallel, and a heat transfer part of at least one of the heat transfer parts between the heat transfer parts. and a large number of pin fins provided on the heat transfer surface of the heat transfer section and extending toward the other heat transfer section, and the height of the tips of the pin fins relative to the airflow is formed so as to become lower as the side receives the airflow. do.

(Function) According to the above configuration, the height of the tips of the pin fins is formed so that it becomes lower as the airflow is received, so that the airflow can pass between the pin fins at an increased flow velocity with low ventilation resistance. , and the new airflow comes into contact with at least a portion of each pin fin, increasing the temperature difference between the airflow and the pin fin. This promotes heat exchange with the pin fins, making it possible to significantly improve heat exchange capacity.

(Example) This invention will be described in detail below.

FIG. 1(a) is a cross-sectional view showing a heat transfer tube as a heat exchanger and a heat transfer portion of an evaporator of an automobile air conditioner according to a first embodiment of the present invention, similar to FIG. 6.

The same figure (b) is a perspective view of the pin fin part. In the pin fin heat exchanger 1, the heat transfer tube 2 is formed in a cylindrical shape with a rectangular cross section, and the pin fins are formed on the upper and lower heat transfer surfaces 2a, 2b.
are installed in large numbers. All of the pin fins 6 have a length between the channels, and are bent in the middle at right angles toward the upstream airflow receiving side, and are composed of a vertical portion 6a and a horizontal bent portion 6b. Then, the bent portion 6b is installed substantially parallel to the airflow A of the conditioned air with its tip facing upstream of the airflow A,
In this state, the base of the vertical portion 6a is fixed to the heat transfer tube 2 by welding or the like.

Further, the ratio of the lengths of the vertical portion 6a and the bent portion 6b of the pin fin 6 is set to gradually change, and the pin fin 6A on the upstream side of the airflow A has the vertical portion 6a shorter and the bent portion 6b longer.

On the other hand, the bent portion 6b becomes shorter and the vertical portion 6a becomes longer as the pin fins 6B, 6C-φ are located on the downstream side of the conditioned air A.

In this way, the height of the tip of the pin fin 6 with respect to the airflow A is gradually lowered toward the receiving side of the airflow. In other words, the bending portion 6
b gradually becomes shorter from a long state, and is configured such that the line connecting the tips of the pin fins 6 becomes lower as it goes upstream of the airflow A (to the left in FIG. 1(a)). Further, due to the configuration of the pin fins 6, a passage B for the cooling air A is formed in a tapered manner between the pin fin group 60 of the upper heat transfer tube 2 and the pin fin group 61 of the lower heat transfer tube 2. Ru.

Next, the operation of this embodiment will be explained.

First, when the airflow A hits one side of the pin fin heat exchanger 1, the airflow A is guided by the passage B between the pin fin groups 60 and 61 and easily passes through while increasing the flow velocity. Therefore, the new air-conditioning airflow A will spread over the entire area above and downstream of the pin fin 6, and with respect to this new airflow A, the bent portion 6b of the pin fin 6 will be on the upstream side, and at least one of the vertical portions 6a will be on the downstream side. part touches, pin fin 6
Heat exchange is carried out effectively throughout. The heat exchange action of the pin fins 6 allows efficient heat exchange with the refrigerant C inside the heat transfer tube 2.

Therefore, the ability of the heat exchange function will be explained in more detail.

In general, the ventilation resistance of the pin fin 6 having the cross-sectional shape shown in FIG. 2 can be divided into a shape resistance of only the shape, ignoring friction, and a frictional resistance, ignoring the shape.

Here, the shape resistance approximates the shape resistance of a cylinder with diameter a,
Since the frictional resistance can be approximated to the frictional resistance of a flat plate with a representative length a+b-0-, the resistance R acting on one pin fin 6 per 1 meter length can be expressed as the sum of the geometrical resistance RD and the frictional resistance RF using the following equation. Ru.

R-RD+R,mcD-p/24 tLax'-a
+CF・ρ/2・U m * x′ ・21U□8;
Maximum flow velocity between pin fins; Co, Cp: resistance coefficient, ρ; air density; therefore, the pin fin 601 with length h
The ventilation resistance R of the book is Ro −Co ”/)/2 ”Umax'”
a h1CF・ρ/2・U 1B a K′・21
h. The second term on the right side of the above equation, 21h, is the bin fin 6
It can be regarded as the contact area that comes into contact with the air. Since this embodiment has the same length as the conventional example, there is no change in the frictional resistance of the second term on the right side. In other words, what is replaced by bending the bin fin 6 is the portion of the first term. In this embodiment, when viewed from the direction of the airflow A, it can be regarded as a cylinder with a length h' shorter by the bent portion 6b of the bottle fin 6, so the difference in ventilation resistance ΔR
is ΔR-Co ” p/2 ” Umax ”
a (hh'). This is illustrated in diagrams as shown in FIGS. 3 and 4, and it can be seen that in this example, the ventilation resistance is significantly reduced according to the 8/8 radius of the bent portion 6b.

Further, as the ventilation resistance decreases, the flow rate of the airflow A flowing between the bin fins 6 also increases if the ability of the fan to create the airflow A is the same.

Next, the heat exchange capacity of the bottle fin heat exchanger 1 will be explained. First, the average Nusselt number N of a group of tubes when fluid flows at right angles to a group of 10 or more tubes. is approximately expressed by the following equation.

Nu-C-R.

C, r: Constant determined by various conditions, R1: Reynolds number and average Nusselt number N. is a function of the average heat transfer coefficient α1, the tube group diameter d1, and the thermal conductivity λ of the fluid, and is expressed by the following equation.

Nu-α force ◆d/λ From these equations, it can be seen that the average heat transfer coefficient α is proportional to R and r. Since R1 is proportional to the flow rate U, it is the average heat transfer coefficient α. is proportional to U'. The value of r is approximately 0.6 in the case of a simple circular pipe, and if the ventilation resistance is reduced by 50% in this example, the flow rate will be 472 times greater, so the average heat transfer coefficient α is , CJ 2
) 06-1°23 times, which can be said to be an improvement of 23%.

By the way, the heat exchange capacity Q of the bottle fin heat exchanger 1 is defined by the following equation.

Q- is φS・ΔTII K: Heat transfer rate of heat exchanger, S: Heat transfer area, ΔT; Logarithmic average temperature difference S between the refrigerant of heat transfer tube 2 and air flow A is the same as before, and the value of K is is the average heat transfer coefficient α19
It is known that it is closely controlled.

Therefore, a 23% improvement in the average heat transfer coefficient α means that the heat exchange capacity Q increases by approximately 20%.

Furthermore, in this embodiment, the new low-temperature airflow A hits at least a portion of the bottle fin 6 on the downstream side, so the value of ΔT1 increases. Therefore, the heat exchange capacity Q becomes even larger than that described above. Thus, the formula also proves that the ventilation resistance is reduced and the heat exchange capacity is increased.

FIG. 5(a) is a sectional view showing a heat transfer tube according to a second embodiment of the present invention, and FIG. 5(b) is a perspective view of a bin fin portion.
In this embodiment, the cross-sectional shape of the heat transfer tube 2' is triangular, and the upper and lower heat transfer surfaces 2a' and 2b' are configured to be inclined toward the upstream side of the air flow A. Straight bottle fins 6' are fixed perpendicularly to these heat transfer surfaces 2a' and 2b', and in this case as well, between the bottle fin groups 60' and 61' of the upper and lower heat transfer tubes 2'. A passage B for the airflow A is formed in the airflow A, and the height of the tip of the bottle fin 6' with respect to the airflow A is gradually lowered toward the airflow receiving side.

Therefore, in this embodiment as well, the bottle fins 6' act to absorb heat as in the above embodiment, and the heat exchange ability can be improved. Furthermore, in this embodiment, the shape of the heat transfer tube 2' itself has a small ventilation resistance, which is highly effective. Further, since the bottle fin 6' does not need to be bent, manufacturing is easy and cost is reduced.

Note that this invention is not limited to the above embodiments. For example, the pin fin may have a cross-sectional shape other than a prism. The bent portion of the pin fin may be provided at an angle with respect to the flow of the airflow A. In the example of FIG. 1, all tips of the pin fins on the wake side could extend to the airflow receiving end. In this case, although passage B is not formed, heat can be exchanged with the new airflow at the longer bent portion toward the downstream side, and the heat exchange capacity no.
It is possible to improve this. This invention can also be applied to radiators, heater cores, etc.

[Effects of the Invention] As is clear from the above, according to the present invention, in a pin fin heat exchanger, the height of the tips of the pin fins is formed so as to be gradually lower toward the receiving side of the airflow, so that the heat exchange temperature can be lowered. This makes it possible to widen the difference and significantly improve heat exchange capacity. The structure can also be made more compact since only the shapes of the pin fins and heat transfer parts need to be changed.

Therefore, for heat exchangers of the same size, the blower fan can be made smaller, and the overall heat exchanger system can be made lighter, smaller, and lower in cost.

[Brief explanation of drawings]

FIG. 1(a) is a sectional view according to a fourth embodiment of the present invention;
(b) is a perspective view of the main part, Figure 2 is a cross-sectional view of the shape of the pin fin, Figure 3 is a diagram of the ventilation resistance of 11 pin fins, Figure 4 is a diagram of the air temperature distribution around the pin fins, Figure 4 is a diagram of the air temperature distribution around the pin fins, Figure 5 (
6(a) is a cross-sectional view of the second embodiment of the present invention, (b) is a perspective view of the same essential parts, FIG. 6(a) is a perspective view of a conventional pin fin heat exchanger, and (b) is the same cross-sectional view. It is a diagram. 1... Bin fin heat exchanger 2... Heat transfer tube (heat transfer part) 2a, 2b, 2a', 2b' -=-Heat transfer surface 6...
Pin fin agent Patent attorney Hidekazu Miyoshi 1.Pin fin heat exchanger 2.Heat transfer tube (heat transfer part) 2m, 2b, 2a', 2b' - heat transfer surface 6 Pin fin Figure 1 (a) A/ Figure 1 (b) D Figure 2 [m/s]

Claims (1)

[Claims] A plurality of transfer parts arranged in parallel, and a large number of pin fins provided on a heat transfer surface of at least one heat transfer part between the transfer parts and extending toward the other heat transfer part, and a tip of the pin fin. A pin fin heat exchanger characterized in that the height of the pin fin heat exchanger is formed such that the height of the pin fin heat exchanger relative to the airflow becomes lower toward the receiving side of the airflow.