CN100467998C - Arrangement method and device for a flow path of a heat exchanger - Google Patents

Abstract

The invention discloses a heat exchanger flow path design method and its device. The method can be used to design condensers and evaporators in refrigeration and air-conditioning equipment using single and mixed refrigerants. This method takes a variety of factors and principles into consideration, including the principle of equal heat flow and the principle of field synergy. It is proposed that with the change of the phase state of the refrigerant flowing in the tube, the number of processes, the type of fins outside the tube, and the strengthening structure inside the tube should be changed, and the appropriate node on the tube should be selected to branch or merge the processes. Using the heat exchanger designed according to this method can significantly improve the heat transfer performance of the heat exchanger in refrigeration and air-conditioning equipment.

Description

Arrangement method and device for a flow path of a heat exchanger

1. Technical field

The invention relates to a refrigeration equipment and an air conditioner heat exchanger using single and mixed refrigerants, in particular to a flow path arrangement method and device for the heat exchanger.

2. Background technology

In the past, when people increased the heat transfer coefficient of the heat exchanger, they focused more on changing the fin type and the internal structure of the heat exchange tube. The type of fins has developed from the original flat sheet to the current corrugated sheet, "X" type slotted sheet, etc., and the inner structure of the tube has developed from the original light pipe to the current two-dimensional threaded pipe, and even three-dimensional threaded pipe. These measures have obvious effects on improving the heat transfer coefficient. The commonly used small air-conditioning heat exchangers (double-row tube heat exchangers) generally adopt the following flow path arrangements: "Z" shaped flow path, "single double one single" flow path arrangement, "double inlet and double outlet" ( According to the position of the entrance and exit, it can be divided into middle entry, middle exit, top entry and top exit, bottom entry and bottom exit), etc. These layout schemes have their own advantages and disadvantages. To sum up, the disadvantages of the above-mentioned various layout methods are: they often only consider the problem from a single point of view (such as strengthening heat transfer), lack of comprehensive consideration, and do not use the principle of field synergy and the idea of equal heat flow layout.

3. Contents of the invention

The purpose of the present invention is to overcome the above-mentioned shortcomings of the prior art, and provide a method and device for arranging flow paths of a heat exchanger that can improve heat exchange efficiency.

For achieving the above object, the method that the present invention adopts is:

1. A heat exchanger flow path arrangement method, characterized in that:

1) According to the principle of pure countercurrent arrangement, arrange and select the position of the inlet and outlet of the refrigerant in the horizontal direction, that is, the flow direction of the refrigerant is opposite to the direction of the air flow;

2) In accordance with the principle of preventing reverse heat conduction in the fins, partial slits are made on the fins between the inlet and outlet of the refrigerant;

3) Arrange the inlet and outlet of the heat exchanger according to the phase state of the refrigerant, and arrange and select the position of the inlet and outlet of the refrigerant in the vertical direction. If the refrigerant is in a gaseous state, the inlet and outlet of the refrigerant flow path are located at the lower end of the heat exchanger , that is, the flow direction of the inlet is opposite to the direction of gravity; if it is liquid, the inlet and outlet of the refrigerant flow path are at the upper end of the heat exchanger, that is, the flow direction of the inlet is the same as the direction of gravity;

4) According to the principle that the local heat flux is close to uniform, high and low tooth internal thread pipes with good heat exchange effect are used in the single-phase area to enhance the heat exchange effect in the single-phase area; while single internal thread with low resistance is used in the two-phase area Tube;

5) According to the principle of matching heat transfer enhancement and pressure loss, a dual-flow path arrangement is adopted at the beginning of the two-phase region;

6) According to the principle of field synergy, no slits or less slits are used in the area of the fins where the air just flows in, or fins with weak reinforcement and relatively low pressure drop are used, while after the air flows In the fin area, fin surfaces with high heat transfer performance such as slotted double bridge fins are used.

The heat exchanger made according to the above method is: the flow direction of the refrigerant is opposite to the flow direction of the air; when used as a condenser, the inlet of the refrigerant side of the heat exchanger is gaseous, and the inlet of the refrigerant is set at the lower end of the heat exchanger; the refrigerant at the outlet becomes liquid, and the outlet It is installed at the lower end. When the heat exchanger is used as an evaporator, the opposite is true. The inlet and outlet are arranged at the upper end. There is a gap between the two rows of tubes between the condenser and the evaporator; an internal thread with a better strengthening effect is installed in the single-phase area. In the two-phase area, there are enhanced heat exchange tubes with less resistance; double bridges with slots are used at the air outlet, and fins or straight sheets with fewer slots are used at the air inlet.

The heat exchanger made by adopting the flow path arrangement of the present invention can significantly improve the heat exchange performance of the heat exchanger in refrigeration and air-conditioning equipment, and with the increase of the mass flow rate, the improvement effect will be more obvious, thereby reducing the The volume of the equipment reduces the cost of the product.

4. Description of drawings

Fig. 1 is a structural schematic diagram of the flow path arrangement of the heat exchanger of the present invention, Fig. 1 (a) is a structural schematic diagram when the refrigerant of the present invention is in a gaseous state, and Fig. 1 (b) is a structural schematic diagram when the refrigerant of the present invention is in a liquid state;

Figure 2 is a schematic diagram of the thermal resistance distribution along the path in a general condenser;

Fig. 3 is a distribution diagram along the course of the heat transfer coefficient in a general condenser;

Figure 4 is a distribution diagram of the pressure drop along the path in a general condenser, where the dotted line represents the pressure at the pipe joint.

5. Specific implementation

Referring to Fig. 1, the flow path arrangement method of the present invention is as follows:

1) Pure countercurrent arrangement

According to the basic principle of heat transfer, under the same inlet and outlet temperature conditions, the average temperature and pressure of countercurrent flow is the largest, and the average temperature and pressure of downstream flow is the smallest. Therefore, at the same temperature of the hot and cold fluids, the countercurrent arrangement is better than the forward flow arrangement, that is, the flow direction of the refrigerant is opposite to the flow direction of the air;

2) Prevent reverse heat conduction in fins

The inlet and outlet of the refrigerant are both at one end of the heat exchanger, where there is a large temperature difference in the fins, and reverse heat conduction will inevitably occur. In order to avoid reverse heat conduction, the method adopted is to slit the middle part of the two rows of tubes of the heat exchanger. Partial slots are used instead of overall slots because the temperature difference in the unslit part of the fin is already very small, and the influence of reverse heat conduction can be ignored. In addition, partial slits facilitate fabrication and installation.

3) Arrangement of the inlet and outlet of the heat exchanger

Since gravity can make the liquid flow from a high place to a low place automatically, the flow path should allow the liquid to flow from a high place to a low place as much as possible to reduce flow resistance. When the heat exchanger is used as a condenser, since the phase state at the inlet of the refrigerant side of the condenser is gaseous and the outlet is liquid, it is optimal to set the inlet and outlet of the heat exchanger at the lower end; when used as an evaporator, because The inlet refrigerant of the evaporator is liquid, so contrary to the condenser, the inlet and outlet are all set at the upper end.

4) Make the local heat flux density of the heat exchanger close to uniform

According to the principle of equal heat flow, if the local heat flux density of the heat exchanger can be close to uniform everywhere, the overall heat transfer effect of the heat exchanger will be the best. Therefore, it is necessary to conduct a comprehensive analysis of the thermal resistance and temperature difference inside and outside the tube. According to q=kΔt, to make q close to uniform, it can be realized by adjusting the overall heat transfer coefficient k and temperature difference Δt.

Taking the heat transfer in a general condenser as an example, the thermal resistance and heat transfer coefficient distribution of the refrigerant side are qualitatively shown in Figure 2 and Figure 3 . Obviously, the thermal resistance of the refrigerant in the single-phase region is much greater than that of the two-phase region, and the single-phase region on the steam side is already equivalent to the thermal resistance on the air side. The heat transfer coefficient of the phase zone. The pipeline layout divided into two is adopted, and the mass flow rate of the refrigerant is reduced by this method, so as to achieve the purpose of appropriately reducing the heat transfer coefficient and reducing the resistance of the two-phase region.

Since the thermal resistance of the refrigerant in the single-phase region is much greater than that in the two-phase region, and the resistance along the path of the single-phase region is relatively low. Therefore, using a tube with a better heat transfer effect, such as a high-low tooth internal thread tube, to strengthen the heat transfer in the tube in the single-phase region can also achieve a certain effect. And there is no need to think too much about the consequences of increased resistance.

5) Comprehensive consideration of heat transfer enhancement and pressure loss

The distribution of pressure drop along the general condenser is shown in Figure 4. Obviously, in the initial stage of the two-phase region, due to the high flow velocity, the pressure drop is very large, and the local heat transfer coefficient in this region is also large. From the principle of reducing pressure drop and equal heat flow, this region can be arranged with a double flow path. Divide the refrigerant flow to reduce the flow rate. The result of this is to reduce the excessively high local heat transfer coefficient and reduce the pressure drop. At this time, the selection of the appropriate distributor and the position of the opening and closing point is the key, which needs to be determined through experiments. The experimental method is very simple, just change the position of the opening and closing points under the same test conditions for testing. By comparing the experimental results to choose the best split point position.

6) Follow the principle of field synergy

In the area where the air enters the fins (the first row of tubes in the air side flow direction), the velocity vector is consistent with the direction of the local temperature gradient, that is, the coordination of the two fields in this area is better, and measures to enhance heat transfer (such as fins) Slit) effect is not obvious, but the resistance will increase significantly. But at the back of the fins, due to fluid separation, the degree of coordination between the temperature gradient field and the velocity field becomes worse, and measures to enhance heat transfer can receive obvious results. From this point of view, the air inlet can have no slits or less slits, or use fins with weak reinforcement and relatively low pressure drop (such as straight sheets with less or no slits), while Fin surfaces with high heat transfer performance such as slotted double bridge fins can be used at the air outlet.

The above six basic principles proposed by the present invention are not only applicable to the condenser, but also applicable to the evaporator. These principles are also applicable when arranging heat exchangers with a large number of tube rows. When laying out the flow path, there may be contradictions between different principles, which need to be considered comprehensively to grasp the main factors.

Referring to Fig. 1, the refrigerant flow direction of the heat exchanger made according to the design method of the present invention is opposite to the air flow direction; when the inlet refrigerant is gaseous, the lift force of the gas is used to reduce the resistance along the way, and at this time the refrigerant gas is exchanged by heat The lower end inlet 1 enters; when the refrigerant becomes liquid, the gravity of the liquid is used to reduce the resistance along the way, and the outlet 2 of the heat exchanger is also placed at the lower end; when the imported refrigerant is liquid, the refrigerant liquid flows from the upper end of the heat exchanger Inlet 1 enters; when the refrigerant becomes gaseous, the outlet 2 of the heat exchanger is also set at the upper end; measures to reduce reverse heat conduction are adopted, and a slit 3 is opened in the middle of the two rows of pipes to achieve the purpose of reducing reverse heat conduction; through The form of the heat exchange surface inside and outside the tube is selected to make the heat flux as uniform as possible; since the thermal resistance of the refrigerant in the single-phase region 7 is much greater than that in the two-phase region 6, and the resistance along the path of the single-phase region 7 is relatively low. Therefore, in the single-phase zone 7, a high-low-tooth internal thread tube with good heat exchange effect is used to enhance the heat exchange effect in the tube in the single-phase zone; while in the two-phase zone 6, a single internal thread tube with low resistance is used. The air side fins follow the principle of field synergy, using slotted double bridges 4 at the air outlet;

Heat exchangers with other specific structures can also be designed according to the method for arranging the flow paths of the heat exchanger in the present invention.

Claims (2)

1. A heat exchanger flow path arrangement method, characterized in that: 1) According to the principle of pure countercurrent arrangement, arrange and select the position of the inlet and outlet of the refrigerant in the horizontal direction, that is, the flow direction of the refrigerant is opposite to the direction of the air flow; 2) In accordance with the principle of preventing reverse heat conduction in the fins, partial slits are made on the fins between the inlet and outlet of the refrigerant; 3) Arrange the inlet and outlet of the heat exchanger according to the phase state of the refrigerant, and arrange and select the position of the inlet and outlet of the refrigerant in the vertical direction. If the refrigerant is in a gaseous state, the inlet and outlet of the refrigerant flow path are located at the lower end of the heat exchanger , that is, the flow direction of the inlet is opposite to the direction of gravity; if it is liquid, the inlet and outlet of the refrigerant flow path are at the upper end of the heat exchanger, that is, the flow direction of the inlet is the same as the direction of gravity; 4) According to the principle that the local heat flux is close to uniform, high and low tooth internal thread pipes with good heat exchange effect are used in the single-phase area to enhance the heat exchange effect in the single-phase area; while single internal thread with low resistance is used in the two-phase area Tube; 5) According to the principle of matching heat transfer enhancement and pressure loss, a dual-flow path arrangement is adopted at the beginning of the two-phase region; 6) According to the principle of field synergy, no slits or less slits are used in the area of the fins where the air just flows in, or fins with weak reinforcement and relatively low pressure drop are used, while after the air flows In the fin area, fin surfaces with high heat transfer performance such as slotted double bridge fins are used. 2. The heat exchanger manufactured according to the arrangement method of the flow path of the heat exchanger according to claim 1, characterized in that: the flow direction of the refrigerant is opposite to the flow direction of the air; when used as a condenser, the inlet of the refrigerant side of the heat exchanger is in a gaseous state, The refrigerant inlet [1] is set at the lower end of the heat exchanger; the refrigerant at the outlet becomes liquid, and the outlet [2] is set at the lower end. When the heat exchanger is used as an evaporator, the opposite is true, and both the inlet and outlet are set at the upper end. There is a slit [3] in the middle of the two rows of tubes in the evaporator; internally threaded tubes with better strengthening effect are set in the single-phase area [7], and enhanced heat exchange tubes with less resistance are set in the two-phase area [6]; Slotted double bridges [4] are used at the air outlet, and fins or straight sheets [5] with less slits are used at the air inlet.

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