CN101978236A - Heat exchanger - Google Patents

Abstract

Provided is a heat exchanger which is suitable for use in a refrigerant circuit employing either a single refrigerant consisting of a refrigerant represented by the molecular formula C3HmFn (wherein m is 1-5 and n is 1-5, provided that m+n=6) and having one double bond in the molecular structure or a refrigerant mixture including the single refrigerant. In the heat exchanger (10), the center-to-center distance (S) for heat transfer pipes adjacent to each other in the vertical direction and the outer diameter (D) of the heat transfer pipes satisfy the relationship 2.5<S/D<3.5, and the length (L) of the refrigerant passage and the outer diameter (D) of the heat transfer pipes satisfy the relationship 0.28*D1.17<L<1.10*D1.17. An outdoor heat exchanger (4) and an indoor heat exchanger (6) have been designed based on the relationships.

Description

heat exchanger

technical field

The present invention relates to heat exchangers, and more particularly to heat exchangers suitable for use in refrigerant circuits using low-pressure refrigerants.

Background technique

From the viewpoint of protecting the global environment, refrigerants used in the refrigerant circuits of air-conditioning devices are seeking refrigerants with a low global warming coefficient and no ozone layer damage. In fact, refrigerants corresponding to the requirements have been developed (such as , refer to Patent Document 1).

The refrigerant (C ₃ H _m F _n ) disclosed in Patent Document 1 has characteristics of a relatively high theoretical COP and a low global warming coefficient. However, since this refrigerant has a relatively high boiling point and is a so-called low-pressure refrigerant, the input of the compressor may be increased due to the pressure loss of the heat exchanger, resulting in a decrease in operating efficiency.

Patent Document 1: (Japanese) Unexamined Patent Publication No. 4-110388

Contents of the invention

The object of the present invention is to provide a heat exchanger suitable for use with molecular formulas represented by C ₃ H _m F _n (where m=1 to 5, n=1 to 5, and m+n=6) A refrigerant circuit in which a single refrigerant or a mixed refrigerant containing the single refrigerant is formed by a refrigerant having one double bond in its structure.

In the heat exchanger of the first invention, the refrigerant circuit is represented by the molecular formula C ₃ H _m F _n (where m=1 to 5, n=1 to 5, and m+n=6) and the molecular structure has A single refrigerant composed of an organic compound with a double bond or a mixed refrigerant containing the single refrigerant includes a plurality of heat transfer tubes and a plurality of plate-shaped fins. The heat transfer tubes form one or more refrigerant paths for circulating the refrigerant. The plate-shaped fins are arranged to overlap at predetermined intervals, and a plurality of heat transfer tubes penetrates substantially vertically therethrough. The relationship between the distance S between the centers of adjacent heat transfer tubes in the vertical direction and the outer diameter D of the heat transfer tube is: 2.5<S/D<3.5, the length L of the refrigerant path and the outer diameter D of the heat transfer tube The relationship is: 0.28×D ^1.17 <L<1.10×D ^1.17 .

Since the refrigerant is a low-pressure refrigerant, it is easily affected by pressure loss in the heat transfer tubes. The relationship between the refrigerant path length L in the heat exchanger, the outer diameter D of the heat transfer tube, and the center-to-center distance S of the heat transfer tube is set as the above relational expression, whereby the pressure of the refrigerant in the heat transfer tube can be expressed as The impact of losses is kept to a minimum.

In the heat exchanger of the second invention based on the heat exchanger of the first invention, the refrigerant is a single refrigerant formed from 2,3,3,3-tetrafluoro-1-propene or contains the single refrigerant refrigerant mixture.

A single refrigerant formed from 2,3,3,3-tetrafluoro-1-propene or a mixed refrigerant containing the single refrigerant is a low-pressure refrigerant and therefore is easily affected by pressure loss in the heat transfer tube, but , the relationship between the refrigerant path length L in the heat exchanger, the outer diameter D of the heat transfer tube, and the center-to-center distance S of the heat transfer tube is set as the relational expression, thereby the refrigerant in the heat transfer tube can be The influence of pressure loss is suppressed to a minimum.

In the heat exchanger of the third invention, in the heat exchanger of the first invention, the refrigerant is a mixed refrigerant containing 2,3,3,3-tetrafluoro-1-propene and difluoromethane.

The mixed refrigerant containing 2,3,3,3-tetrafluoro-1-propene and difluoromethane is a low-pressure refrigerant, so it is easily affected by the pressure loss in the heat transfer tube, however, the The relationship between the refrigerant path length L, the outer diameter D of the heat transfer tubes, and the center-to-center distance S of the heat transfer tubes is set to the above relational expression, whereby the influence of the pressure loss of the refrigerant in the heat transfer tubes can be suppressed to a minimum. .

In the heat exchanger of the fourth invention, based on the heat exchanger of the first invention, the refrigerant is a mixed refrigerant containing 2,3,3,3-tetrafluoro-1-propene and pentafluoroethane.

The mixed refrigerant containing 2,3,3,3-tetrafluoro-1-propene and pentafluoroethane is a low-pressure refrigerant, so it is easily affected by the pressure loss in the heat transfer tube, however, in this heat exchanger The relationship between the refrigerant path length L of the heat transfer tube, the outer diameter D of the heat transfer tube, and the center-to-center distance S of the heat transfer tube is set to the above relational expression, whereby the influence of the pressure loss of the refrigerant in the heat transfer tube can be suppressed to a minimum. limit.

In the heat exchanger of any one of the first invention, the second invention, the third invention, and the fourth invention, the relationship between the refrigerant path length L, the outer diameter D of the heat transfer tube, and the center-to-center distance S of the heat transfer tube By using the above relational expression, the influence of the pressure loss of the refrigerant in the heat transfer tube can be suppressed to the minimum.

Description of drawings

Fig. 1 is the refrigerant circuit of the air conditioner;

2 is a front view of a heat exchanger according to an embodiment of the present invention;

Fig. 3 is a sectional view of the heat exchanger when cut along the A-A line of Fig. 2;

Fig. 4 is a curve showing the relationship between S/D and heat exchanger performance when the blower power is constant and D=7mm;

Fig. 5(a) is a conceptual diagram of the heat exchanger when the refrigerant path of the heat exchanger in Fig. 2 is made into one, and (b) is a conceptual diagram when the refrigerant path of the heat exchanger in Fig. 2 is made into two A conceptual diagram of the heat exchanger, (c) is a conceptual diagram of the heat exchanger when the refrigerant path of the heat exchanger in Fig. 2 is formed into two halfway;

Fig. 6 is a graph showing the relationship between refrigerant path length and pressure loss;

Fig. 7 is a graph showing the relationship between the refrigerant path length and the refrigerant side heat transfer rate and pressure loss when D = 7mm;

Fig. 8 is a graph showing refrigerant path length and heat exchanger performance when D = 7mm;

Fig. 9 is a graph showing the refrigerant path length L versus the outer diameter D of the heat transfer tube;

Fig. 10 is a composition table of refrigerants used in the refrigerant circuit including the heat exchanger according to the present embodiment.

Symbol Description

4 outdoor heat exchangers

6 indoor heat exchanger

10 heat exchangers

11 plate heat sink

12 heat transfer tubes

Detailed ways

<refrigerant circuit>

Figure 1 is a refrigerant circuit of an air conditioner. The air conditioner 1 has a refrigeration circuit in which a compressor 2 , a four-way switching valve 3 , an outdoor heat exchanger 4 , an expansion valve 5 , and an indoor heat exchanger 6 are connected through refrigerant piping. In FIG. 1 , solid and dotted arrows indicate the flow direction of the refrigerant, and the air conditioner 1 can switch between the heating operation and the cooling operation by switching the flow direction of the refrigerant through the four-way switching valve 3 . During cooling operation, the outdoor heat exchanger 4 becomes a condenser, and the indoor heat exchanger 6 becomes an evaporator. In addition, during heating operation, the outdoor heat exchanger 4 serves as an evaporator, and the indoor heat exchanger 6 serves as a condenser.

In the refrigerant circuit, a mixed refrigerant composed of two organic compounds, HFO-1234yf (2,3,3,3-tetrafluoro-1-propene) and HFC-32 (difluoromethane), is filled. The refrigerant used in this embodiment is a mixed refrigerant composed of 78.2% by mass of HFO-1234yf and 21.8% by mass of HFC-32. In addition, the chemical formula of HFO-1234yf is represented by CF ₃ CFCH ₂ , and the chemical formula of HFC-32 is represented by CH ₂ F ₂ .

<Structure of heat exchanger>

Fig. 2 is a front view of the heat exchanger according to the embodiment of the present invention. In FIG. 2 , the heat exchanger 10 is a cross-fin heat exchanger, and is a basic model of the outdoor heat exchanger 4 and the indoor heat exchanger 6 shown in FIG. 1 . The heat exchanger 10 includes fins 11 and heat transfer tubes 12 . The heat sink 11 is a flat plate made of thin aluminum, and a plurality of through holes are formed in one heat sink 11 . The heat transfer tube 12 is composed of a straight tube 12a inserted into the through hole of the fin 11, a first U-shaped tube 12b and a second U-shaped tube 12c connecting the ends of adjacent straight tubes 12a. The straight pipe 12a and the first U-shaped pipe 12b are integrally formed, and the second U-shaped pipe 12c is connected to the end of the straight pipe 12a by welding or the like after the straight pipe 12a is inserted into the through hole of the heat sink 11 .

(The relationship between the outer diameter of the tube and the distance between the centers of the heat transfer tube and the performance of the heat exchanger)

Fig. 3 is a sectional view of the heat exchanger taken along line A-A of Fig. 2 . In FIG. 3 , the outer diameter of the straight tube 12 a is D, and the distance between the centers of the adjacent heat transfer tubes 12 in the vertical direction is S. Generally, the smaller the center-to-center distance S, the higher the efficiency of the heat sink, but the higher the ventilation resistance. Conversely, the larger the distance S between the centers, the lower the efficiency of the heat sink, but the ventilation resistance is also reduced. In addition, the so-called heat sink efficiency refers to the ratio of the actual heat dissipation emitted from the entire heat transfer surface of the heat sink to the heat dissipation amount emitted when the temperature of the entire heat transfer surface of the heat sink is assumed to be equal to that of the refrigerant.

In addition, when the distance S between centers is constant, the larger the outer diameter D of the tube, the higher the efficiency of the heat sink and the higher the ventilation resistance. Conversely, the smaller the outer diameter D of the tube, the lower the efficiency of the heat sink and the lower the ventilation resistance. That is, there is an optimum condition for improving the performance of the heat exchanger between the tube outer diameter D and the distance S between centers.

Fig. 4 is a graph showing the relationship between S/D and heat exchanger performance when the blower power is constant and D = 7mm. In FIG. 4 , the heat exchanger performance shows a high value in the range of 2.5<S/D<3.5, and outside this range, the heat exchanger performance deteriorates. That is, FIG. 4 shows that when the relationship between the outer diameter D and the center-to-center distance S is 2.5<S/D<3.5, the outdoor heat exchanger 4 and the indoor heat exchanger 4 of the refrigerant circuit using a mixed refrigerant of HFO-1234yf and HFC-32 are shown. Exchanger 6 yields the best heat exchanger performance.

(The relationship between the refrigerant path length of the heat exchanger and the performance of the heat exchanger)

Fig. 5(a) is a conceptual diagram of the heat exchanger when the refrigerant path of the heat exchanger in Fig. 2 is made into one, and (b) is a conceptual diagram when the refrigerant path of the heat exchanger in Fig. 2 is made into two A conceptual diagram of the heat exchanger, (c) is a conceptual diagram of the heat exchanger when the refrigerant path of the heat exchanger in FIG. 2 is divided into two halfway.

In FIG. 5( a ), since the heat exchanger 10 has one refrigerant path, it is called a one-path heat exchanger 101 . Assuming that the heat exchanger 10 has six heat transfer tubes, and the length of one heat transfer tube 12 is H, the refrigerant path length of the one-path heat exchanger 101 is about 6H.

In FIG. 5( b ), the heat exchanger 10 forms two refrigerant paths through the flow divider 90 , so it is called a two-path heat exchanger 102 . The refrigerant path length of the two-path heat exchanger 102 is about half of that of the one-path heat exchanger 101 , which is approximately equivalent to 3H.

In FIG. 5( c ), one refrigerant path of the heat exchanger 10 is divided into two refrigerant paths through a flow divider 90 in the middle, so it is called a one-two path heat exchanger 103 . Since the one-two path heat exchanger 103 has a common refrigerant path and an independent refrigerant path, the length of the refrigerant path cannot be simply calculated. Therefore, the actual pressure loss of the one-two path heat exchanger 103 is calculated, assuming one refrigerant path, then the pressure loss corresponding to the length of the refrigerant path is calculated, and the value is the length of the refrigerant path.

Fig. 6 is a graph showing the relationship between refrigerant path length and pressure loss. For example, when the pressure loss of the refrigerant in the one-two path heat exchanger 103 in FIG. 5( c ) is p, it can be seen from the curve that the length of the refrigerant path is 3.6H. In this way, the one-path heat exchanger 101 , the two-path heat exchanger 10 , and the one-two-path heat exchanger 103 having different refrigerant path lengths can be manufactured from one basic heat exchanger 10 . In other words, the refrigerant path length can be set by changing the number of refrigerant paths.

Next, the relationship between the refrigerant path length and the performance of the heat exchanger will be described. That is, the heat exchanger performance Q is expressed by the formula Q=KA×dT using the heat return rate K, the heat transfer area A, and the temperature difference dT between the air and the refrigerant. The heat return rate K is the reciprocal of the combined resistance of the air-side thermal resistance and the refrigerant-side thermal resistance. The combined resistance 1/K is represented by the formula 1/K=1/ha+R/hr using the air side heat transfer rate ha, the refrigerant side heat transfer rate hr, and the internal and external heat transfer area ratio R.

When the number of refrigerant paths is reduced and the length of the refrigerant path is increased, the amount of refrigerant flowing through one refrigerant path increases, and the heat transfer rate hr on the refrigerant side increases, but due to the increase in pressure loss, the evaporation temperature at the inlet of the heat exchanger increases , so the temperature difference dT between the air and the refrigerant decreases, and the performance Q of the heat exchanger decreases.

On the other hand, when the number of refrigerant paths is increased and the length of the refrigerant path is shortened, the pressure loss decreases, the evaporation temperature at the inlet of the heat exchanger decreases, and the temperature difference dT between the air and the refrigerant increases, flowing through one refrigerant path The amount of refrigerant is reduced, so the heat transfer rate hr on the refrigerant side decreases, and the performance Q of the heat exchanger decreases.

That is, the outdoor heat exchanger 4 and the indoor heat exchanger 6 of the refrigerant circuit using the mixed refrigerant of HFO-1234yf and HFC-32 cannot use the outdoor heat exchanger and the outdoor heat exchanger corresponding to the current refrigerant (for example, 410A refrigerant). The indoor heat exchanger is replaced, and in order to achieve the best performance of the heat exchanger, it must be designed on the basis of clarifying the relationship between the outer diameter D of the heat transfer tube and the length L of the refrigerant path.

Fig. 7 is a graph showing the relationship between the refrigerant path length and the refrigerant-side heat transfer rate and pressure loss when D = 7 mm, and Fig. 8 is a graph showing the refrigerant path length and heat exchanger performance when D = 7 mm . As shown in Figure 7, the shorter the refrigerant path length, the smaller the pressure loss, but the refrigerant side heat transfer rate also decreases. As a result, as shown in FIG. 8 , due to a decrease in the heat transfer rate on the refrigerant side, the performance of the heat exchanger also decreases. On the other hand, when the refrigerant path length is gradually increased, the performance of the heat exchanger reaches a peak and then drops. That is, FIG. 8 shows that there is a refrigerant path length suitable for the outer diameter of the heat transfer tube.

FIG. 9 is a graph showing the refrigerant path length L versus the outer diameter D of the heat transfer tube. In Fig. 9, the square black dot represents the optimal refrigerant path length relative to the outer diameter of the heat transfer tube, and the lower limit value of the refrigerant path length relative to the outer diameter of the heat transfer tube is located on the straight line y=0.28x ^1.17 , The upper limit lies on the straight line y= ^1.10x1.17 . That is, the refrigerant path length L of the outdoor heat exchanger 4 and the indoor heat exchanger 6 representing the refrigerant circuit using the mixed refrigerant of HFO-1234yf and HFC-32 is set at 0.28×D ^1.17 <L<1.10×D The range of ^1.17 , thus can get the best heat exchanger performance.

<Refrigerant used in the refrigerant circuit>

(single refrigerant)

In the above-mentioned embodiments, the mixed refrigerant composed of two organic compounds, HFO-1234yf and HFC-32, is used as the refrigerant, but the present invention is not limited thereto. For example, Fig. 10 is a composition table of refrigerant used in the refrigerant circuit including the heat exchanger of this embodiment, and it is also possible to use C ₃ H _m F _n for the molecular formula such as HFO-1234yf (where m=1 to 5. n=1-5, and m+n=6) represents a single refrigerant formed by an organic compound having a double bond in its molecular structure.

Specifically, HFO-1225ye (1,2,3,3,3-pentafluoropropene, chemical formula: CF ₃ -CF=CHF), HFO-1234ze (1,3, 3,3 tetrafluoro-1-propene, chemical formula: CF ₃ -CH=CHF), HFO-1234ye (1,2,3,3 tetrafluoro-1-propene, chemical formula: CHF ₂ -CF=CHF), HFO- 1234zf (3,3,3 trifluoro-1-propene, chemical formula: CF ₃ -CH=CH ₂ ), 1,2,2 trifluoro-1-propene (chemical formula: CH ₃ -CF=CF ₂ ), 2- Tetrafluoro-1-propene (chemical formula: CH ₃ -CF=CH ₂ ), etc. In addition, these single refrigerants are classified as basic refrigerants for convenience of description.

(mixed refrigerant)

In addition, a mixed refrigerant composed of any of the above-mentioned basic refrigerants and any of the second components shown in FIG. 10 may also be used. For example, it is a mixed refrigerant with 22% by mass of HFC-32. In addition, the ratio of HFC-32 should just be 6 mass % - 30 mass %, Preferably it is 13 mass % - 23 mass %, More preferably, it is 21 mass % - 23 mass %.

In addition, it may be a mixed refrigerant of any one of the above-mentioned basic refrigerants and HFC-125 (pentafluoroethane, CF ₃ -CHF ₂ ) at 10% by mass or more, and the ratio of HFC-125 is preferably 10% by mass % to 20% by mass.

In addition, any of the above-mentioned basic refrigerants and HFC-134 (1,1,2,2-tetrafluoroethane, CHF ₂ -CHF ₂ ), HFC-134a (1,1,2,2- Tetrafluoroethane, CH ₂ F-CF ₃ ), HFC-143a (1,1,1-trifluoroethane, CH ₃ CF ₃ ), HFC-152a (1,1-difluoroethane, CHF ₂ - CF ₃ ), HFC-161 (fluoroethane, CH ₃ -CH ₂ F), HFC-227ea (1,1,1,2,3,3,3-heptafluoropropane, CF ₃ -CHF-CF ₃ ), HFC-236ea (1,1,1,2,3,3-hexafluoropropane, CF ₃ -CHF-CHF ₂ ), HFC-236fa (1,1,1,3,3,3-hexafluoroethane, Any mixed refrigerant of CF ₃ -CH ₂ -CF ₃ ) and HFC-365mfc (1,1,1,3,3-pentafluorobutane, CF ₃ -CH ₂ CF ₂ -CH ₃ ).

In addition, the above-mentioned mixed refrigerant is a mixed refrigerant of any one of the above-mentioned basic refrigerants and an HFC-based refrigerant, but is not limited thereto, and may be a mixture of any of the above-mentioned basic refrigerants and a hydrocarbon-based refrigerant. Mixed refrigerant.

Specifically, any of the above-mentioned basic refrigerants and methane (CH ₄ ), ethane (CH ₃ -CH ₃ ), propane (CH ₃ -CH ₂ -CH ₃ ), propylene (CH ₃ -CH=CH ₃ ), butane (CH ₃ -CH ₂ -CH ₂ -CH ₃ ), isobutane (CH ₃ -CH(CH ₃ )-CH ₃ ), pentane (CH ₃ -CH ₂ -CH ₂ -CH ₃ ), 2-methylbutane, and a mixed refrigerant of any one of cyclopentane (cyclo-C5H ₁₀ ).

In addition, any of the above-mentioned basic refrigerants and dimethyl ether (CH ₃ -O-CH ₃ ), bis(trifluoromethyl)sulfide (CH ₃ -S-CH ₃ ), carbon dioxide (CO ₂ ) and any mixture of helium (He).

In addition, in the above-mentioned embodiment, a mixed refrigerant composed of two kinds of refrigerants HFO-1234yf and HFC-32 is used as the refrigerant, but any one of the above-mentioned basic refrigerants and any two of the above-mentioned second components may be used. A mixed refrigerant formed. For example, a mixed refrigerant composed of 52% by mass of HFO-1234yf, 23% by mass of HFC-32, and 25% by mass of HFC-125 is preferable.

<feature>

The heat exchanger 10 is used as an organic compound represented by the molecular formula C ₃ H _m F _n (where m=1 to 5, n=1 to 5, and m+n=6) and has one double bond in the molecular structure. A heat exchanger for a refrigerant circuit of a single refrigerant formed by a compound or a mixed refrigerant containing the above-mentioned single refrigerant. The heat exchanger 10 includes a plurality of heat transfer tubes 12 and a plurality of plate-shaped fins 11 . The heat transfer tubes 12 form one or more refrigerant paths for circulating the refrigerant. The plate-shaped cooling fins 11 are arranged substantially parallel to the air flow direction, and a plurality of heat transfer tubes pass therethrough substantially vertically. The relationship between the distance S between the centers of adjacent heat transfer tubes in the vertical direction and the outer diameter D of the heat transfer tube is 2.5<S/D<3.5, and the relationship between the length L of the refrigerant circuit and the outer diameter D of the heat transfer tube 0.28×D ^1.17 <L<1.10×D ^1.17 . As a result, the influence of the pressure loss of the refrigerant in the heat transfer tube can be suppressed to the minimum. In addition, the specific refrigerant used is a single refrigerant formed from 2,3,3,3-tetrafluoro-1-propene or a mixed refrigerant containing the above-mentioned single refrigerant, or a refrigerant containing 2,3,3,3 - Mixed refrigerants of tetrafluoro-1-propene and difluoromethane, or mixed refrigerants containing 2,3,3,3-tetrafluoro-1-propene and pentafluoroethane.

Industrial Utilization Possibility

As described above, the present invention is applied to a heat exchanger of a refrigerant circuit using a low-pressure refrigerant.

Claims (4)

1. A heat exchanger (4, 6, 10), whose refrigerant circuit uses C ₃ H _m F _n (wherein, m=1～5, n=1～5, and m+n=6 ) represents a single refrigerant formed by an organic compound having a double bond in its molecular structure or a mixed refrigerant containing the single refrigerant, characterized in that: having, a plurality of heat transfer tubes (12) forming one or more refrigerant paths for communicating said refrigerant; and A plurality of plate-shaped fins (11) are arranged to overlap at predetermined intervals, and the plurality of heat transfer tubes (12) penetrate substantially vertically therethrough, The relationship between the distance S between the centers of adjacent heat transfer tubes (12) in the vertical direction and the outer diameter D of the heat transfer tubes (12) is: 2.5＜S/D＜3.5 The relationship between the length L of the refrigerant path and the outer diameter D of the heat transfer tube (12) is: 0.28×D ^1.17 <L<1.10×D ^1.17 . 2. The heat exchanger (4, 6, 10) according to claim 1, wherein the refrigerant is a single refrigerant formed from 2,3,3,3-tetrafluoro-1-propene or contains the Mixed refrigerants of the above single refrigerants. 3. The heat exchanger (4, 6, 10) as claimed in claim 1, wherein the refrigerant is a mixed refrigerant containing 2,3,3,3-tetrafluoro-1-propene and difluoromethane . 4. The heat exchanger (4, 6, 10) as claimed in claim 1, wherein the refrigerant is a mixed refrigerant containing 2,3,3,3-tetrafluoro-1-propene and pentafluoroethane agent.

Images