JPS6230691Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a two-stage compression screw refrigerator, and more specifically, to a screw refrigerator equipped with a lower stage compressor and a higher stage compressor.

Generally, the refrigerating capacity of a refrigerator used at low temperatures has an important relationship with the specific volume of the gas refrigerant sucked into the compressor, and as this specific volume increases, the amount of refrigerant sucked into the compressor decreases, and The enthalpy difference between the refrigerants in the evaporator decreases, leading to a decrease in capacity.

For example, if we use Freon 22 as a refrigerant and specifically explain the refrigerating capacity when performing evaporation at -40°C at a condensation temperature of 40°C and when performing evaporation at 0°C, the Mollier curve shown in Figure 3 As shown in the figure, the 0 of the gas refrigerant located on the saturated vapor line
The specific volume at ℃ is 0.047m ³ /Kg, and its enthalpy is 149.05kcal/Kg, while -40
The specific volume in °C is 0.206m ³ //Kg and the enthalpy is
It is 145.05kcal/Kg, and the enthalpy of liquid refrigerant is 111.87kcal/Kg.

However, if the suction flow rate of the compressor is m ³ /h,
The refrigerating capacity Q is the enthalpy difference between the gas and liquid regions of the refrigerant x flow rate x 1/specific volume. Therefore, the refrigerating capacity when evaporating at 0°C Q ₁ = (149.05-111.87) x v/0.047 = 791.1v kcal/h Refrigeration capacity at -40° evaporation Q ₂ = (145.05-111.87) x v/0.206 = 161.1 vkcal/h, and the refrigeration capacity at -40°C evaporation decreases to about 20% compared to 0°C evaporation. be.

Conventionally, in the case of refrigerators used at temperatures as low as -30°C, two-stage compression is performed using a low-stage compressor and a high-stage compressor, and a portion of the liquid refrigerant flowing out from the condenser is removed. By supercooling the refrigerant and supplying it to the evaporator, the difference in utilization enthalpy of the refrigerant circulating through the refrigerator is increased, thereby increasing the refrigerating capacity.

That is, in the refrigeration cycle as shown in FIG. 4, the low-stage compressor _c1 and the high-stage compressor _c2 are connected in series, and an intermediate pipe is connected to the high-pressure liquid pipe on the refrigerant outlet side of the condenser b. A cooler d is provided, and the cooling part e of the cooler d is communicated with the refrigerant suction side of the high-stage compressor _c2 , while the liquid refrigerant flowing out from the condenser b is supercooled by the cooler d. The refrigerant is supplied to the evaporator a to lower the refrigerant temperature in the high-pressure liquid pipe of the refrigeration cycle, thereby increasing the enthalpy difference between the circulating refrigerants in the cycle.

In FIG. 4, f is the first expansion valve provided in the middle of the pipe connecting the intercooler d and the evaporator a, and g is the cooling section between the outlet pipe of the condenser b and the intercooler d. This is the second expansion valve provided in the middle of the branch pipe connecting to e.

Therefore, in the refrigeration cycle, the refrigerant outflow point from the high-stage compressor _c2 is A, the refrigerant outflow point from the condenser b is B, and the outflow point from the intercooler d is c,
The outflow point from the first expansion valve f is connected to D, the outflow point from the evaporator a is connected to E, and the cooling part e of the cooler d is communicated between the low and high stage compressors c ₁ and c ₂ . Point F
Then, the Mollier diagram of the refrigeration cycle is
The result is as shown in FIG.

As is clear from this Mollier diagram, if the intercooler d is not provided, the difference in available enthalpy △i ₁
= iE−iB, whereas when the cooler d is provided, the difference in utilization enthalpy is △i ₂ = iE−iC, and compared to the case where the cooler d is not provided, △i ₂
−Δi ₁ = iB−iC, that is, the utilization enthalpy difference increases by this iB−iC, and the refrigeration capacity can be increased.

However, the temperature is even lower than in the above case, for example -60
In the case of refrigerators used at temperatures around ℃, even if the intercooler d is installed, the refrigerating capacity will significantly decrease due to the increase in the specific volume of the refrigerant and the decrease in the difference in available enthalpy, as described above. .

For the above reasons, in the case of refrigerators that operate at extremely low temperatures, multi-stage compression refrigeration systems with multiple compressors or binary refrigeration systems are used, but these systems have extremely complex structures. However, there were problems in that not only maintenance was difficult, but also the external dimensions and weight increased, and the price was high.

This invention was devised in view of the various problems mentioned above, and it increases the difference in enthalpy of refrigerant utilization in the refrigeration cycle by using two stages of compressors. It is an object of the present invention to provide a two-stage compression type screw-refrigerator capable of freezing with a high refrigerating capacity similar to the multi-stage compression type.

That is, in the present invention, a first intercooler is provided in the high-pressure liquid pipe, and the cooling section of the cooler is connected to the upstream side of the cooler in the high-pressure liquid pipe and the suction side of the high-stage compressor. A second intercooler is provided downstream of the cooler in the high-pressure liquid pipe, and a cooling part of the second intercooler is connected to the high-pressure liquid pipe upstream of the first intercooler. It is characterized in that it is connected between the side and an intermediate pressure port provided in the middle of the compression process of the low-stage compressor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The two-stage compression type screw refrigerator of the present invention will be explained below with reference to the drawings.

FIG. 1 shows the refrigeration cycle of the refrigerator, in which 1 is a screw-type low-stage compressor, 2 is a screw-type high-stage compressor connected to the refrigerant discharge side, and 2 is a screw-type high-stage compressor connected to the refrigerant discharge side. An oil separator 4 and a condenser 5 are connected to the refrigerant discharge side of the side compressor 2 via a high-pressure gas pipe 31, and the outlet side of the condenser 5 is connected to a high-pressure liquid pipe 32, an expansion valve 18, and a low-pressure liquid pipe. 3
3 through which an evaporator 6 is connected, and said evaporator 6
and the low-stage compressor 1 are connected by a low-pressure gas pipe 34.

The oil separator 4 is equipped with a cooler 4a for cooling with water or liquid refrigerant, which is connected by a pair of communication pipes 4b, 4b, and is separated from the discharged refrigerant, and the cooled oil is supplied to the oil supply pipe 4c. supply to the department.

Therefore, a first intercooler 8 having a coil-shaped cooling section 8a is interposed in the high-pressure liquid pipe 32, and one end of this cooling section 8a is placed on the outlet side of the condenser 5 in the high-pressure liquid pipe 32. Cooling is achieved by connecting via a first branch pipe 10 having a first expansion valve 9 in the middle, and by connecting the other end of the cooling section 8a to an intermediate point between the two compressors 1 and 2 via a pipe 11. The cooling section 8a of the cooler 8 is connected between the upstream side of the cooler 8 in the high-pressure liquid pipe 3 and the suction side of the high-stage compressor 2.

A temperature sensing cylinder 12 is provided in the middle of the pipe 11, the temperature of the refrigerant in the pipe 11 is detected by the temperature sensing cylinder 12, and the degree of superheating of the refrigerant is adjusted by adjusting the opening degree of the first expansion valve 10. .

Further, on the downstream side of the first cooler 8 in the high pressure liquid pipe 32 and upstream of the expansion valve 18,
A second intercooler 13 having a cooling section 13a is interposed, one end of which is connected to the high pressure liquid pipe 32 on the outlet side of the condenser 5, and a second branch pipe having a second expansion valve 14 in the middle. 15, and the other end of the cooling part 13a is connected to the intermediate pressure port 1a formed in the middle of the refrigerant compression process of the low-stage compressor 1 through the pipe 16.
The cooling part 13a of the second intercooler 13 is connected between the upstream side of the first intercooler 8 in the high pressure liquid pipe 32 and the intermediate pressure port 1a provided in the middle of the compression process of the low stage compressor 1. are doing.

A temperature sensing cylinder 17 is provided in the middle of the pipe 16, similar to the first cooler 8, and the temperature sensing cylinder 17 detects the temperature of the refrigerant in the pipe 16.
The degree of superheating of the refrigerant is adjusted by adjusting the opening degree in step 4.

In the figure, reference numeral 19 denotes a temperature-sensitive tube of the expansion valve 18, which is provided in the low-pressure gas pipe 34, and is used to adjust the degree of superheat of the refrigerant.

The screw refrigerator of the present invention has the above configuration, and the refrigerant compressed by the low-stage compressor 1 is further compressed to a high pressure by the high-stage compressor 2, and the refrigerant is compressed to an oil separator 4, a condenser 5, The refrigerant passes through the first and second coolers 8 and 13 and reaches the evaporator 6, where the refrigerant evaporates and cools the inside of the freezer.The refrigerant is then returned to the low stage compressor 1, and the above cycle is repeated. Freezing is carried out inside.

The high pressure liquid pipe 32 that has passed through the condenser 5
A part of the refrigerant inside reaches the cooling section 8a of the first cooler 8 through the first branch pipe 10, where it evaporates and supercools the refrigerant flowing through the high-pressure liquid pipe 32. The gas refrigerant evaporated in the cooling section 8a is supplied from the pipe 11 to the middle of the low and high stage compressors 1 and 2, and is sucked into the high stage compressor 2 together with the refrigerant discharged from the low stage compressor 1. It is.

In addition, a part of the refrigerant in the high-pressure liquid pipe 32 that has passed through the condenser 5 reaches the cooling part 13a of the second cooler 13 from the second branch pipe 15, evaporates there, and leaves the first cooler 13. The refrigerant passing through the high-pressure liquid pipe 32 is further supercooled. Moreover, the cooling section 13a
The evaporated gas refrigerant is supplied to the intermediate pressure port 1a of the low-stage compressor 1 through the pipe 16, and cools the refrigerant in the middle of the compression process by the compressor 1.

The liquid refrigerant that has passed through the condenser 5 as described above is
After being supercooled in the cooler 8, it is supercooled again in the second cooler 13, and the degree of supercooling can be increased and the enthalpy difference can be increased. That is, the refrigerant discharge point of the high-stage compressor 2 is set to A,
The refrigerant outflow point of the condenser 5 is B, the outflow point of the first cooler 8 is C, the outflow point of the second cooler 13 is D, and the evaporator 6
E is the inflow point of the lower stage compressor 1, F is the suction point of the lower stage compressor 1, G is the point where the cooling part 8a of the first cooler 8 is communicated between the lower and higher stage compressors 1 and 2, and the first The inflow point to the cooling part 8a of the cooler 8 is H, the outflow point is I, the inflow point to the cooling part 13a of the second cooler 13 is J, the outflow point is K, and the suction in the low stage compressor 1 If the point at the intermediate pressure port 1a immediately before (before merging) is L, the point at the intermediate pressure port 1a immediately after suction (after merging) is M, and the discharge point is N, the Mollier diagram of the refrigeration cycle is as follows: The result is as shown in Figure 2.

As is clear from this Mollier diagram, when only the first intercooler 8 is provided, as explained in the conventional example above, the difference in available enthalpy △i ₂ =
In contrast to iE−iC, when the first and second coolers 8 and 13 are provided, the difference in enthalpy used is △i ₂
= iE - iD, therefore, compared to the case where only the first cooler 8 is provided, the difference in available enthalpy is larger by △i ₃ - △i ₂ = iC - iD, and the refrigerating capacity is significantly increased. It is.

As explained above, in the present invention, the first cooler 8
Separately, a second intercooler 13 is further used to transfer the refrigerant supercooled by the first cooler 8 to the second intercooler 13.
The cooling section 8a of the first cooler 8 is placed on the suction side of the high-stage compressor 2, and the cooling section 13a of the second cooler 13 is placed on the suction side of the high-stage compressor 2.
are communicated with the intermediate pressure ports formed in the low-stage compressor 1, so the difference in enthalpy of refrigerant utilization in the refrigeration cycle is reduced to 1 as in the conventional case.
This makes it possible to increase the number of intercoolers compared to one that uses two intercoolers, thereby significantly increasing the refrigerating capacity of the refrigerator and improving the build-up coefficient of the refrigerator.

Moreover, in this invention, by using two intercoolers, a two-stage compression type refrigerator can obtain a high refrigeration capacity equivalent to that of a multi-stage compression type refrigerator. Therefore, compared to conventional multi-stage compression type refrigerators, maintenance is very easy, and the refrigerator can be made small and lightweight, and can also be provided at a low price.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a refrigeration cycle of a refrigerator according to the present invention, Fig. 2 is a Mollier diagram of the same cycle,
FIG. 3 is a Mollier diagram explaining a conventional example, FIG. 4 is a refrigeration cycle diagram showing a conventional refrigerator, and FIG. 5 is a Mollier diagram thereof. 1...Low stage side compressor, 1a...Intermediate pressure port,
2...High stage side compressor, 8...First intercooler, 8
a...Cooling section, 13...Second intercooler, 13a
...Cooling section, 32...High pressure liquid pipe.

Claims (1)

[Scope of utility model registration request] 2 comprising a low-stage compressor 1 and a high-stage compressor 2
In a stage compression screw refrigerator, high pressure liquid pipe 3
2, a first intercooler 8 is provided, and the cooling section 8a of the cooler 8 is connected between the upstream side of the cooler 8 in the high-pressure liquid pipe 32 and the suction side of the high-stage compressor 2. A second intercooler 13 is connected to the high-pressure liquid pipe 32 downstream of the cooler 8.
A cooling section 13a of this second intercooler 13 is provided.
is connected between the upstream side of the first intercooler 8 in the high-pressure liquid pipe 32 and the intermediate pressure port 1a provided in the middle of the compression process of the low-stage compressor 1. Stage compression screw refrigerator.