JPS5888484A - Method of improving adiabatic efficiency in engine drive system screw refrigerator - Google Patents

Abstract

PURPOSE:To provide readily the best adiabatic efficiency by permitting a through hole provided in a slide valve to communicate to the outside of a casing for controlling the position of the slide valve so as to provide the optimum value of differential pressure before and after discharge. CONSTITUTION:A slide valve 10 is provided with a through hole 11 while this through hole 11 communicates to the outside of a casing 1 so that pressure just before discharge from a compression chamber is taken out while pressure right after discharge from a discharge port is taken out. Pressure before and after discharge is compared and the position of the slide valve 10 is controlled to provide the optimum value of the differential pressure. Thus, the adiabatic efficiency of a screw refrigerator can be improved. Further, since the differential pressure before and after the discharge is lessened, pulsation of discharge pressure causing mainly noise and vibration is reduced to reduce the noise and vibration and simplify equipment for preventing vibration and sound.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for improving adiabatic efficiency in an engine-driven screw refrigerator equipped with a slide valve.

Conventionally, a device similar to a screw refrigerator equipped with a slide valve is known, for example, in Japanese Patent Publication No. 37-321. The device in this publication is provided with at least one axially movable slide valve that is disposed within the wall of the jacket of the working chamber and is sealed to at least one screw rotor (hereinafter referred to as rotor). Gas is sucked in from one side in the axial direction of a pair of male and female rotors that rotate while meshing with each other, and adiabatic compression (or expansion, In the following, only compression will be considered.Compressed gas is discharged from the other side in the axial direction, and the length of the compression stroke is made variable by moving the slide valve in the axial direction.

In this device, as described below, when the pressure difference between the gas discharged from the rotor and the gas immediately before discharge is within a predetermined value, the efficiency of the shaft power of the rotor (hereinafter referred to as adiabatic efficiency) is Maximum.

That is, the horizontal axis represents the gas pressure P inside the casing when the adiabatic compression start position (the engagement point is at a distance S from the confinement axis), and further, let sl be the position of the discharge point, and Pd be the discharge pressure. For example, the gas pressure P in the casing increases continuously as shown in FIG. 1, and reaches the discharge pressure Pd at the discharge point S1.
For example, as shown in Fig. 2, if the discharge pressure rises above Pd immediately before the discharge point S1, extra work will be done in the area exceeding the discharge pressure Pd (the shaded area in Fig. 2). It has been done.

However, in the above device, although it is possible to change the internal compression ratio Vi (hereinafter referred to as compression ratio Vi) by adjusting the position of the slide valve, it is difficult to know whether the compression ratio Vi is actually adjusted to the optimum compression ratio. is unknown, and at the same time,
There was a problem in that the amount of suction gas also decreased.

The present invention has been made in view of the above-mentioned conventional problems, and the present invention has been made in view of the above-mentioned conventional problems.
By providing a through hole in the casing (in which the amount of suction gas does not decrease) and by communicating this through hole to the outside of the casing, the pressure immediately before discharge from the compression chamber is derived, while the pressure immediately after discharge is derived from the discharge port, and the pressure before and after discharge is derived from the discharge port. Provides a method for improving adiabatic efficiency in an engine-driven screw refrigerator that makes it possible to easily obtain the best adiabatic efficiency by comparing and controlling the position of the slide valve so that the differential pressure becomes the optimal value. This is what I am trying to do.

Next, the present invention will be explained with reference to the drawings, which are one embodiment.

3 to 5 show a screw refrigerator to which the method according to the present invention is applied. In the figure, 1 is a casing of the main body of the screw refrigerator, and the main casing 1 has parts that are mutually compatible in the axial direction. Two rotating cylindrical spaces are formed, and a pair of male and female rotors 2 and 3 that mesh with each other are rotatably supported within these spaces.

Further, a suction casing 5 having a suction port 4 that opens into the tooth groove of the rotor 2゜3 is attached to one side of the main casing 1, while the other side is attached to the main casing 1.
, 3 is attached to the main body casing 1.

Further, a cylindrical space 8 is formed in the main body casing 1 so as to partially overlap with the two cylindrical spaces described above, and the compression space of the rotors 2 and 3 is sealed in this space and the compression space is A slide valve 1 having a substantially circular cross section is slidable by a hydraulic cylinder 9 so as to change the position of the space.
0 is insertion. In this slide valve 10, a through hole 11 is formed which extends from the vicinity of the tip end on the discharge port side on the rotor 2, 3 side of the slide valve 10 to the surface on the main body casing 1 side. A pipe 12 is connected through the main body casing 1 so as to communicate with the main body casing 1 to derive the compressed gas pressure immediately before discharge, while a pipe 13 is similarly connected from the discharge port 6 side to connect the gas at the discharge port 6 side. It brings out pressure. Both pipes 12 and 13 are connected to the differential pressure switch 14.
At this point, the differential pressure between the above two pressures is determined, and the hydraulic cylinder 9 is controlled by the differential pressure switch or the control device 14 via a control device (not shown) so that the differential pressure becomes the optimum value. The position of the slide valve 10 is controlled by actuation.

Next, a method for improving heat insulation efficiency according to the present invention will be explained.

The compression ratio Vi of the screw refrigerator mentioned above is the slide valve 10
The compression ratio P2//P1 (here, PI
is the suction pressure, and P2 is the discharge pressure. ) is determined.

Then, if the horizontal axis is the compression ratio P2//P1 and the vertical axis is the adiabatic efficiency ηad, and the compression ratio Vi is taken as a parameter, then
If the calculated value of the adiabatic efficiency ηaa is as shown in Figure 6, then the adiabatic efficiency ηad is calculated when the difference between the compression ratio Vi and P2/P1 is small.
is the best. That is, for example, P2/P1=
Looking at case 3, Vi=4.3°3.5,2.
The adiabatic efficiency ηad increases in the order of 6 (points A, B, and C in FIG. 6). The broken line in FIG. 6 indicates the best value of the adiabatic efficiency ηad at each compression ratio P2/P1.

Therefore, the differential pressure is detected by the differential pressure switch 14 from the pressure of the compressed gas before and after discharge derived from the operating screw refrigerator, and further, in the control device, this differential pressure and the pressure shown in FIG. 6 are detected. The optimum differential pressure at the optimum compression ratio Vi is compared, and the hydraulic cylinder 9 is operated to control the position of the slide valve 10 so that the two differential pressures become equal.

Therefore, for example, when using the above-mentioned screw refrigerator in an air-conditioning system, the value of the compression ratio P2/P□ is different between cooling operation and heating operation, but the value of the compression ratio Vi is adjusted as appropriate according to the operating condition. It's convenient because I can do it. That is, during heating operation (P2/P1 - about 59), the compression ratio Vi=3.
A value of about 6 is good, and during cooling operation (P2/P1 = about 3.2 months, the compression ratio V i = about 2.6 (in this case, the screw refrigerator is in a partial load operation)).

Note that in the past, the compression ratio Vi remained unchanged even during partial load operation, so in the above example, cooling operation had to be performed in a state where Vi = 3.5.

As is clear from the above explanation, according to the present invention, the slide valve is provided with a through hole, and this through hole is communicated with the outside of the casing to derive the pressure immediately before discharge from the compression chamber, and the pressure immediately after discharge from the discharge port. The pressure before and after discharge is compared, and the position of the slide valve is controlled so that the differential pressure becomes the optimal value. Therefore, it is possible to improve the adiabatic efficiency of the screw refrigerator, and the compression ratio P, which is often required from the system side especially during cooling, can be improved.
The efficiency improvement effect is significant when 2/P1=3 or less.

θ) When using expensive gas fuel to drive a screw refrigerator, running costs can be significantly reduced.

Furthermore, since the pressure difference before and after the discharge is small, the pulsation of the discharge pressure, which is the main cause of noise and vibration, is reduced, and these can be reduced, and vibration-proofing and sound-proofing equipment can be simplified. become.

Generally, there is a correlation between the adiabatic efficiency and suction volume efficiency of screw refrigerators, and in addition to the improvement in adiabatic efficiency shown in Figure 6, a synergistic effect of improving suction volume efficiency is added, resulting in energy savings. It can make a big contribution.

In addition, the present invention can be applied to conventional slide-type screw refrigerators with only slight modification, and can be used with any refrigerant. It has various effects, such as being particularly effective when it is performed by changing the rotational speed of the rotor. In particular, regarding starting torque, which is the most problematic issue when driving an engine, if we use a slide valve structure with an integrated fixed valve, there will be no gas compression during unloading, and the rotor itself will only need GD2, so accessories such as clutches will be unnecessary. Therefore, the initial cost is also low.

[Brief explanation of drawings]

Figures 1 and 2 are curve diagrams of changes in gas pressure within the casing, Figure 3 is a cross-sectional view of a screw refrigerator to which the method according to the present invention is applied, and Figure 4 is line 1-I in Figure 3. 5 is a sectional view taken along the line n-II of FIG. 4, and FIG. 6 is a diagram of the adiabatic efficiency curve. Engineering...Casing, 2, 3...Rotor, 4...Suction port, 10...Slide valve, 11...Through hole. To Figure 3 V/PI

Claims (1)

[Claims] (1) In an engine-driven screw refrigerator equipped with a slide valve, a through hole is provided in the slide valve from near the tip on the discharge port side on the rotor side of the slide valve to the surface on the casing side. The pressure immediately before discharge from the compression chamber is derived by communicating with the outside of the casing, while the pressure immediately after discharge from the discharge port is derived, the pressure before and after discharge is compared, and the position of the slide valve is adjusted so that the differential pressure becomes the optimal value. A method for improving adiabatic efficiency in an engine-driven screw refrigerator, characterized by controlling.