A sealing performance test device and test method for a labyrinth compressor

Abstract

The present invention relates to the technical field of compressors, and specifically provides a labyrinth compressor sealing performance test device which can conveniently realize the tests of labyrinth throttling and gas leakage. The device includes a crankcase transmission case and a cylinder. A crankshaft is arranged in the crankshaft transmission case. The crankshaft is connected to one end of a piston rod through a connecting rod transmission mechanism. A piston located in a piston chamber within the cylinder is installed on the piston rod. The upper end of the piston chamber communicates with an intake passage and an exhaust passage. A stuffing box that cooperates with the piston rod is arranged in the cylinder. Packing is arranged in the stuffing box. The outer surface of the piston and the inner wall of the piston chamber are in a toothed shape and there is a gap between them. The lower end of the piston chamber communicates with a leakage gas measurement chamber. A flow sensor is installed in the measurement chamber. A pressure sensor is installed on the side wall of the piston. A pressure relief valve and a pressure gauge are also installed in the measurement chamber. At the same time, the present invention also provides a corresponding test method.

Description

Technical Field

[0001] The present invention relates to the technical field of compressors, and particularly to a labyrinth compressor sealing performance test device and a test method thereof. Background Art

[0002] A labyrinth compressor refers to a new type of compressor that adopts non-contact labyrinth sealing technology between the piston and the cylinder wall, and between the piston rod and the stuffing box. The sealing structure of the labyrinth piston compressor is non-contact, and both the piston and the stuffing box rely on the labyrinth for sealing. The working cycle is suction, compression, and exhaust. Since it is a labyrinth non-contact seal, in actual use, it is inevitable that a small amount of gas passes through the gap between the piston and the cylinder wall. It is necessary to test the labyrinth throttling and gas leakage during the reciprocating motion process to provide a design basis and data verification for improving the sealing performance of the labyrinth compressor, improving the compression efficiency, and reducing energy consumption. The existing test devices cannot conveniently conduct the test. Summary of the Invention

[0003] In order to solve the problem that the labyrinth piston sealing performance of the existing labyrinth compressor cannot be conveniently monitored at the piston, the present invention provides a labyrinth compressor sealing performance test device, which can conveniently realize the test of labyrinth throttling and gas leakage. At the same time, the present invention also provides a corresponding test method.

[0004] The technical solution is as follows: A labyrinth compressor sealing performance test device includes a crankcase transmission case and a cylinder. A crankshaft is arranged in the crankshaft transmission case. The crankshaft is connected to one end of a piston rod through a connecting rod transmission mechanism. A piston located in a piston cavity in the cylinder is installed on the piston rod. The upper end of the piston cavity communicates with an intake passage and an exhaust passage. A stuffing box matching with the piston rod is arranged in the cylinder. Packing is arranged in the stuffing box. The outer surface of the piston and the inner wall of the piston cavity are tooth-shaped and there is a gap between them. It is characterized in that the lower end of the piston cavity communicates with a leakage gas measurement cavity. A flow sensor is installed in the measurement cavity. A pressure sensor is installed on the side wall of the piston. A pressure relief valve and a pressure gauge are also installed in the measurement cavity.

[0005] It is further characterized in that the stuffing box includes an upper stuffing box and a lower stuffing box located at both ends of the piston. The packing is floatingly arranged in the stuffing box;

[0006] A stepped section is arranged on the piston rod. The lower end of the piston abuts against the step surface of the stepped section, and the upper end is fixed by a locking nut installed on the piston rod;

[0007] An outer shell is sleeved on the outer wall of the piston. The outer surface of the outer shell and the inner wall of the piston cavity are tooth-shaped with different sizes;

[0008] The piston includes a middle shaft sleeve, the end of the middle shaft sleeve is connected to the middle of the disc body, the end of the disc body is connected to the ring body, there is an empty area between the middle shaft sleeve and the ring body, and the middle shaft sleeve, the disc body and the ring body are of an integral structure;

[0009] The outer shell is fixed to the ring body by screws, and pressure sensor mounting holes are provided at the bottom of the labyrinth teeth on the side wall of the ring body and the side wall of the outer shell.

[0010] A method for testing the sealing performance of a labyrinth compressor is characterized in that the gap length b, the gap width c, and the cross-sectional area A of the annular labyrinth gap between the piston and the inner wall of the piston chamber are measured, the tooth pitch B on the piston is measured, and the pressure on the high-pressure side of the piston is measured P 0. At the N pressure at the tooth of the labyrinth P N , and the above measured values are sent to the data acquisition system, and the system calculates the above parameter values. The leakage amount of the labyrinth seal: , where , , K = b / c, R is the gas constant, T0 is the gas temperature on the high-pressure side of the piston, P 0 is the measured pressure on the high-pressure side of the piston, P N is the N pressure at the tooth of the labyrinth; , where is the inlet and outlet pressure ratio of the piston; n is the rotational speed of the compressor; S is the stroke of the compressor, , θ and γ are fitting parameters, h is the radial gap which is the same as the gap width c, D is the piston diameter, v u is the speed of sound of the gas before suction.

[0011] After adopting the present invention, when the labyrinth compressor is working, the gas on the compression side of the piston has a tendency to leak to the non-compression side. When a small amount of compressed gas leaks into the gap between the piston and the inner wall of the piston chamber, each labyrinth tooth cavity will form a throttling cavity, and the pressure of the gas gradually decays through multiple throttling cavities until it is equivalent to the pressure on the non-compression side. A pressure sensor is installed on the piston to detect the pressure value of the labyrinth throttling cavity and test the effect of the labyrinth throttling; there may still be a very small amount of gas that enters the measurement cavity after the gas is depressurized through the labyrinth throttling, and the gas leakage flow rate can be detected through the flow sensor, so as to know the leakage amount within a certain period of time, and the test of gas leakage is conveniently realized. Description of the Drawings

[0012] Figure 1 is a schematic structural diagram of the present invention;

[0013] Figure 2 is a schematic structural diagram of the piston;

[0014] Figure 3 It is an enlarged schematic diagram of the piston and the inner wall of the piston chamber. Specific embodiments

[0015] See Figure 1 , Figure 2 , Figure 3 As shown, a sealing performance test device for a labyrinth compressor includes a crankcase transmission case 1 and a cylinder 2. A crankshaft 3 is arranged in the crankshaft transmission case 1. The crankshaft 3 is connected to one end of a piston rod 5 through a connecting rod transmission mechanism 4. A piston 7 located in a piston chamber 6 inside the cylinder 2 is installed on the piston rod 5. One end of the piston chamber 6 is communicated with an intake passage 8 and an exhaust passage 9. A stuffing box cooperating with the piston rod 5 is arranged inside the cylinder 2. The stuffing box includes an upper stuffing box 10 and a lower stuffing box 11 located at both ends of the piston. A packing 12 is floatingly arranged inside the stuffing box. The other end of the piston chamber 6 is communicated with a measuring chamber 13. A flow sensor 14 and a pressure relief valve 15 are installed in the measuring chamber 13.

[0016] Two pressure sensors 16 are installed on the side wall of the piston 7 and are arranged axially staggered. Due to the pressure difference at both ends of the piston, the two pressure sensors 16 are used for measurement.

[0017] A housing 17 is installed on the cylinder 2 at the other end of the piston rod 5. A displacement sensor 18 is installed on the inner wall of the housing 17, which can detect the radial displacement of the piston rod 5 and understand the swinging condition of the piston.

[0018] A stepped section is arranged on the piston rod 5. One end of the piston abuts against the step surface of the stepped section, and the other end is fixed through a locking nut 19 installed on the piston rod 5.

[0019] An outer shell 20 is sleeved on the outer wall of the piston 7. The outer surface of the outer shell 20 and the inner wall of the piston chamber 6 are of tooth shapes with different sizes and there is a gap between them. When a small amount of compressed gas leaks into the gap between the piston and the inner wall of the piston chamber, each labyrinth tooth cavity will form a throttling chamber. Under a certain small gap, a very small part of the medium flows from the high-pressure side to the low-pressure side through each throttling point. When passing through each node, the gas converts pressure energy into kinetic energy. When the gas enters the tooth groove, due to the sudden expansion of the volume, the gas velocity drops rapidly (almost to zero). Part of its kinetic energy is converted into heat energy, and the other part is converted into eddy energy. Through the repeated action of continuous uniformly distributed throttling and the tooth groove vortex chamber, the pressure of the leaked gas is reduced to the low-pressure side pressure, meeting the airtightness requirements.

[0020] The piston 7 includes a middle shaft sleeve 7-1 for key fitting with the piston rod 5. The end of the middle shaft sleeve 7-1 is connected to the middle of a disc body 7-2. The end of the disc body 7-2 is connected to an annular body 7-3. There is an empty area between the middle shaft sleeve 7-1 and the annular body 7-3, which plays a role in weight reduction. The middle shaft sleeve 7-1, the disc body 7-2, and the annular body 7-3 are of an integral structure.

[0021] The outer shell 20 is fixed to the ring body by screws 21, which is convenient for installation and replacement. Pressure sensor mounting holes are provided on the side walls of the ring body 7-3 and the outer shell 20.

[0022] The outer shell 20 can be replaced. On the one hand, when the outer shell 20 is severely worn, only the outer shell 20 needs to be replaced, and the internal piston body can still be used, reducing costs. On the other hand, during experiments, the outer shell 20 with different tooth profiles can be replaced for comparative experiments, also reducing costs. A regulating valve and a buffer device are also provided on the exhaust side.

[0023] A method for testing the sealing performance of a labyrinth compressor is characterized in that the length b, width c of the gap between the piston and the inner wall of the piston chamber, and the cross-sectional area A of the annular labyrinth gap are measured, the tooth pitch B on the piston is measured, and the pressure on the high-pressure side of the piston is measured P 0, at the N tooth of the labyrinth P N , and the above measured values are sent to the data acquisition system, and the system calculates the above parameter values. The leakage rate of the labyrinth seal: , where , , K = b / c, R is the gas constant, T0 is the gas temperature on the high-pressure side of the piston, P 0 is the measured pressure on the high-pressure side of the piston, P N is the pressure at the N tooth of the labyrinth; , where is the pressure ratio of the piston inlet and exhaust; n is the rotational speed of the compressor; S is the stroke of the compressor, , θ and γ are fitting parameters, h is the same as the radial gap width c, D is the piston diameter, v u is the speed of sound of the gas before suction.

[0024] The following is the specific experimental process:

[0025] Test compressor data sheet

[0026]

[0027] Orthogonal experiments with three factors and three levels are carried out on the test device, which can effectively reduce the number of experiments without reducing the test accuracy. The test scheme is arranged as shown in Table 2.

[0028] Table 2 Orthogonal test scheme for labyrinth seal

[0029]

[0030] The test data is collected by the data acquisition system and calibrated and transformed by LabVIEW software. According to the test result data, the formula parameters can be fitted by using Statistic software to obtain

[0031]

[0032] Substituting the above formula into the leakage rate calculation formula, the corresponding leakage rate can be calculated. Then, comparing this leakage rate with the actual value measured by the flow sensor, there will be a slight deviation between the two values. Because there will also be errors in the measurement of the flow sensor, therefore, if the leakage rate obtained by calculation is within the agreed range of the actually measured value, it can be considered that the two are consistent. According to the calculated leakage rate, the leakage situation at the piston can be understood. According to the formula, the factors affecting leakage can be understood. The main factors affecting the leakage rate are as follows:

[0033] 1. Labyrinth shape

[0034] The geometric shape and size of the labyrinth seal cavity have a great influence on the labyrinth seal effect. It directly affects the magnitude of the vortex intensity formed in the cavity, that is, it affects the degree of conversion of kinetic energy into heat energy in the cavity. Two important geometric parameters of the cavity are the cavity depth and the cavity width, and there is an optimal value for the ratio of the two, that is, the depth-width ratio.

[0035] The labyrinth seal tooth profile is an important parameter affecting the labyrinth structure. The common tooth profiles mainly include: rectangular teeth, trapezoidal teeth, triangular teeth, etc. Considering the comprehensive processing conditions and use experience, isosceles trapezoidal teeth are generally used in labyrinth compressors to form an equilateral triangle labyrinth cavity.

[0036] 2. Clearance width

[0037] The clearance width between the sealing pairs has a great influence on the labyrinth seal performance. Theoretically, in order to reduce leakage, the clearance width of the labyrinth should be as small as possible. However, in actual situations, too small a clearance width is rather unfavorable. If the inertial force is unbalanced during machine operation, causing the piston to deflect, and at this time, if the clearance width is designed too small, it will lead to contact wear between the piston and the cylinder, not only losing the sealing effect but also damaging the components; in addition, due to the differences in the material properties of the sealing parts (such as aluminum pistons supporting cast iron cylinders, and graphite packings mating with steel piston rods), if the expansion is too large, filling the original clearance and causing severe friction with the wall surface, the friction will cause the vibration to intensify and the temperature to rise, resulting in serious damage to both the sealing parts and the wall surface, and even triggering a whole-machine failure. Therefore, on the premise that the processing and assembly level, operating conditions, and economy permit, the clearance width can be appropriately increased. Generally, in order to obtain the optimal clearance, a labyrinth compressor needs to complete a "running-in" process. By slowly increasing the compression ratio, the piston temperature gradually increases and expands. The running-in process will cause the contact between the cylinder wall and the piston labyrinth end, thereby forming the optimal clearance through running-in.

[0038] 3. Number of labyrinth teeth

[0039] Theoretically speaking, from the perspective of energy dissipation in the labyrinth cavity, the longer the sealing length, the better the sealing effect. However, in practice, the length of the sealing pair is restricted by many conditions, and its length design must be based on the stable performance of the whole machine and good economic performance. Reference [2] points out that there is an optimal number of teeth under the condition of a given sealing length, which minimizes the leakage rate.

[0040] 4. Compressor speed

[0041] Speed is an extremely important performance parameter of the labyrinth compressor. Improper selection will bring some adverse factors to the labyrinth compressor. On the basis of ensuring the reliability and high efficiency of the compressor, increasing the speed can not only reduce the volume and weight of the machine, thus saving processing costs and materials, but also significantly improve the labyrinth sealing performance. The higher the speed, the smaller the leakage rate.

[0042] According to the leakage rate requirements, each parameter can be adjusted to obtain a qualified leakage rate, which can provide data reference for the unit design.

Claims

1. A method for testing the sealing performance of a labyrinth compressor, characterized in that, The sealing performance test device of a labyrinth compressor includes a crankcase transmission case and a cylinder. A crankshaft is arranged in the crankshaft transmission case. The crankshaft is connected to one end of a piston rod through a connecting rod transmission mechanism. A piston located in a piston chamber within the cylinder is installed on the piston rod. The upper end of the piston chamber communicates with an intake passage and an exhaust passage. A stuffing box cooperating with the piston rod is arranged in the cylinder. Packing is arranged in the stuffing box. The outer surface of the piston and the inner wall of the piston chamber are tooth-shaped and there is a gap between them. The lower end of the piston chamber communicates with a leakage gas measurement chamber. A flow sensor is installed in the measurement chamber. A pressure sensor is installed on the side wall of the piston. A pressure relief valve and a pressure gauge are also installed in the measurement chamber. The stuffing box includes an upper stuffing box and a lower stuffing box located at both ends of the piston. The packing is floatingly arranged in the stuffing box. A stepped section is arranged on the piston rod. The lower end of the piston abuts against the stepped surface of the stepped section and the upper end is fixed by a locking nut installed on the piston rod. An outer shell is sleeved on the outer wall of the piston. The outer surface of the outer shell and the inner wall of the piston chamber are tooth-shaped with different sizes. The piston includes a middle shaft sleeve. The end of the middle shaft sleeve is connected to the middle of a disc body. The end of the disc body is connected to an annular body. There is an empty area between the middle shaft sleeve and the annular body. The middle shaft sleeve, the disc body, and the annular body are of an integral structure. The outer shell is fixed to the annular body by screws. Pressure sensor installation holes are provided at the bottom of the labyrinth teeth on the side walls of the annular body and the outer shell. Measure the gap length b, gap width c, and cross-sectional area A of the annular labyrinth gap between the piston and the inner wall of the piston chamber, measure the tooth pitch B on the piston, and measure the pressure on the high-pressure side of the piston P 0. At the N teeth of the labyrinth P N . Send the above measured values to a data acquisition system. The system calculates the above parameter values. The leakage rate of the labyrinth seal: , where , , K = b / c, R is the gas constant, T0 is the gas temperature on the high-pressure side of the piston, P 0 is the pressure on the high-pressure side of the measured piston, P N . At the N teeth of the labyrinth , where is the intake and exhaust pressure ratio of the piston; n is the rotational speed of the compressor; S is the stroke of the compressor, , θ and γ are fitting parameters, h is the radial gap and is the same as the gap width c, D is the piston diameter, v u is the speed of sound of the gas before suction.

Images