CN117948531A - Storage tank capable of pressurizing working medium and storage tank system - Google Patents

Abstract

The invention provides a storage tank capable of pressurizing working media and a storage tank system, comprising a storage tank and a pressurizing unit; a soft bag is arranged in the storage tank, and divides the storage tank into a liquid cavity positioned at the upper side and an air cavity positioned at the lower side; the upper side of the liquid cavity is provided with a vacuumizing port, a working medium inlet and a working medium outlet, and the vacuumizing port, the working medium inlet and the working medium outlet are all provided with closed structures; the lower side of the air cavity is communicated with a pressurizing unit; the liquid cavity is in a vacuum state. The device provided by the invention divides the storage tank into the liquid cavity and the air cavity through the soft bag, and simultaneously, the air in the liquid cavity is pumped out through the vacuumizing port, so that the working medium and the air are prevented from being mixed when the working medium is filled; and the pressurizing unit is communicated with the air cavity, so that the soft bag is deformed by increasing the pressure intensity in the air cavity when the working medium is filled, the working medium in the liquid cavity is extruded, the working medium filling is realized, and the degassing quality of the working medium is improved.

Description

Storage tank capable of pressurizing working medium and storage tank system

Technical Field

The invention relates to the technical field of aerospace working medium filling, in particular to a storage tank capable of pressurizing working medium and a storage tank system.

Background

The vacuum pressurizing process is one process of filling working medium into sealed pipeline, and includes the following steps: and the working medium is injected into the storage tank for storage, the storage tank working medium is degassed, the inner loop system is vacuumized, and the working medium is pressurized and injected into the inner loop system. Mainly comprises the following steps: (1) working medium storage function: the working medium to be filled can be stored, the storage capacity is measured, and the working medium liquid level can be observed: (2) vacuumizing function: the air cavity (the lower part) of the storage tank can be vacuumized; the liquid cavity (upper part) of the storage tank can be vacuumized (deaerated); the inner loop can be vacuumized through the vacuumized path interface; and can measure each vacuum degree; and (3) working medium filling function: the tank can be pressurized, filling operation can be implemented, filling pressure can be regulated, pressurization and pressure relief can be implemented, and filling pressure and filling quantity can be measured; the gas cylinder used for pressurizing the storage tank can be used for measuring the pressure of the gas cylinder and the output pressure; (4) working medium discharging and equipment cleaning functions: after filling, the working medium can be discharged; the equipment can be cleaned, and impurities and redundant substances are not introduced into the working medium; (5) control function: the operation of vacuumizing, pressurizing, pressure releasing, filling, discharging, cleaning and the like of each path can be controlled (buttons or knobs).

Under the condition that the pipelines have a large height difference, the upper pipeline may have a cavity, and the working medium needs to be pressurized in order to ensure that the working medium can fill the pipeline. The existing liquid storage tank belongs to a gas-liquid non-separation type, and high-pressure gas in a pressurizing stage can be dissolved into a working medium which is just degassed to influence the degassing of the working medium.

Disclosure of Invention

In order to solve the problem that the existing liquid storage tank can dissolve gas into working medium to affect the degassing of the working medium when in pressurization, the invention provides a liquid storage tank capable of pressurizing the working medium, which comprises a storage tank and a pressurizing unit;

A soft bag is arranged in the storage tank, and divides the storage tank into a liquid cavity positioned at the upper side and an air cavity positioned at the lower side;

the upper side of the liquid cavity is provided with a vacuumizing port, a working medium inlet and a working medium outlet, and the vacuumizing port, the working medium inlet and the working medium outlet are all provided with closed structures;

The lower side of the air cavity is communicated with a pressurizing unit;

The liquid cavity is in a vacuum state.

Preferably, the storage tank comprises a storage tank cover, a liquid cavity part and an air cavity part;

the liquid cavity part is of an annular structure;

the air cavity part is of a cover-shaped structure which is inverted;

The storage tank cover, the liquid cavity part and the air cavity part are arranged from top to bottom and are connected in a coaxial line in sequence in a sealing way;

The soft bag is arranged at the connecting position of the air cavity part and the liquid cavity part;

The pressurizing unit is connected to one side of the air cavity part, which is far away from the liquid cavity part.

Preferably, a transparent observation window is mounted on the liquid cavity portion.

Preferably, the soft capsule comprises a flexible membrane;

The periphery of the flexible diaphragm is connected with the air cavity part in a sealing way.

Preferably, the flexible membrane body is made of cloth-sandwiched rubber, and the surface material is ethylene propylene diene monomer rubber.

Preferably, the pressurizing unit comprises a pressurized gas cylinder;

a pressure reducing valve is arranged at the bottle mouth of the pressurized gas bottle;

The other end of the pressure reducing valve is communicated with the air cavity part through a pipeline.

Preferably, the vacuumizing port is connected with a vacuum pump.

Preferably, the working medium outlet is provided with a filling spanner.

Based on the same conception, the invention also provides a tank system capable of pressurizing the working medium, which comprises a filling operation table and a tank capable of pressurizing the working medium;

The filling operation platform is electrically connected with the storage tank of the storage tank and the pressurizing unit respectively.

Preferably, the filling console and the tank lower part are respectively provided with a mobile unit.

Compared with the prior art, the invention has the beneficial effects that:

The invention provides a storage tank capable of pressurizing working media, which comprises a storage tank and a pressurizing unit; a soft bag is arranged in the storage tank, and divides the storage tank into a liquid cavity positioned at the upper side and an air cavity positioned at the lower side; the upper side of the liquid cavity is provided with a vacuumizing port, a working medium inlet and a working medium outlet, and the vacuumizing port, the working medium inlet and the working medium outlet are all provided with closed structures; the lower side of the air cavity is communicated with a pressurizing unit; the liquid cavity is in a vacuum state. The device provided by the invention divides the storage tank into the liquid cavity and the air cavity through the soft bag, and simultaneously, the air in the liquid cavity is pumped out through the vacuumizing port, so that the working medium and the air are prevented from being mixed when the working medium is filled; and the pressurizing unit is communicated with the air cavity, so that the soft bag is deformed by increasing the pressure intensity in the air cavity when the working medium is filled, the working medium in the liquid cavity is extruded, the working medium filling is realized, and the degassing quality of the working medium is improved.

Drawings

FIG. 1 is an overall block diagram of a tank of the present invention capable of pressurizing a working fluid;

FIG. 2 is an overall block diagram of a tank system of the present invention that can pressurize a working fluid;

FIG. 3 is a front view of a reservoir system for pressurizing a working fluid in accordance with the present invention;

FIG. 4 is a side elevational view of the reservoir system of the present invention for pressurizing a working fluid;

1, a storage tank; 2. a soft capsule; 3. a tank cover; 4. a liquid chamber section; 5. an air cavity portion; 6. a transparent viewing window; 7. a pressurized gas cylinder; 8. a cart; 9. an electronic scale; 10. a working medium inlet; 11. a vacuum pumping port; 12. and a working medium outlet.

Detailed Description

For a better understanding of the present invention, reference is made to the following description of the invention taken in conjunction with the accompanying drawings.

The invention provides a storage tank capable of pressurizing working media, which is characterized in that a storage tank is divided into a liquid cavity and an air cavity through a soft bag, and gas in the liquid cavity is pumped out through a vacuumizing port to prevent the working media from being mixed with air when the working media are filled; and the pressurizing unit is communicated with the air cavity, so that the soft bag is deformed by increasing the pressure intensity in the air cavity when the working medium is filled, the working medium in the liquid cavity is extruded, the working medium filling is realized, and the degassing quality of the working medium is improved.

Example 1:

A tank capable of pressurizing working medium, as shown in fig. 1 and 2, comprises a storage tank 1 and a pressurizing unit; a soft bag 2 is arranged in the storage tank 1, and the soft bag 2 divides the storage tank 1 into a liquid cavity positioned at the upper side and an air cavity positioned at the lower side; the upper side of the liquid cavity is provided with a vacuumizing port 11, a working medium inlet 10 and a working medium outlet 12, and the vacuumizing port 11, the working medium inlet 10 and the working medium outlet 12 are all provided with a closed structure; the lower side of the air cavity is communicated with a pressurizing unit; the liquid cavity is in a vacuum state.

The storage tank 1 comprises a storage tank cover 3, a liquid cavity part 4 and an air cavity part 5; the liquid cavity part 4 is of an annular structure; the air cavity part 5 is of a flip-chip cover-shaped structure; the storage tank cover 3, the liquid cavity part 4 and the air cavity part 5 are arranged from top to bottom and are connected in a coaxial line and sequential sealing way; the soft bag 2 is arranged at the connecting position with the liquid cavity part 4 in the air cavity part 5; the pressurizing unit is connected to the side of the air chamber portion 5 remote from the liquid chamber portion 4. The storage tank cover 3 can be detached, so that the pouring of working medium and the cleaning of the liquid cavity are facilitated. In this embodiment, the tank cover 3, the liquid cavity portion 4 and the air cavity portion 5 are detachably and fixedly connected through bolts, and a sealing ring is further installed at the connection position.

As shown in fig. 3, a transparent observation window 6 is installed on the liquid cavity portion 4, and specifically, a transparent and visible window is designed for the outer wall of the storage tank 1, so that the liquid level condition can be observed conveniently and intuitively. Transparent observation windows 6 are provided in 2 numbers and are respectively installed at both ends of the diameter of the liquid chamber section 4.

The storage tank 1 selects small tank equipment shaped by Tianjin pressure vessel equipment company as a prototype, and is required to be modified and customized according to the application, so that the design index specified by technical requirements can be met, and the design weight of the storage tank 1 is 30kg. The shell of the storage tank 1 is made of 316L stainless steel material, has good compatibility with glycol, has a volume of 50L and meets the requirement of 30Kg of filling amount. The soft bag 2 is embedded in the storage tank 1, so that the working medium and gas can be isolated, meanwhile, when the gas with certain pressure is filled between the soft bag 2 and the tank wall, the soft bag 2 can be turned over, all the working medium can be discharged out of the storage tank, and the working medium is saved. The design pressure of the storage tank 1 is 0.5MPa, so that the safety of the equipment with pressure is ensured. The design of the storage tank 1 considers good maintainability and is convenient to clean and overhaul. In the embodiment, the diameter of the storage tank 1 is 350mm, the height is 550mm, and the wall thickness is 5mm; the transparent observation window 6 is made of toughened glass; the sealing material of the storage tank 1 is polytetrafluoroethylene; the tank weight was 30kg.

The storage tank 1 used in the embodiment is a gas-liquid separation type storage tank, and in order to ensure the isolation of working media and gas, the storage tank 1 is isolated by using a soft bag 2. The poor selection of the material of the soft bag 2 can cause the problems of exceeding the capacity of working medium gas or difficult filling caused by insufficient elasticity. To avoid this risk, the soft bag 2 material is selected to be cloth-sandwiched rubber, and the surface material is ethylene propylene diene monomer. The ethylene propylene diene monomer and the ethylene glycol solution have good compatibility, and the molecular structure of the ethylene propylene diene monomer ensures that the elasticity is inferior to that of natural rubber and butadiene rubber, so that the elasticity requirement in the filling process is ensured; meanwhile, compared with natural rubber, the rubber has excellent strength characteristics, ageing resistance, erosion resistance and the like, and has a durable service life. The cloth-sandwiched rubber can ensure better material strength and flexibility and can ensure good compatibility of materials and media. The peripheral side of the flexible diaphragm is connected with the air cavity part 5 in a sealing way. In particular a flexible membrane is embedded in the air cavity portion 5.

As shown in fig. 4, the pressurizing unit includes a pressurizing gas cylinder 7; the opening of the pressurized gas cylinder 7 is provided with a pressure reducing valve; the other end of the pressure reducing valve is communicated with the air cavity part 5 through a pipeline.

The vacuumizing port 11 at the top of the storage tank 1 facilitates degassing treatment on the upper part of the liquid cavity of the storage tank 1. The bottom of the storage tank 1 is provided with a vacuumizing interface to ensure that the lower part of the air cavity of the storage tank 1 is vacuumized. Meanwhile, a working medium outlet 12 is formed in the top of the storage tank 1 and is used for filling outwards. The vacuum pump is connected to the vacuum suction port 11. The vacuumizing flange interface is reserved at the vacuumizing port 11 on the storage tank cover, a manual stop valve is arranged, and the manual stop valve is connected with a vacuum pump, so that vacuumizing of a liquid cavity can be realized, and the aim of degassing working media is fulfilled. The vacuum can be pumped to the air cavity of the storage tank and the liquid cavity of the storage tank, and the vacuum degree can reach 50Pa. The vacuum gauge measures 0-1 atmosphere pressure, and the accuracy requirement is not lower than 50Pa in the range of 50 Pa-1000 Pa (if the vacuum gauge is selected, the measuring range is-100 kPa-0, and the accuracy is 0.5 level).

And the working medium outlet 12 is provided with a filling wrench to realize filling output of working medium. The working medium outlet 12 is also provided with a liquid filter, so that impurities are prevented from flowing into the rear-end flowmeter, and the liquid filter is arranged on the storage tank 1 to be replaced and cleaned conveniently.

Example 2:

the invention also provides a tank system capable of pressurizing the working medium, as shown in fig. 1 and 2, comprising a filling operation table and a tank capable of pressurizing the working medium; the filling station is electrically connected to the tank 1 and the pressurizing unit, respectively.

The storage tank system is used for weighing the weight of the medium in the filling process, and the measured value of the electronic scale 9 is used for calculating the propellant filling amount, so that the filling parameters are ensured to meet the filling task requirements. The method can facilitate the injection of the working medium, store the working medium, measure the quality of the working medium and ensure that the measuring precision is not lower than 50g.

The storage tank system comprises a storage tank, an electronic scale 9 and a connecting pipeline, and has the main functions of completing storage of working media and storage of nitrogen for pressurization, and is used for weighing the weight of the working media in the filling process, the electronic scale 9 monitors weight change in real time in the filling process, and the filling quantity of the cooling medium is calculated through the weight, so that the filling accuracy of the cooling medium is ensured, and filling parameters are ensured to meet the filling task requirements. In this embodiment, the working medium is glycol circulation coolant.

As shown in fig. 3 and 4, the filling station and the tank lower part are respectively provided with a moving unit. The storage box system is designed into a trolley 8 structure, the size of the placed electronic scale 9 and the storage box is about 730 multiplied by 550 multiplied by 1150 (mm), and 2 fixed casters and 2 movable casters are arranged at the bottom, so that the equipment can be conveniently moved and used.

The tank system consists of a cart 8, a tank and an electronic scale 9. The cart 8 is used as a bearing assembly and is used for placing components such as a storage tank, an electronic scale 9 and the like, and casters are arranged at the bottom of the cart for convenient movement and use; the membrane arranged in the storage tank 1 of the storage tank separates the storage tank 1 into an upper layer and a lower layer which are independent, and working medium filling can be realized by respectively pumping and pressurizing the upper layer and the lower layer; the electronic scale 9 is placed at the bottom of the storage tank 1 and displays the weight change of the storage tank 1 in real time; the pressurizing unit of the storage tank is a 12L nitrogen bottle, is provided with a bottleneck valve and is arranged on the trolley 8 for providing an air source for the inner loop filling equipment.

The storage tank 1 in the storage tank system is provided with 4 gas/liquid path interfaces, namely a working medium inlet 10, a working medium outlet 12, a vacuumizing port 11 and a vacuumizing port 11, which are respectively arranged at the upper end of the storage tank 1, and the vacuumizing port 11 is arranged at the lower end of the storage tank 1, wherein the working medium outlet 12, the vacuumizing port 11 and the vacuumizing port 11 are arranged at the upper end of the storage tank 1 and can be connected with a filling control console by using hoses, and the working medium inlet 10 is arranged at the upper end of the storage tank 1 and is connected with a filling working medium barrel; the nitrogen bottle bottleneck valve is provided with 1 gas path interface which is connected with the filling control console.

The matched filling electronic scale 9 is an electronic scale 9 of a Mettler-Tolyduo (Changzhou) weighing equipment system limited company; the electronic scale 9 adopts a new weighing platform, is matched with a high-precision weighing sensor and a high-precision weighing instrument, has the advantages of 6000 division numbers, high accuracy, quick weighing, stable and reliable work and simple installation and maintenance.

The high-precision electronic scale 9 has the following detailed indexes:

Model: WS150L, display instrument IND560P1;

Measuring range: 150kg;

precision: 50g (task book requirements 50 g);

The material of the balance body: stainless steel table top, other carbon steel;

weighing the size of the platform: 0.45m multiplied by 0.55m, and can be customized according to the requirements;

Weighing platform height: 125mm;

Display instrument material: a stainless steel housing;

communication interface: profibusDP;

communication cable: CB-5m shields the signal cable.

The high-precision electronic scale 9 communicates with the control module through a ProfibusDP communication interface. The adoption of the ProfibusDP communication interface for communication has the advantages of high communication speed, long transmission distance and strong anti-interference capability, and the display value of the display instrument of the electronic scale 9 is consistent with the computer display of the control module; meanwhile, even if a computer fails in the filling process, the execution of the automatic control flow being executed cannot be influenced.

The electronic scale head can be taken off and placed on the front panel of the equipment, and is convenient to display.

The storage box system is provided with 2 paths of electric interfaces, namely a power interface of the electronic scale 9 and a communication interface of the electronic scale 9, and is connected with 220VAC commercial power and a communication interface of the electronic scale 9 at the rear part of the filling control console. Finally, the electronic scale 9 instrument (7 inch touch screen) can be displayed and controlled (peeled and cleared) in real time in the filling control console.

Tank system principle:

The tank system is used for weighing the weight of working medium in the filling process, the electronic scale 9 monitors weight change in real time in the filling process, and the filling amount of the working medium is calculated through the weight, so that the accuracy of the working medium filling is ensured.

The tank system is divided into an air source system and a filling system in principle.

The gas source system mainly provides 15MPa high-pressure nitrogen for the nitrogen cylinder, and the nitrogen cylinder is provided with a cylinder valve and is required to be inflated before filling.

The filling system mainly monitors the weight change of the storage tank in real time through the electronic scale 9, the storage tank 1 on the electronic scale 9 is provided with a membrane, the storage tank 1 is divided into an upper layer and a lower layer which are independent, and working medium filling can be realized by respectively pumping and pressurizing the upper layer and the lower layer.

The working medium outlet 12 at the upper end of the storage tank 1 is provided with a liquid filter of 80um, so that impurities are prevented from flowing into the rear-end flowmeter, and the liquid filter is arranged on the storage tank 1 and is convenient to replace and clean.

The application solves the problems of the working medium storage function and the working medium pressurization function in the vacuum pressurization filling method, and can realize the operation vacuumizing function by matching with a vacuum pump. Has stronger use function and can better realize the main steps of the vacuum pressurizing filling method.

The working medium is injected into the liquid cavity of the energy accumulator of the closed pipeline in the process of filling the inner loop, so that the flexible diaphragm generates elastic deformation, elastic potential energy is stored, the generated initial pressure provides a stable inlet pressure for the operation of a subsequent loop pump, and the filling process controls the filling pressure to be related to whether the loop working medium can be effectively filled or not, so that the stable operation of the loop is affected. The control of filling pressure is to realize self-priming filling of working media and avoid generation of cavities, taking manned spacecraft as an example, the difference between the height of a pressure gauge of a filling control console (the pressure of an air cavity of a storage tank) and the height of the highest end of a hydraulic circuit is about 4.5m, and the difference is converted into 0.046MPa, so that the filling pressure is required to be higher than the pressure, the pressure at the bottom of the storage tank is required to be regulated to be more than 0.046MPa, and the absolute pressure of each part of the hydraulic circuit after the working media are filled can be ensured to be higher than atmospheric pressure.

Secondly, on the premise of ensuring that the working medium is filled in the pipeline, according to the initial pressure requirement of the flexible diaphragm, the pressure of the air cavity at the bottom of the storage tank is regulated according to the height difference between the pressure gauge and the flexible diaphragm, so that the filling pressure P required by the energy accumulator can be controlled.

In the filling process of the manned spacecraft and the space station, the pressure of the pump inlet near the flexible diaphragm is regulated through the filling storage tank, the weight of the storage tank and other parameters are monitored in real time, the pressure of the air cavity at the bottom of the storage tank is controlled to finely regulate the pressure of the pump inlet, and the filling pressure is ensured to reach 163+/-3 kPa.

In the prior art, a similar storage tank is arranged in filling, but the gas-liquid cavities of the storage tank are not separated, a pressurizing gas filling port is arranged above the storage tank, and a liquid outlet is arranged at the bottom of the storage tank, so that nitrogen can be dissolved in working medium during filling pressurization after vacuum degassing, and the actual quality of the vacuum degassing is not controlled.

The embodiment is improved on the basis of the original storage tank, has a gas-liquid separation function, has liquid level, working medium weight and other detection functions, is provided with a vacuum pumping port 11, and can realize vacuum pumping and degassing of working medium by matching with a vacuum pump.

The embodiment of the tank system capable of pressurizing the working medium comprises a tank, a pressurizing gas cylinder 7, an electronic scale 9 and a connecting pipeline shell, and has the main functions of completing storage and pressurization of the working medium and monitoring weight change in a filling process. The pressurized gas cylinder 7 is filled with high-pressure nitrogen, the storage tank is provided with flexible diaphragms, the storage tank is divided into an upper layer and a lower layer which are independent, the upper layer is a liquid cavity, the lower layer is an air cavity, the air cavity of the storage tank is connected with the pressurized gas cylinder 7, and working media can be upwards ejected and extruded through ventilation and pressurization of the air cavity, so that the pressurization and the outward filling of the working media are realized. The transparent observation window 6 is installed to the tank liquid chamber, can be used to observe the liquid level change of working medium in the filling process tank, and pressurization gas cylinder 7 takes the relief pressure valve to be used for to the regulation of filling pressure in the filling process, can adjust the filling pressure according to the needs of pressurization pipeline, and the tank is laid on electronic scale 9, can realize the real-time supervision of filling in-process weight variation, calculates the outside filling volume of working medium through weight variation, guarantees the accuracy of working medium filling.

The foregoing is illustrative of the present invention and is not to be construed as limiting thereof, but rather as providing for the use of additional embodiments within the spirit and scope of the present invention.

Claims (10)

1. A storage tank capable of pressurizing working media, which is characterized by comprising a storage tank (1) and a pressurizing unit;

a soft bag (2) is arranged in the storage tank (1), and the soft bag (2) divides the storage tank (1) into a liquid cavity positioned at the upper side and an air cavity positioned at the lower side;

the upper side of the liquid cavity is provided with a vacuumizing port (11), a working medium inlet (10) and a working medium outlet (12), and the vacuumizing port (11), the working medium inlet (10) and the working medium outlet (12) are all provided with closed structures;

The lower side of the air cavity is communicated with a pressurizing unit;

The liquid cavity is in a vacuum state.

2. -A tank capable of pressurizing a working medium according to claim 1, characterized in that the tank (1) comprises a tank cover (3), a liquid chamber part (4) and a gas chamber part (5);

the liquid cavity part (4) is of an annular structure;

the air cavity part (5) is of a cover-shaped structure which is inverted;

the storage tank cover (3), the liquid cavity part (4) and the air cavity part (5) are arranged from top to bottom and are connected in a coaxial line and sequentially sealed manner;

The soft bag (2) is arranged at the connecting position of the liquid cavity part (4) in the air cavity part (5);

The pressurizing unit is connected to one side of the air cavity part (5) away from the liquid cavity part (4).

3. A tank for pressurizing a working medium according to claim 2, characterized in that the liquid chamber part (4) is provided with a transparent viewing window (6).

4. -A tank capable of pressurizing a working medium according to claim 2, characterized in that the flexible bladder (2) comprises a flexible membrane;

The peripheral side of the flexible diaphragm is connected with the air cavity part (5) in a sealing way.

5. The tank capable of pressurizing working medium according to claim 4, wherein the flexible membrane body is cloth-sandwiched rubber, and the surface material is ethylene propylene diene monomer rubber.

6. -A tank capable of pressurizing a working medium according to claim 2, characterized in that the pressurizing unit comprises a pressurized gas cylinder (7);

A pressure reducing valve is arranged at the bottle mouth of the pressurized gas bottle (7);

the other end of the pressure reducing valve is communicated with the air cavity part (5) through a pipeline.

7. -Tank capable of pressurizing a working medium according to claim 1, characterized in that the evacuation port (11) is connected with a vacuum pump.

8. -Tank capable of pressurizing a working medium according to claim 1, characterized in that the working medium outlet (12) is equipped with a filling wrench.

9. A tank system for pressurizing a working medium, comprising a filling station and a tank for pressurizing a working medium according to any one of claims 1 to 8;

The filling operation platform is electrically connected with the storage tank (1) of the storage tank and the pressurizing unit respectively.

10. A tank system for pressurizing a fluid according to claim 9, wherein the filling station and the tank lower portion are provided with a moving unit, respectively.