A transcritical two-stage gas-liquid separator for carbon dioxide refrigeration

Abstract

This invention relates to the field of gas-liquid separators for refrigeration, specifically a transcritical two-stage gas-liquid separator for carbon dioxide refrigeration. The separator includes a cylinder, a first partition, and a second partition. The first and second partitions divide the inner side of the cylinder from bottom to top into a primary chamber, a buffer chamber, and a secondary chamber. An inlet pipe is installed on the upper sidewall of the primary chamber, entering tangentially along the primary chamber and equipped with a nozzle. A spiral guide plate and swirl blades are sequentially arranged from top to bottom on the inner sidewall of the primary chamber. A riser hole is located at the center of the first partition, and multiple liquid return holes are located at its edge. A vent hole is located at the center of the second partition, and multiple drain holes are located at its edge. A wire mesh assembly is installed in the secondary chamber. A drain pipe is located at the bottom of the primary chamber, and an outlet pipe is located at the top of the secondary chamber. This invention effectively solves the problem of insufficient gas-liquid separation efficiency caused by the extremely small gas-liquid density difference in the transcritical carbon dioxide refrigeration cycle.

Description

Technical Field

[0001] This invention relates to the field of gas-liquid separators for refrigeration, and more particularly to a transcritical two-stage gas-liquid separator for carbon dioxide refrigeration. Background Technology

[0002] Carbon dioxide, as a natural refrigerant, is increasingly widely used in cold chain logistics, food freezing and refrigeration, and other fields. In the transcritical carbon dioxide refrigeration cycle, the high-temperature, high-pressure carbon dioxide gas discharged from the compressor is cooled by a gas cooler, and its pressure is typically maintained at 8-10 MPa, while its temperature is in the range of 30-50°C. The critical temperature of carbon dioxide is 31.1°C, and its critical pressure is 7.38 MPa. Under these conditions, the temperature of carbon dioxide approaches or exceeds the critical point, the density difference between the gas and liquid phases is extremely small, or even in a supercritical state, and the gas-liquid interface is indistinct.

[0003] The gas-liquid separator is a key component in the transcritical carbon dioxide refrigeration cycle. Its function is to effectively separate the gas-liquid mixture at the outlet of the gas cooler, preventing liquid carbon dioxide from entering the compressor or expander, avoiding liquid slugging damage to the equipment, and ensuring the purity of the gas phase to maintain the system's heat exchange efficiency. Existing gas-liquid separators are mostly single-stage structures, typically using a vertical cylindrical tank with a tangential inlet pipe on the side wall to introduce the gas-liquid mixture, relying on gravity settling or simple swirling flow for separation. However, under transcritical carbon dioxide conditions, because the density difference between gas and liquid approaches zero, the gravity settling velocity is extremely low, and liquid droplets are suspended in the gas phase, making separation difficult. Simultaneously, the system pressure is high and the flow rate is fast, causing small droplets to pass directly through the separator with the high-speed airflow, resulting in severely insufficient separation efficiency. Insufficient gas-liquid separation can lead to liquid refrigerant entering the compressor and causing liquid slugging, or entering the expander and causing efficiency reduction. In severe cases, it can damage the compressor cylinder and valves, requiring the cold storage system to be shut down for major repairs.

[0004] Therefore, for the special operating conditions of the transcritical refrigeration cycle of carbon dioxide, there is an urgent need for a gas-liquid separator that can effectively address the problem of insufficient separation efficiency under the conditions of extremely small gas-liquid density difference in the near-critical region and high-pressure, high-speed gas flow. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the prior art by proposing a transcritical two-stage gas-liquid separator for carbon dioxide refrigeration.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A transcritical two-stage gas-liquid separator for carbon dioxide refrigeration includes a cylindrical body. A first partition and a second partition are arranged from bottom to top within the cylindrical body, dividing the inner side of the body into a primary chamber, a buffer chamber, and a secondary chamber. An inlet pipe is installed on the upper sidewall of the primary chamber, entering tangentially into the primary chamber and fitted with a nozzle. A spiral guide plate and swirl vanes are arranged from top to bottom on the inner sidewall of the primary chamber. The nozzle is positioned near the top of the spiral guide plate. A riser hole connecting the primary chamber and the buffer chamber is opened at the center of the first partition, and multiple return liquid holes are opened at the edge of the first partition. A vent hole connecting the buffer chamber and the secondary chamber is opened at the center of the second partition, and multiple drain holes are opened at the edge of the second partition. A wire mesh assembly is provided within the secondary chamber. A drain pipe is provided at the bottom of the primary chamber, and an outlet pipe is provided at the top of the secondary chamber.

[0007] Preferably, the inner flow channel of the nozzle is a tapered flow channel with a gradually narrowing cross section, and the outlet direction of the nozzle is obliquely downward.

[0008] Preferably, the primary cavity is provided with an expansion section below the swirl blade, and the inner diameter of the expansion section gradually increases from top to bottom.

[0009] Preferably, the inner diameter of the buffer cavity is greater than or equal to the maximum inner diameter of the expansion section.

[0010] Preferably, a vortex-breaking plate is provided below the diameter-expanding section. The vortex-breaking plate has a conical structure and is arranged with a smaller top and a larger bottom. The bottom of the vortex-breaking plate is fixedly connected to the bottom of the cylinder by a support rod, and a gap is left between the outer edge of the vortex-breaking plate and the inner wall of the cylinder.

[0011] Preferably, the top edge of the return hole is provided with a plurality of liquid collection grooves, which are arranged radially along the return hole and are arranged in a circular pattern to uniformly surround the return hole.

[0012] Preferably, the second partition is a conical structure with a top-smaller and bottom-larger arrangement. The vent is located at the top center of the second partition, and the drain hole is located at the bottom edge of the second partition.

[0013] Preferably, the wire mesh assembly is a multi-layered, horizontally laid stainless steel wire mesh.

[0014] Compared with the prior art, the beneficial effects of the present invention are: This invention divides the internal space of the cylinder into a primary chamber, a buffer chamber, and a secondary chamber from bottom to top by setting a first and a second partition, forming a two-stage synergistic separation structure. The high-pressure gas-liquid mixture enters tangentially through the inlet pipe of the primary chamber and is accelerated by a nozzle, causing the mixture to rapidly form a strong vortex within the primary chamber. This vortex, reinforced by the spiral guide plate and vortex blades, significantly enhances centrifugal force, thus overcoming the technical bottleneck of traditional gravity settling and inertial separation failure caused by the extremely small gas-liquid density difference of carbon dioxide in the transcritical state. The liquid phase is thrown against the cylinder wall by centrifugal force and slides down the wall surface, exiting through the drain pipe at the bottom of the primary chamber; the gas phase enters the buffer chamber through the riser hole in the center of the first partition, achieving a stable flow transition after the initial gas-liquid separation and avoiding disturbance; subsequently, the gas phase enters the secondary chamber through the vent hole in the center of the second partition, where a wire mesh assembly deeply intercepts residual tiny droplets, ensuring gas phase purity. Simultaneously, the return liquid holes at the edge of the first partition and the drain holes at the edge of the second partition guide the incompletely separated liquid phase back to the primary chamber, achieving centralized recovery and unified discharge of the liquid phase and avoiding secondary entrainment. This structure, through a synergistic mechanism, significantly improves the separation efficiency of ultra-high density differential gas-liquid mixtures under near-critical conditions, solving key technical challenges in transcritical carbon dioxide refrigeration systems such as incomplete separation, liquid carryover in exhaust gas, and decreased system energy efficiency due to the similarity of gas and liquid properties. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a partial structural diagram of the present invention. Figure 1 ; Figure 3 This is a partial structural diagram of the present invention. Figure 2 Figure 4 This is a cross-sectional view of the present invention; Figure 5 for Figure 4 Enlarged view of point A in the middle; Figure 6 for Figure 4 Enlarged diagram of point B in the middle.

[0016] In the picture: 1. Cylinder body; 101. Primary cavity; 1011. Expanded diameter section; 102. Buffer cavity; 103. Secondary cavity; 2. First partition; 201. Air riser hole; 202. Liquid return hole; 203. Liquid collection tank; 3. Second partition; 301. Vent hole; 302. Drain hole; 4. Inlet pipe; 5. Nozzle; 6. Spiral guide plate; 7. Swirl blade; 8. Wire mesh assembly; 9. Drain pipe; 10. Outlet pipe; 11. Vortex breaker; 12. Support rod. Detailed Implementation

[0017] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0018] like Figures 1-6 As shown, this embodiment of the invention provides a transcritical two-stage gas-liquid separator for carbon dioxide refrigeration, including a cylindrical body 1. A first partition 2 and a second partition 3 are arranged inside the cylindrical body 1 from bottom to top. The first partition 2 and the second partition 3 divide the inner side of the cylindrical body 1 from bottom to top into a primary chamber 101, a buffer chamber 102, and a secondary chamber 103. An inlet pipe 4 is installed on the upper sidewall of the primary chamber 101. The inlet pipe 4 enters tangentially along the primary chamber 101 and is equipped with a nozzle 5. A spiral guide plate 6 and a swirl plate are arranged sequentially from top to bottom on the inner sidewall of the primary chamber 101. The blade 7 and nozzle 5 are positioned near the top of the spiral guide plate 6. The center of the first partition 2 has an air riser hole 201 that connects the primary chamber 101 and the buffer chamber 102. The edge of the first partition 2 has multiple liquid return holes 202. The center of the second partition 3 has an air vent 301 that connects the buffer chamber 102 and the secondary chamber 103. The edge of the second partition 3 has multiple liquid drain holes 302. The secondary chamber 103 is equipped with a wire mesh assembly 8. The bottom of the primary chamber 101 is equipped with a liquid drain pipe 9. The top of the secondary chamber 103 is equipped with an air outlet pipe 10.

[0019] Before entering the primary chamber 101, the high-pressure carbon dioxide gas-liquid mixture is throttled by nozzle 5, reducing pressure and temperature, thus moving the mixture away from its critical point and restoring the gas-liquid density difference, thereby laying the physical foundation for subsequent efficient separation. The inner wall of the primary chamber 101 is sequentially equipped with a spiral guide plate 6 and a swirl vane 7 from top to bottom. The nozzle 5 is positioned near the top of the spiral guide plate 6, causing the throttled mixture to form a strong swirling flow within the primary chamber 101. The gas phase, due to its lower density, moves upward and enters the buffer chamber 102 through the riser hole 201 in the center of the first partition 2, while the liquid phase, due to its higher density, sinks down the cylinder wall to the bottom of the primary chamber 101 and is finally discharged through the drain pipe 9, achieving initial efficient gas-liquid separation. The gas phase enters the secondary chamber 103 from the buffer chamber 102 through the vent 301 in the center of the second partition 3. The wire mesh assembly 8 installed in the secondary chamber 103 further intercepts residual micro-droplets. The purified gas phase is discharged from the vent pipe 10 at the top of the secondary chamber 103, while the intercepted droplets flow back to the buffer chamber 102 along multiple drain holes 302 on the edge of the second partition 3, and then return to the bottom of the primary chamber 101 through the return liquid hole 202, forming a closed-loop liquid phase recovery path. This two-stage separation structure achieves density difference reconstruction through the throttling and pressure reduction of the nozzle 5. Combined with the synergistic effect of cyclone separation and wire mesh capture, it significantly improves the gas-liquid separation efficiency under transcritical carbon dioxide conditions, and completely solves the technical problem of insufficient performance of traditional separators due to the extremely small gas-liquid density difference.

[0020] Specifically, the inner flow channel of nozzle 5 is a tapered flow channel with a gradually narrowing cross section, and the outlet direction of nozzle 5 is set obliquely downward. The tapered structure of the inner flow channel of nozzle 5 causes the high-pressure carbon dioxide gas-liquid mixture to undergo throttling expansion when passing through the flow channel, and the pressure and temperature decrease simultaneously, thereby effectively restoring the rapidly shrinking gas-liquid density difference in the near-critical state. At the same time, the outlet direction of nozzle 5 is set obliquely downward, so that the mixture after throttling expansion is directly guided at a specific angle to the top area of ​​the spiral guide plate 6 in the first-stage cavity 101, so that the mixture gains a downward momentum component before entering the swirling zone, which enhances the initial contact efficiency with the spiral guide plate 6 and avoids the problem of gas-liquid mixture stagnation or short-circuit flow in the upper part of the first-stage cavity 101 that is easily caused by traditional horizontal tangential air intake. This significantly improves the initial separation effect under low density difference conditions and creates favorable conditions for the strong swirling separation formed by the subsequent swirling blades 7.

[0021] Specifically, a diameter expansion section 1011 is provided below the swirl vane 7 in the primary cavity 101, and the inner diameter of the diameter expansion section 1011 gradually increases from top to bottom. When the gas-liquid mixture enters the diameter expansion section 1011 after forming a high-speed downward swirling flow through the swirl vane 7, the axial velocity of the airflow naturally decreases due to the gradual increase in the flow cross-sectional area of ​​the diameter expansion section 1011. This significantly weakens the re-entrainment ability of the high-speed airflow on the wall-attached droplets, allowing the droplets to slide stably downward along the inner wall of the primary cavity 101 under the action of gravity. This effectively avoids the secondary entrainment phenomenon caused by excessively high airflow velocity in traditional structures, and improves the separation efficiency and stability of the liquid phase in the primary cavity 101.

[0022] Specifically, the inner diameter of the buffer cavity 102 is greater than or equal to the maximum inner diameter of the expansion section 1011. After being acted upon by the swirl vanes 7, the downward airflow is effectively decelerated when passing through the expansion section 1011 due to the cross-sectional expansion. Upon entering the buffer chamber 102, since its inner diameter does not contract, the airflow channel remains wide, keeping the airflow velocity at a low level. The inner wall of the buffer chamber 102 is smooth and has no additional structure, allowing the airflow to move in an approximately direct current motion within the buffer chamber 102. The residual momentum of the swirling flow naturally decays through friction with the inner wall of the buffer chamber 102 and the dissipation of internal viscosity. The residual droplets settle under gravity and slide down the inner wall of the buffer chamber 102 to the upper surface of the first partition 2. This significantly suppresses the backflow and swirling disturbance of the airflow within the buffer chamber 102, thus providing a stable gravity settling environment for the residual droplets. This avoids the velocity rebound and secondary entrainment problems caused by the small inner diameter of the buffer chamber 102, greatly improving the thoroughness and stability of gas-liquid separation in the primary chamber 101. This ensures that the droplet content in the gas phase entering the secondary chamber 103 is further reduced, reducing the load on the subsequent fine separation of the wire mesh assembly 8.

[0023] Specifically, a vortex-breaking plate 11 is provided below the expansion section 1011. The vortex-breaking plate 11 has a conical structure and is arranged with a smaller top and a larger bottom. The bottom of the vortex-breaking plate 11 is fixedly connected to the bottom of the cylinder 1 by a support rod 12. A gap is left between the outer edge of the vortex-breaking plate 11 and the inner wall of the cylinder 1. The vortex-breaking plate 11 effectively blocks the direct impact of the airflow, which still has a certain swirling kinetic energy after being decelerated by the expansion section 1011, on the liquid surface at the bottom of the primary chamber 101. Under the guidance of the conical surface of the vortex-breaking plate 11, the gas phase is deflected back upward from its central area, avoiding secondary entrainment of droplets. The separated droplets slide down along the inner wall of the cylinder 1 and flow smoothly back to the bottom through the gap between the outer edge of the vortex-breaking plate 11 and the inner wall of the cylinder 1, and are discharged by the drain pipe 9.

[0024] Specifically, multiple liquid collection grooves 203 are provided on the top edge of the return hole 202. The liquid collection grooves 203 are arranged radially around the return hole 202. The multiple liquid collection grooves 203 are arranged in a circular and uniform manner around the return hole 202. The upper surface of the first partition 2 is a horizontal plane. After the droplets spread on the upper surface of the first partition 2, they converge towards the return hole 202 under the combined action of surface tension and gravity. The droplets falling on the upper surface of the first partition 2 can flow smoothly radially inward along the guide path of the liquid collection grooves 203 under the action of gravity, ensuring that the liquid phase can quickly and uniformly gather at the return hole 202 and flow back to the bottom of the primary cavity 101.

[0025] Specifically, the second partition 3 has a conical structure with a top-smaller and bottom-larger arrangement. The vent 301 is located at the top center of the second partition 3, and the drain hole 302 is located at the bottom edge of the second partition 3. The gas phase entering the secondary chamber 103 from the buffer chamber 102 can rise smoothly through the vent 301, while the droplets intercepted by the wire mesh assembly 8 slide naturally down the inclined surface of the conical structure under the action of gravity, gather at the lowest position of the edge of the second partition 3, and flow directly back to the buffer chamber 102 through the drain hole 302, avoiding the droplets from being stuck on the upper surface of the second partition 3 or being entrained by the rising airflow.

[0026] Specifically, the wire mesh assembly 8 is a multi-layered horizontally laid stainless steel wire mesh. When the gas phase enters the secondary chamber 103 through the vent 301 of the second partition 3, it needs to pass through multiple layers of stainless steel wire mesh in sequence. When the residual tiny droplets in the gas phase approach the wire mesh fibers with the airflow, they cannot bypass the fibers with the airflow due to inertia and directly collide with the wire mesh surface and are intercepted, or they are directly intercepted because their particle size is larger than the wire mesh openings. The captured droplets gather on the surface of the wire mesh fibers to form larger droplets, and then flow downward along the wire mesh surface under the action of gravity and flow back to the buffer chamber 102.

[0027] The technical solution process of this application is described below: A high-pressure carbon dioxide gas-liquid mixture enters through inlet pipe 4, and is throttled by nozzle 5, causing a sudden drop in pressure and temperature. This transforms the mixture, which was originally in the near-critical region with a very small density difference between the gas and liquid phases, into a subcritical state, restoring the density difference between the gas and liquid phases. The throttled mixture then enters the primary chamber at an oblique downward direction along the top region of the spiral guide plate 6, forming a downward swirling flow. The swirling flow intensity is further enhanced by the swirling blades 7. Under centrifugal force, the liquid phase is thrown towards the inner wall of the primary chamber 101, while the gas phase, due to its lower density, moves upward. After the downward airflow enters the expansion section 1011, the axial velocity of the airflow naturally decreases as the inner diameter of the expansion section 1011 gradually increases from top to bottom. The liquid phase moves upward along the inner wall of the primary chamber 101. The gas phase flows steadily downwards; when it reaches below the expansion section 1011, it is blocked by the vortex-breaking plate 11 from directly impacting the liquid surface at the bottom of the primary cavity 101. Guided by the conical surface of the vortex-breaking plate 11, the gas phase reverses and rises from its central region, passing through the rising air hole 201 in the center of the first partition 2 and entering the buffer cavity 102. The liquid phase slides down along the inner wall of the primary cavity 101 and flows back to the bottom of the primary cavity 101 through the gap between the outer edge of the vortex-breaking plate 11 and the inner wall of the cylinder 1. The airflow entering the buffer cavity 102 maintains a low speed because the inner diameter of the buffer cavity 102 is greater than or equal to the maximum inner diameter of the expansion section 1011. The inner wall of the buffer cavity 102 is smooth and has no additional structure. The airflow moves almost within the buffer cavity 102. Similar to direct current motion, the residual momentum of the swirling flow naturally decays through friction with the inner wall of the buffer chamber 102 and the dissipation of viscosity within the airflow. The residual droplets settle under gravity and slide down the inner wall of the buffer chamber 102 to the upper surface of the first partition 2. The upper surface of the first partition 2 is horizontal. After spreading on the upper surface of the first partition 2, the droplets converge towards the return hole 202 under the combined action of surface tension and gravity. They are then guided radially inward through the collection groove 203 at the top edge of the return hole 202, converging at the return hole 202 and flowing back to the bottom of the primary chamber 101. The gas phase enters the secondary chamber from the buffer chamber 102 through the vent 301 in the center of the second partition 3, passing through multiple layers of horizontally laid stainless steel wire mesh. When residual tiny droplets approach the mesh fibers with the airflow, they are unable to bypass the fibers due to inertia and are directly intercepted by the mesh surface, or they are directly trapped because their particle size is larger than the mesh openings. The captured droplets gather on the mesh fiber surface to form larger droplets, and then flow downwards along the mesh surface under the action of gravity, dripping onto the conical upper surface of the second partition 3, and naturally sliding down the conical surface to the lowest edge. They then flow back to the buffer chamber 102 through the drain hole 302, and then return to the bottom of the primary chamber 101 through the return hole 202. All the liquid phase collected at the bottom of the primary chamber 101 is discharged through the drain pipe 9, while the pure gas phase purified by the mesh assembly is discharged from the gas outlet pipe 10 at the top of the secondary chamber 103.

[0028] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A transcritical two-stage gas-liquid separator for carbon dioxide refrigeration, characterized by, Includes a cylindrical body (1), inside which a first partition (2) and a second partition (3) are arranged from bottom to top. The first partition (2) and the second partition (3) divide the inner side of the cylindrical body (1) into a primary chamber (101), a buffer chamber (102) and a secondary chamber (103) from bottom to top. An air inlet pipe (4) is installed on the upper side wall of the primary chamber (101). The air inlet pipe (4) enters the primary chamber (101) tangentially and is equipped with a nozzle (5). A spiral guide plate (6) and a swirl vane (7) are arranged from top to bottom on the inner side wall of the primary chamber (101). The nozzle (5) is close to the spiral guide plate (6). The first partition (2) is provided with a rising air hole (201) at the center of the first partition (2) connecting the first-stage chamber (101) and the buffer chamber (102). The first partition (2) is provided with multiple return air holes (202) at the edge. The second partition (3) is provided with a vent hole (301) at the center of the second partition (3) connecting the buffer chamber (102) and the second-stage chamber (103). The second partition (3) is provided with multiple drain holes (302) at the edge. The second-stage chamber (103) is provided with a wire mesh assembly (8). The bottom of the first-stage chamber (101) is provided with a drain pipe (9). The top of the second-stage chamber (103) is provided with an air outlet pipe (10).

2. The transcritical two-stage gas-liquid separator for carbon dioxide refrigeration according to claim 1, characterized in that, The inner flow channel of the nozzle (5) is a tapered flow channel with a gradually narrowing cross section, and the outlet direction of the nozzle (5) is set obliquely downward.

3. The transcritical two-stage gas-liquid separator for carbon dioxide refrigeration according to claim 1, characterized in that, The primary cavity (101) is provided with an expansion section (1011) below the swirl blade (7), and the inner diameter of the expansion section (1011) gradually increases from top to bottom.

4. The transcritical two-stage gas-liquid separator for carbon dioxide refrigeration according to claim 3, characterized in that, The inner diameter of the buffer cavity (102) is greater than or equal to the maximum inner diameter of the expansion section (1011).

5. The transcritical two-stage gas-liquid separator for carbon dioxide refrigeration according to claim 3, characterized in that, Below the expanded section (1011) is a vortex-breaking plate (11), which is a conical structure. The vortex-breaking plate (11) is arranged with a smaller top and a larger bottom. The bottom of the vortex-breaking plate (11) is fixedly connected to the bottom of the cylinder (1) by a support rod (12). There is a gap between the outer edge of the vortex-breaking plate (11) and the inner wall of the cylinder (1).

6. The transcritical two-stage gas-liquid separator for carbon dioxide refrigeration according to claim 1, characterized in that, The top edge of the return hole (202) is provided with a plurality of liquid collection grooves (203), which are arranged radially along the return hole (202), and the plurality of liquid collection grooves (203) are arranged in a circular and uniform manner around the return hole (202).

7. The transcritical two-stage gas-liquid separator for carbon dioxide refrigeration according to claim 1, characterized in that, The second partition (3) has a conical structure and is arranged with a smaller top and a larger bottom. The vent (301) is located at the top center of the second partition (3), and the drain hole (302) is located at the bottom edge of the second partition (3).

8. The transcritical two-stage gas-liquid separator for carbon dioxide refrigeration according to claim 1, characterized in that, The wire mesh assembly (8) is a multi-layered horizontally laid stainless steel wire mesh.

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