A low-selectivity vacuum dehumidification membrane and its preparation and testing method

Abstract

This invention discloses a low-selectivity vacuum dehumidification membrane and its preparation and testing methods. The low-selectivity vacuum dehumidification membrane of this invention has a four-layer structure, including a support layer, a hydrophobic layer, a hydrophilic layer, and an active layer. The hydrophobic layer is placed on the support layer, the hydrophilic layer is adhered to the hydrophobic layer, and the active layer is uniformly coated on the hydrophilic layer. The performance of the low-selectivity vacuum dehumidification membrane can be tested using the testing method proposed in this invention. The low-selectivity vacuum dehumidification membrane of this invention enables vacuum membrane dehumidification systems to operate under the drive of a low-power vacuum pump, which is expected to reduce the noise of the vacuum membrane dehumidification system and improve the system energy efficiency. The testing method of this invention solves the problem of difficulty in measuring the water vapor partial pressure on the permeate side, making the testing process simple and feasible.

Description

Technical Field

[0001] This invention relates to the field of HVAC energy-saving equipment manufacturing technology, specifically to a low-selectivity vacuum dehumidification membrane and its preparation and testing methods. Background Technology

[0002] To better control indoor temperature and humidity, achieve high-precision air conditioning, reduce the energy consumption of air conditioning systems, and realize the goal of "carbon neutrality" as soon as possible, it is necessary to develop new air dehumidification technologies. Common dehumidification technologies include rotary dehumidifiers, fluidized bed dehumidifiers, and solution dehumidifiers. These technologies often require heating for regeneration and have good energy-saving potential under conditions where low-grade heat sources are abundant. However, these technologies and equipment are often large in size, requiring significant space for actual installation. Vacuum membrane dehumidification technology, with its advantages of small size and no need for heating for regeneration, has received widespread attention from scholars both domestically and internationally in recent years.

[0003] The basic principle of vacuum membrane dehumidification technology is similar to that of vacuum drying technology. It utilizes the suction effect of a vacuum pump to create a chemical potential difference across a water vapor selectively permeable membrane, allowing water vapor in the humid air to pass through the membrane and be discharged through the vacuum pump. The vacuum dehumidification membrane is one of the core components of a vacuum membrane dehumidification device, and its performance is generally evaluated using two indicators: water vapor permeability and water vapor selectivity. However, these two indicators change with variations in the pressure on the feed side and the permeate side, thus failing to accurately reflect the overall performance of the vacuum membrane dehumidification system. For example, under conditions of high permeate-side vacuum, some membranes exhibit high water vapor permeability and water vapor selectivity. However, when the vacuum level is low, these membranes may show very low water vapor permeability and water vapor selectivity. Therefore, from the perspective of the energy efficiency of a vacuum membrane dehumidification system, different vacuum dehumidification membranes have different optimal permeate-side vacuum levels. Previous research has shown that the permeate-side vacuum level is one of the most important parameters affecting the energy efficiency of a vacuum membrane dehumidification system; reducing the permeate-side vacuum level can significantly improve the energy efficiency of the system.

[0004] In measuring the water vapor permeability of vacuum dehumidification membranes, the problem of measuring the partial pressure of water vapor on the permeate side is often encountered. This is mainly because conventional temperature and humidity sensors are calibrated under normal pressure and are not suitable for vacuum or near-vacuum environments.

[0005] To improve the operational efficiency of vacuum membrane dehumidification systems, this invention proposes a low-selectivity vacuum dehumidification membrane. Utilizing this membrane, the vacuum membrane dehumidification system retains a certain dehumidification capacity even under conditions of low vacuum on the permeate side. Furthermore, to address the difficulty in measuring water vapor partial pressure under vacuum conditions on the permeate side, a convenient method for testing the performance of the vacuum dehumidification membrane is proposed. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides a low-selectivity vacuum dehumidification membrane and its preparation method, enabling vacuum membrane dehumidification systems to maintain significant dehumidification effects and high energy efficiency even under low vacuum conditions. It offers advantages such as wider applicability, low energy consumption, and excellent dehumidification performance. Furthermore, it provides a vacuum membrane dehumidification component and a convenient measurement method for testing the dehumidification performance of vacuum membranes. This allows for rapid testing of the vacuum dehumidification membrane's performance, enabling the selection of qualified low-selectivity vacuum dehumidification membranes, and offers advantages such as simple measurement and high reliability.

[0007] This invention provides a low-selectivity vacuum dehumidification membrane, characterized by comprising a support layer, a hydrophobic layer, a hydrophilic layer, and an active layer; the hydrophobic layer is disposed on the support layer, the hydrophilic layer is adhered to the hydrophobic layer, and the active layer is uniformly coated on the hydrophilic layer. While water vapor permeates through the low-selectivity vacuum dehumidification membrane, some air also permeates. This permeated air has a purging effect on the permeate side of the vacuum membrane dehumidification component, allowing the vacuum membrane dehumidification system to maintain a significant dehumidification effect even with a low vacuum level and low pump power on the permeate side, demonstrating significant energy-saving and noise-reduction potential.

[0008] To ensure the membrane has a certain mechanical strength, a support layer is used to maintain the shape of the membrane. The support layer is a perforated plate made of aluminum, stainless steel, or carbon steel, with a thickness of 1-3 mm, a hole spacing of 1-5 mm, and a hole diameter of 1-5 mm.

[0009] Because the active layer of the low-selectivity vacuum dehumidification membrane swells and becomes liquid after absorbing water, a hydrophobic layer is provided to prevent the active layer from contacting the support layer and causing corrosion. The hydrophobic layer has good water-blocking and air-permeable properties, and the material of the hydrophobic layer is one or more of hydrophobic textile fabric, PTFE membrane, and hydrophobic nonwoven fabric. The total thickness of the hydrophobic layer is 0.01mm-3mm.

[0010] To maintain a uniformly distributed shape of the active layer, a hydrophilic layer is formed on the surface of the hydrophobic layer. The hydrophilic layer has good air permeability, and the material of the hydrophilic layer is one or more combinations of nylon mesh, hydrophilic coating, and hydrophilic nonwoven fabric. The total thickness of the hydrophilic layer is 0.001 mm to 3 mm.

[0011] To enable the low-selectivity vacuum dehumidification membrane to exhibit good water vapor selectivity, an active layer is provided. The active layer is a water vapor selectively permeable layer containing readily absorbent components. The active layer is made of one or more blends or copolymers of polyvinyl alcohol, sodium alginate, polyacrylamide, and sodium p-toluenesulfonate, and also includes one or more blends or copolymers of lithium chloride, calcium chloride, graphene oxide, and hydrophilic nano-titanium dioxide.

[0012] The method for preparing a low-selectivity vacuum dehumidification membrane is characterized by comprising the following steps:

[0013] (I) Prepare the casting solution required to form the active layer; add one or more of polyvinyl alcohol, sodium alginate, polyacrylamide, and sodium p-toluenesulfonate to a beaker, slowly add distilled water to the beaker, place the beaker in a constant temperature water bath at 80~95℃ and heat for 1~5 hours, while continuously stirring the substances in the beaker; the total mass ratio of one or more of the polyvinyl alcohol, sodium alginate, polyacrylamide, and sodium p-toluenesulfonate to the mass ratio of distilled water is 1:100~2:25;

[0014] (II) After the mixture in the beaker cools to 10~30℃, add one or more of lithium chloride, calcium chloride, graphene oxide, and hydrophilic nano titanium dioxide to the beaker, and then place the beaker in a constant temperature water bath at 10~40℃ and stir the substances in the beaker continuously for 1~5 hours; the total mass ratio of one or more of the materials such as lithium chloride, calcium chloride, graphene oxide, and hydrophilic nano titanium dioxide to the mass ratio of the distilled water in step (I) is 1:100~2:25;

[0015] (III) Allow to stand for 10-1500 minutes to degas and form a casting solution;

[0016] (IV) A support layer is made of aluminum, stainless steel or carbon steel. A hydrophobic layer made of one or more of hydrophobic textile fabric, PTFE membrane or hydrophobic nonwoven fabric is adhered to the upper surface of the support layer. Then, a hydrophilic layer made of one or more of nylon mesh, hydrophilic coating or hydrophilic nonwoven fabric is adhered to the upper surface of the hydrophobic layer. It is necessary to ensure that the support-hydrophobic-hydrophilic membrane surface formed after the hydrophilic layer is adhered is flat and smooth, without bulging.

[0017] (V) Apply the casting solution prepared in step (III) evenly to the support-hydrophobic-hydrophilic membrane prepared in step (IV), with the active layer coating thickness being 10um~500um. Transfer the coated membrane to a constant temperature oven and dry it at 40~80℃ for 5~15min.

[0018] (VI) Place the membrane prepared in step (V) on a horizontal and smooth glass plate, and apply the casting solution prepared in step (III) to the membrane prepared in step (V) again evenly. The coating thickness is 10um~500um. Transfer the membrane after recoating to a constant temperature oven and dry it at 40~80℃ for 5~15min.

[0019] (VII) Place the membrane prepared in step (VI) on a horizontal and smooth glass plate, and apply the casting solution prepared in step (III) to the membrane prepared in step (VI) again evenly. The coating thickness is 10um~500um. Transfer the membrane after recoating to a constant temperature oven and dry it at 40~80℃ for 5~15min.

[0020] (VIII) Thus, a low-selectivity vacuum dehumidification membrane is obtained.

[0021] The vacuum membrane dehumidification assembly for testing vacuum dehumidification performance is characterized in that: the vacuum membrane dehumidification assembly includes a feeding side and a permeation side, and a low-selectivity vacuum dehumidification membrane is located between the feeding side and the permeation side; an upper cover plate is sealed and installed above the feeding side, and a lower cover plate is sealed and installed below the permeation side.

[0022] The feeding side has at least two holes, one for humid air inlet and the other for humid air outlet; the inlet and outlet are located on the same side.

[0023] To ensure a good seal and facilitate disassembly during testing, a groove is provided at the contact point between the feeding side and the permeation side for installing a sealing gasket. The groove has a width of 0.5mm to 2mm and a depth of 0.5mm to 2mm.

[0024] The feeding side and the permeation side each provide a platform for installing a low-selectivity vacuum dehumidification membrane. The length and width of the platform are 0.5mm to 5mm larger than the length and width of the vacuum dehumidification membrane, and the depth of the platform is 0.5mm to 5mm.

[0025] The feed side is provided with several partitions perpendicular to the membrane to increase the residence time of humid air on the feed side. The thickness of the partitions is 0.2mm to 2mm.

[0026] The permeation side has at least one hole that connects to the suction end of the vacuum pump.

[0027] The inlet of the humid air is connected to an inlet temperature and humidity sensor, which is connected to an inlet flow meter. The outlet flow meter is connected to an air pump. The outlet of the humid air is connected to an outlet temperature and humidity sensor, which is connected to an outlet flow meter. The orifice on the permeation side is connected to a vacuum pressure gauge, which is connected to a vacuum pump.

[0028] A test method for a low-selectivity vacuum dehumidification membrane, characterized by the following steps:

[0029] (I) Install the prepared low-selectivity vacuum dehumidification membrane inside the vacuum membrane dehumidification assembly, and clamp and fix the entire vacuum membrane dehumidification assembly with the low-selectivity vacuum dehumidification membrane installed with G-clamps;

[0030] (II) Turn on the air pump and vacuum pump. The air pump is used to pump humid air into the humid air inlet to the feeding side, and the vacuum pump is used to draw air from the permeation side. When the values ​​of the vacuum pressure gauge, inlet flow meter, outlet flow meter, inlet humidity and temperature sensor, and outlet humidity and temperature sensor are relatively stable, use the inlet flow meter, outlet flow meter, inlet humidity and temperature sensor, and outlet humidity and temperature sensor to record the inlet humid air mass flow rate, outlet humid air mass flow rate, inlet temperature, outlet temperature, inlet relative humidity, and outlet relative humidity flowing through the vacuum membrane dehumidification component. Use the vacuum pressure gauge to record the vacuum degree on the permeation side. Based on the measured inlet temperature and inlet relative humidity data, consult the enthalpy-humidity chart of the humid air to easily obtain the inlet moisture content. Based on the measured outlet temperature and relative humidity data, the outlet moisture content can be easily obtained by consulting the enthalpy-humidity chart of humid air. The average temperature on the feed side is obtained by arithmetically averaging the measured inlet and outlet temperatures, and the average saturated water vapor partial pressure on the feed side is obtained by consulting the humid air moisture content chart. The average relative humidity on the feed side is obtained by arithmetically averaging the measured inlet and outlet relative humidity. The average water vapor partial pressure on the feed side is obtained by multiplying the average saturated water vapor partial pressure on the feed side with the average relative humidity on the feed side. Based on the measured or consulted values ​​of inlet humid air mass flow rate, outlet humid air mass flow rate, inlet moisture content, and outlet moisture content, the inlet dry air mass flow rate and outlet dry air mass flow rate can be easily obtained by simultaneously calculating using formulas (1) and (2).

[0031] (III) Calculate the water vapor permeability, selectivity coefficient, and dehumidification COP of the low-selectivity vacuum dehumidification membrane; calculate using formulas (3), (4), and (5), respectively.

[0032] (IV) The parameters calculated in step (III) are used to determine whether the performance of the tested low-selectivity vacuum dehumidification membrane is qualified:

[0033] The water vapor permeability calculated by formula (3) represents the amount of water vapor passing through the membrane under the conditions of unit area, unit water vapor partial pressure, and unit time. When its value is greater than 1×10 -7 mol / (Pa m 2s), then it indicates that the dehumidification capacity of the tested low-selectivity vacuum dehumidification membrane is qualified; and the larger its value, the stronger the dehumidification capacity of the tested vacuum dehumidification membrane; the water vapor permeability calculated by formula (3) is actually the equivalent value of water vapor permeability coefficient when the permeation side pressure is 0Pa.

[0034] The selectivity coefficient calculated by formula (4) represents the selectivity of the membrane to water vapor. When its value is greater than 0.01, it indicates that the selectivity of the tested low-selectivity vacuum dehumidification membrane is qualified; and the higher its value, the stronger the selectivity of the tested vacuum dehumidification membrane.

[0035] The dehumidification COP calculated by formula (5) represents the dehumidification latent heat of the vacuum pump per unit power consumption. When its value is greater than 1, it indicates that the energy-saving performance of the tested low-selectivity vacuum dehumidification membrane is qualified; and the larger its value is, the better the energy-saving performance of the tested vacuum dehumidification membrane.

[0036]

[0037]

[0038]

[0039]

[0040]

[0041] Among them, K w Water vapor permeability, expressed in mol / (Pa·m) 2 s); K a Air permeability, expressed in mol / (Pa·m) 2 s); This indicates the inlet dry air mass flow rate, in kg / s; The mass flow rate of dry air at the outlet is expressed in kg / s; m in Indicates the inlet humid air mass flow rate, kg / s; m out ω represents the outlet humid air mass flow rate, kg / s; in Indicates inlet moisture content, kg / kg; ω out Indicates the moisture content at export, kg / kg; p w q represents the average partial pressure of water vapor on the feed side, in Pa; l The latent heat of vaporization of water is represented by 43942 J / mol, which can be approximated in engineering terms; S represents the membrane dehumidification area, in m². 2 M a M represents the relative molecular mass of air, in kg / mol. w S represents the relative molecular mass of water vapor, in kg / mol. w / aThis represents the selectivity coefficient of the membrane.

[0042] The present invention discloses a low-selectivity vacuum dehumidification membrane and its preparation and testing method, which have the following beneficial effects:

[0043] 1. The invention provides a low-selectivity vacuum dehumidification membrane that is applicable to a wider range of working conditions, and has low energy consumption and good dehumidification effect. Even when the vacuum degree on the permeation side is low and the vacuum pump power is low, it still has a significant dehumidification effect and has a significant energy-saving and noise-reducing effect.

[0044] 2. This invention provides a method for preparing a low-selectivity vacuum dehumidification membrane. This method can obtain a low-selectivity vacuum dehumidification membrane with wider applicability, lower energy consumption, and better dehumidification effect. Furthermore, this method improves the stability and smoothness of the low-selectivity vacuum dehumidification membrane.

[0045] 3. This invention provides a vacuum membrane dehumidification component for testing vacuum dehumidification performance and a method for testing low-selectivity vacuum dehumidification membranes using this component. It can solve the problem of difficulty in measuring water vapor partial pressure under vacuum conditions on the permeation side, and can conveniently measure various performance indicators of low-selectivity vacuum dehumidification membranes. It can more accurately obtain qualified low-selectivity vacuum dehumidification membranes with wider applicability, lower energy consumption, and better dehumidification effect. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the low-selectivity vacuum dehumidification membrane of the present invention.

[0047] Figure 2 This is an enlarged view of point A in the schematic diagram of the low-selectivity vacuum dehumidification membrane of the present invention.

[0048] Figure 3 This is a schematic diagram of the vacuum membrane dehumidification component used for testing vacuum dehumidification performance according to the present invention.

[0049] Figure 4 This is an exploded view of the vacuum membrane dehumidification component used for testing vacuum dehumidification performance according to the present invention.

[0050] Figure 5 This is another perspective of the exploded view of the vacuum membrane dehumidification assembly used for testing the vacuum dehumidification performance of the present invention.

[0051] Figure 6 This is a schematic diagram of the low-selectivity vacuum dehumidification membrane performance testing system of the present invention.

[0052] The markings in the diagram are as follows:

[0053] Vacuum dehumidification membrane 1, active layer 1-1, hydrophilic layer 1-2, hydrophobic layer 1-3, support layer 1-4. Upper cover plate 3, lower cover plate 6, feeding side 4, permeation side 5, humid air inlet 4-3, humid air outlet 4-4, sealing gasket grooves 4-1 and 5-1, vacuum dehumidification membrane mounting platform 4-2 and 5-2, vacuum pump suction end connection hole 5-3. Air pump 7-1, vacuum pump 7-2, outlet temperature and humidity sensor 8-1, inlet temperature and humidity sensor 8-2, inlet flow meter 9-2, outlet flow meter 9-1, vacuum pressure gauge 10, vacuum membrane dehumidification assembly with low-selectivity vacuum dehumidification membrane installed 11. Detailed Implementation

[0054] The invention will now be further described with reference to the accompanying drawings.

[0055] like Figure 1 and Figure 2 As shown, the present invention provides a low-selectivity vacuum dehumidification membrane 1, characterized in that: it includes a support layer 1-4, a hydrophobic layer 1-3, a hydrophilic layer 1-2, and an active layer 1-1; the hydrophobic layer 1-3 is placed on the support layer 1-4, the hydrophilic layer 1-2 is adhered to the hydrophobic layer 1-3, and the active layer 1-1 is uniformly coated on the hydrophilic layer 1-2.

[0056] To ensure the membrane has a certain mechanical strength, the support layer is used to maintain the shape of the membrane. The support layer 1-4 is a perforated plate made of materials such as aluminum, stainless steel or carbon steel, with a thickness of 1~3mm, a hole spacing of 1~5mm, and a hole diameter of 1~5mm.

[0057] Because the active layer of the vacuum dehumidification membrane swells and becomes liquid after absorbing water, a hydrophobic layer is provided to prevent the active layer from contacting the support layer and causing corrosion. The hydrophobic layers 1-3 have good water-blocking and air-permeable properties and include one or more of the following: hydrophobic textile fabric, PTFE membrane, and hydrophobic nonwoven fabric. The total thickness of the hydrophobic layers is 0.01mm-3mm.

[0058] To maintain a uniformly distributed shape of the active layer, a hydrophilic layer is provided on the surface of the hydrophobic layer. The hydrophilic layer is a breathable hydrophilic layer, including one or more of nylon mesh, hydrophilic coating, and hydrophilic nonwoven fabric, and the thickness of the hydrophilic layer is 0.001mm to 3mm.

[0059] To ensure the vacuum dehumidification membrane exhibits good water vapor selectivity, an active layer is provided. The active layer is a water vapor selectively permeable layer containing readily absorbent components. The active layer is made of one or more blends or copolymers of polyvinyl alcohol, sodium alginate, polyacrylamide, and sodium p-toluenesulfonate, and also includes one or more blends or copolymers of lithium chloride, calcium chloride, graphene oxide, and hydrophilic nano-titanium dioxide.

[0060] A method for preparing a low-selectivity vacuum dehumidification membrane, characterized in that the method includes the following steps:

[0061] (I) Prepare the casting solution required to form the active layer; add one or more of polyvinyl alcohol, sodium alginate, polyacrylamide, and sodium p-toluenesulfonate into a beaker, slowly add distilled water into the beaker, place the beaker in a constant temperature water bath at 80~95℃ and heat for 1~5h, and stir the substance in the beaker continuously.

[0062] (II) After the mixture in the beaker cools to 10~30℃, add one or more of lithium chloride, calcium chloride, graphene oxide, and hydrophilic nano titanium dioxide to the beaker. Then place the beaker in a constant temperature water bath at 10~40℃ and stir the substance in the beaker continuously for 1~5 hours.

[0063] (III) Allow to stand for 10-1500 minutes to degas and form a casting solution;

[0064] (IV) A support layer is made of aluminum, stainless steel or carbon steel. A hydrophobic layer made of one or more of hydrophobic textile fabric, PTFE membrane or hydrophobic nonwoven fabric is adhered to the upper surface of the support layer. Then, a hydrophilic layer made of one or more of nylon mesh, hydrophilic coating or hydrophilic nonwoven fabric is adhered to the upper surface of the hydrophobic layer. It is necessary to ensure that the support-hydrophobic-hydrophilic membrane surface formed after the hydrophilic layer is adhered is flat and smooth, without bulging.

[0065] (V) Apply the casting solution prepared in step (III) evenly to the support-hydrophobic-hydrophilic membrane prepared in step (IV), with an active layer coating thickness of 10 mm to 500 mm. Transfer the coated membrane to a constant temperature oven and dry it at 40 to 80°C for 5 to 15 minutes.

[0066] (VI) Place the membrane prepared in step (V) on a horizontal and smooth glass plate, and apply the casting solution prepared in step (III) to the membrane prepared in step (V) again evenly. The coating thickness is 10 mm to 500 mm. Transfer the membrane after recoating to a constant temperature oven and dry it at 40 to 80°C for 5 to 15 minutes.

[0067] (VII) Place the membrane prepared in step (VI) on a horizontal and smooth glass plate, and apply the casting solution prepared in step (III) evenly to the membrane prepared in step (VI) again. The coating thickness is 10 mm to 500 mm. Transfer the membrane after recoating to a constant temperature oven and dry it at 40 to 80°C for 5 to 15 minutes.

[0068] (VIII) Thus, a low-selectivity vacuum dehumidification membrane is obtained.

[0069] like Figure 3 , Figure 4 and Figure 5 As shown, a vacuum membrane dehumidification assembly for testing the performance of a vacuum dehumidification membrane is characterized in that: the vacuum membrane dehumidification assembly includes a feeding side 4 and a permeation side 5, and the vacuum dehumidification membrane is located between the feeding side 4 and the permeation side 5. An upper cover plate 3 is sealed and installed above the feeding side, and a lower cover plate 6 is sealed and installed below the permeation side.

[0070] The feeding side has at least two holes, one for humid air inlet 4-3 and the other for humid air outlet 4-4. The inlet and outlet are located on the same side.

[0071] The feed side is provided with several partitions perpendicular to the membrane to increase the residence time of humid air on the feed side. The thickness of the partitions is 0.2mm to 2mm.

[0072] To ensure a good seal and facilitate disassembly during testing, grooves 4-1 and 5-1 are provided at the connection between the feeding side 4 and the permeation side 5 for installing sealing gaskets. The width of the grooves is 0.5mm to 2mm, and the depth is 0.5mm to 2mm.

[0073] The feeding side and the permeation side are each provided with a low-selectivity vacuum dehumidification membrane mounting platform 4-2 and 5-2, respectively. The length and width of the platform are 0.5mm to 5mm larger than the length and width of the vacuum dehumidification membrane, and the depth of the platform is 0.5mm to 5mm.

[0074] The permeation side 5 has at least one hole 5-3 connected to the suction end of the vacuum pump.

[0075] The inlet 4-3 of the humid air is connected to the inlet temperature and humidity sensor 8-2, which is connected to the inlet flow meter 9-2, and the inlet flow meter 9-2 is connected to the air pump 7-1; the outlet 4-4 of the humid air is connected to the outlet temperature and humidity sensor 8-1, which is connected to the outlet flow meter 9-1; the hole 5-3 on the permeation side is connected to the vacuum pressure gauge 10, which is connected to the vacuum pump 7-2.

[0076] like Figure 6As shown, a test method for a low-selectivity vacuum dehumidification membrane is characterized by the following steps:

[0077] (I) Install the prepared low-selectivity vacuum dehumidification membrane 1 on the following... Figure 3 , Figure 4 , Figure 5 The vacuum membrane dehumidification assembly shown is placed inside the vacuum membrane dehumidification assembly, and the entire vacuum membrane dehumidification assembly 11 with the low-selectivity vacuum dehumidification membrane installed is clamped and fixed with G-type clamps;

[0078] (II) Turn on air pump 7-1 and vacuum pump 7-2. Air pump 7-1 is used to pump humid air into humid air inlet 4-3 to the feed side 4, and vacuum pump 7-2 is used to draw air from the permeation side 5. When the values ​​of vacuum pressure gauge 10, inlet flow meter 9-2, outlet flow meter 9-1, inlet humidity temperature sensor 8-2, and outlet humidity temperature sensor 8-1 are relatively stable, use inlet flow meter 9-2, outlet flow meter 9-1, inlet humidity temperature sensor 8-2, and outlet humidity temperature sensor 8-1 to record the inlet humid air mass flow rate, outlet humid air mass flow rate, inlet temperature, outlet temperature, inlet relative humidity, and outlet relative humidity of the vacuum membrane dehumidification assembly 11 with the low-selectivity vacuum dehumidification membrane 1 installed. Use pressure gauge 10 to record the vacuum degree of the permeation side 5. Based on the measured inlet temperature and inlet relative humidity data, consult the humid air enthalpy-humidity chart to easily obtain the inlet moisture content. Based on the measured outlet temperature and outlet relative humidity data, consult the humid air enthalpy-humidity chart. The outlet moisture content is easily obtained; the measured inlet temperature and outlet temperature are arithmetically averaged to obtain the average temperature on the supply side, and the average saturated water vapor partial pressure on the supply side is obtained by referring to the humid air moisture content chart; the measured inlet relative humidity and outlet relative humidity are arithmetically averaged to obtain the average relative humidity on the supply side; the average saturated water vapor partial pressure on the supply side is multiplied by the average relative humidity on the supply side to obtain the average water vapor partial pressure on the supply side; based on the measured or consulted values ​​of inlet humid air mass flow rate, outlet humid air mass flow rate, inlet moisture content, and outlet moisture content, the inlet dry air mass flow rate and outlet dry air mass flow rate are easily obtained by using formulas (1) and (2) in combination.

[0079] (III) Calculate the water vapor permeability, selectivity coefficient, and dehumidification COP of the low-selectivity vacuum dehumidification membrane; calculate using formulas (3), (4), and (5), respectively.

[0080] (IV) The parameters calculated in step (III) are used to determine whether the performance of the tested low-selectivity vacuum dehumidification membrane is qualified:

[0081] The water vapor permeability calculated by formula (3) represents the amount of water vapor passing through the membrane under the conditions of unit area, unit water vapor partial pressure, and unit time. When its value is greater than 1×10 -7 mol / (Pa m 2 s), then it indicates that the dehumidification capacity of the tested low-selectivity vacuum dehumidification membrane is qualified; and the larger its value, the stronger the dehumidification capacity of the tested vacuum dehumidification membrane; the water vapor permeability calculated by formula (3) is actually the equivalent value of water vapor permeability coefficient when the permeation side pressure is 0Pa.

[0082] The selectivity coefficient calculated by formula (4) represents the selectivity of the membrane to water vapor. When its value is greater than 0.01, it indicates that the selectivity of the tested low-selectivity vacuum dehumidification membrane is qualified; and the higher its value, the stronger the selectivity of the tested vacuum dehumidification membrane.

[0083] The dehumidification COP calculated by formula (5) represents the dehumidification latent heat of the vacuum pump per unit power consumption. When its value is greater than 1, it indicates that the energy-saving performance of the tested low-selectivity vacuum dehumidification membrane is qualified; and the larger its value is, the better the energy-saving performance of the tested vacuum dehumidification membrane.

[0084]

[0085]

[0086]

[0087]

[0088]

[0089] Among them, K w Water vapor permeability, expressed in mol / (Pa·m) 2 s); K a Air permeability, expressed in mol / (Pa·m) 2 s); This indicates the inlet dry air mass flow rate, in kg / s; The mass flow rate of dry air at the outlet is expressed in kg / s; m in Indicates the inlet humid air mass flow rate, kg / s; m out ω represents the outlet humid air mass flow rate, kg / s; in Indicates inlet moisture content, kg / kg; ω out Indicates the moisture content at export, kg / kg; p w q represents the average partial pressure of water vapor on the feed side, in Pa; lThe latent heat of vaporization of water is represented by 43942 J / mol, which can be approximated in engineering terms; S represents the membrane dehumidification area, in m². 2 M a M represents the relative molecular mass of air, in kg / mol. w S represents the relative molecular mass of water vapor, in kg / mol. w / a This represents the selectivity coefficient of the membrane.

[0090] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a low-selectivity vacuum dehumidification membrane, characterized in that: The low-selectivity vacuum dehumidification membrane comprises a support layer, a hydrophobic layer, a hydrophilic layer, and an active layer; the hydrophobic layer is disposed on the support layer, the hydrophilic layer is adhered to the hydrophobic layer, and the active layer is uniformly coated on the hydrophilic layer; the hydrophobic layer has good water-blocking and air-permeable properties, the hydrophilic layer has good air permeability, and the active layer is a water vapor selectively permeable layer containing easily absorbent components. The method includes the following steps: (I) Prepare the casting solution required to form the active layer; add one or more of polyvinyl alcohol, sodium alginate, polyacrylamide, and sodium p-toluenesulfonate into a beaker, slowly add distilled water into the beaker, place the beaker in a constant temperature water bath at 80~95℃ and heat for 1~5h, and stir the substance in the beaker continuously. (II) After the mixture in the beaker cools to 10~30℃, add one or more of lithium chloride, calcium chloride, graphene oxide, and hydrophilic nano titanium dioxide to the beaker. Then place the beaker in a constant temperature water bath at 10~40℃ and stir the substance in the beaker continuously for 1~5 hours. (III) Allow to stand for 10-1500 minutes to degas and form a casting solution; (IV) A support layer is made of aluminum, stainless steel or carbon steel. A hydrophobic layer made of one or more of hydrophobic textile fabric, PTFE membrane or hydrophobic nonwoven fabric is adhered to the upper surface of the support layer. Then, a hydrophilic layer made of one or more of nylon mesh, hydrophilic coating or hydrophilic nonwoven fabric is adhered to the upper surface of the hydrophobic layer. It is necessary to ensure that the support-hydrophobic-hydrophilic membrane surface formed after the hydrophilic layer is adhered is flat and smooth, without bulging. (V) Apply the casting solution prepared in step (III) evenly to the support-hydrophobic-hydrophilic membrane prepared in step (IV), with the active layer coating thickness being 10um~500um. Transfer the coated membrane to a constant temperature oven and dry it at 40~80℃ for 5~15min. (VI) Place the membrane prepared in step (V) on a horizontal and smooth glass plate, and apply the casting solution prepared in step (III) to the membrane prepared in step (V) again evenly. The coating thickness is 10um~500um. Transfer the membrane after recoating to a constant temperature oven and dry it at 40~80℃ for 5~15min. (VII) Place the membrane prepared in step (VI) on a horizontal and smooth glass plate, and apply the casting solution prepared in step (III) to the membrane prepared in step (VI) again evenly. The coating thickness is 10um~500um. Transfer the membrane after recoating to a constant temperature oven and dry it at 40~80℃ for 5~15min. (VIII) Thus, a low-selectivity vacuum dehumidification membrane is obtained.

2. A vacuum membrane dehumidification assembly for testing vacuum dehumidification performance, characterized in that: The vacuum membrane dehumidification assembly includes a feeding side and a permeation side, and the low-selectivity vacuum dehumidification membrane prepared by the method of preparing the low-selectivity vacuum dehumidification membrane as described in claim 1 is located between the feeding side and the permeation side; an upper cover plate is sealed and installed above the feeding side, and a lower cover plate is sealed and installed below the permeation side. The feeding side has at least two holes, one for humid air inlet and the other for humid air outlet; the inlet and outlet are located on the same side. The feed side is provided with several partitions perpendicular to the membrane to increase the residence time of humid air on the feed side. The thickness of the partitions is 0.2mm to 2mm. A groove is provided at the contact point between the feeding side and the permeation side for installing a sealing gasket. The width of the groove is 0.5mm to 2mm and the depth is 0.5mm to 2mm. The feeding side and the permeation side each provide a platform for installing a low-selectivity vacuum dehumidification membrane. The length and width of the platform are 0.5mm to 5mm larger than the length and width of the vacuum dehumidification membrane, respectively, and the depth of the platform is 0.5mm to 5mm. The permeation side has at least one hole that connects to the suction end of the vacuum pump.

3. The vacuum membrane dehumidification assembly as described in claim 2, characterized in that: The inlet of the humid air is connected to an inlet temperature and humidity sensor, which is connected to an inlet flow meter, and the inlet flow meter is connected to an air pump; the outlet of the humid air is connected to an outlet temperature and humidity sensor, which is connected to an outlet flow meter; the orifice on the permeation side is connected to a vacuum pressure gauge, which is connected to a vacuum pump.

4. A test method for a low-selectivity vacuum dehumidification membrane, characterized in that: The method includes the following steps: (I) The prepared low-selectivity vacuum dehumidification membrane is installed in the vacuum membrane dehumidification assembly as described in any one of claims 2-3, and the entire vacuum membrane dehumidification assembly with the low-selectivity vacuum dehumidification membrane installed is clamped and fixed with G-type clamps; (II) Turn on the air pump and vacuum pump. The air pump is used to pump humid air into the humid air inlet to the feed side, and the vacuum pump is used to draw air from the permeate side. When the vacuum pressure gauge reading is relatively stable, use the inlet flow meter, outlet flow meter, inlet humidity and temperature sensor, and outlet humidity and temperature sensor to record the inlet humid air mass flow rate, outlet humid air mass flow rate, inlet temperature, outlet temperature, inlet relative humidity, and outlet relative humidity flowing through the vacuum membrane dehumidification component. Use the vacuum pressure gauge to record the vacuum degree on the permeate side. Based on the measured inlet temperature and inlet relative humidity data, consult the humid air enthalpy-humidity chart to easily obtain the inlet moisture content. Based on the measured outlet temperature and outlet relative humidity data, consult the humid air enthalpy-humidity chart. The outlet moisture content can be easily obtained from the graph; the average temperature on the supply side is obtained by arithmetically averaging the measured inlet and outlet temperatures, and the average saturated water vapor partial pressure on the supply side is obtained by referring to the humid air moisture content graph; the average relative humidity on the supply side is obtained by arithmetically averaging the measured inlet and outlet relative humidity; the average water vapor partial pressure on the supply side is obtained by multiplying the average saturated water vapor partial pressure on the supply side with the average relative humidity on the supply side; the inlet dry air mass flow rate and outlet dry air mass flow rate can be easily obtained by combining the measured or consulted values ​​of inlet humid air mass flow rate, outlet humid air mass flow rate, inlet moisture content, and outlet moisture content using formulas (1) and (2); (III) Calculate the water vapor permeability, selectivity coefficient, and dehumidification COP of the low-selectivity vacuum dehumidification membrane; calculate using formulas (3), (4), and (5), respectively. (IV) The parameters calculated in step (III) are used to determine whether the performance of the tested low-selectivity vacuum dehumidification membrane is qualified: The water vapor permeability calculated by formula (3) represents the amount of water vapor passing through the membrane under the conditions of unit area, unit water vapor partial pressure, and unit time. When its value is greater than 1×10 -7 mol / (Pa m 2 If s), it indicates that the dehumidification capacity of the tested low-selectivity vacuum dehumidification membrane is qualified; and the larger the value, the stronger the dehumidification capacity of the tested vacuum dehumidification membrane; the water vapor permeability calculated by formula (3) is actually the equivalent value of water vapor permeability coefficient when the permeation side pressure is 0Pa. The selectivity coefficient calculated by formula (4) represents the selectivity of the membrane to water vapor. When its value is greater than 0.01, it indicates that the selectivity of the tested low-selectivity vacuum dehumidification membrane is qualified; and the higher its value, the stronger the selectivity of the tested vacuum dehumidification membrane. The dehumidification COP calculated by formula (5) represents the dehumidification latent heat of the vacuum pump per unit power consumption. When its value is greater than 1, it indicates that the energy-saving performance of the tested low-selectivity vacuum dehumidification membrane is qualified; and the larger its value is, the better the energy-saving performance of the tested vacuum dehumidification membrane. （1） （2） （3） （4） （5） in, Water vapor permeability, expressed in mol / (Pa·m) 2 s); Air permeability, expressed in mol / (Pa·m) 2 s); This indicates the inlet dry air mass flow rate, in kg / s; This indicates the dry air mass flow rate at the outlet, in kg / s. This indicates the inlet humid air mass flow rate, in kg / s; The mass flow rate of the outlet moist air is expressed in kg / s. Indicates inlet moisture content, kg / kg; The moisture content at export is expressed in kg / kg. This represents the average partial pressure of water vapor on the feed side, in Pa. The latent heat of vaporization of water can be approximated as 43942 J / mol in engineering. S Indicates the membrane dehumidification area, m 2 ; M a The relative molecular mass of air is expressed in kg / mol. M w The relative molecular mass of water vapor is expressed in kg / mol. Indicates the selectivity coefficient of the membrane; This indicates the power of the vacuum pump, expressed in W.

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