CN113237729A - VOCs (volatile organic compounds) trapping device and method for regulating heat transfer mode by utilizing air pressure change - Google Patents

VOCs (volatile organic compounds) trapping device and method for regulating heat transfer mode by utilizing air pressure change Download PDF

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CN113237729A
CN113237729A CN202110516725.6A CN202110516725A CN113237729A CN 113237729 A CN113237729 A CN 113237729A CN 202110516725 A CN202110516725 A CN 202110516725A CN 113237729 A CN113237729 A CN 113237729A
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vocs
trapping
cavity
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曾立民
郭鹏
于雪娜
崔金会
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Peking University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
    • G01N1/40—Concentrating samples
    • G01N1/405—Concentrating samples by adsorption or absorption
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
    • F25D31/00—Other cooling or freezing apparatus
    • F25D31/005—Combined cooling and heating devices
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
    • G01N1/40—Concentrating samples
    • G01N1/4022—Concentrating samples by thermal techniques; Phase changes

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Abstract

The invention discloses a VOCs (volatile organic compounds) trapping device and method for regulating and controlling heat transfer modes by utilizing air pressure change. During low-temperature adsorption, the cold block is in contact with the trapping component to enable the trapping component to be fully refrigerated to the specified temperature, and the pressure is controlled by the vacuum pump to ensure that the heat loss and the cold supply of the trapping trap are balanced, so that the trapping temperature is stable. When the pressure in the cavity is reduced to the limit during high-temperature analysis, the heat transfer mode in the cavity is mainly heat radiation, the heat transfer rate is slow, the transfer of cold and heat of the trapping component is reduced to the minimum, and the heating power of the trapping component is minimum; when the collecting component returns to the low-temperature adsorption state, the pressure in the cavity is increased, the heat transfer mode in the cavity mainly takes the heat transfer of the gas medium, the heat transfer rate is accelerated, the collecting component can quickly return to the temperature, and the utilization efficiency of cold energy is improved.

Description

VOCs (volatile organic compounds) trapping device and method for regulating heat transfer mode by utilizing air pressure change
Technical Field
The invention relates to the field of heat transfer control in an environment monitoring instrument, in particular to a control device and a method for adjusting the heat transfer mode in a sealing system by using air pressure change.
Background
In the theory of heat conduction, the heat transfer process can be divided into three types of gas heat transfer, liquid heat transfer and solid heat transfer according to different heat transfer media, and the solid heat transfer is divided into metal heat transfer and nonmetal heat transfer. The three heat conduction modes have different microscopic mechanisms, gas heat conduction is mainly completed through energy transfer when gas molecules collide due to thermal motion, and according to the gas molecular kinetic theory, the heat conductivity of a gas medium is as follows:
Figure BDA0003062586910000011
(v: root mean square velocity of gas molecules;. rho: gas density;. l: mean free path of gas molecules;. cv: gas molecule constant specific heat). When the temperature is unchanged, the thermal conductivity of the gas is less along with the change of the gas pressure under normal pressure, the gas density is reduced under the low-pressure condition that the gas pressure is less than 2600Pa, the mean free path is increased, the probability of mutual collision between molecules is reduced, the thermal conductivity is reduced along with the reduction of the pressure, and the heat can only be transferred through heat radiation in absolute vacuum.
In the field of environmental monitoring, enrichment and analysis of gaseous pollutants, particularly Volatile Organic Compounds (VOCs) in the atmosphere, are mainly realized through a low-temperature adsorption-high-temperature thermal desorption process, the process comprises two steps, wherein the first step is to reduce the temperature of a trapping trap to be below 150 ℃ below zero, a trapping component and a cold block are integrated together, the cold energy of the cold block can be sufficiently and quickly transferred to the trapping component, and after the refrigerating temperature is reached, the VOCs in the trapping component are converted from a gaseous state to a solid state to be adsorbed and collected; the second step is to raise the trap temperature to above 100 ℃, and the VOCs are completely thermally analyzed and then enter the subsequent analysis system. However, because the trapping component and the cold block are integrated together, when the trapping component is heated, the low-temperature cold block adjacent to the trapping component can cause the trapping component to have larger heating power and prolong the heating time of the trapping component, and the heated trapping component can also influence the stability of the cold source; similarly, when the trap member is returned to the low-temperature adsorption state, the hot trap member increases the cooling power of the cold source, which results in unnecessary energy waste and also prolongs the time of the adsorption heat analysis step. Therefore, in order to save the loss of the cooling and heating power of the system and to accelerate the time of the adsorption and thermal desorption steps, it is necessary to improve the heat transfer form between the trap member and the cooling and heating member to reduce the energy loss.
Disclosure of Invention
In view of the above problems, an object of the present invention is to provide a device and a method for trapping VOCs that change the heat transfer form between a trapping member and a cooling/heating member, so as to ensure that the heat trapping member affects the heating/cooling member as little as possible during adsorption-thermal desorption, thereby improving the overall energy utilization efficiency of the device.
The technical scheme of the invention is as follows:
a VOCs entrapment device, includes VOCs entrapment part, heating part, refrigeration part and atmospheric pressure regulation and control part, wherein: the air pressure regulating and controlling component comprises a sealed cavity, a vacuum pump, an inflating device, a first electromagnetic valve, a second electromagnetic valve and a vacuum gauge, wherein the vacuum pump is connected with the sealed cavity through a pipeline provided with the first electromagnetic valve so as to vacuumize the sealed cavity, the inflating device is connected with the sealed cavity through a pipeline provided with the second electromagnetic valve so as to inflate the sealed cavity, and the vacuum gauge is used for monitoring the vacuum degree in the sealed cavity; the refrigeration component comprises a cold block positioned in the sealed cavity and external refrigeration equipment; the heating part comprises a heating power supply, a heating connector and an electric wire for connecting the heating power supply and the heating connector; the main body of the VOCs trapping component is positioned in the sealing cavity and is in contact with the cold block in the sealing cavity, and the upper part of the VOCs trapping component penetrates out of the sealing cavity and is in contact with the heating joint.
In the VOCs catching device, the VOCs catching component mainly carries out enrichment and concentration operation on VOCs, and the VOCs are adsorbed at low temperature; at high temperature, VOCs resolve. The VOCs capture components may be one or more sets of capture tubes made of stainless steel or other composite materials. Preferably, a temperature sensor is mounted at the bottom of the VOCs trapping member, so that the temperature of the trapping member can be monitored in real time.
In above-mentioned VOCs trapping apparatus, the refrigeration part includes cold piece and outside refrigeration plant, and cold piece sets up in sealed intracavity. The heating device comprises a heating power supply, a heating connector and a plurality of electric wires. The heating joint is contacted with the upper part of the VOCs trapping component, the heating power supply is positioned outside the sealed cavity, and a loop is formed between the heating joint and the heating power supply through an electric wire.
In the device for capturing the VOCs, the air pressure regulating and controlling component comprises a sealed cavity, a vacuum pump, an inflating device, a vacuum gauge, an electromagnetic valve and the like. Preferably, the sealing cavity comprises a cavity body and a sealing cover, and the cavity body and the sealing cover are fixedly connected through screws or bolts to play a role in sealing. The pressure inside the sealed cavity is changed through inflation and deflation operations, so that the heat conductivity of the gas in the cavity is changed. The cavity body of the sealing cavity and the sealing cover can be made of composite materials such as polytetrafluoroethylene. The vacuum pump can carry out the evacuation to sealed chamber, and the vacuum gauge measures the vacuum degree in the sealed chamber. The inflation device can inflate the sealed cavity, and the gas content of the sealed cavity is improved. And sealing rings are arranged at the positions where the vacuum pump, the air charging device and the vacuum gauge are communicated with all pipelines of the sealing cavity and the trapping part penetrate through the sealing cover for sealing. The first electromagnetic valve can control whether the vacuum pump carries out vacuumizing operation on the sealed cavity or not according to requirements. When the low-temperature adsorption starts, the vacuum pump is started to vacuumize the sealed cavity, the vacuum gauge detects the air pressure in the sealed cavity in real time, and the switching electromagnetic valve is closed to stop vacuuming after the air pressure meets the requirement; when the thermal analysis step is carried out, the first electromagnetic valve is opened, the pressure in the sealed cavity is further reduced by using the vacuum pump, the heat conductivity of gas in the cavity is further reduced, and the temperature of the heating device has less influence on the cold block; after thermal desorption is completed and before the next low-temperature adsorption step is carried out, the second electromagnetic valve is opened, the sealed cavity is inflated, the pressure intensity in the cavity is increased, the heat conductivity of gas in the cavity is increased, the heat transfer rate between the cold block and the VOCs trapping component is accelerated, and the time for cooling the trapping component is shortened.
The invention also provides a method for enriching and analyzing volatile organic compounds in the atmosphere by using the VOCs trapping device, which comprises the following steps:
1) starting a vacuum pump to vacuumize the sealed cavity to enable the sealed cavity to reach a set vacuum degree, simultaneously starting refrigeration equipment to refrigerate the cold block, refrigerating the VOCs trapping component immediately, and entering a low-temperature adsorption process;
2) after VOCs are adsorbed at low temperature, stopping refrigerating, starting the vacuum pump again to vacuumize the sealed cavity to further reduce the air pressure in the sealed cavity, then starting the heating component to heat the VOCs trapping component, and entering a thermal desorption process;
3) and after thermal analysis is finished, stopping heating, and inflating the sealed cavity through the inflating device to accelerate the heat transfer rate between the cold block and the VOCs trapping component, so that the VOCs trapping component is rapidly cooled.
Preferably, the vacuum degree set in the step 1) is 0.1-10 pa.
Further, vacuumizing in the step 2) to reduce the vacuum degree in the sealing cavity to 0.01-10 pa.
In the step 3), preferably, the air is inflated by an inflating device, so that the air pressure in the sealing cavity reaches 5-50 pa.
In the method for enriching and analyzing VOCs by utilizing the air pressure change regulation and control heat transfer mode, the refrigerating component, the heating component, the trapping component and part of the air pressure regulation and control component are all positioned in the sealed cavity, and the air charging and discharging pipe and the electric wire are connected with external related equipment through the sealed cover. When the device works, the vacuum pump is started to vacuumize the sealed cavity to enable the sealed system to reach a set vacuum degree, meanwhile, the refrigeration equipment is started to refrigerate the cold block, and the trapping component is refrigerated immediately; during low-temperature adsorption, the VOCs in the trapping part are frozen and adsorbed; then, a thermal desorption process is carried out, the first electromagnetic valve is opened, the vacuum pump carries out vacuum pumping operation on the sealing system again, so that the pressure of the sealing system is further reduced, the density of gas in the cavity is reduced, the mean free path is increased, the thermal motion among molecules is weakened, and the number of molecular collision times is reduced, so that the heat exchange is reduced, the heat transfer mode between the hot trapping part and the cold block is mainly changed from gas medium heat transfer to thermal radiation heat transfer, the heat transfer effect is greatly reduced, the heat loss is reduced, and the uniformity of the temperature of the cold block is stabilized; before the next low-temperature adsorption heat analysis step is started, the air charging device is opened to charge air into the sealing cavity, the pressure in the sealing cavity is increased, the gas density is increased, the mean free path is reduced, the molecular thermal motion is enhanced, the heat exchange is increased, at the moment, the heat transfer mode in the sealing cavity is changed from mainly heat radiation to mainly gas medium heat transfer, the heat transfer rate is increased, the cold block can reduce the temperature of the trapping component more quickly, and the time resolution of the instrument can be improved.
Compared with the prior art, the invention has the following advantages:
1. the invention adopts the method of changing the air pressure in the sealed cavity to change the heat transfer mode in the cavity, reduces the power and simultaneously can improve the utilization efficiency of cold energy. When the device adsorbs at a low temperature, the cold block is in contact with the trapping component to enable the trapping component to be fully refrigerated to the specified temperature, and the pressure is controlled by the vacuum pump to ensure that the heat loss and the cold supply of the trapping trap are balanced, so that the trapping temperature is stable. When the pressure in the cavity is reduced to the limit during high-temperature analysis, the heat transfer mode in the cavity is mainly heat radiation, the heat transfer rate is slow, the transfer of cold and heat of the trapping component is reduced to the minimum, and the heating power of the trapping component is minimum; when the collecting component returns to the low-temperature adsorption state, the pressure in the cavity is increased, the heat transfer mode in the cavity mainly takes the heat transfer of the gas medium, the heat transfer rate is accelerated, the collecting component can quickly return to the temperature, and the utilization efficiency of cold energy is improved.
2. On the premise of ensuring good performance, the invention integrates the heating component, the refrigerating component, the collecting component and part of the air pressure regulating component together through the sealing system, and the air path and the electric wire are led out by the sealing cover, so that the device is simple and small and is easy to operate.
3. The present invention can perform adsorption thermal desorption operation using a plurality of trapping members.
Drawings
FIG. 1 is a schematic diagram of the overall construction of a VOCs capture device of the present invention;
wherein: 1: sealing the cavity body; 2: a sealing cover; 3: a set screw; 4: heating the joint; 5: a VOCs trapping member; 6: a vacuum gauge; 7: a vacuum pump; 8: a first solenoid valve; 9: a second solenoid valve; 10: a seal ring; 11: and (5) cooling.
Detailed Description
The invention is described in detail below with reference to the drawings and the implementation process.
As shown in fig. 1, the VOCs trapping apparatus of the present invention includes a VOCs trapping part 5, a cooling part, a heating part, and an air pressure adjusting part.
The VOCs trapping component 5 is a VOCs trapping pipe made of stainless steel or other composite materials, VOCs are adsorbed at low temperature, and VOCs are analyzed at high temperature and enter a subsequent analysis system for detection. The upper part of the VOCs trapping component 5 passes through the sealing cover 2 to be in contact with the heating joint 4 outside the sealed cavity, and the rest part is positioned inside the sealed cavity body 1 to carry out low-temperature adsorption-high-temperature thermal desorption operation. The VOCs trapping member 5 is sealed by a sealing ring 10 at a portion thereof passing through the sealing cover 2, thereby preventing the entry of outside air.
The refrigeration component comprises a cold block 11 and external refrigeration equipment, and the cold block 11 is positioned in the sealed cavity. The VOCs trapping member 5 is attached in contact with the cold block 11 in the sealed chamber, and the cold block 11 cools the VOCs trapping member 5 by heat transfer of the gas medium at the time of low-temperature adsorption. The heater block mainly includes heating power supply, heating joint 4 and a plurality of electric wire, and heating joint 4 contacts outside the sealed chamber with VOCs entrapment part 5, and when carrying out thermal analysis operation, heating power supply started, and heating joint 4 heats VOCS entrapment part 5. The air pressure adjusting assembly comprises a sealed cavity body 1, a sealing cover 2, a vacuum gauge 6, a vacuum pump 7 and an inflating device, wherein the sealed cavity body 1 and the sealing cover 2 are connected through a fixing screw 3 to form a sealed cavity; the vacuum pump 7 is connected with the sealing cavity through a pipeline provided with a first electromagnetic valve 8, the inflation device is connected with the sealing cavity through a pipeline provided with a second electromagnetic valve 9, the vacuum gauge 6 detects the air pressure in the sealing cavity in real time through a detection tube extending into the sealing cavity, and a sealing ring 10 is arranged at the position where each pipeline penetrates through the sealing cover to seal.
The atmospheric pressure regulation and control subassembly mainly changes the thermal conductivity of intracavity gas through the atmospheric pressure of regulation and control sealed intracavity, and then adjusts the form of intracavity heat transfer, and VOCs entrapment part 5 can reach appointed refrigeration temperature fast when guaranteeing to refrigerate, and hot VOCs entrapment part 5 influences the temperature of cold piece 11 as far as possible during the heating.
Taking the VOCs capture device shown in fig. 1 as an example, the first cryosorption-pyrolysis analysis operation is as follows: first, the first electromagnetic valve 8 is opened, the vacuum pump 7 is started to vacuumize the sealed cavity, the sealed system reaches a set vacuum degree, meanwhile, the refrigeration equipment is started to refrigerate the cold block 11, the VOCs trapping component 5 is refrigerated immediately and adsorbs VOCs at low temperature. And then, a thermal desorption process is carried out, the first electromagnetic valve 8 is opened, the vacuum pump 7 carries out vacuum pumping operation on the sealing system again, so that the pressure of the sealing system is further reduced, at the moment, the pressure in the sealing system is smaller than 5pa, the density of gas in the cavity is reduced, the mean free path is increased, and the thermal motion between molecules is weakened, so that the heat exchange efficiency is reduced, the heat transfer mode between the hot VOCs trapping part 5 and the cold block 11 is mainly changed from gas medium heat transfer to thermal radiation heat transfer, the heat transfer effect is greatly reduced, the heat loss is reduced, and the uniformity of the temperature of the cold block 11 is stabilized. When the VOCs trapping component 5 is heated to a low-temperature adsorption state, the electromagnetic valve 9 is opened to charge air into the sealed cavity, the pressure in the sealed cavity is increased, the gas density is increased, the mean free path is reduced, the molecular thermal motion is enhanced, the heat exchange is increased, at the moment, the heat transfer mode in the sealed cavity is mainly changed from heat radiation to gas medium heat transfer, the heat transfer rate is increased, the temperature of the trapping pipe can be reduced more quickly by the cold block 11, and the time resolution of the instrument can be improved.
The present invention has been described only in the above embodiments, and the structure and connection of the various parts may be changed, and the changes made according to the present invention should not be excluded from the scope of the present invention.

Claims (10)

1. A VOCs entrapment device, includes VOCs entrapment part, heating part, refrigeration part and atmospheric pressure regulation and control part, wherein: the air pressure regulating and controlling component comprises a sealed cavity, a vacuum pump, an inflating device, a first electromagnetic valve, a second electromagnetic valve and a vacuum gauge, wherein the vacuum pump is connected with the sealed cavity through a pipeline provided with the first electromagnetic valve so as to vacuumize the sealed cavity, the inflating device is connected with the sealed cavity through a pipeline provided with the second electromagnetic valve so as to inflate the sealed cavity, and the vacuum gauge is used for monitoring the vacuum degree in the sealed cavity; the refrigeration component comprises a cold block positioned in the sealed cavity and external refrigeration equipment; the heating part comprises a heating power supply, a heating connector and an electric wire for connecting the heating power supply and the heating connector; the main body of the VOCs trapping component is positioned in the sealing cavity and is in contact with the cold block in the sealing cavity, and the upper part of the VOCs trapping component penetrates out of the sealing cavity and is in contact with the heating joint.
2. The VOCs capture device of claim 1, wherein the VOCs capture components are one or more sets of capture tubes made of stainless steel or composite materials.
3. The VOCs capture device of claim 1, wherein a temperature sensor is mounted at the bottom of the VOCs capture assembly.
4. The VOCs trapping device of claim 1, wherein the sealed chamber comprises a chamber body and a sealed cover, and the chamber body and the sealed cover are fixedly connected by screws or bolts.
5. The VOCs trapping device of claim 4, wherein the vacuum pump, the inflator, and the vacuum gauge are each connected to the sealed chamber by a conduit passing through the sealing cap, and wherein a sealing ring is provided at each conduit and at a portion of the VOCs trapping member passing through the sealing cap.
6. The VOCs capture device of claim 1, wherein the sealed chamber is a polytetrafluoroethylene material.
7. A method for enriching and desorbing VOCs in the atmosphere by using the VOCs trapping device of any one of claims 1 to 6, comprising the steps of:
1) starting a vacuum pump to vacuumize the sealed cavity to enable the sealed cavity to reach a set vacuum degree, simultaneously starting refrigeration equipment to refrigerate the cold block, refrigerating the VOCs trapping component immediately, and entering a low-temperature adsorption process;
2) after VOCs are adsorbed at low temperature, stopping refrigerating, starting the vacuum pump again to vacuumize the sealed cavity to further reduce the air pressure in the sealed cavity, then starting the heating component to heat the VOCs trapping component, and entering a thermal desorption process;
3) and after thermal analysis is finished, stopping heating, and inflating the sealed cavity through the inflating device to accelerate the heat transfer rate between the cold block and the VOCs trapping component, so that the VOCs trapping component is rapidly cooled.
8. The method according to claim 7, wherein the degree of vacuum set in the step 1) is 0.1 to 10 pa.
9. The method according to claim 7, wherein the vacuum is applied in step 2) to reduce the vacuum degree in the sealed chamber to 0.01-10 pa.
10. The method according to claim 7, wherein the step 3) is carried out by inflating the gas through an inflating device so that the pressure in the sealed cavity reaches 5-50 pa.
CN202110516725.6A 2021-05-12 2021-05-12 VOCs (volatile organic compounds) trapping device and method for regulating heat transfer mode by utilizing air pressure change Pending CN113237729A (en)

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