Method for calculating actual heat leakage amount and storage heat leakage amount of low-temperature heat insulation container

Abstract

The invention provides a method for calculating the actual heat leakage amount and the storage heat leakage amount of a low-temperature heat-insulating container, and the method is used for distinguishing the difference between the heat leakage amounts according to the heat transfer analysis of the low-temperature heat-insulating container, and analyzing and calculating the actual heat leakage amount and the storage heat leakage amount based on the daily evaporation rate value of the low-temperature heat-insulating container. The vacuum insulation performance of the low-temperature insulation container can be reflected.

Description

Technical Field

[0001] The invention belongs to the technical field of low-temperature liquid storage, and in particular relates to a method for calculating actual heat leakage and stored heat leakage of a low-temperature insulation container. Background Art

[0002] With the rapid development of the domestic cryogenic liquid storage industry in the past decade, many companies use liquid cryogenic storage containers to replace high-pressure normal temperature storage containers. They have the advantages of large storage capacity and higher safety. For example, LNG (liquefied natural gas) replaces CNG on large transport vehicles, and LO2 (liquid oxygen) replaces high-pressure normal temperature oxygen cylinders in hospitals, which has strongly promoted the development and application of domestic low-insulation containers. During the use of cryogenic insulation containers, daily evaporation measurements need to be carried out regularly to detect the heat leakage of cryogenic insulation containers during use and storage, reflect their vacuum insulation performance, and ensure the safe use of cryogenic insulation containers. Summary of the invention

[0003] To solve the above problems, the present invention provides a method for calculating the actual heat leakage and storage heat leakage of a low-temperature insulation container. The actual heat leakage and storage heat leakage are obtained by analyzing and calculating the daily evaporation rate measurement value of the low-temperature insulation container, providing a reliable basis for scientifically evaluating the performance of the low-temperature insulation container.

[0004] A method for calculating the actual heat leakage and storage heat leakage of a low-temperature insulation container. The actual heat leakage Q of a low-temperature insulation container during the daily evaporation rate measurement process t1 The calculation method is as follows:

[0005] Q t1 =Q WG +Q WL

[0006] Total heat leakage Q of low temperature insulation container under storage condition t2 The calculation method is as follows:

[0007] Q t2 =0.5Q WG +Q WL

[0008] Among them, Q WG Q is the heat absorbed by the gas inside the cryogenic insulation container from the inner wall part of the cryogenic insulation container in contact with the gas, and the inner wall part in contact with the gas includes the vertical inner side wall in contact with the gas and the inner wall of the top head; WL The heat absorbed by the liquid inside the low-temperature insulation container from the part of the inner wall in contact with the liquid and the part of the inner wall in contact with the gas in the low-temperature insulation container, and the part of the inner wall in contact with the liquid includes the vertical inner side wall in contact with the liquid and the bottom inner wall.

[0009] Furthermore, Q WG The calculation method is as follows:

[0010] Q WG =m VG (h GE -h V )

[0011] Among them, m VG is the gas mass discharged from the cryogenic insulation container during the daily evaporation rate measurement, h GE is the enthalpy of the gas discharged from the cryogenic insulation container during the daily evaporation rate measurement, h V It is the enthalpy value corresponding to the evaporation of the liquid inside the low-temperature insulation container into saturated gas;

[0012] Furthermore, Q WG The calculation method is as follows:

[0013]

[0014] Where D is the inner diameter of the cryogenic insulation container, H is the inner height of the cryogenic insulation container, Le is the liquid level inside the cryogenic insulation container, T E is the ambient temperature of the low temperature insulation container, T V is the temperature of saturated gas, a is the set linear slope, R out-G It is the thermal resistance of heat transfer between gas and low-temperature insulation container.

[0015] Furthermore, Q WL The calculation method is as follows:

[0016] Q WL =m VG (h V -h L )

[0017] Among them, m VG is the gas mass discharged from the cryogenic insulation container during the daily evaporation rate measurement, h V is the enthalpy value corresponding to the evaporation of the liquid inside the low-temperature insulation container into saturated gas, h L is the enthalpy of the liquid inside the cryogenic insulated container.

[0018] Furthermore, Q WG The calculation method is as follows:

[0019]

[0020] Where D is the inner diameter of the cryogenic insulation container, H is the inner height of the cryogenic insulation container, Le is the liquid level inside the cryogenic insulation container, △T out-L is the temperature difference between the inner wall in contact with the liquid and the liquid, Rout-L is the thermal resistance of heat transfer between liquid and low temperature insulation container, δ is the thickness of the heat conduction cross-sectional area of ​​low temperature insulation container, λ GL is the average thermal conductivity of the inner wall of the low-temperature insulation container and the multi-layer insulation material that constitutes the inner wall along the wall direction, and a is the set linear slope

[0021] Beneficial effects:

[0022] The present invention provides a method for calculating the actual heat leakage and storage heat leakage of a low-temperature insulation container. According to the heat transfer analysis of the low-temperature insulation container, the differences between various heat leakages are distinguished. Based on the daily evaporation rate value of the low-temperature insulation container, a method for analyzing and calculating the actual heat leakage and storage heat leakage is established, which can reflect the vacuum insulation performance of the low-temperature insulation container. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The daily evaporation rate measurement principle diagram provided by the present invention;

[0024] Figure 2 A schematic diagram of heat transfer of the gas portion of the cryogenic insulated gas cylinder provided by the present invention;

[0025] Figure 3 A schematic diagram of heat transfer in the liquid part of a cryogenic insulated gas cylinder provided by the present invention;

[0026] Figure 4 The heat leakage analysis diagram of the low insulation provided by the present invention;

[0027] 1- cryogenic liquid, 2- evaporating liquid, 3- gas, 4- cryogenic insulated gas cylinder, 5- exhaust valve, 6- pressure sensor, 7- air bath vaporizer, 8- mass flow meter, 9- outlet valve, 10- exhaust gas. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application.

[0029] Low temperature insulation container and its daily evaporation rate measurement principle Figure 1 As shown, the cryogenic insulated container is composed of an outer shell, a vacuum insulation interlayer, an inner shell, and accessories such as pipeline valves. The daily evaporation measurement process of the cryogenic insulated container is as follows according to the requirements of relevant standards:

[0030] Fill the cryogenic insulation container to the test liquid level value, generally above 90% liquid level; open the vent valve to ensure that the gas phase of the cryogenic insulation container is connected to the ambient atmosphere; then let it stand for more than 48 hours to allow the cryogenic insulation container to enter a thermally stable state; finally, connect a gas mass flowmeter to the outlet of the vent valve to measure the daily evaporation rate of the cryogenic insulation container, and the measurement time is required to be no less than 24 hours. After the measurement, perform data processing on the daily evaporation rate as required to give the test value of the daily evaporation rate of the tested cryogenic insulation container.

[0031] It should be noted that the temperature of the gas portion of the cryogenic insulation container increases as the distance of the gas from the gas-liquid interface increases, and is much higher than the saturation temperature. Therefore, in the measurement of the daily evaporation rate of the cryogenic insulation container, the evaporation gas generated at the gas-liquid interface is saturated and has a very low temperature. However, when the evaporation gas flows outward through the gas phase space, it will exchange heat with the gas in the gas phase space, causing the temperature of the evaporation gas flowing through the gas phase to continue to rise, becoming unsaturated, and flowing out of the cryogenic insulation container. This part of the heat leakage is ignored by the current measurement method.

[0032] Based on this, the present invention provides a method for calculating the actual heat leakage and storage heat leakage of a low-temperature insulation container. The actual heat leakage Q of the low-temperature insulation container during the daily evaporation rate measurement process is t1 The calculation method is as follows:

[0033] Q t1 =Q WG +Q WL

[0034] Total heat leakage Q of low temperature insulation container under storage condition t2 The calculation method is as follows:

[0035] Q t2 =0.5Q WG +Q WL

[0036] Among them, Q WG Q is the heat absorbed by the gas inside the cryogenic insulation container from the inner wall part of the cryogenic insulation container in contact with the gas, and the inner wall part in contact with the gas includes the vertical inner side wall in contact with the gas and the inner wall of the top head; WL The heat absorbed by the liquid inside the low-temperature insulation container from the part of the inner wall in contact with the liquid and the part of the inner wall in contact with the gas in the low-temperature insulation container, and the part of the inner wall in contact with the liquid includes the vertical inner side wall in contact with the liquid and the bottom inner wall.

[0037] The following is a heat transfer analysis of gas and liquid in a low-temperature insulated container.

[0038] First, gas heat transfer analysis

[0039] In the daily evaporation rate measurement, the heat transfer analysis of the gas in the low-temperature insulation container is as follows: Figure 2 As shown, it includes two parts: the heat absorbed by the gas and the heat transferred to the outside.

[0040] (1) Heat transferred from the gas to the outside

[0041] like Figure 2 As shown in the figure, the heat transferred from the gas to the outside consists of two parts: the heat Q transferred from the gas to the liquid through the gas-liquid interface face , and the heat Q taken away by the exhaust gas in the daily evaporation rate measurement GE Since the gas temperature and liquid temperature at the gas-liquid interface are basically the same, the heat transferred is very small, so it can be considered that Q face = 0, which is not considered in the analysis; therefore, the heat transferred to the outside by the gas is the heat taken away by the evaporating gas leaving the low-temperature insulation container, which can be expressed as:

[0042] Q GE =m VG h GE (1)

[0043] In the equation, m VG is the gas mass discharged from the cryogenic insulation container during daily evaporation rate measurement, h GE is the enthalpy of the gas discharged from the low-temperature insulated container.

[0044] (2) Heat absorbed by the gas

[0045] like Figure 2 As shown in the figure, the heat absorbed by the gas includes two parts, namely, the heat Q absorbed by the gas through the inner wall and WG ; and the heat Q brought into the gas by the evaporating liquid Levap Among them, the heat absorbed by the gas through the inner wall comes from the heat transferred by the gas to the corresponding vertical outer wall and the heat transferred from the top head to the gas, which consists of two parts, namely:

[0046] Q WG =Q out-G (2)

[0047] The heat Q transferred from the gas to the outer wall out-G It can be expressed as:

[0048]

[0049] In the equation, A out-G Heat transfer area, ΔT out-G The average temperature difference between the environment and the gas, R out-G Thermal resistance during heat transfer. For ease of analysis, the head of the low-temperature insulation container can be regarded as a circle, and the heat transfer area of ​​the gas is:

[0050]

[0051] In the equation, D is the inner diameter of the cryogenic insulation container, H is the inner height of the cryogenic insulation container, and Le is the liquid level in the cryogenic insulation container.

[0052] (3) Gas temperature distribution

[0053] The gas temperature distribution in the cryogenic insulation container changes linearly with the liquid level. At any liquid level Le, the evaporating gas temperature T S-IN .

[0054]

[0055] For low-temperature insulated containers, the temperature outside is the ambient temperature. The ambient temperature changes very little during the test and can be considered constant, that is, the test ambient temperature T E =const. Then the temperature difference between the corresponding parts of the gas inside and outside the low-temperature insulation container is

[0056]

[0057] (4) Heat brought into the gas by the evaporating liquid

[0058] In the daily evaporation rate measurement, the evaporating liquid enters the gas through the gas-liquid interface. At the gas-liquid interface, the liquid and gas can be regarded as saturated. Therefore, the heat brought into the gas by the evaporating liquid can be expressed as:

[0059] Q Levap =M VG h V (9)

[0060] In the equation, M VG is the evaporation mass of the liquid, h V is the enthalpy value corresponding to the evaporation of liquid into saturated gas. In the daily evaporation rate measurement, since the density of the test medium gas is very small compared to the density of the liquid, it can be considered that the mass of the evaporated liquid is equal to the mass of the gas flowing out of the low-temperature insulation container, that is, M VG =m VG .

[0061] During the test, the temperature of the gas in the cryogenic insulation container is constant, so the gas energy equation is:

[0062] -Q GE +Q out-G +Q Levap =0 (10)

[0063] Substituting equations (1) and (9) into equation (10) yields:

[0064] Q out-G =Q GE-Q Levap =m VG (h GE -h V ) (11)

[0065] From equation (11), we can know that the evaporation rate m of the low-temperature insulation container can be measured. VG , liquid enthalpy value at saturation state h V , and the enthalpy of the gas under the head h GE , we can obtain the heat absorbed by the gas in the low-temperature insulation container. Substituting equations (4) and (8) into equation (11), we can obtain

[0066]

[0067] Second, liquid heat transfer analysis

[0068] Heat transfer of liquid in a cryogenically insulated container Figure 3 As shown, it includes two parts: the heat absorbed and the heat transferred outward:

[0069] (1) Heat absorbed by the liquid

[0070] The heat absorbed by the liquid consists of two parts: the leakage heat Q perpendicular to the liquid wall and the heat Q transferred from the liquid to the outer wall. out-L ; and because the wall temperature corresponding to the gas is higher than that of the liquid, the heat Q transferred to the liquid through the inner wall of the low-temperature insulation container and the insulation material GL .

[0071] Among them, the heat transferred by the liquid to the external wall is absorbed by the liquid because the temperature of the liquid is lower than the gas temperature and the heat absorption capacity is stronger than that of the gas. Therefore, the heat leakage of this part is completely absorbed by the liquid, which can be expressed as:

[0072]

[0073] In the formula, A L Heat transfer area, △T out-L The temperature difference between the liquid and the outer wall, that is, the temperature difference between the ambient temperature and the saturated liquid under atmospheric pressure. Since the ambient temperature is basically constant, it can be regarded as a constant. R out-L Thermal resistance during heat transfer. In the analysis, the head of the low-temperature insulation container is regarded as a circle. When the liquid level is Le, the heat transfer area of ​​the liquid is:

[0074]

[0075] Therefore, the total heat leakage absorbed by the liquid is:

[0076] Q WL =Q out-L +Q GL(15)

[0077] According to the above analysis, the heat Q transferred from the gas to the liquid by the inner wall and the insulation material is GL For the heat conduction process, the distance from the gas center to the liquid center in the low-temperature insulation container is H / 2. In summary, the heat Q transferred from the gas to the liquid by the inner wall and insulation material is GL It can be expressed as:

[0078]

[0079] In the equation, λ GL Average thermal conductivity of the inner wall and multi-layer insulation materials along the wall, ΔT GL is the temperature difference between the average temperature of the gas and the temperature of the liquid, and H / 2 is the distance between the center positions of the corresponding inner walls of the gas and liquid in the low-temperature insulation container.

[0080] From equation (7), we can see that the temperature difference between the average gas temperature and the liquid temperature is:

[0081]

[0082] (2) Heat removed by evaporating liquid

[0083] In the daily evaporation rate measurement, a small part of the liquid evaporates into gas, which reduces the energy of the liquid. The heat taken away by the evaporating liquid can be expressed as Q LE for:

[0084] Q LE =M VG (h V -h L ) (18)

[0085] h L is the enthalpy of the liquid.

[0086] After the test is stable, the temperature of the liquid part is constant, so the energy equation of the liquid is

[0087] Q out-L +Q GL -Q LE =0 (19)

[0088] Substituting equations (13), (14), (16), (17) and (18) into equation (19) yields:

[0089]

[0090] To simplify equation (20), the following definitions are made:

[0091]

[0092] qGL =πδλ GL a (22)

[0093] From equations (21) and (22), equation (20) is simplified to

[0094]

[0095] For a given test cryogenic insulation vessel, due to a, ΔT L , T E , T V is a constant, and the other parameters are the physical and geometric parameters of the material. Therefore, q out-L ,q GL Considered as a constant.

[0096] According to equation (23), q can be analytically solved by measuring the latent heat of vaporization of the evaporating liquid at different liquid levels. out-L ,q GL Parameters, and then calculate the heat Q absorbed by the liquid in the low-temperature insulation container through the wall out-L , and the heat Q transferred from the gas to the inner wall and insulation material GL .

[0097] Thirdly, the total heat leakage measured by the daily evaporation rate of the low-temperature insulation container

[0098] The total heat leakage of the low temperature insulation container is as follows Figure 4 shown.

[0099] According to the above heat transfer analysis of gas and liquid in the cryogenic insulation container, and equations (10) and (19), the total heat leakage of the cryogenic insulation container Q can be obtained: t for:

[0100] Q t =Q WG +Q WL =m VG (h GE -h L ) (twenty four)

[0101] According to equation (24), the total heat leakage of the cryogenic insulation container is composed of the heat absorbed by the gas and liquid Q WG and Q WL Therefore, the heat transferred and absorbed by each part of the cryogenic insulation container can be analyzed and solved by measuring the evaporation rate of the cryogenic insulation container and the temperature of the gas under the head.

[0102] Fourthly, the total heat leakage of the low temperature insulation container under storage conditions

[0103] For normal storage containers, the daily evaporation rate measurement process and the storage process are different. In the daily evaporation rate measurement, the evaporation gas is generated at the gas-liquid interface, and when it flows to the outlet of the low-temperature insulation container, the temperature is consistent with the temperature under the corresponding top head; in the actual storage process, the evaporation gas will diffuse into the entire gas phase space, and its temperature is consistent with the average temperature of the gas phase space. Therefore, for storage containers, The total heat leakage is Figure 4 shown.

[0104] Q t =0.5Q WG +Q WL (25)

[0105] In summary, the present invention provides the difference and relationship between the latent heat of vaporization for measuring daily evaporation rate and the actual heat leakage of the low-temperature insulation container based on the heat and mass transfer analysis of the low-temperature insulation container; the latent heat of vaporization of the evaporating gas in the daily evaporation rate measurement is equal to the product of the mass flow rate of the evaporating gas and the latent heat of vaporization per unit mass of the measured gas, and the actual heat leakage in the daily evaporation rate measurement of the low-temperature insulation container also requires the calculation of the heat absorbed by the evaporating gas flowing through the gas phase space, and the larger the gas phase space, the higher the corresponding gas temperature and the more heat absorbed.

[0106] Based on the heat and mass transfer analysis of the cryogenic insulation container, the present invention provides the difference and relationship between the vaporization latent heat for measuring the daily evaporation rate and the storage heat leakage of the cryogenic insulation container; during the storage process, the evaporated gas diffuses to the entire gas phase space; therefore, the total heat leakage includes the heat absorbed by the evaporated gas diffusing to the gas phase space. In the measurement of the daily evaporation rate of the cryogenic insulation container, the heat absorbed by the liquid comes from two parts, namely, the heat transferred from the liquid corresponding to the outer wall in the horizontal direction to the liquid and the heat transferred from the gas corresponding to the inner wall and the insulation material in the vertical direction to the liquid. The calculation method of the measured heat leakage, actual heat leakage and storage heat leakage of the daily evaporation rate of the cryogenic insulation container and the conversion relationship between them.

[0107] It can be seen that the advantages of the present invention compared with the existing analysis and calculation methods are: in the current daily evaporation rate measurement, the gas is considered to be in a saturated state and will not absorb heat during measurement and storage, causing the heat of the gas part of the low-temperature insulation container to be ignored during measurement and storage, resulting in a difference between the heat leakage obtained by the current measurement method and the actual heat leakage. The present invention distinguishes the differences between the various heat leakages based on the heat transfer analysis of the low-temperature insulation container, and constructs a method for calculating the actual heat leakage and storage heat leakage of the low-temperature insulation container based on the daily evaporation rate value.

[0108] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art may certainly make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for calculating the actual heat leakage and storage heat leakage of a low-temperature insulation container, characterized in that: The actual heat leakage Q of the low-temperature insulation container during the daily evaporation rate measurement process t1 The calculation method is as follows: Q t1 =Q WG +Q WL Total heat leakage Q of low temperature insulation container under storage condition t2 The calculation method is as follows: Q t2 =0.5Q WG +Q WL Among them, Q WG Q is the heat absorbed by the gas inside the cryogenic insulation container from the inner wall part of the cryogenic insulation container in contact with the gas, and the inner wall part in contact with the gas includes the vertical inner side wall in contact with the gas and the inner wall of the top head; WL The heat absorbed by the liquid inside the low-temperature insulation container from the part of the inner wall in contact with the liquid and the part of the inner wall in contact with the gas in the low-temperature insulation container, and the part of the inner wall in contact with the liquid includes the vertical inner side wall in contact with the liquid and the bottom inner wall.

2. The method for calculating the actual heat leakage and storage heat leakage of a low-temperature insulation container according to claim 1, characterized in that: Q WG The calculation method is as follows: Q WG =m VG (h GE -h V ) Among them, m VG is the gas mass discharged from the cryogenic insulation container during the daily evaporation rate measurement, h GE is the enthalpy of the gas discharged from the cryogenic insulation container during the daily evaporation rate measurement, h V It is the enthalpy value corresponding to the evaporation of the liquid inside the low-temperature insulation container into saturated gas.

3. A method for calculating actual heat leakage and stored heat leakage of a low-temperature insulation container as claimed in claim 2, characterized in that: Q WG The calculation method is as follows: Where D is the inner diameter of the cryogenic insulation container, H is the inner height of the cryogenic insulation container, Le is the liquid level inside the cryogenic insulation container, T E is the ambient temperature of the low temperature insulation container, T V is the temperature of saturated gas, a is the set linear slope, R out-G It is the thermal resistance of heat transfer between gas and low-temperature insulation container.

4. The method for calculating the actual heat leakage and storage heat leakage of a low-temperature insulation container according to claim 1, characterized in that: Q WL The calculation method is as follows: Q WL =m VG (h V -h L ) Among them, m VG is the gas mass discharged from the cryogenic insulation container during the daily evaporation rate measurement, h V is the enthalpy value corresponding to the evaporation of the liquid inside the low-temperature insulation container into saturated gas, h L is the enthalpy of the liquid inside the cryogenic insulated container.

5. A method for calculating actual heat leakage and stored heat leakage of a low-temperature insulation container as claimed in claim 4, characterized in that: Q WG The calculation method is as follows: Where D is the inner diameter of the cryogenic insulation container, H is the inner height of the cryogenic insulation container, Le is the liquid level inside the cryogenic insulation container, △T out-L is the temperature difference between the inner wall in contact with the liquid and the liquid, R out-L is the thermal resistance of heat transfer between liquid and low temperature insulation container, δ is the thickness of the heat conduction cross-sectional area of ​​low temperature insulation container, λ GL is the average thermal conductivity of the inner wall of the low-temperature insulation container and the multi-layer insulation material constituting the inner wall along the wall direction, and a is the set linear slope.

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