CN111365606B - Method for determining optimal screen position of multi-screen heat-insulation liquid helium container - Google Patents

Method for determining optimal screen position of multi-screen heat-insulation liquid helium container Download PDF

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CN111365606B
CN111365606B CN202010336732.3A CN202010336732A CN111365606B CN 111365606 B CN111365606 B CN 111365606B CN 202010336732 A CN202010336732 A CN 202010336732A CN 111365606 B CN111365606 B CN 111365606B
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screen
liquid helium
neck
total length
temperature
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CN111365606A (en
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徐烈
孙恒
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Sichuan Benaji Liquid Nitrogen Biological Container Co ltd
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Chongqing Benaji Ultra Low Temperature Application Technology Research Institute Co ltd
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C1/00—Pressure vessels, e.g. gas cylinder, gas tank, replaceable cartridge
    • F17C1/12—Pressure vessels, e.g. gas cylinder, gas tank, replaceable cartridge with provision for thermal insulation
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C13/00—Details of vessels or of the filling or discharging of vessels
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2203/00—Vessel construction, in particular walls or details thereof
    • F17C2203/03—Thermal insulations
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2221/00—Handled fluid, in particular type of fluid
    • F17C2221/01—Pure fluids
    • F17C2221/014—Nitrogen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2250/00—Accessories; Control means; Indicating, measuring or monitoring of parameters
    • F17C2250/03—Control means
    • F17C2250/032—Control means using computers
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2260/00—Purposes of gas storage and gas handling
    • F17C2260/03—Dealing with losses
    • F17C2260/035—Dealing with losses of fluid
    • F17C2260/036—Avoiding leaks

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Filling Or Discharging Of Gas Storage Vessels (AREA)

Abstract

The invention provides a method for determining the optimal screen position of a multi-screen heat insulation liquid helium container, which comprises the steps of firstly setting the evaporation capacity of the liquid helium container, then calculating the radiant heat transfer capacity of the bottom surface of a bottle plug to liquid helium, and the heat transfer capacity of the bottom surface of the bottle plug for transferring helium vapor to a liquid surface, selecting a heat exchange proportional coefficient R as an iteration variable, sequentially calculating the screen hanging temperature and the screen hanging position of each transfer screen of the liquid helium container from inside to outside, finally judging whether the estimated total length of a neck pipe is matched with the actual total length of the neck pipe or not, if not, adjusting the value of the heat exchange proportional coefficient R, and continuing iterative calculation until the estimated total length of the neck pipe and the actual total length of the neck pipe are estimated, thereby obtaining the optimal screen position. The method for determining the optimal screen position of the multi-screen heat-insulating liquid helium container is simple, convenient and clear in meaning, high in calculation process efficiency and easy to converge, and can effectively reduce the evaporation capacity of liquid helium, minimize the heat leaked from the joint of the conduction screen and the neck pipe and prolong the storage time of the liquid helium.

Description

Method for determining optimal screen position of multi-screen heat-insulation liquid helium container
Technical Field
The invention relates to the technical field of liquid helium storage and transportation, in particular to a method for determining the optimal screen position of a multi-screen heat-insulation liquid helium container.
Background
Helium is widely used in the industrial field, plays an irreplaceable role in the fields of aerospace, national defense, low-temperature physics, gas phase analysis, welding, leakage detection, chemical vapor deposition, crystal growth, plasma dry etching, particle accelerators, low-temperature superconduction, nuclear magnetic resonance imaging and the like, and most of helium relates to storage and transportation of liquid helium. However, liquid helium is a liquefied gas which has a very low boiling point and very low latent heat of vaporization, is very easy to vaporize and is very difficult to store. The liquid helium has a large ratio of sensible heat to latent heat of vaporization, and therefore sensible heat can be recovered by utilizing this characteristic, heat leakage can be blocked, and the heat insulation performance can be improved. Therefore, a multi-screen heat insulation structure can be adopted, namely sensible heat of the evaporated gas on the neck pipe is introduced to the conduction screen through a small number of cooling screens, so that the temperature of the screen is reduced, heat leakage of the multi-screen heat insulation layers is reduced, and the overall heat insulation level of the liquid helium container is improved. Because of different evaporation capacity, different length and different thickness of the neck tube, the temperature distribution in the length direction of the neck tube is different, so the position of the conduction screen has great influence on the total heat leakage quantity passing through the liquid helium container. The invention provides a method for determining the optimal screen position of a multi-screen heat-insulating liquid helium container, which can determine the optimal screen position and minimize the heat leaked from the joint of a conduction screen and a neck pipe.
Disclosure of Invention
The invention provides a method for determining the optimal screen position of a multi-screen heat-insulating liquid helium container, which mainly solves the technical problems that: how to accurately determine the optimal screen position and minimize the heat leaked from the joint of the conduction screen and the neck pipe.
To solve the above technical problem, the present invention provides a method for determining an optimal screen position of a multi-screen thermal insulation liquid helium vessel, comprising:
s1: selecting an evaporation rate m set by a liquid helium container;
s2: calculating the amount of radiant heat transfer to the liquid helium through the bottom surface of the liquid helium vessel stopper and calculating the amount of heat transfer to the liquid surface as helium vapor through the bottom surface of the liquid helium vessel stopper;
s3: selecting a heat exchange proportionality coefficient R;
s4: sequentially calculating the temperature of each conducting screen hanging screen of the liquid helium container from inside to outside according to the evaporation rate m, the heat exchange proportionality coefficient R, the radiant heat transfer quantity and the heat conduction quantity, and calculating the hanging screen position of the conducting screen according to the temperature of the conducting screen hanging screen;
s5: hanging the temperature T of the current (i + 1) th conduction screeni+1And the temperature T of the outer shell of the liquid helium vesselfComparing and judging the Ti+1Whether or not T is greater than or equal tofIf yes, go to step S6; if not, turning to step S4, and calculating the temperature of the (i + 2) th conduction screen hanging position;
s6: calculating the estimated total length of the neck pipe based on the screen hanging positions of the 1 st to i th conduction screens;
s7: comparing the estimated total length of the neck with the actual total length of the neck, judging whether the estimated total length of the neck is matched with the actual total length of the neck, if so, turning to the step S8; if not, turning to the step S3, and adjusting the value of the heat exchange proportionality coefficient R; until the estimated total length of the neck pipe is matched with the actual total length of the neck pipe;
s8: and obtaining the optimal screen position of the liquid helium container based on the screen hanging positions of the conductive screens.
Optionally, the calculating the radiant heat transfer amount of the liquid helium through the bottom surface of the liquid helium container stopper includes calculating the radiant heat transfer amount according to the following formula (1):
Figure GDA0003275746090000021
in the formula, sigma is the radiation constant, epsilon is the radiance of bottle plug bottom surface, F is the radiation angle coefficient, S is the area of bottle plug bottom, TdIs the temperature of the bottom of the bottle stopper, T0Is the temperature of liquid helium.
Optionally, the calculating the heat transfer from the bottom surface of the liquid helium container stopper to the liquid surface by helium vapor includes calculating the heat transfer according to the following formula (2):
Figure GDA0003275746090000022
in the formula, the lambdaeIs the helium vapor equivalent thermal conductivity, L is the actual total length of the neck tube, L0Is the length of the bottle stopper.
Optionally, sequentially calculating the temperature of each conducting screen hanging screen of the liquid helium container from inside to outside according to the evaporation rate m, the heat exchange proportionality coefficient R, the radiant heat transfer amount and the heat transfer amount, and calculating the temperature of the 1 st conducting screen hanging screen according to the following formula (3):
Figure GDA0003275746090000031
in the formula, the LbIs the latent heat of vaporization of liquid helium, e0The radiance S of the 1 st conductive screen and the inner container0The delta T is the temperature difference between the temperature of the conduction screen and the temperature at the position of the hanging screen, and is the total area of the outer surface of the inner container; t is1- Δ T is the screen temperature of the 1 st conductive screen;
after the temperature of the screen hanging position of the ith screen is obtained, the temperature of the screen hanging position of the ith screen and the screen hanging position of the (i + 1) th screen is calculated according to the following formula (4):
Figure GDA0003275746090000032
in the formula, the HiIs the enthalpy value of helium at the temperature of the hanging screen of the ith conduction screen, H0Is the enthalpy of saturated helium,. epsiloniIs the emissivity between the (i + 1) th conductive screen and the (i) th conductive screen, SiIs the total area of the i-th conductive screen, TiThe temperature at the ith block of the conductive screen is measured.
Optionally, the calculating the screen hanging position of the conductive screen according to the temperature at the conductive screen hanging position includes calculating the screen hanging position of the 1 st conductive screen according to the following formula (5):
Figure GDA0003275746090000033
in the formula, the delta1The distance between the position of the screen of the 1 st conduction screen and the interface of the neck tube and the liner is lambda (T)0) The thermal conductivity of the neck tube material at the temperature of the liner is shown, wherein A is the cross-sectional area of the neck tube;
calculating the screen hanging position of the (i + 1) th conductive screen according to the following formula (6):
Figure GDA0003275746090000034
Figure GDA0003275746090000041
in the formula, the lambda (T)i) The thermal conductivity of the material of the neck pipe at the temperature of the ith conductive screen hanging screen is deltai+1And the distance between the screen hanging position of the (i + 1) th conductive screen and the screen hanging position of the ith conductive screen is obtained.
Optionally, judging the Ti+1Greater than or equal to TfWhen, still include: let Ti+1＝TfAnd n is i +1, and the screen hanging position delta of the i +1 th conduction screen is determined according to the following formula (7)i+1Corrected to deltan：
Figure GDA0003275746090000042
In the formula, the TfIs the shell temperature of the liquid helium vessel, saidnThe distance between the last calculation screen and the screen hanging position of the ith conduction screen is HfIs the enthalpy of helium at the temperature of the enclosure.
Optionally, calculating the estimated total length of the neck pipe based on the screen hanging positions of the 1 st to i th conduction screens includes calculating the estimated total length L of the neck pipe according to the following formula (8)P：
Figure GDA0003275746090000043
Optionally, comparing the estimated total length of the neck pipe with the actual total length of the neck pipe, and determining whether the estimated total length of the neck pipe is matched with the actual total length of the neck pipe comprises:
when the difference value between the estimated total length of the neck and the actual total length of the neck is judged to be within a set threshold range, judging that the estimated total length of the neck is matched with the actual total length of the neck; and on the contrary, judging that the estimated total length of the neck pipe is not matched with the actual total length of the neck pipe.
Optionally, when it is determined that the estimated total length of the neck pipe is not matched with the actual total length of the neck pipe, adjusting the value of the heat exchange proportionality coefficient R includes:
when the estimated total length of the neck pipe is larger than the actual total length of the neck pipe, the value of the heat exchange proportionality coefficient R is reduced; and when the estimated total length of the neck pipe is smaller than the actual total length of the neck pipe, increasing the value of the heat exchange proportionality coefficient R.
Optionally, when it is determined that the estimated total length of the neck pipe is not matched with the actual total length of the neck pipe, adjusting the value of the heat exchange proportionality coefficient R includes calculating the adjusted heat exchange proportionality coefficient according to the following formula (9):
Figure GDA0003275746090000051
in the formula, the RNAnd t is a relaxation coefficient for the adjusted heat exchange proportionality coefficient.
Alternatively, Δ T is 6K for a copper conductive shield and 16K for an aluminum conductive shield.
Optionally, the shell temperature TfSimplified to ambient temperature Te。
Optionally, the shell temperature TfTaking values according to the following formula (10):
Figure GDA0003275746090000052
in the formula, the TeIs ambient temperature, said SfIs the surface area of the shell, and the alpha is the natural convection heat transfer coefficient of air.
Optionally, the natural convection heat transfer coefficient α of the air is 5-15.
Optionally, the initial value of the heat exchange proportionality coefficient R is within the range of 0.15-0.3.
The present invention also provides a computer readable storage medium having one or more programs stored thereon that are executable by one or more processors to perform the steps of the method for determining an optimal screen position for a multi-screen insulated liquid helium vessel as described above.
The invention has the beneficial effects that:
according to the method for determining the optimal screen position of the multi-screen heat-insulation liquid helium container, firstly, the evaporation capacity of the liquid helium container is set, then the radiant heat transfer capacity of the bottom surface of the bottle stopper to liquid helium and the heat transfer capacity of the bottom surface of the bottle stopper conducted to the liquid level by helium vapor are calculated, a heat exchange proportional coefficient R is selected as an iteration variable, the screen hanging temperature and the screen hanging position of each conducting screen of the liquid helium container are sequentially calculated from inside to outside, finally, whether the estimated total length of the neck pipe is matched with the actual total length of the neck pipe or not is judged, if the estimated total length of the neck pipe is not matched with the actual total length of the neck pipe, the value of the heat exchange proportional coefficient R is adjusted, iterative calculation is continued until the estimated total length of the neck pipe and the actual total length of the neck pipe are estimated, and therefore the optimal screen position is obtained. The method for determining the optimal screen position of the multi-screen heat-insulating liquid helium container is simple, convenient and clear in meaning, high in calculation process efficiency and easy to converge, and can effectively reduce the evaporation capacity of liquid helium, minimize the heat leaked from the joint of the conduction screen and the neck pipe and prolong the storage time of the liquid helium.
Drawings
FIG. 1 is a schematic diagram of a heat transfer network model of a liquid helium vessel according to a first embodiment of the present invention;
fig. 2 is a flowchart illustrating a method for determining an optimal screen position of a multi-screen thermal insulation liquid helium vessel according to a first embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following detailed description and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The first embodiment is as follows:
because the position of the conductive shield has a significant effect on the total heat leakage of the liquid helium vessel, it is necessary to design and determine the optimal shield position of the liquid helium vessel using multi-shield insulation to minimize the total heat leakage and achieve the optimal insulation performance. However, the heat transfer network inside the liquid helium container adopting multi-screen heat insulation is relatively complex, and the heat transfer network has radiation heat exchange between the conduction screen and between the conduction screen and the inner container, radiation heat exchange between the bottle stopper and the liquid level of the liquid helium, heat conduction along the neck pipe and heat conduction along the helium in the neck pipe, and the heat transfer processes are influenced mutually, and the temperature of each conduction screen and the position of the hanging screen have influence on each link of the heat exchange. And any node in the heat exchange calculation must strictly satisfy the heat balance equation. In the traditional calculation process, a satisfactory result is difficult to obtain through concise and rapid calculation on the basis of comprehensively considering the problems.
In the liquid helium container adopting multi-screen heat insulation, 4 main ways for transferring heat from the outside to the liquid helium in the container are heat leakage mainly through radiation heat exchange in a multi-screen structure, heat conduction through a neck tube, radiation heat exchange between a bottle stopper and the liquid level of the liquid helium and heat conduction along the helium in the neck tube. Wherein the heat leakage that mainly radiates the heat transfer through many screen structures does:
Figure GDA0003275746090000061
the heat conduction through the neck is:
Figure GDA0003275746090000062
the radiation heat exchange between the bottle stopper and the liquid helium level is as follows:
Figure GDA0003275746090000063
the heat transfer along the helium in the neck tube is:
Figure GDA0003275746090000071
on the sensible heat introduction conduction screen of evaporating gas on the neck pipe is shielded with the cooling screen in many screens adiabatic, the difference of radiation heat transfer volume between two adjacent screens is by evaporating gas's sensible heat absorption, evaporating gas's sensible heat is:
Δh＝mcpΔT；
based on the model of the heat transfer network of the multi-panel heat-insulating liquid helium container shown in fig. 1, it can be obtained that:
Figure GDA0003275746090000072
Figure GDA0003275746090000073
Figure GDA0003275746090000074
Figure GDA0003275746090000075
in order to solve the above mutually coupled heat transfer networks and obtain an optimal screen position for minimizing the total heat leakage of the multiple-screen heat-insulating liquid helium containers, the present invention provides a method for determining an optimal screen position of a multiple-screen heat-insulating liquid helium container, as shown in fig. 2, the method mainly includes:
s1: selecting an evaporation rate m set by a liquid helium container;
the unit is kg/s; the evaporation rate m is a performance index of the liquid helium container, and can be flexibly set according to the performance design requirement of the liquid helium container. It should be appreciated that after the evaporation rate m of the liquid helium vessel is selected, the relative positions of the outer shell and the inner container of the liquid helium vessel can be theoretically determined.
S2: calculating the radiant heat transfer to the liquid helium through the bottom surface of the liquid helium container bottle stopper, and calculating the heat transfer to the liquid surface through the bottom surface of the liquid helium container bottle stopper by helium vapor;
optionally, calculating the radiant heat transfer to the liquid helium through the bottom of the liquid helium container stopper includes calculating the radiant heat transfer according to the following formula (1):
Figure GDA0003275746090000076
wherein, sigma is radiation constant, epsilon is the radiance of the bottom surface of the bottle stopper, F is radiation angle coefficient, S is the area of the bottom of the bottle stopper, TdIs the temperature of the bottom of the bottle stopper, T0Is the temperature of liquid helium.
Optionally, calculating the heat transfer from the helium vapor to the liquid surface through the bottom surface of the stopper of the liquid helium vessel includes calculating the heat transfer according to the following equation (2):
Figure GDA0003275746090000081
in the formula, λeIs helium vapor equivalent thermal conductivity, S is the stopper bottomArea of (d), TdIs the temperature of the bottom of the bottle stopper, T0The temperature of liquid helium, L the actual total length of the neck, L0Is the length of the bottle stopper.
S3: selecting a heat exchange proportionality coefficient R;
optionally, the initial value of the heat exchange proportionality coefficient R is within the range of 0.15-0.3.
S4: sequentially calculating the temperature of each conducting screen hanging screen of the liquid helium container from inside to outside according to the evaporation rate m, the heat exchange proportional coefficient R, the radiation heat transfer quantity and the heat conduction quantity, and calculating the hanging screen position of the conducting screen according to the temperature of the conducting screen hanging screen;
optionally, the temperature of each conducting screen hanging position of the liquid helium container from inside to outside is sequentially calculated according to the evaporation rate m, the heat exchange proportionality coefficient R, the radiant heat transfer capacity and the heat conduction capacity, and the temperature of the 1 st conducting screen hanging position is calculated according to the following formula (3):
Figure GDA0003275746090000082
in the formula, LbLatent heat of vaporization, epsilon, for liquid helium evaporation0The radiance S of the No. 1 conductive screen and the inner container0The total area of the outer surface of the inner container is shown, and delta T is the temperature difference between the temperature of the conduction screen and the temperature at the position of the hanging screen; t is1- Δ T is the screen temperature of the 1 st conductive screen;
alternatively, Δ T is 6K for a copper conductive shield and 16K for an aluminum conductive shield.
After the temperature of the screen hanging position of the ith screen is obtained, wherein i is greater than or equal to 1, the temperature of the screen hanging position of the (i + 1) th screen is calculated according to the following formula (4):
Figure GDA0003275746090000083
in the formula, HiIs the enthalpy value of helium at the temperature of the hanging screen of the ith conduction screen, H0Is the enthalpy of saturated helium,. epsiloniIs the emissivity between the (i + 1) th conductive screen and the (i) th conductive screen, SiFor the ith blockTotal area of the screen, TiThe temperature at the ith block of the conductive screen is measured.
Calculating the hanging screen position of the conduction screen according to the temperature of the hanging screen of the conduction screen, wherein the hanging screen position of the 1 st conduction screen is calculated according to the following formula (5):
Figure GDA0003275746090000091
in the formula, delta1The distance between the position of the screen of the 1 st conduction screen and the interface of the neck tube and the inner container is lambda (T)0) The thermal conductivity of the neck tube material at the temperature of the liner, A is the cross-sectional area of the neck tube;
calculating the screen hanging position of the (i + 1) th conductive screen according to the following formula (6):
Figure GDA0003275746090000092
in the formula, λ (T)i) The thermal conductivity of the material of the neck pipe at the temperature of the ith conduction screen hanging screen is deltai+1And the distance between the screen hanging position of the (i + 1) th conductive screen and the screen hanging position of the ith conductive screen is obtained.
S5: hanging the temperature T of the current (i + 1) th conduction screeni+1Temperature T of outer shell of liquid helium vesselfComparing and judging Ti+1Whether or not T is greater than or equal tofIf yes, go to step S6; if not, turning to step S4, and calculating the temperature of the (i + 2) th conduction screen hanging position;
that is, after the current temperature of the hanging screen of the conduction screen is obtained through calculation, the temperature of the hanging screen of the conduction screen is compared with the temperature of the shell, and if the current temperature of the hanging screen of the conduction screen reaches the temperature of the shell, the temperature and the position of the hanging screen of the next conduction screen are not calculated; if the temperature of the hanging screen of the current conduction screen does not reach the temperature of the shell, the temperature and the position of the hanging screen of the next conduction screen are continuously calculated until the temperature of the hanging screen of a certain subsequent conduction screen reaches the temperature of the shell.
Optionally, the temperature T of the outer shellfSimplified to ambient temperature Te。
Optionally, the temperature T of the outer shellfTaking values according to the following formula (10):
Figure GDA0003275746090000101
in the formula, TeIs the ambient temperature, SfIs the surface area of the shell, and alpha is the natural convection heat transfer coefficient of air.
Optionally, the natural convection heat transfer coefficient alpha of the air is 5-15.
Optionally, the temperature T at the current hanging position of the conductive screen is judgedi+1Greater than or equal to the temperature T of the shellfWhen, still include: let Ti+1＝TfN is i +1, according to the following formula (7), to locate the screen hanging position δ of the i +1 th conductive screeni+1Corrected to deltan：
Figure GDA0003275746090000102
In the formula, TfIs the shell temperature, delta, of the liquid helium vesselnThe distance from the last conductive screen (the outer shell is considered as the last conductive screen) to the screen hanging position of the ith conductive screen, HfIs the enthalpy of helium at the temperature of the enclosure.
S6: calculating the estimated total length of the neck pipe based on the screen hanging positions of the 1 st to i th conduction screens;
optionally, calculating the estimated total length of the neck pipe based on the screen hanging positions of the 1 st to i th conduction screens includes calculating the estimated total length of the neck pipe according to the following formula (8):
Figure GDA0003275746090000103
s7: comparing the estimated total length of the neck with the actual total length of the neck, judging whether the estimated total length of the neck is matched with the actual total length of the neck, and if so, turning to the step S8; if not, turning to the step S3, and adjusting the value of the heat exchange proportionality coefficient R; until the estimated total length of the neck pipe is matched with the actual total length of the neck pipe;
optionally, when the difference between the estimated total length of the neck and the actual total length of the neck is judged to be within the set threshold range, judging that the estimated total length of the neck is matched with the actual total length of the neck; on the contrary, the estimated total length of the neck is judged not to match with the actual total length of the neck. The threshold range can be flexibly set, and is not described herein again.
For example, if L is judgedpAnd when the temperature is approximately equal to L, the temperature and the screen hanging position of each conduction screen are the optimal temperature and screen hanging position of the conduction screen. Otherwise, adjusting the value of R, and recalculating until Lp≈L。
Optionally, when judging that the estimated total length of the neck pipe is not matched with the actual total length of the neck pipe, adjusting the value of the heat exchange proportionality coefficient R includes:
when the estimated total length of the neck pipe is larger than the actual total length of the neck pipe, the value of the heat exchange proportionality coefficient R is reduced; and when the estimated total length of the neck pipe is smaller than the actual total length of the neck pipe, increasing the value of the heat exchange proportionality coefficient R.
Optionally, the method includes calculating the adjusted heat exchange proportionality coefficient according to the following formula (9):
Figure GDA0003275746090000111
in the formula, RNT is a relaxation coefficient for the adjusted heat exchange proportionality coefficient.
The value of the relaxation coefficient t is preferably 0.2-0.5.
S8: and obtaining the optimal screen position of the liquid helium container based on the screen hanging positions of the conductive screens.
The invention creatively provides the heat exchange proportionality coefficient R as a core variable of a calculation process and an iteration, which obviously simplifies the complexity of heat exchange calculation in the iteration process and improves the convergence of circulation;
by adopting the method provided by the invention to determine the optimal screen position and calculate the temperature at the screen hanging position of the corresponding conduction screen, the technical advantages of multi-screen heat insulation can be effectively exerted, heat leakage is reduced under the limited number of the conduction screens, the performance of multi-screen heat insulation is improved, the evaporation capacity of liquid helium is reduced, and the storage time of the liquid helium is prolonged;
the method provided by the invention is adopted to calculate the temperature and the corresponding position of the hanging screen of the optimal conduction screen, the calculation method is simple, convenient, clear in physical significance, easy to understand, high in efficiency and speed in the calculation process, good in stability and easy to converge;
the method provided by the invention has high precision;
the method provided by the invention has good applicability, not only can be suitable for liquid helium containers with different structural sizes, but also can be used for calculation for different purposes. The method can be adopted in the calculation of the daily evaporation rate of the multi-screen heat-insulating liquid helium container, the calculation of the screen number and the design of the length of the neck pipe.
It will be apparent to those skilled in the art that the modules or steps of the invention described above may be implemented in a general purpose computing device, they may be centralized on a single computing device or distributed across a network of computing devices, and optionally they may be implemented in program code executable by a computing device, such that they may be stored on a computer storage medium (ROM/RAM, magnetic disks, optical disks) and executed by a computing device, and in some cases, the steps shown or described may be performed in an order different than that described herein, or they may be separately fabricated into individual integrated circuit modules, or multiple ones of them may be fabricated into a single integrated circuit module. Thus, the present invention is not limited to any specific combination of hardware and software.
The foregoing is a more detailed description of the present invention that is presented in conjunction with specific embodiments, and the practice of the invention is not to be considered limited to those descriptions. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.

Claims (13)

1. A method for determining an optimal screen position for a multi-panel insulated liquid helium vessel, comprising:
s1: selecting an evaporation rate m set by a liquid helium container;
s2: calculating the amount of radiant heat transfer to the liquid helium through the bottom surface of the liquid helium vessel stopper and calculating the amount of heat transfer to the liquid surface as helium vapor through the bottom surface of the liquid helium vessel stopper;
s3: selecting a heat exchange proportionality coefficient R of a conduction screen in a liquid helium container;
s4: sequentially calculating the temperature of each conducting screen hanging screen of the liquid helium container from inside to outside according to the evaporation rate m, the heat exchange proportionality coefficient R, the radiant heat transfer quantity and the heat conduction quantity, and calculating the hanging screen position of the conducting screen according to the temperature of the conducting screen hanging screen;
s5: hanging the temperature T of the current (i + 1) th conduction screeni+1And the temperature T of the outer shell of the liquid helium vesselfComparing and judging the Ti+1Whether or not T is greater than or equal tofIf yes, go to step S6; if not, turning to step S4, and calculating the temperature of the (i + 2) th conduction screen hanging position;
s6: calculating the estimated total length of the neck pipe based on the screen hanging positions of the 1 st to i th conduction screens;
s7: comparing the estimated total length of the neck with the actual total length of the neck, judging whether the estimated total length of the neck is matched with the actual total length of the neck, if so, turning to the step S8; if not, turning to the step S3, and adjusting the value of the heat exchange proportionality coefficient R; until the estimated total length of the neck pipe is matched with the actual total length of the neck pipe;
s8: and obtaining the optimal screen position of the liquid helium container based on the screen hanging positions of the conductive screens.
2. A method for determining an optimal screen position for a multi-panel insulated liquid helium vessel as defined in claim 1, wherein calculating the radiant heat transfer to liquid helium through a bottom of the liquid helium vessel stopper comprises calculating the radiant heat transfer as defined in equation (1) as follows:
Figure FDA0003275746080000011
in the formula, sigma is the radiation constant, epsilon is the radiance of bottle plug bottom surface, F is the radiation angle coefficient, S is the area of bottle plug bottom, TdIs the temperature of the bottom of the bottle stopper, T0Is the temperature of liquid helium.
3. A method for determining an optimal screen position for a multi-panel insulated liquid helium vessel as defined in claim 2, wherein calculating a heat transfer rate from helium vapor to a liquid surface through a bottom surface of a stopper of the liquid helium vessel comprises calculating the heat transfer rate according to equation (2) as follows:
Figure FDA0003275746080000021
in the formula, the lambdaeIs the helium vapor equivalent thermal conductivity, L is the actual total length of the neck tube, L0Is the length of the bottle stopper.
4. A method for determining an optimal screen position for a multi-panel thermal insulation liquid helium vessel as claimed in claim 3, wherein said sequentially calculating the temperature of each of the conductive screens of the liquid helium vessel from inside to outside according to the evaporation rate m, the heat exchange proportionality coefficient R, the radiant heat transfer amount and the heat transfer amount comprises calculating the temperature of the 1 st conductive screen according to the following equation (3):
Figure FDA0003275746080000022
in the formula, the LbIs the latent heat of vaporization of liquid helium, e0The radiance S of the 1 st conductive screen and the inner container0The delta T is the temperature difference between the temperature of the conduction screen and the temperature at the position of the hanging screen, and is the total area of the outer surface of the inner container; t is1- Δ T is the screen temperature of the 1 st conductive screen;
after the temperature of the screen hanging position of the ith screen is obtained, the temperature of the screen hanging position of the ith screen and the screen hanging position of the (i + 1) th screen is calculated according to the following formula (4):
Figure FDA0003275746080000031
in the formula, the HiIs the enthalpy value of helium at the temperature of the hanging screen of the ith conduction screen, H0Is the enthalpy of saturated helium,. epsiloniIs the emissivity between the (i + 1) th conductive screen and the (i) th conductive screen, SiIs the total area of the i-th conductive screen, TiThe temperature at the ith block of the conductive screen is measured.
5. A method for determining an optimal screen position for a multi-panel insulated liquid helium vessel as defined in claim 4, wherein calculating the hanging position of the conductive panel based on the temperature at the hanging panel of the conductive panel comprises calculating the hanging position of the 1 st conductive panel according to equation (5) as follows:
Figure FDA0003275746080000032
in the formula, the delta1The distance between the position of the screen of the 1 st conduction screen and the interface of the neck tube and the liner is lambda (T)0) The thermal conductivity of the neck tube material at the temperature of the liner is shown, wherein A is the cross-sectional area of the neck tube;
calculating the screen hanging position of the (i + 1) th conductive screen according to the following formula (6):
Figure FDA0003275746080000033
in the formula, the lambda (T)i) The thermal conductivity of the material of the neck pipe at the temperature of the ith conductive screen hanging screen is deltai+1And the distance between the screen hanging position of the (i + 1) th conductive screen and the screen hanging position of the ith conductive screen is obtained.
6. A method for determining an optimal screen position for a multi-panel insulated liquid helium vessel as claimed in claim 5, wherein T is determinedi+1Greater than or equal to TfWhen, still include: let Ti+1＝TfAnd n is i +1, and the screen hanging position delta of the i +1 th conduction screen is determined according to the following formula (7)i+1Corrected to deltan：
Figure FDA0003275746080000041
In the formula, the TfIs the shell temperature of the liquid helium vessel, saidnThe distance between the last calculation screen and the screen hanging position of the ith conduction screen is HfIs the enthalpy of helium at the temperature of the enclosure.
7. A method for determining an optimal screen position for a multi-panel insulated liquid helium vessel as defined in claim 6, wherein calculating the estimated total length of the neck based on the screen hanging positions of the 1 st to i th conductive panels comprises calculating the estimated total length L of the neck according to the following equation (8)P：
Figure FDA0003275746080000042
8. A method for determining an optimal screen position for a multi-panel insulated liquid helium vessel as defined in claim 7, wherein comparing the estimated total length of the neck to an actual total length of the neck and determining whether the estimated total length of the neck matches the actual total length of the neck comprises:
when the difference value between the estimated total length of the neck and the actual total length of the neck is judged to be within a set threshold range, judging that the estimated total length of the neck is matched with the actual total length of the neck; and on the contrary, judging that the estimated total length of the neck pipe is not matched with the actual total length of the neck pipe.
9. A method for determining an optimal screen position for a multi-panel insulated liquid helium vessel as defined in claim 8, wherein adjusting the value of the heat transfer proportionality coefficient R when the estimated total neck length is determined not to match the actual total neck length comprises:
when the estimated total length of the neck pipe is larger than the actual total length of the neck pipe, the value of the heat exchange proportionality coefficient R is reduced; and when the estimated total length of the neck pipe is smaller than the actual total length of the neck pipe, increasing the value of the heat exchange proportionality coefficient R.
10. A method for determining an optimal screen position for a multi-panel insulated liquid helium vessel as claimed in claim 9, wherein adjusting the value of the heat transfer proportionality coefficient R upon determining that the estimated total neck length does not match the actual total neck length comprises calculating the adjusted heat transfer proportionality coefficient according to equation (9) as follows:
Figure FDA0003275746080000051
in the formula, the RNAnd t is a relaxation coefficient for the adjusted heat exchange proportionality coefficient.
11. A method for determining an optimal screen position for a multi-panel insulated liquid helium vessel as defined in any of claims 4-10, wherein Δ T is 6K for a copper conductive panel and 16K for an aluminum conductive panel.
12. A method for determining an optimal screen position for a multi-panel insulated liquid helium vessel as claimed in any one of claims 6 to 10, wherein the enclosure temperature TfTaking values according to the following formula (10):
Figure FDA0003275746080000052
in the formula, the TeIs ambient temperature, said SfIs the surface area of the shell, and the alpha is emptyNatural convection heat transfer coefficient of gas.
13. A method for determining an optimal screen position for a multi-panel insulated liquid helium vessel as claimed in any one of claims 1 to 10, wherein the initial value of the heat transfer proportionality coefficient R is in the range of 0.15-0.3.
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