CN111398337A - Loop heat pipe service life estimation method based on non-condensable gas combination test - Google Patents
Loop heat pipe service life estimation method based on non-condensable gas combination test Download PDFInfo
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N25/00—Investigating or analyzing materials by the use of thermal means
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Abstract
The invention relates to a loop heat pipe service life prediction method based on a non-condensable gas combined test, belonging to the technical field of service life prediction of aerospace thermal control products; the method comprises the following steps: step one, establishing a loop heat pipe service life testing system; step two, fitting a time-noncondensable gas content curve chart; step three, fitting a curve graph of nitrogen capacity-temperature; step four, establishing an extrapolation linear graph of time-noncondensable gas content; judging whether the loop heat pipe fails within the service life according to an extrapolated linear graph of time-non-condensable gas content and a nitrogen volume-temperature curve chart; the invention realizes the estimation of the service life of the loop heat pipe in a relatively short time, has the characteristics of short test period, high estimation accuracy and the like, and has strong practicability in the engineering application of the loop heat pipe.
Description
Technical Field
The invention belongs to the technical field of life prediction of aerospace thermal control products, and relates to a loop heat pipe life prediction method based on a non-condensable gas combination test.
Background
As a space thermal control product, the loop heat pipe needs to meet the use requirements of on-orbit unremaintainable and long service life of a spacecraft. The loop heat pipe is a loop formed by an evaporator, a heat dissipation surface, a liquid storage device and a pipeline, wherein a capillary core made of a compact porous material is arranged in the evaporator and used for generating sufficient capillary force to drive working media in the loop to circulate, liquid on the surface layer of the porous material absorbs heat and then evaporates, steam flows to the heat dissipation surface through the pipeline to be condensed and dissipated, then returns to the liquid storage device from another pipeline under the action of the capillary force and then enters the capillary core in the evaporator to complete the whole circulation.
At present, two reasons for failure of a loop heat pipe using liquid ammonia as a working medium exist in the operation process, namely generation of non-condensable gas in L HP and leakage of the working medium during operation, the problem of leakage of the working medium is basically solved along with the development of modern welding technology and leakage rate detection means, so that research on L HP service life mostly focuses on generation of NCG and influence of the NCG on operation of the heat pipe, and understanding of decomposition rate of the ammonia working medium in the loop heat pipe and influence of the non-condensable gas on performance of the loop heat pipe is an important means for researching and evaluating service life of the loop heat pipe.
The method for predicting the service life of the loop heat pipe is a ground 1:1 service life test, namely, a plurality of sets of loop heat pipes are operated under the same actual using condition of the loop heat pipe until the loop heat pipe fails to work, so that the service life of the loop heat pipe can be judged, the method is feasible, two obvious defects exist, the test period is long, and the service life of the loop heat pipe is generally longer than five years under the existing manufacturing technology of the loop heat pipe.
Disclosure of Invention
The technical problem solved by the invention is as follows: the method for estimating the service life of the loop heat pipe based on the non-condensable gas combination test overcomes the defects of the prior art, achieves estimation of the service life of the loop heat pipe in a relatively short time, has the characteristics of short test period, high estimation accuracy and the like, and has strong practicability in engineering application of the loop heat pipe.
The technical scheme of the invention is as follows:
a loop heat pipe service life estimation method based on a non-condensable gas combined test comprises the following steps:
step one, establishing a loop heat pipe service life testing system, which comprises a liquid storage device, an evaporator, a loop heat pipe, a constant-temperature water tank and a water chilling unit; the loop heat pipe comprises a gas pipeline, a condensation pipeline and a liquid pipeline;
selecting 8 sets of completely consistent loop heat pipes as experimental samples; testing in a loop heat pipe service life testing system; measuring the content of the non-condensable gas in the loop heat pipe in 4 periods by taking 2 months as a period; the non-condensable gas is ammonia gas; obtaining the content of non-condensable gas in the loop heat pipes with different periods; fitting a time-noncondensable gas content curve graph according to the content of the noncondensable gas in the four periods;
establishing a non-condensable gas doping test system which comprises a standard container, a pressure gauge, a first valve, a second valve, a third valve and a vacuum pump; 1 set of completely consistent loop heat pipes is selected again, and a non-condensable gas doping test is carried out on the loop heat pipes; fitting a curve chart of nitrogen capacity-temperature;
establishing an extrapolation linear graph of the time and the content of the non-condensable gas according to the time and non-condensable gas content curve chart;
step five, setting the failure threshold value of the loop heat pipe to be Tmax(ii) a And judging whether the loop heat pipe fails within the service life according to the extrapolated linear graph of the time-the content of the non-condensable gas and the curve graph of the nitrogen volume-the temperature.
In the above method for estimating the life of the loop heat pipe based on the non-condensable gas combination test, in the first step, the method for establishing the loop heat pipe life test system includes: the gas pipeline, the condensation pipeline and the liquid pipeline are communicated in sequence; the evaporator is communicated with the liquid storage device; the gas pipeline is communicated with the evaporator; the liquid pipeline is communicated with the liquid storage device; liquid ammonia is stored in the liquid storage device; the condensing pipeline is arranged in the constant-temperature water tank; the water chilling unit is communicated with the constant-temperature water tank to realize constant-temperature control on the constant-temperature water tank;
the working process of the loop heat pipe service life testing system is as follows:
the evaporator heats and evaporates the liquid ammonia in the liquid storage device into ammonia gas; ammonia enters a condensation pipeline through a gas pipeline; condensing ammonia gas in the condensing pipeline through a constant-temperature water tank to form liquid ammonia; liquid ammonia flows back to the liquid storage device from the liquid pipeline.
In the above method for estimating the life of the loop heat pipe based on the non-condensable gas combination test, in the first step, the working power of the evaporator is 50W; the heating temperature is controlled to be 13-17 ℃.
In the above method for estimating the life of the loop heat pipe based on the non-condensable gas combination test, in the second step, the method for measuring the content of the non-condensable gas in the 8 loops of loop heat pipes comprises:
s1, testing for 2 months, and randomly selecting 2 loops of heat pipes; measuring the content of non-condensable gas in the two sets of loop heat pipes; taking the average value and recording as a; the 2 loop heat pipe was not tested further;
s2, testing for 4 months, and randomly selecting 2 loops of loop heat pipes from the rest 6 loops of loop heat pipes; measuring the content of non-condensable gas in the two sets of loop heat pipes; taking the average value and recording as b; the 2 loop heat pipe was not tested further;
s3, testing for 6 months, and randomly selecting 2 loops of loop heat pipes from the rest 4 loops of loop heat pipes; measuring the content of non-condensable gas in the two sets of loop heat pipes; taking the average value and recording as c; the 2 loop heat pipe was not tested further;
s4, measuring the content of non-condensable gas in the remaining 2 loops of heat pipes when testing for 8 months; taking the average value and recording the average value as d;
and fitting a time-noncondensable gas content curve graph according to the content a, b, c and d of the noncondensable gas in the four periods and the corresponding test time.
In the above method for estimating the life of the loop heat pipe based on the non-condensable gas combined test, in the third step, the method for establishing the non-condensable gas doping test system is as follows:
the first valve, the second valve and the third valve are respectively communicated with the standard container through independent pipelines; the pressure gauge is communicated with the standard container to measure the internal pressure of the standard container; the vacuum pump is communicated with a pipeline where the third valve is located; the loop heat pipe is communicated with a pipeline where the second valve is located; the temperature of the loop heat pipe is always kept at-20 ℃; the loop heat pipe is filled with ammonia, and the internal state of the loop heat pipe is a gas-liquid saturated state of ammonia at the temperature of minus 20 ℃.
In the above method for estimating the life of the loop heat pipe based on the non-condensable gas combination test, in the third step, the specific method of the non-condensable gas doping test is as follows:
s1, first valve and second valveAnd the third valve is kept in a closed state to keep the temperature of the standard container at Tcont；
S2, opening a third valve, and vacuumizing the standard container through a vacuum pump; closing the third valve;
s3, opening the first valve, and filling high-purity nitrogen into the standard container until the pressure of the nitrogen in the standard container reaches P0(ii) a Closing the first valve;
s4, measuring the pressure inside the loop heat pipe to be P1(ii) a Opening a second valve, and moving the nitrogen in the standard container into the loop heat pipe; observing the pressure gauge until the pressure in the standard container is from P0Down to P1(ii) a Closing the second valve;
s5, calculating the volume n of the nitrogen filled in the loop heat pipe at the moment; measuring the temperature T of the loop heat pipe at the moment;
s6, taking another 3P values0(ii) a Repeating S3-S5 3 times to obtain 3 different P0Under the condition, the volume n of the nitrogen filled in the loop heat pipe and the temperature T of the corresponding loop heat pipe are calculated; a nitrogen capacity-temperature plot was fit.
In the above method for estimating the life of a loop heat pipe based on the non-condensable gas combination test, in S1, TcontIs 300K; in S2, the vacuum degree of the standard container is 10-3Pa is above; in S4, P1＜P0。
8. The method for estimating the life of the loop heat pipe based on the non-condensable gas combined test according to claim 7, wherein the method comprises the following steps: in S5, the method for calculating the volume n of the nitrogen gas filled in the loop heat pipe includes:
wherein R is a gas constant;
V0is a standard container volume.
In the fourth step, the method for establishing the time-noncondensable gas content extrapolation linear graph comprises the following steps:
y＝6.5×10-4x
wherein y is the content of non-condensable gas;
x is time;
and (3) establishing a time-noncondensable gas content extrapolation linear graph by taking 0 time and 0 noncondensable gas content as initial values, taking the testing time of 2 months and the noncondensable gas content a as a process point.
In the above method for estimating the life of the loop heat pipe based on the non-condensable gas combination test, in the fifth step, the method for judging whether the loop heat pipe fails within the life duration is as follows:
when the service life of the loop heat pipe is required, searching the non-condensable gas content corresponding to the service life required time according to the time-non-condensable gas content extrapolation linear graph; substituting the content of the non-condensable gas into a nitrogen volume-temperature curve chart, searching the corresponding temperature, and when the temperature is not more than a threshold value TmaxJudging that the loop heat pipe does not lose efficacy within the service life; otherwise, judging that the loop heat pipe fails within the service life.
Compared with the prior art, the invention has the beneficial effects that:
(1) the invention adopts the non-condensable gas doping test system, can accurately and quantitatively charge the non-condensable gas, and can not cause the change of the original working medium in the loop heat pipe;
(2) the invention can effectively shorten the time of the life test of the loop heat pipe and accurately estimate the life of the loop heat pipe.
Drawings
FIG. 1 is a flowchart illustrating the life estimation of a loop heat pipe according to the present invention;
FIG. 2 is a schematic view of a loop heat pipe life testing system according to the present invention;
FIG. 3 is a schematic view of a non-condensable gas doping test system according to the present invention;
FIG. 4 is a graph and extrapolated linear plot of time versus non-condensable gas content according to the present invention.
Detailed Description
The invention is further illustrated by the following examples.
The invention provides a loop heat pipe life estimation method based on a non-condensable gas combination test, which comprises the steps of obtaining the generation amount and the generation rate of the non-condensable gas in a short period of a loop heat pipe through a loop heat pipe life test system; the non-condensable gas doping test consists of a non-condensable gas doping system and a performance test system, and aims to obtain the influence of different amounts of non-condensable gas on the thermal performance of the loop heat pipe; and (4) applying the test data obtained by the two tests to estimate the service life of the loop heat pipe by using a linear extrapolation and index fitting method or judging whether the loop heat pipe fails within the designed service life.
As shown in fig. 1, the method for estimating the life of a loop heat pipe mainly includes the following steps:
step one, establishing a loop heat pipe service life testing system, as shown in fig. 2, comprising a liquid storage device, an evaporator, a loop heat pipe, a constant temperature water tank and a water chilling unit; the loop heat pipe comprises a gas pipeline, a condensation pipeline and a liquid pipeline; the method for establishing the loop heat pipe life test system comprises the following steps: the gas pipeline, the condensation pipeline and the liquid pipeline are communicated in sequence; the evaporator is communicated with the liquid storage device; the gas pipeline is communicated with the evaporator; the liquid pipeline is communicated with the liquid storage device; liquid ammonia is stored in the liquid storage device; the condensing pipeline is arranged in the constant-temperature water tank; the water chilling unit is communicated with the constant-temperature water tank to realize constant-temperature control on the constant-temperature water tank;
the working process of the loop heat pipe service life testing system is as follows:
the evaporator heats and evaporates the liquid ammonia in the liquid storage device into ammonia gas; ammonia enters a condensation pipeline through a gas pipeline; condensing ammonia gas in the condensing pipeline through a constant-temperature water tank to form liquid ammonia; liquid ammonia flows back to the liquid storage device from the liquid pipeline. The working power of the evaporator is 50W; the heating temperature is controlled to be 13-17 ℃.
Selecting 8 sets of completely consistent loop heat pipes as experimental samples; testing in a loop heat pipe service life testing system; measuring the content of the non-condensable gas in the loop heat pipe in 4 periods by taking 2 months as a period; the non-condensable gas is ammonia gas; obtaining the content of non-condensable gas in the loop heat pipes with different periods; fitting a time-noncondensable gas content curve graph according to the content of the noncondensable gas in the four periods; as shown in fig. 4.
The method for measuring the content of the non-condensable gas in the 8-loop heat pipe comprises the following steps:
s1, testing for 2 months, and randomly selecting 2 loops of heat pipes; measuring the content of non-condensable gas in the two sets of loop heat pipes; taking the average value and recording as a; the 2 loop heat pipe was not tested further;
s2, testing for 4 months, and randomly selecting 2 loops of loop heat pipes from the rest 6 loops of loop heat pipes; measuring the content of non-condensable gas in the two sets of loop heat pipes; taking the average value and recording as b; the 2 loop heat pipe was not tested further;
s3, testing for 6 months, and randomly selecting 2 loops of loop heat pipes from the rest 4 loops of loop heat pipes; measuring the content of non-condensable gas in the two sets of loop heat pipes; taking the average value and recording as c; the 2 loop heat pipe was not tested further;
s4, measuring the content of non-condensable gas in the remaining 2 loops of heat pipes when testing for 8 months; taking the average value and recording the average value as d;
and fitting a time-noncondensable gas content curve graph according to the content a, b, c and d of the noncondensable gas in the four periods and the corresponding test time.
Step three, establishing a non-condensable gas doping test system, as shown in fig. 3, comprising a standard container, a pressure gauge, a first valve, a second valve, a third valve and a vacuum pump; the method for establishing the non-condensable gas doping test system comprises the following steps:
the first valve, the second valve and the third valve are respectively communicated with the standard container through independent pipelines, the pressure gauge is communicated with the standard container to measure the internal pressure of the standard container, the vacuum pump is communicated with a pipeline where the third valve is located, the loop heat pipe is communicated with a pipeline where the second valve is located, the temperature of the loop heat pipe is always kept at-20 ℃, the loop heat pipe is filled with ammonia, the internal state of the loop heat pipe is a gas-liquid saturated state of ammonia at-20 ℃, the internal volume of the standard container is smaller than 1/10 of the total volume in the loop heat pipe, the heat exchange pipeline, the standard container and the valves are all made of 316L stainless steel, and the sealing gasket is made of corrosion-resistant nickel materials.
1 set of completely consistent loop heat pipes is selected again, and a non-condensable gas doping test is carried out on the loop heat pipes; a nitrogen capacity-temperature plot was fit. The specific method of the non-condensable gas doping test comprises the following steps:
s1, keeping the first valve, the second valve and the third valve in a closed state, and keeping the temperature of the standard container at Tcont；TcontIs 300K;
s2, opening a third valve, and vacuumizing the standard container through a vacuum pump; closing the third valve; vacuum degree of standard container is 10-3Pa is above;
s3, opening the first valve, and filling high-purity nitrogen into the standard container until the pressure of the nitrogen in the standard container reaches P0(ii) a Closing the first valve; the purity of nitrogen is better than 99.9999%;
s4, measuring the pressure inside the loop heat pipe to be P1(ii) a Opening a second valve, and moving the nitrogen in the standard container into the loop heat pipe; observing the pressure gauge until the pressure in the standard container is from P0Down to P1(ii) a Closing the second valve; p1＜P0。
S5, calculating the volume n of the nitrogen filled in the loop heat pipe at the moment; measuring the temperature T of the loop heat pipe at the moment; the method for calculating the capacity n of the nitrogen filled in the loop heat pipe comprises the following steps:
wherein R is a gas constant;
V0is a standard container volume.
S6, taking another 3P values0(ii) a Repeating S3-S5 3 times to obtain 3 different P0Under the condition, the volume n of the nitrogen filled in the loop heat pipe and the temperature T of the corresponding loop heat pipe are calculated; a nitrogen capacity-temperature plot was fit.
And step four, gradually reducing the decomposition rate of ammonia in the closed pipeline of the loop heat pipe. If the amplitude of the initial non-condensable gas is taken as the generation rate of the non-condensable gas in the loop heat pipe, linear extrapolation of the data of the content of the non-condensable gas is performed, and the data of the content of the non-condensable gas in the final operation stage of the extrapolated loop heat pipe is far higher than the content of the non-condensable gas in the actual loop heat pipe. Fitting with an exponential is more realistic. Fig. 4 shows a comparison of the actual incondensable gas content change exponential fit curve and the incondensable gas content change curve linearly extrapolated from the initial amplification. Establishing an extrapolation linear graph of the time and the content of the non-condensable gas according to the time and non-condensable gas content curve graph; as shown in fig. 4. The method for establishing the time-noncondensable gas content extrapolation linear graph comprises the following steps:
y＝6.5×10-4x
wherein y is the content of non-condensable gas;
x is time;
and (3) establishing a time-noncondensable gas content extrapolation linear graph by taking 0 time and 0 noncondensable gas content as initial values, taking the testing time of 2 months and the noncondensable gas content a as a process point.
Step five, setting the failure threshold value of the loop heat pipe to be Tmax(ii) a And judging whether the loop heat pipe fails within the service life according to the extrapolated linear graph of the time-the content of the non-condensable gas and the curve graph of the nitrogen volume-the temperature.
The method for judging whether the loop heat pipe fails within the service life duration is as follows:
when the service life of the loop heat pipe is required, searching the non-condensable gas content corresponding to the service life required time according to the time-non-condensable gas content extrapolation linear graph; substituting the content of the non-condensable gas into a nitrogen volume-temperature curve chart, searching the corresponding temperature, and when the temperature is not more than a threshold value TmaxJudging that the loop heat pipe does not lose efficacy within the service life; otherwise, judging that the loop heat pipe fails within the service life.
Examples
Step one, establishing a loop heat pipe service life testing system, which comprises a liquid storage device, an evaporator, a loop heat pipe, a constant-temperature water tank and a water chilling unit; the loop heat pipe comprises a gas pipeline, a condensation pipeline and a liquid pipeline; the method for establishing the loop heat pipe life test system comprises the following steps: the gas pipeline, the condensation pipeline and the liquid pipeline are communicated in sequence; the evaporator is communicated with the liquid storage device; the gas pipeline is communicated with the evaporator; the liquid pipeline is communicated with the liquid storage device; liquid ammonia is stored in the liquid storage device; the condensing pipeline is arranged in the constant-temperature water tank; the water chilling unit is communicated with the constant-temperature water tank to realize constant-temperature control on the constant-temperature water tank;
the working process of the loop heat pipe service life testing system is as follows:
the evaporator heats and evaporates the liquid ammonia in the liquid storage device into ammonia gas; ammonia enters a condensation pipeline through a gas pipeline; condensing ammonia gas in the condensing pipeline through a constant-temperature water tank to form liquid ammonia; liquid ammonia flows back to the liquid storage device from the liquid pipeline. The working power of the evaporator is 50W; the heating temperature is controlled to be 13-17 ℃.
Selecting 8 sets of completely consistent loop heat pipes as experimental samples; testing in a loop heat pipe service life testing system; measuring the content of the non-condensable gas in the loop heat pipe in 4 periods by taking 2 months as a period; the non-condensable gas is ammonia gas; obtaining the content of non-condensable gas in the loop heat pipes with different periods; fitting a time-noncondensable gas content curve graph according to the content of the noncondensable gas in the four periods; as shown in fig. 4.
The method for measuring the content of the non-condensable gas in the 8-loop heat pipe comprises the following steps:
s1, testing for 2 months, and randomly selecting 2 loops of heat pipes; measuring the content of non-condensable gas in the two sets of loop heat pipes; taking the average value and recording as a; the 2 loop heat pipe was not tested further;
s2, testing for 4 months, and randomly selecting 2 loops of loop heat pipes from the rest 6 loops of loop heat pipes; measuring the content of non-condensable gas in the two sets of loop heat pipes; taking the average value and recording as b; the 2 loop heat pipe was not tested further;
s3, testing for 6 months, and randomly selecting 2 loops of loop heat pipes from the rest 4 loops of loop heat pipes; measuring the content of non-condensable gas in the two sets of loop heat pipes; taking the average value and recording as c; the 2 loop heat pipe was not tested further;
s4, measuring the content of non-condensable gas in the remaining 2 loops of heat pipes when testing for 8 months; taking the average value and recording the average value as d;
according to the content a, b, c and d of the non-condensable gas in four periods and corresponding test time, a time-non-condensable gas content curve graph is fitted, and through tests, the content of the non-condensable gas is shown in table 1.
TABLE 1 table of non-condensable gas content
Step three, establishing a non-condensable gas doping test system, as shown in fig. 3, comprising a standard container, a pressure gauge, a first valve, a second valve, a third valve and a vacuum pump; the method for establishing the non-condensable gas doping test system comprises the following steps:
the first valve, the second valve and the third valve are respectively communicated with the standard container through independent pipelines, the pressure gauge is communicated with the standard container to measure the internal pressure of the standard container, the vacuum pump is communicated with a pipeline where the third valve is located, the loop heat pipe is communicated with a pipeline where the second valve is located, the temperature of the loop heat pipe is always kept at-20 ℃, the loop heat pipe is filled with ammonia, the internal state of the loop heat pipe is a gas-liquid saturated state of ammonia at-20 ℃, the internal volume of the standard container is smaller than 1/10 of the total volume in the loop heat pipe, the heat exchange pipeline, the standard container and the valves are all made of 316L stainless steel, and the sealing gasket is made of corrosion-resistant nickel materials.
1 set of completely consistent loop heat pipes is selected again, and a non-condensable gas doping test is carried out on the loop heat pipes; a nitrogen capacity-temperature plot was fit. The specific method of the non-condensable gas doping test comprises the following steps:
s1, keeping the first valve, the second valve and the third valve in a closed state, and keeping the temperature of the standard container at Tcont；TcontIs 300K;
s2, opening a third valve, and vacuumizing the standard container through a vacuum pump; closing the third valve; vacuum degree of standard container is 10-3Pa is above;
s3, beatingOpening a first valve, and filling high-purity nitrogen into the standard container until the pressure of the nitrogen in the standard container reaches P0(ii) a Closing the first valve; the purity of nitrogen is better than 99.9999%;
s4, measuring the pressure inside the loop heat pipe to be P1(ii) a Opening a second valve, and moving the nitrogen in the standard container into the loop heat pipe; observing the pressure gauge until the pressure in the standard container is from P0Down to P1(ii) a Closing the second valve; p1＜P0。
S5, calculating the volume n of the nitrogen filled in the loop heat pipe at the moment; measuring the temperature T of the loop heat pipe at the moment; the method for calculating the capacity n of the nitrogen filled in the loop heat pipe comprises the following steps:
wherein R is a gas constant;
V0is a standard container volume.
S6, taking another 3P values0(ii) a Repeating S3-S5 3 times to obtain 3 different P0Under the condition, the volume n of the nitrogen filled in the loop heat pipe and the temperature T of the corresponding loop heat pipe are calculated; a nitrogen capacity-temperature plot was fit.
By controlling P0The amount of the non-condensable gas filled into the loop heat pipe can be controlled. The volumetric ratio of non-condensable gas to reservoir may also be expressed as the non-condensable gas will eventually accumulate in the reservoir. The amount of the non-condensable gas charged into the loop heat pipe according to the test requirements is shown in table 2, it can be seen that the loop heat pipe can still normally operate when the amount of the non-condensable gas reaches 10%, only the stable temperature of the evaporator is about 8 ℃ higher than that when the non-condensable gas does not exist, the temperature of the loop heat pipe evaporator is increased by 20 ℃ compared with that when the life test starts according to the criterion of the failure of the loop heat pipe in the loop heat pipe specification for the spacecraft, and the loop heat pipe can be judged to have no failure at the moment.
TABLE 2 non-condensable gas fill
Establishing an extrapolation linear graph of the time and the content of the non-condensable gas according to the time and non-condensable gas content curve chart; as shown in fig. 4. The method for establishing the time-noncondensable gas content extrapolation linear graph comprises the following steps:
y＝6.5×10-4x
wherein y is the content of non-condensable gas;
x is time;
and (3) establishing a time-noncondensable gas content extrapolation linear graph by taking 0 time and 0 noncondensable gas content as initial values, taking the testing time of 2 months and the noncondensable gas content a as a process point.
Step five, setting the failure threshold value of the loop heat pipe to be Tmax(ii) a And judging whether the loop heat pipe fails within the service life according to the extrapolated linear graph of the time-the content of the non-condensable gas and the curve graph of the nitrogen volume-the temperature.
The method for judging whether the loop heat pipe fails within the service life duration is as follows:
when the service life of the loop heat pipe is required, searching the non-condensable gas content corresponding to the service life required time according to the time-non-condensable gas content extrapolation linear graph; substituting the content of the non-condensable gas into a nitrogen volume-temperature curve chart, searching the corresponding temperature, and when the temperature is not more than a threshold value TmaxJudging that the loop heat pipe does not lose efficacy within the service life; otherwise, judging that the loop heat pipe fails within the service life.
For example, if a certain spacecraft requires 5 years for the service life of the loop heat pipe, according to the analysis, the increase of the non-condensable gas content of the loop heat pipe is 0.13% in the previous 2 months, and the non-condensable gas content of the loop heat pipe is 3.9% after the loop heat pipe operates for 5 years. And the content of the non-condensable gas is calculated to be 0.246% according to an exponential fitting curve, which is far less than a linear extrapolation value. The experimental conclusion of the influence of different doped non-condensable gas contents on the operation performance of the loop heat pipe shows that under the condition that the content of the non-condensable gas in the loop heat pipe is less than or equal to 6%, all performance indexes of the loop heat pipe meet the temperature control requirement, so that the loop heat pipe can meet the 5-year service life requirement and has a large margin.
For another example, according to the usage requirement, if the temperature of the loop heat pipe evaporator exceeds the initial operation temperature by 5 ℃, the loop heat pipe is considered to be failed, then according to the experimental data, the corresponding non-condensable gas amount is 6% when the temperature difference of the evaporator is 5 ℃, and the linear extrapolation value of the increase of the non-condensable gas content of the loop heat pipe is taken as 0.13% of the increase of the non-condensable gas content of the loop heat pipe in the previous 2 months, so that the service life of the loop heat pipe is 7.5 years and the margin is particularly large.
The method can be flexibly changed in practical application, the selection of test sample points and the selection of an extrapolation curve can be determined according to practical conditions.
Although the present invention has been described with reference to the preferred embodiments, it is not intended to limit the present invention, and those skilled in the art can make variations and modifications of the present invention without departing from the spirit and scope of the present invention by using the methods and technical contents disclosed above.
Claims (10)
1. A loop heat pipe service life estimation method based on a non-condensable gas combined test is characterized by comprising the following steps: the method comprises the following steps:
step one, establishing a loop heat pipe service life testing system, which comprises a liquid storage device, an evaporator, a loop heat pipe, a constant-temperature water tank and a water chilling unit; the loop heat pipe comprises a gas pipeline, a condensation pipeline and a liquid pipeline;
selecting 8 sets of completely consistent loop heat pipes as experimental samples; testing in a loop heat pipe service life testing system; measuring the content of the non-condensable gas in the loop heat pipe in 4 periods by taking 2 months as a period; the non-condensable gas is ammonia gas; obtaining the content of non-condensable gas in the loop heat pipes with different periods; fitting a time-noncondensable gas content curve graph according to the content of the noncondensable gas in the four periods;
establishing a non-condensable gas doping test system which comprises a standard container, a pressure gauge, a first valve, a second valve, a third valve and a vacuum pump; 1 set of completely consistent loop heat pipes is selected again, and a non-condensable gas doping test is carried out on the loop heat pipes; fitting a curve chart of nitrogen capacity-temperature;
establishing an extrapolation linear graph of the time and the content of the non-condensable gas according to the time and non-condensable gas content curve chart;
step five, setting the failure threshold value of the loop heat pipe to be Tmax(ii) a And judging whether the loop heat pipe fails within the service life according to the extrapolated linear graph of the time-the content of the non-condensable gas and the curve graph of the nitrogen volume-the temperature.
2. The method for estimating the life of the loop heat pipe based on the non-condensable gas combined test according to claim 1, wherein the method comprises the following steps: in the first step, the method for establishing the loop heat pipe life test system comprises the following steps: the gas pipeline, the condensation pipeline and the liquid pipeline are communicated in sequence; the evaporator is communicated with the liquid storage device; the gas pipeline is communicated with the evaporator; the liquid pipeline is communicated with the liquid storage device; liquid ammonia is stored in the liquid storage device; the condensing pipeline is arranged in the constant-temperature water tank; the water chilling unit is communicated with the constant-temperature water tank to realize constant-temperature control on the constant-temperature water tank;
the working process of the loop heat pipe service life testing system is as follows:
the evaporator heats and evaporates the liquid ammonia in the liquid storage device into ammonia gas; ammonia enters a condensation pipeline through a gas pipeline; condensing ammonia gas in the condensing pipeline through a constant-temperature water tank to form liquid ammonia; liquid ammonia flows back to the liquid storage device from the liquid pipeline.
3. The method for estimating the life of the loop heat pipe based on the non-condensable gas combined test according to claim 2, wherein the method comprises the following steps: in the first step, the working power of the evaporator is 50W; the heating temperature is controlled to be 13-17 ℃.
4. The method for estimating the life of the loop heat pipe based on the non-condensable gas combined test according to claim 1, wherein the method comprises the following steps: in the second step, the method for measuring the content of the non-condensable gas in the 8-loop heat pipe comprises the following steps:
s1, testing for 2 months, and randomly selecting 2 loops of heat pipes; measuring the content of non-condensable gas in the two sets of loop heat pipes; taking the average value and recording as a; the 2 loop heat pipe was not tested further;
s2, testing for 4 months, and randomly selecting 2 loops of loop heat pipes from the rest 6 loops of loop heat pipes; measuring the content of non-condensable gas in the two sets of loop heat pipes; taking the average value and recording as b; the 2 loop heat pipe was not tested further;
s3, testing for 6 months, and randomly selecting 2 loops of loop heat pipes from the rest 4 loops of loop heat pipes; measuring the content of non-condensable gas in the two sets of loop heat pipes; taking the average value and recording as c; the 2 loop heat pipe was not tested further;
s4, measuring the content of non-condensable gas in the remaining 2 loops of heat pipes when testing for 8 months; taking the average value and recording the average value as d;
and fitting a time-noncondensable gas content curve graph according to the content a, b, c and d of the noncondensable gas in the four periods and the corresponding test time.
5. The method for estimating the life of the loop heat pipe based on the non-condensable gas combined test according to claim 4, wherein the method comprises the following steps: in the third step, the method for establishing the non-condensable gas doping test system comprises the following steps:
the first valve, the second valve and the third valve are respectively communicated with the standard container through independent pipelines; the pressure gauge is communicated with the standard container to measure the internal pressure of the standard container; the vacuum pump is communicated with a pipeline where the third valve is located; the loop heat pipe is communicated with a pipeline where the second valve is located; the temperature of the loop heat pipe is always kept at-20 ℃; the loop heat pipe is filled with ammonia, and the internal state of the loop heat pipe is a gas-liquid saturated state of ammonia at the temperature of minus 20 ℃.
6. The method for estimating the life of the loop heat pipe based on the non-condensable gas combined test according to claim 5, wherein the method comprises the following steps: in the third step, the specific method of the non-condensable gas doping test is as follows:
s1, keeping the first valve, the second valve and the third valve in a closed state, and keeping the temperature of the standard container at Tcont；
S2, opening a third valve, and vacuumizing the standard container through a vacuum pump; closing the third valve;
s3, opening the first valve, and filling high-purity nitrogen into the standard container until the pressure of the nitrogen in the standard container reaches P0(ii) a Closing the first valve;
s4, measuring the pressure inside the loop heat pipe to be P1(ii) a Opening a second valve, and moving the nitrogen in the standard container into the loop heat pipe; observing the pressure gauge until the pressure in the standard container is from P0Down to P1(ii) a Closing the second valve;
s5, calculating the volume n of the nitrogen filled in the loop heat pipe at the moment; measuring the temperature T of the loop heat pipe at the moment;
s6, taking another 3P values0(ii) a Repeating S3-S5 3 times to obtain 3 different P0Under the condition, the volume n of the nitrogen filled in the loop heat pipe and the temperature T of the corresponding loop heat pipe are calculated; a nitrogen capacity-temperature plot was fit.
7. The method for estimating the life of the loop heat pipe based on the non-condensable gas combined test according to claim 6, wherein the method comprises the following steps: in the S1, TcontIs 300K; in S2, the vacuum degree of the standard container is 10-3Pa is above; in S4, P1＜P0。
8. The method for estimating the life of the loop heat pipe based on the non-condensable gas combined test according to claim 7, wherein the method comprises the following steps: in S5, the method for calculating the volume n of the nitrogen gas filled in the loop heat pipe includes:
wherein R is a gas constant;
V0is a standard container volume.
9. The method for estimating the life of the loop heat pipe based on the non-condensable gas combination test according to one of claims 1 to 8, wherein the method comprises the following steps: in the fourth step, the method for establishing the time-noncondensable gas content extrapolation linear graph comprises the following steps:
y＝6.5×10-4x
wherein y is the content of non-condensable gas;
x is time;
and (3) establishing a time-noncondensable gas content extrapolation linear graph by taking 0 time and 0 noncondensable gas content as initial values, taking the testing time of 2 months and the noncondensable gas content a as a process point.
10. The method for estimating the life of the loop heat pipe based on the non-condensable gas combined test according to claim 9, wherein the method comprises the following steps: in the fifth step, the method for judging whether the loop heat pipe fails within the service life duration is as follows:
when the service life of the loop heat pipe is required, searching the non-condensable gas content corresponding to the service life required time according to the time-non-condensable gas content extrapolation linear graph; substituting the content of the non-condensable gas into a nitrogen volume-temperature curve chart, searching the corresponding temperature, and when the temperature is not more than a threshold value TmaxJudging that the loop heat pipe does not lose efficacy within the service life; otherwise, judging that the loop heat pipe fails within the service life.
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