CN217005469U - Three-dimensional pulsating heat pipe with unidirectional circulation flow characteristic - Google Patents
Three-dimensional pulsating heat pipe with unidirectional circulation flow characteristic Download PDFInfo
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Abstract
The utility model provides a three-dimensional pulsating heat pipe with unidirectional circulation flow characteristic, which is a multi-elbow pulsating heat pipe consisting of a heating section, an insulating section and a condensing section, wherein an upper elbow of the condensing section and a lower elbow of the heating section adopt an asymmetric heating mode and are used for promoting the formation of unidirectional flow. The pulsating heat pipe adopts a structural form, under the condition of not increasing additional parts and flow resistance, the structural asymmetry is utilized to promote unidirectional flow to be effectively formed in the pulsating heat pipe, and the flow direction is fixed. The utility model adopts an asymmetric heating mode to promote the formation of unidirectional flow, and can further promote the formation of single-row circulation flow by reducing the curvature radius of the upper elbow, simultaneously reducing the curvature radius of the elbows at two ends or increasing the pipe diameter, thereby improving the heat transfer performance of the pulsating heat pipe.
Description
Technical Field
The utility model relates to the technical field of heat transfer elements, in particular to a three-dimensional pulsating heat pipe with a unidirectional circulation flow characteristic.
Background
The pulsating heat pipe is a novel and efficient heat transfer element which can be used in a micro space and a high heat flow density place. The pulsating heat pipe generally consists of a plurality of groups of capillary tubes, and is generally divided into a heating section (heat absorption end), a heat insulation section and a condensation section (heat release end). The working fluid filled in under vacuum forms a gas-liquid slug interval state under the action of surface tension and flow resistance. The saturated steam pressure difference formed by the temperature difference between the cold end and the hot end pushes and maintains the working medium to move in the pipe. Besides the heat transfer through the phase change of the working medium, the heat transfer performance of the pulsating heat pipe is greatly improved by forced convection caused by random oscillation of the working medium at the heat absorption end and the heat release end. Along with the increase of input heat, the working medium moves more intensely in the pipe, forced convection is further enhanced, and the heat transfer capacity of the pulsating heat pipe is obviously improved. Therefore, pulsating heat pipes are considered to be one of the most effective means of addressing heat transfer at high heat flux densities.
Compared with the pulsating heat pipe with a two-dimensional structure, the pulsating heat pipe with the three-dimensional structure has better heat transfer performance and higher heat transfer limit. In addition, the heat transfer performance of the pulsating heat pipe can be greatly improved by the formation of the unidirectional circulation flow. The scheme adopted at present is that a one-way check valve is added locally, the pulsation effect of the working medium is weakened, and then one-way flow is formed, but the flow resistance and the complexity of the structure are increased, and meanwhile, the design cost and the sealing difficulty are increased. Therefore, under the condition that no additional part is added, the flowing state of the working medium is improved through reasonable structural design and optimization, the working medium is promoted to form stable unidirectional circulation flow in the three-dimensional pulsating heat pipe, and the heat transfer performance of the three-dimensional pulsating heat pipe is greatly improved.
SUMMERY OF THE UTILITY MODEL
According to the scheme provided by the prior art, the one-way check valve is added locally to weaken the pulsation effect of the working medium and further form one-way flow, but the technical problems of flow resistance and structural complexity are increased, and meanwhile, the design cost and the sealing difficulty are increased, so that the three-dimensional pulsating heat pipe with the one-way circulating flow characteristic is provided. The utility model promotes the formation of unidirectional flow mainly by adopting an asymmetric heating mode, further promotes the formation of single-row circulating flow by reducing the curvature radius of the upper elbow, simultaneously reducing the curvature radius of the elbows at two ends or increasing the pipe diameter, and promotes the heat transfer performance of the pulsating heat pipe.
The technical means adopted by the utility model are as follows:
a three-dimensional pulsating heat pipe with unidirectional circulation flow characteristic is a multi-elbow pulsating heat pipe consisting of a heating section, a heat insulation section and a condensation section, wherein an upper elbow of the condensation section and a lower elbow of the heating section adopt an asymmetric heating mode and are used for promoting the formation of unidirectional flow; the structure of the pulsating heat pipe is a first structure or a second structure;
the first structure is a spiral pulsating heat pipe which is distributed on different sides of an asymmetric cold and heat source;
the second structure is a convolute structure pulsating heat pipe distributed on the same side of the asymmetric cold and heat source.
Further, the first structure and the second structure are pulsating heat pipe structures with the curvature radius of the upper bend and the curvature radius of the lower bend changed, wherein the change of the curvature radius of the upper bend and the curvature radius of the lower bend means that: the radius of curvature of the upper bend is reduced, or the radius of curvature of the lower bend is increased, or both are reduced.
Further, the first structure and the second structure are pulsating heat pipe structures with increased pipe diameters.
Furthermore, the convolution structure pulsating heat pipe is obtained by rotating the upper part and the lower part of the pulsating heat pipe by 180 degrees according to the center line on the basis of the spiral structure pulsating heat pipe, and is shaped like a 8.
Further, when the first structure and the second structure are pulsating heat pipe structures with reduced upper elbow curvature radius, the upper elbow curvature radius is reduced on the basis of the original upper elbow curvature radius, and the reduced curvature radius cannot be smaller than 0.5 time of the pipe diameter.
Further, when the first structure and the second structure are pulsating heat pipe structures with increased lower elbow curvature radius, the lower elbow curvature radius is increased on the basis of the original lower elbow curvature radius, and the increased curvature radius cannot be larger than the sum of the straight pipe length and the top elbow curvature radius.
Further, when the first structure and the second structure are pulsating heat pipe structures capable of simultaneously reducing the curvature radius of the upper elbow and the lower elbow, the curvature radius of the upper elbow and the lower elbow is simultaneously reduced on the basis of the original curvature radius of the upper elbow and the lower elbow, and the reduced curvature radius cannot be smaller than 0.5 time of the pipe diameter.
Furthermore, when the first structure and the second structure are pulsating heat pipe structures after the pipe diameter is increased, the pipe diameter of the pulsating heat pipe structures is increased on the basis of the pipe diameter of the original pulsating heat pipe, and the increased pipe diameter cannot exceed 2 times of the curvature radius of the minimum elbow to the maximum.
The utility model also provides a structural design method of the three-dimensional pulsating heat pipe with the unidirectional circulation flow characteristic, which is a structural design method for promoting the working medium to form stable unidirectional flow in the pipe and greatly improving the heat transfer performance of the pulsating heat pipe, and comprises the following steps:
step one, adopting an asymmetric heating mode to respectively establish a first model, a second model and a third model; the first model is a pressure drop brought by a gravity term when a working medium moves a small distance ds in the process of respectively carrying out anticlockwise flow and clockwise flow; the second model is a flow pressure drop brought by the shearing force of the pipe wall surface when the working medium moves a small distance ds in the process of respectively carrying out anticlockwise flow and clockwise flow; the third model is the elbow two-phase pressure drop obtained when the working medium moves a small distance ds in the process of respectively carrying out anticlockwise and clockwise flow on the working medium;
combining the first model, the second model and the third model to obtain a fourth model and a fifth model, wherein the fourth model is the flow pressure drop of the working medium in the pipe when the working medium flows clockwise for a small distance ds, and the fifth model is the flow pressure drop of the working medium in the pipe when the working medium flows anticlockwise for the small distance ds;
step three, obtaining a sixth model by taking a difference value between the fifth model and the fourth model, wherein the sixth model is a flow pressure drop difference of working medium flowing anticlockwise and clockwise, namely the pressure drop difference of the working medium flowing towards two sides along the heat absorption end in the three-dimensional pulsating heat pipe;
step four, based on the fact that the working medium is uniformly distributed in the pipe, after the working medium works stably, the gravity pressure drop is ignored, a seventh model is obtained according to the second model and the third model, and the seventh model is the flowing pressure drop of the working medium after the working medium works stably in the pipe;
and step five, analyzing the influence of the curvature radius and the pipe diameter on the flow pressure drop according to the sixth model and the seventh model to obtain the structure of the three-dimensional pulsating heat pipe with the unidirectional circulation flow characteristic.
Further, the first step satisfies: the cross section shapes of all parts in the pulsating heat pipe are kept constant; neglecting the shearing force between the air plug and the wall surface of the pipe; the air plugs and the liquid plugs are uniformly distributed in the pipe, namely the length of the liquid plugs in any pipe length is as follows:
wherein
For the liquid filling rate, L is any tube length; when the working medium flows at the cold end and the hot end, the working medium can be seen as the movement of a single liquid plug; the flowing pressure drop of the working medium in the pipe comprises gravity pressure drop, shearing force pressure drop and elbow pressure drop: Δ P ═ Δ PG+ΔPS+ΔPBIn which Δ PGIs the gravitational pressure drop; delta PSIs the shear force pressure drop; delta PBIs the elbow pressure drop.
Further, the first model satisfies the following formula:
in the formula,. DELTA.PG,upIn the anticlockwise flow of the working medium, when the working medium moves a small distance ds, the pressure drop is caused by a gravity term; delta PG,downIn the clockwise flow of the working medium, when the working medium moves a small distance ds, the pressure drop is caused by a gravity term; the negative sign indicates a decrease in pressure drop in the flow direction; rholIs the density of the liquid; g is the acceleration of gravity;
the filling rate is shown.
Further, the second model satisfies the following formula:
wherein the content of the first and second substances,
in the formula,. DELTA.PS,upIn the anticlockwise flow of the working medium, when the working medium moves a small distance ds, the flow pressure drop is caused by the shearing force of the wall surface of the pipe; delta PS,downWhen the working medium flows clockwise and moves a small distance ds, the flow pressure drop is caused by the shearing force of the wall surface of the pipe; l iseffIs the effective length of the pulsating heat pipe; l iscThe length of the cooling section; l is a radical of an alcoholeIs the length of the heating section; d is the inner diameter of the pipe; f is the friction coefficient; u is the flow velocity of the liquid plug; a is the channel cross-sectional area.
Further, the third model satisfies the following formula:
wherein, the first and the second end of the pipe are connected with each other,
in the formula,. DELTA.PB,upThe pressure drop of two phases of the elbow is generated when the working medium moves a small distance ds in the anticlockwise flow of the working medium; delta PB,downThe pressure drop of two phases of the elbow is caused when the working medium moves a small distance ds in the clockwise flow of the working medium;
is the mass flow rate of the working fluid; x is dryness; rhovIs the gas phase density; r is the curvature radius; l isBThe length of the elbow is the arc length.
Further, the fourth model satisfies the following formula:
the fifth model satisfies the following formula:
in the formula,. DELTA.PupWhen the working medium flows clockwise for a small distance ds, the flow pressure of the working medium in the pipe is reduced; delta PdownWhen the working medium flows counterclockwise for a small distance ds, the flow pressure of the working medium in the pipe is reduced.
Further, the sixth model satisfies the following formula:
in the formula,. DELTA.PdThe difference of flow pressure drop for the counterclockwise and clockwise flowing of the working medium;
when the lengths of the cold end and the hot end of the pulsating heat pipe are consistent, the value of the sixth model is constantly larger than zero, the possibility that the working medium flows along a single direction is higher, the value of the sixth model is higher, the flowing direction of the liquid plug is more uniform, and the heat transfer performance of the pulsating heat pipe is better;
the seventh model satisfies the following formula:
in the formula,. DELTA.PfThe pressure drop of the working medium after stable operation in the pipe is obtained;
the smaller the value of the seventh model is, the smaller the flow resistance of the liquid plug in the pulsating heat pipe is, the more violent the movement is, and the better the performance of the pulsating heat pipe is;
the unidirectional flowability and the heat transfer performance of the pulsating heat pipe can be improved by reducing the curvature radius of the upper elbow of the pulsating heat pipe, or increasing the curvature radius of the lower elbow, or increasing the pipe diameter.
Compared with the prior art, the utility model has the following advantages:
1. the three-dimensional pulsating heat pipe with the unidirectional circulation flow characteristic provided by the utility model has the advantages that the heat transfer performance of the pulsating heat pipe can be greatly enhanced due to the formation of unidirectional flow, the unidirectional flow is effectively formed in the pulsating heat pipe by utilizing the asymmetry of the structure under the condition of not increasing additional parts and flow resistance, and the flow direction is fixed.
2. The three-dimensional pulsating heat pipe with the unidirectional circulation flow characteristic provided by the utility model can promote unidirectional flow to further strengthen the heat transfer performance of the pulsating heat pipe, and in the embodiment, the thermal resistance of the B2 pulsating heat pipe reaches 0.25 ℃/W under 100W input power. The structural design and optimization scheme not only reduces the design and manufacturing cost of the pulsating heat pipe on the unidirectional flow structure, but also is more favorable for the wide application of the pulsating heat pipe.
3. The three-dimensional pulsating heat pipe with the unidirectional circulation flow characteristic provided by the utility model can promote the formation of unidirectional flow by adopting an asymmetric heating mode, and can further promote the formation of single-row circulation flow by reducing the curvature radius of the upper elbow, simultaneously reducing the curvature radius of the elbows at two ends or increasing the pipe diameter, thereby improving the heat transfer performance of the pulsating heat pipe.
In conclusion, the technical scheme of the utility model can solve the problems that the currently adopted scheme is to add a one-way check valve locally, weaken the pulsation effect of the working medium and further form one-way flow, but the flow resistance and the complexity of the structure are increased, and the design cost and the sealing difficulty are increased.
Based on the reasons, the utility model can be widely popularized in the fields of heat transfer and the like.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
Fig. 1 is a schematic diagram of a conventional pulsating heat pipe having a three-dimensional structure, in which (a) is a bilaterally symmetrical cooling and heating source distribution pattern, (b) is a side view of (a), (c) is an ipsilateral cooling and heating source distribution pattern, and (d) is a side view of (c).
Fig. 2 is a schematic diagram of a pulsating heat pipe with a three-dimensional structure and asymmetric cold and heat source distribution according to the present invention.
Fig. 3 is a side view of fig. 2.
FIG. 4 is a schematic diagram of theoretical analysis of working medium flowing in the tube, wherein (a) is a structural unit, (b) is counterclockwise flowing, and (c) is clockwise flowing.
FIG. 5 shows the theoretical calculation results of elbow pressure drop difference and flow pressure drop of the present invention, wherein (a) is elbow pressure drop difference and (b) is flow pressure drop.
FIG. 6 is a schematic diagram of a three-dimensional pulsating heat pipe with an improved structure according to the present invention.
Fig. 7 is a side view of fig. 6.
Fig. 8 is a schematic diagram of an improved structure of a three-dimensional pulsating heat pipe under the distribution of cold and heat sources on the same side.
Fig. 9 is a side view of fig. 8.
Fig. 10 is a schematic diagram of a further improved three-dimensional pulsating heat pipe structure under the same-side cold and heat source distribution of the present invention.
Fig. 11 is a side view of fig. 10.
FIG. 12 is a temperature profile for the non-operating, pulsating, unstable unidirectional, unidirectional operation of the present invention, wherein (a) is the non-operating state, (b) is the pulsating state, (c) is the unstable unidirectional flow state, and (d) is the stable unidirectional flow state.
FIG. 13 is a comparison of the performance of pulsating heat pipes of various configurations of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in the figure, the utility model provides a three-dimensional pulsating heat pipe with unidirectional circulation flow characteristic, which is a multi-elbow pulsating heat pipe consisting of a heating section, a heat insulation section and a condensation section, wherein an upper elbow of the condensation section and a lower elbow of the heating section adopt an asymmetric heating mode and are used for promoting the formation of unidirectional flow; the structure of the pulsating heat pipe is a first structure or a second structure;
the first structure is a spiral pulsating heat pipe which is distributed on different sides of an asymmetric cold and heat source; the asymmetrical different-side distribution of cold and heat sources means that a cold source is applied to one side of the upper elbows of the plurality of condensing sections, a heat source is applied to one side of the lower elbows of the plurality of heating sections, and the applied cold and heat sources are positioned on different sides;
the second structure is a convoluted pulsating heat pipe distributed on the same side of the asymmetric cold and heat source; the asymmetrical cold and heat source distribution on the same side means that a cold source is applied to one side of the upper elbows of the plurality of condensing sections, a heat source is applied to one side of the lower elbows of the plurality of heating sections, and the applied cold and heat sources are positioned on the same side.
In a preferred embodiment, the first structure and the second structure are pulsating heat pipe structures that change the radius of curvature of the upper bend and the lower bend, where the change of the radius of curvature of the upper bend and the lower bend means: the radius of curvature of the upper bend is reduced, or the radius of curvature of the lower bend is increased, or both are reduced.
In a preferred embodiment, the first structure and the second structure are pulsating heat pipe structures having increased pipe diameters.
In a preferred embodiment, the spiral-structure pulsating heat pipe is obtained by rotating the upper part and the lower part of the pulsating heat pipe by 180 degrees according to the center line on the basis of the spiral-structure pulsating heat pipe, and is shaped like a figure "8".
In a preferred embodiment, when the first structure and the second structure are pulsating heat pipe structures with reduced upper bend curvature radius, the upper bend curvature radius is reduced on the basis of the original upper bend curvature radius, and the reduced curvature radius cannot be smaller than 0.5 times of the pipe diameter.
In a preferred embodiment, when the first structure and the second structure are pulsating heat pipe structures in which the radius of curvature of the lower bend is increased, the radius of curvature of the lower bend is increased from the original radius of curvature of the lower bend, and the increased radius of curvature is not larger than the sum of the length of the straight pipe and the radius of curvature of the top bend.
In a preferred embodiment, when the first structure and the second structure are pulsating heat pipe structures that simultaneously reduce the radius of curvature of the upper and lower bends, the radius of curvature of the upper and lower bends is simultaneously reduced on the basis of the original radius of curvature of the upper and lower bends, and the reduced radius of curvature is not less than 0.5 times the pipe diameter.
Furthermore, when the first structure and the second structure are pulsating heat pipe structures with increased pipe diameters, the pipe diameters of the first structure and the second structure are increased on the basis of the pipe diameters of the original pulsating heat pipes, and the increased pipe diameters cannot exceed 2 times of the curvature radius of the minimum elbow to the maximum extent.
Example 1
The conventional three-dimensional pulsating heat pipe structure is shown in fig. 1. The structure is mainly characterized in that the upper elbow and the lower elbow are consistent, and the heating and the cooling are carried out on the same side. In the pulsating heat pipe in the form (a) and (b) in fig. 1, because the distribution of cold and heat sources has symmetry, the flow of working medium in the pipe has randomness, and the pulsating flow is the main working form of heat transfer. In fig. 1, (c) and (d) are disposed on the same side of the cold and heat sources, and the possibility of the unidirectional flow is higher than that in fig. 1 (a), but the structure still has an optimizable space.
Aiming at the structural improvement of the three-dimensional pulsating heat pipe shown in figure 1, as shown in figures 2 and 3, the utility model adopts an asymmetric heating mode (the heating power of straight pipes on two sides of an elbow is the same, namely uniform heating, and the heating power is different, namely non-uniform or asymmetric heating). One of the cells was taken as the study, as shown in FIG. 4. And assume that: (1) the cross section shapes of all parts in the tube are kept constant; (2) neglecting the shearing force between the air plug and the wall surface of the pipe; (3) the air plug and the liquid plug are uniformly distributed in the pipe, namely the length of the liquid plug in any pipe length is as follows:
wherein
For the liquid fill rate, L is any tube length; (4) when the working medium flows at the cold end and the hot end, the working medium can be seen as the movement of a single liquid plug; (5) the pressure drop of the working medium flowing in the tube comprises a gravitational pressure drop (delta P)G) Shear force pressure drop (Δ P)S) And elbow pressure drop (Δ P)B)：
ΔP＝ΔPG+ΔPS+ΔPB (1)
As shown in fig. 4 (b), the working medium flows counterclockwise, and the pressure drop caused by the gravity term when the working medium moves a small distance ds is:
wherein the negative sign indicates a decrease in pressure drop in the direction of flow; rholIs the density of the liquid; g is the acceleration of gravity;
the filling rate is shown. The flow pressure drop brought by the shearing force of the tube wall surface at the moment is as follows:
wherein:
in the formula, LeffIs the effective length of the pulsating heat pipe; l iscIs the length of the cooling section; d is the inner diameter of the pipe; f is the friction coefficient; u is the flow velocity of the liquid plug; a is the channel cross-sectional area. The pressure drop of the two phases of the elbow is as follows:
wherein the content of the first and second substances,
is the mass flow rate of the working fluid, and C and KspRespectively as follows:
wherein x is dryness; ρ is a unit of a gradientvIs the gas phase density; r is the curvature radius; l isBIs the arc length of the elbow; c and KspIs a coefficient expression.
Substituting equations (2), (3), (4) and (5) into equation (1) yields the pressure drop if the counterclockwise flow ds:
similarly, assuming that the working fluid flows clockwise by a small distance ds as in (c) of fig. 4, the pressure drop of the working fluid flowing in the pipe is:
wherein L iseIs the length of the heating section; delta PB,downThe pressure drop of the two phases of the elbow when the working medium flows clockwise.
The difference in pressure drop for counterclockwise and clockwise flow is therefore:
the above formula is the pressure drop difference when the working medium flows to two sides along the heat absorption end in the three-dimensional pulsating heat pipe. And when the lengths of the cold end and the hot end are consistent, the above formula is constantly larger than zero. Therefore, the possibility that the working medium flows along a single direction is higher, the higher the value of the above formula is, and the better the heat transfer performance of the pulsating heat pipe is.
The working medium is uniformly distributed in the pipe, and the gravity pressure drop can be ignored after the stable work. The flow pressure drop of the working medium in the pipe mainly comprises shearing force pressure drop and elbow pressure drop:
the above formula is the flow resistance pressure drop after the working medium works stably in the pipe. The larger the value is, the larger the resistance of the working medium in the pipe is, the more restricted the working medium flows, and the worse the heat transfer performance of the pulsating heat pipe is.
Equations (10) and (11) above are derived as the flow pressure drop difference and the flow pressure drop, respectively. Theoretically, the larger the value of the formula (10), the more uniform the flow direction of the liquid plug is, and the better the performance of the pulsating heat pipe is. Theoretically, the smaller the value of the formula (11), the smaller the flow resistance of the liquid plug in the pulsating heat pipe, the more violent the movement, and the better the performance of the pulsating heat pipe. The effect of the radius of curvature and the pipe diameter on the flow pressure drop is calculated for equations (10) and (11), and the theoretical analysis results are shown in fig. 5. The flow pressure drop difference can be increased by reducing the curvature radius of the upper elbow, and the flow pressure drop can be reduced by increasing the pipe diameter. The two modes can improve the one-way fluidity and the heat transfer performance of the pulsating heat pipe.
The analysis shows that the adoption of an asymmetric heating mode can improve the consistency of the flowing direction of the working medium in the pipe and promote the formation of unidirectional flow. In order to increase the asymmetry of the pressure drop of the flowing working medium in the pipe, further improve the consistency of the flowing direction of the working medium in the pipe and promote the formation of unidirectional flow, the formation of unidirectional flow can be realized by reducing the curvature radius of the upper elbow (or increasing the curvature radius of the lower elbow), as shown in fig. 6 and 7. When the air plug absorbs heat at the heat absorption end and expands to push the liquid plugs at the two sides to flow, the curvature radius of the lower elbow is larger than that of the upper elbow, so that the pressure drop loss generated when the liquid plugs flow through the lower elbow is larger, and the flow resistance is larger than that of the upper elbow. Thus, the air lock tends to push the liquid lock to flow upwards along the straight pipe, and the unidirectional flow is promoted to be formed.
In practical use, heating and cooling are often in the same plane, and based on the above analysis, a pulsating heat pipe with a three-dimensional structure as shown in fig. 8, 9, 10 and 11 is further proposed, which is in the form of a design scheme of heating and cooling on the same side. In the scheme shown in fig. 8, when the air plug expands to push the liquid plug to flow upwards along the heat absorption end, due to the existence of the convolution structure, the liquid plug flows through the heat release end back side straight pipe and flows to the heat release end on the same side through the upper elbow, and unidirectional flow is formed. The arrangement shown in figure 10 is based on the arrangement shown in figure 8 and adds a radius of curvature to the lower bend to further promote the formation of unidirectional flow. The convolution structure pulsating heat pipe is obtained by rotating the upper part and the lower part of the pulsating heat pipe by 180 degrees according to the center line on the basis of the spiral structure pulsating heat pipe, and is shaped like a figure 8.
Example 2
In the embodiment, an 8-elbow pulsating heat pipe with the structure type shown in FIG. 6 is adopted, water is used as a working medium, and a comparison experiment is carried out with the liquid filling rate of 50%. The specific example parameters are shown in table 1 (table 1 shows the detailed structural parameters of three tube-type pulsating heat pipes of example A, B, C). In the examples, the temperature distribution method was used to judge the formation of the unidirectional flow, as shown in FIG. 12. When the pulsating heat pipe does not reach the operating condition, the hot end temperature will gradually increase due to the heat input, as shown in fig. 12 (a). When the temperature difference between the cold end and the hot end reaches the starting condition, the temperatures of the heat absorption end, the heat release end and the heat insulation section of the pulsating heat pipe obviously fluctuate, as shown in fig. 12 (b). After the pulsating heat pipe forms unidirectional flow, the temperature distribution of the heat absorption end, the heat release end and the heat insulation section can be obviously layered, as shown in fig. 12(d), namely, the temperature of the three ends can tend to be divided into 4 groups. If the input power cannot maintain the unidirectional flow of the working medium, the pulsating flow and the unidirectional flow alternately occur, and the temperature distribution of the three terminals is as shown in fig. 12 (c). Therefore, the unidirectional flow condition can be counted according to the temperature distribution condition of each type of pulsating heat pipe in the power interval, as shown in table 2 (table 2 is the flow condition statistical result of each embodiment). Comparing a, it can be seen that a single reduction in the radius of curvature B of the upper bend facilitates unidirectional flow at lower input powers. In addition, the formation of unidirectional flow is also facilitated by increasing the pipe diameter C. The thermal resistance of each example is shown in fig. 13, and the result shows that the heat transfer performance of the pulsating heat pipe can be further improved by improving the one-way fluidity by the means.
TABLE 1 structural parameters of the examples
Table 2 flow statistics for the examples
Note: x is not working; OU is unstable unidirectional flow; u is a steady unidirectional flow.
In conclusion, the formation of unidirectional flow can be promoted by adopting an asymmetric heating mode, the formation of single-row circulating flow can be further promoted by reducing the curvature radius of the upper elbow and simultaneously reducing the curvature radius of the elbows at two ends or increasing the pipe diameter, and the heat transfer performance of the pulsating heat pipe is improved.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the utility model has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (8)
1. A three-dimensional pulsating heat pipe with unidirectional circulation flow characteristic is characterized in that the three-dimensional pulsating heat pipe is a multi-elbow pulsating heat pipe consisting of a heating section, an insulating section and a condensing section, wherein an upper elbow of the condensing section and a lower elbow of the heating section adopt an asymmetric heating mode and are used for promoting the formation of unidirectional flow; the structure of the pulsating heat pipe is a first structure or a second structure;
the first structure is a spiral pulsating heat pipe which is distributed on different sides of an asymmetric cold and heat source;
the second structure is a convolute structure pulsating heat pipe distributed on the same side of the asymmetric cold and heat source.
2. The three-dimensional pulsating heat pipe having unidirectional circulation flow characteristics as claimed in claim 1, wherein said first structure and said second structure are pulsating heat pipe structures that change the radius of curvature of upper and lower bends, wherein said change of the radius of curvature of upper and lower bends is: the radius of curvature of the upper bend is reduced, or the radius of curvature of the lower bend is increased, or both are reduced.
3. A three-dimensional pulsating heat pipe having unidirectional circulation flow characteristics as claimed in claim 1, wherein said first structure and said second structure are pulsating heat pipe structures having increased pipe diameter.
4. The three-dimensional pulsating heat pipe with unidirectional circulation flow characteristic as claimed in any one of claims 1 to 3, wherein said convolute structure pulsating heat pipe is obtained by rotating the upper and lower portions of the pulsating heat pipe 180 ° from the center line based on the spiral structure pulsating heat pipe, and is shaped like a "8".
5. A three-dimensional pulsating heat pipe having unidirectional circulation flow characteristic as claimed in claim 2, wherein when said first structure and said second structure are pulsating heat pipe structures with reduced upper bend curvature radius, the upper bend curvature radius is reduced based on the original upper bend curvature radius, and the reduced curvature radius is not less than 0.5 times of the pipe diameter.
6. A three-dimensional pulsating heat pipe having unidirectional circulation flow characteristics as claimed in claim 2, wherein when said first structure and said second structure are pulsating heat pipe structures with increased lower elbow curvature radius, the lower elbow curvature radius is increased based on the original lower elbow curvature radius, and the increased curvature radius is not greater than the sum of the straight pipe length and the top elbow curvature radius.
7. A three-dimensional pulsating heat pipe having unidirectional circulation flow characteristic as claimed in claim 2, wherein when said first structure and said second structure are pulsating heat pipe structures that simultaneously reduce the radius of curvature of upper and lower bends, the radius of curvature of upper and lower bends is simultaneously reduced based on the original radius of curvature of upper and lower bends, and the reduced radius of curvature is not less than 0.5 times of the pipe diameter.
8. A three-dimensional pulsating heat pipe having unidirectional circulation flow characteristic as claimed in claim 3, wherein when said first structure and said second structure are pulsating heat pipe structures with increased pipe diameter, the pipe diameter is increased based on the original pulsating heat pipe diameter, and the increased pipe diameter is not more than 2 times of the minimum bend curvature radius at maximum.
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