CN108934152B - Heat exchange enhancement device for natural convection heat dissipation and design method thereof - Google Patents
Heat exchange enhancement device for natural convection heat dissipation and design method thereof Download PDFInfo
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- CN108934152B CN108934152B CN201810849988.7A CN201810849988A CN108934152B CN 108934152 B CN108934152 B CN 108934152B CN 201810849988 A CN201810849988 A CN 201810849988A CN 108934152 B CN108934152 B CN 108934152B
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- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K7/00—Constructional details common to different types of electric apparatus
- H05K7/20—Modifications to facilitate cooling, ventilating, or heating
- H05K7/20009—Modifications to facilitate cooling, ventilating, or heating using a gaseous coolant in electronic enclosures
- H05K7/20127—Natural convection
Abstract
The invention discloses a heat exchange strengthening device for natural convection heat dissipation and a design method thereof, wherein the heat exchange strengthening device comprises: an auxiliary heat dissipation wall; the auxiliary heat dissipation wall is fixedly arranged on the surface of the equipment to be cooled, and the auxiliary heat dissipation wall and the surface of the equipment to be cooled form a cylindrical ventilation channel; the cross-sectional area of the cylindrical ventilation channel is kept unchanged or gradually reduced along the airflow flowing direction; the auxiliary heat dissipation wall is provided with a plurality of ventilation holes. The heat exchange enhancement device can be applied to the surface of equipment based on natural convection heat exchange, and can improve the natural convection heat dissipation effect of air; the solar radiation can be slowed down, and the surface temperature of outdoor equipment to be cooled is reduced. The auxiliary heat dissipation wall can prevent sunlight from directly radiating on the surface of the equipment to be cooled, so that the total heat dissipation amount of the equipment is reduced; the cylindrical ventilation channel structure can form a chimney suction effect, effectively improve the natural convection velocity of air near the surface of the equipment to be cooled, and can strengthen heat exchange.
Description
Technical Field
The invention belongs to the technical field of natural cooling, mainly aims at electronic equipment, electrical equipment, energy power equipment and the like which naturally convect and radiate heat outdoors by air, and particularly relates to a heat exchange strengthening device for natural convection and radiation and a design method thereof.
Background
Electronic equipment, electrical equipment, energy power equipment and the like operate in an outdoor environment and rely on natural convection of air for natural cooling. In outdoor environments, equipment generates heat when working, the surface of the equipment is directly radiated by the sun, and the surface heat flux density of the equipment, particularly high-power equipment, can reach several kilowatts per square meter. In the strong period of solar irradiation, the temperature of outdoor air rises, the heat dissipation effect on the surface of the equipment to be cooled is greatly influenced, the control and the adjustment of the equipment are greatly influenced, the equipment can be shut down in severe cases, and the reliability of the operation of the equipment is seriously influenced. Promote the natural convection radiating effect of air, reduce outdoor equipment surface temperature of waiting to cool off, be the important problem that awaits solving in fields such as industrial production and military science and technology.
Disclosure of Invention
The invention aims to provide a heat exchange strengthening device for natural convection heat dissipation and a design method thereof, so as to solve the technical problems. The heat exchange enhancement device can be applied to the surface of equipment based on natural convection heat exchange, and can improve the natural convection heat dissipation effect of air; the solar radiation can be slowed down, and the surface temperature of outdoor equipment to be cooled is reduced.
In order to achieve the purpose, the invention adopts the following technical scheme:
a heat exchange enhancement device for natural convection heat dissipation comprises: an auxiliary heat dissipation wall; the auxiliary heat dissipation wall is fixedly arranged on the surface of the equipment to be cooled, and the auxiliary heat dissipation wall and the surface of the equipment to be cooled form a cylindrical ventilation channel; the cross-sectional area of the cylindrical ventilation channel is kept unchanged or gradually reduced along the airflow flowing direction; the auxiliary heat dissipation wall is provided with a plurality of ventilation holes.
Furthermore, the device also comprises a plurality of fins; the fins are all fixedly arranged on the surface of the equipment to be cooled; the arrangement form of the fins is whole strip arrangement or sectional arrangement; the fins are arranged in a row or in a fork manner; the height of the fins is greater than the thickness of the boundary layer of the surface of the device to be cooled.
Furthermore, the fins are provided with a plurality of flow guide holes which are arranged along the flowing direction of the air flow.
Furthermore, the fins are right-angle V-shaped fins; the open ends of the right-angled V-shaped fins face the airflow outlet end of the cylindrical ventilation channel.
Further, the coating also comprises a first coating layer for improving the absorption ratio and a second coating layer for improving the radiance; the first coating is fixedly arranged on the inner surface of the auxiliary heat dissipation wall; the second coating is fixedly arranged on the surface of the equipment to be cooled.
Furthermore, the section of the cylindrical ventilation channel formed by the auxiliary heat dissipation wall and the surface of the equipment to be cooled is trapezoidal, circular arc or sawtooth square.
A design method of a heat exchange strengthening device for natural convection heat dissipation comprises the following steps:
and 5, determining the shape, size, density and arrangement mode of the vent holes on the auxiliary heat dissipation wall by taking the natural convection heat transfer coefficient of the surface of the equipment to be cooled as an index according to the influence rule of the heat flow conditions determined in the step 1 on the ambient air speed and the annual statistical wind speed of the place where the equipment to be cooled is located.
Furthermore, in the step 2, the geometric dimension of the cylindrical ventilation channel is selected to utilize the chimney suction effect to achieve the equipment surface cooling, and the air flow in the cylindrical ventilation channel is not limited as the guidance; the section shape of the cylindrical ventilation channel is determined according to the temperature distribution of the surface of the equipment to be cooled and the heat dissipation requirement.
Further, in the step 4, the expanded heat dissipation area of the fins is 20% -400% of the surface area of the equipment to be cooled; when the fins are too high to influence the flow of the airflow in the vertical direction, the fins are provided with flow guide holes; the shape and the geometric dimension of the flow guide hole are designed by taking the heat exchange coefficient improvement as an index.
Furthermore, in the step 5, part of the vent holes are formed in the direction facing the natural wind, and part of the vent holes are formed in the upstream position of the surface temperature extreme value area of the equipment to be cooled through which airflow flows.
Compared with the prior art, the invention has the following beneficial effects:
the invention takes the surface of the equipment to be cooled as the basis, and utilizes the auxiliary heat dissipation wall to build the cylindrical ventilation channel, and the sunlight can be prevented from directly radiating the surface of the equipment to be cooled by the blocking of the auxiliary heat dissipation wall, so that the total heat dissipation amount required by the equipment can be reduced. The chimney suction effect formed by constructing the cylindrical ventilation channel can effectively improve the natural convection speed of air near the surface of the equipment to be cooled, the cooling condition in the surface temperature extreme value area of the equipment to be cooled can be effectively improved, the heat flux density of different wall surfaces in the cylindrical ventilation channel is uneven, and the hot air easily forms spiral flow in the rising process. The ventilation opening is formed in the auxiliary heat dissipation wall, so that low-pressure environment and natural wind formed when hot air in the cylindrical ventilation channel rises in an accelerated mode can be fully utilized. Air in the environment can be sucked into the cylindrical ventilation channel under the action of the internal and external pressure difference, the flow in the cylindrical ventilation channel is further disturbed, and the convection heat transfer coefficient of the air on the surface of the equipment to be cooled can be effectively improved. Meanwhile, when the ambient wind speed is increased, the convection effect in the cylindrical ventilation channel is more obvious due to the existence of the ventilation holes, the convection heat exchange effect of the air on the surface of the equipment to be cooled is better, and the contact between the equipment and the surrounding space is avoided due to the construction of the cylindrical ventilation channel. Therefore, the invention can reduce the total heat dissipation amount required by the equipment and obviously enhance the natural convection heat exchange efficiency of the surface of the equipment to be cooled, thereby realizing the heat dissipation requirement of the equipment and improving the safe and reliable operation of the equipment.
Furthermore, the fins in different forms are distributed on the surface of the equipment to be cooled, so that the development of a boundary layer in the process that air flows vertically upwards when the surface of the equipment to be cooled is heated can be effectively destroyed, the heat exchange coefficient of the surface of the equipment to be cooled is improved, a local low-pressure area can be formed, surrounding fluid is introduced into a wake area, and the heat exchange capacity of the wake area is further improved. And the addition of the fins can greatly expand the heat dissipation area of the surface of the equipment to be cooled, which is in contact with air, and can effectively improve the heat dissipation effect of the equipment. The fins fixedly arranged on the surface of the equipment to be cooled can adjust the movement path of the airflow in a row or fork arrangement mode, so that more air flows through the temperature extreme value area, and the effective cooling of the temperature extreme value area is realized.
Furthermore, for the high fins, in order to prevent the high fins from influencing the ascending motion of the airflow, the fins can be perforated, so that the weight of the fins is reduced, and airflow ascending channels are formed.
Furthermore, after the cylindrical ventilation channel is built, coating is only needed to be carried out on the outer side of the auxiliary heat dissipation wall, and the surface of the equipment to be cooled is located in the cylindrical ventilation channel, so that the equipment to be cooled is not limited by coating requirements, a coating for improving the radiance can be additionally coated, and the surface temperature of the equipment to be cooled is further reduced.
Furthermore, the section area of the cylindrical ventilation channel formed by the auxiliary heat dissipation wall and the surface of the equipment to be cooled is trapezoidal, circular arc or sawtooth square, and the main difference of various different sections is that the included angle between the auxiliary heat dissipation wall and the surface of the equipment to be cooled is different, and the area of the auxiliary heat dissipation wall is different; the auxiliary heat dissipation wall mainly aims at shielding sunlight from directly irradiating the surface of the equipment to be cooled and forming a chimney suction effect with an obvious effect, the height of the auxiliary heat dissipation wall is generally higher than that of the surface of the equipment, the auxiliary heat dissipation wall is beneficial to shielding the obliquely irradiated sunlight and forming a longer channel to strengthen the chimney suction effect.
Drawings
FIG. 1 is a schematic structural diagram of a heat exchange enhancement device based on natural convection heat dissipation, with a sawtooth square cross section, of a cylindrical ventilation channel according to the present invention;
FIG. 2 is a schematic structural diagram of a heat exchange enhancement device based on natural convection heat dissipation, with a circular arc-shaped section, for a cylindrical ventilation channel according to the present invention;
FIG. 3 is a schematic structural diagram of a heat exchange enhancement device based on natural convection heat dissipation with a trapezoidal cross section of a cylindrical ventilation channel according to the present invention;
FIG. 4 is a schematic structural diagram of a heat exchange enhancement device of an arc-shaped cylindrical ventilation channel and a rectangular vent in parallel arrangement based on natural convection heat dissipation according to the present invention;
FIG. 5 is a schematic structural diagram of a heat exchange enhancement device of the present invention based on natural convection heat dissipation for circular arc-shaped cylindrical ventilation channels and parallel rectangular ventilation holes and V-shaped discontinuous ribs;
FIG. 6 is an enlarged schematic view of the fins of FIG. 5;
FIG. 7 is a cloud of temperature profiles of the surface of the device to be cooled;
FIG. 8 is a cloud of temperature profiles of the surface of the equipment to be cooled with the addition of the semi-circular auxiliary heat dissipating walls and the V-shaped fins;
in fig. 1 to 6, 1, the surface of the device to be cooled; 2. an auxiliary heat dissipation wall; 3. a vent hole; 4. and (4) ribs.
Detailed Description
The invention is described in further detail below with reference to the figures and specific examples.
Referring to fig. 1 to 6, fig. 1 to 3 are schematic views illustrating a natural convection heat transfer enhancing structure of a cylindrical ventilation channel with different cross sections, which sequentially include: saw-tooth square, circular arc and trapezoidal. Fig. 4 is a natural convection heat transfer enhancing structure of a cylindrical ventilation channel having a circular arc cross section and having rectangular ventilation holes 3 arranged in line. Fig. 5 is a natural convection heat transfer enhancing structure of a circular arc-shaped cylindrical ventilation passage and having rectangular ventilation holes 3 arranged in parallel and right-angled V-shaped intermittent ribs 4. The invention relates to a heat exchange strengthening device for natural convection heat dissipation, which comprises: a secondary heat dissipating wall 2 and a plurality of fins 4.
The auxiliary heat dissipation wall 2 is fixedly arranged on the surface 1 of the equipment to be cooled, and the auxiliary heat dissipation wall 2 and the surface 1 of the equipment to be cooled form a vertical upward cylindrical ventilation channel; the cross-sectional area of the cylindrical ventilation channel is kept unchanged or gradually reduced along the airflow flowing direction; the auxiliary heat dissipation wall 2 is provided with a plurality of vent holes 3. The fins 4 are fixedly arranged on the surface 1 of the equipment to be cooled, the vertical cross section of each fin is square, triangular, semicircular and the like, the arrangement type of each fin is a whole piece, a section and the like, the arrangement mode of each fin is a row, a fork row and the like, and the shape and the arrangement mode of the fins 4 are preliminarily selected according to the heat flow density and the heat source distribution of the surface 1 of the equipment to be cooled. And finally determining the arrangement density and the geometric dimension by taking the heat exchange coefficient lifting proportion and the resistance coefficient lifting proportion as indexes. The height of the fins 4 needs to be larger than the thickness of the boundary layer of the surface 1 of the equipment to be cooled, so that the development of the boundary layer in the process that air flows vertically upwards when the surface 1 of the equipment to be cooled is heated is effectively damaged, and the heat exchange coefficient of the surface 1 of the equipment to be cooled is improved. The heat dissipation area of the surface 1 of the equipment to be cooled, which is contacted with air, can be greatly expanded by increasing the height of the fins 4, but the excessively high fins 4 can block the ascending movement of airflow, so that a plurality of flow guide holes are formed in the high fins 4, and the flow guide holes are arranged along the airflow flowing direction, thereby not only reducing the weight of the fins 4, but also forming airflow channels. A coating for improving the absorption ratio is fixedly provided on the inner surface of the auxiliary heat dissipation wall 2. The emissivity-promoting coating is fixedly arranged on the surface 1 of the device to be cooled. Based on the equipment needing heat dissipation, the auxiliary heat dissipation wall 2 is utilized to build a cylindrical ventilation channel. The ventilation holes 3 are formed in the surfaces of the newly added auxiliary heat dissipation walls 2, and measures such as arrangement of the fins 4 on the surface 1 of the equipment to be cooled and coating of the surface of the equipment to be cooled are combined, so that the natural convection heat exchange efficiency of the surface 1 of the equipment to be cooled can be greatly enhanced, the heat dissipation requirement of the equipment is met, and the safety and reliability of the operation of the equipment are improved. The arrangement mode of the vent holes 3 on the auxiliary heat dissipation wall 2 is arranged in a sequential or staggered manner, the shapes of the vent holes are square, round, triangular and the like, the arrangement density and the geometric dimension are variable, and the parameters are determined according to the operation condition of equipment, the surface temperature, the ambient annual statistical wind speed and the like. The fins 4 on the surface 1 of the equipment to be cooled can be all-solid fins or fins with holes in the middle, and the height of the fins needs to be larger than the thickness of a boundary layer on the surface 1 of the equipment to be cooled. The fins 4 have a square, triangular, semicircular and other vertical cross-sectional shapes, are arranged in a whole or segmented manner, are arranged in a staggered or staggered manner, and have variable arrangement density and geometric dimensions, and the above parameters are determined according to equipment operation conditions, equipment dimensions, the thickness of a thermal boundary layer on the surface 1 of the equipment to be cooled, surface temperature, ambient temperature and the like.
The section area of the cylindrical ventilation channel formed by the auxiliary heat dissipation wall 2 and the surface 1 of the equipment to be cooled can be trapezoidal, circular arc or sawtooth square, and the main difference of various different section areas is that the included angle between the auxiliary heat dissipation wall 2 and the surface 1 of the equipment to be cooled is different, and the area of the auxiliary heat dissipation wall 2 is different. The auxiliary heat dissipation wall 2 mainly aims at shielding sunlight from directly irradiating the surface 1 of the equipment to be cooled and forming a chimney suction effect with an obvious effect, the height of the auxiliary heat dissipation wall is generally higher than that of the surface of the equipment, the auxiliary heat dissipation wall is beneficial to shielding the sunlight which is obliquely irradiated, and a longer channel is formed to strengthen the chimney suction effect. The horizontal cross-sectional area size and the shape of tube-shape ventilation passageway can be based on treating 1 temperature in cooling device surface, ambient temperature and treat conditions such as cooling device surface 1 coating and carry out the reasonable selection collocation, for example cross-sectional shape can select semi-circle, triangle-shaped, trapezoidal, sawtooth square etc. cross-sectional area can reduce gradually or keep mutually the same along with the air current ascending direction, supplementary radiating wall 2 is inside also can lay the water conservancy diversion structure, compromise the high-efficient heat transfer in treating 1 temperature extreme area in cooling device surface through these modes. The height of the auxiliary heat dissipation wall 2 is flexibly matched with the height of the surface 1 of the equipment to be cooled according to the ambient temperature, the sunlight irradiation condition, the annual statistical wind speed and the like, and can be equal to, higher than or lower than the height of the surface 1 of the equipment to be cooled.
The invention is based on the surface 1 of the equipment to be cooled, and the auxiliary heat dissipation wall 2 is utilized to construct the semi-cylindrical ventilation channel to avoid the temperature rise of the surface 1 of the equipment to be cooled due to the direct radiation of sunlight, so the heat quantity required to be dissipated to the environment by the equipment is reduced. This may be referred to as "reducing the total amount of heat dissipated" and reducing the amount of heat that needs to be dissipated outwardly from the surface 1 of the device to be cooled. And the newly-added auxiliary heat dissipation wall 2 which absorbs solar radiation and heat radiation of the surface 1 of the equipment to be cooled and the surface 1 of the equipment to be cooled heat the air in the cylindrical ventilation channel, the air is heated by the surrounding wall surfaces to form updraft, and the flow speed is increased. The structure of the cylindrical ventilation channel utilizes the suction effect of the chimney to accelerate the ascending air flow, and compared with a direct natural cooling mode of the equipment, the convection velocity of the air near the surface 1 of the equipment to be cooled is effectively improved, and the heat exchange coefficient is obviously increased. In addition, the further acceleration of the air flow around the temperature extreme value area of the surface 1 of the equipment to be cooled can be adjusted by effectively utilizing the modes that the sectional area of the cylindrical ventilation channel is gradually reduced along with the air flow direction or a flow guide structure is arranged, and the like, so that a more efficient cooling effect is obtained. Meanwhile, the wall surface of the equipment in the cylindrical ventilation channel and the newly-added heat flux are uneven, so that a secondary flow effect is generated in the rising process, spiral flow is easily formed in the rising process of air, and the heat exchange efficiency of the surface 1 of the equipment to be cooled is further enhanced. This may be referred to as "introducing a new effect" which increases the heat transfer coefficient of the surface 1 of the device to be cooled. Under the condition that the flow velocity of ascending air flow in the cylindrical ventilation channel is increased, the pressure intensity is reduced, the auxiliary heat dissipation wall 2 is provided with the ventilation holes 3, the air in the environment is sucked into the cylindrical ventilation channel by fully utilizing the pressure intensity difference between the inside and the outside of the cylindrical ventilation channel, the flow in the cylindrical ventilation channel is further disturbed, and the air convection heat transfer coefficient of the surface 1 of the equipment to be cooled is effectively improved. Meanwhile, when the wind speed of the environmental natural wind rises, the convection effect in the cylindrical ventilation channel is more obvious due to the existence of the ventilation holes 3, the air convection heat exchange effect on the surface 1 of the equipment to be cooled is better, and the contact between the equipment and the surrounding space is not closed due to the construction of the cylindrical ventilation channel. This may be referred to as "lift effect" which increases the heat transfer coefficient of the surface 1 of the device to be cooled. After the surface 1 of the equipment to be cooled is heated, air mainly flows vertically and upwards along the surface 1 of the equipment to be cooled, in the flowing process, the boundary layer is gradually increased, and the heat exchange coefficient of the surface 1 of the equipment to be cooled is reduced. The fins 4 are distributed on the surface 1 of the equipment to be cooled, so that the development of a boundary layer can be effectively damaged, the heat exchange coefficient of the surface 1 of the equipment to be cooled is improved, a local low-pressure area is formed behind the fins, surrounding fluid is introduced into a wake area, and the heat exchange capacity of the wake area is further improved. The addition of the fins 4 can greatly expand the heat dissipation area of the surface 1 of the equipment to be cooled, which is in contact with air, and can effectively improve the heat dissipation effect of the equipment. In addition, for the high fins 4, in order to prevent the high fins from affecting the air flow rising movement, a punching process may be performed on the fins 4, which not only reduces the weight of the fins 4, but also forms air flow rising channels. Moreover, the fins 4 fixedly arranged on the surface 1 of the equipment to be cooled can adjust the moving path of the air flow in a row or fork arrangement mode, so that more air can flow through the temperature extreme value area, and the effective cooling of the temperature extreme value area is realized. For the field where the surface 1 of the device to be cooled has a coating requirement, a coating for increasing the emissivity cannot be used. The auxiliary heat dissipation wall 2 is coated to effectively avoid the problem, and the surface 1 of the equipment to be cooled is positioned at the inner side of the cylindrical ventilation channel and can not be limited by coating requirements, so that a coating for improving the radiance can be additionally coated, and the temperature of the surface 1 of the equipment to be cooled is further reduced.
The invention relates to a design method of a heat exchange strengthening device for natural convection heat dissipation, which comprises the following steps:
and 2, determining the geometric size and the cross section shape of the cylindrical ventilation channel according to the self characteristics and the temperature distribution of the surface 1 of the equipment to be cooled obtained in the step 1 and the heat dissipation requirement of the surface 1 of the equipment to be cooled. The choice of channel geometry is guided primarily by the goal of maximizing the use of stack suction to achieve equipment surface cooling and not limiting the air flow in the cylindrical channel. The cross-sectional shape is determined mainly according to the temperature distribution of the surface 1 of the equipment to be cooled and the heat dissipation requirements. For example, when the cooling requirement of the surface 1 of the device to be cooled is high and the heat flux density is high, the cross-sectional shape of the cylindrical ventilation channel with a large cross-sectional area, such as a sawtooth square shape, is selected, wherein the included angle between the auxiliary heat dissipation wall 2 and the surface 1 of the device to be cooled is large. When the included angle is small, the heat exchange effect is poor due to the mutual interference of the boundary layer formed by the ascending air flow on the auxiliary heat dissipation wall 2 and the surface 1 of the equipment to be cooled. The large area of the auxiliary heat dissipation wall 2 is beneficial to absorbing the radiation heat of the surface 1 of the equipment to be cooled, and the total heat dissipation capacity of the surface 1 of the equipment to be cooled is reduced. Therefore, when the temperature extreme value area of the surface 1 of the equipment to be cooled is concentrated in the middle of the surface of the equipment and the heat flux density is not very high, the trapezoidal cross section with a compact structure is selected, and the arc cross section takes the characteristics of the trapezoid and the sawtooth square into consideration, so that the equipment to be cooled is suitable for the conditions that the cooling requirement of the peripheral edge of the surface 1 of the equipment to be cooled is high, the heat flux density is high and the structure is required to be compact.
And 3, determining the material, the thickness and the like of the coating on the inner surface of the auxiliary heat dissipation wall 2 according to the temperature distribution of the surface 1 of the device to be cooled obtained in the step 1 and the heat flow condition. The main focus of the coating is to obtain the maximum receiving quantity of the heat radiation of the auxiliary heat dissipation wall 2 on the surface 1 of the device to be cooled; moreover, the auxiliary heat dissipation wall 2 blocks the direct solar radiation on the surface 1 of the equipment to be cooled, and the heat dissipation requirement is reduced. Therefore, the wall surfaces (the surface 1 of the equipment to be cooled and the auxiliary heat dissipation wall 2) of the cylindrical ventilation channel are the wall surfaces capable of heating air, and the internal flow can be enhanced by the suction effect of a chimney on hot air flow.
And 4, according to the temperature distribution, the air flow condition and the boundary layer thickness distribution of the surface 1 of the equipment to be cooled determined in the step 1, carrying out geometric optimization by taking the heat exchange coefficient of the surface 1 of the equipment to be cooled to the maximum degree and taking high-efficiency cooling of a temperature extreme value area into consideration as indexes, designing the arrangement type, the size and the arrangement mode of the fins 4, and enabling the expanded heat dissipation area to reach 20% -400% of the surface 1 of the equipment to be cooled. The height of the fins 4 is at least higher than the thickness of the boundary layer, and it should be noted that, for the surface 1 of the device to be cooled, the increased height of the fins 4 significantly increases the newly added heat exchange area, but the flow in the vertical direction of the airflow is also affected when the fins 4 are too high, so that the fins 4 are provided with orifices, the heat exchange area is increased, and the influence on the vertical movement of the airflow is reduced. The shape and the geometric dimension of the orifice also need to be designed according to the heat exchange coefficient of the lifting wall surface as an index.
And 5, determining the ventilation holes 3 on the auxiliary heat dissipation wall 2 according to the influence rule of the heat flow conditions determined in the step 1 on the ambient air speed and the local year statistical wind speed by taking the natural convection heat transfer coefficient of the surface 1 of the equipment to be cooled as an index, such as the shape, the size, the density, the arrangement mode and the like. The area ratio of the vent holes 3 is about 5% of the area of the auxiliary heat dissipation wall 2, a part of the vent holes 3 are arranged in the direction facing the natural wind to fully utilize the natural wind to accelerate heat dissipation, and a part of the vent holes 3 are arranged at the upstream position of the temperature extreme value area of the surface 1 of the equipment to be cooled through which the airflow flows to increase the flow, so that the heat dissipation effect of the temperature extreme value area is improved.
The invention provides a natural convection heat transfer strengthening structure and a design method thereof, wherein the structure comprises a to-be-cooled equipment surface 1 and an auxiliary heat dissipation wall 2. On the basis of the equipment, the auxiliary heat dissipation wall 2 is utilized to build a cylindrical ventilation channel, so that the direct radiation of sunlight to the surface 1 of the equipment to be cooled is avoided, and the total heat dissipation amount of the equipment is reduced. In addition, the cylindrical ventilation channel structure can form a chimney suction effect to effectively improve the natural convection speed of air near the surface 1 of the equipment to be cooled, and the sectional area of the cylindrical ventilation channel is gradually reduced along with the airflow direction to adjust the further acceleration of the airflow around the temperature extreme value area of the surface 1 of the equipment to be cooled. And the wall surface of the equipment in the cylindrical ventilation channel and the newly-added heat flux density are not uniform, and the spiral flow is easily formed in the rising process of the hot air, so that the natural convection heat exchange efficiency of the surface 1 of the equipment to be cooled is further enhanced. In order to fully utilize the low-pressure environment and natural wind in the cylindrical ventilation channel, the auxiliary heat dissipation wall 2 is provided with the ventilation holes 3, and measures such as arranging the fins 4 which effectively destroy the development of the boundary layer on the surface 1 of the equipment to be cooled are combined to greatly enhance the natural convection cooling efficiency of the equipment, so that the heat dissipation requirement of the equipment is met, and the safety and the reliability of the operation of the equipment are improved.
Example 1
Referring to fig. 7 and 8, the comparative calculation of the surface temperature distribution of the equipment to be cooled before and after adding the semicircular auxiliary heat dissipation surface and the V-shaped fins in the outdoor environment is shown. The basic conditions are as follows: the surface of the equipment to be cooled is exemplified by a rectangular plate with an aspect ratio of 5/3, and is used in an outdoor environment. The surface heat flux density of the equipment to be cooled is regarded as 2 times of the average solar radiation heat flux density, and the influence of natural wind is not counted.
Fig. 7 shows the surface temperature distribution of the device to be cooled, with the surface average temperature: 506.746K.
FIG. 8 is a graph showing the temperature distribution on the surface of the equipment to be cooled after the addition of the semicircular auxiliary radiating surface and the V-shaped fins. The semicircular auxiliary radiating surface takes the length of a rectangular plate as the diameter, and the upper height and the lower height of the semicircular auxiliary radiating surface respectively exceed the width of the original rectangular plate by 6.7 percent. The new area of the surface of the equipment to be cooled is increased by 16.8 percent of the area of the original rectangular plate due to the arrangement of the V-shaped fins. The final average temperature of the surface is: 428.295K.
Claims (7)
1. The utility model provides a natural convection heat dissipation's heat transfer reinforcing means which characterized in that includes: an auxiliary heat dissipation wall (2);
the auxiliary heat dissipation wall (2) is fixedly arranged on the surface (1) of the equipment to be cooled, and the auxiliary heat dissipation wall (2) and the surface (1) of the equipment to be cooled form a cylindrical ventilation channel; the cross-sectional area of the cylindrical ventilation channel is kept unchanged or gradually reduced along the airflow flowing direction; a plurality of vent holes (3) are arranged on the auxiliary heat dissipation wall (2);
also comprises a plurality of fins (4); the fins (4) are all fixedly arranged on the surface (1) of the equipment to be cooled; the arrangement form of the fins (4) is whole strip arrangement or subsection arrangement; the arrangement mode of the fins (4) is in a row or a fork row;
the height of the fins (4) is greater than the thickness of the boundary layer of the surface (1) of the equipment to be cooled;
the fins (4) are provided with a plurality of flow guide holes which are arranged along the flowing direction of the airflow;
the fins (4) are right-angled V-shaped fins; the open ends of the right-angled V-shaped fins face the airflow outlet end of the cylindrical ventilation channel.
2. The heat exchange enhancement device for natural convection heat dissipation of claim 1, further comprising a first coating layer for enhancing absorption ratio and a second coating layer for enhancing emissivity; the first coating is fixedly arranged on the inner surface of the auxiliary heat dissipation wall (2); the second coating is fixedly arranged on the surface (1) of the equipment to be cooled.
3. The heat exchange enhancement device for natural convection heat dissipation according to claim 1, wherein the cross section of the cylindrical ventilation channel formed by the auxiliary heat dissipation wall (2) and the surface (1) of the equipment to be cooled is trapezoidal, circular arc or sawtooth square.
4. A design method of a heat exchange enhancement device for natural convection heat dissipation, which is based on the heat exchange enhancement device for natural convection heat dissipation of claim 1, and comprises the following steps:
step 1, analyzing a flow field, a temperature field and an air velocity field of a surface (1) of equipment to be cooled, and obtaining the temperature distribution, the air flow condition and the influence rule of heat flow conditions on the ambient air velocity of the surface (1) of the equipment to be cooled;
step 2, determining the geometric size and the cross-sectional shape of the cylindrical ventilation channel according to the self characteristics and the temperature distribution of the surface (1) of the equipment to be cooled obtained in the step 1 and the heat dissipation requirement of the surface (1) of the equipment to be cooled;
step 3, determining the first coating of the inner surface of the auxiliary heat dissipation wall (2) and the material of the second coating of the surface (1) of the equipment to be cooled according to the temperature distribution and the heat flow condition of the surface (1) of the equipment to be cooled obtained in the step 1;
step 4, designing the arrangement form, size and arrangement mode of the fins (4) according to the temperature distribution, air flow condition and boundary layer thickness distribution of the surface (1) of the equipment to be cooled determined in the step 1 by taking the heat exchange coefficient of the surface (1) of the equipment to be cooled and the cooling of the temperature extreme value area as indexes;
and 5, determining the shape, size, density and arrangement mode of the vent holes (3) on the auxiliary heat dissipation wall (2) by taking the natural convection heat transfer coefficient of the surface (1) of the equipment to be cooled as an index according to the influence rule of the heat flow conditions determined in the step 1 on the ambient air speed and the annual statistical wind speed of the place where the equipment to be cooled is located.
5. The design method of the heat exchange enhancement device for natural convection heat dissipation of claim 4, wherein in the step 2, the geometric dimension of the cylindrical ventilation channel is selected to utilize the chimney suction effect to achieve the surface cooling of the equipment without limiting the air flow in the cylindrical ventilation channel; the cross-sectional shape of the cylindrical ventilation channel is determined according to the temperature distribution of the surface (1) of the equipment to be cooled and the heat dissipation requirement.
6. The design method of the heat exchange enhancement device for natural convection heat dissipation according to claim 4, wherein in the step 4, the expanded heat dissipation area of the fins (4) is 20-400% of the area of the surface (1) of the equipment to be cooled; when the fins (4) are too high to influence the flow of the airflow in the vertical direction, the fins (4) are provided with flow guide holes; the shape and the geometric dimension of the flow guide hole are designed by taking the heat exchange coefficient improvement as an index.
7. The design method of the heat exchange enhancement device for natural convection heat dissipation according to claim 4, characterized in that, in step 5, some of the ventilation holes (3) are opened in the direction facing the natural wind, and some of the ventilation holes (3) are opened at the upstream position of the temperature extreme region of the surface (1) of the equipment to be cooled through which the airflow passes.
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