CN110008547B - Heat transfer analysis method for direct-current power supply module of underwater data acquisition cabin - Google Patents
Heat transfer analysis method for direct-current power supply module of underwater data acquisition cabin Download PDFInfo
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Abstract
The invention belongs to the technical field of heat transfer analysis, and particularly relates to a heat transfer analysis method for a direct-current power supply module of an underwater data acquisition cabin. The method is used for analyzing and modeling the heat transfer condition in the pressure-resistant cabin by combining the heat dissipation condition of the high-power supply module aiming at the existing closed pressure-resistant cabin body of the marine equipment, is used for analyzing the heat transfer condition of the pressure-resistant cabin in a closed environment, and can analyze and obtain the influence of the heat generated by the direct-current power supply module on the direct-current power supply in the acquisition cabin and the temperature at different positions in the cabin.
Description
Technical Field
The invention belongs to the technical field of heat transfer analysis, and particularly relates to a heat transfer analysis method for a direct-current power supply module of an underwater data acquisition cabin.
Background
At present, the submarine observation network has become an important means for people to know and research the ocean. As an important means of ocean observation, the seabed observation network can continuously acquire the ocean environment information of the observed sea area in a long-term real-time manner, and has great strategic significance for ocean disaster reduction and prevention, ocean ecosystem protection, ocean equity maintenance, ocean shipping, national defense safety and the like.
The data acquisition cabin is an important component of the seabed observation network and is a relay for connecting the sensor and the connection box. Because the seawater needs to bear huge pressure, the data acquisition cabin is generally of a cylindrical structure and small in size, and a plurality of electronic devices with different functions are installed in the cabin and are responsible for providing energy and data communication links for various sensors. The direct current power supply module in the cabin has high power and serious heating, and the reliability and the service life of the power supply module are reduced due to low heat dissipation efficiency in the closed cabin; meanwhile, the temperature in the cabin is increased, and the measurement precision, the working reliability and the service life of other electronic devices are influenced. Therefore, the heat dissipation of the high-power direct-current power supply module of the data acquisition cabin becomes a key influencing the long-term operation reliability of the system.
In the prior art, a mature heat transfer analysis model in a cabin does not exist for a closed underwater pressure-resistant cabin body.
Disclosure of Invention
In order to solve the technical problems, the invention provides a heat transfer analysis method for a direct current power supply module of an underwater data acquisition cabin, which can analyze the influence of heat generated by the direct current power supply module on the direct current power supply in the acquisition cabin and the temperature of different positions in the cabin.
The invention is realized by the following technical scheme:
a heat transfer analysis method of a direct current power supply module in an underwater data acquisition cabin is used for analyzing the heat transfer and temperature distribution conditions of heat generated by the direct current power supply module in the data acquisition cabin in the cabin; the method comprises the following steps:
under the condition that two ends of the cabin body are closed, the heat transfer model of the circuit board in the cabin body is simplified as follows: the cabin comprises a lining plate with the length of l, and two ends of the lining plate respectively have the temperature of t 1 And the temperature is t 2 Is in contact with the environment outside the cabin, the temperature of the surface of the lining plate and the temperature inside the cabin is t f The air convection heat exchange is carried out; establishing a coordinate system by taking the direct current power supply module as a coordinate axis, wherein x represents the horizontal distance of a certain point in the cabin far away from the direct current power supply module as a heat source;
according to the law of conservation of energy, the heat generated by the DC power supply module is phi 1 ：
φ 1 ＝φ 2 +φ 3
Wherein phi is 2 Heat conducted by the DC power supply module 3 Heat for convection heat transfer between the direct current power supply module and air;
wherein t represents the temperature corresponding to the x position in the cabin, lambda is the heat conductivity coefficient of the printed circuit board in the cabin, b is the width of the direct current power supply module, delta is the thickness of the printed circuit board, and h represents the heat exchange coefficient between the surface of the direct current power supply module and the air;
finishing to obtain:
substituting boundary conditions: x ∈ [0, l ], deriving a differential equation having:
calculating the temperature t of a point at a distance x from the direct current power supply module in the x-axis direction through the differential equation;
calculating the temperature variation delta t of the surface of the direct-current power supply module:
q unit area direct current power supply module heat productivity, h is the heat exchange coefficient of the direct current power supply module surface and air;
wherein, the first and the second end of the pipe are connected with each other,
phi is the heating power of the direct current power supply module, and A is the surface area of the direct current power supply module for heat dissipation;
Nu r ＝B(Gr * c Pr) m wherein, gr * c Is a number of the Grossiazodiac marks,
the air expansion coefficient alpha is 0.003; the gravity acceleration g is 9.8m/s 2 (ii) a λ is the thermal conductivity of the internal printed circuit board; v represents kinematic viscosity, and q is the heat productivity of the direct current power supply module in unit area; B. m is a constant;
the temperature change of the dc power supply module itself, i.e., x =0, can be obtained from Δ t.
Further, when the ambient temperature t outside the cabin 2 The standard room temperature is 25 ℃, when the size of the direct current power supply module is 110mm multiplied by 60mm, the temperature is gradually reduced along with the distance from the direct current power supply module in the x direction, and the surface temperature t of the direct current power supply module is obtained by calculation 1 The temperature is 75 ℃, and the temperature of the position 0.5m away from the direct current power supply module in the X direction is 42 ℃.
Further, in order to ensure that the data acquisition cabin can operate reliably for a long time, the average temperature in the cabin needs to be controlled below 45 ℃ based on the upper temperature limit of a common commercial-grade electronic device, and according to the heat transfer analysis method, various electronic devices in the cabin need to be far away from the direct-current power supply module by more than 40 cm.
A heat dissipation system for DC power supply modules of an underwater data acquisition cabin is characterized in that all DC power supply modules in the underwater data acquisition cabin are welded on the same circuit board so as to centralize a heat source; a heat conduction path is established between the bulkhead of the data acquisition cabin and a heat source of the direct-current power supply module by adopting a radiator made of an aluminum alloy material; the bottom of the radiator is connected with the direct-current power supply module through a bolt, and the top of the radiator is in a circular arc shape with the same inner diameter as the cabin body;
the size of the bottom of the radiator is larger than that of the upper part of the direct-current power supply module, namely, the bottom of the radiator extends outwards relative to the direct-current power supply module to form an extension part; the radiator and the lining plate are connected through a support guide pillar, one end of the support guide pillar is fixed on the lining plate, the other end of the support guide pillar penetrates through holes of the extending parts on two sides of the bottom of the radiator, and a spring is sleeved on the support guide pillar between the radiator and the lining plate;
when external force acts on the radiator, the radiator moves up and down along the supporting guide post under the action of the spring to adjust the height of the radiator, and after the external force is removed, the radiator is tightly attached to the bulkhead of the data acquisition cabin under the action of the thrust of the spring so as to avoid interference with the cabin body during assembly and eliminate a gap between the radiator and the cabin body due to factors such as processing and assembly errors.
The invention has the beneficial technical effects that:
the method provided by the invention aims at the unique design concept and application scene of the existing marine equipment sealed pressure-resistant cabin body, and combines the heat dissipation condition of the high-power supply module to analyze and model the heat transfer condition inside the pressure-resistant cabin, so as to analyze the heat transfer condition of the pressure-resistant cabin in a sealed environment; in practical application, an optimized design scheme of a heat dissipation structure can be provided on the basis of the heat transfer analysis method provided by the invention, and the optimized design scheme is used for evaluating the effect of a heat dissipation system.
Drawings
FIG. 1 is a schematic diagram illustrating the establishment of coordinate axes of a heat transfer model of a sealed cabin according to an embodiment of the present invention;
FIG. 2 is a diagram illustrating a heat transfer model and theoretical calculation results in a sealed cabin according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a heat dissipation system of a DC power supply module of a first underwater data collection cabin according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a heat dissipation system of a DC power supply module of a second underwater data collection cabin in an embodiment of the present invention;
FIG. 5 shows the temperature change of the DC power supply module before and after the data acquisition module is provided with a heat sink;
FIG. 6 shows the temperature at different locations in the front and rear compartments of a data acquisition compartment with a heat sink according to an embodiment of the present invention;
FIG. 7 is a graph of the outside cabin temperature of the data acquisition cabin during a marine test in an embodiment of the present invention;
fig. 8 shows the time for stabilizing the temperature of the dc power supply module after the data acquisition module is powered on during the sea test in the embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not delimit the invention.
On the contrary, the invention is intended to cover alternatives, modifications, equivalents and alternatives which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the present invention, certain specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent to one skilled in the art that the present invention may be practiced without these specific details.
As shown in fig. 1, the dc power supply module and various electronic devices are densely installed on two lining boards in a cabin with an inner diameter of phi 190mm, and because the dc power supply module has certain impedance and loss during voltage conversion (48-12V/5V), a large amount of heat is generated when the load is heavy and the output power is high. In order to research the influence of the heat on the direct-current power supply module and the temperature at different positions in the cabin, the embodiment of the invention provides a heat transfer analysis method of the direct-current power supply module of the underwater data acquisition cabin according to the related theory of heat transfer science, and an in-cabin heat transfer model is established.
The heat transfer path inside the cabin is analyzed:
according to the theory of heat transfer, the heat transfer modes are as follows: the heat transfer mode of the direct current power supply module is mainly heat transfer and heat convection, and the heat radiation can be ignored because the temperature of a heat source and the ambient temperature are in the same order of magnitude. The transfer path is simplified as follows: heat source-heat conducting medium in cabin-metal cabin-air (sea water).
Analysis of the heat transfer in the cabin:
according to the experience of previous experiments, the size of the direct current power supply module is 110mm multiplied by 60mm, and the heating power is about 2.4W. In the heat transfer analysis method of the direct-current power supply module of the underwater data acquisition cabin, the direct-current power supply module is not in contact with the cabin body and other electronic devices, only natural convection heat transfer with air exists during heating, the influence of surrounding circuit boards on air flow is ignored on the premise of analysis, and the ambient temperature is 25 ℃.
Under the condition that two ends of the cabin body are closed, simplifying a heat transfer model of the circuit board in the cabin into: the cabin comprises a lining plate with the length of l, and two ends of the lining plate respectively have the temperature of t 1 And the temperature is t 2 Is in contact with the environment outside the cabin, the temperature of the surface of the lining plate and the temperature inside the cabin is t f The air convection heat exchange is carried out; as shown in fig. 1, a coordinate system is established by taking the dc power module as a coordinate axis, and x represents a horizontal distance from a certain point in the cabin to a heat source position of the dc power module;
specifically, the heat phi emitted by the power module is recorded 1 The method comprises the following steps:
heat phi transferred by heat generation power supply module 2 The method comprises the following steps:
recording heat phi of heat transfer of heat generation module and air in convection mode 3 The method comprises the following steps:
φ 3 ＝bdxh(t-t f )--------(3)
further, according to the law of conservation of energy, it can be known that:
φ 1 ＝φ 2 +φ 3 --------(4)
in the above formula, λ is the thermal conductivity of the internal printed circuit board, b is the width of the power module, and δ is the thickness of the printed circuit board.
According to the four formulas, the compound is obtained by sorting,
substituting the boundary conditions: x ∈ [0, l ], deriving a differential equation having:
calculating the temperature t of a point which is at a distance of x from the direct-current power supply module in the x direction through the differential equation;
further, the calorific value q of the power module in unit area is calculated by the following formula:
wherein phi is the heating power of the power module, and A is the heat dissipation surface area of the power module.
Then Gr according to the Grashof number * c Is calculated by the formula of
In the formula, the air expansion coefficient alpha is 0.003; the gravity acceleration g is 9.8m/s 2 ；l r The length of the short side of the power module is 0.06m; λ is the thermal conductivity of the internal printed circuit board; v represents kinematic viscosity.
Further calculating Nu number Nu of Nu number of Nu' s r The equation is:
Nu r ＝B(Gr * c Pr) m --------(9)
wherein Nu r Is the Nussel number; the values of constants B and m are in accordance with Gr * c The calculation result can be 1.076 and 0.698; pr is a modeling parameter and can be 0.698.
And then calculating the convection heat exchange coefficient h of the fluid according to the following formula:
h is the heat exchange coefficient between the surface of the power module and air; nu (Nu) r Is the Nussel number; l r The length of the short edge of the direct current power supply module; l. the r The value range is 0.05-0.2m, preferably, l r Taking 0.06m; λ is the thermal conductivity of the internal printed circuit board.
Finally, the temperature variation on the surface of the power module can be obtained, and the method comprises the following steps:
wherein, Δ t is the variation of the surface temperature of the module, and q is the heat productivity in unit area; h represents the heat exchange coefficient between the surface of the power module and the air.
The temperature change of the dc power supply module itself, i.e. the x =0 position, can be obtained according to Δ t, specifically: if the ambient temperature in the sealed cabin is taken as the standard room temperature of 25 ℃, the derivation of the formulas (7) to (11) is combined to calculate Δ t, Δ t = t 1 -t f The temperature difference calculated by the equations (7) to (11) actually determines that the surface temperature of the dc power supply module is increased by heat generationThe actual temperature, with the variation, can be applied to the model derived by formula (6) in combination with the room temperature of 25 ℃ before the start of the test to determine the temperature t of the DC power supply module in the heating state 1 (ii) a Thereby obtaining the heat transfer and temperature distribution in the sealed cabin under the condition, as shown in figure 2.
The formula derivation and calculation results of the method show that:
the temperature of the power module can reach 75 ℃, and the generated heat can increase the temperature of electronic devices at each position in the cabin; the temperature of the dc power supply module decreases gradually with increasing distance from it in the x direction, but reaches a minimum of 42 ℃.
For every 10 c increase in the temperature of the individual semiconductor elements, the system reliability will decrease by 50%, and over 55% of failures of the electronic equipment are caused by excessive temperatures. By applying the method for analyzing the heat transfer of the sealed cabin, the heating device and the heat transfer state in the pressure-resistant sealed cabin can be analyzed, and then the heat dissipation device is arranged on the basis of the analysis, so that the safe and stable operation of the system is ensured. According to the derived calculation results, the electronic device at the position can be kept at a favorable working temperature after being away from the power supply module by 40 cm.
According to the research, the heating device in the cabin is mainly a direct current power supply module, and the heat resistance in the heat transfer process is very large due to the small heat conductivity coefficient of air, so that the heat is prevented from being rapidly transferred to the external environment, and the temperature in the cabin is obviously increased.
The circuit board in the cabin adopts many kinds of electronic devices, the normal working temperature of the electronic devices is not uniform, and in order to ensure that the data acquisition cabin can reliably run for a long time, the temperature upper limit of a common commercial grade electronic device is taken as a reference, and corresponding heat dissipation measures are needed to reduce the average temperature in the cabin to below 45 ℃.
At present, there are various heat dissipation methods for electronic devices, and various cooling methods can be classified into two major categories, namely passive refrigeration and active refrigeration, according to the relationship between the cold source temperature and the ambient temperature.
The passive cooling refers to an electronic component heat dissipation mode that the temperature of a cold source is higher than the ambient temperature, and is characterized in that the temperature of a chip is always higher than the ambient temperature, and a refrigeration mechanism is not arranged. Air cooling and passive liquid cooling are further classified according to the cooling medium.
Active cooling is a heat dissipation method in which the temperature of a cold source is lower than the ambient temperature, and is characterized by comprising a refrigeration mechanism for obtaining a lower temperature, so that the temperature of a chip can be reduced to a level lower than the ambient temperature. It can be classified into active liquid cooling, semiconductor cooling, micro-refrigeration system cooling, and the like. The heat dissipation mode can obtain lower chip temperature, and is beneficial to improving the performance of the chip; but it consumes more power and is less reliable.
In the existing heat dissipation research of marine equipment, heat is conducted to the outer wall of a cabin body through a heat conducting medium, and seawater cooling is used as a main mode. The American ALVIN manned submersible connects a high-power device to a heat dissipation base with good heat conduction performance, and the base is connected to an end cover of a pressure-resistant sealed cabin body and dissipates heat by utilizing seawater. An underwater connection box developed by Zhejiang university injects insulating oil with high heat conductivity coefficient into a cabin, transfers heat to the surface of a pressure-resistant sealed cabin body by utilizing the flow of the oil, and dissipates heat by utilizing seawater; the oil filling mode, the maintenance and the replacement are complex, and the equipment is not beneficial to upgrading, transformation, expansion and maintenance.
Because the volume in the cabin is limited, the method of increasing the distance between the cabin and the power supply module cannot be adopted to reduce the influence of the heat generated by the power supply module on other electronic devices. Therefore, the reasonable heat dissipation mode is a necessary condition for ensuring the long-term reliable operation of the data acquisition cabin. The heat dissipation structure design for the data acquisition cabin mainly follows the following principle:
(1) The heat dissipation mode is matched with the heat flux density of the equipment, so that the equipment can be cooled to the target temperature;
(2) The thermal resistance between a heat source and a heat dissipation medium is effectively reduced;
(3) The structure is reliable, and the installation and the maintenance are convenient;
(4) Does not interfere with the operation of other equipment, and the like.
The heat dissipation modes of electrical equipment on land are various, such as air cooling and water cooling, or the heat dissipation mode based on the porous micro heat sink technology. However, these methods cannot be directly applied according to the structural characteristics and the use environment of the data acquisition cabin. With reference to the heat dissipation method of the electronic device, the following heat dissipation schemes are designed:
in the scheme 1, materials with good heat conduction performance are used for transferring heat generated by a power module to the outer wall of a cabin body in a heat conduction mode, and seawater is used for heat dissipation;
in the scheme 2, heat pipes are adopted for cooling, cooling liquid in the heat pipes absorbs heat, the heat is conducted to the outer wall of the cabin body through liquid flow, and seawater is used for heat dissipation;
scheme 4 adopts the semiconductor refrigeration piece, utilizes the Peltier effect of semiconductor to cool power module.
The scheme is compared by combining the characteristics of limited space, more electronic devices, compact arrangement and the like in the data acquisition cabin and the principle followed by heat dissipation design:
although the scheme 2 can achieve a good heat dissipation effect, the heat pipe is complex in structure, high in processing difficulty and not beneficial to installation and maintenance; scheme 3 can effectively reduce the heat conduction and heat resistance in the cabin, but the mode causes the maintenance work of the data acquisition cabin to be very complicated, and the oil can accelerate the aging of devices, so that the method is not feasible; the cooling efficiency of the semiconductor material in the scheme 4 is low, and the problem cannot be solved by installing a large number of refrigerating sheets due to limited space in the cabin.
In summary, according to the scheme 1, the metal heat dissipation structure is installed between the surface of the power module and the cabin wall, so that the generated heat is transferred to the surface of the cabin body in a heat conduction manner, the heat is reduced from being transferred in the cabin through air convection, and then the heat is taken away through seawater flowing through the surface of the cabin body, so that the purpose of dissipating heat of the power module is achieved.
According to a certain heat dissipation scheme, as shown in fig. 3, the present embodiment provides a first heat dissipation device, which includes:
(1) Firstly, welding all direct current power supply modules on the same circuit board to centralize heat sources;
(2) According to the heat flux density of the power module, an aluminum alloy material with good heat conduction performance is adopted to establish a heat conduction path between the bulkhead and a heat source;
(3) The bottom of the radiator is connected with the power supply module through the bolt, so that the surface of the power supply module is tightly attached to the radiator, the radiator is firmly and reliably mounted, and the radiator is convenient to dismount. The top of the radiator is designed into a circular arc shape with the same inner diameter as the cabin body, so that the radiator is ensured to be tightly attached to the inner wall of the data acquisition cabin, and the phenomenon that air exists between the radiator and the data acquisition cabin to increase thermal resistance is avoided.
(4) The size of the bottom of the radiator is designed to be consistent with the size of a power supply module on a circuit board, so that the radiator can completely cover a heat source and cannot interfere with other electronic devices to work.
Calculating the heat resistance and heat transfer:
calculating the surface temperature of the power supply after the radiator is installed according to a thermal resistance analysis method in the heat transfer process, wherein the heat transfer coefficient is as follows:
wherein λ is 1 、λ 2 The heat conductivity coefficient of the aluminum alloy fins and the titanium alloy bulkhead, and h is the heat exchange coefficient of the external fluid and the bulkhead. Query the relevant manual to obtain, λ 1 ＝107(W/m 2 ·K)，λ 2 ＝22(W/m 2 K), when the external fluid is air, h takes the empirical value h =13 (W/m) 2 ·K)。δ 1 、δ 2 The thicknesses of the aluminum alloy fins and the bulkhead are respectively 0.04m and 0.012m, and A is the effective heat dissipation surface area. Heat flow calculation formula according to heat conduction:
neglecting the convective heat transfer of metal surface and air in the cabin, can calculate the temperature t =53.3 ℃ (outside temperature t) on the surface of the power module when using this heat dissipation mode f =25 ℃), it can be seen that the temperature of the power module can be significantly reduced by this heat dissipation method.
Problem analysis:
in the assembling and experiment processes of the data acquisition cabin, the radiator cannot be tightly attached to the cabin wall after being installed, namely, air with high heat conduction resistance is added in a heat conduction path, so that the heat dissipation effect of the power module is seriously influenced. Research shows that the main reason for the problem is that certain errors exist in the processing and assembling processes of the internal fixing lining plate and the radiator, so that a gap exists between the internal fixing lining plate and the radiator.
In order to solve the problem, the invention provides a second embodiment of a heat dissipation system for a direct current power module of an underwater data acquisition cabin, as shown in fig. 4, each direct current power module in the underwater data acquisition cabin is welded on the same circuit board to concentrate a heat source; a heat conduction channel is established between the bulkhead of the data acquisition cabin and the heat source of the direct current power supply module by adopting a radiator made of an aluminum alloy material; the bottom of the radiator is connected with the direct-current power supply module through a bolt, and the top of the radiator is in the shape of a circular arc with the same inner diameter as the cabin body;
the size of the bottom of the radiator is larger than that of the upper part of the direct-current power supply module, namely, the bottom of the radiator extends outwards relative to the direct-current power supply module to form an extension part; the radiator and the lining plate are connected through a support guide pillar, one end of the support guide pillar is fixed on the lining plate, the other end of the support guide pillar penetrates through holes of the extending parts on two sides of the bottom of the radiator, and a spring is sleeved on the support guide pillar between the radiator and the lining plate;
when external force acts on the radiator, the radiator moves up and down along the supporting guide post under the action of the spring to adjust the height of the radiator, and after the external force is removed, the radiator is tightly attached to the bulkhead of the data acquisition cabin under the action of the thrust of the spring.
The working mode of the heat dissipation system is as follows: the external force acts on the radiator to compress the spring, so that the radiator moves along the guide post to randomly adjust the height of the radiator, and after the external force is removed, the elasticity of the spring pushes the radiator to cling to the cabin wall. The structure can avoid interference with the cabin body during assembly, and eliminates a gap between the cabin body and the cabin body caused by factors such as processing and assembly errors.
And (3) heat dissipation simulation analysis of the data acquisition cabin:
and (3) analyzing the heat transfer in the direct current power supply module cabin: establishing an intra-cabin geometric model according to the related parameters of the data acquisition cabin and the power module, performing simulation analysis by using Ansys Icepak software, simplifying and replacing a circuit board installed in the cabin, selecting a Turbule mode for simulation analysis, wherein the simulation result shows that:
1) The cabin air flows to a position with lower temperature in the cabin after being heated above the power supply module, and the generated heat is transferred to other electronic devices, and the flow speed of the generated heat is 0.14m/s at most.
2) The lower flow rate results in less heat being exchanged with the cabin wall per unit time, most of the heat being transferred within the cabin, and the surface temperature of other electronic components increasing.
Both theoretical analysis and simulation show that the temperature at the power supply module reaches 345K (72 ℃), electronic devices at other positions are influenced by the temperature, the temperature is approximately distributed in 340K (67 ℃), 319K (46 ℃), and the lowest value is 313K (40 ℃), and the temperature is basically consistent with the result of the previous theoretical calculation.
Simulation analysis of heat dissipation in the cabin: in order to verify the effect of the adopted heat dissipation mode, the model is led into ANSYS for simulation analysis, the environmental temperature is set to be 25 ℃, and the heat exchange coefficient h between the surface of the cabin body and the air 1 ＝10W/(m 2 K), coefficient of heat transfer in the cabin h 2 ＝5W/(m 2 ·K)。
From the simulation results, it appears that: the surface temperature of the module is reduced to about 47 ℃, and the temperature of other positions in the cabin is below 35 ℃. The heat dissipation mode enables heat generated by the power module to be mainly transferred to the cabin wall along the heat sink, so that the temperature of the power module is reduced, and the condition that the temperature of other positions in the cabin is higher is obviously improved.
Heat transfer test in cabin
Place 4 groups of thermistors at the inboard apart from power module different positions department, be connected 4 groups of sensors such as dissolved oxygen after airtight with the cabin body, measure the inboard temperature of data acquisition cabin normal during operation in 25 ℃ windless environment in laboratory, survey through the experiment and find:
(1) When the direct current power supply module normally works, the temperature of the power supply module tends to be stable after about 1 hour, the surface temperature reaches 69.3 ℃, the temperature is about 4 ℃ lower than the theoretical calculated value, and the result belongs to an acceptable error range in engineering application considering that the surface of the heat dissipation fin still has convective heat transfer with air in a cabin.
(2) It can be seen from fig. 6 that although the temperature of the rest points is different from the calculation and simulation results, the temperature variation trend of different positions in the cabin is basically consistent with the simulation results, the temperature at 0.6 m from the power module is still about 45 ℃, effective heat dissipation measures must be taken, and the influence of overhigh temperature on the working reliability of the data acquisition cabin is reduced.
Testing a heat dissipation system: the radiator in the radiating system of the underwater data acquisition cabin direct-current power supply module is installed on the surface of the power supply module for testing, the rest experimental conditions are the same, and the experimental data are shown in the figures 5-6. Through experiments, the following results can be found:
(1) After a radiator is additionally arranged (a radiating system of the second underwater data acquisition cabin direct-current power supply module provided by the embodiment is additionally arranged), the surface temperature value of the power supply module is obviously reduced, the temperature rising rate is also obviously reduced, and the temperature is stably maintained at about 47 ℃ after about 3.5 hours;
(2) The temperature of other positions in the cabin is obviously and greatly reduced compared with the prior temperature, and is basically stabilized below 35 ℃, so that the aim of controlling the temperature in the cabin below 45 ℃ can be completely fulfilled.
The heat radiator can transfer most of heat generated by the power module to the cabin wall, effectively inhibits the heat from being conducted in the cabin through natural convection, reduces the influence of the heat on other electronic devices through natural convection, shows that the heat radiation mode can completely meet the heat radiation requirement in the sealed cabin body during long-term test in land air, and effectively reduces the influence of overhigh temperature in the cabin on the reliability and service life of the electronic devices.
Sea test of a data acquisition cabin: in order to test the reliability of the data acquisition cabin in the actual working environment, the data acquisition cabin and the sensor perform a sea test for 3 months in the offshore sea area of the Qingdao, the equipment is arranged at 8 meters under water of an offshore wharf, and the water temperature is 25 ℃.
The temperature of the power module is estimated through a formula (9), and as the device is placed in seawater, the heat exchange mode belongs to natural convection heat transfer, and the reference shows that the approximate numerical range of the heat transfer coefficient of the natural convection surface in the water is about 200-1000, h =200 is taken for testing, and the temperature difference between the surface of the power module and the external seawater is estimated to be about 2.2 ℃ according to the formula.
And measuring the temperature of the power module and the seawater through a sensor. After 3 monthly trials, 34 thousands of pieces of temperature measurement data were obtained, as shown in fig. 7-8. Through comparing the seawater temperature data in the cabin and outside the cabin, the following results are found:
(1) The power module is 0.2-2.4 ℃ higher than the temperature of the seawater during the sea test, and the average value is 1.48 ℃;
(2) The power module temperature reached constant after about 4.3 hours after operation.
Considering that factors such as the temperature and the flow velocity of the seawater change along with seasons, the surface heat transfer coefficient of the seawater also changes, and experimental results show that:
(1) The temperature difference between the inside and the outside of the cabin is more consistent with the estimation result through a formula, the heat dissipation mode can transfer the heat generated by the power supply module to the cabin wall, the temperature of the power supply module and the temperature in the cabin are effectively reduced through the convection heat transfer of seawater,
(2) The trend that the temperature rises sharply in a short time after the power module works is restrained, the influence of sharp temperature change on the service life of the power module is reduced, and the reliability of the data acquisition cabin is improved.
And (4) conclusion: theoretical analysis and experiments show that under the condition of only natural convection heat transfer, the surface temperature of a direct-current power supply module in a data acquisition cabin can reach 73.3 ℃ when the direct-current power supply module works, and the temperature of other electronic devices in the cabin is about 50 ℃, so that the reliability and the service life of the electronic devices are seriously influenced; the heat dissipation method that the aluminum alloy radiator is additionally arranged on the surface of the power module and the radiator is tightly attached to the bulkhead is adopted, so that the heat transfer resistance on the surface of the power module can be reduced, most of heat is transferred to the surface of the bulkhead, and experimental results show that the heat dissipation method can effectively reduce the heat conduction in the cabin, inhibit the temperature rise in the cabin, contribute to improving the reliability and service life of electronic devices, and meet the heat dissipation requirement of the data acquisition cabin for long-term work.
The heat dissipation performance of the direct current power supply module in the underwater data acquisition cabin is an important factor influencing the long-term stable operation of the underwater data acquisition cabin. According to the theory related to heat transfer science, the method analyzes the heat transfer condition in the data acquisition cabin, establishes a heat transfer model and calculates the temperature of each position in the cabin. Simulation analysis is carried out on the heat transfer process inside the cabin body by using ANSYS Icepak, and influence factors of heat dissipation of the power module and overhigh temperature in the cabin body are determined. According to theoretical calculation and analysis results, a heat dissipation system of the direct-current power supply module of the underwater data acquisition cabin is designed, so that heat is mainly transferred to a cabin wall through a radiator, and the temperature rise in the cabin is restrained. Simulation analysis and experimental tests show that the heat dissipation mode and the structure can meet the heat dissipation requirement of long-term work of the data acquisition cabin.
Claims (3)
1. A heat transfer analysis method for a direct current power supply module of an underwater data acquisition cabin is characterized by being used for analyzing the heat transfer and temperature distribution conditions of heat generated by the direct current power supply module in the data acquisition cabin in the cabin; the method comprises the following steps:
under the condition that two ends of the cabin body are closed, the heat transfer model of the circuit board in the cabin body is simplified as follows: the cabin comprises a lining plate with the length of l, and two ends of the lining plate respectively have the temperature of t 1 And the temperature is t 2 The temperature of the lining plate surface and the temperature in the cabin is t f The air convection heat exchange is carried out; establishing a coordinate system by taking the direct current power supply module as a coordinate axis, wherein x represents the horizontal distance of a certain point in the cabin far away from the direct current power supply module as a heat source;
according to the law of conservation of energy, DC power supply moduleHeat generated phi 1 ：
φ 1 ＝φ 2 +φ 3
Wherein phi is 2 Heat conducted by the DC power supply module 3 Heat for convection heat transfer between the direct current power supply module and air;
in the formula, t represents the corresponding temperature at the position x in the cabin, lambda is the heat conductivity coefficient of the internal printed circuit board, b is the width of the direct current power supply module, delta is the thickness of the printed circuit board, and h represents the heat exchange coefficient between the surface of the direct current power supply module and air;
finishing to obtain:
substituting the boundary conditions: x ∈ [0, l ], deriving a differential equation having:
calculating the temperature t of a point which is at a distance of x from the direct current power supply module in the direction of the x axis through the differential equation;
calculating the temperature variation delta t of the surface of the direct current power supply module:
q is the heat productivity of the direct current power supply module in unit area, and h is the heat exchange coefficient between the surface of the direct current power supply module and air;
wherein the content of the first and second substances,
phi is the heating power of the direct current power supply module, and A is the heat dissipation surface area of the direct current power supply module;
Nu r ＝B(Gr * c Pr) m wherein, gr * c Is the Grashof number, pr is a modeling parameter,
alpha is the air expansion coefficient; g is the acceleration of gravity; λ is the thermal conductivity of the internal printed circuit board; v represents kinematic viscosity, and q represents the heat productivity of the direct current power supply module in unit area; B. m is a constant;
the temperature change of the dc power supply module itself, i.e., x =0, can be obtained from Δ t.
2. The heat transfer analysis method of the direct-current power supply module of the underwater data acquisition cabin according to claim 1, characterized in that when the outdoor environment temperature t is 2 The standard room temperature is 25 ℃, when the size of the direct current power supply module is 110mm multiplied by 60mm, the temperature is gradually reduced along with the distance from the direct current power supply module in the x direction, and the surface temperature t of the direct current power supply module is obtained by calculation 1 The temperature is 75 ℃, and the temperature of the position 0.5m away from the direct current power supply module in the X direction is 42 ℃.
3. The method for analyzing the heat transfer of the direct-current power module of the underwater data collection cabin according to claim 2, wherein in order to ensure that the data collection cabin can operate reliably for a long time, the average temperature in the cabin needs to be controlled below 45 ℃ based on the upper temperature limit of general commercial-grade electronic devices, and according to the method for analyzing the heat transfer, various electronic devices in the cabin need to be away from the direct-current power module by more than 40 cm.
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