Design and simulation analysis of heat dissipation structure of motherboard of a certain type of portable rugged computer

The portable rugged computer generally needs to adapt to high temperatures, hot and humid, and other harsh environments, while taking into account its portability, the machine cooling space is limited, and the motherboard carries the CPU, graphics cards, and other major heat-producing components. Therefore, some problems often occur due to the irrational design of the motherboard cooling structure, resulting in poor adaptability to high-temperature environments, arithmetic performance being difficult to fully play, and so on. In this paper, based on the use of a certain type of portable rugged computer requirements, a motherboard cooling structure is designed through the thermal structure, fan and increasing the heat dissipation area and other forms, and the type of computer cooling effect has been measured by simulation analysis and experimental verification to verify that it can enhance the cooling effect, to provide a better reference for the same type of portable rugged computer motherboard cooling structure design.


Introduction
Portable rugged computers are specially designed computers intended to be able to provide reliable performance and durability in harsh environments.These computers are usually rugged, waterproof and dustproof, corrosion-resistant, shock-resistant, and can resist the effects of shock, vibration, water, dust, and other harsh environments.At the same time, due to their frequent outdoor use, they must be portable in design, with a compact and lightweight structure, easy to carry and use [1] .Portable rugged computers usually also have a wide temperature operating range and can work normally in extreme temperatures, so their heat dissipation problem is particularly prominent.If the heat dissipation is poor, it will lead to a high internal temperature of the computer, thus affecting the performance and stability of the computer [2] , and even causing the crash phenomenon, so the design of the heat dissipation structure of the portable rugged computer is very important.The motherboard carries the CPU, graphics card, and other major heat-generating components, and its thermal structure design directly determines the cooling effect of the machine [3][4] .
the ordinary computer thermal structure design technology at home and abroad is mature.In the rugged computer machine thermal design, the three ways of heat transfer chassis thermal design are often used, that is, to increase the design of heat conduction, it is suggested to increase the convection of heat and radiation technology.The market also has some relatively mature rugged computer products.With today's rapid development of science and technology, microelectronic device packaging density continues to improve, resulting in the chip's power density (heat flow density) value increasing rapidly [3] .Most of the high-performance requirements of the rugged computer need to be

Background
Portable rugged computers reduce the size of their cooling structure to improve their portability, which inevitably reduces their cooling efficiency.In addition to this, the cooling structure is usually dissipated by fins, and as there are a large number of dust particles in the air, this will lead to the adsorption of a large amount of dust on the fins, which reduces the cooling effect and affects the computer's computational performance, and damages computer electronic components, easily leading to equipment failure [5] .A certain type of portable rugged computer needs to meet extreme environmental requirements such as high and low temperatures, humidity and heat, and anti-mould, so the design of the cooling structure needs to take full account of the actual working environment and performance requirements of the equipment, in order to achieve effective heat dissipation and ensure the stable operation of the equipment.
The motherboard, also known as the motherboard, installed in the computer case, is the most basic and most important part of the computer.In the entire computer system, the motherboard plays a pivotal role in the motherboard manufacturing quality and determines the stability of the hardware system.The motherboard and CPU relationship is close, the CPU in the operation process is prone to high-temperature problems, and the sustained high temperature will lead to impaired performance, and will directly affect the use of computer performance and life [6] .When the computer is in the process of operation, the main heat-generating components CPU, and graphics cards are usually installed on the motherboard.If the heat is not dispersed in a timely manner, it will affect the stable operation of the equipment [7] , so a reasonable motherboard thermal structure design program is essential to maintain the performance of portable rugged computers.

Content
In view of the above deficiencies in the prior art, considering the advantages and disadvantages of two cooling methods, natural convection and forced convection [5] , a certain type of portable ruggedized computer, by designing a forced convection cooling structure, ensures a very good sealing effect, at the same time, solves the above-mentioned problems in the background technology of the existing portable ruggedized computer with poor heat dissipation.The heat dissipation structure has a large size, thereby affecting the computer's portability, reliability, and stability.
The heat dissipation structure of the motherboard of a certain portable rugged computer comprises: A heat-conducting substrate comprising a base plate and a heat-conducting block disposed on the base plate, with a number of heat-conducting holes disposed on the heat-conducting block; A heat dissipation fan, provided on the above heat-conducting block, the heat-conducting holes being provided in the direction of the air inlet of the heat dissipation fan; A heat dissipation cover plate, provided on the heat dissipation fan, and the heat dissipation cover plate being provided with a vent located in the direction of the air outlet of the heat dissipation fan.
The heat dissipation base is provided on the heat dissipation cover plate, the heat dissipation base is provided with a mounting port connected to the vent, the mounting port is provided with a number of heat dissipation fins, the heat dissipation base is provided with a protective casing, and the heat dissipation fins are provided in the protective casing.
The base plate is symmetrically provided with a plurality of mounting holes, and the mounting holes are evenly arranged.The cooling fan is provided with a plurality of first threaded posts, the cooling cover plate is provided with a plurality of first threaded holes corresponding to the first threaded posts, the cooling cover plate is provided with a plurality of second threaded posts, and the base plate is provided with a plurality of second threaded holes corresponding to the second threaded posts.The inner wall of the heat dissipation cover plate is provided with sound-insulating cotton.The protective case is provided with a number of heat dissipation holes, the bottom of the heat dissipation base is provided with a layer of thermally conductive silicone grease, and the heat dissipation base is provided with a number of mounting slots.

Design advantages
Compared with the prior art, the motherboard heat dissipation structure has the following advantages: 1) The portable reinforced computer motherboard heat dissipation structure improves the heat dissipation effect of the heat dissipation structure by absorbing heat from the motherboard and concentrating it to the heat dissipation fins, and finally accelerating the heat dissipation of the heat dissipation fins by using a heat dissipation fan.
2) The heat dissipation structure of the motherboard of the portable reinforced computer, the heat conduction substrate, the heat dissipation fan, the heat dissipation cover, and the heat dissipation base are mounted closely together in sequence, reducing the occupying volume of the heat dissipation structure when it is mounted, which is conducive to reducing the overall size of the computer.
3) The heat dissipation structure of the motherboard of the portable reinforced computer, through the installation of a protective case, avoids contact between the heat dissipation fins and the external air, prevents dust in the air from adhering to the heat dissipation fins, and improves the long-term heat dissipation effect.

Design realization
Based on the above design elements, this section describes the design technical solutions in detail.Marks in Figure 2: heat sink base 12, heat sink fins 13, protective case 14, sink holes 15, mounting slots 16, heat sink window 17.
A certain portable rugged computer motherboard heat dissipation structure is shown in Figures 1  and 2, including a heat-conducting substrate, a heat-conducting fan 5, a heat-conducting cover plate 6, and a heat-conducting base 12.
The thermally conductive substrate includes a base plate 1 and a thermally conductive block 2 set on the base plate 1, the thermally conductive block 2 is provided with a number of thermally conductive holes 3, the thermally conductive holes 3 pass through the base plate 1 and the thermally conductive block 2, the base plate 1 is provided with a number of symmetrically mounting holes 4, the mounting holes 4 are arranged uniformly, and it is easy to mount the base plate 1 to a motherboard by setting up the mounting holes 4.
A heat dissipation fan 5 is provided on the heat conduction block 2, and the heat conduction holes 3 are provided in the direction of the air inlet of the heat dissipation fan 5.
The heat dissipation cover plate 6 is provided on the heat dissipation fan 5, the heat dissipation cover plate 6 is provided with a vent 7 located in the direction of the air outlet of the heat dissipation fan 5, the inner wall of the heat dissipation cover plate 6 is provided with sound insulating cotton, which reduces the noise generated by the heat dissipation fan 5 when it is rotating.The heat dissipation fan 5 is provided with a plurality of first threaded columns 8, the heat dissipation cover plate 6 is provided with first threaded holes 9 corresponding to the first threaded columns 8, and the heat dissipation cover plate 6 is provided with a plurality of second threaded columns 10, and the base plate 1 is provided with second threaded holes 11 corresponding to the second threaded columns 10.The first threaded columns 8 are threadedly connected to the first threaded holes 9, and the second threaded columns 10 are threadedly connected to the second threaded holes 11 by means of bolts, to realize a close connection between the heat dissipation fan 5 and the heat dissipation cover plate 6 and a close connection between the heat dissipation cover plate 6 and the base plate 1.
As shown in Figures 1 and 2, the heat dissipation base 12 is provided on the heat dissipation cover plate 6, the heat dissipation base 12 is provided with a mounting port connected to vent 7, and the mounting port is embedded with a violet copper plate.The violet copper plate is provided with a plurality of heat dissipation fins 13, the heat dissipation base 12 is provided with a protective case 14, and the heat dissipation fins 13 are provided inside the protective case 14.The protective case 14 is provided with a plurality of heat dissipation holes 15 at both sides of the protective case 14, and the protective case 14 is provided with an openable heat dissipation hole 15 at the top.The protective case 14 is provided with a number of heat dissipation holes 15 on both sides of the protective case 14, the protective case 14 is provided with a heat dissipation window 17 that can be opened at the top, and the heat dissipation base 12 is provided with a number of mounting grooves 16 to facilitate installation of the heat dissipation base 12 on a motherboard.When the motherboard heat dissipation structure is realized to be installed, the heat dissipation base 12, the heat dissipation cover 6, the heat dissipation fan 5, and the heat-conducting substrate are sequentially mounted on the computer motherboard from the bottom to the top, and a heat-conducting silicone grease layer is provided at the bottom of the heat dissipation base 12 to improve the effect of heat conduction.The heat dissipation base absorbs the heat on the motherboard and concentrates the heat to be transmitted to the heat dissipation fins 13, and the air inlet of the heat dissipation fan 5 generates suction to deliver the hot air to the protective casing.The inlet of the cooling fan 5 generates suction to send hot air to the protective casing 14, and the cooling fan 5 is used to accelerate the heat dissipation of the cooling fins 13, so as to promptly dissipate the heat transferred from the motherboard of the computer, and to improve the heat dissipation effect of the heat dissipation structure.At the same time, the protective shell 14 avoids contact between the heat dissipation fins 13 and the external air, preventing dust in the air from adhering to the heat dissipation fins 13, which is conducive to improving the long-term heat dissipation effect.

Design verification
Based on the above motherboard thermal structure design, this portable rugged computer is designed to enhance thermal conductivity efficiency by installing a thermal base and fins.To verify the above structural design, the following simulation analysis and experimental validation of the portable rugged computer are conducted to validate the thermal effect of the motherboard heat dissipation structure.

Simulation analysis
Firstly, the power density of the whole heat dissipation area is calculated [8] .The portable reinforced computer, through a comprehensive analysis of the heat generated by each module of the machine, optimizes the motherboard and internal structural design, realizes a reasonable arrangement of the board location, which is conducive to the uniform distribution of heat, and makes full use of the heat dissipation area for heat dissipation.Table 1 shows the heat dissipation power consumption of the portable rugged computer.The surface heat dissipation area of the host computer is about 2300 cm 2 , and the power consumption is not more than 69 W.
Then the area power density of the mainframe is 69/2300=0.03W/cm 2 .
According to GJBZ27-1992 "Electronic Equipment Reliability Thermal Design Manual" [ 9] , when heat dissipates naturally, the area power density should be less than 0.04.The area power density of the equipment under natural cooling conditions is 0.03, which meets the requirements of heat dissipation conditions.
The required operating temperature of this portable rugged computer is -20℃~55℃, and the thermal analysis software Ansys Icepak is used to simulate and analyze this portable rugged computer in a 25℃ room temperature environment and 55℃ high-temperature working environment [8][10] [11] .When constructing the simulation model, the highest CPU and GPU temperatures are targeted on the motherboard, simplifying the whole machine model, and the main simulation measures the operating temperatures of the CPU and GPU.
When the environment temperature is 25℃, the thermal analysis software Ansys Icepak is used to simulate and analyze the portable rugged computer.The simulation results are shown in Figure 3.The simulation results show that the temperature of the internal devices of the computer ranges from 35.3℃to 65.6℃.The CPU is server-level, and it runs at the highest temperature of 65.6℃.The heat dissipation structure of the motherboard conducts and emits heat, and 65.6℃ is the normal temperature for CPU operation in a room temperature environment, which is far below the CPU limit temperature.When the environment temperature is 55℃, the thermal analysis software Ansys Icepak is used to simulate and analyze the portable rugged computer.The simulation results are shown in Figure 4.The simulation results show that the temperature range of the internal devices of the computer ranges from 63.1℃ to 87.8℃, of which the CPU temperature is the highest at 87.8℃.However, the maximum operating temperature that this CPU can withstand is more than 100°C.The motherboard transfers the heat to the cooling fins through the heat-conducting substrate and accelerates the heat dissipation by using the cooling fan, which improves the heat dissipation effect so that the CPU basically maintains at the normal temperature and can operate normally.

Experimental validation
After the development of this portable rugged computer is completed, the test is conducted in accordance with the test method specified in GJB150.3A-2009 [12], where the temperature is raised to 55°C at a rate of no more than 3°C/min.The computer is kept off for 4 h to bring it up to temperature and then kept off for another 2 h, then the computer is started up.The temperature measurements are taken by using an infrared thermal imager after 2 hours of continuous operation, and the CPU and GPU measured temperatures are compared with the simulated temperatures, as shown in Table 2.At the end of the above test, the computer is turned off and the temperature is reduced to 25°C at a rate of no more than 3°C/min.The computer is kept off for 4 h to bring it up to temperature, then kept off for another 2 h, and then the computer is started up.After 2 hours of continuous operation, the temperature measurements are carried out by using an infrared thermography camera, and the comparison of the CPU and GPU measured temperatures with the simulated temperatures is shown in Table 3.
Table 3. Experimental and Simulation Temperatures at An Ambient Temperature of 25℃.From the comparison of experimental temperature and simulation results, the temperature deviation is less than 10%, the test process of the portable rugged computer operation is normal, the motherboard heat dissipation structure design is reasonable and effective, the heat is generated in a timely manner so that the operating temperature of the key devices carried by motherboard is far below the limit temperature.

Conclusion
This paper describes the design of a certain type of portable reinforced computer motherboard cooling structure in detail.Through the whole machine simulation analysis and experimental validation, the reasonableness of the design of this motherboard cooling structure is verified, indicating that the motherboard cooling structure of the portable reinforced computer can enhance the motherboard cooling effect in the case of the limitations of the internal space of the computer.

Figure 1 .
Figure 1.Exploded view of the heat dissipation structure of the motherboard of a portable rugged computer.

Figure 2 .
Figure 2. Structure of heat sink base and protective case in the heat sink structure of the motherboard of a certain type of portable rugged computer.

Figure 3 .
Figure 3. Temperature cloud of internal devices of a portable rugged computer at 25℃.

Figure 4 .
Figure 4. Temperature cloud of internal devices of a portable rugged computer at 55℃.

Table 1 .
Mainframe Heat Dissipation Power Consumption.

Table 2 .
Experimental and Simulation Temperatures at An Ambient Temperature of 55℃.