Relationship between ambient temperature and capillary limit under different dissipated power
To calculate the temperature distribution in the heat pipe, the following assumptions and simplifications are required: (1) the heat conduction along the axial direction of the pipe wall is negligible; (2) the wall temperature of the condensation section remains unchanged; (3) the heat input of the evaporation section is uniform; (4) Stable working conditions without heat loss. Using the software to simulate the 1W heat pipe radiator, the comparison between the empirical formula and the software simulation results is given. Optimization of the heat dissipation performance of the heat sink module The heat transfer performance of the heat pipe is affected by many limits of the heat pipe, such as the speed limit, the viscosity limit, the load limit, and the capillary limit. These limits are related to the type of the working fluid, the type of the capillary wick, and the heat pipe. According to the shape calculation, the engineering operation indicates that the working point of the heat pipe must be below the capillary limit to ensure the heat transfer performance of the heat pipe.
Considering the applicability of the project, it is necessary to ensure that the heat pipe can work normally at an ambient temperature of 0 to 45 ° C, and the junction temperature of the chip is controlled below 85 ° C to meet the requirements of the use of the lamp. 1LED power dissipation optimization. The number of LEDs installed is 6 to 11 (that is, the dissipated power of the lamp is 6 to 11 W), and the variation of the capillary limit parameter that limits the maximum heat transfer amount of the heat pipe with the ambient temperature is analyzed. The ambient temperature at which the minimum capillary limit occurs is 0 ° C. Therefore, it is necessary to compare the amount of heat dissipation under each of the dissipated powers under the minimum capillary limit, and it is finally determined that the maximum number of LEDs that can be installed in the heat pipe radiator of the design is nine. That is, the maximum heat dissipation of the luminaire is 9W.
The relationship between ambient temperature and capillary limit at different dissipated powers: the relationship between the number of LEDs and the capillary limit 2 rib length and rib spacing optimization. Since the rib width is determined by the width of the evaporation section of the heat pipe heat sink, this design parameter has been determined by the size of the previous evaporation section. The length of the ribs determines the heat dissipation area of ​​the ribs, and the size of the ribs has an important influence on the number of ribs and the overall heat dissipation area of ​​the ribs. The heat dissipation area is the core element in the design of natural convection heat dissipation, so it is necessary to The above two parameters are optimized. Optimized for the case of 9W dissipated power.
Under the different rib lengths, the relationship between the rib spacing and the minimum capillary limit can be seen. Under the 9W dissipated power, when the rib length B is greater than or equal to 28mm, as long as the rib spacing is appropriate, the heat dissipation requirement can be satisfied. It can be seen that there are many data points that meet the requirements of the chip junction temperature less than 85 ° C, but according to the lower the junction temperature of the chip, the better the heat dissipation effect, and from the perspective of cost saving, the most suitable rib length is 28 mm. The rib spacing is 6.5 mm.
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