If you are not aware of the fundamental factors that affect the performance of the radiator, the design and testing tasks will repeatedly cycle, ultimately leading to delays in the product development process. Generally speaking, when evaluating the performance of the radiator, it may be impossible to select the radiator to meet the cooling requirements of the equipment. There are the following 3 common mistakes. So, let's take a look at the three misconceptions of radiator selection together! 
Evaluate the performance of the radiator using the thermal resistance provided by the product manufacturer. 
The thermal resistance of the radiator is a common method for evaluating the performance of the radiator in a specific APP environment. The common way to select a radiator is to multiply the thermal resistance Rth of the radiator fin by the cooling power q of the cooled device, add the ambient temperature Tamb, and this can determine the shell temperature Tc of the device. First, use expression 1 to calculate the required thermal resistance of the radiator, and then select the radiator whose thermal resistance is less than or equal to the calculated value. 
The thermal resistance provided by the radiator manufacturer is generally measured for a square heat source radiator. The temperature difference is measured. Usually, a square heat source with dimensions of 25.4 mm x 25.4 mm (fixed heat dissipation) can be connected to the center of the base surface of the radiator substrate. The thermal resistance of the radiator can be calculated according to formula 1. 
If the heat resistance values measured by this method are used to select the heat sink, since the heat resistance of the heat sink is not constant, the selected heat sink often fails to meet the heat dissipation requirements. The heat resistance may be much higher than the test value provided by the manufacturer. This is because when heat flows from the heat source area to the top of the heat sink, the heat resistance of the same heat sink varies with the size of the heat source relative to the reference plane of the heat sink. If the heat source is significantly smaller than the heat source used by the manufacturer in the actual test of the heat sink, the total heat resistance of the heat sink will be greater. This is caused by the heat diffusion resistance in forced convection cooling. The greater the ratio of the heat source area to the base area of the heat sink, the greater the heat diffusion resistance of the heat sink, and the influence of convective diffusion resistance on the heat sink is obvious. 
2. Select the radiator solely based on its surface area. 
When determining the required surface area of the radiator, the performance of the radiator is not only dependent on the surface area, but also on all the relevant dimensions of the radiator. Among these, the spacing between the heat sinks is particularly important. The spacing between the heat sinks has a significant impact on the heat dissipation rate on the surface of the heat sink. Many articles usually provide the heat dissipation value per unit area. Many people believe that simply increasing the surface area of the radiator can improve its performance, but this is not the case. This is often referred to as the heat transfer coefficient h. The surface area a and the heat dissipation rate h are shown in Equation 2 and determine the surface temperature Ts of the radiator. 
As the gaps between the heat sinks become smaller, heat transfer deteriorates. This is mainly due to the increase in the thickness of the thermal boundary layer. When air enters the space between the fins and grows along the length of the fins, the thermal boundary layer is thin. The closer the gaps between the heat sinks are, the faster the thermal boundary layer merges with the adjacent heat sinks. This results in hot air areas, and the thermal boundary layer is usually described as an area near the surface of the radiator fins where the air temperature is higher than the ambient temperature. Reducing the air heat transfer speed from the radiator surface to the heat sinks. To achieve a lower radiator temperature and a lower temperature of the cooled source, it is necessary to balance the gap between the heat sinks and the surface area of the radiator. 
3. Estimate the performance of the radiator by using a larger fan flow rate 
Cooling fan manufacturers usually state the larger fan flow rate when listing the fan performance, but this can easily cause confusion for those who are not familiar with fans. 
The higher the density of the heat sink, the greater the air flow resistance, the higher the voltage drop of the fan, and the less the air flow provided by the fan. To obtain a large amount of heat dissipation at a certain air volume, it is necessary to select appropriate fan and heat sink sizes. The intersection point of the pressure-flow curve of the fan and the pressure-flow curve of the heat sink is the working point of the fan. The larger flow rate of the fan should not be used to evaluate the heat dissipation performance. 
The above are the three common mistakes in choosing radiators. If you want to know more, please feel free to contact us at any time!