Utilizing fans in the thermal management of electronics is important for improving overall temperature control and reducing power consumption. However, several factors must be considered when choosing which type of fan to use. Microprocessors and other electronic components require a heat sink to reduce their temperature by transferring thermal energy to the surrounding air. It is accomplished through a metal object brought into contact with the device’s hot surface, with a thin thermal interface mediating the two surfaces.
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Airflow
With the continuing miniaturization of electronic devices, increased functionality, and power consumption, heat must be efficiently dissipated from within a device or its enclosure. Typically, this requires a combination of convection cooling (where warm air escapes the case to be replaced by cooler air) and forced airflow through fans. For optimum performance, fans must overcome the resistance presented by the system’s enclosure. A basic rule is that system resistance versus fan pressure inversely increases with the square of the airflow rate. In other words, doubling the airflow rate requires four times as much pressure from the fan. A good place to start when determining a fan’s suitability for a particular application is the datasheet’s resistance curve. It plots the static zero-pressure point against the maximum free airflow rate in cubic feet per minute or CFM.
In addition, DC fan motors generate a pulsing load current with significant peaks that can interact unfavorably with sensitive circuitry that shares the same power supply. Using a dedicated power supply for the fans can mitigate this problem. A tachometer can also measure fan speed, which is useful for monitoring and identifying problems like excessive wear or short circuits in the drive system. These types of sensors are available in both analog and digital formats.
Cooling Capabilities
Electrical systems generate heat using electrical current to power transistors that turn on and off and amplify electronic signals. These processes waste energy in the form of thermal energy, which needs to be dissipated for safety and performance reasons. A failure to properly manage this excess heat can cause components to overheat and deteriorate. Engineers take temperature management seriously when designing for a specific application. Fans help cool electronics by bringing cooler air into the case or enclosure to dissipate the heat. They also improve the effectiveness of convection cooling by increasing the surface area allowing it to move faster and with greater force. Convection is a natural process that involves the force of attraction between cooler and denser molecules of air, which sink as the hot ones rise. Active thermal management solutions speed this up with forced convection using fans or blowers.
Another way to cool an electronic device is by utilizing Peltier modules, which transfer heat with very little difference in temperature between the hot and cold interfaces. A common example is a CPU fan that uses a Peltier module to draw and blow cool air over the processor. A final option is to use thermal vias, padded holes drilled into the PCB that channel heat away from power-dissipating components. Many companies offer a variety of fans to fit different specifications. These fans vary in size, airflow rate, static pressure, and noise levels, allowing engineers to find the best solution for their applications.
Static Pressure
When a fan is not working properly, or its static pressure is too high, it can cause your system to work harder than it should. Maintaining good static pressure is crucial for thermal management since the added workload may result in increased wear and tear and a shorter lifespan for your equipment. Static pressure is what measures the resistance to airflow within your heating and cooling systems ductwork. It’s a critical measure because for the system to work effectively, the pressure has to be greater than the resistance.
You can test your system’s static pressure with a manometer. It’s like getting your blood pressure read by the doctor; you want to make sure it’s at a healthy level. Some things that can affect static pressure include the size of your building or how much ductwork is used. If your ductwork is too small, the system will have to use more energy to push air through it, which lowers the static pressure. Also, if your ductwork is made from plastic rather than metal, it’s more susceptible to static buildup, which can cause the airflow in your system to decrease.
Noise
Increasingly sophisticated and complex electronic components must be protected against major heat-related threats. The primary tools are fans, thermal interface materials, and Peltier modules for thermal management. These are used in various applications to maintain the temperature of the power-dissipating devices within their design limits and ensure operation and longevity for a wide range of end products. The selection of a suitable fan for a specific application depends on many factors, including the required airflow, size restrictions, and possible electrical or audible noise issues. An engineer may also need to consider the ability of a fan to generate electromagnetic interference (EMI). While most dc fans do not cause significant EMI, some create conducted noise that can be suppressed with ferrite beads or shielding.
Acoustic fan noise varies greatly between models, with some emitting minimal or no sound when operating at nominal conditions. A large part of this variation is due to blade geometry, with curved leading and trailing edges helping reduce the relative strength of blade pass tones. Other less predictable factors include case design and the chassis’s interaction with the fan’s flow. Finally, an important factor is the ability to control the fan speed. A programmable controller can regulate fan speed based on instantaneous cooling requirements. It reduces the fan’s power consumption, extends battery run times, and eliminates acoustic noise.