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How do heatsinks/fans work?

J

JOSHSKORN

Limp Gawd
Joined
May 29, 2007
Messages
262
When it comes to heatsinks or fans, I'm a complete newbie.

How do they work? Just wondering.

What I'm getting at, is, I'm new to overclocking and would like to know if they automatically work harder to keep my system cooler when overclocking, or if I need to do some manual tweaking. Or, is there an application I can use to cool down my system?
 
Purpose of a heat sink is to transfer heat away from the heat source to dissipate it into the atmosphere or liquid medium.

Key word is transfer here, contact surface is crucial to how well the heat is transferred from the CPU to the heat sink/heat pipe itself. After that comes the surface area of the heat sink, which determines how well it dissipates that heat.

The fan is there to move fresh air over the surface area of the heat sink/heat pipes to dissipate the heat into the atmosphere. The faster the fan spins, the more fresh air moves over the surface of the heat sink providing better cooling.

Heat pipes on the other hand are hollow tubes made of copper/aluminum that have a liquid inside that vaporizes at the heat source, moves to the far end of the pipe, cools back down to a liquid and moves back toward heat source. Heat pipes work in conjunction with radiator style fins to increase surface area and increase the dissipation of heat.

Some HSF's come with little dials that you can adjust to change fan speed. I don't really know if there is an app to change fan speed automatically though since I've always used a fan controller.
 
Korben Dallas said:
Some HSF's come with little dials that you can adjust to change fan speed. I don't really know if there is an app to change fan speed automatically though since I've always used a fan controller.
Click to expand...

Your whole reply was great. Thank you. I just have one question (see quoted text). Can you explain what this fan controller is you have? Is it a separate device? Do you have a fan that has a controller?
 
Another thing to consider is that some fans have three pins while others have four. 3 pin fans run at full speed unless you connect them to a controller or a voltage limiting wire. For example the Noctua NF-P12 fan comes with a low noise adapter (7 Volts) and an ultra low noise adapter (5 volts). You simply connect the fan wire to the adapter, and the adapter to the motherboard.

Four pin fans have what is called pulse width modulation (PWM) and they control their speed based on BIOS settings in the motherboard. You can tell the motherboard to keep the thing at full speed, low speed, or to automatically adjust based on CPU temperature.
 
Most motherboards have CPU fan headers that can be set (in the BIOS) to adjust the fan speed based on the reported CPU temperature.
 
Forceman said:
Yes, most can, as long as fan control is supported (not all motherboards have fan control).
Click to expand...

Yep, those mobos typically tweak the voltage going to the fans, as voltage = electrical potential, rather, how fast a fan will spin :p
 
Try to look for liquid-vapor based heat sinks. They work wonders. Or you can just go straight water cooling. ;)
 
For Fan or (for our applications) DC-electrical control (pumps and TECs as well):

PWM - Pulse-Width-Modulation = controlling frequency of power-pulses. Voltage remains at default (12v in most of our applications), and is switched on/off at a rate determined by the PWM-controller. There is very little power-loss, and thus very little heat to dissipate from using this type of control (power control involves some parasitic power losses of its own). The power delivered would then depend roughly upon the "duty cycle" (in percent) ratio of time spent on vs off (w/o PWM = relatively continuous DC power, with PWM = discrete, pulsed power, on/off)

Disadvantages: Some say this type of control can induce audible "ticking" in some fans. I have not been able to prove this, though if one searches back, my posts indicate that I have experienced this, whereas I've been less able to replicate the same issue using voltage control. It is true, however, that some fans exhibit resonances and ticking at lower voltages anyway. It may just be a characteristic of the fan itself in relation to RPM, voltage, or PWM, all independently... or not... could vary fan to fan, motor to motor.

Voltage Control: The Rheobus and Rheobus Extreme (as well as several other external controllers) utilize voltage control. It's not as efficient, more heat must be dissipated, and it's likely that the quality of voltage regulation will depend on each specific unit, but if executed properly, it's a great feature to have. It generally uses principles of variable resistance (as in a rheostat or potentiometer with voltage regulator circuitry). Voltage controllers will utilize larger heatsinks on each channel - a dead giveaway (Though I've seen some newer units which supposedly are able to control voltage, and yet do not feature heatsinks despite high power-handling. I'm not sure how that works yet, nor have I investigated).

Combined PWM and Voltage: This can be useful. For instance, TECs are often most efficient at lower voltages, so one must run multiple TEC's in parallel (physically adjacent) to efficiently transfer heat from one side of the junction to the other in a TEC water-chiller. To maintain efficiency, even if PWM-control is used, a lower voltage must also be used. With the dynamic loads of our PCs, the advantage of tandem PWM and Voltage-control is obvious as part of an advanced temperature control system.

RPM: Both PWM and voltage control will offer control over the RPM, but the RPM must be measured separately (RPM-sense wire) to determine the effect. I think the RPM signal wire sends something like 2 pulses per revolution, so if measured with a scope or multifunction DMM, you could measure RPM by multiplying by 30. Thus the resolution of most RPM-measuring devices is limited to about +-30RPM because the periodic polling-reporting is based upon whole-number pulses per minute, whereas instantaneous rate is easily measured by the aforementioned means.

Temperature Control: Generally adjusts RPM via PWM to keep temperature within a desired range. This is generally done on the motherboard, but some aftermarket controllers can do this as well.

Heatsinks: Utilize principles of conduction and convection to move heat from a smaller area to a larger area to be effectively dissipated. They Conduct heat using a high-conductivity material (copper), distribute it to the high surface area of the fins (via conduction and convection if using heatpipes), and then dissipate heat from the fins by way of convection (using airflow).
Aluminum seems to offer slightly better convective properties compared to copper, and thus the reduced conductivity and mass is slightly offset when using Aluminum fins. It's also just easier to machine and shape - adding a rough surface to aluminum, which is easy, will further increase surface area at the expense of turbulence, and thus disturbance of laminar airflow. I see that most manufacturers are using smoother fins now, concentrating more on their shape to direct airflow, so perhaps the rough surfaces are not optimal.
Heatpipes are a means of conducting heat from the copper solid to a fluid-gas-medium, which, by way of convection, causing a phase-change, is effectively distributed throughout the heatpipe, and then to the fins and into the surrounding air.

Fans: are fans... they blow air over our heatsinks and radiators...

Conclusion: Basic heatsink/fan combinations "just work." Some fans can be motherboard-controlled, which is often just PWM-control based upon temperature. The heatsink remains as-is, obviously. Aftermarket control devices vary greatly in function and form - some are even software-USB and/or touchscreen interfaced now. There are simply too many products to list... however using all of the above information, wikipedia, and some google searching, one can determine how each control device likely operates based upon description, or, failing that, reviews and/or e-mails to the manufacturer.

Edit: Anyone can feel free to correct mistakes I've made... there may be some... but for the most part, the above summary should be quite useful.
 
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