Reflections on watercooling: Difference between revisions

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==Generic cooling notes==

* We don't use Fahrenheit, but it's worth knowing that ~~1℃ ==~~ 1.8℉. We don't really use Kelvins either, but Kelvins are equivalent to Celsius with an offset of -273.15. Liquids boil at lower temperatures at higher altitudes (boiling occurs when internal vapor pressure equals atmospheric pressure). Water expands both above and below 4℃. A quick table:

* We don't use Fahrenheit, but it's worth knowing that each ℃ is 1.8℉, with an offset of 32. We don't really use Kelvins either, but Kelvins are equivalent to Celsius with an offset of -273.15. Rankines can fuck right off. Liquids boil at lower temperatures at higher altitudes (boiling occurs when internal vapor pressure equals atmospheric pressure). Water expands both above and below 4℃. A quick table:

{| class="wikitable"

! ℉ !! ℃ !! Notes

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| 39.2 || 4 || Water's volume is minimized (density maximum).

|-

| 32 || 0 || STP. Water freezes at sea level.

| 32 || 0 || STP. Water freezes at sea level, expanding by 9%.

|-

|}

* Neither air- nor water-based cooling can get your temperatures below ambient (this can be achieved with phase cooling, thermoelectric aka Peltier, and cyrogenics). If it's 30 degrees in your room, your coolant and component temps are going to be at least 30 degrees. <b>It is useless to report temperatures without reporting ambient temps.</b> The effectiveness of your cooling system is measured by how close it gets to ambient, ΔT. Likewise, your heat-generating components are going to be hotter than your coolant.

* <b>The goal is to move heat from the heat-generating components, and ultimately from the case.</b> Effectively moving heat requires (a) thermal conductivity, (b) contact area and (c) a temperature gradient. The thermal conductivity of air is about two orders of magnitude less than water, which is about two orders of magnitude less than aluminum or copper.

** A processor without a heatsink is depositing heat directly to stagnant air, which will heat up (reducing the temperature gradient) and can't take much heat anyway.

** Adding a heatsink means the heat is deposited into a good conductor with more surface area...which in turn deposits into stagnant air. This air will heat up, and eventually the heatsink will, as well.

** Adding fans moves the hot air (ideally out of the case), to be replaced by ambient air. The ejected hot air will diffuse into the ambient air, which is (ideally) a large convecting volume.

* I don't delid my processors, but it's an intriguing idea. Delidding is the removal of the processor's integrated heat spreader. The IHS is the metal cover atop your processor. The actual heat-generating die elements tend to be only a small portion of this total area (the remainder is mostly devoted to pins). Delidding is a bet that you have better thermal interface material than what was used between the die(s) and the IHS. This was absolutely true in the past, but modern processors often use an indium soldering solution that is just about as good, IMHO, as anything you're going to do.

==Thermal interface material==

TIM is thermally conductive viscous material applied between heat contacts. There's some between your dies and the IHS, and then some between the IHS and your waterblock/heatsink. Its purpose is to smooth out the conducting surface, which is dotted with microscopic pits that would otherwise preclude contact. TIM is one or two orders of magnitude less thermally conductive than metals making direct contact, but much more conductive than the air which would otherwise fill these regions. Thermal conductance is measured in W/Km (watts per kelvin-meter).

@@ Line 4: / Line 4: @@
 ==Generic cooling notes==
-* We don't use Fahrenheit, but it's worth knowing that 1℃ == 1.8℉. We don't really use Kelvins either, but Kelvins are equivalent to Celsius with an offset of -273.15. Liquids boil at lower temperatures at higher altitudes (boiling occurs when internal vapor pressure equals atmospheric pressure). Water expands both above and below 4℃. A quick table:
+* We don't use Fahrenheit, but it's worth knowing that each ℃ is 1.8℉, with an offset of 32. We don't really use Kelvins either, but Kelvins are equivalent to Celsius with an offset of -273.15. Rankines can fuck right off. Liquids boil at lower temperatures at higher altitudes (boiling occurs when internal vapor pressure equals atmospheric pressure). Water expands both above and below 4℃. A quick table:
 {| class="wikitable"
 ! ℉ !! ℃ !! Notes
@@ Line 20: / Line 20: @@
 | 39.2 || 4 || Water's volume is minimized (density maximum).
 |-
-| 32 || 0 || STP. Water freezes at sea level.
+| 32 || 0 || STP. Water freezes at sea level, expanding by 9%.
 |-
 |}
+* Neither air- nor water-based cooling can get your temperatures below ambient (this can be achieved with phase cooling, thermoelectric aka Peltier, and cyrogenics). If it's 30 degrees in your room, your coolant and component temps are going to be at least 30 degrees. <b>It is useless to report temperatures without reporting ambient temps.</b> The effectiveness of your cooling system is measured by how close it gets to ambient, ΔT. Likewise, your heat-generating components are going to be hotter than your coolant.
+* <b>The goal is to move heat from the heat-generating components, and ultimately from the case.</b> Effectively moving heat requires (a) thermal conductivity, (b) contact area and (c) a temperature gradient. The thermal conductivity of air is about two orders of magnitude less than water, which is about two orders of magnitude less than aluminum or copper.
+** A processor without a heatsink is depositing heat directly to stagnant air, which will heat up (reducing the temperature gradient) and can't take much heat anyway.
+** Adding a heatsink means the heat is deposited into a good conductor with more surface area...which in turn deposits into stagnant air. This air will heat up, and eventually the heatsink will, as well.
+** Adding fans moves the hot air (ideally out of the case), to be replaced by ambient air. The ejected hot air will diffuse into the ambient air, which is (ideally) a large convecting volume.
 * I don't delid my processors, but it's an intriguing idea. Delidding is the removal of the processor's integrated heat spreader. The IHS is the metal cover atop your processor. The actual heat-generating die elements tend to be only a small portion of this total area (the remainder is mostly devoted to pins). Delidding is a bet that you have better thermal interface material than what was used between the die(s) and the IHS. This was absolutely true in the past, but modern processors often use an indium soldering solution that is just about as good, IMHO, as anything you're going to do.
 ==Thermal interface material==
 TIM is thermally conductive viscous material applied between heat contacts. There's some between your dies and the IHS, and then some between the IHS and your waterblock/heatsink. Its purpose is to smooth out the conducting surface, which is dotted with microscopic pits that would otherwise preclude contact. TIM is one or two orders of magnitude less thermally conductive than metals making direct contact, but much more conductive than the air which would otherwise fill these regions. Thermal conductance is measured in W/Km (watts per kelvin-meter).

Reflections on watercooling: Difference between revisions

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