Reasoning behind why push vs. pull doesn't matter

cleric_warlock · November 13, 2022

It's pretty well established that cooling a radiator with fans in the push or pull configurations will get you the same cooling performance either way, but I'm kind of curious as to why this is the case from a theoretical standpoint.

My best guess is that it has something to do with laminar vs turbulent flow. Air velocity is clearly much higher in the exhaust than in the intake because the fan blades are what's imparting kinetic energy directly to the air molecules by contact, but due to physical disturbance by the fans, the exhaust airflow is turbulent. In the intake region air is moving to fill the area of low pressure created by the fan pushing air out the back so since a pressure gradient alone is what's driving airflow, that flow would be laminar.

Back to the actual cooling aspect, laminar flow (smooth air flowing in parallel lines, also parallel to nearby surfaces) over cooling fins in a pull configuration would provide the optimal physical interface between the fins and the cool air pretty much by definition so there would be more air molecules available to transfer heat away from the radiator even if the flow is slower. With the radiator in a push configuration, you have much faster turbulent flow with all its eddies and imperfections so the comparatively sub optimal interface between the air and the fins reduces heat transfer effectiveness, but the increased velocity of the airflow compensates for this, leaving you with roughly identical heat transfer.

What do you guys think of my theory about this?

Shimejii · November 13, 2022

Generally speaking on why it doesnt matter, Either direction its still doing the exact same job, moving air over the fins and pipes. Using the same fans in either direction wont impact performance in any meaningful way because most times there just isnt enough heat energy TO make it a difference with large enough rad (280/360/420) . If you substantially increased the amount of heat energy needed to dissipate, id say it would impact it a bit more then that. Most times though its just not enough heat energy to matter. What does matter is the amount of airflow, if its a good static pressure vs general airflow fan, if the fan design itself creates bad air movements (like cheaping out and making the fan outer shell a bad design) and such.

Overall we have nailed down radiator design, it does its job well and most of the time it just comes down to materials used and fin density, otherwise it should be similar. Different materials will react differently, Copper vs Alum can impact it a bit, but with just the amount of energy (although thats been increasing more and more)

thrasher_565 · November 14, 2022

static pressure is for pushing air thow tight gaps and not having all the air fly back out. or that's the theory any way. are they needed no but depends if your getting the most cooling out of the rad. but most times its not worth the cost to buy better fans at all. cheap ones work just fine. back in the old days with people had 120mm thick rads had to do push pull with static pressure fans but we later found out thinner rads and cheaper fans was the best combo for price to proforamce. and so 30mm thick rads is the norm. unless you run out of rad space then ya have to go thicker or faster fan rpm. we do have artic fans that dose a good job and are cheap for static pressure. question is a $7 how long will they last... 30mm thick fans is the sweet spot but there not many on the market. back then there this company that made 55mm fans and clamed they were the best rad fan but later on a shroud added to a fan did the same thing. thow alot of these test may not have been accrete so...

the debate between yatloon $4 fans vs gentle typhoons $20-$25 fan was debated accross all forms for years...

there was some delta server fans that people used and some alowed for reduced voltage well otheres did not but they still pulled alot of power witch required a complex and expensive setup.

i kinda want to do test of fans and see whats the best but that also cost alot of extra moeny and atm so many other thing i want to buy but i have been thinking about it.

Edited November 14, 2022 by thrasher_565