Z320 Posted June 18, 2018 Report Share Posted June 18, 2018 Hi Andreas, I guess ist a combination - 50 % cars have the crankshaft / engine cross to the car - 25% cars have the crankshaft is too deep in relation to the radiator - some fuel saving is wellcome but perhaps overrated Ciao Marco Quote Link to post Share on other sites
Waldi Posted June 18, 2018 Report Share Posted June 18, 2018 Hi Marco, Why not see what it does at the highest speed you can adjust:) Power consuption is not linear with speed, so maybe you can let it run on 750 W. I think this topic is like Lucas PI versus EFI versus carburettors: each system has its pros and cons and personal preferences play a role too. One may doubt the effect on powerconsuption of a mechanical fan, but an electric fan, switch with relays has prooven reliable, so I dont think added complexity impacting reliability is relevant here. PS: jealous on your lathe:) Hi Waldi, I own olny a small lathe with only 750 Watt power, but approx 1HP, god enought for me. If I fit my (BMW 1602) mechanical van on it, it should be only possible to run it until with 2.145 revs? Cioa Marco Quote Link to post Share on other sites
Z320 Posted June 18, 2018 Report Share Posted June 18, 2018 Yeah, I love my little lathe, respect to all who own a TR and no lathe. On the BMW van I will have a closer look one day, but not now. I have no cooling problems at all and that old car has power enough. But I see a benefit from a electric van by "driving" in bad traffic, as I had weeks ago back from italy: 100% sun, no clouds, 30°C in the shadow - but no shadow, 1 h stopp and go on the german Autobahn! Radiator temperature wet up to 110°C - but without any probelm. No boiling, no coolant blown in the overflow bottle, not pertol Problems. So there is no need to do anything at all. Ciao Marco Quote Link to post Share on other sites
Andy Moltu Posted June 18, 2018 Report Share Posted June 18, 2018 We lack (emperical) data, but we can still make an estimate... Electric fan: The electric fan which draws around 10A, has an electric power consumption of 10 A x 13V = 130 W, but the generator has an efficiency too, so the mechanical power consumption from the engine crankshaft (including the generator and fan belt losses) will be say 150W (approx. 0,2 HP). It is only needed at lower speeds (in traffic jam etc), and will run say 50% of the time only then (off course depending on engine condition, ambient air temperature), so the net required power is 0,2 * 50% / 0,1 HP for contiumuous cooling at idle. The efficiency of an electric fan will be better than the standard fan, since it has a shroud to minimize re-circulation, and it runs at a much lower speed, which improves volumetric efficiency. Mechanical fan: The standard mechanical fan (driven from the crackshaft) has a (very) poor efficiency to start with : It does not have a shroud, which increases recirculation It is some distance from the radiator so there is even more recirculation, which costs extra power (or reduces efficiency). Fan (volumetric) efficiency also reduces with fan speed. Power consumption increases to the 3rd power with speed (engine RPM), this is a law of physics. Comparison: Now if we know the mechanical fan is capable of cooling the engine at continuous idle speed (say 1000 rpm for this analysis), we can safely assume it will also absorb around 0,1 HP at 1000 RPM (a bit more due to its poor efficiency and a bit less since no energy conversion via the V belt and dynamo is required which also costs power) , but we lack data for a better guestimate. As fan power increases to the 3rd power with fan speed (rpm), the power absorbed by the mechanical fan at.... 3000 rpm will be around 2,75 HP (0,1 * (3000 / 1000)3 ) 4000 rpm will be around 6,4 HP (0,1 * (4000 / 1000)3 ) 5000 rpm will be around 12,5 HP (yes, do the math) Regards, Waldi But does it? The slight flaw in the equation is that at gphigher fan speeds the fan may reduce the air pressure in front of it and thus turn in less dense air so will it use that much power? Will it be as efficient at high rotational speeds and again less energy? Another factor at odds with my first point is that wil the speed of air flow through the rad push the fan? All of these things really make me question if 12 hp is really taken up by the fan. Is the flimsy biy of plastic really capable of handling 12hp? Quote Link to post Share on other sites
ed_h Posted June 18, 2018 Report Share Posted June 18, 2018 (edited) Let me post this link again for those who may have joined this party late.https://www.motortrendondemand.com/detail/cooling-fan-shoot-out/0_olymz420/Ed Edited June 18, 2018 by ed_h Quote Link to post Share on other sites
Z320 Posted June 18, 2018 Report Share Posted June 18, 2018 Is the flimsy biy of plastic really capable of handling 12hp? Also my question, but minimum different: how can this plastic item pull air with 12 hp through the radiator and therefore with 12 hp axial on the crankshaft. It works like a cork screw? And another thought: at least also 12 hp for the water pump? 5 hp more for the van plate of the generator? The oil pump???? Quote Link to post Share on other sites
Spit_2.5PI Posted June 18, 2018 Report Share Posted June 18, 2018 The one thing those chaps didn't do was have air flow through the fan to simulate the forward motion of the vehicle. At some fortuitous velocity, the fan rotation will match the flow and consume no power except the simple drag of the aerofoils. At this speed the blades will neither accelerate nor decelerate the air (excepting the aforementioned drag), hence there should be a significant power drop. Of course, it's very unlikely that we will ever achieve that condition, but there will be forward motion in normal use. But in the case of our fans, I'll repeat my earlier question: does anyone remember the claim that a "torquatrol" (spelling?) fan saved 2hp ... or was it 4hp? I'm sure I saw this back in the 80's, but I can't remember where. Cheers, Richard Quote Link to post Share on other sites
ed_h Posted June 18, 2018 Report Share Posted June 18, 2018 At 5200 RPM (to make the math easier), 12 HP would only represent about 12 foot pounds of torque. I think my stock fan could handle that torque between the blade tips and hub. Ed Quote Link to post Share on other sites
Waldi Posted June 19, 2018 Report Share Posted June 19, 2018 But does it? The slight flaw in the equation is that at gphigher fan speeds the fan may reduce the air pressure in front of it and thus turn in less dense air so will it use that much power? Will it be as efficient at high rotational speeds and again less energy? Another factor at odds with my first point is that wil the speed of air flow through the rad push the fan? All of these things really make me question if 12 hp is really taken up by the fan. Is the flimsy biy of plastic really capable of handling 12hp? Hi Andy, I agree, a lower suction pressure reduces required power for an axial fan. The warmer air (again: density) will reduce required power too. The air velocity from road speed does too. The fan-efficiency is not constant either, it will change with fan speed, but I have no idea how and how much. These are all unknown factors. The basic principle that power consumption increases to the 3rd power with speed stands, however. I think we all can make up our minds, each to his own. Best regards, Waldi Quote Link to post Share on other sites
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