“I would agree with you if the thermostat is restricting flow into the pump but not if it is restricting flow out of the pump.”
Sorry, a centrifugal pump pumping liquid (incompressible) doesn’t care where the restriction is.
Also, a heater fan on high pulling 10 amps will burn about 2.5 fl.oz. gasoline per hour.
Centrifugal pumps need less power when the flow is restricted and you never restrict water flow on the intake side of the pump because that can cause cavitation which quickly destroys the impeller.
On centrifugal pumps that pump air or gas, you throttle flow on the inlet side.
Stop the air flow of a vacuum cleaner and you can hear the motor speed up, that’s because it takes less power to drive the impeller when the airflow is stopped.
I think the modern dual thermostat does not restrict inlet flow but shunts a percentage of hot water past the radiator to reenter the engine block if the water coming from the radiator is too cold, mixing cold water from the radiator with hot water from the engine coolant outlet to feed warm water to the engine block, holding the feed coolant at a constant temperature regardless of the temperature of the air going through the radiator.
Car engines waste about 75% of the energy they consume by burning gasoline…If you didn’t divert some of it to inside the car, it would be given off as waste heat through the radiator…
I think the OP means to ask “Does running the heater use extra gas compared to not running the heater?”. The answer is no, excepting a very small amount to run the blower fan, there’s no extra gas used to run the heater. You shouldn’t notice any difference in mpg in other words.
The converse – does running the AC use extra gas ? – the answer to that is “yes”. You will usually notice some appreciable degradation of mpg if the AC is on.
I think the OP means to ask "Does running the heater use extra gas compared to not running the heater?".I'm not trying to guess what the question was supposed to be, just answering the actual question asked. Original question,
Does car heater use gas to generate heat?
The answer is yes, the engine needs to be running to produce heat, and with out gas the engine would not run.
You cant compare a vacuum cleaner or blower motor to a water pump simply because the air is compressible and a liquid is not. Horsepower needed to operate the pump is determined by the flow and the ΔP. Both are on top of the equation so as flow decreases, power required goes down, but as ΔP increases, power required goes up.
With a liquid, if the pump was a positive displacement, the pump would either come to a stop or something would break. Water pumps for cars do have enough clearance to prevent the pressure from rising to the point of breaking anything.
The question is, which is changed more by the thermostat, ΔP or flow? Flow backwards through the pump from around the impeller clearances is still flow. I don’t have any references as to which is greater but I do believe that the ΔP is greater that flow reduction.
As for the thermostat location. It has been awhile and I gave away my FSMs when I sold my Saturn, but as I recall when I changed the thermostat on it, the thermostat was mounted at the intake of the water pump. I distinctly remember that the lower radiator hose connected to the thermostat housing. I remember this because when I replaced it, I automatically removed the upper radiator hose thinking I would find it there, then had to get out the FSM to find out where it was.
Water pump energy use decreases if flow is obstructed, it’s doing no work.
It is building pressure and holding it, that is work. And there is flow around the edges of the vanes in the pump and through the tiny peep hole in the thermostat. But we were initially talking about a small restriction to maintain engine temperature, not a complete blockage of a closed thermostat.
I have worked with a lot of centrifugal water pumps and take my word for it, when you restrict the flow, the amps that the electric motor pulls go down. When the water does not flow, the pump just spins the water around. When there is flow, the motor has to accelerate water that is going very slow to a high speed as it reaches the outer rim of the impeller. The power needed to drive the pump is the kinetic energy given to the water as it goes from the center of the impeller to the outer rim.
The volute or diffuser then converts the kinetic energy of the water that has been accelerated into potential energy (pressure) You can closely estimate the zero flow head of a water pump by calculating the velocity of the rim of the impeller and then answering the question, “how far would something have to free fall in earth’s gravity to reach this velocity?” The answer to that question will be very close to the zero flow head of the pump.
At vacuum cleaner pressures, air can for all practical purposes be considered an incompressible fluid. The difference between the simple incompressible fluid formula and the much more complicated compressible fluid formula will be like a rounding error.
If you are dealing with turbochargers or jet engines, you need to take compressibility into account.
PvtPublic, I originally understood the question the same way everyone else did, but I find your interpretation intriguing… and possibly even accurate. Technically, it’s every bit as correct an interpretation as mine. Someone for whom English is not a first language might even wonder why we approached the question the way we did, and the OP might be someone for whom English is not the native language. Thank you for making me realize how easy it is to assume that we’re answering the same question that the OP asked, when in fact that might not be true.
It’s sort of funny, we’re overthinking the question to death, flexing our technical prowess, comparing the sizes of our physics, and we might not even be answering the right question.
No disrespect meant to anyone, but I have to laugh at us, myself included. Thank you for opening my mind,
TSM
The waste heat of a internal combustion engine is the whole idea behind cogeneration plants. Large institutions use internal combustion engines mostly as furnaces to provide hot water to buildings for heating, and using the output of the engine to generate electric power as a by-product.
I always think this in the winter, when I drive past Cheswick power plant (and the ice-free river downstream of its outflow):
YOU, the electric co, have hot water (that’s a minor PITA to get rid of). All around you (say 1/4 mile in any direction) are poor folks, struggling to keep the heat on. SURELY, you could figure out a way to fix both problems, and maybe make a few bucks…or a charitable write off…or at least unspecified “brownie points” amongst the local citizenry and government??
Yeah, the problem is that huge volumes of water at 100F would require large flows through large heaters to do any real heating in a home. Very expensive.
Edit: That’s 100F in Summer, much less in Winter…just not doable.
The geese like it though.
sciconf I hope you have learned not to ask a “plague” of engineers who are extremely knowledgeable in a variety of subjects a simple question. Wink, Wink.
The gasoline heater in the Corvair got about 30 mpg. The car got about 30 mpg, The car with the heater blasting got about 15 mpg.
My father in law had a 37 Ford V860 with a gasoline heater under the das thatgot so hot it glowed red if you left it on high. He said it sometimes dripped gasoline on the floor of the car.
No smoking in that one.
Which would be the better heater for the Corvairs: 1.the gasoline heater of the 1960 model or 2.the exhaust manifold heater of the 1961 and later models?
With the gasoline heater, you probably should carry a big fire extinguisher. With the exhaust manifold heater you should always have a canary in the cabin.
Bing “No smoking in that one.” I would be more than a little leery mixing a glowing red heater with gasoline fumes!
Now that we’re talking about it, I mentioned it before that a kid in high school back in 65 or so folks bought a new Ford. He talked about how nice the ELECTRIC heater in it was. That you didn’t have to wait for the engine to warm up to get heat. Must not have lasted very long though 'cause I don’t remember anyone else having it ever. Must have been the high end LTD or something but not a T Bird. I imagine that would have put a little load on the engine though.