Amps v Amp hours v Amps/Hr

[Lars_L]

I want to start from the beginning and look how far we can agree.
Lets do the same way as when you eye is tested. How far down the list can you agree?

Some one-dimensional units:

Time:
Day (d)
Hour (h)
Minutes (m)
Seconds (s)

Length:
Meter (m)
Decimeter (dm)
Centimeter (cm)
Foot (ft)
Inch (in)

Volume:
Cubic meter (m³)
Cubic decimetre (dm³) even called litre (l)
Cubic centimetre (cm³)
Gallons (g)
Cubic foot (ft³)
Cubic inch (in³)

Two-dimensional unit:

Flow = Volume per Time

Cubic meter per hour (m³/h)
Litre per hour (l/h)
Litre per minutes (l/m)
Litre per seconds (l/s)
Gallons per hour (g/h) or (gph)
Cubic inch per minutes (in³/m)

[Wotname]

Originally Posted by sailorchic34

Hum, If your engine uses 1 GPH of diesel per hour, is that a unit of speed or of volume. A unit of 1 GPH does not imply speed or how fast it's flowing. The speed of flow would be the product of velocity. That would be Feet per second or meters per second. So if your moving a GPH in a 1/4" diameter pipe it has one speed of flow (how fast it travels). In 1" pipe that speed of flow would be much slower, but the flow rate of 1 gph would be the same. So in my mind GPH is not a speed of flow but a volume of flow per time period.

I hope that is somewhat clear.

It is somewhat clear

Your conclusion is correct, your reasonings in reaching that conclusion are incorrect.

For instance, let's rewrite your first sentence out again replacing the acronyms with the full words. It becomes "Hum, If your engine uses 1 gallon per hour of diesel per hour, is that a unit of speed or of volume."

That equates to gallons divided by hours divided (again) by hours or more simply put G/H/H. It also equates to volume/time/time.

So now you can see 1GPH of diesel per hour is neither a unit of speed or of volume., rather it is change of rate of volume.

If it helps, consider the same maths using displacement (distance ) and time rather than volume and time. I assure you the maths remains constant in both cases

So using displacement is say in feet (F) and the time in seconds (S).
As you know, velocity is displacement divided by time and acceleration (or rate of change of velocity) is velocity divided by time.
Hence velocity in these units = F/S and acceleration is F/S/S.
Written another way velocity is FPS and acceleration is FPSPS.

Thus when using volume and time (gallons and hours for instance)
GPH per hour quotes to GPHPH or G/H/H

If you had written Hum, If your engine uses 1 GPH of diesel for an hour, is that a unit of speed or of volume the whole thing changes considerably. Then it becomes G/H.H or simply G which is of course, simply volume.

There are some other inaccuracies in your reasoning above but enough for today , I'm sure you can work them out if you want to. If not, no problem!

[StuM]

Originally Posted by sailorchic34

I agree with this completely, it's flow volume per time.

So guys, In another thread today I was talking about heating water. So if we have a flow rate of 10 GPM. The water is at 40 degrees. I want to heat that to 100 degrees F, How many BTU's BTU hours (or MBH) do I need to heat that 10GPM.

For the answer we convert 10 gpm to pounds lbs/min. 1 gallon is 8.33 pounds at stp. So 10 GPM would be 83.3 pounds. lbs/min We then multiply that by the delta of the temperature, 100-40 for 60 degrees. 83.3 pounds lbs/min *60 (F. delta T) gives an input of 4,998 btu/minute. Times 60 gives 299,880 btu's/hr. So 299MBH output will heat 10 GPM or 600 gallons in for one hour (or 600 gallons) 60 degrees F. This is a basic formula used in mechanical engineering around the world. Though some might use Cubic liters per minute.

Where did the pounds come from if 10 GPM is not also a unit of volume.

If you can't see the reason for the corrections, then I really do despair for you.


And the pounds came from the gallons part of 10GPH .

And you still haven't given a simple Yes/No answer to:
"Can we now agree that GPH is not a volume? "

[StuM]

Originally Posted by sailorchic34

Q = flow per GPM

Now you've excelled yourself.

Please explain, in simple physical terms, the meaning of "flow per GPM"

[StuM]

Originally Posted by sailorchic34

So to heat 10GPM by 100 degrees F. I would need 8330 btu's per minute. No time limit required. That's because you have the same time on both sides of the equation so that cancel out to "1".

For a domestic water heating system of 1000 gpm with a 100 degree F rise I would need 50,000 MBH per minute.
.
Guys this really is basic engineering 101.

OK, can you give us a Basic Engineering 101 reference which explains what a "MBH per minute" represents since MBH is 1000 BTU per hour.

(A reference, not just what you think it means)

[sailorchic34]

Originally Posted by StuM

OK, can you give us a Basic Engineering 101 reference which explains what a "MBH per minute" represents since MBH is 1000 BTU per hour.

(A reference, not just what you think it means)

Sorry a minor booboo. Lets call it 50,000 MBTU, not MBH. So no we don't need a additional time measurement.

[sailorchic34]

Originally Posted by StuM

If you can't see the reason for the corrections, then I really do despair for you.


And the pounds came from the gallons part of 10GPH .

And you still haven't given a simple Yes/No answer to:
"Can we now agree that GPH is not a volume? "

No it is a two dimensional unit with one dimension being volume and other unit being time.

I do not need to calculate it an pounds per minute. Simple pounds works quite well. Its flow in GPM * weight X delta T Not weight/minute.

[sailorchic34]

Originally Posted by StuM

Now you've excelled yourself.

Please explain, in simple physical terms, the meaning of "flow per GPM"

q = volume flow (gal/min) Note the word Volume.

from: Hazen-Williams Equation - calculating Friction Head Loss in Water Pipes

f = 0.2083 (100 / c)1.852 q1.852 / dh4.8655 (1)
where
f = friction head loss in feet of water per 100 feet of pipe (fth20/100 ft pipe)

c = Hazen-Williams roughness constant
q = volume flow (gal/min) (note that q is a volume flow in GPM)

dh = inside hydraulic diameter (inches)

[fryewe]

Originally Posted by sailorchic34

Dude, That is how engineers calculate it day in and day out.

BTW fryewe, what's your engineering background. Myself I've sat and passed the principles and practices (PE) exam and worked over 35 years as a consulting engineer.

Its basic engineering.

Dudette,

Your engineering acumen is, in my opinion, quite good, but your reasoning in this thread is baffling, because you seem to be unable to grasp the most basic concepts, even when several very clear (in my opinion) attempts have been made by a variety of persons who have boxed the compass for you on the subject.

I commend you for passing the PE exam. But, as you may or may not know, the PE exam and PE practices are distillations of science...shortcuts and thumb rules and estimations (that are "good enough") that are used in the field for speed and economy and to avoid having to derive equations and calculate results for problems that have already been solved many times, and for which little to no added value to a project would result from doing those derivations and calculations.

My engineering experience is in both EE and Nuc Eng, with extensive formal training and almost forty years of experience in operations and maintenance of basic and complex electronic, electrical and mechanical systems. I have passed the most rigorous practical engineer curriculum on the planet (I'll leave it to you to guess what that is) with high honors. I have overseen operations of the most complex engineering systems in the most rigorous conditions while distant from support, requiring a high degree of understanding of fundamentals when unique issues arose. I have taught both science and engineering in the classroom to middle and high school students and to adults in the field. I have managed multi-billion dollar engineering budgets. I have inspected activities for operations and maintenance, including testing the knowledge of engineering personnel associated with those ops and maintenance.

And I am sailor who has owned the same sailboat for 32 years, an ocean capable sloop with diesel auxiliary power. And every wrench that's touched it has been mine. Sail inspection and repair and one swage fitting repair are the only things that ever been done on her that I didn't do personally. And she's ready to cross an ocean now if needed (readier than I).

And I don't think in all that time I ever encountered an engineer, nay, not even a technician, who had a poorer understanding of unit (or dimensional) analysis...the most basic engineering technique of them all.

[sailorchic34]

Originally Posted by StuM

If you can't see the reason for the corrections, then I really do despair for you.


And the pounds came from the gallons part of 10GPH .

"

Yes pounds came from the gallon part of 10GPM. By Goerge you have it.

Oh and my formula was fine before your additions.

How many BTU's do I need to heat that 10GPM.

I do not need a duration to calculate a BTU per GPM. Quite simple
its BTU=GPM* 8.33 pounds per gallon * delta T. You don't use pounds per minute and I've never heard an engineer describe it as pounds per minute. Not even once.

So based on my previous post before you fooled it up, we would have 4,998 btu/minute. no duration required. Simple and I've designed many a building using that equation.

Stu can you tell me how many hydronic heating systems you've designed. I can't tell you a total number that I've done, but it's in the hundreds. About 25 were >1000 ton or >1000MBH range.

Please feel free to insult me as much as you like. But I'm pretty sure I know more about hydronics then you do.

[StuM]

"Please explain, in simple physical terms, the meaning of "flow per GPM""

Originally Posted by sailorchic34

q = volume flow (gal/min) Note the word Volume.

Don't get hung up on "gallon". It's irrelevant.
Concentrate on the extra "per"

Wrong: q = flow per gallon per minute
Correct: q = flow (gallons per minute)

[transmitterdan]

Originally Posted by sailorchic34

No sir. The formula could be written as BTU per minute=GPM*8.33*Delta T where 8.33 is the weight of one gallon of water and delta T is temperature rise. The formula is used by engineers to calculate heat load and GPM flow rates as found in hydronic and domestic water systems. I do not need to know how many minutes that GPM rate continues for to calculate a BTU per minute heat load. Weight implies volume and mass. I could not use weight, if GPM was not based on a volume moved per minute.

GPM is not just a number. It implies a volume, weight and mass if you know the type of fluid. Every engineer knows this.

GPM is not just a number. But it ain't volume either. It is gallons per minute. There is no such thing as a bucket that holds 5 gallons per minute.

The exact unit balanced equation you quote goes like this:

Q [BTU/minute] = Flow [gallons/minute] * (Tout-Tin) [F] * 1 [BTU/(lb F)] * 8.33 [lb/gallon]

units enclosed in []

The units of gallons, degrees F and pounds all cancel out to leave BTU/minute. There is nothing magic about it. It does not prove your argument that GPM is a measure of volume.

[transmitterdan]

Originally Posted by sailorchic34

I do not need a duration to calculate a BTU per GPM.

There is a mistake in this first sentence. You can talk about BTU and gallons in the same sentence but you can't talk about BTU and GPM because the units don't balance. You can talk about BTU/minute and gallons/minute because these units balance. A BTU is the thermal energy required to raise one pound of water one degree Fahrenheit. There is no time in that description, only volume (assuming 8.33 pounds per gallon).

[sailorchic34]

Originally Posted by fryewe

Dudette,

Your engineering acumen is, in my opinion, quite good, but your reasoning in this thread is baffling, because you seem to be unable to grasp the most basic concepts, even when several very clear (in my opinion) attempts have been made by a variety of persons who have boxed the compass for you on the subject.

I commend you for passing the PE exam. But, as you may or may not know, the PE exam and PE practices are distillations of science...shortcuts and thumb rules and estimations (that are "good enough") that are used in the field for speed and economy and to avoid having to derive equations and calculate results for problems that have already been solved many times, and for which little to no added value to a project would result from doing those derivations and calculations.

My engineering experience is in both EE and Nuc Eng, with extensive formal training and almost forty years of experience in operations and maintenance of basic and complex electronic, electrical and mechanical systems. I have passed the most rigorous practical engineer curriculum on the planet (I'll leave it to you to guess what that is) with high honors. I have overseen operations of the most complex engineering systems in the most rigorous conditions while distant from support, requiring a high degree of understanding of fundamentals when unique issues arose. I have taught both science and engineering in the classroom to middle and high school students and to adults in the field. I have managed multi-billion dollar engineering budgets. I have inspected activities for operations and maintenance, including testing the knowledge of engineering personnel associated with those ops and maintenance.

I congratulate and thank you for your service in the navy. So sub or carrier. I'm betting that in that 40 years as a EE you not once calculated a BTUH requirement from GPM. Not a problem Btw. But I've done it a time or two... I've worked on multi billion dollar projects too. Micron Lehi and the Venetian come to mind off the top of my head. Though the Venetian was only 1.2 billion, But I was senior engineer there.. Micron was 2 billion and was fun too. But not a contest.

[fryewe]

Originally Posted by StuM

Dunning-Kruger.

Good call, I must admit...