

14102015, 08:36

#151

Moderator
Join Date: Feb 2011
Location: SF Bay Area
Boat: Islander 34
Posts: 5,025

Re: Amps v Amp hours v Amps/Hr
Quote:
Originally Posted by valhalla360
How are those 04.45ish GPH jugs working out for you?

This disagrees with your prior posts where you said GPH is a volume and we challenged you to tell us the volume without adding more information (such as how long the flow rate lasts).
GPH is the volume of flow per hour. Gallon is the volume and per hour is the unit of time. I don't need an extra unit of time to define a flow per hour.
It is a Volumetric rate But before you were saying it was a volume...hmmm...
Definition of Volumetric: of or relating to the measurement of volume.
__________________



14102015, 08:43

#152

Registered User
Join Date: Apr 2013
Posts: 5,463

Re: Amps v Amp hours v Amps/Hr
Quote:
Originally Posted by sailorchic34
This disagrees with your prior posts where you said GPH is a volume and we challenged you to tell us the volume without adding more information (such as how long the flow rate lasts).
Definition of Volumetric: of or relating to the measurement of volume.

Just taking my Mom's advice when talking to someone who can't grasp something and refuses to learn.
PS: "Relating to" is not the same as "being"...opps sorry... I hear you have a lovely 100GPS water tank on your boat.
__________________



14102015, 08:46

#153

Moderator
Join Date: Feb 2011
Location: SF Bay Area
Boat: Islander 34
Posts: 5,025

Re: Amps v Amp hours v Amps/Hr
Quote:
Originally Posted by fryewe
and used in every science and engineering course you would have taken in college.

Ah, sorry I'm an Autodidact, Never went to collage. But I did sit and pass the PE exam, first try.
You said 10 CFPS is a volume per unit time but not a volume.
You have to know the volume of flow to get cubic feet per second. So why would it not include the volume.



14102015, 08:52

#154

Moderator
Join Date: Feb 2011
Location: SF Bay Area
Boat: Islander 34
Posts: 5,025

Re: Amps v Amp hours v Amps/Hr
Quote:
Originally Posted by valhalla360
Just taking my Mom's advice when talking to someone who can't grasp something and refuses to learn.
PS: "Relating to" is not the same as "being"...opps sorry... I hear you have a lovely 100GPS water tank on your boat.

I do this just for the insults. Thank you for being a good sport and providing them.
100GPS is 100 gallons flowing in one second. That gallon thingy is a volume measurement. So 100GPS is 100 gallons moving past a point in one second.



14102015, 10:37

#155

Moderator
Join Date: Feb 2011
Location: SF Bay Area
Boat: Islander 34
Posts: 5,025

Re: Amps v Amp hours v Amps/Hr
OK guys, lets try it this way. I have a big pot with 10 gallons of water in it. If I pour it out so that after exactly a minute, the pot is empty of water, how much water did I pour out.
I of course poured out 10 gallons at a rate of 10 gallons per minute (10GPM) So a volume of 10 gallons moved over a period of 60 seconds.
What is not clear about that.
Why wouldn't 10gpm in the example above, not have unit of volume per time period. What other unit would it be?



14102015, 10:51

#156

Registered User
Join Date: Apr 2012
Posts: 577

Re: Amps v Amp hours v Amps/Hr
Yep. I'm done....



14102015, 11:51

#157

Registered User
Join Date: Oct 2011
Boat: Valiant 42
Posts: 4,313

Re: Amps v Amp hours v Amps/Hr
Quote:
Originally Posted by sailorchic34
OK guys, lets try it this way. I have a big pot with 10 gallons of water in it. If I pour it out so that after exactly a minute, the pot is empty of water, how much water did I pour out.

There are usually several "obvious answer" questions like this on PE exams where they give you more information than required to answer the question. The extra information is meaningless as in this example.
The answer is 10 gallons regardless of the rate at which you poured or the time required. This is precisely the point others have been trying to explain but it doesn't seem to be taking hold.
The units for volume (gallons, m^3, ft^3, etc.) do not include any consideration of time. GPH is not a volume unit. There are various units of volume but no such thing a unit known as "volumetric". Just as there are units of volts and amperes there is no unit known as "electric".



14102015, 12:16

#158

Registered User
Join Date: Aug 2010
Location: Arctic Ocean
Boat: Under construction 35' ketch
Posts: 1,874

Re: Amps v Amp hours v Amps/Hr
Quote:
Originally Posted by sailorchic34
OK guys, lets try it this way. I have a big pot with 10 gallons of water in it. If I pour it out so that after exactly a minute, the pot is empty of water, how much water did I pour out.
I of course poured out 10 gallons at a rate of 10 gallons per minute (10GPM) So a volume of 10 gallons moved over a period of 60 seconds.
What is not clear about that.
Why wouldn't 10gpm in the example above, not have unit of volume per time period. What other unit would it be?

But you have the same 10 gallons without pouring it at all, and that is volume. GPM is a rate of flow volume per time, not volume alone.



14102015, 12:56

#159

Moderator
Join Date: Feb 2011
Location: SF Bay Area
Boat: Islander 34
Posts: 5,025

Re: Amps v Amp hours v Amps/Hr
Quote:
Originally Posted by TeddyDiver
But you have the same 10 gallons without pouring it at all, and that is volume. GPM is a rate of flow volume per time, not volume alone.

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 do I need to heat that 10GPM.
For the answer we convert 10 gpm to pounds. 1 gallon is 8.33 pounds at stp. So 10 GPM would be 83.3 pounds. We then multiply that by the delta of the temperature, 10040 for 60 degrees. 83.3 pounds*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 one hour 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.



14102015, 13:12

#160

Registered User
Join Date: Aug 2010
Location: Arctic Ocean
Boat: Under construction 35' ketch
Posts: 1,874

Re: Amps v Amp hours v Amps/Hr
Quote:
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 do I need to heat that 10GPM.
In this stage we have no volume yet
For the answer we convert 10 gpm to pounds. 1 gallon is 8.33 pounds at stp. So 10 GPM would be 83.3 pounds. We then multiply that by the delta of the temperature, 10040 for 60 degrees. 83.3 pounds*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 one hour 60 degrees F. This is a basic formula used in mechanical engineering around the world. Though some might use Cubic liters per minute.
Now we have volume becouse you have included time frame for the flow
Where did the pounds come from if 10 GPM is not also a unit of volume.

From the time limit you made...



14102015, 13:37

#161

Registered User
Join Date: Apr 2012
Posts: 577

Re: Amps v Amp hours v Amps/Hr
Quote:
Originally Posted by sailorchic34
...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 do I need to heat that 10GPM.
You keep mixing apples and oranges. A question such as "how many BTUs do I need to heat that 10GPM" can't be answered because the number of BTUs needed to heat flowing water depends on how long the water flows. If the question were "how many BTU per hour are needed to heat 10 gallons per minute, that question can be answered.
For the answer we convert 10 gpm to pounds. 1 gallon is 8.33 pounds at stp. So 10 GPM would be 83.3 pounds. No. 10 GPM is 83.3 pounds per minute.We then multiply that by the delta of the temperature, 10040 for 60 degrees. 83.3 pounds*60 (F. delta T) gives an input of 4,998 btu/minute. No, it doesn't. Your result would be 4998 poundsdegree F. By implication (not by calculation) that's really 4998 poundsdegree F per minute because you incorrectly dropped the "per minute" unit when you made the first incorrect statement above (10 GPM would be 83.3 pounds) Times 60 gives 299,880 btu's/hr. No. Multiplying by 60 minutes gives poundsdegree Fminutes integrates your flow rate over an hour. If you then multiply times 1 BTU per pounddegree F, you get 299,880 BTU So 299MBH output will heat 10 GPM or 600 gallons in one hour 60 degrees F. If 299 MBTU/hr are absorbed that will heat 600 gallons of liquid water (no phase change) by 60 degrees in one hour. But you can't know if it heats 10 GPM by 60 degrees in one hour, because that flow rate could be entering a tank that already contains a mass of water, for example.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. Your question makes no sense...apples and oranges again. It asks "where did the mass come from if the flow rate is not a unit of volume?" The pounds came from you mentally (apparently) integrating the flow rate over a one minute period, then mentally (apparently) converting volume to mass. You can't do that if you want to be rigorous in your calculations, and doing so can result in remarkable errors when problems get more complex than the simple ones we are discussing here.

Guess I wasn't done...



14102015, 14:17

#162

Moderator
Join Date: Feb 2011
Location: SF Bay Area
Boat: Islander 34
Posts: 5,025

Re: Amps v Amp hours v Amps/Hr
Quote:
Originally Posted by fryewe
Guess I wasn't done...

Dude, That is how engineers calculate it day in and day out. It's how the PE's taught me ages ago. It's also on the PE exam. So it's not just me. It's a whole lotta Professional engineers out there using it the exact same way I am.
The equations BTUH= Q*500*delta T. This really is an mechanical engineering formula.
Q = flow per GPM
500 = 8.33 pounds x60 minutes per gallon flowing. that is per GPM
Delta T is the temperature delta that is the difference between starting and ending temperature.
That equation is used in sizing heat exchangers, chillers, boilers etc. You can also write it as GPM=BTUH/500/deltaT, to find a hydronic flow rate. It's not something I made up. It's used every day by engineers all across the country.
your question makes no sense...apples and oranges again. It asks "where did the mass come from if the flow rate is not a unit of volume?" The pounds came from you mentally (apparently) integrating the flow rate over a one minute period, then mentally (apparently) converting volume to mass. You can't do that if you want to be rigorous in your calculations, and doing so can result in remarkable errors when problems get more complex than the simple ones we are discussing here.
Again that is EXACTLY the way a mechanical engineer would determine Heat input required to heat a given flow rate a given delta temperature in the USA. I'm an engineer, I know that. It's on the PE exam, exactly like that.
So fryewe, how would you determine the BTUH heat input required to heat a given water flow rate 60 degrees F.
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. I have used the equation above countless times to determine heat required per minute or per hour of fluid flow. I've also used it to determine a flow rate in GPM, say for a chilled water system. Its basic engineering.



14102015, 14:51

#163

Moderator
Join Date: Feb 2011
Location: SF Bay Area
Boat: Islander 34
Posts: 5,025

Re: Amps v Amp hours v Amps/Hr
Quote:
Originally Posted by TeddyDiver
From the time limit you made...

I can write the formula as BTUM=GPM*8.33*Delta T. Where 8.33 is weight of water. Were we using a different fluid we would use a different weight per GPM.
So to heat 10GPM by 100 degrees F. I would need 8330 btu's per minute. No time limit required.
For a domestic water heating system of 1000 gpm with a 100 degree F rise I would need 50,000 MBtu per minute. I've actually designed that instantaneous hot water system at the Venetian hotel in Vegas. Again no time limit. That water was heated by a few 700BHP cleaver brooks dry back scotch marine steam boilers.
There were seven boilers in all. But there were other loads too. Such as restaurant water heating and HVAC hydronic heating. The domestic hot water load was larger then the hydronic portion of the load. I designed the domestic hot water and steam systems and am fairly confident that they worked just fine.
I don't need to use weight per minute as it does not change the BTU input requirement.
Guys this really is basic engineering 101.



14102015, 14:56

#164

Registered User
Join Date: Oct 2011
Boat: Valiant 42
Posts: 4,313

Re: Amps v Amp hours v Amps/Hr
Quote:
Originally Posted by sailorchic34
Where did the pounds come from if 10 GPM is not also a unit of volume.

That's easy. You multiplied the GPM by minutes to get gallons. Gallons is the volume which can be converted to pounds. GPM is not a volume, gallons is a volume.



14102015, 15:10

#165

Moderator
Join Date: Feb 2011
Location: SF Bay Area
Boat: Islander 34
Posts: 5,025

Re: Amps v Amp hours v Amps/Hr
Quote:
Originally Posted by transmitterdan
That's easy. You multiplied the GPM by minutes to get gallons. Gallons is the volume which can be converted to pounds. GPM is not a volume, gallons is a volume.

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.
__________________





Thread Tools 

Display Modes 
Rate This Thread 
Linear Mode


Posting Rules

You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts
HTML code is Off




