Calculating Flow Rate of 180°F and 3 GPM

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Discussion Overview

The discussion revolves around calculating the energy required to heat water to 180°F (80°C) while maintaining a flow rate of 3 gallons per minute (11 liters per minute). The context includes both theoretical calculations and practical applications, particularly in relation to solar thermal energy systems.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Experimental/applied

Main Points Raised

  • Adam seeks to understand how to calculate the energy needed to heat water to 180°F while maintaining a flow rate of 3 GPM.
  • Some participants inquire whether the goal is to heat water to 180°F before pumping or to heat water while it is being pumped at the specified flow rate.
  • There is a request for the input temperature of the water being heated, which is necessary for calculations.
  • One participant suggests that Adam is likely working on a solar water heater project based on his inquiries.
  • Adam clarifies that he is pumping water at 11 liters per minute and needs to calculate the energy input required to heat it from 20°C to 80°C.
  • A mathematical formula is presented, indicating the relationship between volumetric flow rate, heat flow rate, specific heat capacity, density, and temperature difference, leading to a calculated heat flow rate of 42 kW for the specified conditions.

Areas of Agreement / Disagreement

Participants express varying interpretations of Adam's initial question, leading to some confusion regarding the specifics of the heating process. While there is a general understanding of the calculations involved, no consensus is reached on the exact parameters or methods to be used.

Contextual Notes

Key assumptions include the specific heat capacity and density of water, as well as the initial temperature of the water. The discussion does not resolve these assumptions or clarify the exact conditions under which the calculations apply.

adamjbradley
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I'll elaborate a little. I trying to work out how to calculate and how to make at least 180 F (80 C) and 3 gallons per minute (11 liters/min)?

Thanks in advance!
Adam
 
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Elaborate a bit more please. Would you like to know how to make a flow rate of 3gal/min at 180F?
 


viscousflow said:
Elaborate a bit more please. Would you like to know how to make a flow rate of 3gal/min at 180F?

I'd like to know how to calculate how many J of energy I need to provide in order to satisfy that requirement and some suggestions on how (preferably solar thermal, ideally with storage!)

This is a little residential project.


Adam
 


Do you mean you want to raise the temperature to 180 and then pump at 3 gallons a minute (provide energy for both)?

Or

Do you mean you are pumping at 3 gallons a minute and you need the energy input required to heat that flow rate to 180?
 


You'll also need the temperature of the input water being heated.
 


...and that's assuming he means water.
 


brewnog said:
...and that's assuming he means water.

True. Based on his posts it sounds like he's making (or trying to make) a solar water heater.
 


93mb.png
 


Erm, what? Is that the most constructive thing you can post? Don't bother.
 
  • #10


der's a srtain seemilarity
 
  • #11


kandelabr said:
der's a srtain seemilarity

English lad, English.

No wonder you went straight in with a picture.
 
  • #12


jarednjames said:
Do you mean you want to raise the temperature to 180 and then pump at 3 gallons a minute (provide energy for both)?

Or

Do you mean you are pumping at 3 gallons a minute and you need the energy input required to heat that flow rate to 180?

Sorry I dropped off the radar, been caught up in the floods in Brisbane Australia.

The latter, I'm pumping water at 11 litres/minute and need to know the energy input required to heat that flow rate to 80C (from 20C).

Thanks for your patience.


Adam
 
  • #13


I think the following applies for heating water 11L/minute (0.183 kg/s) at 80C (dt is 55C)

q = h / ( cp ρ dt )
where
q = volumetric flow rate
h = heat flow rate
cp = specific heat capacity
ρ = density
dt = temperature difference

h = q ( cp ρ dt ) and
h = 0.183 ( 4.2 ) ( 55)
h = 42 kW
 

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