Effect of Pressure on Heating (not boiling) water


by TandemDrip
Tags: heating water, pressure, thermodynamics
TandemDrip
TandemDrip is offline
#1
May5-11, 12:54 AM
P: 1
I understand that if I apply pressure to water in a closed system, the boiling point increases. So at atmospheric pressure, it boils at 100 degrees C and at 100 PSI, this number increases to 164 degrees C. In my experiment, I'm using the sun to heat the water as it runs through a solar water heater on the roof. What I don't understand is why if I have the system at atmospheric pressure, it gets hotter than is I pressurize the circuit at 100 PSI. For example, at atmospheric pressure, I can get 65 degrees from my collector, but if I prime the circuit to mains pressure of 100 PSI, I struggle to get 47 degrees C. Why ? Can someone please explain this and provide a reference for me to research this more.
Phys.Org News Partner Physics news on Phys.org
Physicists design quantum switches which can be activated by single photons
'Dressed' laser aimed at clouds may be key to inducing rain, lightning
Higher-order nonlinear optical processes observed using the SACLA X-ray free-electron laser
SpectraCat
SpectraCat is offline
#2
May5-11, 10:37 AM
Sci Advisor
P: 1,395
Quote Quote by TandemDrip View Post
I understand that if I apply pressure to water in a closed system, the boiling point increases. So at atmospheric pressure, it boils at 100 degrees C and at 100 PSI, this number increases to 164 degrees C. In my experiment, I'm using the sun to heat the water as it runs through a solar water heater on the roof. What I don't understand is why if I have the system at atmospheric pressure, it gets hotter than is I pressurize the circuit at 100 PSI. For example, at atmospheric pressure, I can get 65 degrees from my collector, but if I prime the circuit to mains pressure of 100 PSI, I struggle to get 47 degrees C. Why ? Can someone please explain this and provide a reference for me to research this more.
Are you sure it's not just a question of flow rates? Unless you are regulating the flow somehow, the rate will be much faster at 100 psi, and so there will be less time for the water to absorb heat as it runs through the solar heater. There could also be a small increase in the heat capacity due to changes in the density at the higher pressure, but since water isn't very compressible, I would think that it is basically negligible.


Register to reply

Related Discussions
Heating water at constant volume and pressure Introductory Physics Homework 2
Boiling water with ice Biology, Chemistry & Other Homework 2
Effect of pressure on electrolysis of water General Physics 6
Water heater warms 137 kg water from 20C to 45 C in 16 min. - Heating element resist? Introductory Physics Homework 2
A pot of boiling water? General Physics 3