Does Watt's Law apply to flowing water in a pipe?

  • Context: Undergrad 
  • Thread starter Thread starter Jack of some trades
  • Start date Start date
  • Tags Tags
    Apply Law Pipe Water
Jack of some trades
Messages
7
Reaction score
3
Is the heat generated by flowing water in a pipe proportional to the product of the rate of flow and the pressure drop across the section of pipe in question, analogous to an electrical circuit? If so, what units would you plug into get an answer in watts?
 
  • Like
Likes   Reactions: Delta2
If the flow is at steady state and the pipe is insulated, then then change in specific enthalpy of the water is zero. So, $$C_p\Delta T+v(1-\alpha \bar{T})\Delta P=0$$where ##\alpha## is the volumetric coefficient of thermal expansion, ##C_p## is the specific heat capacity, v is the specific volume of the water and ##\bar{T}## in the second term is the average temperature in the pipe (that doesn't change much). So, the change in temperature from inlet to outlet is $$\Delta T=\frac{v(1-\alpha \bar{T})(-\Delta P)}{C_p}$$
If you imagine that the "heat generated" is ##\dot{m}C_p\Delta T## where ##\dot{m}## is the mass flow rate, then$$\dot{m}C_p\Delta T=\dot{m}v(1-\alpha \bar{T})(-\Delta P)=(1-\alpha \bar{T})\dot{V}(-\Delta P)$$,where ##\dot{V}## is the volumetric flow rate.
 
  • Like
  • Informative
Likes   Reactions: vanhees71, Delta2 and Dale
Jack of some trades said:
Summary:: Is the heat generated by flowing water in a pipe proportional to the product of the rate of flow and the pressure drop?

Is the heat generated by flowing water in a pipe proportional to the product of the rate of flow and the pressure drop across the section of pipe in question, analogous to an electrical circuit? If so, what units would you plug into get an answer in watts?
This seems to be a correct statement (we do not want to confuse Temperature with Heat). With the electrical analogue I think the flow rate would be Amperes and the pressure drop Volts.
 

Similar threads

  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 11 ·
Replies
11
Views
5K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 2 ·
Replies
2
Views
8K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 57 ·
2
Replies
57
Views
15K
  • · Replies 20 ·
Replies
20
Views
4K
  • · Replies 9 ·
Replies
9
Views
3K