Water friction in pipes, hot vs cold?

In summary, the speaker usually uses an average of 2 kPa friction loss for normal tap water in pipes. However, they are questioning if this number significantly changes for water at a temperature of 80 degrees C instead of 5 degrees C. Another person responds that although there is a 3% change in density, there is a factor of 4 change in viscosity, resulting in a similar friction factor when looking at Reynolds numbers. The speaker suggests doing a few calculations to adjust for the change in density and viscosity, but it seems unlikely that there will be a noticeable difference.
  • #1
TSN79
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I usually use an average number of 2 kPa friction loss for normal tap water in pipes. Does anyone know if this number changes significantly up or down for water which is around 80 degrees C instead of 5?
 
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  • #2
Well, you're looking at only a 3% change in density but a factor of 4 change in the viscosity. Looking at Reynolds numbers (with a constant velocity and ID), this results in a very similar friction factor. I get about .01 vs. .012 for a smooth pipe. I didn't really go any further with the numbers. It looks though like you're not going to see anything noticible. You might do a couple of quick calcs adjusting your density and viscosity to match the two temps.
 
  • #3


The friction loss in pipes for hot water is generally greater than that of cold water due to the differences in viscosity and density. Hot water has a lower viscosity and a higher density compared to cold water, which leads to increased friction as it flows through the pipes. This means that the average number of 2 kPa for friction loss may not be accurate for hot water at 80 degrees C.

According to the Darcy-Weisbach equation, which is used to calculate friction loss in pipes, the friction factor (a key component in the equation) is affected by the temperature of the water. As the temperature increases, the friction factor decreases, resulting in a higher friction loss in the pipes.

In fact, studies have shown that for every 10 degrees C increase in water temperature, there is a 5-10% increase in friction loss. This means that the friction loss for water at 80 degrees C could be significantly higher than the average of 2 kPa.

It is important to consider the temperature of the water when calculating friction loss in pipes, as it can have a significant impact on the overall flow and pressure in the system. Therefore, it is recommended to use more accurate values for the friction factor when dealing with hot water in pipes to ensure accurate calculations and efficient water flow.
 

What causes water friction in pipes?

Water friction in pipes is caused by the resistance of water molecules rubbing against the inner surface of the pipe as it flows through. This resistance is known as drag and is affected by factors such as pipe material, pipe diameter, and water velocity.

Does water friction increase with hot or cold water?

Water friction is generally greater with hot water compared to cold water. This is because hot water has lower viscosity, or resistance to flow, which allows it to move faster and create more friction within the pipes.

How does water temperature affect the flow rate in pipes?

The flow rate of water in pipes increases with higher temperature. This is due to the decrease in water viscosity as temperature increases, allowing the water to flow more easily and with less resistance.

Can water friction be reduced in pipes?

Yes, water friction can be reduced in pipes through various methods such as using smoother pipe materials, increasing pipe diameter, or decreasing the velocity of the water flow. These methods can help to minimize the resistance and improve the efficiency of water flow in pipes.

What are the practical implications of understanding water friction in pipes?

Understanding water friction in pipes is important for engineers and plumbers to design and maintain efficient plumbing systems. It can also help to conserve water and energy by minimizing the amount of friction and pressure needed to move water through pipes.

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