Calculate Water Temperature in Pond Receiving Hot Water: Formula Included

In summary: The temperature depends largely on the evaporation - assuming it is well insulated, ie in the ground. The evaporation depends on humidity and any wind, you will need to know the humidity.In summary, the water will exit the pond at a temperature that is lower than the water entering due to evaporation.
  • #1
mrhook
2
0
I have an open water pond which will be receiving hot water (75oC) at a continuous steady rate. I want to know the temperature of the water leaving the pond at the other end. Is there a formula I can use to calculate this from the following information?

Volume of pond (1650m3) (25mx25mx2m at base, with sloping sides)
Volume of water entering/leaving (165 l/min)
Temp of water entering 75oC
Ambient temp (assume 50oC as maximum - its in a hot country!)

Thanks for any help
 
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  • #2
You need to work out the heat loss from the pond.
If it was perfectly insulated the water would leave with the same temperature it entered once it had heated all the water in the pond to that temperature.
In real life the heat loss will mostly be by evaporation, especially in a hot country - it's not going to be easy to work out, it will depend on relative humidity, any wind and the degree of turbulence and mixing of the incoming water.
 
  • #3
mrhook said:
I have an open water pond which will be receiving hot water (75oC) at a continuous steady rate. I want to know the temperature of the water leaving the pond at the other end. Is there a formula I can use to calculate this from the following information?

Volume of pond (1650m3) (25mx25mx2m at base, with sloping sides)
Volume of water entering/leaving (165 l/min)
Temp of water entering 75oC
Ambient temp (assume 50oC as maximum - its in a hot country!)

Thanks for any help

Put a thermometer "at the other end".

Out of curiosity, why are you pumping the water in the first place? It seems rather queer that you have just sort of happened upon a small pond whose volume is an exact multiple of the pumping rate (1650 versus 165)? Hmm...
 
  • #4
I would have thought you could assume all heat loss is evaporation, assume a particular humidity above the pond (e.g. zero under dry weather and unrestricted ventilation), look up the vapour pressure and integrate the energy given to vaporisation over the surface area..
 
  • #5
Well, I may have mislead you when I said I have a pond, as technically it hasn't yet been built! So I can't just put a thermometer at the other end!

What I need to prove is that the water won't be too hot when it reaches the other end (as I want to use a certain type of pipe that won't withstand the upper temperature range). So I was wondering if there was some sort of rule of thumb I could use to estimate the cooling. Unfortunately I don't have data on humidity etc, and it would vary throughout the year. Turbulence would be minimised as the water is entering via a delivery chamber.

Any further thoughts?
 
  • #6
The temperature depends largely on the evaporation - assuming it is well insulated, ie in the ground. The evaporation depends on humidity and any wind, you will need to know the humidity.
Look at swimming pool heating calculators, losts of makers of swimming pools have programs or web sites to estimate the amount of heating a pool needs - you are just doing the same calculation!

Since you are not cooling the water very much and you are going to lose a lot of the pool water by evaporation it might be easier to just run the water through loops of copper pipe and have water dripping over the outside of the pipes and evaporating - google for cooling towers.
 
Last edited:

1. How does heat loss occur in a pond?

Heat loss in a pond can occur through several mechanisms, including conduction, convection, evaporation, and radiation. Conduction is when heat travels through a solid material, such as the bottom of the pond. Convection is when heat is transferred through the movement of water. Evaporation is when heat is lost as water turns into vapor. And radiation is when heat is emitted as infrared radiation from the surface of the pond.

2. What factors can affect heat loss in a pond?

Some of the factors that can affect heat loss in a pond include the temperature difference between the water and the air, wind speed, humidity, and the amount of sunlight hitting the pond. These factors can impact the rate of heat transfer through conduction, convection, evaporation, and radiation.

3. How does the shape and depth of a pond impact heat loss?

The shape and depth of a pond can have a significant impact on heat loss. A shallow, wide pond will lose heat more quickly than a deep, narrow pond due to a larger surface area being exposed to the environment. Additionally, a pond with a lot of surface area relative to its volume will lose heat more rapidly than a pond with a smaller surface area.

4. Can vegetation in and around a pond affect heat loss?

Yes, vegetation in and around a pond can have an impact on heat loss. Plants can act as insulators, reducing the rate of heat loss through the water. They can also block wind and provide shade, which can reduce the rate of heat loss through convection and radiation. However, dense vegetation can also limit the amount of sunlight reaching the pond, which can decrease the rate of heat gain.

5. How can we reduce heat loss in a pond?

There are several ways to reduce heat loss in a pond, including adding insulation to the sides and bottom of the pond, using windbreaks and shading to reduce the impact of wind and sunlight, and minimizing the surface area of the pond by creating a more narrow and deep shape. Additionally, using a pond cover or adding a layer of floating material, such as foam, can also help to reduce heat loss. Regular maintenance, such as removing excess vegetation and debris, can also help to improve heat retention in a pond.

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