In this post, I want to share to you how to size cooling pond. Cooling pond is used to remove heat from water by means of air. Example of application of cooling pond is to remove heat from brine water in geothermal power plant facilities.

To design cooling pond, you need process data and environment data. Process data are flow rate of liquid to be cooled, initial temperature, final temperature, and density of liquid. Environent data are relative humidity, wind velocity, average air temperature, and solar heat gain. Here is example of cooling pond sizing.

We have these process data:

- Fluid type = brine water
- Brine mass flow = 1000 ton per hour
- Initial temperature = 45
^{o}C (113^{o}F) - Final temperature (after cooling) = 40
^{o}C (104^{o}F) - Brine density = 980 kg/m
^{3}

Environment data:

- Relative humidity = 80%
- Wind velocity = 7 mil per hour
- Average air temperature = 26
^{o}C (78.8^{o}F) - Solar heat gain = 65 Btu/(ft
^{2}.h). Solar heat gain is a function of lattitude and month.

Other data:

- Cooling pond is designed with additional 20% safety factor

Let’s start to estimate cooling pond size.

**Step 1: Calculate volumetric flow rate of brine water.
**

Volumetric flow rate = brine mass flow x (1/density) x safety factor

= 1000 ton/h x 1000 kg/ton x (1/980 kg/m^{3}) x (1+20%)

= 1224 m^{3}/h (5388 gpm)

**Step 2: Determine Equilibrium Temperature (E _{scale})
**

Equilibrium temperature or E_{scale} is determined by using nomograph. It is a function of relative humidity and air temperature. At relative humidity of 80% and air temperature of 78.8^{o}F, we get equilibrium temperature of 74^{o}F.

Nomograph below is used to get data in Step 2 until Step 5.

**Step 3: Determine Reference Scale and Solar Heat Gain (Q _{scale})
**

Q_{scale} is determined from E_{scale} and wind velocity by using nomograph. With Escale 74^{o}F and wind velocity of 7 mph, we get reference scale and solar heat gain (Q_{scale}) of 300 Btu/(ft^{2}.h).

**Step 4: Add Q _{scale} and Solar Heat Gain
**

Q_{scale} = 300 Btu/(ft^{2}.h)

Solar heat gain = 65 Btu/(ft^{2}.h)

Q_{new} = Qscale + solar heat gain = 365 Btu/(ft^{2}.h)

**Step 5: Determine new equlibrium temperature (E _{value})
**

E_{value} is determined by using nomograph. It is a function of Q_{new} and wind velocity. By using Q_{new} of 365 Btu/(ft^{2}.h) and wind velocity of 7 mph, we get E_{value} of 85^{o}F.

**Step 6: Determine Q factor
**

Q factor is determined by using the following nomograph. It is a function of equlibrium temperature (value in Step 5).

When E_{value} is 85^{o}F, we get Q factor of 0.9.

**Step 7: Determine D _{1} and D_{2
}**

D_{1} = initial temperature of liquid – E_{value
}

= 113 – 85 = 28^{o}F

D_{2 }= final temperature of liquid – E_{value
}

= 104 – 85 = 19^{o}F

**Step 8: Determine P factor
**

P factor is determined by nomograph. It is a function of D_{1} and D_{2}. When D_{1} is 28^{o}F and D_{2} is 19^{o}F, we get P factor of 20.

**Step 9: Determine A
**

A = P factor x Q factor (Step 8 x Step 6)

= 20 x 0.9 = 18 ft^{2}/gal/min

**Step 10: Determine area of cooling pond
**

Area of cooling pond = A x volumetric flow rate (Step 9 x Step 1)

= 18 x 5388 = 96980 ft^{2} (9010 m^{2})

**Step 11: Determine height of pond and volume of pond
**

If height of pond is 2.5 meter (8.2 ft), we get volume of pond is 20272 m^{3}.

**Last Step (Step 12): Check holding time of pond
**

Holding time of pond is = volume of pond/volumetric flow rate of brine

= 20272/1224 = 16.6 hours

I hope this step-by-step cooling pond sizing is easy to undestand and helpful.

Reference:

Perry’s Chemical Engineers’ Handbook.