Cooling in a Cooling Tower: Oper. Conds Tab

CoolingInTowerOperConds.jpg
Variable Definitions, Ranges and Default Values

The following table shows a brief description of the variables appearing in this tab. The table also displays their default values and their generally acceptable range:

Variable

Default Value

Range

 

 

 

○ Cold Water (Output) Temperature (°C)

25.0

Positive

○ Water Component Name
Choose the pure component that represents water; in this manner, the user indicates to the model what component to remove from the incoming mixture due to evaporation and add it to the air stream. Click on the list box to bring up a list of available components in order to select one.

<Water>

Any Pure Compo­nent

● Hot Water Temperature (°C)
The temperature of inlet (hot) water.

25.0

Positive

○ Cold Water Temperature (°C)
The temperature of water after evaporative cooling. If a cold water pump is included in the simulation, the outlet water stream temperature may differ slightly from this value. If a cold water pump is not included in the simulation, the outlet water stream temperature will be identical to this value.

25.0

Positive

○ Drift (% of Hot Water)
The percentage of water droplets from the inlet (hot) water stream that are entrained in the outlet air stream; in this simulation model, these droplets are sent to a separate drift stream.

0.0

[0,100)

○ Blowdown (% of Cold Water)
The percentage of cold water that is sent to the blowdown stream.

0.0

[0,100)

● Inlet Air Stream Name
The name of the stream that is connected to the input port for the inlet air.

<None>

Dedi­cated Input Port

○ Water to Air Ratio (wt/wt)
The ratio of inlet water mass flow rate to inlet air mass flow rate.

0.75

Positive

● Max Water to Air Ratio (wt/wt)
The maximum possible water-to-air ratio.

0.0

Positive

● Inlet Air Dry-Bulb Temperature (°C)
The dry-bulb temperature of the inlet air stream.

25.0

Positive

◙ Inlet Air Wet-Bulb Temperature (°C)
The wet-bulb temperature of the inlet air stream.

15.0

Positive

◙ Inlet Air Relative Humidity (%)
The relative humidity of the inlet air stream.

50.0

Positive

● Inlet Air Humidity (wt water/wt dry air)
The humidity of the inlet air stream.

0.0

Positive

● Inlet Air Water Vapor (%)
The percentage of water in the inlet air stream.

0.0

[0,100)

● Outlet Air Humidity (wt water/wt air)
The humidity of the outlet air stream.

0.0

Positive

● Makeup Stream Name
The name of the stream that is connected to the input port for the makeup water.

<None>

Dedi­cated Input Port

● Cooling Range (°C)
The temperature difference between hot and cold water.

0.0

Positive

● Approach Temperature (°C)
The temperature difference between cold water temperature and inlet air wet-bulb temperature.

15.0

Positive

● Cooling Load (kcal/h)
The enthalpy difference between the hot and cold water streams.

0.0

Positive

● Evaporating Water (kg/h)
The mass flow rate of evaporating water moving from the inlet water stream to the outlet air stream.

0.0

Positive

○ Water Loading (m3/m2-h)
The volumetric flux of inlet (hot) water, which is calculated by dividing the inlet water volumetric flow rate by the total cooling tower floor area.

14.4

3-22.5

○ Power Type
Indicates the power type that is used by the operation if an induced draft fan or a cold water pump is included. Click on the list box to bring up a list of available power types in order to select one.

<Std Power>

Any Power Type

○ Include Induced Draft Fan?
Check this box to include an induced draft fan.

Yes

Yes/No

○ Induced Draft Fan Pressure Change (bar)
The pressure change in the induced draft fan.

0.005

Positive

○ Induced Draft Fan Efficiency (%)
The efficiency of the induced draft fan.

80.0

(0,100)

● Induced Draft Fan Power (kW)
The total power consumption of the induced draft fan for the entire operation (per cycle).

0.0

Positive

○ Include Cold Water Pump?
Check this box to include a cold water pump.

Yes

Yes/No

○ Cold Water Pump Pressure Change (bar)
The pressure change in the cold water pump.

3.000

Positive

○ Cold Water Pump Efficiency (%)
The efficiency of the cold water pump.

70.0

(0,100)

● Cold Water Pump Power (kW)
The total power consumption of the cold water pump for the entire operation (per cycle).

0.0

Positive

Symbol Key: ○ User-specified value (always input); ● Calculated value (always output); ◙ Sometimes input, sometimes output

Specification Choices / Comments

The following list describes the available specification choices in this tab; for more details on how these are implemented, see Cooling in a Cooling Tower: Modeling Calculations.

•Drift ...

You don’t need to add a drift stream if the drift % is zero.

•Blowdown...

You don’t need to add a blowdown stream if the drift % is zero.

•Inlet Air Stream Humidity Specification Options...

If you select the “Available in Stream” option, the mass fraction of water in the inlet air stream is used to calculate the inlet air stream’s humidity, wet-bulb temperature, and relative humidity.

If you select the “Calculated Based On Wet-Bulb-Temperature” option, you must specify the inlet air stream’s wet-bulb temperature. The program will then calculate the inlet air stream’s humidity and relative humidity based on this value. In this case, the moisture content of the inlet air stream can be left as zero. However, if the moisture content of the inlet air stream is not zero and its corresponding humidity differs significantly from the model’s calculated inlet air humidity, a warning message will be displayed.

If you select the “Calculated Based On Relative Humidity” option, you must specify the inlet air stream’s relative humidity. The program will then calculate the inlet air stream’s humidity and wet-bulb temperature based on this value. In this case, the moisture content of the inlet air stream can be left as zero. However, if the moisture content of the inlet air stream is not zero and its corresponding humidity differs significantly from the model’s calculated inlet air humidity, a warning message will be displayed.

•Makeup Stream...

Add a makeup stream containing a water component to let the program calculate the mass flow rate of makeup water (added water that accounts for evaporated, drift, and blowdown water so that the inlet and outlet water mass flowrates are the same). If you don’t add a makeup stream, zero makeup water will be assumed.

 

•Induced Draft Fan...

You may check the “Include?” option to let the program calculate the power consumption of the cooling tower’s induced draft fan. Alternatively, you may choose to uncheck this option and add an explicit fan procedure to the flowsheet to simulate the cooling tower’s fan.

•Cold Water Pump...

You may check the “Include?” option to let the program calculate the power consumption of the cooling tower’s cold water pump. Alternatively, you may choose to uncheck this option and add an explicit pump procedure to the flowsheet to simulate the cooling tower’s water pump.