Range = Cooling water Inlet Temperature-Cooling Water Outlet Temperature
Calculation :
Hot water Inlet Temperature = 43 °C
Cold water Temperature = 33 °C
Range= 43-33 = 10 °C
Approach=cooling tower cold water temperature-ambient wet bulb temperature
Calculation :
Cooling Tower Cold water Temp. = 33°C
Ambient Wet bulb Temperature = 27 °C
Approach = 33-27 = 6 °C
Cooling tower effectiveness=Range / (Range + Approach)
Calculation :
Range Calculated = 10 °C
Approach Calculated = 6 °C
Cooling Tower Effectiveness = 10/(10+6)=62.5%
Cooling tower Heat Load (Q ) = m* Cp *dT
Calculation:
Water Circulation rate = 10,000 m3/Hr= 10,000*1000 Kg/Hr
Sp. Heat of water , Cp= 1 Kcal/Kg °C
dT=43-33= 10 °C
Cooling Tower Heat Load= 10,000*1000*1*10 Kcal/Hr.
= 10,000,0000 Kcal/Hr.
= 10,000,0000/3024=33068 TR
Evaporation Loss (m3 /hr) = 0.00085 x 1.8 x circulation rate (m3 /hr) x (T1-T2)
T1-T2 = Temp. difference between inlet and outlet water
Calculation :
Circulation rate = 10,000 m3/Hr.
T1-T2=10
Evaporation Loss= 0.00085*1.8*10,000*10=153 m3/Hr.
Cycles of concentration (C.O.C) = dissolved solids in circulating water / dissolved solids in make up water.
Calculations :
Dissolved solids in Circulating water= 1500
Dissolved Solids in make up water = 250
COC= 1500/250=6
Blow Down = Evaporation Loss / (C.O.C. – 1)
Calculation :
Evaporation Loss calculated=153m3/Hr.
COC Calculated =6
Blowdown Loss= 153/(6-1)=30.6 m3/Hr.
Drift Loss= 0.005% of Circulating water
Calculation :
Circulating water=10,000 m3/Hr.
Drift Loss= 0.005/100*10,000= 0.5 m3/Hr.
Makeup water = Evaporation loss + Blowdown loss+ Drift Loss
Calculation :
Evaporation Loss = 153 m3/Hr.
Blowdown Loss = 30.6 m3/Hr.
Drift Loss= 1 m3/Hr. Makeup water = 153 + 30.6 + 1 = 184.6 m3/Hr.
Liquid/Gas (L/G) ratio, of a cooling tower is the ratio between the water and the air mass flow rates.
Thermodynamics also dictate that the heat removed from the water must be equal to the heat absorbed by the surrounding air:
L(T1 –T2) = G(h2 – h1)
L/G = (h2 – h1) / (T1– T2)
where: L/G = liquid to gas mass flow ratio (kg/kg)
T1 = hot water temperature (°C)
T2 = cold water temperature (°C)
h2 = enthalpy of air-water vapor mixture at exhaust wet-bulb temperature (same units as above)
h1 = enthalpy of air-water vapor mixture at inlet wet-bulb temperature (same units as above)
Checks for Low Cooling Tower Efficiency
-Scaling reduce the Heat transfer efficiency of Fill media.
-Algae, bacteria and other microorganisms within the cooling tower, clogging pipes and fouling the Fill media restricts the water flow and decreases the cooling tower Efficiency.
-Uneven water distribution over the Fill media can lead to inefficient cooling.
-Insufficient water flow decreases the contact time between water and air, reducing the heat transfer efficiency.
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