Cooling tower

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Cooling tower

  1. 1. COOLING TOWERBy. Engr. Yuri G. Melliza
  2. 2. B Air Out hB,WB, ma Hot water 1 m1 t1 h1 Fan A Air int3, h3, m3 hA,WA, maMake-up water 3Cold water 2t 2, h 2, m 2 Catch Basin
  3. 3. Cooling TowerA Cooling tower is a wind braced enclosure orshell usually made of wood, concrete or metalwith fillings on the inside to aid water exposure.The water to be cooled is pumped into adistributing header at the top of the tower fromwhich it drops in sprays to the filling. The waterspreads out in the filling thus exposing newwater surfaces to the air circulating through thetower. The cooled water drops to the bottom ofthe tower called the catch basin. The aircirculating through the tower becomes partiallysaturated with moisture by evaporating some
  4. 4. Fundamental Equations:1. Actual Cooling Range (ACR) ACR = t1 - t22. Cooling Tower Approach (A) A = t2 - tWA3. Theoretical Cooling Range (TCR) TCR = t1 – tWA4. Cooling Tower Efficiency t1 − t 2 e= x 100% t 1 − t WA
  5. 5. Vapor Pressure PV = PW - PA(td - tW)here: A = 6.66 x 10-4 (For tW of equal or greater than 0°C. A = 5.94 x 10-4 (For tW of less than 0° Specific Humidity or Humidity Ratio 0.622 Pv kgm W= P − Pv kgda7. Relative Humidity Pv Φ= x 100 % Pd
  6. 6. 8. Enthalpy h = 1.0045td + W(2501.3 + 1.86td) KJ/kgda9. Specific Volume 0.287(t d + 273) m 3 υ= (P − Pv) kgda10. Degree of Saturation  P − Pd  μ = Φ   P − Pv 
  7. 7. 11. By moisture balance in the tower: a) With make up water, m1 = m2 m3 = ma(WB - WA) kg/sec b) Without make up water available, m1 ≠ m2:12. By Energy Balance in the (W - W ) m1 - m2 = ma tower B A a. Considering make up water kg/sec m1 (h1 − h2 ) ma = kg/sec (hB − hA ) − (WB − WA )h3 m1h1 − ma [ (hB − hA ) − (WB − WA )h3 ] h2 = KJ/kg m1
  8. 8. b. Without considering make up water m1 (h1 − h 2 ) ma = kg/sec (h B − h A ) − (WB − WA )h 2 m1h1 − m a (h B − h A ) h2 = KJ/kg m1 − m a (WB − WA )13. Driving Pressure gH( ρ o - ρ i ) ΔPd = KPa 1000
  9. 9. 14. Mass Flow rate of air and vapor mixture m = ma(1+W) kg/sec m = ma + mv15. Cooling water flow rate related to BrakePower of an Engine Brake Power m w = 904.3 L/hr t1 - t 2
  10. 10. where:m1 - mass flow rate of water enteringtower in kg/secm2 - mass flow rate of cooled water inkg/secm3 - make up water in kg/sec h1 - enthalpy of hot water in KJ/kg h2 - enthalpy of cooled water in KJ/kg h3 - enthalpy of make up water inKJ/kg t1 - temperature of hot water, °C hA - enthalpy of air entering tower in t2 - temperature of cooled water, °CKJ/kgda t3 - temperature of make up water, °C hB - enthalpy of air leaving tower in H - tower height, metersKJ/kgda ρo - density of outside air and vapor mixture WA - humidity ratio of air entering kg/m3tower in kgm/kgda ρi - density of inside air and vapor mixture, 3

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