冷却水系统计算.ppt

Cooling System CalculationMarch 2014 Content Cooling Tower Mass Balance Concentration Rate (CR) L.S.I. pH adjustment with Acid Cooling Tower Type Function of Cooling Towers remove heat from process operation HVAC, industrial, power generation mostly by evaporation (80%) partially by sensible heat loss (20%) contact hot water with cooler air also act as air scrubbers corrosion and fouling problems Tower Design Considerations heat load, supply temperature needed location, wet bulb cost water quality and availability footprint, other towers materials fill type Cooling Tower Heat Transfer Mechanisms Sensible Heat 显热 Sensible heat is heat energy transferred between the water droplets and air when there is a difference in temperature between them. Latent Heat 潜热 Latent Heat of Vaporization is the heat energy removed by evaporating a small percentage of recirculated tower water. Each pound of water evaporated removes approximately 1,000 Btu in the form of heat. Review of Basic Cooling TowerDefinition of Terms Cooling Tower Water Balance Cooling Tower Terms Range The Difference between the Hot Water Temperature and the Cold Water Temperature Approach The Difference between the Cold Water Temperature and the Ambient or Inlet Wet Bulb Temperature Wet Bulb temperature of air saturated with water measured by psychrometer calculated from psychrometric chart at 100% RH, wet bulb = dry bulb wet bulb is lowest possible cooling temperature at low RH, cold water temperature can be less than dry bulb temperature Psychrometers COOLING TOWER TERMS HOT WATER TEMPERATURE COLD WATER TEMPERATURE DRY BULB TEMPERATURE WET BULB TEMPERATURE Heat Exchange Q = 8.33 x R x delta T x Cp R = water recirculation, gpm delta T = temperature drop across tower, F Q = heat exchanged or dissipated across tower, Btu/min (1 Ton = 200 Btu/min) Cp = specific heat of water, 1 Btu/lb-F Evaporation need about 1000 Btu/lb to evaporate water at ambient conditions E = R x delta T x Cp x f/1000 f = evaporation