environment engineering Chapter1.pdf

1CIVL1005 - Environmental Engineering Mass and Energy Transfer Office: Rm. 6-30, Haking Wong Building ? Phone: 2859-1973 ? E-mail: kshih@hku.hk Dr. Kaimin Shih DEPARTMENT OF CIVIL ENGINEERING THE UNIVERSITY OF HONG KONG ? Units of Measurement ? Materials Balance ? Energy Fundamentals - OUTLINES - 2Units of Measurement ? Environmental quantities were commonly measured and reported in both: ? U.S. Customary System (USCS). ? International System of Unit (SI). Units of Measurement 3? Liquids are usually reported with “concentrations”, such as the weights of substances dissolved in water: ? 1 mg/L =1 g/m3 = 1ppm (parts per million) ? 1 ?g/L = 1mg/m3 = 1ppb (parts per billion) ? 0.053 mM (millimole/liter) NaF = ? mg/L 0.053 ? 10-3 ? 42 (42 = molecular weight of NaF) = 2.226 ? 10-3 g = 2.226 mg Therefore, 0.053 mM = 2.226 mg/L * 1 m3 water = 1000 L = 1000 kg * m = 10-3, ? = 10-6 ? Gases: ? 1 volume of gaseous pollutant / 106 volumes of air = ppmv (parts per million by volume) ? Idea gas law: PV = nRT P = absolute pressure (atm) V = volume (L) n = mass (mol) R = idea gas constant = 0.082056 L?atm?K-1?mol-1 T = absolute temperature (K), where K = oC +273.15 ? How much volume does 1 mole of idea gas occupy at 1am of pressure and 25oC? 1 ? V = 1 ? 0.082056 ? 298.15 ? V = 22.465 L ? 1 mole of every ideal gas occupies the same volume, so: 1 ppmv = 1molecule of pollutant / 106 molecules of air 4Materials Balance ? Law of Conservation of Mass: Materials Balance Accumulation rate = Input rate – Output rate + Reaction rate CsQs + CwQw = CmQm 5Mass Balance/Metabolism of System s ± Δs A C B D Systems boundary Santorio Santorio (1561-1636), an Italian physician and professor ? Reaction rate, r, in a completely mixed batch reactor (CMBR): ? dC/dt = r ? If r is positive ? Generation, negative ? Decay * Zero-order: r is a constant (k) Ex.: Rate of water evaporates from a bucket. * First-order: r = kC Ex.: Decay of radioactive materials. * Second-order: r = kC2