Answer Happy

= = = stp 12.5 A gas-fired fluid heater is intended to operate in a remote area where electricity is limited. Thus, the air flow to the burners must be supplied by natural-draft means (i.e. with benefit of a long, vertical chimney), rather than forced-draft blowers. Assuming the chimney is adiabatic (no heat loss to surroundings), determine whether dimensions Di= 0.5 m, L= 30.0 m , and ε = 0.2 mm will provide enough draft to exhaust Vs 6000 Nm3/h when the outside temperature is To = 25 °C and the chimney temperature is T;= 200 °C. Assume the molar mass for the exhaust gas is Ñ = 29.0 kg/kmol, and use Appendix A.1 for dynamic viscosity of air at the chimney temperature. Show your work. Answer. Yes. With no other flow resistances, the draft-induced flow rate could be greater than 6000 Nm3/h. = =
A.1 Properties of Air (Gas, 3.76 N2 + 1.00 O2, by Mole) The enthalpy of formation of air is Ah, = 0.0 kJ /kmol. The molar mass of air is Ñ = 28.85 kg/kmol. These properties were derived from the oxygen and nitrogen data sources by Linstrom and Mallard (2017–2021). = S T(K) P 3 v (m (kPa) /kg) ср (/g*K) 1.012 388 h су (kJ/kg) (kJ/kg) (J/gK) (/g*K) 197.6982 276.9092 6.653 0.722 516 656 214.4522 300.3551 6.735 0.723 407 (Pa*s) k Air (W/m*K) phase 1.729E-05 0.024 270 vapor 275 101.33 0.781 698 298.15 101.33 0.847 709 1.012 950 1.843E-05 0.025 915 vapor 526 300 101.33 0.852 980 0.723 495 1.013 087 1.852E-05 0.026 044 215.7949 302.2239 6.741 763 vapor 325 101.33 0.924 243 0.724 900 1.014 194 1.970E-05 0.027 776 233.9149 327.5672 6.822 926 vapor 350 101.33 0.995 468 0.726 770 1.015 914 2.085E-05 0.029 472 vapor 252.0682 352.9438 6.898 145 270.2771 378.3683 6.968 275 375 101.33 1.066 650 0.729 140 1.018 144 2.196E-05 0.031 139 vapor 400 101.33 1.137 911 0.732 012 1.020 921 2.304E-05 0.032 784 288.5540 403.8532 7.034 067 vapor 425 101.33 1.209 091 0.735 380 1.024 130 2.409E-05 0.034 411 vapor 450 101.33 1.280 247 0.739 223 1.027 965 2.511E-05 0.036 024 vapor 306.9036 429.4160 7.096 045 325.3410 455.0668 7.154 764 343.8788 480.8179 7.210 422 362.5299 506.6746 7.263 474 475 101.33 1.351 427 0.743 511 1.032 162 2.611E-05 0.037 625 vapor Back to page 295 122 506 0.748 193 1.036 771 2.709E-05 0.039 216 vapor 525 101.33 1.493 686 381.3066 532.6569 7.314 10.753 236 1.041 766 2.804E-05 0.040 799 vanor