Question

The figure shows data for a portion of the ducting in a ventilation system operating at steady state. The ducts are well insulated and the pressure is very nearly 1 atm throughout. The volumetric flow rate entering at state 2 is AV2 = 4800 ft/min. Assume the ideal gas model for air with cp = 0.24 Btu/lb-R and ignore kinetic and potential energy effects. (AV)1 = 5000 ft/min Air, Cp = 0.24 Btu/lbºR T = 80°F p = 1 atm 3 V2 = 400 ft/min Insulation (AV) ft3/min T2 = 40°F Determine the temperature of the air at the exit, in °F, and the rate of entropy production within the ducts, in Btu/min.°R.

Answer 1

A given, T, = 9097 2 = 400F.. a (Av), = 5000ft/min (A) = 4800 ft/min from steady-state mass and Energy balanci. 0- oc - WI° +mithi tamil gaj) + mechatrat +522) - miz (nat vg! +973) By cessing th=pOT, :o--m. [op-{=to)7+inn [4p(72–73) 40 mi- (AVP, . 5000 x 14.7 litlin / muin RT = 367 53 lb/min 1545 from ca 4800 x :14.3 Ciny), 128.99 * (500). : 381.1 lb) min eqt T3= in oprit maltz miti na Tz (m, + MY is 367.53 (540) + (381.1) (500) (367:53+887.) T3 519.67 OR = 60 °F) . Mitm2

Now, from Entropy rate Balance equation or Eaj + mis + masa & in z toev. we know that ingam, ting dev = (n + m2) s3 - misi-masz : = m; lsz-sı) + m2 ($3-sz) - 0 [n, en niet mis im E] 2 054 (857.92) and - eatin) en (san 519.6 yo ܠܘܠ = 0.140 Btu minor