Question

Problem #2 A duct 2m by Ime in size carrying conditioned air runs in a straight line for Umrom the supply an. It divides into two parts each of 80 m long and 2 m m Section as shown in Fig. 20.6. T 80 m Fan 50 m 80m — Fig. 20.6 Insulated air ducts. If the quantiry of air discharged at C is 1600 m/min, calculate the quantity discharged at D and the static pressure at the fan outler A. Calculate the duct friction loss in Nm taking the alue of friction factor as 0.005.

Answer 1

Griven Farn с 8orm a 2 m b Im, L280 m - 80 m L3 1600 m3/min f 0. oos air dischnged at Puantity 0f D, of air dischged puantity at D CYO Sectional ea of ducts and Bc AB, DB

A,- A2-A ab A, - A2 A3 2 A A, A3 2 Velocity aair in duct BC, V3 A3 1600 V3 2 800 m/mio 9 V3 V313.33 we bnow that veloaty Prepude, Pr 2 I.2 2 Pr Py 0.6 V N

veloaty Prepwe n duct BC, (vs) Pv3 O6 20-6 (13.33) Pvz 2 106.6 N/ Pes Since, each duct is 2m by lm, therefore hydraulic mean depth for BC , ducts AB, BD, and ab 2(ath) 2 2(21) due to frictior in Prewe lass duct Bc, fly (Ps)

0.00S80 lo6.6 N/m Phs 2 129 and total Prenide at B, PT Rg Pre- t PTB 128 + 106.6 234.6 N/ PrB -G) Let Preywe in the duct Veloaty BD, and v vetoaty in the duct BD Prese la due the we tro that the duc, BP, to frictan flz CPe) 0.00580 (P)

P 2 P N/ from equation (i) , we get, 234.6 j2 106.6 N/m Pvz We Can knos that, Pv2 0.6 (v) (ov) 0.6 (v, J06.6 2 13-33 2 Ne bno that uantity af ar dischagad A2 V1 2 22213.33 2 26.66 m3

Static Preiude at the fan Outlt, We bno that the Quentiy of air flowing through the duct AR, 2 1600 t 160o 3200 in the duct AB velocity of air 3200 V 2 A (600 rofmio - 26.6 the duct AB, Prebuwe veloa'ty o.6 (v) 0.6 (26.6) Pv 42 N/

Preswe loss duo to frichion in the duct AB, Pv 0.0oS50 427 P320 N/m the fan autbt, Total PreHue at Ci.e, at A) PTB PTA 2 234.6 t 320 PTA PTA 554.6 N/w at the fan outlel, Prepwe Static Ci.e, at A

PSA PAPr O554 6 427 27.6 N/ PA 2