1. The free convection effect in a forced flow may be significant for: (a) small (T w -T m ) (b)…

1. The free convection effect in a forced flow may be
significant for: (a) small (Tw-Tm) (b) highly compact
exchanger (c) shell-and-tube exchanger (d) high Reynolds number

2. A crossflow heat exchanger uses strip fins on the air
side with the following geometry: fin pitch = 549 m-1, plate spacing
= 9:53 mm, fin length = 3:18 mm, flow passage hydraulic diameter = 2:68 mm, fin
metal thickness = 0:25 mm, total heat transfer area/volume between plates =
1250 m2 =m3, and fin area/total area = 0:840. Fins and
parting sheets are made of stainless steel (kw = 20:77 W=m .K).
Parting sheet thickness
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1. The free convection effect in a forced flow may be
significant for: (a) small (Tw-Tm) (b) highly compact
exchanger (c) shell-and-tube exchanger (d) high Reynolds number

2. A crossflow heat exchanger uses strip fins on the air
side with the following geometry: fin pitch = 549 m-1, plate spacing
= 9:53 mm, fin length = 3:18 mm, flow passage hydraulic diameter = 2:68 mm, fin
metal thickness = 0:25 mm, total heat transfer area/volume between plates =
1250 m2 =m3, and fin area/total area = 0:840. Fins and
parting sheets are made of stainless steel (kw = 20:77 W=m .K).
Parting sheet thickness is 0.381 mm. Air flows at u1 = 3:05 m/s with p = 1:1213
kg=m3, v = 1:58 10-5 m2 /s, Pr =
0:70, and cp = 1:00 kJ=kg K. For the air side, = Ao/Afr
= 0:402.

(a) Determine h for Re ¼ 1000.

(b) If the fin thickness is reduced from 0.25 mm to 0.16 mm,
how would h and f be affected? Give qualitative reasons only.

(c) If every geometric dimension of the strip fin geometry
is scaled up by a factor of 5, estimate j and f factors for operation at Re =
1000. Use j = 0:0192 and f = 0:0927 at Re = 1000 for this surface.

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