Question

A finned heat exchanger tube is made of aluminum alloy (k=186W/m· K) and contains 125 annular fins per meter of tube length. The bare tube between fins has an OD of 50 mm. The fins are 4mm thick and extend 15mm beyond the external surface of the tube. The outer surface of the tube will be at 200◦C and the tube will be exposed to a fluid at 20◦C with a heat-transfer coefficient of 40W/m2 · K. Calculate:

(a) The rate of heat transfer per meter of tube length for a plain (un-finned) tube.

(b) The fin efficiency.

(c) The fin and prime surface areas per meter of tube length.

(d) The weighted efficiency of the finned surface.

(e) The rate of heat transfer per meter of tube length for a finned tube.

(f) If the cost per unit length of finned tubing is 25% greater than for plain tubing, determine whether plain or finned tubing is more economical for this service.

Ans. (a) 1130W. (b) 98.6% (c) 0.8946m2 and 0.07854m2. (d) 98.7%. (e) 6920W.

Answer 1