Outside film heat transfer coefficient

A jacketed reaction vessel containing 0.25 nv1 of liquid of specific gravity 0.9 and specific heat 3.3 kJ/kg K is heated by means of steam fed to a jacket on the walls. The contents of the tank are agitated by a stirrer rotating at 3 Hz. The heat transfer area is 2.5 nr ami the steam temperature is 380 K. The outside film heat transfer coefficient is 1.7 kW/m2 K and the 10 mm thick wall of the tank has a thermal conductivity of 6.0 W/m K... 

Rain, hail, and sun protection for the tube bundles, thus better outside film heat-transfer coefficients... 

Outside film heat transfer coefficient = 267 W7m K (from previous plant operating data), and fouling coefficient on inside = 2500 W7m K. 

Temperature inside the furnace at the wall Air temperature outside wall Heat transfer coefficients Outside air film (h)... 

A low-carbon steel tube with a 25.4 mm (1 in.) outside diameter is radially finned with an aluminum (Alloy 1100) strip 15.8 mm (0.625 in.) high and 0.483 mm (0.019 in.) average thickness uniformly spaced at 400 fins/m (10.2 fins/in.). The outside surface of the steel tube is 80°C (176°F), and the tube is cooled by air in cross flow, with a bulk air temperature of 30°C (86°F) with a film heat-transfer coefficient of 70 W/m K (12.3 Btu/h fF °F), assumed uniform over the entire outside surface... 

Estimate outside and inside film heat transfer coefficient. 

Of these special surfaces, only the double-fluted tube has seen extended services. Most of the gain in heat-transfer coefficient is due to the condensing side the flutes tend to collect the condensate and leave the lauds bare [Caruavos, Proc. First Int. Symp. Water Desalination, 2, 205 (1965)]. The coudeusiug-film coefficient (based on the actual outside area, which is 28 percent greater than the nominal area) may be approximated from the equation... 

The overall heat transfer coefficient, U, is a measure of the conductivity of all the materials between the hot and cold streams. For steady state heat transfer through the convective film on the outside of the exchanger pipe, across the pipe wall and through the convective film on the inside of the convective pipe, the overall heat transfer coefficient may be stated as ... 

Consider a single-zone jacket where there is an increase in the jacket flow, and a corresponding increase in the outside film coefficient because hj =f(Njjg, G). Therefore, a two-fold increase in the jacket flow results in an increase in hjj by 2 h . The overall heat transfer coefficient U = l/[FpoL + 1/hj], and a larger outside coefficient subsequently increases the overall heat transfer coefficient. The overall heat flux will increase due to the combined effects of the increased flow and lower jacket outlet temperature. The net result is an increase in the pressure drop. 

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