Square ducts convection

A. R. Chandrupatla, and V. M. K. Sastri, Laminar Forced Convection Heat Transfer of a Non-Newtonian Fluid in a Square Duct, Int. J. Heat Mass Transfer, (20) 1315-1324,1977. 

M. K. Gangal, and B. D. Aggarwala, Combined Free and Forced Convection in Laminar Internally Finned Square Ducts, Z. Angew. Math. Phys., (28) 85-96,1977. 

Bolinder, C. J. Sunden, B. 1996. Numerical prediction of laminar flow and forced convective heat transfer in a helical square duct with a finite pitch./ . J. Heat Mass Transfer 39(15) 3101-3115. 

Cold conditioned air ai I2°C is flowing inside a 1.5-cm-lhick square aluminum (A = 237 W/m "C) duct of inner cross section 22 cm X 22 cm at a mass flow rale of 0.8 kg/s. 1 he duct is exposed to air at 33°C with a combined convection-radiation heat transfer coefficient of 13 W/m - °C. Tlie convection heat transfer coefficient at the inner surface is 75 W/m C, If the air temperature in the duct should not increase by more than i °C determine the maximuin length of the duct. 

This process governs the rate of deposition of the molecules of nonvolatile compounds on the surface of gas ducts, and contributes to broadening of the chromatographic zones. Being of the order of 0.1 pm at STP, the mean free path of molecules, which is inversely proportional to pressure, reaches 1 cm only at about 0.01 mmHg. In dense enough gas, in the absence of convective flow, the macroscopic picture of migration of molecules (as well as of aerosol particulates) is described by the equations of diffusion. The mean squared diffusional displacement z2D of molecules, the time of diffusion t and the mutual diffusion coefficient >i 2 are related by ... 

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