Conjugated Graetz problems in considering the heat transfer behavior of power-law fluids flowing through a double-pass concentric circular tube with uniform wall temperature are studied theoretically and experimentally. The analytical solution was obtained using an orthogonal expansion technique in terms of power series. The mathematical formulation of such a heat transfer flow problem is developed assuming fully developed laminar velocity distribution in both inner and annular channels with ignoring axial conduction. The theoretical predictions show that the outlet temperature and average Nusselt number decrease with decreasing power-law index. A qualitative agreement is achieved between the analytical solutions and the experimental results. Comparisons made between the results from the double-pass concentric circular heat exchanger and those of a single pass (open conduit) were presented graphically. Considerable improvement in heat transfer is obtainable by employing double-pass devices instead of using single-pass ones. The effect of power-law index on the heat-transfer efficiency enhancement of the double-pass device has also been discussed.
JOURNAL OF CHEMICAL ENGINEERING OF JAPAN 48(7), pp.533-537