Articles written in Sadhana

    • Parametric analysis of axial wall conduction in a microtube subjected to two classical thermal boundary conditions


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      Heat transfer in laminar flow microtube is numerically explored with an objective of discriminating conjugate heat transfer process experienced in a microtube under two different thermal conditions. Two classical thermal conditions – constant heat flux and constant wall temperature – are imposed separately on the outersurface of a microtube. Wide parametric variations are considered in this study, for the two thermal conditions, albeit the problem under consideration being very classical from both geometry and thermal condition point of view. The parametric variations considered in this work include wall thickness, wall conductivity and coolant flow rate. An expression for Nusselt number in terms of radial (or transverse) and axial conduction number is presented and validated against existing theoretical correlation as well as reported experimental data for bothcircular and non-circular channels. Dominance of axial conduction over radial (or transverse) conduction is explored and it is found that the effect of wall material on conjugate heat transfer plays an important role. Additionally, it is also observed that with the increase in coolant flow rate, the ratio of radial to axial conductionnumber increases for both thermal boundary conditions.

    • Effect of conjugate heat transfer in single-phase laminar flow through partially heated microtubes


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      To analyze conjugate effect under partially heated condition, two-dimensional numerical study is performed for single-phase laminar flow through microtubes. Constant heat flux is applied on outer surface along the heating length of the microtube. For partial heating, the microtube is divided into three parts of 6 mm (L1), 48 mm (L2) and 6 mm (L3). Three cases are considered for partial heating: (a) insulated across 1 and L3 and heating across L2, (b) insulated across L1 and heating across L2 and L3 and (c) insulated across L3 and heating across L1 and L2. For direct comparison, heating across full length of the microtube is also considered. Parametric variations include microtube wall thickness to inner radius ratio (dsf), and solid to fluid conductivity, ratio (ksf) and flow Re. Presence of axial wall conduction is assessed in terms of dimensionless wall temperature and heat flux at the solid–fluid interface, dimensionless bulk fluid temperature, and local and average Nusselt number. The results indicate that there exists an optimal value of average Nusselt number for certain value of ksf at which dominance of axial wall conduction is smaller. Additionally, to highlight the effect of axial wall conduction, local heat flux distribution at the solid–fluid interface is also explored

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