• D R Chaudhary

      Articles written in Pramana – Journal of Physics

    • Measurement of effective specific heat of packed bed materials by the continuous flow electrical method

      P B Lal Chaurasia D R Chaudhary R C Bhandari

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      The theory of the continuous flow electrical method for the determination of specific heat of liquids has been extended to the measurements of effective specific heat of packed bed materials consisting of solid-liquid phase systems. Experimental data are reported showing the variation of effective specific heat with mass porosity and saturating liquid specific heat. The weighted arithmetic mean equation of constituent specific heats is in fair agreement with the measured values.

    • Bounds on the effective thermal conductivity of two-phase systems

      R N Pande V Kumar D R Chaudhary

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      The weighted geometric mean of resistors considered for determining the effective thermal conductivityKE of two-phase systems has been optimised. Solutions of the equations lead to a useful set of bounds. When compared with other bounds the present bounds give the better results in estimating the upper and lower values of the effective thermal conductivity of a two-phase system.

    • Thermal conduction in a homogeneous two-phase system

      R N Pande V Kumar D R Chaudhary

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      Assuming a regular geometry of dispersed phase (λ2) an integrated theory for the effective thermal conductivityλe of all kind of two-phase materials (including loose materials) is developed. The flux modification is carried out by considering the effective neighbouring interactions in the solution of Poisson’s equation. A comparison of calculatedλe values with the reported experimental results over a wide range of two-phase materials shows a good agreement.

    • Thermal conduction through loose and granular two-phase materials at normal pressure

      R N Pande D R Chaudhary

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      The integrated theory derived for the lattice-type dispersions is modified and extended to estimate the effective thermal conductivity of loose and granular two-phase materials at normal pressure assuming an effective continuous media approximation. A comparison of calculated values ofλe with the reported experimental results over a wide range of loose and granular two-phase materials shows a good agreement.

    • Effective thermal conductivity of granulated two-phase systems at interstitial air pressures

      R N Pande D R Chaudhary

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      Considering the htermal conduction through molecular collisions an expression for the effective thermal conductivityλe of loose and granular two-phase materials at different interstitial air pressure has been derived. The dependence ofλe on pore and particle sizes, characteristic pressure and radiative heat transfer is also discussed. Calculated values ofλe of glass beads and loose building materials are compared with reported results.

    • Thermal conduction through porous and dispersed three-phase systems

      Ramvir Singh R S Beniwal R N Pande D R Chaudhary

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      A loose three-phase system made of metal, non-metal and air is considered resulting from small successive dispersions in effective continuous medium (ecm). The effective thermal conductivity of loose three-phase systems is estimated by extending theecm approach to multi-phase systems. The unsteady state line source (needle) method is employed to determine the effective thermal conductivity of some selected three-phase materials. The calculated and observed values show good agreement suggesting that the continuous medium approach can be applied to estimate effective thermal conductivity of multi-phase systems.

    • Effective medium in dispersed systems

      R N Pande D R Chaudhary F Gori

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      A structural analysis of effective medium formed by dispersed systems from the viewpoint of flux modification at large dispersions is presented. The effective medium coefficient is investigated for its parametric dependence and the effective properties are estimated through this dependence. This estimation covers all highly dispersed two-phase systems including the effect of container.

    • Heat conduction through moist soils at different temperatures

      Ashok K Singh Ramvir Singh D R Chaudhary

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      A numerical model has been described to estimate the effective thermal conductivity of moist soils, considering the effective continuous medium approximation and taking all possible interactions. Numerical solutions of the exact formulations are presented. Experimental measurements have been carried out for the thermal conductivity of dune sand at different moisture contents employing the method of unsteady state line source. The predicted and measured values show reasonable agreement.

    • Heat conduction and moisture migration in unsaturated soils under temperature gradients

      Ashok K Singh Ramvir Singh D R Chaudhary

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      An experimental study has been done to investigate the heat conduction and moisture distribution through the different layers of unsaturated soil. The soil is taken in the form of cylindrical columns in vertical and horizontal positions. The two ends of the cylindrical column were maintained at different constant temperature. The effective thermal conductivity was measured by dynamical method after achieving steady state. The distribution of moisture in the soil column was determined by gravimetric technique. The effective thermal conductivity (ETC) has also been predicted by temperature dependent model developed by Singhet al (1988). A close agreement has been found in experimental and predicted values of ETC.

    • Differential temperature sensors method for simultaneous determination of thermal conductivity and diffusivity

      L S Verma A K Shrotriya Ramvir Singh D R Chaudhary

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      An attempt has been made to minimize the sources of error involved in the transient probe method for thermal conductivity determination. Two sensors (thermocouples) are mounted parallel to the needle probe at known distances. This modification makes it a device for simultaneous conductivity and diffusivity determination. Thermal conductivity and diffusivity for glycerine, dune sand and mustard seed are determined by this method. Results obtained are compared with those obtained by a calibrated transient probe for conductivity and by a parallel wire method for diffusivity. Analysis of the results prove it to be a better instrument over the traditional ones. The technique can also be used as a direct reading device for conductivity and diffusivity measurements.

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