Articles written in Sadhana

    • Wood gas generators for small power (∼ 5 hp) requirements

      U Shrinivasa H S Mukunda

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      This paper reports experimental and developmental studies on wood gas generators meant for running 5 hp diesel engines in irrigation water pumping. Critical inputs for the design of small reactors are presented. A prototype of the gas generator based on these inputs has been built and tested along with a diesel engine pumpset. The results of various tests on the system are described along with some critical operational features. The lowest amount of diesel at which the engine could be run with a mixture of diesel and gas is about 15% of the consumption with diesel alone. However, to obtain the same energy, that is the same amount of water at a given height, the best replacement of diesel obtained is about 75%. The paper also comments on the economics of such systems.

    • Variable property analysis-is there anything to it?

      H S Mukunda

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      This paper discusses a few situations in combusting flows and attempts to demonstrate that including variable thermodynamic and transport properties in the analysis does more than simply improve the accuracy of predictions. The qualitative behaviour of the result itself is altered. Three examples are considered-single droplet combustion, forced convective turbulent boundary layer combustion, and free convective combustion.

      The flame to droplet radius ratio is very well predicted by variable property theory and the improvement is a direct consequence of the property variation. In the case of turbulent boundary layer combustion of solid/liquid fuels it is shown that the fuel exerts a significant influence on regression rate as is found in the experiments. The constant property theory, however, shows relative independence of regression rate with regard to the nature of the fuel. The prediction of regression rate is improved substantially in the case of free convective combustion.

    • Portable single-pan wood stoves of high efficiency for domestic use

      H S Mukunda U Shrinivasa S Dasappa

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      We describe and evaluate here certain new designs for single-pan wood stoves of high efficiency. The novelty in the design consists chiefly in the use of improved geometries for the combustion chamber and the vessel support. Extensive tests on water boiling and cooking demonstrate efficiencies exceeding 40%; these high values are attributable to stove operation at near stoichiometric conditions. The configuration termed Swosthee is among the most efficient stoves available to date, and is able to burn wet wood under partial loading with little accompanying smoke. Two versions of the same basic design provide inexpensive stoves that retain to a large extent the advantages of the original design like the generation of pollutants at low levels in the flue gases and the ability to handle wet wood.

      For the proposed designs the dependence of their cooking efficiency on vessel size has been obtained. These are reflected in terms of specific fuel consumption (whose variation is a function of vessel size). The present designs, when compared to other currently available improved stove designs like Priyagni, Tara, the Tamil Nadu Stove and theAstra three-pan stove, are better with respect to at least one of the following criteria-efficiency, cost, CO emission and portability. The stoves are presently being disseminated in small numbers.

    • Five-kilowatt wood gasifier technology: Evolution and field experience

      S Dasappa U Shrinivasa B N Baliga H S Mukunda

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      Various elements of an efficient and reliable 5k W wood gasifier system developed over the last ten years are described. The good performance obtained from the system is related to the careful design of its components and sub-systems. Results from extensive testing of gasifier prototypes at two national centres are discussed along with the experience gained in the field from their use at more than one hundred and fifty locations spread over five states in the country. Issues related to acceptance of the technology are also included. Improvements in design to extend the life, to reduce the cost, and to reduce the number of components are also discussed. A few variants of the design to meet the specific requirements of water pumping, power generation and to exploit specific site characteristics are presented.

    • Gasifier-based power generation: Technology and economics

      B N Baliga S Dasappa U Shrinivasa H S Mukunda

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      The paper describes a 100 kW power generation system installed at Port Blair, Andaman and Nicobar Islands, under a project sponsored by the Department of Non-Conventional Energy Sources, Government of India. The system consists of a wood gasifier utilising the waste wood from a saw mill and a diesel engine genset. The performance of the total system and its elements are presented along with economics of operation. To bring out the economics of using such renewable energy devices for power generation, some realistic situations are considered for which the effective cost of power and the pay-back period for the investment are evaluated. The economics is compared with that of a similar system of 3·7 kW capacity.

    • Foreword

      R Narasimha H S Mukunda

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    • Experiments on unsteady pool fires – effects of fuel depth, pan size and wall material


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      This paper presents specifically designed experiments to understand the effect of range of parameters on pool burn behavior with liquid fuels. Experiments have been conducted on pool fires with 0.1–2 m diameter pans and depths of 40, 50, 60 and 90 mm with n-heptane fuel depths up to 30 mm floated on water andwithout water in an indoor fire laboratory. Pans of 0.2 m dia are made of glass, stainless steel, mild steel and aluminum and larger diameter pans only of mild steel. The experiments conducted include some with fuel initial temperature effects at 300, 319 and 343 K. Data on temporal evolution of mass burn, pan wall temperatures, temperatures inside the liquid at some depths and gas phase temperatures at select heights from the pool surface have been obtained from the experiments. Results show that at larger fuel depths of ( ~ 30 mm), a burn mass flux of 60–75 g/m2s is reached even in 0.2 m dia pans. This flux is expected only in large pans of about 2 m size. Regarding pan material effect, glass pans show mildly increasing low flux values (10–15 g/m2s) and mild steel and aluminum pans show an initial low flux value ( ~ 10 g/m2s) and then a sharp change to large flux values depending on the depth. At larger depths, the flux values go up to 65 g/m2s. In case of stainless steel, the mass flux variation occurs smoothly all through towards increasing values. As regards the water depth below the fuel, the decrease in the average burn rate is about 1 % per mm water depth up to 20 mm for all pans with diameter below 0.5 m. Larger size pans with burn rate controlled largely by radiation show much reduced effect of thewater depth. In order to correlate the data with diverse parameters a dimensionless number, Mpc, has been invoked using scaling laws, and a correlation that provides a good estimate of the mass burn flux including allthe effects considered earlier has been deduced. The data set thus generated provides the basis for a more detailed model to predict the mass loss history and other parameters.

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