Articles written in Sadhana

    • Performance evaluation of sorption compressor based J-T refrigerator using R134a and mixture refrigerants as working fluids


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      The idea of adsorption based refrigerator was conceived in the year 1961 by Vickers. The present work reports development of a sorption compressor based J-T refrigerator with R134a alone as a working fluid and a three component mixture of R134a, Ethane and Methane. Commercially available activated carbon,obtained from coconut shell, is used as an adsorbent. The reported compressor is a four cell structure and uses isenthalpic expansion of R134a for cooling purpose. A lowest temperature of -8°C is obtained giving 5 W of refrigeration effect for R134a. The work is further extended to study the effect of various parameters likeadsorption-desorption cycle time, heater power input and capillary tube length on the low temperature obtained from the refrigerator. Experiments are then carried out using a three component mixed refrigerant, a low temperature of -54°C at no load is achieved. Also a continuous trouble-free operation is observed.

    • Effect of cryogenic temperature and frequency on copper coils


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      There is increasing interest in development of magnetic energy storage with conduction cooling. In contrast with the liquid- and gas-cooled coils, the conduction-cooled coils are expected to have significant amount of thermally conducting structures. These thermal structures are usually made of copper, which is also a good electrical conductor. Thus, it is expected that the support structures would modify the resistances and inductances seen by the front-end converters connected to these coils. The paper, thus, presents detailed analysisand experimental results investigating the impact of temperature and frequency variations on conduction-cooled coils. The frequency variations are considered because the front-end converters are likely to produce high frequencycurrents in the coil. The results indicate that there is a significant reduction in the inductance of the coil when temperature is reduced and remarkable change is also observed when operating frequency is increased. The increase in frequency is known to increase the resistance, but significant increase in resistance isalso observed at low temperature when frequency is increased. The results indicate that beyond a certain frequency, the frequency effects dominate the observed resistance values of the coils.

    • Experimental study and analysis of a thermoacoustically driven thermoacoustic refrigerator


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      Experimental investigations are performed on a half-wavelength standing wave type thermoacoustically driven thermoacoustic refrigerator also known as TADTAR. Present TADTAR device conceived to be a quarter wavelength standing wave type thermoacoustic engine (TAE) coupled to a quarter wavelength standing wave thermoacoustic refrigerator (TAR). A TAE generates acoustic work using heat, and this produced acoustic work is directly fed to TAR where a useful cooling effect is developed. The study here aims to projectthe enhancement in the performance of a TADTAR system by using better geometric choices and operating conditions. In the present work, by keeping the engine part unaltered, parametric variations on the refrigerator side are performed. Two geometric parameters namely resonator length and TAR stack position and one operating parameter, working gas, have been varied at three distinct choices. The performance of TADTAR is examined for three output parameters of TADTAR namely frequency of oscillations, pressure amplitude, andtemperature difference across TAR stack. The present study should be useful for assisting select these parameters for starting the designing of a TADTAR. It also helps in concluding in a more generalized way the dependence of the above-said output of TADTAR on the varying parameters. This paper shows that longerresonator and He-Ar mixture as working gas among the choices is better for a TADTAR system for achieving better performance. It also highlights the potential existence of a unique position for a stack length for a TADTAR to attain maximum performance in terms of the temperature difference across the TAR stack. Thepresent paper reports the maximum temperature difference of 16.3 K across the TAR stack

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