Articles written in Sadhana

    • Heat and mass transfer analysis on multiport mini channel shelf heat exchanger for freeze-drying application


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      An experimental study on heat transfer characteristics of shelf heat exchangers, which are used in small-scale freeze dryers, is presented in this paper. The proposed heat exchanger consists of the multiport minichannel flow paths, and a comparison with a conventional serpentine is carried out based on uniformity of the product temperature achieved. The experimental results indicate that the mini-channel shelf has better temperature uniformity than the latter. Skimmed milk is used as the test fluid. In the freezing and drying process, the product temperature variation is minimal in the mini-channel heat exchanger, with a variation of 12.5 % and 25%, respectively, and the heat transfer coefficient is found to be from 140 to 267 Wm-2 K-1. The moisture content in the product reduces to 50 % in 2 hours, and the drying rate is higher at 0.032 kg hr-1 after 1 hour of the drying process. The redesign of the heat exchanger will be an essential tool to improve the performance with uniform temperature distribution on the product and to improve the product quality.

    • An investigation on heat and mass transfer characteristics during spray drying of saline water


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      The paper presents the heat and mass transfer characteristics during spray drying of a saline solution using a full cone pressure-swirl nozzle of 0.2 mm diameter. The phase change behaviors are studied numerically using a 2D axisymmetric model and experimentally validated in a tailor-made apparatus. The operating conditions are chosen such that the magnitude of Weber and Ohnesorge numbers of spray liquid ensures the spray pattern is under atomization regime. The numerical model is validated experimentally using a commercially available saline solution with a concentration of 0.9% weight per volume at 1 g/s. The system uses air as a carrier gas with an inlet temperature and axial velocity maintained at 340°C and 1.2 m/s, respectively. Watersensitivepaper is used to validate droplet diameters for the said operating condition. The model is further extended to different operating conditions and saline mass fractions between 0.1 and 0.3. Based on the results, the particle heat and mass transfer characteristics are discussed.

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