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In this article, the behavior of heat and mass transfer relation during khoa making has been investigated. Various indoor experiments have been performed for simulation of developed thermal model for maximum evaporation during heating of milk. The data obtained from experimentation have been used to determine values of constant “C” and exponent “n” by simple regression analysis. Based on the values of “C” and “n,” convective and evaporative heat transfer coefficients for milk were determined. It was observed that the convective and evaporative heat transfer coefficients decrease with the increase in rate of heating (varying voltage). It was also observed that convective and evaporative heat transfer coefficients increase with the increase in operating temperature. The rate of increment of evaporative heat transfer coefficient is higher than the convective heat transfer coefficient. The experimental error in terms of percent uncertainty was also calculated. PRACTICAL APPLICATIONS The traditional method of khoa making (i.e., open pan evaporation process) requires a large quantity of energy and in the present era, energy saving is needed to pay sufficient attention. In rural India, generally, wood, cattle dung, coal, kerosene, etc. are used in open chulah as fuel for khoa making which is hardly 8–10% thermally efficient. A number of research articles are available in the literature explaining the mechanization of khoa making process. But even today, the khoa making technology in rural India much remains the same. Thus, by keeping energy saving aspect in mind, the traditional method of khoa making has been further explored.

Acoustic metamaterials hold great potential for attenuation of low frequency acoustic emissions. However, a fundamental challenge is achieving high transmission loss over a broad frequency range. In this work, we report a double negative acoustic metastructure for absorption of low frequency acoustic emissions in an aircraft. This is achieved by utilizing a periodic array of hexagonal cells interconnected with a neck and mounted with an elastic membrane on both ends. An average transmission loss of 56 dB under 500 Hz and an overall absorption of over 48% have been realized experimentally. The negative mass density is derived from the dipolar resonances created as a result of the in-phase movement of the membranes. Further, the negative bulk modulus is ascribed to the combined effect of out-of-phase acceleration of the membranes and the Helmholtz resonator. The proposed metastructure enables absorption of low frequency acoustic emissions with improved functionality that is highly desirable for varied applications.

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