DEVELOPMENT AND PERFORMANCE EVALUATION OF CONTINUOUS KHOA MAKING MACHINE
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Date
1998
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Publisher
AAU, Anand
Abstract
Khoa, a traditional Indian dairy product has considerable market potential as the milk utilized for the manufacture of khoa is higher than the milk handled by organized dairy sectors. The organized dairy plant have shown interest for the manufacture of khoa which requires suitable mechanized equipment for commercial application It has been also suggested by many research worker and policy makers to find alternative method for the continuous manufacture of khoa. Keeping these aspects in view the present work was under taken to develop a continuous khoa making machine and to evaluate the performance of the machine. The present work covers development of three stage scraped surface heat exchanger (SSHE) and its components, evaluation of heat transfer behaviour and determination heat transfer co-efficients, development of co-relationship between heat transfer and various operating parameters like scraper speed, steam pressure, milk flow rate, etc., estimation of energy requirement and energy analysis of the process. The product prepared under different operating conditions was also evaluated for its chemical, sensory and rheological attributes. The shelf life of the product was also evaluated at room temperature as well as under refrigerated conditions. The suitability of khoa prepared in the continuous khoa making machine for the manufacture of khoa based sweets was also evaluated. The design of the continuous khoa making machine which consists of three SSHE (denoted as HE1, HE2 and HE3), Teflon coated spring loaded scraper assemblies, drive for scraper assemblies and constant milk supply arrangement can be successfully used for the manufacture of khoa from milk and from vacuum concentrated milk. The present design offers advantage of gravity flow and it is easy to control the operating variables as the milk is concentrated in three stages. The overall heat transfer co-efficients (U-values) under different operating conditions were determined by using a Fourier's heat flow equation, Q = UxAx(Ts-Tp). The U-value during manufacture of khoa depends on the milk flow rate, steam pressure, scraper speed, TS of the feed and changes in the properties of milk in each stage of concentration. The U-values obtained ranged from 725.43 to 999.64 W/m2°K in HE1, 497.48 to 712.65 W/m2°K in HE2 and 318.33 to 554.57 W/m2°K in HE3 under different operating conditions of the khoa making machine. The U-value decreased from HE1 to HE3 due to reduction in mass flow rate on concentration together with increase in TS in the subsequent stages. The rates of evaporation and U-values decreased as the TS of milk increased in the khoa making machine. Linear regression equations were obtained between TS of milk and U-values under different operating conditions which are useful to predict the U-value at different TS during the process. The graphical method, based on Nusselt theory and experimental values of AT and U, used to determine steam side film heat transfer co-efficient (ho) and steam side wall temperature (Tw) is simple to adopt in similar heat exchangers. The values of ho obtained in HE1, HE2 and HE3 were 10700, 11850 and 14625 W/m2°K respectively at 98.1 Kpa steam pressure. The feed rate is not anindependent variable as it depends on the rate of evaporation which is governed by various operating parameters of the machine during manufecture of khoa. Therefore, the output of khoa depends on the rate of feed achieved, TS of the feed and final moisture content of the product. The output of khoa was 11.1 kg/h when TS of milk was 13.73 %. The output rate increase to 25.1 kg/h and 38.2 kg/h when vacuum concentrated milk of 23.77 % TS and 35.08 % TS were used respectively.
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Keywords
DAIRY ENGINEERING, EVALUATION