Kanawade.V.L.Atkari.V.T.2019-03-152019-03-152014http://krishikosh.egranth.ac.in/handle/1/5810098668Pasteurizers are commonly used heat exchangers for pasteurization of milk that involves mild heat treatment to enhance shelf life of milk. In the existing pasteurizers there are problems like holding coil contamination during diversion, reinfection through back growth of microorganisms from return lines and syphonage of raw milk into pasteurized line due to vacuum creation during diversion. To overcome these problems new pasteurizer was designed as per the new quality guidelines for effective and hygienic pasteurization of milk. It was developed at M/s. Tetra Pak India Pvt. Ltd., Pune as per new holding coil design, new balance tank design, new flow monitoring system design, new FDV design, new PMS design, new temperature sensors and its response time design which were not found in old milk pasteurizers. The newly developed pasteurizer was tested at Model Dairy Plant, NDRI, Karnal. The performance was tested at milk inlet temperature of 2, 4, 6 and 8 C and total milk solids of 15 and 18 per cent. The pasteurization temperature of 78 to 80 C for 20 seconds was used for the testing. The pasteurizer was tested for overall heat transfer coefficient, regeneration efficiency, total heat load and pressure drop. Thetemperature, pressure and milk flow rates were recorded at an interval of 5 min during the run. After the trial plate heat exchanger was inspected for fouling on plate surfaces. The calculated values for the regeneration efficiency, logarithmic mean temperature difference, overall heat transfer coefficient, total pressure drop in plate heat exchanger were statistically analyzed. The logarithmic mean temperature difference was used to find the running time of the newly developed system. The LMTD of heating section and chilling section varied between 5.01 C to 8.08 C and 3.39 C to 6.80 C, respectively. The value of LMTD increased marginally (maximum up to 1 C) over the entire run of 8 h. Since, the variation in LMTD was less than 4 C the pasteurizer can be operated continuously for up to 8 h. The pasteurization temperature and pasteurized chilled milk temperature was kept constant during the operation. The overall heat transfer coefficient (U) varied from 2.13 to 2.83 kW/m2 K for heating section and 1.72 to 2.40 kW/m2 K for chilling section. The optimum overall heat transfer coefficient (U) of 2.83 and 2.40 kW/m2 K were found in S1T1 treatment for heating and chilling sections, respectively. Since, the overall heat transfer coefficient and milk flow rate values were almost constant during the operation. It can be concluded that no fouling occurs. The regeneration efficiency of the pasteurizer was found between 84.81 to 90.17 per cent for both the sides. It was found to be declining with the running time due to the fouling in the pasteurizer. An optimum regeneration efficiency of 90.17 and 90.07 per cent were found in treatment S1T1. The total heat load (Q) was varied from 84.32 to 101.58 kW for heating section and 84.30 to 131.95 kW for chilling section. A minimum total heat load (Q) of 84.32 and 84.30 kW were found in S1T1 treatment for heating and chilling sections respectively. The SPC counts for raw milk was 35  103 cfu/ml and it was reduced to 27  102 cfu/ml in pasteurized milk sample. The coliform of 72  103 cfu/ml was found in raw milk sample but there was zero count of coliform in pasteurized milk sample. Also the MBRT reading increased from 1 to 7 hours from raw to pasteurized milk samples. The pasteurized milk side was always at higher pressure than raw milk side. The product side was also at higher pressure than hot and chilled water side. This was found to be effective to avoid the cross contamination. The foaming was not observed in balance tank during operation.Key words: Holding coil, balance tank, flow monitoring system, FDV, PMS, regeneration efficiency.ennullThesis