RESUMO
Computational fluid dynamics (CFD) analysis using ANSYS Fluent software has been carried out to investigate velocity profiles and thermal characteristics of milk during heating under mechanically agitated condition. In earlier article experimental data on forced convection heat transfer coefficient h - and correlations of the form N u = a · R e b · P r 0.33 for cow milk, standardised milk and full cream milk in Baffled vessel and Unbaffled vessel with scraping, using Propeller, Flat Six Blade Turbine (FBT), Inclined Six Blade Turbine (IBT) and Paddle impellers were reported. It was noted milk in Baffled vessel with Paddle impeller provided highest h - even at lower rotational speeds followed by Propeller, FBT and IBT impellers. In Unbaffled vessel with scraping, Propeller provided the highest h - followed by FBT and IBT impellers. Hence, the present investigation has been carried out to validate and understand how different velocity of flow currents and their magnitude influence the heat transfer coefficient values in CFD simulation. It also justifies the relative performance of the impellers delineated in the earlier paper. In addition, theoretical values of heat transfer coefficients computed using CFD shows close agreement with experimental values.
RESUMO
Heating of milk is an important unit operation to produce many milk based products. This process is done either in heat exchangers or in agitated vessels, where the mode and type of heat transfer plays a significant role. Use of mechanical agitator with suitable impeller would result in uniform agitation of the liquid. Data for forced convection heat transfer coefficients for milk in agitated vessel have not been documented. In the present investigation, forced convection heat transfer coefficients for milk, using mechanical agitators in vessels have been determined. Experiments have been conducted in vessels (Baffled as well as Unbaffled vessel) that were designed and fabricated under standard procedure employing: (1) Flat Six Blade Turbine impeller, (2) Inclined Six Blade Turbine impeller, (3) Three Blade Propeller impeller and (4) Two Bladed Paddle. Heat transfer coefficients were determined for h¯ for cow milk (3.5% fat), standardised milk (4.5% fat) and full cream milk (6.0% fat). The Two Bladed Paddle was found to as yield the highest heat transfer coefficient h¯ for all three types of milk. In addition, empirical correlations for the forced convection heat transfer using Nu=a·Reb·Pr0.33 have been developed for each case. These heat transfer correlations derived will find application in large scale design and the experimental setup would be useful for future investigation with different liquids and impellers.
RESUMO
Protective antigen (PA) is the main component of all the vaccines against anthrax. The currently available vaccines have traces of other proteins that contribute to its reactogenicity. Thus, purified PA is recommended for human vaccination. PA loses its biological activity within 48h at 37 degrees C and its thermolability has been a cause of concern as accidental exposure to higher temperatures during transportation or storage could decrease its efficacy. In the present study, we have used protein engineering approach to increase the thermostability of PA by mutating amino acid residues on the surface as well as the interior of the protein. After screening several mutants, the mutants Gln277Ala and Phe554Ala have been found to be more thermostable than the wild-type PA. Gln277Ala retains approximately 45% and Phe554Ala retains approximately 90% activity, even after incubation at 37 degrees C for 48h while in the same period wild-type PA loses its biological activity completely. It is the first report of increasing thermostability of PA using site-directed mutagenesis. Generation of such mutants could pave the way for better anthrax vaccines with longer shelf life.