Mukund V. Karwe

Fluid Flow and Mixed Convection Transport From a Moving Plate in Rolling and Extrusion Processes

The heat transfer arising due to the movement of a continuous heated plate in processes such as hot rolling and hot extrusion has been studied. Of particular interest were the resulting temperature distribution in the solid and the proper imposition of the boundary conditions at the location where the material emerges from a furnace or die. These considerations are important in the simulation and design of practical systems. A numerical study of the thermal transport process has been carried out, assuming a two-dimensional steady circumstance. The boundary layer equations, as well as full governing equations including buoyancey effects, are solved employing finite difference techniques. The effect of various physical parameters, which determine the temperature and flow fields, is studied in detail. The significance of these results in actual manufacturing processes is discussed.

Physicochemical Properties of Quinoa Extrudates

Response surface methodology (RSM) was used to analyse the effect of temperature, screw speed, and feed moisture content on physicochemical properties of quinoa extrudates. A three-level, three-variable, Box-Behnken design of experiments was used. The experiments were run at 16-24% feed moisture content, 130-170°C temperature, and 250-500 rpm screw speed with a fixed feed rate of 300 g/min. Second order polynomials were used to model the extruder response and extrudate properties as a function of process variables. Responses were most affected by changes in feed moisture content and temperature, and to a lesser extent by screw speed. Calculated specific mechanical energy (SME) values ranged between 170-402 kJ/kg which were lower than those observed for other cereals, most likely due to high (7.2%) fat content of quinoa. High levels of feed moisture alone, and in combination with high temperature, resulted in poor expansion. The best product, characterised by maximum expansion, minimum density, high degree of gelatinization and low water solubility index, was obtained at 16% feed moisture content, 130°C die temperature, and 375 rpm screw speed, which corresponds to high SME input. It was demonstrated that the pseudo-cereal quinoa can be used to make novel, healthy, extruded, snack-type food products.

NUMERICAL SIMULATION OF FLUID FLOW AND HEAT TRANSFER IN A SINGLE-SCREW EXTRUDER FOR NON-NEWTONIAN FLUIDS

Thermal transport within the channel of a single-screw extruder has been studied numerically for non-Newtonian fluids, the computations art carried out for a given barrel temperature distribution and adiabatic screw. Numerical results are obtained using finite-difference techniques. The results indicate that the temperature variation in the downstream direction has a small effect on the corresponding velocity field, which is determined mainly by the total volume flow rate. It is also found that heat may be transferred from the flowing material to the barrel farther downstream under certain conditions. The residence time distribution is obtained numerically. Screw characteristics are presented in terms of bulk temperature rise versus screw speed

Numerical simulation of the extrusion process for food materials in a single-screw extruder

Abstract A numerical study of extrusion cooking of starch based materials in a single-screw extruder is carried out. The low moisture levels and high temperatures typically encountered in practical circumstances are considered. The starch conversion process is studied in the rheological region of the extruder which is often the last few turns of the screw, where the material is treated as a non-Newtonian fluid. A numerical method based on finite-difference approximation is employed to solve the governing non-linear equations for momentum, energy and mass conservation for a non-Newtonian fluid undergoing physicochemical changes. The initial conditions for the problem are taken from experimental observations. The screw configuration and the operating parameters, such as barrel temperature, screw speed and throughput, are varied to study their influence on the conversion of starch. It is found that 28% conversion is obtained due to viscous dissipation alone, whereas 61% conversion occurs by raising the barrel temperature by about 25 °C above the inlet. It is also observed that, at any screw speed, a smaller flow rate caused by a smaller die diameter leads to a higher degree of conversion. Furthermore, it is found that the compression ratio of the screw has a significant influence on pressure rise, bulk temperature and average residence time. As the compression ratio increases the temperature increases but the residence time decreases. The former effect increases the degree of conversion where as the latter decreases the degree of conversion. Therefore there exists a compression ratio at which a minimum degree of conversion at the die is obtained.

p-Coumaric Acid and Ursolic Acid from Corni fructus Attenuated β-Amyloid25–35-Induced Toxicity through Regulation of the NF-κB Signaling Pathway in PC12 Cells

Neuroinflammatory responses induced by amyloid-beta peptide (Aβ) are important causes in the pathogenesis of Alzheimers disease (AD). Blockade of Aβ has emerged as a possible therapeutic approach to control the onset of AD. This study investigated the neuroprotective effects and molecular mechanisms of p-coumaric acid (p-CA) and ursolic acid (UA) from Corni fructus against Aβ(25-35)-induced toxicity in PC12 cells. p-CA and UA significantly inhibited the expression of iNOS and COX-2 in Aβ(25-35)-injured PC12 cells. Blockade of nuclear translocation of the p65 subunit of nuclear factor κB (NF-κB) and phosphorylation of IκB-α was also observed after p-CA and UA treatment. For the upstream kinases, UA exclusively reduced ERK1/2, p-38, and JNK phosphorylation, but p-CA suppressed ERK1/2 and JNK phosphorylation. Both compounds comprehensively inhibited NF-κB activity, but possibly with different upstream pathways. The results provide new insight into the pharmacological modes of p-CA and UA and their potential therapeutic application to AD.

Processing Stability of Squalene in Amaranth and Antioxidant Potential of Amaranth Extract

The processing stability of squalene in amaranth and the antioxidant capacity of the oil-rich fraction of amaranth were studied. The processes investigated were continuous puffing and roasting. Puffing was carried out using a single screw extruder, while roasting was carried out in a convection oven. High-performance liquid chromatography was used to quantify squalene content before and after processing. The L-ORAC method was used to study the antioxidant activity of pure squalene and lipophilic amaranth extract containing squalene. It was found that squalene was stable during all of the processing operations with a maximum loss of 12% during roasting (150 degrees C, 20 min) and no loss during puffing. The L-ORAC test showed pure squalene to be a weak antioxidant, whereas the lipophilic extract of amaranth showed higher antioxidant activity as compared to pure squalene at the same concentration, suggesting that tocotrienols and other minor ingredients also played a role as antioxidants.

Velocity distributions and volume flow rates in the nip and translational regions of a co-rotating, self-wiping, twin-screw extruder

Abstract Velocity measurements were carried out in the nip and translational regions of a co-rotating, self-wiping, twin-screw extruder using laser Doppler anemometry. Significantly higher values of axial and tangential velocity components were measured in the nip region, indicating that the fluid accelerated as it moved through the nip. The local volume flow rates in the nip and translational regions were calculated from the measured velocity field. The volume flow rate in the nip was about four times higher than that in the translational region, indicating the positive displacement character of the nip region. The total volume flow rate calculated over the entire cross-section of the extruder was in agreement with the experimentally measured volume flow rate.

Heat and mass transfer in a single screw extruder for non-Newtonian materials

Abstract Numerical simulation of the transport processes arising in a single screw extruder for non-Newtonian fluids such as plastics and food is considered. The study is directed mainly at simulating the heat and mass transfer inside the screw channel, for a power-law fluid. Moisture is taken as the species for mass transfer, since it is of particular interest in food processing. Finite difference computations are carried out to solve the governing set of partial differential equations for the velocity, temperature and moisture fields, over a wide range of governing parameters. The variation of viscosity with temperature and moisture is taken into account. The basic physical approach for modeling the complicated heat and mass transfer processes for inelastic non-Newtonian materials is outlined. As an application of this analysis to starchbased food systems, the reactive nature of the food constituents is incorporated by including the rate of reaction (gelatinization) between moisture and food. Results are presented in terms of the velocity, temperature and moisture concentration contours. Strong viscous dissipation effects are found to arise for typical operating conditions. The moisture contours indicate that starch gelatinization typically occurs first at the screw root. The effect of the various governing parameters on pressure build-up within the extruder channel is determined and discussed in terms of the underlying physical processes. Experimental validation of some of the numerical results has been carried out, and the comparisons are quite good. Results are also presented for the residence time distribution (RTD), an important design parameter in extrusion. Though this study considers moisture transport, the basic approach presented may easily be extended to reactions and mass transfer of other species in polymers and in other non-Newtonian materials.

Numerical simulation of conjugate transport from a continuous moving plate in materials processing

The conjugate mixed convection and conduction transport that arises due to the continuous movement of a heated plate has been numerically investigated. The temperature distribution in the solid, as well as in the flow, along with Ike associated velocity field, need to be studied in detail. A numerical study is carried out, assuming a two-dimensional, transient circumstance. The governing elliptic equations are solved, employing finite difference techniques. The transient effects in heat transfer from the plate are studied for the heated plate moving horizontally as well as vertically. The steady state results are obtained for various values of the governing dimensionless parameters, such as the ratio of the thermal conductivity of the fluid Kr to that of the material Ks the Peclet number Pe, Prandtl number Pr, Grashof number Gr, and Reynolds number Re.

Effect of high hydrostatic pressure and pressure cycling on a pathogenic Salmonella enterica serovar cocktail inoculated into creamy peanut butter.

The ability of Salmonella enterica serovars to survive in high fat content, low water activity foods like peanut butter has been demonstrated by large foodborne illness outbreaks in recent years. This study investigates the potential of high hydrostatic pressure processing, including pressure cycling, to inactivate Salmonella inoculated into creamy peanut butter. A cocktail of pathogenic strains of Salmonella Enteritidis PT30, Salmonella Tennessee, Salmonella Oranienburg, Salmonella Anatum, Salmonella Enteritidis PT 9c, and Salmonella Montevideo obtained from peanut butter- and nut-related outbreaks was inoculated (10(6) to 10(7) CFU/g) into creamy peanut butter and high pressure processed under five different sets of conditions, which varied from 400 to 600 MPa and from 4 to 18 min. The log CFU reductions achieved varied from 1.6 to 1.9. Control experiments in which Salmonella was inoculated (10(9) CFU/g) into 0.1% peptone buffer and high pressure processed at 600 MPa for 18 min showed inactivation to below the detection limit of 100 CFU/g, confirming that high pressure processing is effective at destroying Salmonella in high-moisture environments. Pressure cycling under three sets of conditions consisting of pressures from 400 to 600 MPa, 3 to 10 pressure cycles, and hold times of 6 min for each cycle showed reductions similar to those seen in noncycling experiments. The results of our experiments suggest that the peanut butter food matrix facilitates the survival of Salmonella when exposed to high hydrostatic pressure processing.