Robert E. Altomare

An Analysis of Residence Time Distribution Patterns in A Twin Screw Cooking Extruder

The influence of a co‐rotating twin screw extruders controlling variables on its residence time distribution (RTD) patterns were measured and analyzed. Variables studied included: screw profile, throughput, screw speed, moisture content and die diameter. Throughput, screw speed and screw profile had strong influence on the mean residence time. Water content, die size and temperature did not.

Heat Transfer in Bakery Ovens

A wide assortment of ovens are available to the commercial baker. These include rack, reel, deck, continuous band, direct gas-fired tunnel ovens, tunnel ovens with enhanced convection and impingement or high velocity convection ovens. To highlight similarities and differences, heat transfer characteristics and air temperature profiles in common home and commercial ovens are discussed in this paper. Heat transfer coefficients were measured experimentally by heating blocks of aluminum in the ovens under test. Ovenable data collection systems recorded pertinent temperature-time data. A semi-log plot of dimensionless temperature against time was used to evaluate the heat transfer coefficients. Coated blocks of known emissivity were used to determine the separate radiation and convection contributions. Home electric and rotary reel ovens had similar heat transfer behavior. For oven temperatures of 150–200°C, overall heat transfer coefficients (h) of 14.2–17.0 W/m2K were obtained with blocks of 0.2 emissivity. Blocks of emissivity 0.88 raised h to about 28 W/m2K. Total h values of 15–30 W/m2K were recorded in low convection, commercial band ovens. Overall h values of 44 W/m2K were obtained in commercial impingement ovens with nozzle velocities of 11 m/s. Values as high as 170 W/m2K were obtained with nozzle velocities of 36 m/s at 150°C., It has been shown that a simple reproducible technique that permits ready comparison of ovens and quantification or radiation heat transfer has been developed. These attributes are valuable to the commercial baker.