Thermal Transport in a Multiple Jet Impingement Oven

Abstract

Three-dimensional numerical simulation of flow field and heat transfer in a jet impingement oven with multiple jets was carried out. Distribution of local heat transfer coefficient on a model cookie in the oven cavity was obtained from the predicted flow and temperature fields, and compared with the experimentally measured values. Effects of air temperature (400, 450K) and air velocity (2.5, 5, 10 m/s), on the surface heat transfer coefficient were studied. Numerical predictions showed good agreement with the experimental results. It was found that heat transfer coefficient was a strong function of air velocity while air temperature had no effect on the heat transfer coefficient. Local heat transfer coefficient values ranged between 11 and 66 W/m 2 K whereas average heat transfer coefficient values ranged between 24 and 42 W/m 2 K. Results also showed that because of the presence of the suction fan in the oven, flow field near the model cookie surface was quite different from that for a jet impinging on a flat surface.

An instrumented oven for the monitoring of thermal reactions during the baking of sponge cake

“…When the ventilation level was reduced, h c fell from 38 to 26 W m À2 K À1 , thus showing strong dependence on convection rather than temperature. These results are in agreement with those of Kocer and Karwe (2005), who found average values of 24-42 W m À2 K À1 in a jet impingement oven with air velocities ranging from 2.5 to 10 m/s for air temperatures ranging from 127-177°C. The relative contribution of radiative flux to total surface heat flux ranged from 22% to 42% for the tested temperature settings at maximum ventilation; it was substantially the same whatever the ventilation level.…”

Conjugate Heat Transfer Associated With a Turbulent Hot Air Jet Impinging on a Cylindrical Object

“…The governing equations for turbulent fluid flow, heat transfer and conduction heat transfer within a solid object are not given here for brevity. They have been described in many textbooks and papers (most recently by Kocer and Karwe 2005). The standard k‐ ε model (Arpaci and Larsen 1984; Jaluria and Torrance 1986) was used to simulate turbulence.…”

“…The lumped mass approach (Nitin and Karwe 2001; Kocer and Karwe 2005) was used to determine the average surface heat transfer coefficient ( h ). This approach is valid when the value of Biot number Bi (= h R/ k s ) is less than 0.1, where R is the radius of the cylinder and k s is the thermal conductivity of this solid.…”

Bakery product characteristics as influenced by convection heat flux

“…As well, Xue and Walker (2003) recently reported values up to 72.2 W/m 2 K for baking using an electrically heated air jet impingement oven, with the air velocity reaching about 9 m/s. Average values of 24-42 W/m 2 K were reported as heat transfer coefficients by Kocer and Karwe (2005) in a numerical simulation analysis validated with experimental data using a commercial jet impingement oven with air velocities ranging from 2.5 to 10 m/s and air temperatures ranging from 400 to 450 K (127-177°C). Those authors concluded that the h value was strongly a function of the air velocity but not the air temperature.…”

“…Thermodor developed the JetDirect oven using the Enersyst technology for domestic applications in order to cook starchy products in a fraction of the conventional baking time (Norris, Abbott, & Dobie, 2002). Kocer and Karwe (2005) reported average heat transfer coefficient values of 24-42 W/m 2 K using a Fujimak multiple jet impingement oven, and found that these values were strongly a function of air velocity ranging from 2 to 10 m/s.…”