Determination of thermal conductivity and convective heat transfer coefficient during deep fat frying of “Kroštula” dough

In this study, the influence of oil temperature, water migration and surface temperature of “Kroštula” dough on convective heat transfer coefficient was investigated. The convective heat transfer coefficient during deep fat frying was determined at temperatures 160, 170, 180 and 190±1 °C. Heat transfer coefficient was the highest at the start of deep fat frying process; 579.12±2.46, 583.88±1.81, 597.05±1.10 and 657.91±0.95 W/m² K for 160, 170, 180 and 190 °C of oil temperature, respectively. The smallest heat transfer coefficient was in the case of setting up a uniform period of water migration from sample, which corresponded to surface temperatures slightly higher than 100 °C; 26.53±0.63, 14.42±0.56, 56.78±0.49 and 37.52±0.54 W/m² K for 160, 170, 180 and 190 °C of oil temperature, respectively. Higher oil temperature for deep fat frying increased values of heat transfer coefficient. A steady-state method was used to determine thermal conductivity of “Kroštula” dough in temperature range of 40–70±1 °C. The thermal conductivity first increased with temperature and then after reaching maximum values decreased. The maximum value 0.5985±0.0196 W/(m K) was determined at 47.5 °C. The minimal value 0.4723±0.0192 W/(m K) was determined at 65 °C.