The effects of drying parameters on heat transfer during drying of fermented ground cassava in a rotary dryer were studied. The fermented ground cassava was dried in a bench-scale rotary dryer at different inlet air temperatures, inlet air velocities, relative humidities, feed rates, drum drive speeds, and feed drive speeds. It is shown that inlet air temperature, inlet air velocity, and feed rate have significant effects on the specific heat transfer coefficient and heat load in the material. Models that predict the specific heat transfer coefficient as a function of inlet air temperature and inlet air velocity and the heat load as a function of inlet air temperature, inlet air velocity, and feed rate are also presented. Predictions of the models are compared with experimental data and good agreement is obtained.

Effects of Drying Parameters on Heat Transfer during Drying of Fermented Ground Cassava in a Rotary Dryer

Summary
Composite wheat–cassava and wheat–maize flours were produced in ratio 100:0. 60:40, 50:50, 40:60 and 0:100 respectively. Thermo-physical properties of bread dough were determined. For wheat –cassava composite bread dough, moisture content ranged between 44.02 ± 2.04 to 51.31 ± 2.99% dry basis (db), density (1035.2 ± 20.4 to 975.6 ± 12.6 kg m−3), specific heat capacity (2.51 ± 0.61 to 3.01 ± 0.42 kJ kg−1 K) and thermal conductivity (0.362 ± 0.13 to 0.473 ± 0.12 W mK−1). While wheat–maize mixture gave 44.14 ± 1.94 to 45.09 ± 1.26%(db) of moisture content, 981.4 ± 16.3–960.4 ± 22.5 kg m−3 density, 1.77 ± 0.17–2.61 ± 0.63 kJ kg−1 K specific heat capacity and 0.36 ± 0.07–0.39 ± 0.02 W mK−1 thermal conductivity. Effects of substitutions was significant on moisture content and thermal conductivity of dough while non significant influence was recorded on density and specific heat capacity at P < 0.05.

Thermo-physical properties of composite bread dough with maize and cassava flours

Central composite rotatable of response surface methodology experimental design was used to determine effect of mash quantity and roasting duration on physical, pasting and sensory properties of gari. Five levels of quantity (317, 400, 600, 800 and 882.2 g) and roasting time (37.1, 35, 40, 45 and 47.1 min) were used at a fixed roasting temperature (95oC). The responses were moisture, pH, bulk density, water absorption capacity, swelling index, and peak, trough, breakdown, final and setback viscosities, peak time, pasting temperature and acceptability of the products. Moisture content, pH, bulk density, water absorption capacity and swelling index of the samples were (11.1 – 18.8 %), (2.4 -3.4), (1.02 – 1.11 g/cm3), (2.0 – 5.4 ml/g) and (2.4 – 3.4 ml/ml) respectively. Among the physical properties determined, only bulk density was not significantly (p > 0.05) affected. Peak and break down viscosities were not significantly (p > 0.05) affected, while other pasting properties studied (trough, final viscosity, set back viscosity, peak time and pasting temperature) were significantly (p < 0 .05) affected by mash quantity and roasting duration. Recorded mean were peak 1907.58 ± 983.3 RVU, trough 1987.42 ± 501.89 RVU, break 228.15 ± 280.43 RVU, final 3827.46 ± 735.51 RVU, set back 1840.04 ± 419.75 RVU, peak time 6.38 ± 0.66 min and pasting temperature 54.02 ± 3.82oC. All samples roasted for more than 35 min were poorly rated.

Effect of mash quantity and roasting duration on some physical and pasting properties of gari.

Summary

The effect of variety on the heat transfer coefficient of four cassava cultivars (TMS 30555, TMS 30572, NR 8082 and one Native type) was investigated. The cultivars were dried at an air temperature of 142 °C, air velocity of 1.397 m/s−1 and relative humidity of 55%. The heat transfer coefficient obtained varied from 0.0622 to 0.0725 kJ kg s °C. The heat transfer coefficient varied for some cultivars, while some cultivars had close heat transfer coefficient. NR 8082 had the lowest heat transfer coefficient while TMS 30555 had the highest heat transfer coefficient. The cultivars with high heat transfer coefficient were found to have low bulk density, smaller particle diameter, high drying rate, low specific heat capacity and high carbohydrate fat and protein contents than other cultivars.

Friday E. Akpan

Papers

Effect of variety on the heat transfer coefficient during drying of fermented ground cassava