Measurement of coupled heat and moisture transfer coefficients for selected vegetables

Two experimental devices, Capped Column and Open Column, were used to measure four heat and mass transfer coefficients of four vegetables: potato, yam, buttersquash and turnip. Two classical coefficients, thermal conductivity, K_T, and moisture diffusivity, D_M, and two coupled coefficients, moisture gradient induced heat transfer coefficient, K_M, and temperature gradient induced moisture migration coefficient, D_T (or δ₁ = D_T/U_M), were measured. The mean measured values of K_T obtained for potato, yam, buttersquash and turnip were 0.50, 0.58, 0.54 and 0.51 W/m-K, respectively. The mean measured values of K_M for potato, yam, buttersquash and turnip were 117.1, 32.8, 41.0 and 190.8 W/m, respectively, of δ_T were 0.00059, 0.00065, 0.00024 and 0.00047 per degree K, respectively and of D_M were 1.32×10^.9, 1.16×10^-9, 1.92×10^-9 and 1.58×10^-8 m^?2/s, respectively. Smaller intercellular spaces seemed to have a positive effect on the thermal conductivity. Moisture content and size of intercellular spaces both seemed to have a positive effect on K_M. The value of δ_T was lower for vegetables with higher moisture content which is consistent with the results reported in literature. The value of D_M seemed to be positively affected by both the porosity and the size of the intercellular spaces in the test vegetables.