It is observed that at all moisture contents, thermal conductivity of guava fruit increases with increase in time. But at lower moisture levels Thermal conductivity is relatively low with higher moisture levels with increase in temperature or time. Because, as the moisture evaporates the sample shrinks and the rate of shrinkage in the initial stage of heating is more, leading to porosity i.e. entrapped air which is a bad conductor of heat, hence decrease in the thermal conductivity [17] and [18].
It is observed that thermal conductivity increases with increase in time at all moisture contents. The analysis shows that at higher moisture contents (70% and 80% (wb)), thermal conductivity values lie in the range of 0.3027 W/m °C to 0.5775 W/m °C and 0.3210 W/m °C to 0.6037 W/m °C results in increased thermal conductivity. Similarly at lower level moisture contents (50% and 40% (wb)), the thermal conductivity values lie in the range of 0.265 W/m °C to 0.5019 W/m °C and 0.1526 W/m °C to 0.4595 W/m °C respectively. This is due to low density, void spaces present and non-homogeneity in the sample structure apparently causes the reduction the thermal conductivity.
The variation of thermal conductivity with respect to center temperature of guava fruit (at different instant of time) in the range of 40% to 80% (wb) moisture content for densities D1 and D2 are shown in Fig. 4 and Fig. 5 respectively.