Drying Efficiency, *η*

The drying efficiency, which gives the ratio of the energy used to evaporate moisture from the product to the energy provided by the drying air, was determined using Equation (3).

$$
\eta = \frac{M\_{ER}L\_v}{M\_{air} \mathbb{C} p\_{air} \Delta T} \times 100 \tag{3}
$$

where η = drying efficiency (%), *MER* = rate of moisture evaporation (kg/hr), *Lv* = latent heat of vaporization of water (kJ/kg), *Mair* = mass flow rate of air (kg/hr), *Cpair* = specific heat capacity of air (kJ/kg. ◦C) and Δ*T* = change in temperature between the ambient and drying air (◦C).

The drying efficiency was converted in specific energy values in MJoules per kilogram of moisture removed using Equation (4).

$$Specific\text{ Energy Consumption} = \frac{M\_{\text{Bioomass}} \times H\_{\text{Biomass}}}{M\_{\text{uv}}}.\tag{4}$$

where *MBiomass* = mass of biomass combusted during drying (kg), *Hv* = heat value of biomass (kJ/kg), *Mw* = mass of moisture removed from maize during drying (kg).

#### *2.2. Economic Performance Study*

The economic assessment on the column drying system was appraised from the perspective of a smallholder maize farmer using the discounted method where the time value of money is considered.

#### 2.2.1. Case Study Scenario

The following assumptions were made for the scenario considered for the study:


**Figure 4.** Schematic description of the model scenario considered in the study.
