Performance analysis of double-pass oscillating bed solar dryer for drying of non-parboiled paddy grains

ABSTRACT

Drying of agricultural produce like paddy grains is necessary for reducing moisture content in them to the required level towards diminishing the deterioration and enhancing the storage time. Conventionally, open-space sun drying is widely used to reduce the moisture content of the most of the agricultural produce.. Now-a-day, so many solar dryers are used for drying agricultural produce. In the present work, a double-pass oscillating bed with a double-pass flat plate collector has been used for drying of non-parboiled paddy grains. The bed oscillated at a frequency of 2.75 Hz. The oscillating bed solar dryer can dry 45 kg of non-parboiled paddy grains in just a single day to the required level of moisture content, and the average moisture present in the dried grains was 13.55%. The average dryer thermal efficiency and pick-up efficiency in non-parboiled paddy were 28.79% and 52.17%, respectively.

KEYWORDS:

• Double-pass oscillating bed solar dryer
• double-pass solar flat plate collector
• dryer thermal efficiency
• pick-up efficiency

Nomenclature

T_di = Dryer inlet air temperature (°C)

T_do = Dryer outlet air temperature (°C)

T_a = Atmosphere temperature (°C)

T_ci = Collector inlet air temperature (°C)

T_co = Collector outlet air temperature (°C)

$C_{P_a}$ = Specific heat of atmosphere air (kJ/kg.K)

${\dot{m}}_a$ = Mass flow rate of air (kg/s)

h_fg = Latent heat of vaporization of water (kJ/kg)

m_w = Mass of moisture evaporated in time interval ‘dt’ (kg)

W_ai = Absolute humidity of air at the inlet of the bed (kg of water vapor/kg of dry air)

W_ao = Absolute humidity of air at the outlet of the bed (kg of water vapor/kg of dry air)

RH = Relative humidity (%)

η_d = Thermal efficiency of the dryer

η_p = Pick-up efficiency

A_c = Cross-sectional area of the flat plate collector (m²)

I = Solar irradiation (W/m²)