Abstract:
Black pepper is an agricultural crop that is extensively used as a spice and as an additive in
numerous other applications. Postharvest drying of pepper is an important step to enhance the
pepper quality and shelf life. Among many types of dryers spouted bed dryer is suitable for
wide range of agricultural products. Knowledge on mass transfer analysis in the drying process
is vital for improvements in the drying process and for dryer design. In this study, nondimensional
analysis of the mass transfer process of black pepper drying, in a spouted bed
dryer was performed. Experimental results of a research conducted on black pepper drying
using a conventional spouted bed dryer along with a cyclone separator was used for the
analysis. The drying experiments were conducted to study the effect of operating variables;
inlet air temperature, bed height and air velocity.
Non- dimensional analysis of mass transfer coefficient was employed using the Buckingham
pi theorem and the data generated in a series of black pepper drying experiments in a spouted
bed dryer were used to develop the model equation. The model consists of dimensionless
parameters; Sherwood (Sh) number, Reynolds (Re) number, Schmidt (Sc) number and bed
height to particle diameter (H/dp). R software (Version 4.1.2) was employed for the
determination of the coefficients of the model using the non-linear regression method and for
statistical analysis. The model shows mass transfer coefficient is a function of the inlet air
temperature, air velocity, dynamic viscosity of air, moisture diffusivity, bed height and air
density.
The mass transfer coefficient values predicted from the developed correlation varied between
0.012 m/s and 0.032 m/s. The model predicted results were validated against experimentally
determined values of mass transfer coefficients. The experimentally estimated mass transfer
coefficients varied between 0.012 and 0.031 m/s and were in good agreement with model
predicted values. Further, mass diffusivity values of the drying process varied between 2.87 x
10-5 – 3.6 x 10-5 m2/s.
The results show that an increase in inlet air temperature reduces the mass transfer coefficient
and the Sh number. However, increase in air velocity increases the mass transfer coefficient,
which is in agreement with available relations for other similar products. Furthermore, mass
transfer coefficient values decreased while increasing static bed height. This is an acceptable
trend because of lower turbulence created by the higher static bed and the spouting of more
particles in the higher bed rather than lower static bed heights.
Citation:
Abeysooriya, S.H. (2023). Non-dimensional analysis of mass transfer in a spouted bed dryer for black pepper drying [Master’s theses, University of Moratuwa]. Institutional Repository University of Moratuwa. http://dl.lib.uom.lk/handle/123/22811