Moisture dependent mechanical and thermal properties of Locust bean (Parkia biglobosa)

Abstract

The mechanical and thermal properties of African locust bean (Parkia biglobosa) seeds were investigated as a function of moisture content in the range of 5.9%–28.2% dry basis (d.b.).  These properties are required for the engineering design of equipment for handling and processing locust bean.  Universal Testing Machine was used to determine the mechanical properties at 5 mm/min load rating transversely.  Normal and shear stresses were determined for 200–500 g loads at 100 g interval.  Specific heat and thermal conductivity were determined using the method of mixtures and steady-state heat flow method respectively.  Linear decreases in rupture force (214.42–129.86 N) and rupture energy (109.17–73.46 N mm) were recorded, while deformation of the seed samples increased (0.98-1.13 mm).  Linear increase in normal stress at 200, 300, 400 and 500 g loads were 8.38–8.69, 9.39–9.70, 10.40–10.71 and 11.41–11.72 g/cm² respectively, while shear stress ranged from 0.589 to 0.845, 0.688 to 0.998, 0.638–1.213 and 0.688–1.359 g/cm² at 200, 300, 400 and 500 g with increasing seed moisture content.  The specific heat and thermal conductivity of locust bean increased from 2.74 to 4.38 kJ kg^{-1 o}C^-1 and 0.052 to 0.118 W m^{-1 o}C^-1 respectively.  Seed moisture content effect was statistically significant (p<0.05) on all properties investigated except rupture force, rupture energy and thermal diffusivity while baseline data were generated for the development of necessary handling and processing equipment.

Keywords: bulk density; deformation; rupture force, shear stress, moisture content, thermal conductivity