COMPARISON OF SOME ESSENTIAL AND HEAVY METALS IN THE TOENAILS AND FINGERNAILS OF SCHOOL-AGE CHILDREN IN KENYA

This paper describes the determination of the levels of lead (Pb), cadmium (Cd), zinc (Zn), calcium (Ca) and iron (Fe) in the toenails and fingernails of children under the age of six years in urban and rural areas in Kenya by atomic absorption spectrophotometer. Lead levels in urban areas ranged from 8.0-49.0 μg/g in fingernails and 7.0-62.0 μg/g in toenails as compared to those in rural areas (5.0-36.5 μg/g and 5.5-31.5 μg/g, respectively). A similar trend was observed for Cd where significantly high levels were found in children in urban areas than those in rural areas. The Fe and Zn levels were significantly higher in children in rural areas than those in the urban areas. The levels of all the metals studied were higher in the toenails except for Fe and Ca where the levels were higher in fingernails; however, the difference in the levels was not significant. These results indicate that either the toenails or fingernails can be used as a reference for levels of metals environmental exposure. KEY WORDS: Children, Essential elements, Heavy metals, Fingernails, Toenails, Kenya Bull. Chem. Soc. Ethiop. 2009, 23(1), 117-122

Numerical model to optimize the refrigerant charge for maximum refrigeration capacity

Refrigeration systems require optimal amount of refrigerant for maximum system performance. Undercharged or overcharged systems experience reduced efficiency and accessories deterioration. Optimal amount of refrigerant to be charged in a refrigeration system depends on the physical and thermal dynamic properties of the evaporator and the refrigerant. This paper presents formulation of a numerical model that can be used in determination of optimal amount of refrigerant charged in a system for maximum cooling rate as hence maximum system performance. Rayleigh’s method of dimensional analysis was used obtain the relationship between the maximum cooling rates of direct expansion evaporators as a function of thermodynamic properties of refrigerant R-134a, Different sizes of evaporator were fitted in the refrigeration system and charged with systematically varying amount of refrigerant until a maximum cooling rate was determined. The variation of pressures and temperatures both at the inlet and exit of the evaporator were observed and analyzed. The cooling rate of the numerical model formulated was compared with the cooling rate the actual physical refrigeration system. A t-test of 95% confidence interval indicated no significance difference between the numerical model, and the physical refrigeration system