Abstract: A geoelectric survey was carried out in some parts of
Angwan Gwari, an outskirt of Lapai Local Government Area on
Niger State which belongs to the Nigerian Basement Complex, with
the aim of evaluating the soil corrosivity, aquifer transmissivity and
protective capacity of the area from which aquifer characterisation
was made. The G41 Resistivity Meter was employed to obtain fifteen
Schlumberger Vertical Electrical Sounding data along profiles in a
square grid network. The data were processed using interpex 1-D
sounding inversion software, which gives vertical electrical sounding
curves with layered model comprising of the apparent resistivities,
overburden thicknesses, and depth. This information was used to
evaluate longitudinal conductance and transmissivities of the layers.
The results show generally low resistivities across the survey area
and an average longitudinal conductance variation from
0.0237Siemens in VES 6 to 0.1261Siemens in VES 15 with almost
the entire area giving values less than 1.0 Siemens. The average
transmissivity values range from 96.45 Ω.m2 in VES 4 to 299070
Ω.m2 in VES 1. All but VES 4 and VES14 had an average
overburden greater than 400 Ω.m2, these results suggest that the
aquifers are highly permeable to fluid movement within, leading to
the possibility of enhanced migration and circulation of contaminants
in the groundwater system and that the area is generally corrosive.
Abstract: This paper presents effects of the mean operating
pressure on the optimal operating frequency based on temperature
differences across stack ends in a thermoacoustic refrigerator. In
addition to the length of the resonance tube, components of the
thermoacoustic refrigerator have an influence on the operating
frequency due to their acoustic properties, i.e., absorptivity,
reflectivity and transmissivity. The interference of waves incurs and
distorts the original frequency generated by the driver so that the
optimal operating frequency differs from the designs. These acoustic
properties are not parameters in the designs and be very complicated
to infer their responses. A prototype thermoacoustic refrigerator is
constructed and used to investigate its optimal operating frequency
compared to the design at various operating pressures. Helium and air
are used as working fluids during the experiments. The results
indicate that the optimal operating frequency of the prototype
thermoacoustic refrigerator using helium is at 6 bar and 490Hz or
approximately 20% away from the design frequency. The optimal
operating frequency at other mean pressures differs from the design
in an unpredictable manner, however, the optimal operating
frequency and pressure can be identified by testing.