Development of a dual purpose refrigeration system for domestic use

Refrigeration and air conditioning are very important in the daily activities of man, particularly in the tropical regions of the world; used in the preservation of perishable items, storage of pharmaceutical drugs, controlling of an atmospheric environment either for human/animal thermal comfort or effective performance of a scientific process. This paper is aimed at the design and construction of a dual purpose domestic refrigeration system, that can simultaneously function as a refrigerator and as well as an air conditioner henceforth known as REFACON. The refrigeration system employed was a vapour compression system. The machine was a split configuration with an Indoor and an outdoor unit (condensing unit). The machine used a singular 1,119 W single phase hermetically sealed reciprocating compressor, a fabricated condenser and split evaporator operated by temperature controlled solenoid valve. The system used 0.620 kg of R 22 refrigerant, with a discharge pressure of 1,355 kPa and suction pressure of 360 kPa. The input power was 1,350 W with an output cooling effect of 5,280 W. The combined cooling load/cooling capacity of the machine was 4,500 W. The results of tests conducted showed a total heat rejected of 6,680 W and a total evaporator heat absorption of 5,179 W. The Energy Efficiency Ratio was 3.91 while the Coefficient of Performance was 4.72. This research has shown that the design employed for the heat exchangers was appropriate and Thermal contact resistance cannot be neglected. http://dx.doi.org/10.4314/njt.v35i4.1

Influence of Some Variable Parameters on Horizontal Elliptic Micro-Channels with Internal Longitudinal Fins

The study investigates the laminar flow and heat transfer characteristics in elliptic micro-channels of varying axis ratios and with internal longitudinal fins, operating in a region that is hydrodynamically and thermally fully developed; purposely to determine the effects of some salient fluid and geometry parameters such as Reynolds number, Prandtl number, aspect ratio ( and fin heights on flow pattern and rate of heat transfer. Numerical method using the finite difference technique was adopted for the solution. A code in Quick Basic was developed to generate the results. Results show that fin height of H=0.6 provided the optimum heat transfer enhancement for the configuration of e = 0, e= 0.433 and e=0.714; for e=0.866, fin height of H= 0.4 is tolerable. Result also show that Nusselt number increases with Reynolds number for all axis ratios investigated. However, at Re=200 a slight trough was observed in Nusselt number Versus Reynolds number relationship indicating a critical flow condition. It was also established that at , Nusselt number and bulk fluid temperature, are independent of fluid properties

Comparative study of biogas from cattle dung and mixture of cattle dung with plantain peels

This paper compares the rate of biogas production of cattle dung and a mixture of plantain peels with cattle dung. 18kg of cattle dung mixed with 36kg of water were charged to a digester while 9kg each of cattle dung and plantain peels mixed together with 36kg of water were charged to a separate digester. Both digesters were filled to three quarter of their capacity of 88litres. They were subjected to anaerobic digestion for forty days. The digesters were made of mild steel 2mm thick. 297K more characteristic of the ambient temperature was the lowest and 303K which was more of the digesters temperatures were the maximum temperatures recorded. 13998.88N/m2 and 27864.44N/m2 were respectively the initial and highest pressures for the cattle dung digester while 19331.79N/m2 and 27931.10N/m2 were observed as the initial and highest pressures for that of the cattle dung and plantain peels mixture. Also 8.4m3/kg and 17416.2m3/kg of estimated specific volumes were obtained for the cattle dung digester in the same manner. Conversely 6.1m3/kg and 27480.7m3/kg were estimated initial and cumulative specific volume for the biogas in cattle dung with plantain peels mixture digester. It was therefore concluded that the mixture of cattle dung with plantain peels produced more biogas than only the cattle dung.Keywords: Comparative, study, biogas, cattle dung, mixture, plantain peel