Performance enhancement using appropriate mass charge of R600a in a developed domestic refrigerator

This paper presents performance analysis of a domestic refrigeration system using R600a as refrigerant. Investigation was conducted experimentally to select an appropriate refrigerant mass charge for the system and to compute the cooling system performance characteristics under ambient temperature of 29 oC. The choice of the hydrocarbon refrigerant (R600a) became so imperative due to notable influence of chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) on global warming and ozone depletion. UNFCCC and Montreal Protocol regulation have banned the use of halogenated refrigerants in cooling and heating systems. The paper reveals that the power consumed by the system using mass charge of 15 g refrigerant was reduced by 9.3 and 10.9% compared with the 10 and 25 g refrigerant mass charges respectively. In addition, the results show that the coefficient of performance (COP) of the refrigeration system while working with 15 g is 24.7 and 20.2% higher than when the system worked with 10 and 25 g refrigerants mass charge respectively. More so, the system attained an evaporator air temperature of -12 oC in 2 hours, which makes 15 g charge refrigerant appropriate for the running of the developed system that has a volume capacity of 68 liters

Development and performance evaluation of locally fabricated thermal conductivity apparatus

This paper presents the design and construction of a Guarded Hot Plate (GHP) apparatus for the accurate assessment of thermal conductivities of some Nigerian local building materials. The GHP apparatus is a steady-state measurement device. This apparatus is designed to measure the thermal conductivities of masonry building materials of different compositions. The design features included hot and cold plates fabricated with aluminum plates of 6 mm thickness and varying dimensions; the guard plates also made of aluminum, but of 6.35 mm thickness, forms a rigid enclosure for the specimen all encased in a mild steel housing. The operating measuring temperature range is from -20 for varying specimen thickness up to 60mm. Results are presented for concrete, laterite, and a mixture of cement with laterite, clay, and sand respectively, and it covers a range of thermal conductivities of 0.77W/mK to 1.80 W/mK. Moisture effect on concrete was recorded for the lightweight concrete as the thermal conductivity value reduced from 1.80W/m.K to 1.32W/m.K for the oven-dried concrete sample over a 1.5% (by weight) reduction in water content. The performance evaluation of the locally fabricated GHP apparatus showed a 3.03% percentage difference over ASHRAE’s published data on oven-baked concrete thermal conductivitie

Figures of Merit for Wind and Solar PV Integration in Electricity Grids

349-357In future electrical grids, high levels of Variable Renewable Energy (VRE) penetration including solar photovoltaics (PV) and wind energy is expected. This poses a challenge in system operation and planning especially in balancing electricity demand and supply. This paper examines figures of merit for wind and solar integration in electricity grids. Quantitative tools such as load duration curves, correlation analyses, and the Fourier transform were used to study the intermittency/variability of wind and solar PV power. Time series data on power production from the European Network of Transmission System Operators for Electricity (ENTSO-E), and Réseau de Transport d'Électricité (RTE) were used for the analyses. The analyses illustrate that despite the valuable amount of energy that can be obtained from wind and solar PV, these energy sources cannot be used as baseload power supply. Solar PV power is available for approximately 50% of the time year-round. Wind power output on the other hand can reach very small magnitudes of just a few megawatts several times in a year. More to that, wind is positively correlated over long distances, even exceeding 3000 km and aggregating wind fleets over a large geographic area might not guarantee continuous availability of wind power. Nonetheless, these sources can still be integrated in electricity grids in high proportions, provided intermittency mitigation options such as energy storage, curtailment, and demand-response are implemented

Evaluation of biogas yield and kinetics from the anaerobic co-digestion of cow dung and horse dung: a strategy for sustainable management of livestock manure

In this study, investigation was done to deter�mine the optimum combination of cow dung (CD) and horse dung (HD) for enhanced biogas production and plant stability. Anaerobic co-digestion of CD and HD at varying percentage combination was carried out in five (5) identical 25 L cylindrical digesters (A–E) for a retention period of 37 days, at an average ambient temperature of 33 �C. Using the Microsoft excel solver function, 2010 version,the modified Gompertz model was applied to predict the relevant kinetic variables of the digestion process. Result obtained shows that digester D with 25% CD and 75% HD produced the highest daily biogas, followed by C (50% CD and 50% HD), B (75% CD–25% HD), A (100% CD) and E (100% HD). Digester D also had maximum biogas pro�duction potential (A) of 13.8 L/gVS, maximum biogas production rate (l) of 0.69 L/gVS/day and shortest lag phase (k) of 5.20 days. Digester E with 100% HD, though had a short lag phase of 5.72 days, had the least total biogas yield of 5.1 L/gVS. The closeness of the coefficients of determination (R2) to 1 reflects a good fit, between experimental and simulated data. The study found that increase in the amount of cow dung beyond 25% led to decrease in biogas yield. It has also shown that biogas production from CD and HD is feasible and can serve as way of removing CD and HD from the environment while serving as a source of bioenergy. Further study on best ways of pre-treating the substrates for greater biogas yield is recommended

Characterization of Lignocellulosic Biomass Samples in Omu-Aran Metropolis, Kwara State, Nigeria, as Potential Fuel for Pyrolysis Yields

This study deals with a preliminary investigation of biomass samples' physicochemical, structural composition, and thermal properties to aid the appropriate selection of biomass utilized for pyrolysis operation. The proximate, ultimate, structural composition and thermal analyses were conducted using seven lignocellulose biomass samples obtained in Ajase market, Ajasse Ipo, Kwara State, Nigeria, and Omu-Aran, Kwara State, Nigeria. Results showed that the average moisture contents (MC) ranged from 0.12 to 0.44%, and volatile matter (VM) ranged from 73.70 to 83.82%. Fixed carbon (FC) varied from 12.79 to 22.80%, and Ash contents varied between 01.20 to 5.52%. Similarly, the average carbon contents ranged from 45.11 to 50.00%. Hydrogen contents ranged from 5.38 to 6.15%, nitrogen contents varied between 0.20 to 1.24%, and oxygen contents from 43.79 to 48.51%. Also, sulphur contents varied between 0.01 to 0.19%, while the biomass species' average cellulose, hemicellulose, and lignin contents ranged from 28.34 to 45.80%, 25.83 to 34.01%, and 21.96 to 49.63% respectively. The high percentage of VM, C, H, HHV, ignitability index, cellulose, and hemicellulose content recorded in the biomass samples would enhance devolatilization reactivity, ignitability, and burn gases in the reactor, as well as a good production of hydrocarbons content during the pyrolysis process. Also, the low ash content would prevent harmful chemical deposits in the reactor during the pyrolysis process. It can be deduced that shea butter wood was best suited for biofuel generation, closely followed by sugarcane bagasse and palm kernel shell. At the same time, corn cobs possessed the least properties for the pyrolysis process

Behavioural Study of High Carbon Steel Material in Hot and Cold Working Media: A Review

Due to its exceptional mechanical properties, such as its high strength and hardness, high-carbon steel is utilised extensively in various industries. The way of behaving of high-carbon steel is impacted by various handling strategies, for example, hot working and cold working, which can influence its microstructure and mechanical properties. The review aims to Study the behaviour of high-carbon steel material in hot and cold working media. Also, to look at the effects of hot and cold working on the macrostructure of the high carbon steel and the mechanical properties such as hardness, comprehension, impact tests, tensile stress and strain analysis. From the review, the hot and cold working processes, such as bending, rolling, and squeezing, for the result obtained from the hardness test shows the hardness value for hot rolling is higher than that of cold rolling (it is generally expected for hardness obtained from cold rolling should be higher than that from hot rolling) this may be due to the variations in the rolling parameters. While the hardness obtained from cold bending s higher than that from hot bending, and the hardness value obtained from hot squeezing is higher than that of cold squeezing. The results for hot bending of high-carbon steel show improved ductility and reduced risk of cracking compared to cold bending. This viable finding is highly significant to manufacturers to enable the production of sustainable materials for structural applications

Figures of Merit for Wind and Solar PV Integration in Electricity Grids

In future electrical grids, high levels of Variable Renewable Energy (VRE) penetration including solar photovoltaics (PV) and wind energy is expected. This poses a challenge in system operation and planning especially in balancing electricity demand and supply. This paper examines figures of merit for wind and solar integration in electricity grids. Quantitative tools such as load duration curves, correlation analyses, and the Fourier transform were used to study the intermittency/variability of wind and solar PV power. Time series data on power production from the European Network of Transmission System Operators for Electricity (ENTSO-E), and Réseau de Transport d'Électricité (RTE) were used for the analyses. The analyses illustrate that despite the valuable amount of energy that can be obtained from wind and solar PV, these energy sources cannot be used as baseload power supply. Solar PV power is available for approximately 50% of the time year-round. Wind power output on the other hand can reach very small magnitudes of just a few megawatts several times in a year. More to that, wind is positively correlated over long distances, even exceeding 3000 km and aggregating wind fleets over a large geographic area might not guarantee continuous availability of wind power. Nonetheless, these sources can still be integrated in electricity grids in high proportions, provided intermittency mitigation options such as energy storage, curtailment, and demand-response are implemented