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Njoku H.O.,University of Nigeria | Ekechukwu O.V.,University of Nigeria | Ekechukwu O.V.,National Universities Commission | Onyegegbu S.O.,University of Nigeria
Solar Energy | Year: 2016

This paper presents the performance assessment of stratified sensible thermal energy stores (SSTES) on the basis of the normalized exergy efficiency, η‾x. Assessments based on η‾x provide comparisons with performances of both the perfectly stratified and the fully mixed stores, which offer the best and worst performances, respectively. This is in contrast with energy and exergy efficiencies, which compare SSTES with only the perfectly stratified store. A dimensionless unsteady axisymmetric model of vertical cylindrical SSTES was implemented using a finite volume numerical scheme. The effect of some significant parameters on SSTES performance were considered by performing computations for aspect ratios (AR) between 1 and 4, Peclet number (PeD) varying from 5×103 to 100×103, Richardson number (Ri) varying from 10 to 104, and overall heat loss coefficients (U) varying from 0 to 100 W m−2 K−1. η‾x increases with PeD, Ri and AR, with the most significant increases occurring at low values of these parameters, and appreciable increases are no longer obtained beyond PeD≈30×103, Ri≈103 and AR≈3. η‾x also falls monotonically as the U values increase. © 2016 Elsevier Ltd

Njoku H.O.,University of Nigeria | Ekechukwu O.V.,National Universities Commission
International Journal of Sustainable Energy | Year: 2011

Results of exergetic performance analysis of three shallowsolar pond (SSP) types - the CSSP, the RASSPgc, and RASSPins - are presented for the first time. The study shows that the highest irreversibilities are encountered in the components of the RASSPgc and that better exergetic performances in SSPs may be obtained by improving the surface properties: absorptivity, reflectivity, and transmissivity. Steady-state analysis also shows that exergy 'losses' in the SSPs due to irreversibilities in their water masses are significant and result from the direct absorption of solar radiation. Transient analysis reveals that the RASSPgc achieves the highest overall exergetic efficiency (4.37%), followed by the RASSPins (3.96%) and then the CSSP (2.87%). At the end of a 24 h operation, the exergy content of the water masses in the RASSPgc and the CSSP is negligible, whereas the water mass in the RASSPins retains 0.057 MJ of the exergy accumulated during daytime heating. © 2011 Taylor & Francis.

Ibeagha O.A.,Raw Materials Research and Development Council | Onwualu A.P.,National Universities Commission
Agricultural Engineering International: CIGR Journal | Year: 2015

Castor is possibly one of Nigeria’s most under-appreciated assets. Its potential as an industrial raw material can be fully realized by a critical appraisal of its value chain. This article reviews castor value chain in Nigeria and identifies the constraints and strategies for improving its use as an industrial raw material. The strategies proposed can serve as a guide for castor value addition among operators and policy makers in a bid to maximize castor industrial potentials. A review of the uses of castor after value addition indicated that it can be used in over ten industries, namely; agriculture, food, paper, electronics and telecommunication, textile, pharmaceutical, cosmetic and perfume, paint, lubricant, plastic and rubber industries. Constraints such as insect and disease problems, weak input/service market, inadequate knowledge and skill, post-harvest losses and inadequate process technology serve as obstacles to successful value addition for castor. Strategies bordering on developing the input market, provision of quality seedlings and fertilizers, capacity development and development of farmers institutions were proposed to bridge the gaps, encourage value addition and ensure the development of castor as an industrial raw material. It is believed that if the recommendations are implemented, castor can attract up to 25 billion Naira (105,488,032 million dollars) to the Nigerian economy. © 2015, Int. Comm. of Agricultural and Biosystems Engineering. All rights reserved.

Ekechukwu O.V.,National Universities Commission | Sam-Amobi C.,University of Nigeria
30th ISES Biennial Solar World Congress 2011, SWC 2011 | Year: 2011

Preliminary survey on the energy profile and usage in selected hotels in the warm humid climate of South East Nigeria are presented. The survey shows the various energy sources utilized by the hotels. A detailed analysis of a number of physical and operational factors that may influence the energy use in the hotels is being carried out. The statistical methodology employed to determine the magnitude of effects of the factors; utility bill for one year, age of building, worker density, average monthly occupancy level, power for lighting, power for water heating, power for cooling, air-conditioning, lifts, kitchen equipment, gross floor area, year of construction, hotel class, weather, etc on energy use is described. The study would establish the energy use index (EUI) of the hotel buildings and determine the energy saving potential of the hotel buildings under the prevailing climatic conditions. The study reveals huge potentials for integrating renewable energy technology such as solar outdoor lights, solar water heaters and solar cookers to replace fuel wood in the hotels. It is anticipated that the results of the full study will lead to the development of an energy rating scheme and building energy code for hotel buildings in Nigeria.

Njoku H.O.,University of Nigeria | Ekechukwu O.V.,University of Nigeria | Ekechukwu O.V.,National Universities Commission | Onyegegbu S.O.,University of Nigeria
Energy and Buildings | Year: 2016

It is well established that stratification improves the performance of stratified sensible thermal energy stores (SSTES). A detailed review is presented of studies in which the contribution of stratification to the performance SSTES is assessed on the basis of energy and exergy analyses, and lately, entropy generation analysis. To obtain clear and useful distinctions between stratified and non-stratified stores, and for stores at different states of stratification, analyses that incorporate second law considerations (i.e. exergy/entropy generation) are required. Also, based on outcomes of computational fluid dynamics (CFD) simulations of SSTES, we present results of energy efficiency, ηe, normalized exergy efficiency, ηx, and entropy generation number, Ns, assessments of SSTES, corresponding to three possible approaches. Energy efficiencies, are shown to be limited in their ability to quantifying these improvements, while ηx is introduced as an improved exergy-based performance measure. Comparing ηx with Ns it is found that ηx is effective for assessing store performances prior to the exit of the thermocline from the store, while Ns offers useful assessments for the full duration of store operation. The parametric dependence of ηx and Ns on some significant dimensionless variables (Peclet number, PeD, Richardson number, Ri, and aspect ratio, AR) is such that as PeD, Ri and AR increase ηx increases. Ns decreases with increasing PeD and AR but the effect of Ri on it depends on the value of Ri. © 2016 Elsevier B.V. All rights reserved.

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