Browsing by Author "Nwaji, Godswill Nnabuihe"

Now showing 1 - 1 of 1
  • No Thumbnail Available
    ItemOpen Access
    Transient performance evaluation of diurnal heating and nocturnal cooling of water using a hybrid flat-plate solar collector/radiator
    (Federal University of Technology, Owerri., 2019-02) Nwaji, Godswill Nnabuihe
    Present energy dependence on fossil sources has been identified as the primary cause of the twin menace of global warming and climate change, hence the focus of the ensuing investigation on renewable energy resources to address the current environmental concerns. The transient performance evaluation of a hybrid solar collector/nocturnal radiator (SCONOR) for diurnal water heating and nocturnal water cooling is thus presented. The mathematical models of the physical system are based on the heat transfer mechanism in the SCONOR-bond-tube-water arrangement while for accumulative heating and cooling performances the models were based on lumped energy equations in the SCONOR and multi-zone stratification models in the thermal energy storage tanks. The resulting equations were discretized using finite element numerical scheme for ease of implementation in a digital computer. The transformed equations were solved using a scripted code written with FlexPDE finite element model builder and numerical solver version 7.12. The numerical results obtained from the models were compared with experimental data from literature sourced from three different climatic conditions. In the transient diurnal heating mode, the time of occurrence of SCONOR, bond, tube and water peak temperatures were accurately predicted while a mean deviation of 4-8.6oC was observed between the reported data and numerical predictions. For the transient nocturnal performance evaluation of the SCONOR, the model results closely matched experimental results with a mean deviation of less than 0.2oC, given that the initial conditions varied at about 7oC which was maintained throughout the nocturnal period with minimal fluctuations. The model results from a 24-hour performance cycle covering diurnal heating, cool down and nocturnal cooling of the SCONOR closely matched experimental results for the absorber and radiator functions of the hybrid system with mean deviations of 3-5 oC in the diurnal heating mode and 0.2-0.4oC in the nocturnal cooling mode. The accumulated performance results during the diurnal thermal storage and nocturnal thermal storage were also compared with available experimental data from literature, and the results show good agreement with mean deviations of 0.2-5 oC and 7oC during heating and cooling respectively. The thermal energy accumulated in the hot tank during diurnal heating maintained the modelled room temperature at approximately 5oC above ambient during the cold harmattan night and that accumulated in the cold storage tank maintained the modelled room temperature at 5.7oC below ambient during the hot day. From parametric analyses, the optimal design parameters are 0.26m, 0.003m, 0.1m, and 1 for the bond width, bond thickness, riser tube spacing and number of windscreen respectively. The overall results show that the developed models are useful design tools for the integrated diurnal water heating-and-nocturnal water cooling.