| The development of cheap,inexhaustible,effective and green energy will have huge longer-term benefits.It will increase countries' energy security through dependence on indigenous,inexhaustible resources.It will improve sustainability,reduce pollution and lower the costs of alleviating climate change effects,and keep fossil fuel prices lower than otherwise.In the recent years,solar technologies are being studies investigated to improve the effective use of solar energy though research and development.Crystalline silicon solar cells are capable of converting about 20%of absorbed light energy into electricity.Multi-junction(2-terminal,monolithic)and concentrated solar cells can also convert more than 30%of absorbed light energy in the solar spectrum into electricity.The remaining 70%of absorbed energy increases solar cells temperature and generate heat inside the solar cell.This is a big research challenge that the Chinese research community has been working on for the past decades to address.In order to solve this problem and utilize the solar photovoltaic(PV)cell at a low operating temperature,researchers have been focusing on cooling the solar cells and taking advantage of the heat dissipated from the solar cell using fluid channels at the rear of the solar cell or heat pipe.A typical system that demonstrated these concepts to improve solar cells performance is known as solar photovoltaic thermal(PV/T)hybrid system.PV/T(photovoltaic/thermal)collector system combines a photovoltaic(PV)module and a traditional solar thermal collector in the same frame to convert solar radiation into electrical and thermal energy simultaneously.The PV/T technology is maturing through reseach.Its application and penetration are increasing for electricity generation,solar water heating,and solar air heating.The solar radiation utilization efficiency is higher with PV/T as well as the outputs.Micro-channel heat pipes(MHP)can transfer heat excellently due to the micro nature of its pores.MHP also present more surface to the working fluid due to its microscopic nature compare conventional heat pipes.Although researchers recognize the effectiveness of micro-channel heat pipes(MHP)over conventional heat pipes,there were hardly any studies designed to examine its performance with PV/T.MHP are used in electronic systems to remove a large amount of heat and was only reported by limited studies in solar thermal energy conversion area.Compared to conventional heat pipes such as round tubes heat pipes(RTHP),it has better heat transfer capacity,lower pressure difference,lower filling ratio and more compact structure.It also has the advantage of eliminating a cost and product thickness.The MHP is a high-efficiency heat transfer unit,relying on a phase transition of the refrigerant to transport a large amount of heat.The MHP is a thin aluminium plate,which contains many independent micro-channes.In each micro-channel,there are many inner micro-grooves(or micro-fins)that provide a large surface to the working fluid for quicker evaporation and enhance the heat transfer.For each MHP,there are two parts:evaporator section and the condenser section.As the MHP used in the study is made of aluminum,it is easily manufactured and can be bent into different shape.The typical size of an MHP is 3 mm in thickness and 60 mm in width.The length can be determined according to the demand of particular applications.Even though some studies on the heat pipe PV/T have been conducted,there are still poor heat transfer and freezing challenges that must be addressed through research.The proposed study is tailored to solve all these challenges and the originality of this research work contain sufficient contributions to the new body of knowledge from the international perspective since this novel the MHP-PVT has not been examined so far..Previous studies focused only on the use of circular heat pipes,higher cost and technical difficulty in manufacturing;·Smaller contract area with larger thermal resistance is a challenge associated with the use of circular shape heat pipes;.The condenser sections of the RTHP were in direct contact with the water,as such rusting and scaling were inevitable.The main activities of this study are summarized as follows:a)A novel MHP array solar photovoltaic/thermal system(MHP-PV/T)was designed and constructed to investigate performance characteristics of the MHP-PV/T.The proposed design configuration combined solar cells and wide MHP that were filled with a prescribed amount of acetone as refrigerant under a vacuum condition in the same insulated frame to simultaneously provide electrical and thermal energy.The daily electrical efficiencies of the proposed MHP PV/T and conventional PV/T were 7.8%and 7.9%respectively.The instantaneous thermal efficiencies were also calculated for the warmer day.The results indicated daily average thermal efficiencies of 43.3%and 41.7%for the novel and conventional PV/T system respectively.Heat and mass transfer performance characteristics of the MHP-PV/T system as well as the transient behavior of the MHP were also examined using MATLAB.Parametric analysis and heat transfer limitations of the MHP were investigated in this paper to establish a linear relation between the thermal instantaneous efficiency and the reduced temperature parameter of the system.The transient behavior of the MHP shows a faster thermal response to heat input within the temperature range of 48.8 ?-49.2 ?and slower response when the thermal diffusivity was reduced to 0.05cm2/s.b)Dynamic models of the MHP-PV/T system were proposed,and the experimental results of the systems were used to validate the simulation outputs from the developed models.To compare the simulation results with the experimental measurements,the RMSD(root mean square deviation)were used to estimate the performance of the models.The results reveal good agreements between model simulation and experimental measurement with sufficient confidence.The RMSD values the evaporator and condenser section of the MHP was 3.6550%and 0.6065%respectively.This indicates that the performances of the developed surrogate models were better and can be considered sufficient and accurate enough to simulate the PV/T under different climatic conditions. |
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