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[en] Highlights: • Conic geothermal basket heat exchanger (CBGHE) is experimentally investigated. • Charging and discharging processes of CBGHE are evaluated. • Energy and exergy efficiencies of CBGHE are performed. • High and stable performance of surface geothermal energy in Tunisia is established. - Abstract: Geothermal heat exchangers system composed of two conic baskets serially connected is designed and realized. Both heat exchangers are made in polyethylene high-density material and have a length of 3 m each one. They will be used for greenhouse cooling and heating through a geothermal heat pump. Its conical geometry is selected to reduce the operation cost and the exploited area, compared to vertical and horizontal geothermal heat exchangers often used. It also assures the maximum of heat exchange with the soil. The aim of this study is to determine the thermal performance of one Conic Basket Geothermal Heat Exchanger (CBGHE), buried at 3 m deep, in the exploitation of the soil thermal potential, in summer. A rate of heat exchange with the soil is determined and the global heat exchange of the CBGHE is assessed. Its energy and exergy efficiencies are also evaluated using both first and second law of thermodynamic. Results show that the specific heat exchange ranges between 20 W m"−"1 and 50 W m"−"1. Maximal energetic and exergetic efficiencies of the CBGHE, equal to 62% and 37% respectively, are reached for a mass flow rate of 0.1 kg s"−"1. For this value of mass flow rate, the overall heat exchange coefficient is of 52 W m"−"2 K"−"1.
[en] Highlights: • We studied a thermosyphon solar water heater composed of high-performance components. • A differential equations solution technique is investigated. • The influences of the collector and storage losses on the system performance were examined. • The storage losses have more influence on the long-term performance. - Abstract: A glassed flat plate collector with selective black chrome coated absorber and a low wall conductance horizontal storage are combined in order to set up a high performance thermosyphon system. Each component is tested separately before testing the complete system in spring days. During the test period, effect of different inlet water temperatures on the collector performance is studied and results have shown that the collector can reach a high efficiency and high outlet water temperature even for elevated inlet water temperatures. Subsequently, long term system performance is estimated by using a developed numerical model. The proposed model, accurate and gave a good agreement with experimental results, allowed to describe the heat transfer in the storage. It has shown also that the long-term performances are strongly influenced by losses from the storage than losses from the collector
[en] Highlights: • Experimental study of the new solar air heater with latent heat. • Energy analysis of solar air heaters with and without latent storage energy. • The daily energy efficiency of the solar air heater with phase change materials is 33%. - Abstract: In the present work an experimental study is made to enhance the efficiency of a simple fabricated Solar Air Heater (SAH) by using the thermal heat storage. A rectangular cavity filled with a Paraffin wax is used as a latent storage unit. An experimental study of two similar designed solar air collector (with and without Phase Change Material), is carried out to evaluate the PCM unit importance. The results show that during the night the outlet air temperature of the SAH was enhanced with using PCM. The daily energy efficiency of the SAH without PCM reached 17%, while the daily energy efficiency of the SAH with PCM reached 33%.
[en] Highlights: • Medium temperature parabolic trough solar collector for cooling. • Optical evaluations using photogrammetric technique. • Parabolic reflector surface deformation and slope errors identifications. • Intercept factor determination. • Thermal performance of the parabolic trough medium temperature evaluations. - Abstract: Concentrated solar power technology constitute an interesting option to meet a part of future energy demand, especially when considering the high levels of solar radiation and clearness index that are available particularly in Tunisia. In this work, we study a medium temperature parabolic trough solar collector used to drive a cooling installation located at the Center of Researches and Energy Technologies (CRTEn, Bordj-Cedria, Tunisia). Optical evaluations of the collectors using photogrammetric techniques were performed. The analysis and readjustments of the optical results were conducted using a Matlab code. Therefore, slope errors ranged from −3 to +27 milliradian and the height deviations from the ideal shapes of the parabolic trough collector were 2.5 mm in average with a maximum of 7.5 mm. The intercept factor was determined using both the method of the total optical errors and the camera target method leading respectively to 0.62 and 0.7. Thus, the values of the overall optical efficiency were 0.48 and 0.514. Conversely, a thermal performance testing of the parabolic trough collector was conducted leading to the thermal efficiency and the heat losses evaluations. The instantaneous thermal efficiency reached a maximum of 0.43 but it did not exceed the value of 0.30 when the reflector becomes dirty by dust deposition. This study was also an opportunity for suggesting some recommendations for the enhancement of the PTC performances
[en] Highlights: ► Membrane water content is controlled by the operating conditions in the cathode. ► When the membrane is in contact with water, only pore size varies. ► Membrane water content increase by increasing the functioning temperature. ► Good agreement between computational results and previous reported experimental data. - Abstract: A two-dimensional computational fluid dynamics model of PEM fuel cell is developed by taking into account the electrochemical, mass and heat transfer process occurring in the cathode compartment. Additionally, this model includes the effect of water content in the membrane swelling phenomenon. Several parameters such as gases temperature, inlet velocity and membrane characteristics are too investigated to establish their effect on the PEM fuel cell performance. The membrane water content and the air fraction variation in the gas channel are examined for diverse values of Reynolds number. In particular, the desirable inlet flow for enhancing the performance of the PEM fuel cell is determined by examining membrane water content patterns. The methodology in this study is useful to the control of water management and gas diffusion layer design
[en] Highlights: • Numerical analysis of a latent heat thermal energy storage. • A solar water heater collector using a phase change material. • Experimental study of solar water heater collector with latent storage. - Abstract: The energy production provided by a heat excess or a discontinuous source (solar radiation, waste heat, etc.) involves the utilization of a thermal storage systems. In this work, an experimental study of a storage system using paraffin as phase change material (PCM) has been done. This system takes the form of two rectangular cavities incorporating behind the absorber of a flat plat solar collector. Measurements were performed during different weather conditions and illustrate that the PCM contributes to increase the performance of the solar collector at night. An analysis of the temperature stratification inside the PCM-filled cavities was also carried out. Theoretical solid–liquid of phase change material model is used to evaluate the PCM melted volume fraction, liquid–solid interfaces, PCM temperature and melting/solidification flow in the PCM-filled cavity used in the present experimental study
[en] Highlights: • The present work studies the potential of using innovative SCS in Tunisia. • In cold months the SCS provide about 50–75% of the total exergy provides. • The SCS produces between 70–150% of electric energy needs. • The SCS payback period (Pb) based on electric water heater was 10.2 years. • The SCS payback period (Pb) based on gas/gas town was about and 8.7 years. - Abstract: The endeavor of this paper is to study of the potential offered by the expenditure of an innovative Solar CombiSystem, SCS, used for the space heating load, the domestic hot water supply and the electric energy production. The investigation achieved in this work was based on an experimental and a simulation studies. A TRNSYS simulation program was achieved in order to evaluate the SCS monthly/annual thermal and electric performances. It was found that the proposed SCS covered between 20 and 45% of the SH energy needs by considering only solar energy. The result shows also that the SCS provided from 40 to 70% of the total DHW needs. It was also found that the SCS electric production ranged between 32 and 225 MJ/m"2 with a gain factor varying between 49 and 125%. An economic appraisal was also achieved to appraise the SCS feasibility. The results of the economic analysis show that the annual energy saved (ARE) and the payback period (Pb) based on electric water heater were respectively equal to 7618.3 kW h/year and 10.2 years. It was found that ARE and Pb based on gas/gas town were about 5825 m"3 and 8.7 years, respectively. The results of the economic analysis shows that the adoption of the SCS saves about 48% of electric energy and about 46% of gas/gas town kept back by the conventional system.
[en] Highlights: • We simulate the power plant with parabolic type under the climatic condition of the southern region of Tunisia. • We examine the economical, thermal and electrical performance of the power plant with the wet and the dry cooling. • Comparison from technical performance and economic efficiency between the two CSP plants in Tataouine and the reference plant Andasol-1. • The system gives good results in all operating states. - Abstract: This work aims to study the performance of deploying concentrated solar power (CSP) parabolic trough plants under the climatic conditions of the southern region of Tunisia “Tataouine”, taking into account the consideration of the limited water availability in such desert regions. The ground meteorological data from the high precision enerMENA station; which are installed in Tataouine are used in the simulations runs. The reference solar power plant is based on parabolic trough concentrating technology and has (50 MW_e) power capacity and (7.5) hours of storage at full load. The results of the simulations are validated by the published data of the reference plant “Andasol Type”, and are compared to each other. In a following step, an examination of the influence of meteorological parameters on the performances of the concentrating solar power plant for both the dry and wet cooling options is carried out. Finally, a comparative study of the power plants in study region for both economic and technical performance of the two simulated cooling options is done and compared with the reference power plant “Andasol-1” in Spain. The technical simulations show excellent results regarding the dry cooled CSP power plants and it will be taken into consideration in the future planning of new projects by cause of high DNI specifically at the study and generally in the desert region. Thus if the Andasol-1 CSP plant in southern Spain is shifted to Tataouine in southern Tunisia, and its wet cooling system is replaced with a dry one, it will have a competitive electricity output with a difference that does not exceed (9%), also water consumption will be reduced by (93.3%), and the levelized cost of electricity will be lower by (1.45%) in terms of 18.28 c€/kW h_e.