د. ايمن رشاد نور زيني

Nanoparticle-based volumetric solar absorption has been shown to be an effective technique to realize efficient solar harvesting. However, most of such systems under study are stationary and cannot realize solar energy transport, which limits their potential applications. A novel idea of using directive absorptive nanofluids in oscillating heat pipes (OHP) is investigated in this work, which would achieve efficient solar energy capture and transportation simultaneously without the use of any additional pumping power. The influence of a variety of parameters such as nanoparticle type, nanoparticle concentration, nanofluids filling ratio and solar radiation intensity on the performance of OHPs are investigated. There exists an optimal filling ratio of the nanofluid for the OHP (i.e., 83%), under which single direction circulation of the working fluid is achieved and the thermal resistance of the OHP reaches the minimum. The OHP reaches an extremely high thermal conductivity, i.e., 6000 W/(m∙K), when filled with 3.0 wt% MWCNT nanofluid. The maximum energy conversion efficiency has been observed as much as 92% for the current experimental settings. Strong absorption of solar energy, efficient vapor generation inside the OHP and proper configuration of the OHP should be responsible for the efficient operation of this system.

Steam generation by nanofluid under solar radiation has attracted intensive attention recently. Due to strong absorption of solar energy, nanoparticle-based solar vapor generation could have wide applications in many areas including desalination, sterilization and power generation. Steam generation of different concentrations of gold nanoparticle dispersions under focused sunlight of 5 sun and 10 sun were performed in this work. A numerical model combining radiative heat transfer, moisture transport, and laminar flow was established to investigate the temperature profile, evaporation rate above the surface and radiative intensity distribution inside the nanofluid. It was found that localized energy trapping at the surface of nanofluid was responsible for the fast vapor generation. To convert more solar radiative energy into latent heat of water (i.e., to vaporize water) at the surface, a new method was proposed to optimize the range of nanofluid concentration and optical depth for future solar vapor generator design.

Direct absorption nanofluid has been introduced as an effective alternative to increase solar thermal conversion efficiency. Hybrid nanofluids were also recently proposed to broaden the absorption spectrum. However, a comparative assessment of the performance of commonly used nanomaterials for solar energy harness is still lacking. In this study, a well-controlled experiment was performed using three different categorised nanofluids, i.e., gold, copper, carbon black nanofluids and their hybrids, to assess their performance in terms of photothermal conversion efficiency (PTE), specific absorption rate (SAR) and materials cost. A mathematical model was built based on the Beer’s law to predict the PTE enhancement. The results revealed, contrary to previously reported, the PTE was not increased by blending different nanofluids with different absorbance peaks, which is mainly due to the dilution of nanoparticles’ concentration. Furthermore, it is found that although gold nanofluids have high SAR, their expensive cost limits their practical use, whereas carbon black nanofluids are more feasible. In addition it was found that the theoretical PTE can be well predicted mathematically based on the optical properties of the used nanofluids.

Vaporisation (evaporation and boiling) through direct absorption solar collectors (DASCs) has recently drawn significant attention. Many studies suggested that plasmonic nanoparticles, such as gold nanoparticles, can significantly enhance the photo-thermal conversion efficiency of DASCs. However, there is still a lack of comparative studies of the feasibility of using gold nanoparticles for solar applications. This study performed well-controlled experiments for two different categorised particles, i.e., gold and carbon black suspended in water, and assessed their performance in terms of evaporation rate, materials cost and energy consumption. The results show that gold nanofluids are not feasible for solar evaporation applications, where the cost of producing 1 g/s vapour is ∼300 folds higher than that produced by carbon black nanofluids. This infeasibility is mainly due to the high cost and the low absorbance of gold comparing to carbon black nanoparticles. Moreover, this work reveals that with the increase of nanoparticle concentration or incident solar radiation, more energy is trapped in a small volume of the nanofluid near the interface, resulting in a local higher temperature and a higher evaporation rate. For efficient steam production, future optimisation of the system should consider concentrating more solar energy at the interface to maximize the energy consumed for evaporation.

Steam production is essential for a wide range of applications, and currently there is still strong debate if steam could be generated on top of heated nanoparticles in a solar receiver. We performed steam generation experiments for different concentrations of gold nanoparticle dispersions under a solar intensity of 5 sun (5 kW/m^2). For 12.5 ppm nanofluid, 34.1% of solar energy was consumed to evaporate water, only 30.6% of that was to heat up the bulk fluid. Combined with efficiency analysis, it is found that steam generation is mainly caused by heat localization of the surface due to a highly non-uniform temperature and radiation energy distribution. In the future solar receiver design, more solar energy should be focused and trapped at the surface area while minimizing the temperature rise of the bulk fluid.

Considering pollution problems today, investigations have been concentrated on lowering the concentration of toxic components in combustion products. The purpose of this project is to experimentally study of using Naphtha which is produced in Annajaf city refinery as an alternative fuel instead of the commercial gasoline which is imported to Iraq from the neighborhood countries. In this project, experiments have been done to measure the performance and emissions of a 4-stroke S.I. Engine, one by using the commercial imported gasoline, another by using the Annajaf city naphtha, and finally by using the naphtha-methanol blends. Results showed that; the use of 7 vol. % of methanol blending with the naphtha appears to be a good option for replacing any oxygenate additives in the naphtha, where the CO, CO2 , and HC are minimum and the fuel consumption of the blend is lower than of the commercial gasoline. Also, the noise results showed that; the engine runs smoother at 7 vol. % methanol blend than the commercial gasoline. That is mean increase in engine life due to the lowering vibration.

Considering pollution problems and energy crisis today, investigations have been concentrated on lowering the concentration of toxic components in combustion products and decreasing fuel consumption by using renewable alternative fuels. In the present work, the effect of ethanol addition to gasoline on the exhaust emissions and noise level has been experimentally investigated at various engine loads. Results of the engine test indicated that using ethanol-gasoline blended fuels increases the power output of the engine dramatically (up to 50 %). While the CO and HC emissions decrease as a result of the leaning effect caused by the ethanol addition; and the CO2 emission increases because of the improvement of combustion. Also, it was noted that the noise level emission increases slightly with the increase of ethanol content. Finally, the results showed that ethanol can be used as a supplementary fuel to gasoline in modern spark ignition engines without major changes, and it can help to save our environment from toxic pollutants and to save a considerable part of the available oil.

A comprehensive 3D computational fluid dynamics (CFD) model is developed to explore the thermal performance of a PEM fuel cell liquid-base cooling system. In previous studies, the models were developed to simulate a single cooling plate. While in this study, the model consists of a bipolar plate with gas diffusion and catalyst layers. The heat generation mechanism in the PEM fuel cell stack and the liquid cooling method - to keep their operating temperature in the desired range - are presented and discussed. Fully three-dimensional results of the temperature distribution, velocity, and pressure-flow field are presented and analysed, focusing on the physical insight and fundamental understanding. The index of uniform temperature (IUT) through the bipolar plate is also produced to assess the degree of uniformity of temperature profile through the bipolar plate. The results show that increasing Reynolds number (Re) leads to a lower coolant’s temperature difference between the outlet and inlet of the flow channel. However, increasing Re increases the pressure drop across the flow channel and consequently increases the pumping power consumed to circulate the coolant. The present model is valuable for further development in the cooling flow field design and choosing the coolant used in the PEM fuel cell stacks.