Ahmet Z. Sahin

Heat Transfer, Pressure Drop, and Entropy Generation in a Solar Collector Using SiO2/Water Nanofluids: Effects of Nanoparticle Size and pH

In this paper, an analytical study is carried out on the heat transfer, pressure drop, and entropy generation in a flat-plate solar collector using SiO2/water nanofluid with volume concentration of 1%. In the study, the effects of two different values of pH, i.e., 5.8 and 6.5, and two different sizes of nanoparticles, i.e., 12nm and 16nm, on the entropy generation rate in turbulent flow are investigated. The results are compared with the results obtained for the case of water. The findings show that by using the Brinkman model to calculate the viscosity instead of experimental data one obtains a higher heat transfer coefficient and thermal efficiency than that in the case of water, while, when the experimental data are used, the heat transfer coefficient and thermal efficiency of water are found to be higher than that of nanofluids. The results reveal that using nanofluids increases the outlet temperature and reduces the entropy generation rate. It is also found that for nanofluids containing the particles with a size of 16nm, the increase in pH value would increase the entropy generation rate, while for nanoparticles with a size of 12nm the increase in pH would decrease the entropy generation. [DOI: 10.1115/1.4029870]

Performance Comparison of Diesel and Solar Photovoltaic Power Systems for Water Pumping in Saudi Arabia

Optimum configuration of solar photovoltaic (PV) power generation system has been carried out for achieving a minimum cost of energy (COE) in five different geographic locations in Saudi Arabia, namely, Dhahran, Riyadh, Jeddah, Guriat and Nejran . The ultimate goal in the present study is to investigate and compare the performance of both the diesel and solar PV stand-alone power generating systems for underground water pumping purposes. It is found that the solar PV power generating system not only helps to decrease carbon emission to the atmosphere but also is comparable in the unit COE with the diesel only system in many sites even though the unit price of the diesel fuel is very low. The proposed diesel only system produces annually about 24,069 tons of green house gases which can be otherwise eliminated by using solar PV system. Cost of water pumping from an underground well of 50 m total dynamic head is found to vary from 10–17 US¢/m3 for the five sites considered. When compared with the diesel only system this range of cost is found to be comparable when the diesel fuel price is 0.6

Experimental study of two phase closed thermosyphon using CuO/Water nanofluid in the presence of electric field

/L or more.

Exergy analysis of a thermoelectric power generator: influence of bi–tapered pin geometry on device characteristics

In this article, the effect of applying an electric field on the performance of a two-phase closed thermosyphon is investigated experimentally. A CuO/water nanofluid is used as the working fluid in the present investigation; 40% of the evaporator volume is filled with the working fluid during the tests. An electric field in various voltages ranging from 5 to 20 kV is applied to the system. Also, the input power supplied to the evaporator varies between 60 to 120 W. The thermal efficiency and the thermal resistance of the two-phase closed thermosyphon are evaluated in various strengths of electric field and different volume fractions. It is found that using the nanofluid and applying an electric field could increase the thermal efficiency by up to 30% as compared with the case in which the working media is pure water and no electric field is applied. To illustrate the effect of the electric field on the heat transfer enhancement, the augmentation Nusselt number, defined as the ratio of the Nusselt numbers after and before applying the electric field, is discussed. The results show that utilizing an electric field is more advantageous when the input power applied to the system is lower.

Comparing the Use of Diesel and Wind Power in Pumping Water in Saudi Arabia

The thermal characteristics of bi–tapered thermoelectric generator are investigated. The influence of the dimensionless shape parameter, associated with the device pin geometric configuration, on the first– and second–law efficiencies and device output power is examined. The study is extended to include the effects of the external load parameter and the device operating temperature ratio on the device characteristics. It is found that the first–law efficiency is not considerably influenced by the dimensionless shape parameter; however, the second–law efficiency and the device output power are significantly affected by the shape factor. The external load parameter has an adverse effect on the first– and the second–law efficiencies and the device output power. In this case, increasing external load parameter lowers the thermal performance of the thermoelectric generator. Reducing operating temperature ratio improves the first– and the second–law efficiencies and the device output power significantly.

Costs Due to Entropy Generation in a Vertical Annulus Using Nanofluids and Different Thermophysical Models

This study compares a diesel only power system with wind only power system for pumping water in some cities of Saudi Arabia. Cost of Energy (COE) is found to be very sensitive with respect to annual mean wind speed. For 10% annual capacity shortage, for example, the COE decreases by 11.5, 21.8, 22.3 and 13.5% at Dhahran, Riyadh, Jeddah, and Guriat, respectively for an increase in annual mean wind speed of only 0.4m/s. On the other hand, COE for zero capacity shortage is found to be 0.224, 0.455, 0.294, 0.334, and 1.379

Laser Surface Treatment and Efficiency Analysis

/kWh at Dhahran, Riyadh, Jeddah, Guriat, and Nejran, respectively. The cost of pumping water from a well of 50 m total dynamic head (TDH) is studied for both the wind energy and diesel only systems. Cost of water when using wind energy system is found to be 5.35, 10.4, 6.94, 7.71, and 30.56US¢/m3 for Dhahran, Riyadh, Jeddah, Guriat and Nejran, respectively. Cost of water when using diesel only system is found to vary from 7 to 16.5US¢/m3 depending on the fuel price. Furthermore, the wind based system becomes more cost effective when the diesel fuel cost is more than 0.4

Laser Drilling and Efficiency Analysis

/L for all sites except for Nejran. Last but not the least, the utilization of wind power for water pumping in Saudi Arabia will result into avoidance of addition of around 24,000 tons of CO2 equivalent greenhouse gases from entering into the local atmosphere annually.

Second law analysis of a gravity–driven liquid film flowing along an inclined plate subjected to constant wall temperature

In this paper, for the first time the application of nanofluids is investigated from the point of view of thermoeconomics. For this purpose, the mixed convection flow of Al2O3-EG nanofluid in an isothermal vertical annulus is considered where three sets of models are used to calculate the viscosity and thermal conductivity of nanofluid. The main aim of this work is to estimate the operational costs (

A review of entropy generation in nanofluid flow

) due to entropy generation using nanofluids in the annulus. The results show that using nanofluids is not cost-effective in short periods (i.e., 5–6 months) from the point of view of the second law of thermodynamics.In future works, besides the entropy generation, changes in the heat transfer rate that occurs using nanofluids, and their effects on the costs, can be considered.