Journal of Energy Engineering

Development of a huge wind-sailing solar cell raft (SCR) with dimensions of $5\times 5\mathrm{km}$ is proposed, which can generate electricity comparable to a 1,000-MW nuclear power plant in low-latitude Pacific Ocean. Solar energy of $8\mathrm{k}·\mathrm{Wh}/{\mathrm{m}}^2/\mathrm{day}$ or more is targeted because the SCR navigates in fine weather using weather satellites. The generated electricity will be transported by battery tankers loaded with a tremendous number of high-energy-density batteries. Studies based on available data indicate that there are vast open seas in the tropical Pacific Ocean, where the maximum solar energy attains $7\mathrm{k}·\mathrm{Wh}/{\mathrm{m}}^2/\mathrm{day}$ annually on average and conditions of winds, waves, and sea currents are favorable for the solar energy system to operate. Three major technologies for breakthrough to realize this system are discussed from their future perspectives.

This article presents modeling and experimental verification of conversion of solar irradiation from horizontal to sloped surfaces and photovoltaic cell temperature and an analysis of photovoltaic conversion efficiency. Modeling and validation of the models are carried out on the basis of measurements conducted using the experimental system set in a city in southern Turkey. In addition to current, voltage, and cell temperature of the photovoltaic module, environmental variables such as ambient temperature and solar irradiance were measured and used for validation purposes. Correlation of conversion of solar irradiation from horizontal to sloped surfaces indicated that the presently used model is highly successful because of the fitting parameters: the coefficient of determination $(R^2)=0.97$, and the mean bias error $(\mathrm{MBE})=-2.2$. Similarly, the cell temperature model used in the present article is validated by the following correlation parameters: $(R^2)=0.97$, $\mathrm{MBE}=0.7$, and root-mean-square error $(\mathrm{RMSE})=2.1$.

This paper presents a multiobjective model for optimization of the activated sludge process (ASP) in a wastewater-treatment plant (WWTP). To minimize the energy consumption of the activated sludge process and maximize the quality of the effluent, three different objective functions are modeled [i.e., the airflow rate, the carbonaceous biochemical oxygen demand (CBOD) of the effluent, and the total suspended solids (TSS) of the effluent]. These models are developed using a multilayer perceptron (MLP) neural network based on industrial data. Dissolved oxygen (DO) is the controlled variable in these objectives. A multiobjective model that included these objectives is solved with a multiobjective particle swarm optimization (MOPSO) algorithm. Computation results are reported for three trade-offs between energy savings and the quality of the effluent. A 15% reduction in airflow can be achieved by optimal settings of dissolved oxygen, provided that energy savings take precedence over the quality of the effluent.

An experimental and theoretical study was performed to investigate the thermal performance of heat pipes as a heat exchanger. A series of experiments was conducted using R410A, R134a, R22, and R407C as working fluids. The dimensions of the heat pipes that were used in the test rig included 660 mm length, 20 mm outer diameter and 4 mm fin spacing with staggered arrangements. During the tests, the dry bulb temperature of the evaporator inlet was varied from 35 to 55°C and the condenser inlet dry bulb temperature was varied from 20 to 25°C. The influence of face velocity on the performance of the heat pipe heat exchanger was also studied. Many investigations were made to obtain the thermal performance and to ensure efficient and reliable operation of the heat pipe heat exchanger, and the results are presented in the present paper. Tests showed that using R410A, R134a, and R22 provided comparative results, whereas R407C was the least effective. The experimental thermal effectiveness of the heat pipe heat exchanger obtained from the experiments varied between 25 and 70% for R410A, R134a, and R22, whereas the experimental thermal effectiveness of R407C varied between 15 and 50%. A computer simulation program based on the effectiveness method and the number of transfer units was developed to estimate the thermal performance of the heat pipe heat exchanger and to compare the theoretical and experimental results.

Cavitation in a valve leads to trouble and inconvenience for factories. Valves in a piping system are ruined, leading to costly replacements every several months. To reduce the cost caused by cavitation in a valve, a cage is utilized to make cavitation occur only in the region adjacent to the cage itself; therefore, only the cage needs to be replaced. To validate the design of a cage, simulation of the turbulent flow field inside a globe valve and the occurrence of cavitation are necessary for a valve designer. To reach this purpose, prediction of the cavitation inside the globe valve with and without a cage is undertaken, and a cavitation model is established in this study. The percentage of vapors in each computational cell is calculated using the proposed cavitation model. Two various cages, the one-stage perforated cage and the one-stage step cage, are considered. Vapor resulting from cavitation appears in the vortices existing inside the valve and at the downstream region of the globe valve without a cage. Nevertheless, vapor does not occur in those regions in the globe valve with those two cages; in other words, cavitation inside the globe valve primarily occurs in the vicinity of the cages. In the valve body and downstream region, ruin from cavitation is prevented when those two cages are installed in the globe valve. In addition to the globe valve, the proposed cavitation model can be applied to prediction of cavitation in other control valves.

In this paper, an ${\mathrm{NiSO}}_4/{\mathrm{SiO}}_2$ catalyst was prepared by impregnating an ${\mathrm{SiO}}_2$ support with an aqueous solution of ${\mathrm{NiSO}}_4·6{\mathrm{H}}_2\mathrm{O}$. Through an esterification reaction using various catalysts including zeolite, ${\mathrm{SiO}}_2$, and ${\mathrm{H}}_2{\mathrm{SO}}_4$, free fatty acids (FFAs) in brown grease were converted to fatty acid methyl esters (FAMEs) as biodiesel products that were analyzed by gas chromatography–flame ionization detection, gas chromatography–mass spectrometry, and nuclear magnetic resonance. To optimize the esterification conditions, a molar ratio of methanol/brown grease from 1.57 to 3.70, a weight ratio of catalyst/brown grease from 0.75 to 1.75%, and reaction times from 30 min to 3 h at room temperature and atmospheric pressure were investigated. The chemical compositions of FFAs in brown grease were characterized as n-hexadecanoic acid (${\mathrm{C}}_{16}{\mathrm{H}}_{32}{\mathrm{O}}_2$), 9,12-octadecadienoic acid (${\mathrm{C}}_{18}{\mathrm{H}}_{32}{\mathrm{O}}_2$), and octadecanoic acid (${\mathrm{C}}_{18}{\mathrm{H}}_{36}{\mathrm{O}}_2$). Biodiesels obtained from these FFAs included hexadecanoic methyl ester (${\mathrm{C}}_{17}{\mathrm{H}}_{34}{\mathrm{O}}_2$), 9,12-octadecadienoic methyl ester (${\mathrm{C}}_{19}{\mathrm{H}}_{34}{\mathrm{O}}_2$), 9-octadecenoic methyl ester (${\mathrm{C}}_{19}{\mathrm{H}}_{36}{\mathrm{O}}_2$), and octadecanoic methyl ester (${\mathrm{C}}_{19}{\mathrm{H}}_{38}{\mathrm{O}}_2$). Among the catalysts that were tested, the order of the catalytic activity was ${\mathrm{H}}_2{\mathrm{SO}}_4>{\mathrm{NiSO}}_4/{\mathrm{SiO}}_2>\mathrm{zeolite}>{\mathrm{SiO}}_2$. Through the experiments conducted in this research, the optimized esterification conditions proved to be a methanol/brown grease molar ratio of 2.64, a catalyst/brown grease weight ratio of 1.00%, and a reaction time of 30 min. The use of ${\mathrm{NiSO}}_4/{\mathrm{SiO}}_2$ at room temperature might be significant for biodiesel production because it may allow the catalyst to be reused after recycling and lower the cost of biodiesel production without providing additional heating for the conversion of FFAs.

Availability of cooling water has been one of the major issues in the selection of nuclear power plant sites. Cooling water issues have frequently disrupted the normal operation at some nuclear power plants during heat waves and long droughts. One potential solution is to use ice thermal storage (ITS) systems that reduce cooling water requirements and boost the plants’ thermal efficiency in hot hours. The ITS uses cheap off-peak electricity to make ice and uses the ice for supplemental cooling during peak demand time. The ITS also provides a way to shift a large amount of electricity from off-peak time to peak time. For once-through cooling plants near a limited water body, adding ITS can bring significant economic benefits and avoid forced derating and shutdown during extremely hot weather. For the new plants using dry cooling towers, adding the ITS systems can effectively reduce the efficiency loss during hot weather so that new plants could be considered in regions with a lack of cooling water. This paper will review light water reactor cooling issues and present the feasibility study results.

Because of the up-front costs of add-on solar collection systems, the cost-effectiveness of solar energy is still in doubt. Building integrated solar thermal systems may improve the cost-effectiveness of add-on collection systems given their ability to expand to cover the entire area of a roof at a reasonable cost. The objective of this study was to evaluate the effectiveness of a newly developed flat plate integrated solar collector system. The developed collector system consists of a low-temperature flat plate collector integrated within a concrete building envelope. To evaluate this system, a full-scale test prototype of the solar collector was constructed and instrumented with thermocouples. Measurements were conducted over a 7-month period in which the solar collector was evaluated over different climatic conditions. On the basis of the results of the experimental program, it was determined that the solar collector provided an efficiency ranging from 49–75% in the range of ambient temperature, solar radiation, and inlet temperature evaluated in this experiment. The estimated efficiency of the system was on the high range as compared with the reported efficiency of similar systems. Depending on the extent of the collection area, the developed solar collector can provide a significant portion of the building’s space heating and hot water needs, especially in the spring and summer seasons.

A large part of energy cost on cooling applications is attributable to heat income through external walls. The best way to save energy is to use the optimum insulation thickness. In this study, the optimum insulation thicknesses, insulation-energy costs, and savings resulting from the use of these insulations is calculated in cities selected from four different climate zones in Turkey for four various insulation materials such as foamboard, extruded polystyrene (XPS), rock wool, and expanded polystyrene (EPS) in cold storage applications. Calculations show that rock wool insulation material yields the highest savings. Optimum insulation thicknesses vary between 0.074 and 0.159 m, energy savings vary between 30.59 and 80.61 $$/{\mathrm{m}}^2$, and payback periods for investment cost vary between 3.15 and 3.73 years for the cooling.

In this work, the performance of proton exchange membrane (PEM) fuel cells has been analyzed for different oxidant (air and oxygen) flow rates (supplied at the cathode side). The performance analysis of a single PEM fuel cell coupled with a direct current (DC) permanent magnet motor (as load) was analyzed for air and oxygen. With an increase in the air flow rate, the maximum current values of the PEM fuel cell increase due to the reduction in the concentration of polarization losses (in the polarization curve) and the voltage regulation for the load increases. The maximum power production in a PEM fuel cell is a logarithmic function of different air flow rates. In this system, a DC permanent magnet motor with a reduction gear was used as a load on the PEM fuel cell. With the increase in air flow supply rates, the starting torque of the DC permanent magnet motor load improves. Also, a performance analysis was conducted for pure oxygen, and it has been observed that the PEM fuel cell provides a very good performance, even at the reduced supply flow rate of pure oxygen. For this work, a test bench was developed at Kocaeli University (Turkey), which consists of a PEM electrolyzer, a PEM fuel cell, and a DC permanent magnet motor with an air pump. The results of this work will be very useful for comparing the performances of the PEM fuel cell for different air and oxygen (as oxidants) flow rates for the dynamic loads (e.g., fuel cell vehicles with a DC permanent magnet motor).