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Thermal energy storage (TES) is of great importance in solving the mismatch between energy production and consumption. In this regard, choosing type of Phase Change Materials (PCMs) that are widely used to control heat in latent thermal energy storage systems, plays a vital role as a means of TES efficiency. However, this field suffers from lack of a comprehensive investigation on the impact of various PCMs in terms of exergy. To address this issue, in this study, in addition to indicating the melting temperature and latent heat of various PCMs, the exergy destruction and exergy efficiency of each material are estimated and compared with each other. Moreover, in the present work the impact of PCMs mass and ambient temperature on the exergy efficiency is evaluated. The results proved that higher latent heat does not necessarily lead to higher exergy efficiency. Furthermore, to obtain a suitable exergy efficiency, the specific heat capacity and melting temperature of the PCMs must also be considered. According to the results, LiF-CaF2(80.5 wt%:19.5 wt%) mixture led to better performance with satisfactory exergy efficiency (98.84%) and notably lower required mass compared to other PCMs. Additionally, the highest and lowest exergy destruction are belonged to GR25 and LiF-CaF2(80.5:19.5) mixture, respectively.

Nano-PCMs, which contain nanostructured materials, can enhance the low thermal conductivity of phase change materials (PCMs). It is crucial to predict the precise thermal conductivity of nano-PCM to assess the heat transfer during phase change procedures such as melting and solidification. In this study, artificial neural network (ANN) and response surface method (RSM) were used to develop a model for predicting the thermal conductivity of carbon-based nano-enhanced phase change materials (NEPCMs) using 482 experimental samples collected from various datasets. The carbon-based nano-particles were SWCNTs, MWCNTs, graphite, graphene, and (CNFs). Six input parameters were considered with varying temperature, mass fractions, sizes, thermal conductivities of PCMs and nano-particles, and the phase of PCM. The ANN was designed using a multi-layered feed-forward structure and Levenberg–Marquardt back-propagation algorithm with one hidden layer consisting of eight neurons. The transfer function was varied to achieve optimal performance. It was revealed that the predictive capacity of the ANN model is greater than that of the RSM model based on their corresponding the coefficient of determination (R2) and root mean square error (RMSE) values. The developed ANN achieved a R2value of 0.99, while the RSM method model achieved an R2value of 0.79.

A great significance is attached to the Organic Rankine Cycles (ORCs) as heat recovery technologies and power generation from the low-temperature heat sources. These systems have been utilized in diverse applications since their first emergence in 1883. Working fluid (WF) selection exerts enormous influence over the performance of these cycles. A large variety of WFs has been historically tested in the ORCs, from the ordinary organic fluids to the nowadays hydrofluoro chemicals, to find compatible WFs for these systems. The current generation of the ORCs based on the international protocols needs low global warming potential (GWP) WFs to not only reduce their environmental impacts in the operation stage but also the whole life cycle of the system. This study aims to assess the performance of environmentally-friendly WFs in the ORCs through the literature. This paper firstly reviews screening methodologies and WF selection criteria to provide a better understanding of the WF selection procedure. Afterward, proposes three categories of WFs with a GWP value of lower than 150, including hydrocarbons (HCs), hydrofluoro chemicals, and mixture WF, and evaluates their performance in different configurations of the ORCs based on a variety of performance indicators.

In this study, a deep-borehole ground source heat pump was simulated using computational fluid dynamics (CFD) method. The thermal performance and coefficient of performance (COP) of the vertical ground source heat pump simulated with accuracy using CFD for water and 4 different nanofluids as working fluids were investigated. Two nanofluids contained silver and copper metallic nanoparticles and the other two nanofluids contained copper and aluminum oxide nanoparticles. For each of these nanofluids as well as water, the heat exchange rate, total exchanged heat, outlet temperature and COP were calculated and the results were compared together. The results showed that using nanofluids leads to increased exchanged heat. Nanofluids based on aluminum oxide, copper oxide, copper and silver nanoparticles resulted in 4.83, 5.76, 6.9, 7.69 percent increase in total exchanged heat, respectively. In addition to increased exchanged heat, using nanofluids increased the outlet temperature. Also, the results showed that the maximum and minimum increase in COP were 36.5% and 5.2% which were related to using silver and aluminum oxide nanoparticle-based nanofluids, respectively.

This study investigated the heat pump system connected to the solar collector. The purpose of this study is to determine the amount of energy consumption and exergy and system performance. This system uses high-temperature heat pumps. In this paper, energy-based and exergy currents from the primary energy source to the consumer are plotted by using Sankey and Grassmann diagrams. In this article, Sankey (enthalpy flow) and Grassmann (exergy flow) diagrams of a heat pump connected to a solar collector were investigated. The results show that stream number 12 has the highest amount of exergy of the streams and the exergy destruction of the solar collector is more than other equipment and the highest energy rate is related to stream 11. Exergy analysis in thermal energy systems is very important due to the location and degree of inefficiency of the system equipment. Exergy analysis shows that the highest amount of exergy of currents with 367,092 kW is related to the inlet current of the tank and the highest amount of exergy damage of 15,563 kW equipments is related to the solar collector. This exergy destruction for solar collectors with temperature changes throughout the year with the lowest destruction in July at 14,342 kW and the highest exergy destruction at 15,678 kW is related to June. Among the rotating equipments, the most exergy damage is related to the compressor (k101) water heat transfer cycle. By changing the exergy efficiency, the amount of exergy destruction is significantly reduced.

The immiscibility of oil and alcohol is a severe issue in biodiesel production as it causes a low mass transfer rate and long reaction time. This problem can be overcome by incorporating the intensification method, which significantly increases the contact surface area of oil and alcohol through various techniques. In recent years, ultrasonic cavitation has emerged as one of the most effective ways for this purpose. However, it is still unclear whether this technology will provide the industry with an economically profitable process. This paper attempts to assess the potential of ultrasonic cavitation from a techno-economic viewpoint. Two plants based on the conventional mechanical stirring and ultrasonic cavitation processes were designed using Aspen HYSYS V8.4. Total investment, costs of products, net present value, and internal rate of return were used to compare the two processes together. The total investment in the ultrasonic cavitation process was lower than that of the mechanical stirring process by approximately 20.8%. Compared to the conventional process, using ultrasonic reactors also caused products’ costs to reduce by 5.2%. Owing to a positive net present value and an internal rate of return of 18.3%, the ultrasonic cavitation process was a better choice. Moreover, ultrasonic cavitation resulted in a meaningful decrease in both consumed energy and the production of wastes. The overall energy consumption was reduced by 6.9% when ultrasonic cavitation was employed. The amount of waste produced in the ultrasound-assisted process was one-fifth of that in the mechanical stirring process.

This study presents a simple approach for the exergy analysis of heat exchanger networks (HENs). This approach is based on approximating the irreversibility distribution ratio (φ) and the exergy destruction of a HEN in a large natural gas refinery, without needing to design the individual heat exchangers. Only the thermodynamics properties and the temperatures of the hot and cold streams at the inlets and outlets of the heat exchangers, as well as a model assuming for temperature distributions along the exchangers, are required. The exergy efficiencies and destructions were calculated for the individual heat exchangers and therefore for the HEN by superposing them. Also, φand Bejan number were obtained by approximating irreversibilities arising from the heat transfer and pressure drop due to fluid friction. The total φ(φtot) in the whole network was 0.188, with a Bejan number of 0.842. The results showed that the main source of the exergy destruction in the whole heat exchanger network of the plant is the irreversibility arising from heat transfer and the heat transfer irreversibility contribution to the total irreversibility in all the HENs was 84.2%. Moreover, the overall exergetic efficiency was 63.34%, which shows a great potential for improvement in the network system under consideration.

Hybrid systems composed of solar photovoltaic (PV) and battery storage units are reliable and clean technologies for utilization in off-grid cases. Optimal sizing of these systems results in more cost-effective units, which is the main subject of various researches. The current work focuses on the assessment of an optimization approach for finding the optimum size of PV/battery hybrid unit in order to provide the required electricity of the case study and reach the minimum Total Life Cycle Cost (TLCC). In this regard, the components of the designed systems are modelled; afterwards, the objective function is established on the basis of TLCC. In the optimization procedure, a constraint is considered for the highest possible loss of power in order to have a system with acceptable reliability. In addition, Improved Harmony Search (IHS) algorithm is applied to determine the variables with optimal quantities for satisfying the required electricity in the most cost-effective condition. The calculated results are compared with harmony search and simulated annealing algorithms to evaluate the reliability of the applied method. The outcomes show that employing IHS leads to more promising results and it has higher robustness compared with the HS and simulated annealing algorithms. Moreover, the number of units in the hybrid system reduces by increment in the loss of power supply probability.

Purpose: Because of its increased absorptance in fluid and reduced heat loss, direct absorption nanofluid (DANF) is receiving intense interest as an efficient way to harvest solar energy. This work aims to investigate, for the first time, the application of DANF in parabolic trough collectors (PTC), a promising collector for solar thermal systems. Design/methodology/approach: A representative flow and heat transfer study of different fluids in a straight tube is conducted, and the basic energy equation and radiative transfer equations are numerically solved to obtain the fluid temperature distribution and energy conversion efficiency. Ethylene glycol (EG) and different concentrations of (i.e., 0.1-0.6 per cent) multi-wall carbon nanotubes (MWCNT) in EG are used as sample fluids. Four cases are studied for a traditional PTC (i.e., using metal tube) and a direct absorption PTC (i.e., using transparent tube) including a bare tube, a tube with an air-filled glass envelope and a tube with vacuumed glass envelop. The numerical results are verified by an experimental study using a copper-glass absorber tube, which reveals the good potential of DANFs. Findings: Compared with a conventional PTC, using DANF shows an increase of 8.6 per cent and 6.5 K, respectively, in thermal efficiency and outlet temperature difference at a volume fraction (0.5 per cent) of nanoparticles. The results also show that the improvement in solar efficiency increases with increasing particle concentrations, and the vacuum insulated case has the highest efficiency. Originality/value: In all previous studies, an important section was missing as the effect of photons on the direct solar absorption trough collector, which is considered in this study. This paper proposes a new concept of using direct solar absorption nanofluids for concentrated solar collectors and analyzes the performance of both absorptance and transmittance efficiency considerations. To reveal the potential of the new concept, an analytical model based on energy balance is developed, and two case studies are performed. [ABSTRACT FROM AUTHOR]

In this study, sawdust from a paper factory in north Iran was selected as the biomass resource to supply some of this region's electricity, cooling, and heating demand. Accordingly, a steam Rankine cycle (SRC) based tri-generation system is designed, and exergy analysis is conducted. According to the modeled cycle, the generating power of the process was 41,103kW. The hybrid system could also provide a heating load of nearly 111,000kW, and the cooling load was 1100 KW. The sensitivity analysis has been conducted based on the effects of design parameters on the system's exergy destruction and efficiency.

Energy accessibility especially electrical energy is considered as one of the most appealing factors to achieve energy sustainability. The purpose of this study is to investigate energy sustainability using renewable energies for two high potential cities in the south-east of Iran until the year 2030. In this regard, Homer software is used to evaluate economic and technical analyses of PV-wind-diesel hybrid system for the two cities by the data gathering which was collected from Iran’s meteorological organization. Therefore, the average of solar radiation per month for Zabol and Zahak were about 9 and 9.1 (h/d). Also, mean wind speeds are calculated 5.35 m/s and 4.7 m/s for Zabol and Zahak respectively which proposed that these cities have high potential in order to electrical production by a hybrid system. Furthermore, the amount of electricity production by PV array for Zabol and Zahak were 1700 (kWh/yr) and 1669 (kWh/yr) respectively, and the amount of electricity production by wind turbine were 9036 (kWh/yr) and 7263(kWh/yr) for Zabol and Zahak respectively. Consequently, it is of elaborated that the investments on solar and wind energy sectors for both cities would be economically justified.

ABSTRACTNanofluids have found extended applications in different industrial and engineering systems nowadays. This study aims to investigate the accurate prediction of SiO2nanofluid effect on the heat transfer performance, specifically convective heat transfer coefficient (H), of a quadrangular cross-section channel by considering affecting fluid flow specifications factors of Re, Pr, and concentration of nanoparticles (x) in the employing working fluid. An experimental setup is used to prepare a database consisting of 270 data points on the H, of SiO2nanofluids. These data are then applied to develop predictive models based on three intelligent algorithms, namely multi-layer perceptron (MLP), adaptive neuro-fuzzy inference system (ANFIS), and least squares support vector machine (LSSVM), respectively. Graphical and statistical error criterions are carried out to evaluate the credibility of the proposed approaches. The LSSVM method had the precise performance regarding the mean squared error (MSE) and the coefficient of determination (R2) of 59.7 and 0.9992, respectively. A sensitivity analysis is also carried out to assess the impact of different parameters on the Hdemonstrating that the Prandtl number has the highest impact with a relevancy factor (r) of 0.524.

This paper presents a novel perspective on a thermoacoustic Stirling engine, emphasizing the integration of passivity control and a genetic algorithm (GA) framework. To this end, a brief overview of the mathematical modeling is presented by investigating the movements of pistons and operating frequency. Next, the dynamic error equations are derived, and then, the passivity-based control and GA are employed for estimating the design parameters obtained through the behavior-stabilizing process of the system. Note that the mass of the pistons attached to the second diaphragm, the stiffness of diaphragms 1 and 2, the hot temperature, and the phase difference between diaphragms are the design parameters in this study. Consequently, once the design parameters are assessed, the work and the output power are calculated. Finally, comparing the simulation and the experiment outcomes confirmed that the presented technique is effective in not only predicting the design parameters appropriately but also verifies the engine’s stable oscillations. It is important to note that obtaining such parameters before the design and production phase can significantly enhance the cost-effectiveness and time efficiency of the production process.

This study implements a thermodynamic study of a small-scale transcritical CO2power cycle using flat plate collectors and a storage tank as a heat source and liquefied natural gas (LNG) as the heat sink. A parametric study was carried out to see the influence of key variables on the system performance under various circumstances. Using cost estimation equations and cost indices, the total cost of the system is calculated, and its relation to key parameters is studied. An optimal turbine inlet pressure occurs under assumed circumstances where the system efficiency and the net power output along with the investment cost achieve maximum values. The condensation temperature has the effect on the performance of the system; however, the system efficiency and the net power output are less sensitive to the change in inlet temperature of the turbine. Changes in the turbine inlet pressure have no considerable effect on the heat exchanging area under the assumed circumstances and thus the heat exchangers costs; however, the rise in the turbine inlet temperature causes the increasing surface area of heat exchangers. For optimization purpose, four decision variables comprising turbine inlet temperature, turbine inlet pressure, minimum pinch temperature of the vapor generator and condensation temperature are selected as the effective decision variables. A multi-objective optimization is done to achieve a set of solutions to gain the maximum thermal efficiency and solar fraction while minimum total investment of the plant. Decision making including FUZZY, TOPSIS and LINMAP methods have been used and compared with each other.

A hybrid system is proposed, which integrates a molten carbonate fuel cell, and a supercritical carbon dioxide Brayton cycle. This case deals with waste heat recovery from catalytic burner exhaust gas using a Brayton cycle as a bottoming cycle for additional power production due its very high temperature, which yields high electrical and overall efficiencies. After designing and simulating the process energy and exergy analyses are performed. The greatest exergy destruction is observed in the reformer while the lowest exergy efficiency is attributable to the fuel cell. The main advantage of this kind of hybrid system, in addition to efficiency improvement and cost reduction, is its ability to reduce harmful emissions and negative impacts on the environment.

For analyzing the performance of the studied configuration, consideration of its application is highly crucial. Therefore, analyzing the amount of discharged energy against the temperature margin of the outlet is vital. A 2-D Numerical analysis was performed on various TES cases (under dynamic solar energy conditions). The type of storage media for each column was subject to choice and optimized using a genetic algorithm. The optimal distribution of the HTF rows altitude showed a variety of 12.3 mm (Center) to 29.1 mm (Sidewall) within the structure. The study objective is the selection of the best configuration to maximize the system discharge energy following two scenarios, first when there is no applied outlet threshold temperature constraint for the TES and second, when a specific outlet threshold temperature constraint is applied on the system. Generally, the cascaded structure showed a 14.7 % higher amount of stored energy in comparison with the average of cases with only one PCM, whereas the hybrid-cascaded configuration showed a 7.8 % higher stored energy compared to the same cases. At the first scenario (under no outlet temperature constraint) outputs, a higher figure of energy was discharged by the cascaded structure against the hybrid-cascaded one, however, the difference in the energy discharged amounts has decreased, describing the better thermal performance of hybrid cascaded setup while discharging. In the second scenario (with applied outlet temperature constraint), it was found that the useful discharged energy of the hybrid-cascaded structure is higher, meaning that more amount of energy is discharged in the required temperature range and thermal control is enhanced, and this is the most important result of this research and shows that the use of the sensible storage material as well as latent storage material will cause a very favorable change in the performance of the system.

This paper focuses on modeling, sizing and cost analysis of a photovoltaic (PV)/wind generator (WG)/diesel hybrid system considering two storage devices: battery and fuel cell (FC). In comparison with the traditional PV/WG/diesel/battery systems in which battery banks are used as the storage system, PV/WG/diesel/FC systems combine fuel cell, electrolyzer and hydrogen storage tanks as the energy storage system. For cost analysis, a mathematical model is introduced for each system’s component and then, in order to satisfy the load demand in the most cost-effective way, one discrete version of harmony search (HS) algorithm is developed to optimally size the systems components. As an efficient search method, HS has simple concept, is easy to implement, can escape local optima by use of probabilistic mechanisms, and only needs one initial solution to start its search. Two robust optimization techniques are used for comparison and validation purposes, the simulated annealing (SA) algorithm and HOMER software. In addition the economic aspects of PV/WG/diesel/FC system are compared with those of the traditional PV/WG/diesel/battery system and break down of the total annual cost of the systems is given in detail.

Poly-generation systems have attracted a lot of attention due to the increment of efficiency as well as reducing energy penalties, costs and pollutants. Extensive research has been done on these systems in recent years. The current work is done with the aim of simulating an environmentally friendly poly-generation system in the power plant of Shahrood city in Iran. In this way, a poly-generation system is simulated in Aspen Plus software which consists of: I) a gas turbine (GT) for power generation with natural gas fuel of Shahroud power plant, that its flue gas is utilized to supply heat for other cycles and streams, II) a sorption-enhanced chemical looping reforming (SECLR) which simultaneously generates H2by steam methane reforming (SMR) and uptakes produced CO2by calcium adsorbent during the carbonation/calcination reactions. In this section, there is also a chemical looping combustion (CLC) based on redox reactions of Ni/NiO to provide heat of the reactors, III) a NH3/H2O absorption refrigeration system to yield the cooling demand, IV) a high-pressure steam generation unit and V) a MEA-based post-combustion CO2capture unit (PCC) for flue gas. In this system, an attempt has been made to prevent heat loss by internal streams, especially gas turbine exhaust gas, so that energy loss is minimized. Moreover, environmental issues are also prioritized to reduce the CO2emissions as much as possible. The proposed process is capable of producing 133.3 MW power, 9.875 MW cooling, 50 kg/s high-pressure steam and 0.384 kg/s hydrogen. The mass flow rates of CO2captured in the SECLR and PCC sections are 2.6 kg/s and 15.35 kg/s, respectively. Moreover, the total energy efficiency of the integrated system is 68.74%. Ultimately, a sensitivity analysis was performed to identify the key parameters and their influence on the process performance.

We investigate the effect of soil type and moisture on the operation of a ground source heat pump (GSHP) system in supplying the energy needs of a greenhouse in Karaj, Alborz province, Iran, in terms of the required length of ground heat exchanger, the working hours, the electricity consumption, as well as the coefficient of performance (COP) of heat pumps. In order to predict the capacity of heat pumps, we use the numerical heat transfer model of Noorollahi et al. (2016, “Numerical Modeling and Economic Analysis of a Ground Source Heat Pump for Supplying Energy for a Greenhouse in Alborz Province, Iran,” J. Cleaner Prod., 131, pp. 145–154) in which the governing equations of heat transfer in the ground heat exchanger are numerically solved through a novel finite difference method. Thermal properties of various soil types, namely sandy soil, sand, silty loam, and silty clay, with three different levels of moisture content referred to as dry, damp, and saturated, are considered as the main inputs for the computer code. The simulations indicate that when moisture is increased from dampness to saturation, the annual working hours of heat pumps decrease by 1.1%, 5.1%, 6.1%, and 4.6%, and their annual electricity consumption is reduced by 2.2%, 10.6%, 12.6%, and 9.7% for sandy soil, sand, silty loam, and silty clay, respectively. Moreover, the average COP of heat pumps increase by 0.9%, 4.0%, 5.2%, and 3.7% in heating mode and 2.4%, 13.0%, 16.5%, and 11.7% in cooling mode for the mentioned soils, respectively.