Exergy Efficiency Enhancement Research Articles

Exergy analysis of ejector‐enhanced dual‐evaporator cycle using effective temperature method

AbstractThis study compares the exergy of an ejector‐based two evaporator cycle (EB‐TEC) with a conventional two evaporator cycle (C‐TEC). The analysis utilizes a modified Gouy–Stodola equation, which provides a more accurate insight of the system irreversibility compared to the standard Gouy–Stodola formulation. Furthermore, the comparison includes three working fluids, that is, R134a, R1234ze, and R600 in both the cycles. The study examines the effects of varying evaporators and condenser temperatures and the dryness fraction at the exit of Evaporator 1. The data is analyzed using an Engineering Equation Solver. The findings indicate that increasing the temperature of the low‐temperature evaporator leads to a drop in exergy losses and enhancement in exergy efficiency in both the cycles. When the temperature of Evaporator 1 is increased, the total exergy of the EB‐TEC is decreased but for the C‐TEC, it is increased. Furthermore, increasing the condenser temperature results in higher exergy destruction in both EB‐TEC and C‐TEC. Notably, the maximum exergy destruction is 49.44 kW for R600, whereas the minimum exergy destruction is 14.42 kW for R1234ze in the EB‐TEC.

Development of a modified gas turbine-based sustainable power generation and water treatment system; Economical/environmental considerations and data-driven optimization

Developing environmentally friendly solutions that optimize existing power plants while considering economic factors is crucial for ensuring sustainable energy production and mitigating environmental impact. This study promotes a gas turbine-based power plant design that prioritizes environmental concerns and underscores its versatility. The proposed setup is composed of various components, including a gas turbine, a Rankine cycle (RC), an organic Rankine cycle (ORC), a reverse osmosis (RO) desalination unit, a proton exchange membrane electrolyzer (PEME), and a hydrogen blending module. This system engenders the simultaneous generation of hydrogen, electrical power, and desalinated water. Additionally, the direct utilization of produced hydrogen in the proposed system offers improved technical performance and serves as an effective means to mitigate greenhouse gas emissions. A resilient programming code is formulated to systematically evaluate the system through the lenses of techno-economic and environmental considerations. Incorporating innovative modifications into the existing system resulted in an 8% cost reduction, a 1.2% decrease in carbon dioxide emissions, and a 5% enhancement in exergy efficiency. To attain optimal performance of the system, a data-driven and machine learning methodology is employed, wherein two distinct optimization scenarios are used to define the conditions that yield the utmost system performance. In the first scenario, the optimal values for cost, exergy efficiency, and normalized CO2 emissions have been computed as 39%, 5963 $/h, and 367.4 kg/MWh, respectively. In the subsequent scenario, the optimized system demonstrates the capability to generate a fresh water flow rate of 840.4 kg/s. Concurrently, the cost rate for the system equates to 7054.5 $/h.

Development of a vacuum double-slope solar still for enhanced freshwater productivity

In this study, a solar-energy-driven high performance water purification system is designed, fabricated, and examined, which may be useful for remote areas with limited access to grid electricity and underground freshwater. This research aims to enhance the performance of a conventional solar still (double-slope type) by creating vacuum inside the chamber and using paraffin wax (PCM) as energy storage material. The performance of the modified solar still (SS) is investigated and compared with the conventional solar still (CSS) in terms of productivity, distillation efficiency, and exergy efficiency. The performance analyses show that the hourly productivity and daily cumulative productivity are increased by 22.33 % and 63 % (from 5.46 L/m2 to 7.03 L/m2) respectively for the modified still compared to the conventional still. Nearly 28.72 % distillation efficiency and 22.43 % exergy efficiency enhancement are recorded for the modified system compared to the conventional system. This study also reveals that the thermal performance of the modified system is significantly improved under vacuum condition and using paraffin wax as heat storage material, which enables the still to operate at low solar intensities. The economic analysis shows that the cost of freshwater produced per liter in the modified SS is 41.4 % less than that of the conventional SS.

Exploring the thermal performance of a solar air heater with a V-corrugated and shot-blasted absorber plate comprising nano-enhanced phase change materials

This research aims to carry out an experimental investigation into the performance of a solar air heater using phase change materials in combination with V-corrugated absorber plates and shot blasting. This shot blasting approach is applied to interrupt the boundary layer thickness of the absorber plate material it will increase the absorbance of the material. This study incorporates the analysis of four distinct absorber plates namely (i) V-Corrugated Plate (ii) V-Corrugated with shot blasting, incorporating PCM (iii) V-Corrugated with shot blasting, including NEPCM (0.6 %) (iv) V-Corrugated with shot blasting, including NEPCM (0.9 %). In this study, Paraffin wax was selected as the base PCM, and MWCNT dispersed into base PCM with different weight fractions. The nano-enhanced phase change material with a concentration of 0.9 wt% examined that the latent heat of melting and solidification experienced a significant augmentation. This enhancement resulted in a maximum increase of 12.5 % for melting and 8.2 % solidification was attained at 0.9 % of MWCNTs compared with paraffin wax. The average exergy efficiencies of V-corrugated plate attains an efficiency of 1.023 %, V-corrugated with PCM records 1.357 %, V-corrugated with 0.6 % NEPCM attains 1.698 %, and V-corrugated with 0.9 % NEPCM attains the highest efficiency at 2.167 %. The significant enhancement in exergy efficiency observed in NEPCM configurations with volume fractions of 0.6 % and 0.9 % is primarily attributed to two key factors namely enhanced thermal conductivity and improved heat transfer properties. The maximum sustainability index for the V-corrugated design with 0.9 % NEPCM falls within the range of 1.014 to 1.037. The average “Nu” value of 27.5 was achieved under the conditions of a mass flow rate of 0.02 kg/s and the addition of 0.9 % MWCNTs dispersed in paraffin wax.

Energy, Exergy, and Environment Performance Evaluation of Cascade Refrigeration System with Natural Refrigerants

Cascade refrigeration systems are preferred in applications where low temperature cooling is required, such as in some special industrial and laboratory applications. Since, in these systems, the energy consumed by the compressors is less and the compressor outlet temperature is lower. Due to environmental problems, the use of natural refrigerants in cascade refrigeration systems has become to be of great importance. In this study, two cascade systems consisting of R744/R290 (System 1) and R1270/R290 (System 2) natural refrigerant pairs were designed and thermodynamically examined. In the analyzes performed according to different evaporator temperatures, the highest COP value was 3.66 at -20℃ evaporating temperature was obtained in the cascade system consisting of the R1270/R290 refrigerant pair. Moreover, it was considered that there was a 17.95% enhancement in exergy efficiency with the use of R1270 refrigerant in the low temperature cycle. By the rise in the evaporator temperature, energy consumption decreases and as a result, the amount of carbon dioxide emissions reduced was attained.

Clean production of power and heat for waste water treatment plant by integrating sewage sludge anaerobic digester and solid oxide fuel cell

A Sewage Sludge Anaerobic Digester (SSAD) system integrated with a Solid Oxide Fuel Cell (SOFC) was modeled and optimized to reach an efficient/cost effective system for producing clean power and heat in Parand wastewater treatment plant (WWTP). The system modeling was performed by the use of 4E analyses (energy, exergy, economic, environmental). Based on 4E modeling and by the use of two objective functions (payback period and exergy efficiency) and seven design variables, SSAD-SOFC system was optimized for shorter payback period and higher exergy efficiency. This multi-objective optimization provided the optimum system operating specifications. From this type of investigation which was not observed in literature for SSAD-SOFC system, the results showed 58747 m3/day of biogas production as well as 7.5 MWel and 5.3 MWth electricity and heating generation, respectively at the optimum point. Furthermore, at the optimum point the integrated system overall energy and exergy efficiency were also 28% and 21%, with payback period of 1.7 years. Moreover, in comparison with a traditional system in which WWTP had to buy electricity and natural gas from the grid and burns fuel for heating requirements, the relative annual benefit of the SSAD-SOFC system increased by 17.9%. Finally, results from multi-objective optimization showed 6.9% improvement in overall energy efficiency and 7.5% enhancement in exergy efficiency in comparison with those for single-objective optimization with only payback period as the single objective function. The development of a sustainable and cost-effective procedure for optimum design of WWTP for electricity and heat generation as well as implementing of the above analysis in other integrated systems with similar equipment are implications of this research.

Integration of wind turbine with biomass-fueled SOFC to provide hydrogen-rich fuel: Economic and CO2 emission reduction assessment

Addressing the energy crisis and global warming issues would entail urgent development of efficient and environmentally-benign power generation systems to mitigate the future clean energy policies. The biomass-driven SOFC systems are considered in this regard as pioneer technologies to supply clean power, particularly for decentralized applications. However, enough biomass availability and supply is a main challenge to run these systems. In current research to reduce biomass consumption, the biomass-driven SOFC is hybridized with wind turbines to produce pure hydrogen via a PEM electrolyzer. Produced hydrogen is added to the anode of SOFC to enrich the hydrogen content of the synthesis gas fuel. Feasibility assessment of proposed hybrid SOFC/wind turbine structure is examined considering first and second laws. Then, comprehensive economic and environmental appraisals are considered to inspect trade-offs between increased costs (associated with wind turbine and electrolyzer) and increased power as well as decreased CO2 emission. Finally to determine the optimal conditions for proposed system operation, triple-objective optimization via genetic algorithm is implemented. Obtained results have revealed exergy efficiency enhancement by 7.3% and CO2 emission reduction by 13.0 %, via incorporation of wind turbine. These technical and environmental performance enhancements are achieved at the expense of around 6.4 % increase in unit electricity cost, due to the increment of capital expenditures associated with the wind turbine and water electrolyzer. From parametric analysis, it is found that, the proposed framework yields lower electricity price and CO2 emission under higher cell temperatures and lower fuel utilization factors.

PV/Thermal as Promising Technologies in Buildings: A Comprehensive Review on Exergy Analysis

Solar Photovoltaic (PV) systems are degraded in terms of efficiency by increment in their temperature. To keep away from efficiency degradation regarding the temperature increase, various thermal management techniques have been introduced to keep the temperature low. Besides improvement in electrical efficiency, the overall efficiency can be enhanced by using the extracted thermal energy from the cell. The extracted heat in these systems, known as PV/Thermal (PV/T), can be applied for some purposes including water or air heating. This article reviews the works on the PV/T systems exergy analysis and discusses their findings. Based on the findings of the reviewed works, different factors such as the system configuration, used components and elements, and working conditions affect the exergy efficiency of these systems. As an example, use of coolants with improved thermal features, i.e., nanofluids, can cause improvement in the exergy efficiency. In addition to the nanofluid, making use of the thermal energy storage unit can further enhance the exergy efficiency. Furthermore, it has been observed that the materials of nanostructures can be another element that influences the enhancement of exergy efficiency. Moreover, the usage of some components such as glazing can lead to avoidance of thermal energy loss that would be beneficial from an exergy point of view. Finally, according to the reviewed works and knowledge of the authors, some suggestions are represented for future works in this field.

Transient behavior investigation of a regenerative dual-evaporator organic Rankine cycle with different forms of disturbances: Towards coordinated feedback control realization

This study utilizes an innovative regenerative dual-evaporator organic Rankine cycle (RDORC) with R1234ze to recover solid bulk waste heat by using air as heat transfer medium. A comprehensive transient model for RDORC is constructed based on finite volume method. Furthermore, a novel coordinated feedback control system for RDORC including two PI controllers is proposed to remain turbine inlet main vapor and resupplied vapor superheat degrees constant. The transient behaviors of RDORC and simple ORC (SORC) are compared under external disturbances of heat source inlet temperature. The results indicate that under 10 °C step decrease disturbance, the RDORC presents a 0.5 °C larger undershoot and a 164s longer setting time of superheat degree than that of SORC. Compared with SORC, the exergy efficiency enhancement of RDORC increases from initial value 4.13% to final value 4.51% after the step disturbance. Under sinusoidal disturbance with amplitude of 10 °C in RDORC, the peak amplitude of turbine main vapor inlet pressure (3.6%) is far higher than that of turbine resupplied vapor inlet pressure (0.82%). Besides, under random disturbance with variance of 1, the system exergy efficiency and thermal efficiency fluctuate around the design values of 35.67% and 7.65% with maximum deviations of 2.2% and 0.37%, respectively.

THERMOECONOMIC ANALYSIS AND MULTI-OBJECTIVE OPTIMIZATION OF AN INTEGRATED SOLAR SYSTEM FOR HYDROGEN PRODUCTION USING PARTICLE SWARM OPTIMIZATION ALGORITHM

This study aims to investigate the hydrogen production process using an integrated system based on solar energy. This system includes an evacuated tube collector to absorb solar energy as input energy of the system. A parametric analysis was conducted to determine the most important design parameters and evaluate these parameters' impact on the system's objective functions. For identifying the optimum system conditions, multi-objective optimization was performed using particle swarm optimization (PSO) algorithm. The results obtained from the parametric analysis show that an increment in the collector mass flow rate and the turbine inlet temperature, as well as a decrement in the collector area and the evaporator inlet temperature, results in improving the system exergy efficiency. Furthermore, the optimization results demonstrate that the exergy efficiency of the system can be improved from 1% to 3.5%; however, this enhancement in exergy efficiency of the system leads to increase the system costs from 20$/h to 26$/h, both at optimum states. At the optimum point, the average values for other performance parameters affecting the objective function including total output power production, cooling capacity, and hydrogen production rate are obtained as 24.24 kW, 47.07 kW, and 218.56 g/s, respectively.

Optimization of Solar CCHP Systems with Collector Enhanced by Porous Media and Nanofluid

The low efficiency of solar collectors can be mentioned as one of the problems in solar combined cooling, heating, and power (CCHP) cycles. For improving solar systems, nanofluid and porous media are used in solar collectors. One of the advantages of using porous media and nanoparticles is to absorb more energy under the same conditions. In this research, a solar combined cooling, heating, and power (SCCHP) system has been optimized by porous media and nanofluid for generating electricity, cooling, and heating of a 600 m2 building in a warm and dry region with average solar radiation of Ib = 820 w/m2 in Iran. In this paper, the optimal amount of nanofluid in porous materials has been calculated to the extent that no sediment is formed. In this study, solar collectors were enhanced with copper porous media (95% porosity) and CuO and Al2O3 nanofluids. 0.1%–0.6% of the nanofluids were added to water as working fluids; it is found that 0.5% of the nanofluids lead to the highest energy and exergy efficiency enhancement in solar collectors and SCCHP systems. Maximum energy and exergy efficiency of parabolic thermal collector (PTC) riches in this study are 74.19% and 32.6%, respectively. Figure 1 can be mentioned as a graphical abstract for accurately describing the cycle of solar CCHP.

Energy/exergy analysis of solar driven mechanical vapor compression desalination system with nano-filtration pretreatment

The performance of the mechanical vapor compression desalination system is limited due to the required vacuum pressure and associated high temperature scaling problem. Thus, a new solar driven mechanical vapor compression desalination plant with nano-filtration pretreatment operating at atmospheric pressure is developed for a production of 500 m3/day. The electrical and thermal energies of the new system are generated using the integration of solar photovoltaic modules and parabolic trough collectors. To evaluate the performance of the new system, energy/exergy analysis is performed by employing a MATLAB package and a Graphical User Interface (GUI) tool. Also, an economic evaluation for the plant's direct, indirect, and unit product costs ($/m3) is presented. The predicted results are validated with the available measurements. The effects of different design parameters such as feed water temperature, distilled and brine water temperature difference, salt rejection and recovery ratio on plant performance are investigated. The proposed plant's exergy efficiency is found to vary from 14.59 to 20% consistently with design parameters. The enhancement in exergy efficiency is estimated to be 153.7%, 56.3%, 32.63% and 27% compared with Multi-Effect evaporation mechanical and conventional vapor compression, forward feed multi-effect mechanical vapor compression and reverse osmosis systems, respectively. The salt rejection and recovery ratio are found to be the most significant parameters to enhance the plant exergy efficiency. Furthermore, the photovoltaic unit has a significant effect on exergy destruction of the plant with a percentage of 85.79%. The parabolic trough collectors also have high exergy destruction of about 69.53%. The economic analysis reveals that the unit water price for the proposed plant is equal to 1.54 $/m3. Therefore, the developed solar-NF-MVC system suits small scale units for remote communities.

Heat Transfer and Second Law Analysis of Ethylene Glycol-Based Ternary Hybrid Nanofluid Under Laminar Flow

Abstract Experiments were conducted to evaluate the thermal entropy generation, frictional entropy generation, and exergy efficiency of reduced graphene oxide (rGO)–Fe3O4–TiO2 hybrid nanofluid flow in a circular tube under laminar flow. The ternary nanoparticles were synthesized using the sol–gel technique and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and Fourier transform infrared spectroscopy (FTIR). The stable ethylene glycol-based ternary hybrid nanofluid was prepared and its thermophysical properties, heat transfer, friction factor, and pumping power at various values of particle weight concentrations (0.05–0.2%) and Reynolds number (211–2200) were studied experimentally. Nusselt number, heat transfer coefficient, friction factor, and exergy efficiency augment with increasing values of particle loading and Reynolds number. Results show the thermal conductivity and viscosity increase, as compared to the base fluid, by 10.6% and 108.3% at ψ = 0.2% and 60 °C. Similarly, for ψ = 0.2% and Reynolds number of 1548, and in comparison to the base fluid data, the Nusselt number and heat transfer coefficient enhancement are 17.78% and 24.76%, respectively, the thermal entropy generation reduction is 19.85%, and the exergy efficiency enhancement is 6.23%. At Reynolds number of 221.1, the rise in pressure drop, pumping power, and friction factor is 13.65%, 11.33%, and 16%, respectively, for ψ = 0.2% as compared to the base fluid data. The overall thermal performance of the system is enhanced by 14.32%. New equations are developed for the evaluation of the thermophysical properties, Nusselt number, and friction factor.

Parametric sensitivity analysis of split injection coupled varying methanol induced reactivity strategies on the exergy efficiency enhancement and emission reductions objectives in a biodiesel fuelled CI engine

The present study endeavours to exploit the benefits of reactivity controlled operation by leveraging significantly higher methanol participation through a decoupled methanol utilization strategy with Madhuca Longifolia biodiesel and conventional diesel as the pilot fuel under varying split injection profiles. The investigation was carried out at 10%, 25% and 50% pilot mass percentage, while the injection timings of pilot and main injection were varied in between −35 and −55 and −5 to −15 aTDC respectively. The results showed that the higher methanol participations caused longer ignition delays which lead to the shifting of the CA50 rightwards beyond the top dead centre. Reduction in maximum pressure rise rate was also evident in the RCCI regime. Compared to the baseline operation of single injection, the methanol/biodiesel RCCI operation under split injection strategy observed a maximum of 86% enhancement in exergy efficiency along with the maximum reductions in NOx and Soot emissions as 86% and 96% respectively. Furthermore, the analysis of Pareto solutions revealed that the methanol/biodiesel RCCI operation yielded 2.8% higher exergy efficiency along with 94% lower emissions of soot compared to its diesel counterpart, while the methanol/diesel operations exhibited 35% lower NOx emissions compared to the equivalent biodiesel RCCI operation.

EXERGETIC AND ENERGETIC EVALUATION OF AN INNOVATIVE SOLAR AIR HEATING SYSTEM COATED WITH GRAPHENE AND COPPER OXIDE NANO-PARTICLES

In the 21th century, renewable energy has to play very important role in socio-economic and industrial development. This paper evaluates the exergy- energy analysis, which is based on the second law of thermodynamics. The triangular solar heater is developed to determine the heat transfer rate, thermal efficiency, exergy efficiency and Bejan number. In addition, we have examined the effects of entropy generation with respect to solar radiation and ambient temperature of air. Absorber plates coated with graphene and copper oxide nano-particles by the different percentages (0.1%, 0.2%, 0.3% & 0.4%) doped into black paint which increases the absorption of heat. The Reynolds number (4500≤R_e≤22700) varies for the fixed selective coating on absorber plate and mass flow rate. The experimental observations were performed for constant mass flow rate of air ranging from 0.0035kg/s to 0.018 kg/s. The experimental result gives the average thermal efficiency enhancement of 3.58% for 0.3% graphene/CuO-black paint. Entropy generation is more for 0.1% and minimum for 0.3% graphene/CuO-black paint coating. The entropy generation analysis concludes that the entropy generation increases with increasing the mass flow rate. Exergy efficiency enhancement can be found 0.169%for 0.3% with respect to 0.1% graphene/CuO-black paint.

Performance evaluation of serpentine and multi-channel heat sinks based on energy and exergy analyses

A numerical and experimental study is conducted to enhance and compare the thermo-hydraulic characteristics of two types of rectangular mini-channel heat sinks, namely, the serpentine mini-channel heat sink and multi-mini-channel heat sink. The comparisons of the improvement of heat transfer and fluid flow in the two heat sinks with five designs were conducted in terms of energy and exergy analysis. The finite volume technique was employed to solve the governing equations under laminar flow conditions with water as a cooling medium. The new designs included using two techniques; the first is using only ribs mounted on the sidewall with semi-circular and semi-elliptical shapes. While the second technique is based on integrating the pin fins, that mounted in the center of channels, with grooves on the channels sidewalls. The optimum design obtained from the numerical simulation was fabricated and experimentally tested to verify the reliability of the numerical simulation. The results showed that the incorporation of the pin-fins with grooves is effectively improved the heat dissipation for both designs compared with using only ribs. The Nusselt numbers attain about 33.85, 12.2 for the serpentine mini-channel heat sink, and multi-mini-channel respectively, while the pressure drop reached about 14190, 363.8 Pa. Meanwhile, the percentage of enhancement in exergy efficiency reached 24% and 37% for serpentine minichannel and multi-minichannel heat sinks, respectively.

Exergy Analysis of Advanced Adsorption Cooling Cycles.

This study conducted an exergy analysis of advanced adsorption cooling cycles. The possible exergy losses were divided into internal losses and external losses, and the exergy losses of each process in three advanced cycles: a mass recovery cycle, heat recovery cycle and combined heat and mass recovery cycle were calculated. A transient two-dimensional numerical model was used to solve the heat and mass transfer kinetics. The exergy destruction of each component and process in a finned tube type, silica gel/water working paired-adsorption chiller was estimated. The results showed that external loss was significantly reduced at the expense of internal loss. The mass recovery cycle reduced the total loss to 60.95 kJ/kg, which is −2.76% lower than the basic cycle. In the heat recovery cycle, exergy efficiency was significantly enhanced to 23.20%. The optimum value was 0.1248 at a heat recovery time of 60 s. The combined heat and mass recovery cycle resulted in an 11.30% enhancement in exergy efficiency, compared to the heat recovery cycle. The enhancement was much clearer when compared to the basic cycle, with 37.12%. The observed dependency on heat recovery time and heating temperature was similar to that observed for individual mass recovery and heat recovery cycles.

Energy, exergy and exergoeconomic analyses and optimisation of 137 MW gas power station implementing MOPSOCD

Performance evaluation and optimisation of operating parameters of gas power plants are the key challenges for the researchers and the power plant designers. Traditional performance evaluation techniques being utilised operate on the first law of thermodynamics. Exhaustive studies in this area suggest scope of improvement in view of power output, thermal efficiency and cost effectiveness through more valuable evaluation techniques as second law analysis, exergoeconomic analysis and evolutionary algorithms. In this perspective, energy, exergy and exergoeconomic investigations of the gas power plant are executed in context with 1st and 2nd laws of thermodynamics. The multi-objective optimisation is also performed using NSGA-II and MOPSOCD evolutionary algorithms in MATLAB 9.2 in order to explore best input parameters and to find best trade off amongst two challenging objectives. The validation of the present work is done by correlating the obtained outcomes with 137 MW running gas power plant, Faridabad, India. The analysis illustrates a considerable enhancement in exergy efficiency of the power plant (around 18%) with a drop-in cost of the fuel and product as 15.72% and 13.24% respectively. However, total capital cost is increased by 10.61%.

“Performance comparison of innovative spiral shaped solar collector design with conventional flat plate solar collector”

Flat plate solar collector is an essential device, which facilitate direct application of solar energy for water heating in household and industrial sector. Existing Flat plate solar collectors (FPSC) suffers from stagnant and comparatively low efficiency. Further research to improve efficiency of FPSC by inculcating innovative design is necessary. To fill the gap, the presented work is an experimental investigation of an innovative design and fabrication approach which deals with analysis of flat plate solar collector efficiency. Design modifications of solar collector always offer an important alternative to achieve significant effect on thermal efficiency. In this work single spiral shaped collector tube as compare to number of riser tubes connected with headers in conventional type flat plate solar collector has been developed. Keeping all other parameters similar to conventional design, it has been observed very encouraging outcomes in efficiencies of solar collector. Under forced mode of testing, enhancement in thermal efficiency achieved is, 21.94% compared to conventional flat plate collector design. Enhancement in exergy efficiency is 6.73%. Overall material saving is about ∼30% and cost of manufacturing and maintenance can be significantly reduced at equivalent performance of conventional collector.

Investigation of Exergy of Double-Pipe Heat Exchanger Using Synthesized Hybrid Nanofluid Developed by Modeling

Synthesized copper oxide nanoparticles were incorporated on the surfaces of carbon nanotubes using ultrasonication condition and incipient wetness impregnation technique (IWI). Morphological surfaces and structures of the prepared nanocomposite were investigated by the Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD). Results showed a modification of thermophysical properties of prepared hybrid nanofluids compared to untreated carbon nanotube-water. Four parameters (Reynolds number, nanofluid volume fraction, twisted (pitch) ratio, and cavity diameter ratio) were investigated, and their impacts on the exergy efficiency enhancement of double-pipe heat exchanger were determined. Modifying response surface methodology-central composite design (RSM-CCD) to realize the optimal exergy efficiency of the system (98.4 %) showed the possibility to improve all control variables contemporarily and with significant accuracy. There was a strong correlation between the experimental and predicted values by Artificial Neural Network-Genetic Algorithm (ANN-GA) (R2 = 0.92). Minimum mean square error (MSE) was found using a three-layer ANN with 10 neurons in the hidden layer. The results show that the increased Reynolds number and nanofluid volume fraction lead to increases in the heat transfer and exergy efficiency of the system. However, while adding pitches and cavities of the spiral strip to heat exchanger increases heat transfer due to the increasing turbulence flow, at larger pitches and cavity numbers, heat transfer and exergy efficiency were reduced. This was confirmed using two computer-modeling approaches which allow optimization of the exergy of the system.