Variation Of Mass Flow Rate Research Articles

Highly efficient droplet generation device based on a three-dimensional fractal structure

In this paper, a three-dimensional axisymmetric fractal structure device was proposed for massive production of monodisperse droplets. Its channel number could increase to nm for an m-stage fractal device with n-channel distributors. A fractal device with 36 channels was constructed, and the droplet generation experiment was carried out. The experiment showed that the coefficient of variations (CVs) of the generated droplets were all lower than 4.0% at four different flow rates. Additionally, the relationship between the mass flow rate and fractal structure variation was examined through theoretical and data regression analysis. To elaborate the overall structure deviation, the accumulated deviation was introduced, the formula of accumulated deviation and droplet size was given. The results showed that the droplet products were highly monodisperse. The droplet size deviation was within 2% when the accumulated deviation of dispersed- and continuous-phase distributors was less than 4% and 10%, respectively.

Off-design and control performance analysis of a novel supercritical carbon dioxide power cycle for waste heat recovery

A novel supercritical carbon dioxide power cycle (sCO2) for waste heat recovery (WHR) is developed. This novel cycle has high efficiency, and it could make a more complete utilization of the waste heat. Besides, the flexible and independent controls of recompression compressor and main compressor can be made to obtain the better off-design performance. The off-design and control performance of this system is quantitatively investigated in this paper. The results indicate that the optimal net power output increases as mass flow rate or temperature of flue gas increases, whereas it decreases with increasing ambient temperature. The first and second highest exergy destruction shares always belong to the cooler and LTWHE under various external conditions. The adjustment of two compressor outlet pressures should be a priority under various mass flow rates or temperatures of flue gas, while the adjustment of cycle minimum pressure should be given a high-priority rating in response to variation of ambient temperature. Moreover, the control performance of recompression compressor is more sensitive to the variation of flue gas mass flow rate, while the control performance of main compressor is more sensitive to the variation of flue gas temperature and ambient temperature.

Photovoltaic thermal system with phase changing materials and MWCNT nanofluids for high thermal efficiency and hydrogen production

The performance and electrical output of photovoltaic/thermal (PV/T) systems are significantly affected by an increase in the PV cell temperature. The integration of nanofluids has been explored as a solution to mitigate cell temperature rise in PV/T modules. However, the use of nanofluids raises environmental concerns. Thus, in this study, the attempt has been made to incorporate both MWCNT nanofluids and phase changing materials to reduce the cell temperature and which apparently improvised the electrical output and thermal efficiency. A series of tests conducted on five different samples at varying mass flow rates of 30 LPM, 40 LPM, and 50 LPM. MWCNT was dispersed in water at volumes of 0.05%, 0.1%, and 0.15% v/v using the sonication method. The proposed PV/T hybrid system effectively reduced panel temperature. Additionally, the integration of PCM and nanofluids resulted in an 8% increase in electrical power and a 12% improvement in thermal efficiency. Furthermore, higher nanofluid mass flow rates led to an enhanced electrical efficiency, ranging from 12.5% to 14.5%. Findings reveal that the incorporation of PCM with nanofluids holds promise for sustainable and improved energy production. Moreover, the possibility of hydrogen production through electrolysis is a viable option that permits further investigation.

Simulation of Heat Storage and Heat Regeneration in Phase Change Material

The present study explores numerically the energy storage and energy regeneration during Melting and Solidification processes in Phase Change Materials (PCM) used in Latent Heat Thermal Energy Storage (LHTES) systems. Transient two-dimensional (2-D) conduction heat transfer equations with phase change have been solved utilizing the Explicit Finite Difference Method (FDM) and Grid Generation technique. A Fortran computer program was built to solve the problem. The study included four different Paraffin's. The effects of container geometrical shape, which included cylindrical and square sections of the same volume and heat transfer area, the container volume or mass of PCM, variation of mass flow rate of heat transfer fluid (HTF), and temperatures difference between PCM and HTF were all investigated. Results showed that the PCMs in a cylindrical container melt and solidify quicker than the square container. The increase in mass flow rate and/or temperature difference decreases the time required for complete phase change. Paraffin's solidify quicker than they melt and store more energy than they release

Waste heat recovery optimization in ammonia-based gas turbine applications

E-fuels are promising alternatives to fossil fuels in the transition towards zero-emission energy system. In this study, a novel chemical-recuperated and humidified gas turbine concept aiming at the application of e-fuel ammonia is proposed to overcome the technical hitches and exploit the waste heat to enhance the cycle performance. The thermodynamic analysis shows that the highest net electrical efficiency (56.7%) under the design conditions exceeds that of the ammonia-fueled Brayton cycle by 20.6%-points. The chemical recuperation of fuel contributes to the efficiency improvement by 7%-points under dry condition, while steam injection provides 8%-points to 12%-points efficiency increase corresponding to the ammonia decomposition ratio of 5%–96%. A non-monotonic relation between the net electrical efficiency and steam-to-air ratio is found to be the result of the competition between the enthalpy change from to the varied steam and air mass flow rates. Analyzing the flame characteristics in the combustor under the design conditions, we found that conditions with high decomposition ratio (>88%) and high steam-to-air ratio (>0.3) exhibit similar flame speed with that of methane fueled combustor and thus existing designs can be reused. The prediction shows the NOx emission can be restricted when the steam-to-air ratio exceeds 0.4.

Thermal performance analysis of the parabolic trough solar collector in the Sub-Saharan climate of the Central African Republic

This work proposes a mathematical model of the PTSC in one dimensional (1-D) simulated under the sub-Saharan climate conditions of the Central African Republic (CAR). An optical model of the PTSC system is proposed. Four thermal models of the support bracket were used resulting in four thermal models of the PTSC in addition to a thermal model without support bracket. The Gauss-Seidel method is used and simulated with Matlab software. The five developed mathematical models submitted to validation tests in comparison with the Sandia National Laboratory data show that model 3 is the best with an error of 5.47 %, followed by 5.54 % model 0, 5.69 % model 1 and 5.95 % model 2. The thermal effects of the support bracket on the absorber outlet temperature are quantified at 0.74 % for model 3, 2.61 % for model 1, 7.53 % for model 2 and 19.29 % for model 4 compared to the model without support bracket. The wind speed has significant impacts on the outlet temperatures. Three vegetable oils were used as heat transfer fluids (HTFs) in comparison with Therminol VP-1 showing a sensitivity to mass flow rate variations with high temperatures reached daily on average of about 200 °C for a flow rate of 0.04 kg/s.

Multi-Objective Optimization of a Bi-Metal High-Temperature Recuperator for Application in Concentrating Solar Power

Abstract Supercritical CO2 closed Brayton cycles are a major candidate for future power cycle designs in concentrating solar power applications, with high-temperature recuperators playing an essential role in realizing their high thermal efficiency. Printed circuit heat exchangers (PCHEs) are often chosen for this role due to their thermal-hydraulic and mechanical performance at high temperatures and pressures, all while remaining compact. However, PCHEs can be costly because of the high-performance materials demanded in these applications, and the heat exchanger internal geometry is restricted by their manufacturing process. Additively manufactured heat exchangers can address both of these shortcomings. This work proposes a modular bi-metal high-temperature recuperator with integrated headers to be produced with additive manufacturing. Beginning with existing PCHE channel geometries, a 1D heat exchanger model is developed. Then, multi-objective optimization is used to maximize the heat transfer effectiveness of a lab-scale device while limiting its size. Two distinct channel geometries emerge from the optimization. Optimal designs achieve up to 88% effectiveness with negligible pressure drop. Deterioration of effectiveness due to axial conduction of heat in the heat exchanger walls is found to be a notable problem for lab-scale PCHEs, and the optimal designs obtained here minimize its detrimental effects. A sensitivity analysis reveals that the effectiveness of the recuperator is much less sensitive to variation in mass flowrate in off-design operation when axial conduction is significant, while increasing the length of the device easily increases effectiveness.

Multi-objective optimization on bionic fractal structure for heat exchanging of two fluids by genetic algorithm

Numerous industrial processes involve heat exchange, and the efficiency of energy usage depends heavily on the effectiveness of this exchange. Thermal structure is a critical factor that influences the process of heat transfer. The bionic fractal structure has been heavily researched due to its ability to provide a more uniform flow distribution and improved heat transfer performance. An iterative approach to determining the central wall temperature is suggested for heat transfer between two fluids with varying mass flow rates and physical features. A bionic fractal heat transfer model for two fluids was developed, and the features of the bionic fractal heat transfer structure with supercritical carbon dioxide (supercritical CO2) and H2O were expounded. Furthermore, the variation of heat transfer performance with parameters was analyzed comprehensively. A method for the optimization and design of a bionic fractal heat transfer structure using two fluids was also provided, and the index of heat transfer performance was found to have the best value for various structural factors. The multi-objective optimizations of the bionic fractal heat transfer structure were carried out by a genetic algorithm, and the results showed a 15% reduction in power consumption for the optimized heat transfer structure, a 2.4% increase in heat transfer, and an improvement in the index of heat transfer performance by 17%.

Thermal performance evaluation of a compact two-fluid finned heat exchanger integrated with cold latent heat energy storage

To alleviate the mismatch between thermal energy supply and demand, the use of latent heat thermal energy storage of phase change materials is a reliable and effective solution in thermal systems. The present work aims to introduce an innovative finned-plate air-liquid heat exchanger with phase change material partially embedded in the fins' gap providing airside cooling by thermal energy storage during coolant shutdown periods. The thermal performance and accompanying phase change process are studied using a three-dimensional computational fluid dynamic approach. The developed model is validated with corresponding experimental data at the same geometry and operating conditions. The system performance is examined time-dependently considering the charging/discharging processes of the phase change material. The effect of air mass flow rate variation is studied, and the results are discussed in terms of fluids temperature, heat transfer rates, and the phase change material phase transition process. The results demonstrate that the heat exchanger stores excess thermal energy during the charging process, which is later discharged for air cooling during demand periods. It is observed that the use of phase change material provides a cooling load of 188 kJ and over 9 min of extra cooling time for the airside in the discharging process. The share of latent heat transfer in the discharging process is calculated at an average of 54% of the total heat transfer. Obtained results reveal that increasing the air mass flow rate can reduce the rate of discharged cold thermal energy and cooling time. The presented thermal management system offers a unique solution to manage passenger thermal comfort in hybrid and electric vehicles with a start-stop function. The introduced system could provide efficient cabin air cooling and enable effective energy savings during short periods of engine shutdown.

Three-dimensional simulation of a gas-centered swirl coaxial injector spray under pulsation conditions

Based on steady-state experiments, a three-dimensional (3D) simulation study under pulsation conditions was carried out. This was performed to study the effect of pulsation of the supply system on the atomization characteristics of a gas-centered swirl coaxial injector. The results indicated that the spray shape resembled a pagoda when the Klystron effect occurred. When the low-frequency pulsation (200 Hz) was applied to the liquid inlet, the peak of the exit pressure was close to the trough of the inlet mass flow rate. Meanwhile, the exit mass flow rate and pressure were approximately sinusoidal. There was no significant lag effect in the response of the exit mass flow rate to the inlet mass flow rate but with a small sawtooth-like oscillation. Increasing the amplitude of the liquid inlet disturbance amplified the exit mass flow rate fluctuation, which was greater than the set amplitude of the inlet pulsation. The dominant frequency of the injector exit mass flow rate and pressure variation was significantly less than the inlet pulsation frequency when the frequency of the liquid inlet pulsation was increased to 1000 Hz. This was due to the low-pass filtering effect of the annular slit. There was no significant change in the overall spray morphology for the gas inlet pulsation. By applying the same amplitude and frequency of pulsation to the gas and liquid inlets of the injector, the pulsation of the liquid inlet had a stronger effect on the injector exit spray than that of the gas inlet.

Numerical investigation of thermo-hydraulic ability of STHX with continuous helical baffles on the shell side

The larger quantities of heat transfer rates are possible with the modification of few parameters like baffle cut and shape. Which significantly improves the performance of shell and tube heat exchanger while reducing the pressure drop. From the reported literature review it was proposed to carry the numerical analysis for various helix angles. The present study is to simulate heat transfer rate and liquid movement in a shell-and-tube heat exchanger along with continuous helical-baffles on the shell side. The numerical investigation of seven helix angles, namely 10°, 19°, 21°, 25°, 30°, 38°, and 50°, is done for varying mass flow rates and the inlet temperature of shell side and tube side are 25 °C and 55 °C respectively, modelled a whole length unceasing helical-baffled shell-and-tube heat exchanger. Larger helix angles (30°, 38°, and 50°) result in reduced heat transfer rate and pressure drop too low, while minor helix angles (10°, 19°, 21°, and 25°) result in increased heat transfer rate and pressure drop too high.

Performance evaluation of serpentine tube coupled with modified twisted tapes utilized as heat extraction coil in solar ponds

The thermal energy collected and stored by solar ponds is usually extracted by using some heat exchangers, where curved tubes form their core. The present study aims to appraise the performance of a serpentine tube under varied mass flow rates and inlet temperatures of the working fluid. Three different types of twisted tapes nominated as uniform twist pitches (U), low to high twist pitches (LH), and high to low twist pitches (HL) are employed to enhance the heat extraction rate. This article is the first report addressing the application of non-uniform twisted tapes as turbulators in a serpentine tube. In this regard, a solar pond simulator containing salt water is designed and fabricated. Numerical simulations are also carried out to display the transport phenomena inside the models. The numerical results are compared with the experimental data, and a close agreement is found. From the thermal point of view, the sequence of twisted tapes is LH > HL > U, while it follows the order of U > LH > HL according to the frictional loss. The findings demonstrate that depending on operating conditions, the heat extracted by the modified cases is 4 to 70% more than the base model. It is also found that employing non-uniform twisted tapes results in lower flow resistance compared to the uniform case. The pressure drop augmentations produced by U, LH, and HL TTs are 26.5%, 17.5%, and 10.4%. Further, the overall performance index is higher than unity for all the enhanced cases. The best case is the twisted tape having low to high twist pitches (LH) which has an average performance index from 2.03 to 2.71.

Modelling and analysis of a compression/resorption heat pump system with a zeotropic mixture of acetone/CO2

Industrial processes represent one of the most energy-consuming activities, which are related to fossil fuel utilization and the growing environmental problems. In this way, the heat waste energy recovery has been presented as an efficient solution, to take advantage of low-grade residual heat, where the compressor -resorption heat pump technology has proven to achieve high-temperature levels with a considerable Coefficient of Performance. However, known working fluids such as hydrofluorocarbons represents an environmental hazard due to its Global Warming potential, these have been replaced by natural fluids such as ammonia, but they also have disadvantages like its toxicity. In this way, the CO2 is an available waste heat compound product of fossil combustions, therefore, this research is based on the utilization of novel fluids such as the zeotropic mixture of CO2/Acetone as an eco-friendly working fluid with low Global Warming Potential. Even more, the utilization of the mentioned compound represents the opportunity to explore the utilization of low-grade residual heat that sometimes is not used in subsequent applications. In this sense, the modelling of the binary vapor–liquid equilibria of the mixture CO2/Acetone has been performed based on a thermodynamic model using the Peng-Robinson equation regarding the conditions of pressure, temperature, and concentration of the fluids for operational industry applications. The modelling of the compression/resorption heat pump cycle is based on the mass and energy balance for each component with Engineering Equation Solver software (EES). In this way, the adjustment of equilibria for the mixture determinates the maximum average square deviation of 4.28 % and 8.70 % for a temperature range between 291 and 303 K and 333 to 393 K. The concentration of CO2 from 20 % to 50 % showed that the increasing molar fraction delivers a more efficient cycle, even reaching a coefficient of performance of 3 for a difference of 0.2 between the global concentration of CO2 and the poor solution, and a 20 °C temperature difference between source and sink. Even more, the COP obtained in the simulation was not affected by variations of steam mass flow rate and it was proven that the mathematical model proposed has a correlation with the literature.

The adoption of pressure independent control valves (PICVs) for the simultaneous optimization of energy consumption and comfort in buildings

The optimization of energy consumption in buildings’ HVAC systems plays a crucial role in reducing greenhouse gas emissions worldwide. In new and deeply-renovated buildings, characterized by modulating terminal units and aiming at the maximum exploitation of renewables, an accurate hydraulic balance of the distribution network may become critical, resulting in a significant increase of pumping energy consumptions and a deterioration of indoor thermal comfort conditions. In the present paper, we compare the performance of traditional manual balancing valves and new pressure independent control valves (PICVs), used to balance the hydronic loop of HVAC systems. To perform this analysis, a new MATLAB-Simulink model has been specifically developed to simulate the behavior of PICVs and has been used in an application case study. The efficiency of manual and pressure independent control valves is evaluated numerically by simulating a multi-zone distribution network under variable operating conditions and considering different control strategies of the circulating pump. Results show that in off-design conditions, when some of the branches of the hydraulic network are closed, traditional manual balancing valves are not able to guarantee the nominal mass flow rate in the remaining loops. On the contrary, no significant variations of water mass flow rate are observed when PICVs are adopted, even in partial load conditions. Despite their additional cost, PICVs allow to ensure better indoor thermal comfort sensations for individuals, avoiding under/over-heating of rooms and, moreover, yield a decrease of the pump electric consumption with respect to traditional manual balancing valves. In addition, based on the obtained results, general rules concerning the adoption of PICVs are provided, depending on the extension of the hydraulic loop and the adopted pump control logic. The reported results highlight the role that PICVs can play to ensure energy savings in HVAC systems without penalizing users’ indoor comfort conditions.

Numerical simulation optimization of neutral flow dynamics in low-power Hall thruster

This paper utilizes a low-power Hall thruster to investigate its flow field’s neutral flow dynamics. Specifically, under a free molecular flow with a high Knudsen number (Kn>10), we employ the flow conductance theory to investigate the interplay between the internal structural parameters of the thruster flow field and its conductance, which is directly reflected in the neutral gas distribution.Hence, first, we increase the number and diameter of the orifices in the buffer chamber so that the baffle effectively increases the flow field conductance, and thus the number density (nn) of the neutral gas in the discharge channel increases. This phenomenon reduces the ionization mean free path (λi) and thus increases the utilization rate (ηi) of the neutral gas. Then, we alter the baffle orifices distribution to an unequally spaced distribution and stagger the outlet orifices, resulting in a highly homogeneity neutral gas distribution in the circumferential direction, ultimately increasing the effective outlet area and reducing the backflow probability of the neutral gas molecules. This operation reduces the low-frequency oscillation amplitude and thus enhances the thruster’s operation stability. Finally, we explore the influence of the entire operating conditions, especially temperature and mass flow rate variations, on the universality of the simulation results. Overall, this work provides a new concept for optimizing the neutral flow field dynamics of a Hall thruster.

Analysis of spray characteristics of a jet-film injection element based on Voronoi tessellation

The present paper presents a computational study based on a validated Volume-of-Fluid method on the effects of film thickness and film width on spray characteristics for the simplified jet-film injection element with varying mass flow rate conditions. First, the spray characteristics of a typical jet-film collision were analyzed in terms of the spatial distribution of Sauter Mean Diameter and Voronoi tessellation. Both the Voronoi diagram and the Sauter Mean Diameter contour are useful to evaluate the spray characteristics because they show two different aspects of the sprays. Second, the jet-film spray characteristics were analyzed by decreasing either film thickness or film width to change the mass flow rate. The results show that decreasing film width results in approximately insensitive spray angle and improved uniformity of droplet distribution for different throttleable levels. The present computational results verified our design concept that adopting traditional jet-film injection at a large mass flow rate and modified jet-jet injection at a small mass flow rate to maintain good spray performance during the entire throttleable levels.

Thermal performance investigation of double pipe heat exchanger embedded with extended surfaces using nanofluid technique as enhancement

In the present work, a numerical investigation of heat transfer enhancement in a “double pipe heat exchanger” embedded with an extended surface on the inner tube's outer surface with the addition of “Alumina nanofluid” has been carried out. Through the annuli, water with varying mass flow rates (0.03–0.07 kg/s) and hot de-ionized water with varying Reynolds numbers (250–2500) flows, while hot de-ionized water flows through the inner tube. One type of nanoparticle (Al2O3) having volume concentrations (1%, 3%, and 5%) was used during simulation. Numerical analysis was performed using Computational Fluid dynamics, and the Solid works was used to generate the model. A Semi-Implicit Method for Pressure Linked Equations technique was used to solve the governing equations and discretized using the finite volume method. The simulated results show that the use of a finned tube heat exchanger resulted in an improvement ratio between (2.3) and (3.1). The coefficient of convective heat transfer increased numerically as the volume concentration and Reynolds number increased. The heat transfer coefficient and thermal conductivity rise by 20% and 4.7%, respectively, at a volume concentration of 5%.

Indoor Performance Analysis of a Novel Double-Pass photovoltaic/thermal (PV/T) Asymmetric Compound Parabolic Concentrator (ACPC) Solar Collector

A photovoltaic/thermal (PV/T) solar collector combines solar photovoltaic (PV) modules and solar thermal that operates simultaneously to generate electricity and thermal energy. Design parameters, operating conditions and environmental factors all have a significant impact on the performance of a PV/T solar collector. This research investigates the influence of the variation in the air mass flow rate to the performance of a novel double-pass photovoltaic/thermal (PV/T) asymmetric compound parabolic concentrator (PV/T-ACPC) solar collector. To investigate performance of the solar collector, it was tested indoors using a solar simulator at average solar radiation of 800 W/m2 with the variation in the air mass flow rate ranging from 0.0074 kg/s to 0.0900 kg/s. From the analysis, we found that as the air mass flow rate increases, the thermal efficiency and electrical efficiency increases from 37.15 % to 60.51 %, and 2.51 % to 3.29 % respectively. Meanwhile while the difference in the air output temperature and PV panel temperature were found to decrease from 19.64 °C to 2.63 °C, and 66.83 °C to 41.86 °C respectively. We also found that, as the mass flow rate continues to increase, it will reach its ‘optimum point’ and approaching a plateau at mass flow rate of 0.0262 kg/s. The finding is crucial since the collector needs to be operated at its optimum flow rate to ensure optimum efficiencies at the optimum temperature rise of the useful air supply.

Impact of bumpers position variation on heat exchanger performance: an experimental and predictive analysis using an artificial neural network

Experimentally and numerically, the thermal performance enhancement of counterflow twin-pipe heat exchanger with bumpers position variation was explored. A set of semicircular bumpers were positioned at varying distances from the fluid flow entrance on the annulus gap of the concentric pipe heat exchanger (10–70, 70–130, and 130–190 cm). The hot water entered the inner pipe at a constant mass flow rate of 0.0167 kg/s, whereas the cold air entered the annulus gap of a concentric pipe heat exchanger at changing mass flow rates of 2 × 10−5 to 14 × 10−5 kg/s. The numerical portion comprised simulating the efficacy of the heat exchanger with a smooth pipe and varied bumper placements using an artificial neural network (ANN) model. The experimental portion of the present work consisted of a series of tests to determine the optimal position of the bumpers for maximizing heat exchanger efficiency. At a constant fluid inlet temperature and with varied mass flow rates of the cold air, the numerical model was compared to the experimental results. When the bumpers are put at a distance of 130–190 cm, the heat exchanger has the highest thermal efficiency compared to other bumper placements and a smooth pipe. In all cases of the investigation, there is a good correlation between numerical and experimental data.

Energy, exergy and economic (3E) analysis of flat-plate solar collector using novel environmental friendly nanofluid

The use of solar energy is one of the most prominent strategies for addressing the present energy management challenges. Solar energy is used in numerous residential sectors through flat plate solar collectors. The thermal efficiency of flat plate solar collectors is improved when conventional heat transfer fluids are replaced with nanofluids because they offer superior thermo-physical properties to conventional heat transfer fluids. Concentrated chemicals are utilized in nanofluids' conventional synthesis techniques, which produce hazardous toxic bi-products. The present research investigates the effects of novel green covalently functionalized gallic acid-treated multiwall carbon nanotubes-water nanofluid on the performance of flat plate solar collectors. GAMWCNTs are highly stable in the base fluid, according to stability analysis techniques, including ultraviolet–visible spectroscopy and zeta potential. Experimental evaluation shows that the thermo-physical properties of nanofluid are better than those of base fluid deionized water. The energy, exergy and economic analysis are performed using 0.025%, 0.065% and 0.1% weight concentrations of GAMWCNT-water at varying mass flow rates 0.010, 0.0144, 0.0188 kg/s. The introduction of GAMWCNT nanofluid enhanced the thermal performance of flat plate solar collectors in terms of energy and exergy efficiency. There is an enhancement in efficiency with the rise in heat flux, mass flow rate and weight concentration, but a decline is seen as inlet temperature increases. As per experimental findings, the highest improvement in energy efficiency is 30.88% for a 0.1% weight concentration of GAMWCNT nanofluid at 0.0188 kg/s compared to the base fluid. The collector's exergy efficiency increases with the rise in weight concentration while it decreases with an increase in flow rate. The highest exergy efficiency is achieved at 0.1% GAMWCNT concentration and 0.010 kg/s mass flow rate. GAMWCNT nanofluids have higher values for friction factor compared to the base fluid. There is a small increment in relative pumping power with increasing weight concentration of nanofluid. Performance index values of more than 1 are achieved for all GAMWCNT concentrations. When the solar thermal collector is operated at 0.0188 kg/s and 0.1% weight concentration of GAMWCNT nanofluid, the highest size reduction, 27.59%, is achieved as compared to a flat plate solar collector with water as a heat transfer fluid.