Second-law Analysis Research Articles

Analysis of magneto-natural convection and second law of thermodynamics of Cu-Al2O3-hybrid nanofluid in a vertical wavy cabinet having a localized non-uniform heat source

Improvements in thermal transference rate and minimization of entropy generation are critical issues in many industrial and engineering applications where heat transfer coefficient is essential to achieve optimal performance and minimal energy consumption. In the present investigation, a computational analysis has been conducted to analyze the impact of magnetic field on magneto-free convection and entropy generation inside a vertical wavy cabinet filled by Cu-Al2O3/H2O hybrid nanosuspension. In the geometry of this model, vertical boundaries of the chamber are designed as wavy and kept as cooled temperature (Tc), whereas the horizontal boundaries are modeled as square and are designed to be thermally adiabatic, except the centrally heated portion on the bottom wall. The centered bottom heated section is supposed to be isothermal with linearly changing temperature, and it changes linearly from Th1 to Th2, whereas it is modelled as a non-isothermal condition. The main focus, in this investigation, is on the entire chamber filled with the combination of hybrid nanoparticles regarded the volumetric concentration of copper and alumina nanoparticles (Cu-50 %+Al2O3-50 %) along with base liquid (H2O). The transformed dimensionless partial differential equations were solved by using finite volume method (FVM) with power law differencing scheme. The simulated flow and temperature fields are scrutinized by streamlines, isotherms, entropy formations, total entropy generation and average convective Nusselt number associated with varying number of undulations (0 ≤ N≤3) volume fraction of hybrid nano liquid (0 ≤ φ ≤ 0.04) magnetic orientation angles (0° ≤ ς ≤ 135°), Hartmann number (Ha = 0 and 50), and dimensionless temperature drop (Ω = 0.001–0.1). From this study, it is found that the average Nusselt number and entropy generation increase as the solid volume fraction of hybrid nanoadditives increases, while opposite trend is observed when the values of Hartmann number rises. The findings show that growth of undulation number (N) causes the reduction of convective heat transfer rate as well as average entropy production intensity. The obtained outcomes concluded that hybrid nano liquid is more effective and finest choice for the improvement of cooling of heat transfer process and minimal energy loss than single nanoliquid. According to the new proposed criterion (TPC), the results show that square-shaped enclosure (N=0) manifests the better cooling performance among the considered governing parameters. The novelty of this study is to scrutinize the flat/ vertical wavy boundaries of the cabinet which can be represented as a model of heat transfer controller, in which it manages the thermal and flow field characteristics. Predominantly, the isothermal line source is used to boost the overall convective heat transfer which is applied in buildings and fluid-mounted heaters. Additionally, many investigators have focused only on the enhancement of heat transfer. As it is known, to increase the thermodynamic efficiency of a system, optimization of entropy generation is an excellent tool which reduces the loss of energy. Hence, it recently does a good engineering sense to highlight an entropy irreversibility.

Numerical energy and entropy analyses of a tube with wavy tape insert including CoFe2O4/water nanofluid under laminar regime

The primary objective of this investigation is to assess the impact of vortex generator geometry and nanofluid on thermohydraulic and irreversibility characteristics within a laminar flow regime. The study introduces an original CoFe2O4/H2O (1 % vol.) nanofluid and employs a wave tape insert to induce forced convection in a tube, accompanied by first and second-law thermodynamic analysis. The novelty of this research lies in the numerical exploration of heat transfer and flow profiles for a nanofluid in a tube, varying the wave rate (y = 4-5-6). The investigation considers the laminar model and single-phase approach in all analyses under constant heat flux (q” = 2000 W/m2). The study observed that the nanofluid flowing in the tube with a wave ratio of 4, 5, and 6 resulted in an average enhancement in the Nusselt number of 93.25 %, 86.26 %, and 80.06 %, respectively. The optimal performance evaluation criterion (PEC) for water flowing in the tube with a wave ratio of 6 at Re = 500 exhibited an increase of 11.0 %, whereas the CoFe2O4/H2O flow showed a 9.14 % increment in the average PEC along the Reynolds number. Moreover, the total entropy generation values for water flowing in tubes with wave ratios of 5, 6, and 4 exhibited increases of 101.88 %, 94.66 %, and 51.34 %, respectively, in comparison to the smooth tube.

Energy, exergy, economic, and environmental (4E) analysis of SAHP water heaters in very cold climatic conditions

Solar-assisted heat pumps (SAHPs) are emerging as promising solutions for space/water heating. Compared to conventional air-source heat pumps (ASHPs), SAHPs show superior thermal performance in cold climates where outdoor air temperatures are below freezing most of the heating season. However, given the inherent variability of solar energy, SAHPs have poor thermal performance to meet the load requirements during periods of weak solar radiation. To enhance the reliability of SAHPs, an air-source evaporator can be integrated with a SAHP, forming a dual SAHP – ASHP system with better performance. In this research, the energy, exergy, environmental, and economic performance of a dual-source solar/air source heat pump, which provides hot water for a typical Canadian household, is investigated. The performance of the system is compared with a solar-assisted direct-expansion heat pump (DX-SAHP), an ASHP, and conventional gas/electric water heaters. A thoroughly validated mathematical model based on heat transfer and thermodynamics fundamentals is developed and implemented in MATLAB® coupled with the CoolProp® library, which gives the refrigerant's properties. Results highlight the superior performance of the dual-source heat pump, particularly in the summer, where it surpasses the DX-SAHP. Among the examined heat pump configurations, the dual-source heat pump demonstrates the lowest annual power consumption. The system attains the maximum monthly average COP of 3.94 and achieves a minimum of 2.4 during the severe winter season in Calgary, Alberta. Compared to a conventional ASHP, the energy consumption of the system was reduced by 25%. The second-law analysis shows that the ASHP obtains the highest monthly average exergy efficiencies, followed by the DX-SAHP and the dual-source heat pump. Furthermore, results show that the solar/air source heat pump water heater can reduce CO2 emissions by 1450 kg/year, while the system's payback period is 19 years.

Performing SiO2-MWCNT/water hybrid nanofluid with differently shaped nanoparticles to enhance first- and second-law features of flow by considering a two-phase approach

AbstractThe utilization of hybrid nanofluids has gained essential consideration in thermal engineering. Changes in the thermal characteristics of the base fluid are responsible for the improved thermal conductivity brought about by hybrid nanoparticles and their shapes. For this goal, in this paper, the two-phase 60%:40% SiO2-MWCNT/water hybrid nanofluid flow at the Reynolds number range of 3000–10,000 in a square duct is investigated concerning first- and second-law analysis. The turbulent flow regime is modeled using the RNG k–ε turbulence approximation. The hybrid nanofluid is modeled via a mixed model. The parameters used in this study are three different nanoparticle shapes (cylindrical, spherical, and platelet) and nanoparticle volume fractions (0.2%, 0.6%, and 1.0%). The distributions of the Nusselt number, friction factor, entropy generation, exergy destruction, exergy efficiency, temperature, and velocity contours are investigated in detail for the above parameters. It is found that the most significant increases in PEC are seen in hybrid nanofluids with the PC and PP shapes, at 2.27 and 3.24%, respectively. It has been shown that the exergy destruction of hybrid nanofluids with the second nanoparticle forms C and P is 43.90% and 58.74% more than that of a S one when PS-, PC-, and PP-shaped nanoparticles are utilized. The hybrid nanofluid with the PS shape has the highest exergy efficiency, whereas the SP-shaped nanofluid has the lowest.

Design and Development of a Biomimetic Solar Tree for Sustainable Cogeneration: An Energy and Exergy Assessment

Solar energy is becoming an increasingly popular and important source of renewable energy. Solar trees have emerged as a novel and innovative approach to harvesting solar energy. Solar trees are artificial structures that mimic the shape and function of trees, with branches or leaves that contain photovoltaic cells to convert sunlight into electricity. The solar tree generates both electrical and thermal energy from solar radiation. The present study tested the thermal (module temperature, heat loss coefficient), electrical (power output), and operating parameters of a solar tree at Universiti Malaysia Pahang, Pekan, Malaysia, on a typical sunny day. First-law analysis and second-law analysis were carried out to determine exergy losses during the photovoltaic conversion process of solar trees. The data obtained from the experiment is utilized to determine the energy and exergy efficiencies of the solar tree. The energy efficiency ranges from 16.8% to 8.3% throughout the day, displaying some variability. However, as for the exergy efficiency of the photovoltaic solar tree under consideration, it is observed to be lower, ranging from 16.1% to 6.6% for electricity generation. It is observed that the exergy losses increased with increasing module temperature and a drop in exergy efficiency.

Second-law analysis of nanofluid-based photovoltaic/thermal system modeling and forecasting model based on artificial neural network

The PVT solar collectors can produce the thermal energy and power in a same frame. The improvement of the PVT's efficiency leads to reducing the system size and capital costs. To this end, this paper studied the irreversibilities of the Al2O3Cu/water hybrid nanofluid (NF) in a PVT solar collector considering two single and double serpentine channels (SS and DS). The influences of Re and nanoparticle concentration (φ) on the thermal and frictional entropy generation rates (S˙th and S˙fr) were investigated and the thermal, electrical and overall exergy efficiencies (ψth, ψe, ψov) of the PVT with SS and DS channels were compared and discussed. Based on the results, the DS channel exhibited S˙fr of almost 75 % lower than SS channel due to lower nanofluid inlet velocities and velocity gradients. In addition, S˙th for the DS channel is nearly 65 % lower and 26 % higher than that for the SS channel at Re numbers of 500 and 2000, respectively. Besides, the Re escalation from 500 to 2000 intensifies S˙fr by almost 94 % at different φs in the SS and DS channels. The increase in φ from 0 % to 1 % escalates S˙fr by almost 99.98 % times for two configuration regardless of the Re number. ψth of the DD channel is nearly 14.5 % and 12.77 % higher than that of the SS channel at Res of 500 and 2000, respectively. Besides, ψe of the PVT with the DS channel is 2.36 % higher than that with SS channel at Re=500 at four studied φs. Moreover, the maximum ψe for the PVT with the DS and SS were obtained as 22.29 % and 21.28 %, respectively, which are associated with Re=1500 and φ=0.25 %. Additionally, a predictive model was presented to determine the total entropy generation rate based in the Re and φ as the inputs.

Energy and exergy analyses of a solar PV/T driving hybrid reverse osmosis-thermal distillation system

Solar desalination holds significant promise for providing freshwater to remote and off-grid areas, which includes solar thermal distillation (STD) and solar photovoltaic reverse osmosis (PV-RO). To achieve higher efficiency via full-spectrum utilization of solar energy, this paper proposes a hybrid reverse osmosis-thermal distillation system driven by a solar photovoltaic-thermal collector (PV/T-RO-TD). To evaluate the conversion of solar energy, electrical energy, thermal energy and chemical energy in these three systems, both the first-law and second-law based analyses are adopted. Results show that while PV/T-RO-TD systems only have moderate energy and exergy efficiencies in the desalination process, it achieves better utilization of solar energy. Meanwhile, the energy and exergy efficiencies are 83%, 81%, 13%, and the exergy efficiencies are 20%, 3%, 13% in the solar harvesting process of PV/T-RO-TD, STD, and PV-RO, respectively. In addition, the specific water productivity under one-sun of 26.94–73.92 L/m2 h in the PV/T-RO-TD system surpasses it in STD and PV-RO systems, which are 3.79–9.89 L/m2 h and 22.74–69.63 L/m2 h, respectively. With better performance, the PV/T-RO-TD system can be regarded as an effective choice for boosting the water productivity of solar desalination.

Exergy analysis of an experimental ammonia/water absorption cooling system

This study proposes a second-law analysis of an experimental ammonia-water absorption cooling system, assessed under different operating conditions. The study also includes an analysis of what is considered the most significant research of exergy analyses on experimental absorption systems. The approach proposed in this study takes into consideration two types of exergy: chemical and physical, to determine the irreversibilities in the absorption system. Special attention has been paid to the contributions of the chemical exergy in the absorber, generator, and rectifier. Also, an evaluation of the exergy destruction as a part of the total exergy supplied to the system and its variation within the considered conditions range is presented. The effect of the variation of the dead-state temperature on the system’s irreversibility is also evaluated. Moreover, the components' irreversibilities contribution and their possible causes are discussed and presented for the main system components. Finally, the second-law efficiency or exergy coefficient of performance (ECOP) is reported as a function of the heating and cooling water temperatures. The highest ECOP achieved by the absorption system was 14.4%.

Optimised Electro-Osmotic Flow in Rectangular Microchannels with Smoothed Corners

Electro-osmotic flows are a means of circulating polar fluids through microchannels without resorting to mechanical pumping. The lack of moving parts, of noise and the ease of integration in silicon chips make them an interesting option for microchip cooling and miniaturized total analysis systems. This paper describes an optimization in terms of first- and second-law analysis of the cross-section of a microchannel subject to electro-osmotic flow. Starting from rectangular cross-sections of different aspect ratios, its corners are progressively smoothed and the resulting Poiseuille and Nusselt numbers computed. Performance evaluation criteria are then used to assess the change in, among others, heat transfer rate, temperature difference between wall and bulk fluid, and equivalent pumping power. The entropy number is also computed and the results commented. It is found that the latter criterion highlights a configuration of minimum entropy generation, whereas the trends of the heat transfer and temperature difference are opposite to that of the equivalent pumping power.

Using internal sinusoidal fins and phase change material for performance enhancement of thermal energy storage systems: Heat transfer and entropy generation analyses

In comparison to sensible energy storage, LHTES (Latent Heat Thermal Energy Storage) offers large storage energy densities per unit mass/volume at nearly constant temperatures. This study is carried out to assess thermo-hydraulic performance of the simultaneous utilization of sinusoidal internal fins and PCM (Phase Change Material) in LHTES systems. For this, a validated numerical framework is developed using Ansys-Fluent software. The RT82 is considered as working substance in a transient laminar flow. The geometrical parameters of fins, (including length, height, and thickness) are evaluated by defining 15 different geometries to look for the most optimal case in terms of faster PCM melting. Furthermore, the impact of fins’ material (copper and gold) is also involved in the investigations. A comprehensive sensitivity analysis is conducted to completely investigate different heat transfer and thermodynamic characteristics. The results illustrated that in case 4 (with H/L = 0.125 and thickness of 3 mm), the highest growth of normalized liquid fraction compared to normalized heat transfer coefficient is achieved which results in Dhl number of about 0.55. Also, the second-law analysis revealed that the lowest entropy is generated in this case. So that, 62% increment of liquid fraction and 59.5% reduction of entropy generation is observed in case 4 compared to a case with simple straight fins.

Thermodynamics second-law analysis in an unsteady conduction and radiation heat transfer system with internal heat source

This paper presents an improved thermodynamic analysis method used to evaluate the irreversibility and efficiency of a coupled conductive-radiative heat transfer process. The exergy analysis of the conductive-radiative process is developed based on the exergy balance equation. In the method, the local entropy generation rates due to the radiative heat transfer and heat conduction processes are calculated. Based on the entropy generation analysis, an exergy analysis is performed, the stored exergy of the system and the exergetic efficiency are determined, and the thermodynamic efficiency of the system is further evaluated. The results are verified by the principle of exergy balance and the exergy generation rate calculated by the method does not deviate from the theoretical value by more than 0.1%. Four heat source distributions are specified in the numerical analysis, which include completely uniform, partially uniform, and non-uniform heat source distributions in the numerical analysis. The effects of heat source distribution, conductive-radiative coefficient and total heat generation rate of medium on entropy generation and stored exergy of system are investigated. The numerical results show that the average temperatures and exergy storage rate of the systems with partially uniform heat source distribution are 5.1–79.7 K and 6.8–49.8% higher than the other distributions, and uniform and centralized heat generation in the internal region of the system is proposed. The total stored exergy of the systems has a tendency to first increase and then decrease, reaching its maximum at N = 1 as the conduction and radiation coefficients increase, and increasing as the total heat generation rate increases.

Reaction of Cl Atom with c-C5F8 and c-C5HF7: Relative and Absolute Measurements of Rate Coefficients and Identification of Degradation Products.

Partially and fully fluorinated olefins are a class of compounds with relatively short atmospheric lifetimes and low 100-year global warming potentials, compared to their saturated predecessors, which are used or considered as refrigerants, propellants, solvents, and other end-uses. The cyclic unsaturated compounds c-C5F8 and c-C5HF7 are currently under consideration as etching agents for the semiconductor industry. In this study, we expand on our previous work on the reaction of the OH radical with c-C5F8 and c-C5HF7 and report the rate coefficients, k, for the gas-phase reaction of the Cl atom with c-C5F8 and c-C5HF7 over a range of temperature (245-367 K) and pressure (100-200 Torr of He or N2 and 0 to 4.8 Torr O2) using a pulsed laser photolysis-resonance fluorescence (PLP-RF) technique. In addition, a relative rate (RR) technique, employing multiple reference compounds, was used to study the Cl atom reactions at 296 K, 100 and 630 Torr (N2 or air) total pressure. Reaction rate coefficients, k1, of the Cl atom reaction with c-C5F8 were found to be independent of pressure, over the pressure range used in this work, with k1(296 K), derived as an average of results from the PLP-RF and RR techniques being (1.07 ± 0.02) × 10-12 cm3 molecule-1 s-1 and k1(T) = (7.76 ± 0.73) × 10-13 × (exp[(98 ± 26)/T]) cm3 molecule-1 s-1, where the quoted error limits represent the 2σ data precision. Rate coefficients, k2, for the Cl atom + c-C5HF7 reaction were measured to be k2(296 K) = (4.61 ± 0.10) × 10-12 cm3 molecule-1 s-1 and k2(T) = (7.42 ± 0.89) × 10-13 × (exp[(540 ± 32)/T]) cm3 molecule-1 s-1. The Cl atom temporal profiles, observed with the PLP-RF technique, indicate that the Cl atom with c-C5F8 and c-C5HF7 reactions lead to adduct formation. The equilibrium constants for adduct formation were derived in this work, and a second-law analysis was used to obtain ΔH and ΔS values of -18.5 ± 0.4 kcal mol-1, -30.9 ± 1.2 cal K-1 mol-1, and -13.9 ± 0.5 kcal mol-1, -27.6 ± 1.1 cal K-1 mol-1 for the c-C5F8 and c-C5HF7 reactions, respectively. The Cl-initiated degradation of c-C5F8 and c-C5HF7 in the presence of O2 was studied and stable products were identified via infrared spectroscopy using experimental or theoretically derived spectra from our previous OH reaction work. For c-C5F8, FC(O)CF2CF2CF2C(O)F and FC(O)C(O)F were observed with molar yields of 0.80 and 0.10, respectively. For c-C5HF7, we observed the formation of HC(O)CF2CF2CF2C(O)F and HC(O)C(O)F with a combined molar yield of 0.72. Carbonyl difluoride, F2CO, was also a major product in the decomposition of c-C5F8 and c-C5HF7. The oxidation mechanism of the Cl-initiated degradation of c-C5F8 and c-C5HF7 is discussed. Based on the combined findings from this and our previous work, the atmospheric implications from the use of c-C5F8 and c-C5HF7 are presented.

Energy and Exergy Analysis of Vapor Compression Refrigeration System with Low-GWP Refrigerants

In this paper, a first- and second-law analysis of vapor compression refrigeration is presented to estimate and propose the replacement of R134 with working fluids having less global warming potential (GWP) and less exergy destruction and irreversibilities. Six different refrigerants were studied, namely, R717, R1234yf, R290, R134a, R600a, and R152a. A thermodynamic model was designed on Engineering Equation Solver (EES) software, and performance parameters were calculated. The model was deployed on all six refrigerants, while the used output parameters of performance were cooling capacity, coefficient of performance, discharge temperature, total exergy destruction, relative exergy destruction rates of different components, second-law efficiency, and efficiency defect of each component. The performance parameters were estimated at different speeds of the compressor (1000, 2000, and 3000 rpm) and fixed condenser and evaporator temperatures of 50 °C and 5 °C, respectively. The isentropic efficiency of the compressor was the same as the volumetric efficiency, and it was taken as 75%, 65%, and 55% at the compressor speeds of 1000 rpm, 2000 rpm, and 3000 rpm, respectively. A comparison of the performance parameters was presented by importing the results in MATLAB. It was found that the compressor had the highest exergy destruction compared to the other components. It was found that R152 was the refrigerant with zero ozone depletion potential (ODP) and a GWP value of 140 with less exergy destruction and irreversibilities. Moreover, it was easy to use R152a with good thermodynamic characteristics. It is estimated that R152a is a suitable replacement for R134a, as it can be used with few modifications.

Numerical Investigation of Exergy Loss of Ammonia Addition in Hydrocarbon Diffusion Flames.

In this paper, a theoretical numerical analysis of the thermodynamics second law in ammonia/ethylene counter-flow diffusion flames is carried out. The combustion process, which includes heat and mass transfer, as well as a chemical reaction, is simulated based on a detailed chemical reaction model. Entropy generation and exergy loss due to various reasons in ammonia/ethylene and argon/ethylene flames are calculated. The effects of ammonia addition on the thermodynamics efficiency of combustion are investigated. Based on thermodynamics analysis, a parameter, the lowest emission of pollutant (LEP), is proposed to establish a relationship between the available work and pollutant emissions produced during the combustion process. Chemical reaction paths are also analyzed by combining the chemical entropy generation, and some important chemical reactions and substances are identified. The numerical results reveal that ammonia addition has a significant enhancement on heat transfer and chemical reaction in the flames, and the total exergy loss rate increases slightly at first and then decreases with an increase in ammonia concentration. Considering the factors of thermodynamic efficiency, the emissions of CO2 and NOx reach a maximum when ammonia concentration is near 10% and 30%, respectively. In terms of the chemical reaction path analysis, ammonia pyrolysis and nitrogen production increase significantly, while ethylene pyrolysis and carbon monoxide production decrease when ammonia is added to hydrocarbon diffusion flames.

Mathematical analysis of second law on Casson fluid through a vertical plate with arbitrary shear stress and exponential heating

Mathematical analysis of second law on Casson fluid through a vertical plate with arbitrary shear stress and exponential heating

Numerical simulation of flow in hydrokinetic turbine channel to improve its efficiency by using first and second-law efficiency analysis

Hydrokinetic energy uses the flowing water of the riverine systems to generate electrical power. The technology is used to meet the green energy requirements in remote villages, to provide power for the isolated areas and factories with a small utility scale. The present study aims to conduct an analysis of the Egyptian riverine systems for remote areas. Numerical analysis is applied using the URANS model. Verification and validation had been implemented with the proper boundary condition. Five ducted airfoils have been simulated around the hybrid Savonius-Darrieus current turbine as an augmentation technique. The ducted airfoils are NACA-0012, NACA-0015, NACA-0018, NACA-0021, and NACA-0024. The study concluded that the optimal ducted airfoil is the NACA-0015. The hybrid turbine had an average power coefficient of 0.114. Also, the first and the second laws of efficiencies were revealed, for the NACA-0015, of 64.9% and 83.4% respectively.

Thermodynamics second-law analysis of hydrocarbon diffusion flames: Effects of soot and temperature

In this paper, a computation of the ethylene co-flow diffusion flame is carried out using the Co-flame code with a detailed gas-phase mechanism and soot model. A numerical analysis based on the thermodynamics second-law was conducted for developing a high-efficiency combustion condition of hydrocarbon diffusion flames. The entropy generations and exergy loss ratios due to thermal radiation, heat conduction and convection, and chemical reactions are numerically calculated, in which entropy generations caused by both gasses and soot particle are considered. The effects of soot (controlled by changing stoichiometric mixture fraction Zst from 0.1 to 0.62) and adiabatic flame temperature Tad (2300 K, 2500 K, 2700 K) on entropy generation and exergy loss ratio in flame are investigated. The results suggest that, entropy generation due to soot radiation and soot surface growth and oxidation accounts for about 15% and 5% in total radiation entropy generation and total chemical entropy generation, respectively. Entropy generation due to thermal radiation decreases when soot reduces, and entropy generation due to heat conduction and convection, mass diffusion and chemical reactions increases when Zst increases. When Tad is 2300 K, the change of exergy loss ratio is slight with a reducing of soot and increasing of Zst. When Tad is 2500 K and 2700 K, the exergy loss ratio has tendency of increasing with a reducing of soot and increasing of Zst. The exergy loss ratio increases with increasing of Tad.

Three-dimensional analysis of entropy generation for forced convection over an inclined step with presence of solid nanoparticles and magnetic force

In this work, the interaction impacts of solid nanoparticles and magnetic force on the entropy generation rates for three-dimensional forced convection over an inclined step in the presence of Brownian movement are examined. To achieve this goal, analysis of the thermodynamics second law is used. The working fluids in this three-dimensional problem are the and nanofluids. To consider the impact of Brownian movement on the effective properties of these both nanofluids, the Koo–Kleinstreuer–Li (KKL) correlation is applied. Impacts of magnetic force and nanoparticles concentrations on the entropy generation and the flow irreversibility are investigated in details. The predictions present that the nanofluid is more suitable for the optimal design of the hydrothermal systems. Besides, the highest magnitudes of the total entropy generation number in downstream of step are noted for the case of and

Second-Law Analysis of Micro-Fluidic Counter-Flow Parallel Plate Heat Exchangers: Maximum Effectiveness and its Relation to Minimal Wall Entropy Production

Second-Law Analysis of Micro-Fluidic Counter-Flow Parallel Plate Heat Exchangers: Maximum Effectiveness and its Relation to Minimal Wall Entropy Production

Entropy generation analysis of turbulent convection in a heat exchanger with self-rotating turbulator inserts

Turbulator inserts are commonly applied to enhance the thermal performance of heat exchangers with an accompanying rise in pressure drop due to the generation of the secondary swirl flow. We study the effect of inter-turbulator distance of rotating turbulator inserts on the heat transfer enhancement and entropy generation of forced convection in the turbulent flow region of a heat exchanger. Attributed to the turbulator inserts, the maximum rise of Nusselt number is 360% and 240%, for non-rotating and rotating cases, respectively, while the friction factor is increased significantly in the flow disturbed by the turbulator inserts. The Nusselt number and friction factor are augmented as the inter-turbulator distance is reduced. The partitioning of tube by the turbulator insert induces the swirl flow that leads to the enhancement of forced convection. From the second-law analysis, the entropy generation rate of the non-rotating case increases up to 202% comparing to that of the rotating case. This shows that the rotating turbulator insert is a more thermodynamically advantageous configuration, as it enhances the thermal performance appreciably while reducing the entropy generation significantly.