Biodiesel vs. Diesel Oil in a Marine Engine: A Thermodynamic Study

The present comparative study deals primarily with the thermodynamic performances of the traditional fuel being used in shipping propulsion, Diesel oil and one of its alternatives, namely, the biodiesel. A thermodynamic model was developed based on the first and second law of thermodynamics. It was found that the engine running on biodiesel registers a slight improvement of its performances compared with the one running on Diesel oil in all the departments considered in this study

Biodiesel vs. Diesel Oil in a Marine Engine: A Thermodynamic Study

The present comparative study deals primarily with the thermodynamic performances of the traditional fuel being used in shipping propulsion, Diesel oil and one of its alternatives, namely, the biodiesel. A thermodynamic model was developed based on the first and second law of thermodynamics. It was found that the engine running on biodiesel registers a slight improvement of its performances compared with the one running on Diesel oil in all the departments considered in this study

CFD-Exergy analysis of the flow in a small-sized Venturi

The present study aims to compare cavitation models in predicting the flow in small-sized cavitating venturis. Three cavitation models, namely Schnerr and Sauer model, Zwart et al. Model and Singhal et al. Model have been compared under the mixture approach. Furthermore, the performance of this device has been assessed using the concept of exergy by quantifying the exergy losses accuring in its different parts. It is found that all models are capable of reproducing the physics of cavitation phenomena within the cavitating venturi. However, the Schnerr and Sauer model return higher values than the others model. It is also observed that most of the exergy losses occur in the converging and diverging parts of the venturi due to higher pressure and velocity gradients in these regions

CFD-Exergy analysis of the flow in a small-sized Venturi

The present study aims to compare cavitation models in predicting the flow in small-sized cavitating venturis. Three cavitation models, namely Schnerr and Sauer model, Zwart et al. Model and Singhal et al. Model have been compared under the mixture approach. Furthermore, the performance of this device has been assessed using the concept of exergy by quantifying the exergy losses accuring in its different parts. It is found that all models are capable of reproducing the physics of cavitation phenomena within the cavitating venturi. However, the Schnerr and Sauer model return higher values than the others model. It is also observed that most of the exergy losses occur in the converging and diverging parts of the venturi due to higher pressure and velocity gradients in these regions

Flow and heat transfer features during propane (R290) and isobutane (R600a) boiling in a tube

The purpose of this paper is to present a numerical study of the flow and heat transfer characteristics during boiling of two hydrocarbon-based natural refrigerants, namely propane (R290) and isobutane (R600a) in a smooth horizontal tube of 10.0 mm internal diameter. The cross-sectional average heat transfer coefficients are obtained using the temperatures at the top, bottom, left and right sides of the tube. Trends of the heat transfer coefficient are displayed for different operating conditions in terms of saturation temperature (5 — 65 °C) and heat flux (9 — 24 kW/m2), and mass flux (120 and 220 kg/m2.s). Results showed that the heat transfer coefficient depends strongly on the operating parameters. It is augmented as the wall heat flux and the saturation temperature are raised. A dryout region appears for all refrigerants at vapor quality ranging between 0.7564 and 0.8824. Furthermore, from a heat transfer point of view, R290 and R600a are better than R134a

CFD-based analysis of entropy generation in turbulent double diffusive natural convection flow in square cavity

The present study concerns the problem of natural and double diffusive natural convection inside differentially heated cavity filled with a binary mixture composed of air and carbon dioxide (CO2). Temperature and CO2 concentration gradients are imposed on both perpendicular left and right walls. Simulations have been performed using the CFD commercial code ANSYS Fluent by solving continuity, momentum, energy and species diffusion equations. Numerical results obtained have been compared to data from the literature for both natural convection thermosolutal cases under laminar and turbulent regimes. For turbulent runs the RNG k-ε model has been selected. A good agreement has been noted between the different types of data for both cases for Rayleigh number ranging between 103 and 1010 and buoyancy ratio between -5 and +5. Entropy generation rates due to thermal, viscous and diffusive effects have been calculated in post processing for all cases

CFD-Entropy generation analysis of refrigerant-based nanofluids flow in a tube

The present paper aims to numerically investigate the flow, heat transfer and entropy generation of some hydrocarbon based nanorefrigerants flowing in a circular tube subject to constant heat flux boundary condition. Numerical tests have been performed for 4 types of nanoparticles, namely Al2O3, CuO, SiO2, and ZnO with a diameter equal to 30 nm and a volume concentration of φ = 5%. These nanoparticles are dispersed in some hydrocarbon-based refrigerants, namely tetrafluoroethane (R134a), propane (R290), butane (R600), isobutane (R600a) and propylene (R1270). Computations have been performed for Reynolds number ranging from 600 to 2200. The numerical results in terms of the average heat transfer coefficient of pure refrigerants have been compared to values obtained using correlations from the literature. The results show that the increase of the Reynolds number increases the heat transfer coefficient and decreases the total entropy generation

Numerical simulation of the flow over a tubercled wing

The objective of the present study is to carry out a numerical study of the flow around a NACA0021 modified wing by the incorporation of sinusoidal tubercles on its leading edge at a Reynolds number equal to 225,000. The SST k-ω turbulence model is used as closure to the incompressible governing equations. Runs have been performed for several attack angles. Results show that for lower angles of attack, tubercles reduce the drag coefficient with a slight increase in lift

CFD-Entropy generation analysis of refrigerant-based nanofluids flow in a tube

The present paper aims to numerically investigate the flow, heat transfer and entropy generation of some hydrocarbon based nanorefrigerants flowing in a circular tube subject to constant heat flux boundary condition. Numerical tests have been performed for 4 types of nanoparticles, namely Al2O3, CuO, SiO2, and ZnO with a diameter equal to 30 nm and a volume concentration of φ = 5%. These nanoparticles are dispersed in some hydrocarbon-based refrigerants, namely tetrafluoroethane (R134a), propane (R290), butane (R600), isobutane (R600a) and propylene (R1270). Computations have been performed for Reynolds number ranging from 600 to 2200. The numerical results in terms of the average heat transfer coefficient of pure refrigerants have been compared to values obtained using correlations from the literature. The results show that the increase of the Reynolds number increases the heat transfer coefficient and decreases the total entropy generation

Numerical simulation of the flow over a tubercled wing

The objective of the present study is to carry out a numerical study of the flow around a NACA0021 modified wing by the incorporation of sinusoidal tubercles on its leading edge at a Reynolds number equal to 225,000. The SST k-ω turbulence model is used as closure to the incompressible governing equations. Runs have been performed for several attack angles. Results show that for lower angles of attack, tubercles reduce the drag coefficient with a slight increase in lift