Bio-fuel has come under consideration due to the effect of fossil oil crisis. Bio-fuels are acting as a renewable replacement of petroleum fuels due to some environmental and economic benefits. ...Bio-fuel can be produced from different kinds of raw materials. Researchers have seen that absolute utilization of bio-fuel is not appreciable as it will affect the food chain but the blend of bio-fuel with conventional fuel could precisely reduce its use and become beneficial to green house effect. It has been inferred that in the hot and cold environment bio-fuel is not fully convenient to replace fossil fuel. In the controlled environment with modified combustion equipment, biodiesel can be used as an alternate fuel. Research results reveal that bio-fuel has lower heating value in comparison to diesel fuel so it is consumed more in fuel-break mean effective power ratio and emits more NOx in comparison to the diesel fuel. Thus there remains a compromise between GHG emission and saving of fossil fuel energy by introducing bio-fuel either totally or as a blending component of engine fuel. Finally, bio-fuel could be considered as a replenishable energy source which might pave the future pathway management and planning of energy.
•Finite volume method based on shear stress transport (SST) K–ω Model employed in this paper.•Enhancement of heat transfer with the increase of nanoparticle concentration and Reynolds number ...observed.•The effect of expansion ratio was clearly observed at the downstream inlet region.
This paper presents a numerical study of heat transfer to turbulent and laminar Cu/water flow over a backward-facing step. Mathematical model based on finite volume method with a FORTRAN code is used to solve the continuity, momentum, energy and turbulence equations. Turbulence was modeled by the shear stress transport (SST) K–ω Model. In this simulation, three volume fractions of nanofluid (0%, 2% and 4%), a varying Reynolds number from 50 to 200 for the laminar range and 5000 to 20,000 for the turbulent range, an expansion ratio of 2 and constant heat flux of 4000W/m2 were considered. The results show the effect of nanofluid volume fraction on enhancing the Nusselt number in the laminar and turbulent ranges. The effect of expansion ratio was clearly observed at the downstream inlet region where the peak of the Nusselt number profile was referred to as enhanced heat transfer due to the generated recirculation flow. An increase of pressure drop was evident with an increasing Reynolds number and decreasing nanofluid volume fraction, while the maximum pressure drop was detected in the downstream inlet region. A rising Reynolds number caused an increasing Nusselt number, and the highest heat transfer augmentation in the present investigation was about 26% and 36% for turbulent and laminar range, respectively compared with pure water.
The effect of radiation on laminar and turbulent mixed convection heat transfer of a semitransparent medium in a square enclosure was studied numerically using the Finite Volume Method. A structured ...mesh and the SIMPLE algorithm were utilized to model the governing equations. Turbulence and radiation were modeled with the RNG k - ε model and Discrete Ordinates (DO) model, respectively. For Richardson numbers ranging from 0.1 to 10, simulations were performed for Rayleigh numbers in laminar flow (104) and turbulent flow (108). The model predictions were validated against previous numerical studies and good agreement was observed. The simulated results indicate that for laminar and turbulent motion states, computing the radiation heat transfer significantly enhanced the Nusselt number (Nu) as well as the heat transfer coefficient. Higher Richardson numbers did not noticeably affect the average Nusselt number and corresponding heat transfer rate. Besides, as expected, the heat transfer rate for the turbulent flow regime surpassed that in the laminar regime. The simulations additionally demonstrated that for a constant Richardson number, computing the radiation heat transfer majorly affected the heat transfer structure in the enclosure; however, its impact on the fluid flow structure was negligible.
Different numerical methods have been implemented to simulate internal natural convection heat transfer and also to identify the most accurate and efficient one. A laterally heated square enclosure, ...filled with air, was studied. A FORTRAN code based on the lattice Boltzmann method (LBM) was developed for this purpose. The finite difference method was applied to discretize the LBM equations. Furthermore, for comparison purpose, the commercially available CFD package FLUENT, which uses finite volume Method (FVM), was also used to simulate the same problem. Different discretization schemes, being the first order upwind, second order upwind, power law, and QUICK, were used with the finite volume solver where the SIMPLE and SIMPLEC algorithms linked the velocity-pressure terms. The results were also compared with existing experimental and numerical data. It was observed that the finite volume method requires less CPU usage time and yields more accurate results compared to the LBM. It has been noted that the 1st order upwind/SIMPLEC combination converges comparatively quickly with a very high accuracy especially at the boundaries. Interestingly, all variants of FVM discretization/pressure-velocity linking methods lead to almost the same number of iterations to converge but higher-order schemes ask for longer iterations.
The enhancement of the thermal performance of heat exchanging equipment transport energy at low financial cost by various techniques is presented in this review. Various annular passage ...configurations have been used in the reviewed studies, namely circular, ellipse, rectangular, square, triangular, and rhombic annular channels with different fluid and boundary conditions. The effect of eccentricity in both horizontal and vertical directions on heat transfer rate in most numerical and experimental investigations for horizontal and vertical annular passages is studied. The effects of heater length, as well as the Darcy, Prandtl, Reynolds, Grashof and Rayleigh numbers on heat transfer in concentric and eccentric annular passages are also investigated. In case of rotating the inner, outer or both cylinders of the annular cylinder arrangement, the generated secondary flow influences the heat transfer to fluid flow in an annular passage. The effect of nanofluid on the increased enhancement of heat transfer in an annular channel is presented. Related studies on curved, covered annular channels showed augmented heat transfer rate in comparison with straight annular channels. In this review, a good agreement is evident between experimental and numerical data, which could help researchers design thermal systems supported by annular passages with the goal of retarding energy consumption by equipment and machineries in applications that could ultimately contribute to appeasing the global energy crisis.
•This paper presents review of numerical and experimental studies on forced, natural and mixed heat transfer to fluid and nanolfuid flow in an annular passage.•Heat transfer augmentation observed in different configurations of annular channels.•The augmentation of heat transfer rate in annular passage by using nanofluid.•Influence of rotating cylinder in an annular passage on performance of heat transfer.•Concentric and eccentric annular channels concerned in this review add to circular, elliptical, square, conical, polygonal, triangular and rhombic annular passage.
Heat exchanger performance degrades rapidly during operation due to formation of deposits on heat transfer surfaces which ultimately reduces service life of the equipment. Due to scaling, product ...deteriorates which causes lack of proper heating. Chemistry of milk scaling is qualitatively understood and the mathematical models for fouling at low temperatures have been produced but the behavior of systems at ultra high temperature processing has to be studied further to understand in depth. In diversified field, the effect of whey protein fouling along with pressure drop in heat exchangers were conducted by many researchers. Adding additives, treatment of heat exchanger surfaces and changing of heat exchanger configurations are notable areas of investigation in milk fouling. The present review highlighted information about previous work on fouling, influencing parameters of fouling and its mitigation approach and ends up with recommendations for retardation of milk fouling and necessary measures to perform the task.
Investigation on fouling behaviour of calcium carbonate on heat exchanger surfaces as well as mitigation of fouling are presented in this paper. By varying parameters such as concentration of the ...fouling solution, temperature of the heating surface, type of materials and use of additives, the fouling rate on the test specimens were observed. A set of experiments were performed by using calcium carbonate solution. Fouling rate, fouling resistances and the rate of heat transfers were determined for different heat exchanger material surfaces. Fouling resistance is enhanced by the thermal conductivity and temperature of the heat exchanging surfaces and also by the concentration of the foulant in the solution. The addition of gum arabic additive (benign to the environment) to the solution retarded the rate of deposition. The results of these investigations could be design aid for economic and enhancement of heat exchanger performance.
•Fouling resistance is enhanced by the surface thermal conductivity.•Fouling is enhanced by the heat exchanger surface temperature and concentration of the foulant in the solution.•Additive gum arabic (benign to environment) retards fouling deposition on different metal surfaces.
In the wake of oil crisis, the world is looking for the alternative source of energy where bio-diesel came into play as an attractive renewable alternative fuel. However, it was realized that ...extensive utilization of bio-fuel would tax the food chain and could lead to food shortages. So, the use of a blend of bi-fuel with conventional fuel was suggested to balance its usage which still could provide beneficial green house effect. In the hot and cold climate bio-diesel cannot conveniently replace fossil fuel but in the controlled environment with modified combustion equipment, bio-diesel can be used as an alternate fuel. Having lower heating value, bio-diesel is consumed more in comparison to the fossil diesel fuel. Bio-diesel also generates more NOx emission, which is an adverse environmental pollutant. The raw material source of bio-diesel limits food growing ground which is ultimately becoming a great concern. A dilemma of using bio-diesel as an alternative for mineral fuel has raised a concern about environment, engine performance and involved costs these have to be investigated in depth to provide a recommendation.
The separation and the reattachment of water flow through a sudden expansion in an annular passage have been considered in this paper. In the present work, numerical simulation is performed using the ...computational fluid dynamics package (FLUENT) to study the effect of step flow in an annular passage. In the study, the flowing fluid was considered heated uniformly from the beginning of the expansion, and the constant heat flux approach was also considered for the heat transfer investigation. The annular pipe flow system having step ratio of D/d=1.8 was considered, where d and D are representing the diameter of the pipe before and after expansion. The increase of flow reduces the surface temperature along the pipe to a minimum point, then gradually increases up to the maximum and hold for the rest of the pipe. The minimum surface temperature is obtained at flow reattachment point. The position of the minimum temperature point is dependent on the flow velocity over sudden expansion. In general, the local Nusselt number (Nu) increases with the increase of Reynolds number.
Separation and reattachment of air flow through a sudden expansion in an annular passage are considered in this study. Backward facing steps play a vital role in the design of many heat related ...applications where heat transfer is concerned. In the present work, numerical simulation is performed using computer fluid dynamics package (Fluent) to study the effect of step flow in an annular passage. The results are compared with the preliminary experimental findings. In the study, the flowing fluid was considered heated uniformly from the beginning of the expansion. Constant heat flux approach was also considered for the heat transfer investigation. Annular pipe flow system having a step ratio of D/d=1.8 was considered where d and D are representing the diameter of the pipe before and after expansion. Numerical simulation review shows that the reattachment point extends further with the increase of velocity for different occasions. Finally, the local Nusselt number (Nu) in separation flow increases with the increase of Reynolds number (Re).
► Numerical simulation is performed using CFD package (FLUENT). ► Enhanced Nu is obtained in backward facing steps. ► Nu and Re correlations show similar trend in concentric annular and step flows.
PDF
