R.K. Nayak

Bio: R.K. Nayak is an academic researcher from Indian Institutes of Technology. The author has contributed to research in topics: Bejan number & Reynolds number. The author has an hindex of 2, co-authored 2 publications receiving 99 citations.

Numerical study on mixed convection and entropy generation of Cu–water nanofluid in a differentially heated skewed enclosure

Abstract: A numerical study is made on the mixed convection of copper–water nanofluid inside a differentially heated skew enclosure. Co-ordinate transformations are used to transform the physical domain to the computational domain in an orthogonal co-ordinate. The finite volume based SIMPLEC algorithm is used to solve the transformed equations for fluid flow and heat transfer equations in the computational domain. The fluid flow and heat transfer characteristics are studied for a wide range of skew angles ( 30 ° ⩽ λ ⩽ 150 ° ) , nanoparticle volume fraction ( 0.0 ⩽ ϕ ⩽ 0.2 ) and Richardson number ( 0.1 ⩽ Ri ⩽ 5 ) at a fixed value of Reynolds number. The entropy generation and Bejan number are evaluated to demonstrate the thermodynamic optimization of the mixed convection. It is shown that the heat transfer rate increases remarkably by the addition of nanoparticles. The flow field is sensible to the skew angle variation. Our results show that the heat transfer augmentation through nanoparticles with lower rate in entropy generation enhancement can be achieved in a skewed cavity.

Heat transfer and entropy generation in mixed convection of a nanofluid within an inclined skewed cavity

Abstract: The mixed convection of a Cu–water nanofluid in a skewed cavity which is slightly inclined from the horizontal is investigated. A co-ordinate transformation is used to transform the physical domain into the computational domain in an orthogonal co-ordinate system. A control volume method over a staggered grid arrangement is used to discretize the governing equations. The discretized equations are solved through a pressure-correction based SIMPLEC algorithm. Based on this algorithm a Fortran 95 computer code is developed, which has been executed in the IBM Power 7 server. The effects of relevant parameters such as, Richardson number ( 0.1 ⩽ Ri ⩽ 5 ) , Reynolds number ( 100 ⩽ Re ⩽ 1000 ) , nanoparticle volume fraction ( 0 ⩽ ϕ ⩽ 0.2 ) on the mixed convection of nanofluid is studied by considering acute to obtuse skew angle and inclination angle between −30° to 30°. We made a comparative study between several models for effective thermal conductivity and viscosity of a nanofluid. The entropy generation as well as the Bejan number is evaluated to illustrate the thermodynamic optimization of the mixed convection. Our results show that the flow and thermal fields within a skewed enclosure are sensible to the angle of inclination. The addition of nanoparticles produce an enhancement in the heat transfer but reduce the effect of buoyancy. The impact of the inclination angle on the heat transfer and entropy generation is analyzed for the considered range of the skew angle to determine the optimum heat transfer characteristics.

MHD three-dimensional flow of nanofluid with velocity slip and nonlinear thermal radiation

Abstract: An analysis has been carried out for the three dimensional flow of viscous nanofluid in the presence of partial slip and thermal radiation effects. The flow is induced by a permeable stretching surface. Water is treated as a base fluid and alumina as a nanoparticle. Fluid is electrically conducting in the presence of applied magnetic field. Entire different concept of nonlinear thermal radiation is utilized in the heat transfer process. Different from the previous literature, the nonlinear system for temperature distribution is solved and analyzed. Appropriate transformations reduce the nonlinear partial differential system to ordinary differential system. Convergent series solutions are computed for the velocity and temperature. Effects of different parameters on the velocity, temperature, skin friction coefficient and Nusselt number are computed and examined. It is concluded that heat transfer rate increases when temperature and radiation parameters are increased.

Entropy generation of nanofluid and hybrid nanofluid flow in thermal systems: A review

Abstract: This paper presents a review of the contributions on entropy generation of nanofluids and hybrid nanofluids in the different types of thermal systems for different boundary conditions and physical situations. The relevant papers are classified into three categories: entropy generation in minichannel, entropy generation macrochannel and entropy generation in cavities. The viscous dissipative, streamwise, electromagnetic effects, as well as nanoparticles concentration, the temperature and the flow regime on entropy generation, were analyzed. The reviewed literature indicates that the implementation of nanofluids/hybrid nanofluids in microchannels, minichannels, and cavities may be an important alternative to the traditional thermal systems and an interesting topic of study.

MHD mixed convection and entropy generation of nanofluid filled lid driven cavity under the influence of inclined magnetic fields imposed to its upper and lower diagonal triangular domains

Abstract: In this study, mixed convection of CuO–water nanofluid filled lid driven cavity having its upper and lower triangular domains under the influence of inclined magnetic fields is numerically investigated. The top horizontal wall of the cavity is moving with constant speed of u w with + x direction while no-slip boundary conditions are imposed on the other walls of the cavity. The top wall of the cavity is maintained at constant cold temperature of T c while the bottom wall is at hot temperature of T h and on the other walls of the cavity are assumed to be adiabatic. The governing equations are solved by using Galerkin weighted residual finite element formulation. Entropy generation is produced by using formulation and integrated with calculated velocities and temperatures. The numerical investigation is performed for a range of parameters: Richardson number (between 0.01 and 100), Hartmann number (between 0 and 50), inclination angle of magnetic field (between 0° and 90°) and solid volume fraction of the nanofluid (between 0 and 0.05). Different combinations of Hartmann numbers and inclination angles of the magnetic fields are imposed in the upper and lower triangular domains of the square cavity. It is observed that the local and averaged heat transfer deteriorates when the Richardson number, Hartmann number of the triangular domains increase. When the Hartmann number and magnetic angle of the upper triangle are increased, more deterioration of the averaged transfer is obtained when compared to lower triangular domain. Local and averaged heat transfer increase as the solid volume fraction of the nanoparticles increases and adding nanoparticles is more effective for the local enhancement of the heat transfer when the heat transfer rate is high and convection is not damped with lowering the Hartmann number. Second law analysis of the system for different combinations of flow parameters is also performed.

Natural convection and entropy generation of nanofluid filled cavity having different shaped obstacles under the influence of magnetic field and internal heat generation

Abstract: In this study, natural convection in a nano-fluid filled cavity having different shaped obstacles (circular, square and diamond) installed under the influence of a uniform magnetic field and uniform heat generation was numerically investigated. The cavity was heated from below and cooled from the vertical sides while the top wall was assumed to be adiabatic. The temperatures of the side walls vary linearly. The governing equations were solved by using Galerkin weighted residual finite element formulation. The numerical investigation was performed for a range of parameters: external Rayleigh number (104 ≤ RaE ≤ 106), internal Rayleigh number (104 ≤ RaI ≤ 106), Hartmann number (0 ≤ Ha ≤ 50), and solid volume fraction of the nanofluid (0 ≤ ϕ ≤ 0.05). It is observed that the presence of the obstacles deteriorates the heat transfer process and this is more pronounced with higher values of Re E . Averaged heat transfer reduces by 21.35%, 32.85% and 34.64% for the cavity with circular, diamond and squared shaped obstacles compared to cavity without obstacles at RaI = 106. The effect of heat transfer reduction with square and diamond shaped obstacles compared to case without obstacle is less effective with increasing values of Hartmann number. Second law analysis was also performed by using different measures for the normalized total entropy generation.

Natural convection of nanofluid inside a wavy cavity with a non-uniform heating: Entropy generation analysis

Abstract: Purpose The main purpose of this numerical study is to study on entropy generation in natural convection of nanofluid in a wavy cavity using a single-phase nanofluid model. Design/methodology/approach The cavity is heated non-uniformly from the wavy wall and cooled from the right side while it is insulated from the horizontal walls. The physical domain of the problem is transformed into a rectangular geometry in the computational domain using an algebraic coordinate transformation by introducing new independent variables ξ and η. The governing dimensionless partial differential equations with corresponding initially and boundary conditions were numerically solved by the finite difference method of the second-order accuracy. The governing parameters are Rayleigh number (Ra = 1000-100000), Prandtl number (Pr = 6.82), solid volume fraction parameter of nanoparticles (φ = 0.0-0.05), aspect ratio parameter (A = 1), undulation number (κ = 1-3), wavy contraction ratio (b = 0.1-0.3) and dimensionless time (τ = 0-0.27). Findings It is found that the average Bejan number is an increasing function of nanoparticle volume fraction and a decreasing function of the Rayleigh number, undulation number and wavy contraction ratio. Also, an insertion of nanoparticles leads to an attenuation of convective flow and enhancement of heat transfer. Originality The originality of this work is to analyze the entropy generation in natural convection within a wavy nanofluid cavity using single-phase nanofluid model. The results would benefit scientists and engineers to become familiar with the flow behaviour of such nanofluids, and will be a way to predict the properties of this flow for the possibility of using nanofluids in advanced nuclear systems, in industrial sectors including transportation, power generation, chemical sectors, ventilation, air-conditioning, etc.