Narahari Marneni

A Review on the Viscous and Thermal Transport Properties of Nanofluids

In modern science and engineering nanofluids are playing a vital role in the application of heat transfer devices due to their effective properties. Addition of nanoparticles in the fluid can alter thermophysical properties of the nanofluid. Experimental and theoretical studies are essential to understand the change in fluid dynamics aspects of the fluid by the addition of nanoparticles. This paper presents a brief review on the viscous and thermal transport effects of nanofluids. The main emphasis is on the comparison of previous theoretical and experimental studies for thermophysical properties of nanofluids. These properties include density, viscosity, thermal conductivity and specific heat capacity of nanofluids.

Settling Characteristics of Alumina Nanoparticles in Ethanol-Water Mixtures

Nanofluids are considered as promising heat transfer fluids due to enhanced heat transfer ability as compared to the base fluid alone. Knowledge of settling characteristics of nanofluids has great importance towards stability of nanosuspensions. Sedimentation behavior of Alumina nanoparticles due to gravity has been investigated using different proportions of ethanol-water binary mixtures. Nanoparticles of 40 nm and 50 nm are used in this investigation at 23°C. Sediment height with respect to time is measured by visualization method in batch sedimentation. The effect of sonication on the sedimentation behavior is also studied using ultrasonic agitator. The effect of particle diameter, nanoparticle concentration and ethanol-water proportion on sedimentation behavior of nanofluids has been investigated and discussed.

Stability of Nanofluids

Nanofluids are the dilute suspensions of nanomaterials with distinctive and enhanced features. Nanofluids can be used in a variety of industrial applications because of improved thermophysical properties. Stability of nanofluids is the only quandary factor which decreases the efficiency of such smart fluids in engineering applications. The information and studies on interaction of nanomaterials with the liquid have significant importance toward their usage in industrial applications. Agglomeration among particles is a common issue due to interactive forces, which effects the dispersion, rheology, and overall performance of nanosuspensions. Characterization of nanofluids plays an important role to evaluate the stability of nanofluids. The effect of agglomeration on the stability of nanofluids can be reduced by introducing different mechanical and chemical techniques to prolong dispersion of suspended particles in liquids. Complete understanding on the stability of nanofluids can lead to the preparation of different combinations of stable nanofluids with enhanced properties for variety of applications.

An Exact Solution of Unsteady MHD Free Convection Flow of a Radiating Gas Past an Infinite Inclined Isothermal Plate

The effect of thermal radiation on unsteady magnetohydrodynamic free convection flow of an optically thin gray gas past an infinite inclined plate with constant temperature has been investigated. The governing coupled partial differential equations are solved analytically using the Laplace transform technique. The dimensionless velocity and temperature profiles are shown in graphs and the numerical values of the non-dimensional skin-friction and Nusselt number are presented in tables. The influence of the system parameters such asPrandtl number, inclination angle, magnetic field parameter, Grashof number, radiation parameter and time on flow fields have been discussed in detail. The results indicate that the inclination angle, magnetic field parameter and radiation parameter effects were to decrease the fluid velocity along an inclined plate.

Heat Exchanger Network Optimization by Differential Evolution Method

The synthesis of heat exchanger network (HEN) is a comprehensive approach to optimize energy utilization in process industry. Recent developments in HEN synthesis (HENS) present several heuristic methods, such as Simulated Annealing (SA), Genetic Algorithm (GA), and Differential Evolution (DE). In this work, DE method for synthesis and optimization of HEN has been presented. Using DE combined with the concept of super-targeting, the optimization is determined. Then DE algorithm is employed to optimize the global cost function including the constraints, such as heat balance, the temperatures of process streams. A case study has been optimized using DE, generated structure of HEN and compared with networks obtained by other methods such as pinch technology or mathematical programming. Through the result, the proposed method has been illustrated that DE is able to apply in HEN optimization, with 16.7% increase in capital cost and 56.4%, 18.9% decrease in energy, global costs respectively.

Heat Exchanger Network Optimization Using Differential Evolution with Stream Splitting

Reduction in energy consumption is an important task in process industry. The basic idea of heat exchanger network (HEN) is using cold streams to cool hot streams and hot streams to heat cold streams. Hence, synthesis and optimization of HEN is a main tool for improving heat recovery. This article introduces a new strategy for HEN optimization using differential evolution algorithm. The proposed method considers splitting stream at the pinch point, to minimize the total cost of the network. Primarily, the minimum approach temperature value is determined through super-targeting. Then, differential evolution is employed to specify the heat load of heat exchangers and splitting streams. The HEN structure obtained in this work has better economics and illustrates the better performance by this approach.

Natural Convection Flow in Vertical Channel Due to Ramped Wall Temperature at One Boundary

An exact solution to the problem of unsteady natural convective flow of a viscous and incompressible fluid in a vertical parallel plate channel due to ramp heating at one boundary is presented. The temperature at one of the channel plates increases linearly over a certain time period and then remains constant while that at the other plate is maintained at the initial fluid temperature. The Laplace transform technique has been used to obtain the expressions for the velocity and temperature fields by solving the dimensionless governing partial differential equations under appropriate boundary conditions. The influence of the physical parameters on the velocity field, the temperature field, rate of heat transfer, skin-friction and volume flow rate of the fluid are analyzed systematically. The shear stress at the plate with ramped temperature boundary condition is significantly higher than that at the other plate because of the steeper velocity profiles in the vicinity. The Nusselt number at the plate with ramped temperature is much higher than that at the other plate indicating that much of the energy released from the plate because of its increasing temperature with time is convected out by the fluid before it reaches the second plate. The natural convection due to ramp heating has also been compared with the baseline case of flow with constant temperature.Copyright