A. K. M. Sadrul Islam

Free convection in an enclosure with vertical wavy walls

This paper describes a numerical prediction of heat transfer and fluid flow characteristics inside an enclosure bounded by two isothermal wavy walls and two adiabatic straight walls. Governing equations were discretized using the finite-volume method with collocated variable arrangement. Simulation was carried out for a range of wave ratio λ (defined by amplitude/average width) 0.00–0.4, aspect ratio A (defined by height/average width) 1.0–2.0, Grashof number Gr = 10 0 –10 7 for a fluid having Prandtl number 0.7. Streamlines and isothermal lines are used to present the corresponding flow and thermal field inside the enclosure. Local and global distributions of Nusselt number are presented for the above configuration. Lastly, velocity profiles are presented for some selected locations inside the enclosure for better understanding of the influence of flow field on the thermal field.  2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.

Laminar free convection and entropy generation inside an inclined wavy enclosure

Abstract We investigate numerically the heat transfer and fluid flow characteristics inside a wavy walled enclosure. Second law of thermodynamics is also applied to predict the nature of irreversibility in terms of entropy generation. Finite-volume method is used to discretize the governing differential equations with non-staggered variable arrangement. SIP (strongly implicit procedure) solver solves the linear equation systems with full multigrid (FMG) acceleration. Simulation was carried out for a range of wave ratio (defined by amplitude/average width) λ=0.0–0.4, aspect ratio (defined by height/average width) A=1.0–2.0, Rayleigh number Ra=100–107 for a fluid having Prandtl number equal to 0.7. The angle of inclination (θ) is varied from 0° to 360° with 15° interval. Streamlines and isothermal lines represent the corresponding flow and thermal fields. Local and global Nusselt number distributions express the rate of heat transfer. Contour of Bejan number is plotted. Volume averaged entropy generation rate is also presented.

Separation characteristics of fluid flow inside two parallel plates with wavy surface

Abstract Separation characteristics of fluid flow inside two parallel wavy plates for steady-laminar flow is investigated numerically in the present study. Governing equations are discretized using control volume based finite-volume method with collocated variable arrangement. SIMPLE algorithm is used and SIP solver is applied for solution of system of equations. Effect of surface waviness (defined by amplitude to average interwall spacing ratio, a / H ) and aspect ratio (defined by wavelength to average interwall spacing ratio, w / H ) on separation characteristics of fluid flow is presented. The present work has been carried out for surface waviness a / H =0–0.3, aspect ratio w / H =1.5–2.25. A critical Reynolds number ( Re c ) is used to identify the appearance of first separation of fluid flow in the channel. Critical Reynolds ( Re c ) number is calculated for wide range of surface waviness and aspect ratio. The structure of separation bubble depends strongly on waviness of the surface and aspect ratio for a particular Reynolds number and changes little with wave number ( n ). Finally pressure drop characteristics is presented in terms of average friction factor as a function of Reynolds number.

FULLY DEVELOPED FLOW STRUCTURES AND HEAT TRANSFER IN SINE-SHAPED WAVY CHANNELS

Fully developed unsteady fluid flow and heat transfer are studied numerically in a sine-shaped wavy channel by solving two-dimensional Navier-Stokes and energy equations. The flow in the channel has been observed to be steady up to a critical Reynolds number which depends on the geometric configuration. Beyond the critical Reynolds number a self-sustained oscillatory flow has been observed. The effect of variations of minimum height, amplitude and wavelength are studied. Decreasing channel height and increasing amplitude cause the flow to become more unstable and thereby increase friction factor and heat transfer, but variation of wavelength has minimal effect. The frequencies of oscillations are reported as well

Effect of surface waviness and aspect ratio on heat transfer inside a wavy enclosure

A numerical simulation has been carried out to investigate the buoyancy induced flow and heat transfer characteristics inside a wavy walled enclosure. The enclosure consists of two parallel wavy and two straight walls. The top and the bottom walls are wavy and kept isothermal. Two straight‐vertical sidewalls are considered adiabatic. Governing equations are discretized using the control volume based finite‐volume method with collocated variable arrangement. Simulation was carried out for a range of surface waviness ratios, λ=0.00‐0.25; aspect ratios, A=0.25‐0.5; and Rayleigh numbers Ra=100‐107 for a fluid having Prandtl number equal to 1.0. Results are presented in the form of local and global Nusselt number distributions, streamlines, and isothermal lines for different values of surface waviness and aspect ratios. For a special case of λ=0 and A=1.0, the average Nusselt number distribution is compared with available reference. The results suggest that natural convection heat transfer is changed considerably when surface waviness changes and also depends on the aspect ratio of the domain. In addition to the heat transfer results, the heat transfer irreversibility in terms of Bejan number (Be) was measured. For a set of selected values of the parameters (λ, A, and Ra), a contour of the Bejan number is presented at the end of this paper.

NUMERICAL STUDY OF FORCED CONVECTION IN A PACKED CHANNEL WITH ASYMMETRIC HEATING

Numerical solution based on the control volume method is presented for the study of heat transfer for forced convective flow in a channel filled with a fluid saturated porous media. The solution of the conservative differential equations governing the flow is performed using the SZMPLE algorithm. The wall effects on the variation of porosity and thermal dispersion have been considered. In calculating the thermal dispersive conductivity, a general expression has been obtained taking into account the flow geometry and flow Reynolds number. The expression appears to serve well in the present investigation and also in reproducing the results of previous studies. The analysis includes predictions of temperature profiles and heat flux for the constant wall temperature condition at the wall and have been compared with available experimental data.

Small-Scale Decentralized Renewable Energy Systems for the Remote Communities of the Developing Countries

About 2 billion people of the world, mostly in rural areas of the developing countries, do not have access to grid-based electricity. The most critical factor affecting their livelihoods is access to clean, affordable and reliable energy services for household and productive uses. Under this backdrop, renewable and readily available energy from the nature can be incorporated in several proven renewable energy technology (RET) systems and can play a significant role in meeting crucial energy needs in these remote far flung areas. RETs are ideal as distributed energy source and they can be incorporated in packages of energy services and thus offer unique opportunities to provide improved lighting, health care, drinking water, education, communication, and irrigation. Energy is also vital for most of the income-generating activities, both at the household or commercial levels. Access to energy is strongly connected to the achievement of the Millennium Development Goals (MDGs), which set targets for poverty reduction, improved health, and gender equality as well as environmental sustainability. Environmentally benign renewable energy systems can contribute significantly in the above-mentioned unserved or underserved areas in the developing countries to achieve both local and global environmental benefits. This is important in the context of sustainable development in: (i) poverty alleviation, (ii) education, (iii) gender equity and empowerment, (iv) health including other benefits like improved information access through Information and Communication Technology (ICT) centers, (v) better security, and (vi) increase in social or recreational opportunities. It is evident that proliferation of renewable energy resources through implementing their applications for meeting energy demand will promote all the three dimensions namely, social, economic and environmental of sustainable development in the developing countries. Several small scale enabling RET systems have been suggested in this paper in the light of above-mentioned issues of energy sustainability and they can significantly contribute to the improvement of the livelihood of the remote impoverished rural communities of the developing countries. With the current state of technology development, several RET systems (such as wind, solar photovoltaics, solar thermal, biomass and microhydro) have become successful in different parts of the world. In this paper, an exhaustive literature survey has been conducted and several successful and financially viable small-scale RET systems were analyzed. These systems have relevance to the economies of the developing countries that can be utilized for electrification of domestic houses, micro enterprises, health clinics, educational establishments and rural development centers.Copyright

Wind Power Utilization for Water Pumping in Bangladesh

Publisher Summary This chapter throws the attention on wind power utilization for water pumping in Bangladesh. The possibilities of introducing small scale wind power pumping in Bangladesh have been assessed with regard to wind data supplied by the Bangladesh Meteorological Department. The large-scale wind energy extraction is not feasible in Bangladesh due to low wind speed available. However, there is a potential of small scale wind power pumping in some regions in the country if a proper choice of wind turbine is made. The wind turbine may be useful to drive hand pumps used for irrigating agricultural land. The performance of horizontal axis sailwing rotor coupled to a No. 6 hand tubewell is found to be satisfactory. The combined efficiency of the windmill pump set is found to be about 20% at a wind speed of 2.45 m/s. The Reynolds number based on wind speed and rotor swept diameter is in the range of 4.67e5 to 1.87e6.