Mohammad Z. Hossain

Imperial College London | Imperial · Department of Aeronautics

Flow resistance reduction, quantified as a change in flow rate with respect to a reference isothermal flow driven by the same pressure gradient, is realizable in a channel flow using a thermal wave applied on the bounding wall. Countercurrent waves provide a resistance-reducing effect at any wave velocity, Reynolds number and wavenumber considered....

It is shown that thermal waves applied on the bounding surface of a horizontal slot generate a pumping effect. Reynolds stress developed by the change in the flow field due to the thermal inertia associated with the penetration of the wave into the fluid interior drives the net fluid movement in the horizontal direction. The induced flow rate incre...

Analysis of convection driven by spatial periodic heating shows a wealth of responses due to Prandtl number dependence. The primary convection is delineated by the heating wavenumber and the secondary convection is characterized by the critical wavenumber established by an instability process. The resulting two-wavenumber dynamical system involves...

We report on a high‐fidelity, spectral/hp element algorithm developed for the direct numerical simulation of thermal convection problems. We consider the incompressible Navier‐Stokes and advection‐diffusion equations coupled through a thermal body‐forcing term. The flow is driven by a prescribed flowrate forcing with explicit treatment of the nonli...

Pressure-gradient-driven flows in grooved horizontal channels were investigated. The results show that a significant reduction in pressure losses can be achieved by exposing such channels to spatially distributed heating. The system response strongly depends on the characterization of both patterns and on their relative position, leading to a patte...

Classical Rayleigh–Bénard convection occurs when a horizontal fluid layer is heated sufficiently strongly from below. In more recent times, there has been increased interest in structured convection, when the heating that is applied is no longer uniform but rather spatially varying in some way. Here, we examine the effect of structured convection i...

An external force is required to maintain the relative movement of horizontal plates. It is shown that this force is reduced when the plates are subject to a spatially distributed heating. The largest reduction occurs for heating wavelengths of the order of distance between the plates with its magnitude increasing proportionally to the second power...

The flow of a liquid film over an inclined plane is frequently found in nature and industry, and, under some conditions, instabilities in the free surface may appear. These instabilities are initially two-dimensional surface waves, known as Kapitza waves. Surface waves are important to many industrial applications. For example, liquid films with su...

When the heating intensity is below the critical threshold required for the onset of Rayleigh-Bénard (RB) convection, heat transport across a horizontal fluid layer uniformly heated from below is driven by conduction, placing a limit on its magnitude. A methodology to increase the heat flow through the use of spatial heating non-uniformities is pro...

An algorithm suitable for analysis of convection problems in corrugated conduits has been developed. The algorithm uses the immersed boundary conditions (IBC) concept to capture the effects of corrugated walls. The field equations are discretized on a regular domain surrounding the flow domain using Fourier expansions in the stream-wise direction a...

Natural convection in a two-dimensional horizontal layer has been investigated. The layer is confined between two parallel horizontal plates. The upper plate is kept isothermal, while the lower plate has an externally imposed, long wavelength, spatially sinusoidal heating with the amplitude expressed in terms of the Rayleigh number Ra and the wavel...

Flow in a horizontal channel exposed to external heating which results in sinusoidal temperature variations along the upper and lower walls with a phase shift between them has been studied using a combination of analytical and numerical methods. The most intense convection is observed when the upper and lower hot spots are located above each other....

Photovoltaic (PV) cells are known for poor efficiency within the range of only 6-15%, depending on the type of cells. As a result, those can convert only a small part of the absorbed solar energy into electricity, the rest is wasted as heat, which also contributes to rise in cell temperature. This heating up is undesirable for PV cells because it f...

Natural convection in a horizontal slot heated from above and from below has been considered. Each heating has a certain spatial distribution. It has been demonstrated that a wide variety of convection patterns can be generated by changing the relative position of both heating patterns. A significant intensification of convection, compared to conve...

Mixed convection in a channel with flow driven by a pressure gradient and subject to spatially periodic heating along one of the walls has been studied. The pattern of the heating is characterized by the wavenumber alpha and its intensity is expressed in terms of the Rayleigh number Ra-p. The primary convection has the form of counter-rotating roll...

Effects of grooving in a porous faced hydrostatic circular step thrust bearing are investigated using a mathematical model based on the narrow groove theory. It is shown that enhancement of load capacity by grooving the step is possible at moderate level of permeability of the porous facing. Load capacity drops sharply with the increase of porous f...

Blood pressure is one of the vital health issues and a very commonly measured physiological parameter in clinical practice. Measuring the blood pressure using traditional aneroid manometer with stethoscope requires a trained user. In developed countries, there are plenty of advanced electronic devices, which can easily measure blood pressure in hum...

Natural convection in a horizontal layer subject to periodic heating from above has been studied. It is shown that the primary convection leads to the cooling of the bulk of the fluid below the mean temperature of the upper wall. The secondary convection may lead either to longitudinal rolls, transverse rolls, or oblique rolls. The global flow prop...

A parametric analysis based on narrow groove theory has been presented for estimating the load capacity of a grooved circular step thrust bearing. Three types of grooving arrangements of the bearing surface, namely, (a) both the step and the recess are grooved, (b) only the step is grooved and (c) only the recess is grooved, are considered. It is f...

It is demonstrated that a significant drag reduction for pressure-driven flows can be realized by applying spatially distributed heating. The heating creates separation bubbles that separate the stream from the bounding walls and, at the same time, alter the distribution of the Reynolds stress, thereby providing a propulsive force. The strength of...

We present the numerical investigation of Rayleigh-Benard convection (RBC) in a slot whose bottom wall is subject to a long-wavelength heating and the upper wall is isothermal. It is shown that multiple flow structures associated with the same conditions can be produced by changing the history of the heating; this history can be controlled by using...

Natural convection in an infinite horizontal layer subject to a spatially periodic heating is considered. The analysis is focused on the heating wave number α->0. It has been shown that convection has a simple topology consisting of one pair of counter-rotating rolls per heating period when the heating intensity does not exceed the critical value o...

Natural convection in a horizontal layer exposed to periodic heating is considered. The primary response leads to stationary convection in the form of rolls orthogonal to the heating wave vector. For large α a uniform conductive layer emerges at the upper section of the fluid layer. Secondary convection gives rise either to the longitudinal rolls,...

The present work deals with the natural convection in a horizontal slot whose bottom is subject to a spatially periodic heating and the upper wall is kept isothermal. This type of heating results in the appearance of hot and cold zones along the slot length, and initiates primary convection regardless of the magnitude of the heating. It has been sh...

Natural convection in a fluid contained in an infinite horizontal slot subject to a spatially distributed heating has been investigated for a wide range of Prandtl numbers Pr. Detailed results are presented for the case of the lower wall subject to heating being a sinusoidal function of one of the coordinate, with its spatial distribution described...

Conditions leading to the emergence of convective roll instability have been identified by linear instability analysis of a stationary fluid in a slot subject to spatially distributed heating. It is found that for moderate heating wave numbers the pattern of instability is generally locked-in with the pattern of heating by a sub-harmonic relation,...

The linear stability of channel flow between two horizontal parallel walls in the presence of distributed wall-heating has been investigated. The case of periodic heating applied at the bottom wall has been considered in details. This heating results in the creation of zones of fluid with alternatively increased and decreased temperature. The mean...

A numerical analysis is carried out to study the performance of mixed convection in a rectangular enclosure. Four different placement configurations of the inlet and outlet openings were considered. A constant flux heat source strip is flush-mounted on the vertical surface, modeling an integrated circuit chips affixed to a printed circuit board, an...

Time dependent Navier-Stokes and energy equations have been solved to investigate the fluid flow and heat transfer characteristics in wavy channels. Three different types of two dimensional wavy geometries (e. g. sine-shaped, triangular, and arc-shaped) are considered. All of them are of single wave and have same geometric dimensions. Periodic boun...

Development of a low-cost multi-channel (eight to twenty two channels) data logger can easily be made and easily be used to convert the analog signal of physical parameters of various tests or other purposes of engineering. By a suitable program code it can be used to read the value digitally with a PC. Our aim is to provide with a module and a sof...

Assuming narrow grooves and considering inertia effect, an equation for the pressure distribution in a grooved circular step thrust bearing has been derived. A parametric study has been performed to investigate the effects of step and groove geometry on pressure distribution, load capacity and lubricant flow rate. Three arrangements of the bearing...

Fully developed unsteady fluid flow and heat transfer are studied numerically in a sineshaped 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-sus...

Two -dimensional Navier -Stokes and energy equations have been solved numerically for unsteady laminar flow in periodic wavy (sinusoidal and triangular) channels. The flow in the channels has been observed to be steady up to a critical Reynolds number. Beyond the critical Reynolds number the flow becomes self- sustained quasiperiodic oscillatory. T...

In Bangladesh, most of the potential sites for micro hydro have low head (less than 10m) that also has a seasonal variation. Thus the choice of an appropriate turbine has a vital role on the sustainability of the project. In this paper, several sites for micro hydro projects have been identified and the selection criteria for the turbine for these...