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The building sector's energy consumption has significantly increased due to climate change, emphasizing the need to develop sustainable low-energy buildings using experimental and computational tools. As a joint project between Kuwait and Australia, two portable cabins with internal sizes of 2 m × 2 m × 2.80 m, made from 75 mm thick sandwich panels and metal frames, were built in Kuwait to investigate their thermal and power consumption characteristics under various energy-saving techniques and different climates. This is the first attempt to analyze the energy-saving aspects of portable cabins made from sandwich panels for future sustainable cities. Each cabin has an indoor air-quality-sensing device and a novel power-monitoring system to measure their thermal and power consumption characteristics. First, shingles and novel finned metal cool roof (CR) techniques were experimentally investigated. Then, a new multi-zone SketchUp model of the portable cabins was created and simulated in TRNSYS. Next, the energy saving data of the portable cabins were investigated by adding PCM on the walls and the roof using built-in models of bio-phase change materials (Bio-PCMs) in TRNSYS. The annual energy performance index (EPI) as an important sustainability index was explored for determining heating/cooling/total demands of the portable cabins in the desert climate of Kuwait and in various climate regions of Australia. The findings reveal that both shingles and finned metal roofs contributed to higher power consumption. Meanwhile, the use of sustainable Bio-PCMs in Kuwait demonstrates a significant energy-saving potential of 30%, with variations ranging from 25% to over 45% across different climate regions in Australia. [ABSTRACT FROM AUTHOR]

Summary: The efficiency of photovoltaic (PV) cells is known to degrade with temperature, which limits their efficacy in the many regions around the world having a climate featuring high ambient temperatures. This study reports on field experiments supported by numerical modelling using Ansys steady‐state thermal solver that demonstrates improved PV cell performance when coupled with a passive natural‐convection‐driven heat sink. Heat sink fin spacing was optimized for hot climatic conditions. Experiments were conducted on a pair of PV modules, one fitted with the heat sink, the other serving as a control. Temperature data were acquired at 15 minute intervals from 6.00 am to 5.30 pm at both the front and rear of the modules. The heat sink respectively improved solar‐to‐electrical conversion efficiency and power output by 35% and almost 55%, and led to panel temperature reductions of up to 4°C and 3°C. [ABSTRACT FROM AUTHOR]

This work reports on an extensive investigation of the physicochemical properties, engine performance, exhaust emissions, and fundamental energy and exergy parameters of waste‐plastic oils blended with an additive, diethyl ether and diesel. A four‐stroke single‐cylinder diesel engine was used for the engine experiments. The seven fuels in this study include a neat diesel, a neat waste plastic oil, two binary blends of diesel‐waste plastic oil, and three ternary blends of diesel with waste plastic oil and diethyl ether. The justification for selecting diethyl ether was to augment fuel properties in the blend and to further reduce emissions. The reasons for choosing waste plastic are not only to harness energy from waste plastic but also to offer an effective solution to the plastic waste management issue. The choice of diesel was to use it as a reference fuel for comparison with other fuels. Fuel properties were observed to be similar, and in some cases better, with the blends. Notable reductions in emissions with identical engine performance and energy and exergy parameters were observed with the five oxygenated blends (plastic oil blends) than with a reference diesel fuel. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd [ABSTRACT FROM AUTHOR]

Abstract Natural convection in a square cavity filled with electrically conducting nanofluid that is driven by a periodic temperature profile along on of the vertical wall is studied numerically. The top and bottom horizontal walls are kept adiabatic. The right wall is maintained at low temperature while the temperature of the opposing vertical wall varies sinusoidally with time about a mean temperature. Flow and heat transfer performance through the enclosure is examined over a wide range of oscillation amplitudes and frequencies, Hartmann number, Rayleigh number and solid volume fraction at Prandtl number Pr = 6.2. The results show that oscillation amplitude, A , and frequency, f , of the vertical wall significantly affect the response of heat transfer inside the cavity. For A > 0.5, the forcing frequency is found to remain almost constant at f = 2.5, while it shifts towards a higher frequency f = 5 for A ≤ 0.5. At low Rayleigh number, Nusselt number is found to be independent of Rayleigh and Hartman numbers, while at higher Rayleigh number, convective flow dominates, and Nusselt number becomes independent of Hartmann number. In this regime, the Nusselt scaling with Rayleigh number agrees well with the exponent predicted by theory of natural convection in a cavity without magnetic field or nanoparticles, with a value of 1/4. With the increase of solid volume fraction, the heat transfer rate may increase or decrease depending on the values of Hartmann and Rayleigh numbers. [ABSTRACT FROM AUTHOR]

This study seeks to characterise the breakdown of the steady two-dimensional solution in the flow around a 180-degree sharp bend to infinitesimal three-dimensional disturbances using a linear stability analysis. The stability analysis predicts that three-dimensional transition is via a synchronous instability of the steady flows. A highly accurate global linear stability analysis of the flow was conducted with Reynolds number Re < 1150 and bend opening ratio (ratio of bend width to inlet height) 0:2≤β ≤5. This range of Re and β captures both steady-state two-dimensional flow solutions and the inception of unsteady two-dimensional flow. For 0:2 ≤ β ≤ 1, the two-dimensional base flow transitions from steady to unsteady at higher Reynolds number as β increases. The stability analysis shows that at the onset of instability, the base flow becomes three-dimensionally unstable in two different modes, namely a spanwise oscillating mode for β D 0:2 and a spanwise synchronous mode for β > 0:3. The critical Reynolds number and the spanwise wavelength of perturbations increase as β increases. For 1 < β ≤ 2 both the critical Reynolds number for onset of unsteadiness and the spanwise wavelength decrease as β increases. Finally, for 2 < β ≤ 5, the critical Reynolds number and spanwise wavelength remain almost constant. The linear stability analysis also shows that the base flow becomes unstable to different three-dimensional modes depending on the opening ratio. The modes are found to be localised near the reattachment point of the first recirculation bubble. [ABSTRACT FROM AUTHOR]

The fluid dynamics and heat transfer characteristics of magnetohydrodynamic duct flow often degrade the laminarization caused by the magnetic field. The present work evaluates the performance of a system featuring alternating current injection from a point electrode as a vortex promoter for enhancement of the thermal-hydraulic characteristics. It is found that the vortices generated by the current injection alone generally induce a greater thermal-hydraulic performance with a significantly smaller additional pressure loss than configurations featuring a physical obstacle. A maximum overall efficiency index of 1.83 was recorded within the parameter space investigated. [ABSTRACT FROM PUBLISHER]

The effect of rotation on horizontal convection in a cylindrical enclosure is investigated numerically. The thermal forcing is applied radially on the bottom boundary from the coincident axes of rotation and geometric symmetry of the enclosure. First, a spectral element method is used to obtain axisymmetric basic flow solutions to the time-dependent incompressible Navier-Stokes equations coupled via a Boussinesq approximation to a thermal transport equation for temperature. Solutions are obtained primarily at Rayleigh number Ra = 109 and rotation parameters up to QD60 (where Q is a non-dimensional ratio between thermal boundary layer thickness and Ekman layer depth) at a fixed Prandtl number Pr = 6:14 representative of water and enclosure height-to-radius ratio H/R = 0:4. The axisymmetric solutions are consistently steady state at these parameters, and transition from a regime unaffected by rotation to an intermediate regime occurs at Q ≈ 1 in which variation in thermal boundary layer thickness and Nusselt number are shown to be governed by a scaling proposed by Stern (1975, Ocean Circulation Physics. Academic). In this regime an increase in Q sees the flow accumulate available potential energy and more strongly satisfy an inviscid change in potential energy criterion for baroclinic instability. At the strongest Q the flow is dominated by rotation, accumulation of available potential energy ceases and horizontal convection is suppressed. A linear stability analysis reveals several instability mode branches, with dominant wavenumbers typically scaling with Q. Analysis of contributing terms of an azimuthally averaged perturbation kinetic energy equation applied to instability eigenmodes reveals that energy production by shear in the axisymmetric mean flow is negligible relative to that produced by conversion of available potential energy from the mean flow. An evolution equation for the quantity that facilitates this exchange, the vertical advective buoyancy flux, reveals that a baroclinic instability mechanism dominates over 5 ≾ Q ≾ 30, whereas stronger and weaker rotations are destabilised by vertical thermal gradients in the mean flow. [ABSTRACT FROM AUTHOR]

The design of vortex promoters in a heated-wall duct is often limited by the considerations of practicality, especially in complex systems such as fusion blankets. The present study investigates the use of current injection to invoke a street of vortices in quasi-two-dimensional high transverse magnetic field magnetohydrodynamic duct flows to enhance instability behind a cylinder. The intent is to generate intensive flow vorticity parallel to a magnetic field downstream of a field-aligned cylinder. Electric current enters the flow through an electrode embedded in one of the Hartmann walls, radiates outward, imparting a rotational forcing around the electrode due to the Lorentz force. The quasi-two-dimensional nature of these flows then promotes a vortical rotation across the interior of the duct with axis aligned to the magnetic field. The hot and cold walls are parallel to the magnetic field. Electric current amplitude and pulse width, excitation frequency and electrode position are systematically varied to explore their influences on the convective heat transport phenomenon. This investigation builds on a recommendation from previous work of Bühler (J. Fluid Mech., vol. 326, 1996, pp. 125-150) dedicated to understanding of the flow stability in a similar configuration. This study provides supportive evidence for the use of current injection as an alternative to the conventional mechanically actuated turbuliser, with heat transfer almost doubled for negligible additional pumping power requirements. [ABSTRACT FROM AUTHOR]

We demonstrate that instability in enclosed horizontally driven convection is due to a convective buoyancy-driven transverse-roll instability resembling the classical Rayleigh–Bénard convection in the thermal forcing boundary layer rather than a shear instability in the corresponding kinematic boundary layer. Instability growth is weakly sensitive to the local velocity profile, with velocity shear acting to select a transverse roll mode in preference to longitudinal rolls. The convectively unstable region grows from the hot end of the forcing boundary with increasing Rayleigh number two orders of magnitude lower than the natural onset of unstable horizontal convection. This analysis highlights the importance of the thermal boundary layer to the instability dynamics of horizontal convection, elucidating the path towards an understanding of turbulence and heat transport scaling in horizontal convection at oceanic Rayleigh numbers. [ABSTRACT FROM AUTHOR]

A vortex decay model for predicting spatial evolution of peak vorticity in a wake behind a cylinder is presented. For wake vortices in the stable region behind the formation region, results have shown that the presented model has a good capability of predicting spatial evolution of peak vorticity within an advecting vortex across 0.1 ≤ β ≤ 0.4, 500 ≤ H ≤ 5000, and 1500 ≤ ReL ≤ 8250. The model is also generalized to predict the decay behaviour of wake vortices in a class of quasi-two-dimensional magnetohydrodynamic duct flows. Comparison with published data demonstrates remarkable consistency. [ABSTRACT FROM AUTHOR]

The transient response of optimal linear perturbations of liquid metal flow under a strong axial magnetic field in an electrically insulated rectangular duct is considered. The focus is on the subcritical regime, below the onset of von Kármán vortex shedding, to determine the role of optimal disturbances in developing wake instabilities. In this configuration, the flow is quasi-two-dimensional and can be solved over a two-dimensional domain. Parameter ranges considered include Reynolds numbers 50≤Re<=2100, modified Hartmann numbers 50≤Ha[closed_star]<=500, and blockage ratios 0.1 <= β <= 0.4. In some instances, the optimal disturbances are found to generate energy growth of greater than four orders of magnitude. Variation in the wake recirculation length in the steady flow regime is determined as a function of Reynolds number, Hartman number, and blockage ratio, and a universal expression is proposed. For all β, the energy amplification of the disturbances is found to decrease significantly with increasing Hartmann number and the peak growth shifts towards smaller times. The optimal initial disturbances are consistently located in the vicinity of the boundary layer separation from the cylinder, and the structure of these disturbances is consistent for all Hartmann numbers and blockage ratios considered in this study. The time evolution of the optimal perturbations is presented, and is shown to correspond to sinuous oscillations of the shear layer downstream of the wake recirculation. The critical Reynolds number for the onset of growth at different Hartmann numbers and blockage ratios is determined. It is found that it increases rapidly with increasing Hartmann number and blockage ratio. For all β, the peak energy amplification grows exponentially with Re at low and high Hartmann numbers. Direct numerical simulation in which the inflow is perturbed by a random white noise confirms the predictions arising from the transient growth analysis: that is, the perturbation excites and feeds energy into the global mode. [ABSTRACT FROM AUTHOR]

Using phase change materials (PCMs) in energy storage systems provides various advantages such as energy storage at a nearly constant temperature and higher energy density. In this study, we aimed to conduct a numerical simulation for augmenting a PCM's melting performance within multiple tubes, including branched fins. The suspension contained Al2O3/n-octadecane paraffin, and four cases were considered based on a number of heated fins. A numerical algorithm based on the finite element method (FEM) was applied to solve the dimensionless governing system. The average liquid fraction was computed over the considered flow area. The key parameters are the time parameter ( 100   ≤ t ≤ 600   s) and the nanoparticles' volume fraction ( 0 % ≤ φ ≤ 8 %) . The major outcomes revealed that the flow structures, the irreversibility of the system, and the melting process can be controlled by increasing/decreasing number of the heated fins. Additionally, case four, in which eight heated fins were considered, produced the largest average liquid fraction values. [ABSTRACT FROM AUTHOR]

• Heat transfer efficiency can be promoted in a quasi-two-dimensional MHD duct flow by using surface protrusions on the heated wall. • Optimal blockage, pitch and inclination angle exists for achieving maximum efficiency and depends on the operating Hartmann friction parameter. • Heat transfer improvement of up to 80% with an overall efficiency gain of 50% is achieved by careful selection of geometric parameters of the protrusion. Repeated flow-facing wedge-shaped protrusions are explored as a means to enhance the heat transfer behaviour in a quasi-two-dimensional magnetohydrodynamic duct flow. Quasi-two-dimensionality is achieved under a strong magnetic field which are prevalent in the cooling blankets of fusion reactors. Ranges of Hartmann friction parameters (50 ≤ H ≤ 500) and Reynolds numbers (1300 ≤ R e ≤ 3000) are investigated. The effect of blockage β (wedge height to duct height), pitch γ (distance between wedges) and wedge angle ϕ on heat transfer ratio HR and efficiency η are considered. A monotonic increase in HR with β is observed in the range of β investigated. It is possible to further improve HR by changing the geometric parameter to an optimal pitch and optimal wedge angle. Corresponding to each H there exists an optimal β , γ and ϕ where maximum η could be achieved. In contrast to the optimal β which showed a monotonic increase with H , optimal γ and ϕ showed a reversal in the trend after a critical H. Effectiveness of surface modification on the heated wall is also established through a net power analysis. [ABSTRACT FROM AUTHOR]

An approach is studied for side-wall heat transfer enhancement in the magnetohydrodynamic flow of fluid in a rectangular duct that is damped by a strong transverse magnetic field. The mechanism employs the rotational oscillation of a cylinder placed inside the duct to encourage vortex shedding, which promotes the mixing of fluid near a hot duct wall with cooler fluid in the interior. The effectiveness of the heat transfer enhancement is investigated over a wide range of oscillation amplitudes and forcing frequencies. The motivation for exploring this mechanism is inspired by the transient growth response of this flow, which indicates that the optimal disturbances feeding the vortex shedding process are localized near the cylinder, and are characterized by an asymmetrical disturbance with respect to the wake centreline. The results show that a considerable increase in heat transfer from the heated channel wall due to rotational oscillation of the cylinder can be achieved, with the maximum enhancement of more than 30% over a zone extending 10d downstream of the cylinder. As the angular velocity amplitude of oscillation is increased, the range of oscillation frequencies for effective enhancement is widened, and the frequency at which the peak Nusselt number occurs is shifted slightly to lower frequencies. As the amplitude is increased, the formation of strong discrete wake vortices draws fluid from the wall boundary layers into the wake, enhancing heat transfer. The effect of oscillation amplitude on the distribution of local Nusselt number Nuw along the heated wall is significant. With an increase in Reynolds number, scope for additional heat transfer enhancement is possible. [ABSTRACT FROM AUTHOR]