• Energy Research

Abstract A numerical investigation is performed to study the effects of different nanofluids on the thermal and flow fields through transversely wavy wall channels with different phase shifts between the upper and lower wavy walls. Reynolds numbers are considered in the turbulent range of 6000 ≤ Re ≤ 18,000 and a uniform wall temperature of 400 K is applied on the walls. The two dimensional continuity, Navier–Stokes and energy equations are solved by using finite volume method (FVM). The optimization was carried out by using various phase shifts (θ = 0°, 30°, 60°, 90° and 180°) and three different wavy amplitudes (α = 0.5, 1 and 1.5 mm) to reach the optimal geometry with the maximum performance evaluation criterion (PEC). The main aim of this study is to analyze the effects of SiO2 nanoparticles, its concentration (1–4%), and nanoparticle shapes (i.e. blades, platelets, cylindrical, bricks, and spherical), on the heat transfer and fluid flow characteristics. Simulation results show that the wavy channel performance was greatly influenced by changing the phase shift and the wavy amplitude. The highest PEC was obtained for the phase shift of θ = 30° with α = 0.5 at Re = 6000. It is found that the SiO2-EG nanofluid with platelets nanoparticle shape gives the highest heat transfer enhancement compared with other tested nanofluids.

Abstract Among different sources of renewable energy, solar energy is widely used almost exclusively because of its ease of availability and its lowest environmental effects. The most commonly used solar collectors are the flat plate solar collectors (FPSCs). However, they are less powerful (low capacity to convert solar energy to thermal energy). It is possible to classify the use of nanofluid on FPSCs as an efficient way to boost the solar collectors’ performance. In this paper, studies on metal oxides, non-metal oxides, solid metals, semiconductor nanomaterials, carbon nanostructured, and nanocomposite nanofluids used as heat transfer fluids (HTFs) within FPSCs are examined sequentially. Various parameters affecting the FPSC’s thermal efficiency, such as nanoparticle type, nanoparticle concentration, nanoparticle size/shape, solar radiance, and mass flow rate, are extensively analyzed. Studies have also compared various types of single nanofluids or mixture nanofluids with FPSCs under the same operating conditions. It is found that the use of carbon-based nanofluids compared to metal oxides of nanofluids under the same conditions has resulted in a major improvement in the energetic and exergetic performance of the FPSC. Furthermore, the reviewed research revealed that there is a tremendous opportunity to achieve the commercial application of carbon-based nanofluid FPSC. The obstacles and opportunities for further study are also highlighted.

Studied performance of triangular grooved microchannel heat sink (TGMCHS) using nanofluid.Solved 3D laminar flow and conjugate heat transfer of TGMCHS using FVM.Investigated the effect of geometrical parameters, nanofluid type, and its concentration.Analyzed the effects of particle diameter, base fluid, Reynolds number.TGMCHS efficiency is increased by 179.55% compared to simple MCHS. A numerical simulation is conducted to examine the heat transfer and fluid flow characteristics of nanofluids in a triangular grooved microchannel heat sink (TGMCHS). The governing and energy equations are solved using the finite volume method (FVM). The influence of the geometrical parameters such as the angle (50-100?), depth (10-25µm) and pitch (400-550µm) of the groove on the thermal performance of TGMCHS was examined. The effects of different nanoparticle types (Al2O3, CuO, SiO2, ZnO), volume fraction (O=0.01-O=0.04), particle diameter (25-80nm) and base fluid (water, ethylene glycol, engine oil) at different Reynolds numbers are also studied. The thermal performance of TGMCHS had significant increment with the increment of angle and depth of the groove accompanied with an optimum groove pitch. It is found that the TGMCHS thermal performance of using Al2O3-H2O (O=0.04, dnp=25nm) is outperformed the simple MCHS using water.

Abstract Numerical investigations are performed using finite volume method to study laminar convective heat transfer and nanofluids flows through a circular tube fitted with helical tape insert. The wall of tube was subjected to a uniform heat flux boundary condition. The continuity, momentum and energy equations are discretized and the SIMPLE algorithm scheme is applied to link the pressure and velocity fields inside the domain for plain tube. Four different twist ratios of 1.95–4.89, two different types of nanoparticles, Al2O3 and SiO2 with different nanoparticle shapes of spherical, cylindrical and platelets, and 0.5–2.0% volume fraction in base fluid (water) and nanoparticle diameter in the range of 20–50 nm were used to identify their effect on the heat transfer and fluid flow characteristics through a circular tube fitted with helical tape insert geometries. The results indicate that the four types of nanofluid achieved higher Nusselt number than pure water. Nanofluid with Al2O3 particle achieved the highest Nusselt number. For all the cases studied, the Nusselt number increased with the increase of Reynolds number and with the decrease of twist ratio of helical tape insert.

An effective way to enhance the heat transfer in mini and micro electronic devices is to use different shapes of micro-channels containing vortex generators (VGs). This attracts researchers due to the reduced volume of the electronic micro-chips and increase in the heat generated from the devices. Another way to enhance the heat transfer is using nanofluids, which are considered to have great potential for heat transfer enhancement and are highly suited to application in practical heat transfer processes. Recently, several important studies have been carried out to understand and explain the causes of the enhancement or control of heat transfer using nanofluids. The main aim upon which the present work is based is to give a comprehensive review on the research progress on the heat transfer and fluid flow characteristics of nanofluids for both single- and two- phase models in different types of micro-channels. Both experimental and numerical studies have been reviewed for traditional and nanofluids in different types and shapes of micro-channels with vortex generators. It was found that the optimization of heat transfer enhancement should consider the pumping power reduction when evaluating the improvement of heat transfer.

Laminar mixed convection flow using nanofluids over backward facing step in a heated rectangular duct having a baffle mounted on its wall are numerically simulated. The continuity, momentum and energy equations are solved using finite volume method (FVM) and the SIMPLE algorithm scheme is applied to examine the effects of the baffle on heat transfer characteristics. In this study, several parameters such as different types of nanoparticles (Al2O3, CuO, SiO2 and ZnO), different volume fractions in the range of 1% to 4%, different nanoparticles diameter in the range of 25 to 80 nm, and wall flux in the range of 10 = qw = 70 W/m2 were used. The effects of the baffle height Hb, baffle thickness Wb, and distance between the backward-facing step and baffle D on Nusselt number variation are numerically investigated. The numerical results indicate that the nanofluid with SiO2 has the highest Nusselt number compared with other nanofluids types. The Nusselt number increases as the volume fraction of nanoparticles and the Reynolds number increase, while it decreases as the nanoparticles diameter increases. Effects of baffle distances baffle heights and baffle widths on heat transfer characteristics are significant, while, effects of wall flux are slightly insignificant.

Abstract Experimental and numerical investigations are presented to illustrate the nanofluid flow and heat transfer characteristics over microscale forward-facing step (MFFS). The duct inlet and the step height were 400 μm and 600 μm respectively. All the walls are considered adiabatic except the downstream wall was exposed to a uniform heat flux boundary condition. The distilled water was utilized as a base fluid with two types of nanoparticles Al 2 O 3 and SiO 2 suspended in the base fluid. The nanoparticle volume fraction range was from 0 to 0.01 with an average nanoparticle diameter of 30 nm. The experiments were conducted at a Reynolds number range from 280 to 480. The experimental and numerical results revealed that the water–SiO 2 nanofluid has the highest Nusselt number, and the Nusselt number increases with the increase of volume fraction. The average friction factor of water–Al 2 O 3 was less than of water–SiO 2 mixture and pure water. The experimental results showed 30.6% enhancement in the average Nusselt number using water–SiO 2 nanofluid at 1% volume fraction. The numerical results were in a good agreement with the experimental results.

Abstract Solar energy is an environmentally friendly and renewable energy source which is utilized for electricity generation, domestic water heating and building ventilation. Solar chimney is a solar system that operates as a passive natural ventilation technique for diminishing building’s energy consumption and generating electricity from its power plant. However, the solar chimneys suffer from main drawback of non-operative conditions at night when there is no solar energy. Thermal energy storage using phase change materials (PCMs) is considered as an impressive solution for this limitation. Therefore, the present paper provides a literature survey on the incorporation of PCMs for performance improvement of solar chimneys in both buildings and power plant applications. The results obtained from the previous studies showed a great potential of PCM in enhancing the building’s thermal comfort, extending the ventilation time, improving the electricity generation of solar chimney power plants, and prolonging the generation period. Moreover, it is also observed that the thermal and geometric characteristics of PCMs have high influence on the overall chimney performance where the paraffins are the most used PCM materials in the available literature. Finally, economic, environmental and exergy analysis was recommended as future research directions beside the PCM’s optimal thickness, humidity control and super-cooling reduction.