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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.

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.

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.

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 Chillers consume more than 40% of the total energy used in the commercial and industrial buildings for space conditioning. In this paper, energy consumption by chillers and chilled water pumps, condenser pumps and fan motors has been estimated using data collected by a walkthrough energy audit for the 16 faculties of the University of Malaya. It has been estimated that chillers and motors and pumps used in chillers consume 10,737 MWh (i.e. 51% of total energy consumption) of electric energy for different percentage of loadings. As chillers are major energy users, variable speed drives are applied in chillers to reduce their energy consumption. It has been estimated that about 8368 MWh annual energy can be saved by using efficient chillers at different loadings. It has also been found that about 23,532 MWh annual energy can be saved for chilled water supply pumps, condenser pumps and cooling tower fan motors by matching required speeds using variable speed drives for 60% of speed reduction. About 1,274,692 kg of CO 2 emission could be avoided for using energy efficient chillers at 50% load. It has been also found that about 2,426,769 kg CO 2 emission can be reduced by using variable speed drives for 60% speed reductions. Payback periods found to be only few months for using variable speed drives in chilled water pumps, condensers and fan motors.

A flat plate solar collector (FPSC) was analytically studied, with functionalized graphene nanoplatelets (f-GNPs) as its working fluid. Four samples (wt % nanofluids) were prepared in different base fluids such as ethylene glycol (EG), distilled water (DW):EG (70:30), and DW:EG (50:50). Experimental results (via DW) were used to verify the effectiveness of the analytical model. Some of the operating conditions were taken into account in this research, including temperatures, power, and mass flow rates. Experimental techniques were used to elucidate the modified nanofluids’ physicochemical properties, such as its particle sizes, stability, and morphology, involving electron microscopes (EMs), UV–VIS, and X-ray techniques. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were applied to test the thermal analysis. The findings confirmed that the use of f-GNPs nanofluids enhanced the performance of the FPSC relative to the use of base fluids for all testing conditions. The maximum enhancement of the collector’s effectiveness at a mass flow rate of 1.5 kg min−1 and a weight concentration of 0.1 wt %, increased to 12.69%, 12.60%, and 12.62% in the case of EG, DW:EG (70:30), and DW:EG (50:50), respectively. The results also confirmed an improvement in both the heat gain (FR(τα)) and heat loss (FRUL) coefficients for the f-GNPs nanofluid.

Abstract In this paper forced convection turbulent nanofluid flow is numerically investigated to analyze the effects of different types of nanoparticles with different nanoparticle parameters in a fully detached ribbed channel. The bottom wall of the channel is kept at a constant temperature while the upper wall is thermally insulated. The continuity, momentum and energy equations were discretized and solved by the Finite Volume Method (FVM). The influence of different types of nanoparticles (Al 2 O 3 , CuO, SiO 2 , and ZnO) with nanoparticle concentration (1% to 4%) and nanoparticle diameter (20 nm to 50 nm) suspended in a water as a base fluid is studied on the heat transfer enhancement, friction factor and pressure drop. The Reynolds number was in the range of 10,000 to 50,000 in a rectangular channel having mounted rectangular ribs on its bottom wall with clearance ratio of 0.1. The results indicate that the highest heat transfer enhancement is achieved with SiO 2 nanofluid and the friction factor did not considerably change with using different types of nanoparticles in the base fluid. Furthermore, increment of nanoparticle concentration or Reynolds number has a positive impact on heat transfer enhancement due to the increment of the velocity and thermal conductivity of the mixture. However, a rise of nanoparticle diameter decreases the heat transfer enhancement due to stronger Brownian motion even at lower nanoparticle diameter.

This work investigates the thermal–physical and rheological properties of hexagonal boron nitride/carbon nanotubes (hBN/CNTs) applied to reinforce water-based working fluid in a flat plate solar collector (FPSC). The hybrid nanoadditives of hBN and the chemically functionalized CNTs (CF-CNTs) were suspended in distilled water (DW) with a nonionic surfactant. The hybridization ratio between CF-CNTs and hBN was optimized to be 40:60. The thermal efficiency tests on the solar collector were carried out using different volumetric flow rates (2, 3, and 4 L/min) under the ASHRAE-93-2010 standard. The morphological characteristics of the hybrid nanoadditives were evaluated using X-ray diffraction (XRD), ultraviolet–visible spectroscopy (UV–vis), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). Different concentrations of hBN/CF-CNTs were added to the water-based working fluid to record the optimal wt.% for maximum enhancement in the FPSC’s efficiency. The results revealed that using only 0.1 wt.% of hBN/CF-CNTs with a flow rate of 4 L/min remarkably improved the collector efficiency by up to 87% when compared to the conventional working fluid used in FPSC.