Showing papers on "Pressure drop published in 2019"

Application of Nanofluids in Thermal Performance Enhancement of Parabolic Trough Solar Collector: State-of-the-Art

Abstract: The present review paper aims to document the latest developments on the applications of nanofluids as working fluid in parabolic trough collectors (PTCs). The influence of many factors such as nanoparticles and base fluid type as well as volume fraction and size of nanoparticles on the performance of PTCs has been investigated. The reviewed studies were mainly categorized into three different types of experimental, modeling (semi-analytical), and computational fluid dynamics (CFD). The main focus was to evaluate the effect of nanofluids on thermal efficiency, entropy generation, heat transfer coefficient enhancement, as well as pressure drop in PTCs. It was revealed that nanofluids not only enhance (in most of the cases) the thermal efficiency, convection heat transfer coefficient, and exergy efficiency of the system but also can decrease the entropy generation of the system. The only drawback in application of nanofluids in PTCs was found to be pressure drop increase that can be controlled by optimization in nanoparticles volume fraction and mass flow rate.

Impact of variable fluid properties on forced convection of Fe3O4/CNT/water hybrid nanofluid in a double-pipe mini-channel heat exchanger

Abstract: The objective of this study is to assess the hydrothermal performance of a non-Newtonian hybrid nanofluid with temperature-dependent thermal conductivity and viscosity compared with a Newtonian hybrid nanofluid with constant thermophysical properties. A counter-current double-pipe mini-channel heat exchanger is studied to analyze the effects of the hybrid nanofluid. The nanofluid is employed as the coolant in the tube side, while the hot water flows in the annulus side. Two different nanoparticles including tetramethylammonium hydroxide-coated Fe3O4 (magnetite) nanoparticles and gum arabic-coated carbon nanotubes are used to prepare the water-based hybrid nanofluid. The results demonstrated that the non-Newtonian hybrid nanofluid always has a higher heat transfer rate, overall heat transfer coefficient, and effectiveness than those of the Newtonian hybrid nanofluid, while the opposite is true for the pressure drop, pumping power, and performance evaluation criterion. Supposing that the Fe3O4-carbon nanotube/water hybrid nanofluid is a Newtonian fluid with constant thermal conductivity and viscosity, there leads to large error in the computation of pressure drop (1.5–9.71%), pumping power (1.5–9.71%), and performance evaluation criterion (18.24–19.60%), whereas the errors in the computation of heat transfer rate, overall heat transfer coefficient, and effectiveness are not considerable (less than 2.91%).

Experimental investigation of TiO 2 –water nanofluid flow and heat transfer inside wavy mini-channel heat sinks

Abstract: The present study comprises experimental investigation on heat transfer and hydrodynamic characteristics of TiO2 nanofluid as coolant in wavy channel heat sinks having three different channel configurations. The performance of TiO2 nanofluids having concentrations of 0.006, 0.008, 0.01 and 0.012 vol% is compared with that of distilled water under laminar regime at heating powers of 25 W, 35 W and 45 W. Results indicated that for all heat sinks, nanofluids showed better heat transfer characteristics than distilled water. With an increase in heating power, TiO2 nanofluid thermal performance was decreased. Using 0.012% TiO2 nanofluids, minimum wall base temperature and maximum enhancement in Nusselt number are noted as 33.85 °C and 40.57%, respectively, for heat sink with wavelength of 5 mm and amplitude of 0.5 mm corresponding to Reynolds number of 894 at heating power of 25 W. Pumping power requirement is function of flow rate and pressure drop, and its maximum value of 0.0284 W is associated with heat sink with minimum wavelength. Moreover, variation in wavelength of channel is found to have dominating effect on heat transfer performance of heat sink as compared to the width of channel.

First and second laws of thermodynamics analysis of nanofluid flow inside a heat exchanger duct with wavy walls and a porous insert

Abstract: This paper investigates the combined effects of using nanofluid, a porous insert and corrugated walls on heat transfer, pressure drop and entropy generation inside a heat exchanger duct. A series of numerical simulations are conducted for a number of pertinent parameters. It is shown that the waviness of the wall destructively affects the heat transfer process at low wave amplitudes and that it can improve heat convection only after exceeding a certain amplitude. Further, the pressure drop in the duct is found to be strongly influenced by the wave amplitude in a highly non-uniform way. The results, also, show that the second law and heat transfer performances of the system improve considerably by thickening the porous insert and decreasing its permeability. Yet, this is associated with higher pressure drops. It is argued that the hydraulic, thermal and entropic behaviours of the system are closely related to the interactions between a vortex formation near the wavy walls and nanofluid flow through the porous insert. Viscous irreversibilities are shown to be dominant in the core region of duct where the porous insert is placed. However, in the regions closer to the wavy walls, thermal entropy generation is the main source of irreversibility. A number of design recommendations are made on the basis of the findings of this study.

Numerical study of mixing in wavy micromixers: comparison between raccoon and serpentine mixer

Abstract: We numerically analyze the mixing and pressure drop characteristics for flow through wavy micromixer of two geometrical configurations, namely raccoon and serpentine for different values of amplitude of the waviness of the mixer (α), wavelength of the waviness (λ), Reynolds number(Re) and Schmidt number(Sc). Three different flow regimes are identified depending on the parameters influencing the mixing index. The mixing index for both the raccoon and serpentine mixer is very close to unity in the first regime (0.1

Efficiency assessment of using graphene nanoplatelets-silver/water nanofluids in microchannel heat sinks with different cross-sections for electronics cooling

Abstract: This study aims to model the nanofluid flow in microchannel heat sinks having the same length and hydraulic diameter but different cross-sections (circular, trapezoidal and square).,The nanofluid is graphene nanoplatelets-silver/water, and the heat transfer in laminar flow was investigated. The range of coolant Reynolds number in this investigation was 200 ≤ Re ≤ 1000, and the concentrations of nano-sheets were from 0 to 0.1 vol. %.,Results show that higher temperature leads to smaller Nusselt number, pressure drop and pumping power, and increasing solid nano-sheet volume fraction results in an expected increase in heat transfer. However, the influence of temperature on the friction factor is insignificant. In addition, by increasing the Reynolds number, the values of pressure drop, pumping power and Nusselt number augments, but friction factor diminishes.,Data extracted from a recent experimental work were used to obtain thermo-physical properties of nanofluids.,The effects of temperature, microchannel cross-section shape, the volume concentration of nanoparticles and Reynolds number on thermal and hydraulics behavior of the nanofluid were investigated. Results are presented in terms of velocity, Nusselt number, pressure drop, friction loss and pumping power in various conditions. Validation of the model against previous papers showed satisfactory agreement.

A numerical investigation of the flow of nanofluids through a micro Tesla valve

Abstract: In this study, Al2O3-water nanofluids flowing through a micro-scale T45-R type Tesla valve was investigated numerically. Both forward and reverse flows were investigated based on a verified numerical model. The effects of nanofluids flow rate, temperature, and nanoparticle volume fraction on fluid separation in the bifurcated section and the pressure drop characteristics were analyzed. It was found that most of the nanofluids flow into the straight channel of the bifurcated section when flowing forward, and into the arc channel when flowing reversely. The percentage of the main flow increases with flow rate, temperature, and nanoparticle volume fraction. Additionally, the jet flow from the arc channel leads to a larger pressure drop than forward flow. Finally, the diodicity was found most affected by flow rate, and a correlation used to predict the change in diodicity with the flow rate was proposed.

Nanofluid turbulent flow in a pipe under the effect of twisted tape with alternate axis

Abstract: In this research, nanofluid heat transfer enhancement in a pipe by means of twisted tape with alternate axis is presented. Finite volume method is selected as simulation tool. Influences of revolution angle and Reynolds number on nanofluid hydrothermal treatment have been demonstrated. Suitable formulas for Nusselt number and Darcy factor are provided. Results prove that temperature gradient augments with enhance of revolution angle because of increase in secondary flow but pressure loss augments with rise of revolution angle.

Hydrothermal analysis of turbulent boehmite alumina nanofluid flow with different nanoparticle shapes in a minichannel heat exchanger using two-phase mixture model

Abstract: Exploring the effect of nanoparticle shape on the fluid flow characteristics of boehmite alumina nanofluid in a horizontal double-pipe minichannel heat exchanger is the goal of this study. The proposed boehmite alumina nanofluid could consist of dispersed cylindrical, brick, blade, platelet, and spherical shape nanoparticles in a mixture of water/ethylene glycol. In this study, the water and nanofluid pass through the annulus and tube side of the heat exchanger, respectively. To accurately simulate the behavior of nanofluid, the two phase mixture model is utilized in the simulation. In this investigation, the effect of different Reynolds numbers, nanoparticle concentrations and shapes versus important hydrothermal properties are investigated. The results show that, the spherical and platelet shape lead to the highest and lowest performance index of heat exchanger, respectively. Moreover, it is found that the rates of heat transfer, overall heat transfer coefficient, pressure drop, and pumping power increases with increase in Reynolds number and nanoparticle concentration, while the opposite trend is observed for performance index of the heat exchanger. For instance, at the Reynolds number of 20 000, by boosting the nanoparticle concentration from 0.5 to 2%, the performance index for nanofluid containing platelet shape and spherical shape nanoparticles reduces by 130.63 and 3.88%, respectively.