Showing papers on "Volumetric flow rate published in 2015"

Numerical optimization of microchannel heat sink (MCHS) performance cooled by KKL based nanofluids in saturated porous medium

Abstract: This work presents a thermal and flow analysis of a fin shaped microchannel heat sink (MCHS) cooled by different nanofluids (Cu and Al2O3 in water) based on “saturated porous medium” and least square method then results are compared with numerical procedure. The Forchheimer–Brinkman-extended Darcy equation is used to describe the fluid flow and the two-equation model with thermal dispersion is utilized for heat transfer. The effect of nanoparticle size and volume fraction, volume flow rate, inertial force parameter and channel width investigated on total thermal resistance, friction factor and Nusselt number. The effective thermal conductivity and viscosity of nanofluid are calculated by KKL correlation. Central composite design (CCD) is applied to obtain the desirability of the optimum value of the nanofluid flow characteristics. Results show that Cu–water nanofluid is more lucrative thermally versus Al2O3–water nanofluid. It is found that total thermal resistance, friction factor and Nusselt number are not sensitive to inertial effect while they change significantly due to other parameters such as nanoparticle size and volume fraction, volume flow rate and channel width. We obtained that Nusselt number enhancement has direct relationship with inertial force parameter and volume flow rate.

Formation of surface nanodroplets under controlled flow conditions

Abstract: Nanodroplets on a solid surface (i.e., surface nanodroplets) have practical implications for high-throughput chemical and biological analysis, lubrications, laboratory-on-chip devices, and near-field imaging techniques. Oil nanodroplets can be produced on a solid–liquid interface in a simple step of solvent exchange in which a good solvent of oil is displaced by a poor solvent. In this work, we experimentally and theoretically investigate the formation of nanodroplets by the solvent exchange process under well-controlled flow conditions. We find significant effects from the flow rate and the flow geometry on the droplet size. We develop a theoretical framework to account for these effects. The main idea is that the droplet nuclei are exposed to an oil oversaturation pulse during the exchange process. The analysis shows that the volume of the nanodroplets increases with the Peclet number Pe of the flow as ∝Pe 3/4 , which is in good agreement with our experimental results. In addition, at fixed flow rate and thus fixed Peclet number, larger and less homogeneously distributed droplets formed at less-narrow channels, due to convection effects originating from the density difference between the two solutions of the solvent exchange. The understanding from this work provides valuable guidelines for producing surface nanodroplets with desired sizes by controlling the flow conditions.

Narrow residence time distribution in tubular reactor concept for Reynolds number range of 10–100

Abstract: For chemical reactions, which require residence times of several hours, enhanced heat transfer, or narrow residence time distribution (RTD), good radial mixing combined with poor axial mixing in laminar flow regime has long been desired by industry and R&D. The main goal of this work is to obtain the narrowest RTD curve in a continuously operated reactor at Reynolds numbers smaller than 100. By using a stepwise method the most promising reactor type was chosen to meet the requirements. Design parameters of this reactor, the coiled flow inverter (CFI), were characterized and their effects on RTD were experimentally investigated. Design of CFI includes several straight helix modules, where the tubular reactor is coiled around a coil tube. After each straight helix module, the coil direction is changed by a 90°-bend. As a starting point for designing a CFI reactor for specific applications, the “best performance” design space diagram was investigated. Regarding narrowing RTD, the diagram gives the user the design space for the CFI reactor, which leads to the best performance. The most significant design parameter regarding a narrow RTD was experimentally determined as number of bends. By using a CFI design consisting of 27 bends at volume flow rate of 3 mL/min, which corresponds to Reynolds number of 24 and mean residence time of 2.6 h, a Bodenstein number over 500 was achieved. Beside its narrow RTD behavior, CFI is a compact and cost-efficient reactor concept, which is flexible to scale-up and implement for different processes, even for single-use applications.

Experimental Investigation on the Absorption Enhancement of CO2 by Various Nanofluids in Hollow Fiber Membrane Contactors

Abstract: In this work, suspensions of Fe3O4, CNT, SiO2, and Al2O3 nanoparticles in distilled water are produced and tested as new absorbents in a gas–liquid hollow fiber membrane contactor to investigate the effect of nanoparticles on the rate of mass transfer during CO2 absorption For this purpose, a pilot-scaled hollow fiber membrane contactor was constructed A gas mixture was passed through the shell-side, and the nanofluid flowed cocurrently through the lumen side of the fibers The effects of different operating conditions including gas flow rate, liquid flow rate, inlet CO2 concentration, and nanoparticle concentration on the CO2 absorption have been studied The results showed that among the operating parameters, liquid flow rate and nanoparticle concentration had the greatest effects on the CO2 absorption Moreover, UV–vis spectroscopy and DLS method were employed to explore the dispersion stability and hydrodynamic diameter of nanoparticles in the base fluid The results revealed that nanofluid stabilit

CO2-CH4 conversion and syngas formation at atmospheric pressure using a multi-electrode dielectric barrier discharge

Abstract: The conversion of CO2 and CH4 into value-added chemicals is studied in a new geometry of a dielectric barrier discharge (DBD) with multi-electrodes, dedicated to the treatment of high gas flow rates. Gas chromatography is used to define the CO2 and CH4 conversion as well as the yields of the products of decomposition (CO, O2 and H2) and of recombination (C2H4, C2H6 and CH2O). The influence of three parameters is investigated on the conversion: the CO2 and CH4 flow rates, the plasma power and the nature of the carrier gas (argon or helium). The energy efficiency of the CO2 conversion is estimated and compared with those of similar atmospheric plasma sources. Our DBD reactor shows a good compromise between a good energy efficiency and the treatment of a large CO2 flow rate.

Lattice Boltzmann Simulation of Shale Gas Transport in Organic Nano-Pores

Abstract: Permeability is a key parameter for investigating the flow ability of sedimentary rocks. The conventional model for calculating permeability is derived from Darcy's law, which is valid only for continuum flow in porous rocks. We discussed the feasibility of simulating methane transport characteristics in the organic nano-pores of shale through the Lattice Boltzmann method (LBM). As a first attempt, the effects of high Knudsen number and the associated slip flow are considered, whereas the effect of adsorption in the capillary tube is left for future work. Simulation results show that at small Knudsen number, LBM results agree well with Poiseuille's law, and flow rate (flow capacity) is proportional to the square of the pore scale. At higher Knudsen numbers, the relaxation time needs to be corrected. In addition, velocity increases as the slip effect causes non negligible velocities on the pore wall, thereby enhancing the flow rate inside the pore, i.e., the permeability. Therefore, the LBM simulation of gas flow characteristics in organic nano-pores provides an effective way of evaluating the permeability of gas-bearing shale.

Heat transfer enhancement of car radiator using aqua based magnesium oxide nanofluids

Abstract: The focus of this research paper is on the application of water based MgO nanofluids for thermal management of a car radiator. Nanofluids of different volumetric concentrations (i. e. 0.06%, 0.09%, and 0.12%) were prepared and then experimentally tested for their heat transfer performance in a car radiator. All concentrations showed enhancement in heat transfer compared to the pure base fluid. A peak heat transfer enhancement of 31% was obtained at 0.12% volumetric concentration of MgO in basefluid. The fluid flow rate was kept in a range of 8-16 liter per minute. Lower flow rates resulted in greater heat transfer rates as compared to heat transfer rates at higher flow rates for the same volumetric concentration. Heat transfer rates were found weakly dependent on the inlet fluid temperature. An increase of 8 °C in inlet temperature showed only a 6% increase in heat transfer rate.

Application of X-ray CT investigation of CO 2 -brine flow in porous media

Abstract: A clear understanding of two-phase flows in porous media is important for investigating CO2 geological storage. In this study, we conducted an experiment of CO2/brine flow process in porous media under sequestration conditions using X-ray CT technique. The flow properties of relative permeability, porosity heterogeneity, and CO2 saturation were observed in this experiment. The porous media was packed with glass beads having a diameter of 0.2 mm. The porosity distribution along the flow direction is heterogeneous owing to the diameter and shape of glass beads along the flow direction. There is a relationship between CO2 saturation and porosity distribution, which changes with different flow rates and fractional flows. The heterogeneity of the porous media influences the distribution of CO2; moreover, gravity, fractional flows, and flow rates influence CO2 distribution and saturation. The relative permeability curve was constructed using the steady-state method. The results agreed well with the relative permeability curve simulated using pore-network model.

Pressure drop and thermal performance of CuO/ethylene glycol (60%)-water (40%) nanofluid in car radiator

Abstract: We investigated the role of nanofluid in a special car radiator and the effect of its different volume concentrations on pressure drop and friction factor of fluid flow. A mixture of 60/40 ratio of ethylene glycol (EG) and distilled water was used as the host fluid and CuO nanoparticles were dispersed well to make stable nanofluids. The influence of nanofluid concentrations on pressure drop was evaluated in the radiator at three different inlet fluid temperatures (35, 44, 54 °C). The results demonstrated that the presence of nanoparticles caused an increase in nanofluid pressure drop, which was intensified by increasing nanoparticle concentration as well as decreasing temperature of inlet fluid. A new empirical equation for prediction of nanofluid pressure drop through the radiator was developed as well. Also, with increasing the flow rate, the performance index increased and indicated that application of nanofluid in higher flow rate was affordable.

Effect of fluid rheology on particle migration in a square-shaped microchannel

Abstract: The effect of fluid rheology on particle migration induced by fluid viscoelasticity in a square-shaped microchannel is reported. Three water polymer solutions of PolyEthylene Oxyde at different concentrations, corresponding to different elasticity and degree of shear thinning, are prepared and rheologically characterized. Experiments are carried out for a wide range of flow rates, and the particle distributions over the channel cross section are reconstructed by combining particle tracking measurements and numerical simulations of the fluid velocity profile. The particle distributions show that the migration direction strongly depends on the fluid rheology. Specifically, when particles explore the constant viscosity region of the suspending liquids, they are focused around the channel centerline. Such an effect is more and more pronounced as the flow rate increases. On the other hand, for particles suspended in a shear-thinning fluid, a different scenario appears: At low flow rates, i.e., in the constant viscosity region, particles still migrate toward the channel centerline, while at high flow rates, i.e., in the shear thinning region, the migration reverts direction and the particles are driven toward the corners of the channel cross section. Those experimental observations elucidate the relevant and competing role of elasticity and shear thinning, with obvious implications in designing microfluidic devices for particle manipulation. Finally, our results highlight the weak effect of inertia on particle migration as compared to viscoelastic effects, even for low elastic suspending liquids.

OpenFOAM Computational Fluid Dynamic Simulations of Two-Phase Flow and Mass Transfer in an Advanced-Flow Reactor

Abstract: Advanced-flow reactor (AFR) technology is an alternative to scale-up continuous flow chemistries from micro to milli scales, while retaining mass and heat transfer performance Here we conduct two-phase computational fluid dynamic (CFD) simulations using the open source software OpenFOAM in order to predict hydrodynamic parameters in the AFR for different operating conditions After modification and validation of the interFoam solver based on the volume-of-fluid method to account for mass transfer across immiscible interfaces, it is applied to the AFR to predict specific interfacial areas (a) and individual mass transfer coefficients (kL) to yield overall mass transfer coefficients (kLa) The results are in good agreement with semiempirical values and the surface renewal theory of Danckwerts, except at the largest flow rates for which numerical coalescence is observed A study of the influence of fluid properties yields the following conclusions The contact angle is the variable that affects the flow pat

Heat transfer enhancement using MgO/water nanofluid in heat pipe

Abstract: This study investigates how MgO/water nano-fluid affect the thermal performance of a two-phase closed thermo-syphon heat pipe at various states of operation. The present study experimentally demonstrated the effect of using a nano-fluid obtained from MgO on improving the performance of a heat pipe. Triton X-100 nonionic surfactant was used in the study to produce the 5% (vol.) MgO/water nano-fluid via direct-synthesis. A straight copper tube with an inner diameter of 13 mm, the wall thickness of 2 mm and the length of 1 m was used as the heat pipe in the experimental set-up. The nano-fluid was filled up 33.3% (44.5 ml) of the volume of the heat pipe. Three different heating power levels (200 W, 300 W and 400 W) were used in the experiments with three different flow rates of cooling water (5, 7.5 and 10 g/s) used in the condenser for cooling the system. An improvement level of 26% at 200 W heating power and 7.5 g/s flow rate was reported for the effectiveness of the heat pipe used in the study when the nano-fluid was charged into the system instead of water. The improvement ratio varied with respect to varying heat loads and varying flow rate of condenser cooling water.