Heat transfer characteristics and field synergy analysis of gas–liquid two-phase flow in micro-channels

Journal of Thermal Analysis and Calorimetry - To meet the extreme cooling requirements in many high-tech fields, it is essential and meaningful to reveal the dominant factors of heat transfer...     

Silver–water nanofluid flow and convective heat transfer in a microfin tube equipped with loose-fit twisted tapes

Heat transfer enhancement and performance of compact heat exchangers have been extensively studied in the past century for the purpose of promoting energy efficiency. Microfin tubes in single/two/multiple-phase flow heat exchangers into which twisted tape swirl generators are installed can promote heat transfer with a moderate pressure loss penalty. This article reports on the enhanced heat transfer of silver–water nanofluids in a microfin tube into which loose-fit twisted tapes are installed in a counter-flow arrangement. The experiments were carried out using nanofluids with various silver concentrations (0.007–0.03 vol%), loose-fit twisted tapes with clearance ratios (c/D) of 0.0 (tight-fit), 0.05, 0.075 and 0.1, for a twist ratio, y/W, of 2.0. The results indicate that the heat transfer rate (Nu) and pressure drop (f) increase with a decrease in clearance ratio (c/D) and increase in silver (Ag) nanoparticle concentration. Additionally, the thermal performance factor tends to increase with the decrease in Reynolds numbers.

     

An experimental study on MWCNT–water nanofluids flow and heat transfer in double-pipe heat exchanger using porous media

Journal of Thermal Analysis and Calorimetry - This paper presents the results of an experimental investigation on the heat transfer characteristics of multi-walled carbon nanotube aqueous...     

Experimental investigation of TiO2–water nanofluid flow and heat transfer inside wavy mini-channel heat sinks

Journal of Thermal Analysis and Calorimetry - The present study comprises experimental investigation on heat transfer and hydrodynamic characteristics of TiO2 nanofluid as coolant in wavy channel...     

Darcy–Forchheimer flow under rotating disk and entropy generation with thermal radiation and heat source/sink

Journal of Thermal Analysis and Calorimetry - This article investigates the second law of thermodynamics for chemically reactive Sisko nanofluid by a rotating disk saturated with non-Darcy porous...     

Experimental analyses on heat transfer performance of TiO2–water nanofluid in double-pipe counter-flow heat exchanger for various flow regimes

Journal of Thermal Analysis and Calorimetry - Nanofluids are widely used in heat transfer applications. This article presents the effect of heat transfer and pressure drop of the TiO2–water...     

Numerical investigation of heat and mass transfer of water—silver nanofluid in a spiral heat exchanger using a two-phase mixture method

Journal of Thermal Analysis and Calorimetry - This study numerically investigates the heat and mass transfer characteristics of water—silver nanofluid flowing in a spiral heat exchanger (HX)...     

Thermal performance improvement in water nanofluid/GNP–SDBS in novel design of double-layer microchannel heat sink with sinusoidal cavities and rectangular ribs

In this numerical study, laminar flow of water nanofluid/GNP–SDBS (graphene nanoplatelet–sodium dodecylbenzene sulfonate) for 0–0.1% solid nanoparticles mass fraction was investigated for Reynolds numbers of 50–1000 in 3D space via finite volume method. In the newly proposed microchannel design, the cooling fluid is moving in countercurrent in the upper and lower layers of the microchannels, and there are cavities and sinusoidal routes on the solid walls of the microchannel, and the presence of rectangular ribs on the flow centerline along the fluid path enhances mixing for cooling fluid and creates better heat transfer for warm surfaces. The results of this study show that this special design of the microchannel can have a substantial increase in Nusselt number and heat transfer so that in the considered geometry by adding solid nanoparticles mass fraction it is possible to increase average Nusselt number for each Reynolds number by approximately 20%. Also, the mixing of the fluid because of formation of secondary flows has a strong effect on making the temperature distribution uniform in the cooling fluid and solid bed (wall) of the microchannel, especially in the lower layer. The upper layer of the microchannel always has a lower temperature due to indirect contact with heat flux compared with the lower layer. In this study, by increasing Reynolds number and mass fraction of solid nanoparticles the Nusselt number is increased and heat resistance of the lower wall of the microchannel is reduced. Based on the investigation of flow field and heat transfer, the use of the proposed design of the microchannel is recommended for Reynolds number less than 300.

     

Melting heat transfer in squeezing flow of basefluid (water), nanofluid (CNTs + water) and hybrid nanofluid (CNTs + CuO + water)

Journal of Thermal Analysis and Calorimetry - Unsteady squeezed flow of hybrid nanofluid is investigated in this analysis. Comparison of hybrid nanofluid (using CNTs?+?CuO) and...     

Determination of pesticides by solid phase extraction followed by gas chromatography with nitrogen–phosphorous detection in natural water and comparison with solvent drop microextraction

The European Union specificies that drinking water can contain pesticide residues at concentrations of up to 0.1 μg/L each and 0.5 μg/L in total, and that 1–3 μg/L of pesticides can be present in surface water, but the general idea is to keep discharges, emissions and losses of priority hazardous substances close to zero for synthetic substances. Therefore, in order to monitor pesticide levels in water, analytical methods with low quantification limits are required. The method proposed here is based on solid phase extraction (SPE) followed by gas chromatography with a nitrogen–phosphorous detector (GC-NPD). During method development, six organophosphate pesticides (azinphos-ethyl, chlorfenvinphos, chlorpyriphos, ethoprophos, fenamiphos and malathion) and two organonitrogen pesticides (alachlor and deltamethrin) were considered as target analytes. Elution conditions that could influence the efficiency of the SPE were studied. The optimized methodology exhibited good linearity, with determination coefficients of better than 0.996. The analytical recovery for the target analytes ranged from 70 to 100%, while the within-day precision was 4.0–11.5 %. The data also showed that the nature of the aqueous matrice (ultrapure, surface or drinking water) had no significant effect on the recovery. The quantification limits for the analytes were found to be 0.01–0.13 μg/L (except for deltamethrin, which was 1.0 μg/L). The present methodology is easy, rapid and gives better sensitivity than solvent drop microextraction for the determination of organonitrogen and organophosphate pesticides in drinking water at levels associated with the legislation.     

Entropy generation of turbulent Cu–water nanofluid flow in a heat exchanger tube fitted with perforated conical rings

Entropy generation analysis for the Cu–water nanofluid flow through a heat exchanger tube equipped with perforated conical rings is numerically investigated. Frictional and thermal entropy generation rates are defined as functions of velocity and temperature gradients. Governing equations are solved by using finite volume method, and Reynolds number is in the range of 5000–15,000. The effects of geometrical and physical parameters such as Reynolds number, number of holes and nanoparticles volume fraction on the thermal and viscous entropy generation rates and Bejan number are investigated. The results indicate that the thermal irreversibility is dominant in most part of the tube. But it decreases with increasing the nanoparticle volume fraction. Frictional entropy generation reduces with increasing the number of holes from 4 to 10. This is because of stronger velocity gradient near the perforated holes. Bejan number decreases with augment of Reynolds number.

     

A CFD investigation of the effect of non-Newtonian behavior of Cu–water nanofluids on their heat transfer and flow friction characteristics

Journal of Thermal Analysis and Calorimetry - In the present study, a finite volume method is used to investigate heat transfer and flow friction behavior of non-Newtonian nanofluids. To study a...     

Numerical study of the hydrodynamics and heat transfer characteristics of gas–solid in a slit-less rotating fluidized bed in static geometry

Journal of Thermal Analysis and Calorimetry - A rotating fluidized bed in static geometry (RFB-SG) without slits is presented in this paper as a research objective. The concept of RFB-SG is highly...     

Numerical and artificial neural network modeling study on the first-law and second-law performance of a novel helical heat sink filled with water–silver nanofluid

Journal of Thermal Analysis and Calorimetry - This paper is devoted to studying the first-law and second-law performances of a novel helical heat sink (HS). The biologically synthesized...     

Cu–Al2O3–H2O hybrid nanofluid flow with melting heat transfer,irreversibility analysis and nonlinear thermal radiation

Journal of Thermal Analysis and Calorimetry - We have investigated the influence of hybrid nanoparticles on various physical quantities in a water-based hybrid nanofluid involved in a steady and...     

Selectivity of benzene sulphonation in three gas—liquid reactors with different mass transfer characteristics: II: Mass transfer and selectivity in a cyclone reactor and in a tube reactor

Liquid benzene was sulphonated with gaseous sulphur trioxide in a tube reactor and in a new gas—liquid cyclone reactor. The products are benzenesulphonic acid and diphenyl sulphone (byproduct).The observed selectivity depends on the conversion, the initial benzene concentration and the mass transfer characteristics of the reactor. Minimum diphenyl sulphone formation was obtained for a low initial benzene concentration, a low benzene conversion and with a high liquid-side mass transfer coefficient, as in the cyclone reactor.As the actual mass transfer rate during sulphonation could not be measured, the observed selectivity was related to the mass transfer coefficient determined by the simultaneous absorption of CO₂and O₂ in aqueous sodium hydroxide solution.     

Determination of pesticides and PCBs in honey by solid-phase extraction cleanup followed by gas chromatography with electron-capture and nitrogen–phosphorus detection

A multiresidue method for determination of 15 organochlorine pesticides (OCPs), six polychlorinated biphenyls (PCBs), and seven organophosphorus pesticides (OPPs) is implemented for routine determinations of residues in honey. The method involves solid-phase extraction cleanup and determination by GC–ECD/NPD. Quantitation limits ranged from 0.1 to 0.6 g kg^–1 honey for OCPs and PCBs, and from 5.0 to 25.0 g kg^–1 honey for OPPs. Recoveries of OCPs ranged between 77.4 and 94.0%; for PCBs they were from 63.8 to 73.5%. Recovery assays for OPPs varied from 66.7 to 98.1%. The method was applied to the analysis of 111 honey samples from Aragón, Spain. The results obtained indicated a low level of contamination by pesticide residues and PCBs, which can contribute to ensuring the consumer has a safe wholesome supply of honey.     

Density functional theory study of 1:1 glycine–water complexes in the gas phase and in solution

We present a systematic study of 1:1 glycine-water complexes involving all possible glycine conformers. The complex geometries are fully optimized for the first time both in the gas phase and in solution using three DFT methods (B3LYP, PBE1PBE, X3LYP) and the MP2 method. We calculate the G3 energies and use them as the reference data to gauge hydrogen bond strength in the gas phase. The solvent effects are treated via the integral equation formalism-polarizable continuum model (IEF-PCM). Altogether, we loca...     

Selectivity of benzene sulphonation in three gas—liquid reactors with different mass transfer characteristics I: Mass transfer and selectivity in a stirred-cell reactor

Liquid benzene was sulphonated with gaseous sulphur trioxide in a stirred-cell reactor, a tube reactor and a new gas—liquid cyclone reactor. The man transfer coefficient k_L Varied from low values in the cell reactor to very high values in the cyclone reactor. The products were benzene Sulphonic acid and diphenyl sulphone (byproduct). The selectivity obtained increases with increasing k_L.The results of the stirred-cell reactor experiments are reported in Part I. With reaction, large temperature and Viscosity gradients occurred at the gas—liquid interface and k_L was found to be independent of stirrer speed. The observed selectivity is interpreted using a simple model of mass transfer followed by a mixed parallel consecutive reaction system, the first reaction being instantaneous with respect to mass transfer.