Applications of nanofluids in condensing and evaporating systems

The effect of Fe 3 O 4 nanoparticles and carbon nanotubes (CNTs) on the viscosity of a nanofluid is experimentally investigated from 278 to 313 K by changing the nanoparticle volume fraction. These nanoparticles were put into distilled water with various surfactants, i.e., Colace (docusate sodium), trisodium citrate dihydrate (TSC), polyvinyl pyrrolidone, cetyl trimethylammonium bromide, tetramethylammonium hydroxide (TMAH), acacia senegal (GA), sodium dodecyl benzene sulfonate, sodium dodecyl sulfate (SDS), and sodium laurylsulfonate (SLS). Based on the present measurements, new empirical formulas are proposed for Fe 3 O 4-water, CNT-water and Fe 3 O 4-CNT-water nanofluids to provide accurate predictions for the nanofluid viscosity. Based on the viscosity testing, stabilities and thermal conductivities of Fe 3 O 4-TMAH, Fe 3 O 4-Colace, Fe 3 O 4-TSC, CNT-SDS, CNT-GA, Fe 3 O 4-CNT-SLS, and Fe 3 O 4-CNT-TSC nanofluids with a volume concentration of 0.5% are investigated in the present research. Results indicate that better stability, smaller viscosity, and higher thermal conductivity are obtained, when the surfactants TMAH, SDS, and SLS are added into the Fe 3 O 4-water, CNT-water, and the Fe 3 O 4-CNT-water nanofluid, respectively. The CNT-water and Fe 3 O 4-CNT-water nanofluids exhibit a shear-thinning behavior, whereas a linear rheological behavior can be observed by water-based Colace-Fe 3 O 4 , TMAH-Fe 3 O 4 , and TSC-Fe 3 O 4 nanofluids. Keywords Nanofluid • Thermal conductivity • Carbon nanotube • Viscosity • Surfactant List of symbols k Thermal conductivity (W m −1 K −1) T Temperature (K) U Uncertainty Greek symbols θ Surfactant ratio fraction μ Dynamic viscosity (Pa s) φ Nanoparticle volume fraction Subscripts f Base fluid nf Nanofluid

Section: Introductionmentioning

confidence: 99%

Effect of various surfactants on stability and thermophysical properties of nanofluids

Wang

et al. 2020

“…Over the last two decades the field of heat transfer enhancement has experienced significant advancements. There are now a number of methods that take advantage of rough surfaces [2,3], porous material with high thermal conductivity [4], nanofluids [5,6,7], mounting twisted tape inserts or baffles [8,9] and wavy walls [10], as means of heat transfer enhancement. These are at different stages of maturation.…”

mentioning

confidence: 99%

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

Akbarzadeh

Rashidi

Karimi

et al. 2018

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.

“…Over the last decades, researches deal with the flow boiling heat transfer which has grown at a very rapid rate, and this is, of course, because of various industrial and technological sectors. Recently, there are numerous published papers and several conferences held around the world, which are devoted to this topic [1][2][3][4][5][6][7]. From another side, nanofluids are prepared by Choi [8] in 1995 and are defined as the new generation of heat transfer fluids or a mixture.…”

Section: Introductionmentioning

confidence: 99%

Experimental studies of flow boiling heat transfer by using nanofluids

Kamel

Lezsovits

Hussein

2019

Flow boiling heat transfer widely utilized in numerous industrial applications such as boiler tubes, evaporators and cooling of reactors in a nuclear power plant. Nanofluids are a new category of thermal fluids, made by dispersing a nanometer solid particle which is usually less than 100 nm into conventional liquids such as water, oil engine and ethylene glycol with the intent to enhance the thermal properties of the base fluids. This work reviews the recent experimental studies focusing on the flow boiling heat transfer using nanofluids. The latest results associated with this subject are presented and outlined to account the influence of several parameters, which are related to operating conditions and nanoparticles morphology on the heat transfer coefficient and the critical heat flux. Besides, the effects of nanoparticles on other related sub-phenomenon of the flow boiling by using nanofluids were discussed. Moreover, the latest review papers of the related topic were presented and briefly discussed. Finally, suggestions for future research activities related to this field were also concisely listed.