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Experiments were conducted to investigate the nucleate pool boiling heat transfer of pure water and alumina/water nanofluids on different micro- and nanostructured surfaces prepared via the thermal spray coating method. Results indicate that nanofluids boiling on all the test surfaces led to critical heat flux (CHF) values greater than that obtained for the base fluid (i.e., water). Higher roughness value, however, led to higher CHF values in boiling over the surfaces. Another finding of this study indicated that CHF values obtained with boiling on Cu-coated micro- and nanosurfaces were identical although the heat transfer coefficient (HTC) values obtained for boiling on the micro-structure surface were higher than those obtained for a nanostructured surface with almost the same roughness. A series of consecutive nanofluid boiling cycles were also performed on the aluminum-coated nanostructured surface. The CHF value obtained for water boiling on the surface undergoing repeated nanofluid boiling cycles was by 27% higher than that obtained for a clean surface although the relevant HTC values were nearly identical. [ABSTRACT FROM AUTHOR]

The multiphase micro-structured devices such as microchannels have been recently taken into consideration to replace the conventional equipment in different applications. The mass transfer coefficients and the interfacial area in the multiphase microchannels are much larger than those in the conventional equipment. This paper reviews the experimental studies on mass transfer in gas-liquid and liquid-liquid microchannels. Proposed flow pattern maps are compared. The featured researches corresponding to the effects of the operating conditions and the geometry of the microchannels on mass transfer are discussed. Literature review shows that influences of geometrical parameters are not investigated as extensively as those of operating conditions and thus, vague aspects of geometrical parameters effects exist. There are inconsistencies between results of some researchers and most of these are due to using dissimilar microchannel materials, unalike dominant mechanisms at different investigated operating conditions, different approaches to change the independent variable, etc. [ABSTRACT FROM AUTHOR]

In the present investigation both numerical and experimental studies have been performed for SiO/water nanofluid in different concentrations in the jacket side of a reactor that was equipped with a conventional jacket without baffle. Heat transfer rates were measured for nanofluid and base liquid. In order to solve the continuity, momentum, energy and turbulence equations, finite volume method and k-e turbulence model were utilized in three dimensions. For very dilute nanofluids (<0.1% volume fraction) no heat transfer enhancement was observed. For greater concentrations heat transfer rates augmented to some extent. Nusselt number increased with increasing the nanofluid concentration as well as Reynolds number. By using the least square method to all the experimental data two correlations for water and nanofluid were obtained. [ABSTRACT FROM AUTHOR]

Abstract: Growing attention has been recently paid to nanofluids because of their potential for augmenting transfer processes – i.e., heat and mass transfer. Conflicting results have been reported in the literature on mass transfer in nanofluids. The aim of this paper is to summarize the literature on mass transfer in nanofluids stating the conflicts and possible reasons. Literature on mass transfer in nanofluids has been reviewed in two sections. The first section concentrates on surveying mass diffusivity in nanofluids while the second section focuses on convective mass transfer in nanofluids. In each section, published articles, type of nanofluids used, size and concentration range of nanoparticles, measurement methods, maximum observed enhancement, and suggested mass transport mechanisms are summarized. [Copyright &y& Elsevier]

• Rather than PSD and ED methods, PV was used in methanol recovery section in the TAME process. • Heat integration was conducted by combining R-HIDiC and PV. • All process parameters (especially PV parameters) were considered as optimization parameters. • Heat transfer fraction and number of heat exchangers in R-HIDiC were obtained by the optimization algorithm. The TAME production process involves two main steps. The first step pertains to the reactions that lead to the synthesis of TAME, and the second step to the separation of TAME and recovery of methanol. Part of the TAME reaction and separation is carried out in a reactive distillation (RD) column. The product at the top of the RD column is a methanol- and C 5 -containing azeotropic mixture which can be isolated through pressure swing distillation (PSD) and extractive distillation (ED) methods. In this paper, the mixture was isolated through the pervaporation (PV) process, and all parameters related to RD and PV were considered as optimization variables, in particular the PV-related parameters such as the permeate stream pressure, the number of modules, and the temperature of inflow to each module. All variables were optimized simultaneously. The GA and PSO algorithms were combined to optimize the process and, additionally, total annual cost (TAC) was used as the objective function. The internally heat integrated distillation column (HIDiC) method was used to reduce the RD column energy costs, and the number of heat exchangers between the two rectifying and stripping sections was obtained using the optimization algorithm. The results showed that the hybrid PV/R-HIDiC process with heat integration was the best arrangement, resulting in a TAC reduction of 30% and 40% compared to the hybrid PV/RD process and the hybrid PSD/RD process, respectively. In this case, the number of trays in rectifying and stripping sections is respectively 22 and 6. The number of heat exchangers obtained by R-HIDiC method is 5, the number of PV modules is 11 and permeate pressure equals 18 as the most important parameters obtained from the optimization algorithm. [ABSTRACT FROM AUTHOR]

In the present paper, the heat transfer of slug flow in rectangular microchannels is studied numerically. The Al 2 O 3 -water nanofluid with the volume fraction of 1% is used as a homogeneous liquid. Three different configurations are considered to investigate the hydrodynamics and heat transfer in the microchannels. Boundary mesh adaptation method is used to capture the liquid film around gas bubbles. Slug flow characteristics are simulated with a very low computational time compared to previous researches. Slug and bubble lengths, liquid film properties, pressure drop, gas void fraction and heat transfer characteristics are studied. Results show that different inlet configurations impact on slug and bubble lengths. Gas hold-up is influenced by vortices and high frequency fluctuations that are created in the liquid film due to the difference between gas and slug acceleration. It is found that the Nusselt number is an increasing function of slug length and unit cell length. The results reveal that the hottest point on the wall is where the back tail vortex is generated. The nanofluid enhances the heat transfer coefficient by 10% in comparison with the pure water. • Slug flow heat transfer of Al 2 O 3 /water nanofluid in rectangular microchannels is investigated numerically. • Boundary mesh adaption method decreases the computational time in comparison with the other methods. • The results showed the generation of vortices and fluctuations in the liquid film. • The Nusselt number is a function of slug length and unit cell length. • The nanofluid enhances the heat transfer coefficient by 10% in comparison with the pure water. [ABSTRACT FROM AUTHOR]