Subcooled flow boiling heat transfer of ethanol aqueous solutions in vertical annulus space

The subcooled flow boiling heat-transfer characteristics of water and ethanol solutions in a vertical annulus have been investigated up to heat flux 132kW/m2. The variations in the effects of heat flux and fluid velocity, and concentration of ethanol on the observed heat-transfer coefficients over a range of ethanol concentrations implied an enhanced contribution of nucleate boiling heat transfer in flow boiling, where both forced convection and nucleate boiling heat transfer occurred. Increasing the ethanol concentration led to a significant deterioration in the observed heat-transfer coefficient because of a mixture effect, that resulted in a local rise in the saturation temperature of ethanol/water solution at the vapor-liquid interface. The reduction in the heat-transfer coefficient with increasing ethanol concentration is also attributed to changes in the fluid properties (for example, viscosity and heat capacity) of tested solutions with different ethanol content. The experimental data were compared with some well-established existing correlations. Results of comparisons indicate existing correlations are unable to obtain the acceptable values. Therefore a modified correlation based on Gnielinski correlation has been proposed that predicts the heat transfer coefficient for ethanol/water solution with uncertainty about 8% that is the least in comparison to other well-known existing correlations

Effect of resistance and power training with walking in different directions on the serum concentrations of P3NP and CAF, the lower body muscle strength and motor function in elderly men

Objective(s): Examine the effect of resistance and power training with walking in four directions on the N-terminal peptide of type III procollagen (P3NP), the C-terminal agrin fragment (CAF), the lower body muscle strength and motor function in elderly people. Materials and Methods: Thirty-one elderly men were selected and divided into three groups: control group (C); resistance training (RT) group, and power training (PT) group. RT was performed with 8–10 repetitions during 20–35 seconds of exercise and PT with 8–10 repetitions during 10–13 seconds of exercise. The exercise to which subjects were exposed to, in both resistance and power training groups, consisted in walking in four directions for 12 weeks (two sessions per week). Body mass index (BMI), functional tests, and lower body strength were also measured. The serum levels of P3NP and CAF were evaluated in all groups. Results: Lower body strength (leg press, plantar ankle flexion, knee extension, leg curl) and motor function (chair stand test, timed up and go, 6-minute walking), improved following the exercise, while no effect was found concerning the serum levels of P3NP and CAF. Conclusions: An increase in motor function and lower body strength was observed in both types of exercise programmes discussed in this paper, although the exercise should be done rapidly for a better result.Part of the cost of this article was provided by the Hakim Sabzevari University of Medical Sciences (Sabzevar, Iran)

Boiling Heat Transfer of Alumina Nano-Fluids: Role of Nanoparticle Deposition on the Boiling Heat Transfer Coefficient

This paper focuses on the thermal performance of alumina nano-fluids during the quenching process of a surface at the boiling condition, which can be a good answer to the controversial results available in the nano-fluid related literature. For this purpose, an experimental study is conducted to investigate the potential application of alumina/water nano-fluid for cooling a stainless steel rod under the flow boiling heat transfer mechanism. Nano-fluids are prepared by dispersing the 5, 50 and 80nm alumina nanoparticles into the deionized water. The experimental facility provides conditions to quantify the heat transfer coefficient in forced convection and nucleate boiling heat transfer domains at different operating conditions. In terms of operating time, the experiments are divided into two domains namely short time study and extended time study. For the short time study (0-60 minutes of study with neglecting the role of time on the deposition of nanoparticles) enhancement of heat transfer coefficient is reported for all nano-fluids, however for nano-fluid with smaller nanoparticle size, higher thermal performance is registered. In extended time study (60-1000 minutes) heat transfer coefficient is found to be considerably deteriorated for all nano-fluids. This work demonstrates that the reason for deterioration of heat transfer coefficient is referred to the surface roughness, nanoparticle size, static contact angle and thermal fouling resistance parameters. These four parameters are simultaneously determinative factors, which strongly control the thermal behaviour of nano-fluids over the extended time and are the exact reasons for the controversies raised in the literature

Boiling Thermal Performance of TiO2 Aqueous NanoFluids as a Coolant on a Disc Copper Block

This work focuses on potential application of nano-fluids in cooling of high heat flux surfaces. For this purpose, experimental studies have been performed to quantify the heat transfer coefficient of Titana (TiO2) aqueous nano-fluids under different operating conditions. Boiling mechanism is established on a disc copper made heater at different heat flux, mass concentration of nano-fluids and sub-cooling temperatures. Results demonstrated that heat transfer coefficient of Titana nano-fluids are relatively higher than that of the base fluid. Heat and mass concentration of nano-particles can intensify the pool boiling heat transfer coefficient, while sub-cooling temperature can only have impacts on bubble formation. Also, visual study demonstrates that fouling formation of nano-particles can intensify the bubble transport due to the intensification of nucleation sites in the boiling surface.

Nucleate Pool Boiling Heat Transfer to Al2O3-Water and TiO2-Water Nanofluids on Horizontal Smooth Tubes with Dissimilar Homogeneous Materials

Nucleate pool boiling heat transfer coefficients of Al2O3-water and TiO2-water nanofluids have been experimentally measured on three horizontal tubes with different materials and similar roughness under atmospheric pressure. Results revealed that the presence of nanoparticles in the base fluid leads to an increase in pool boiling heat transfer coefficients on stainless steel and brass tubes in contrast to copper tube. The effect of different materials on excess temperature around the surface of the tubes has also been investigated. In addition, experimental investigations on the effect of different nanoparticles on nucleate boiling heat transfer have been conducted at volumetric concentrations of 0.1 %, 0.5 %, and 1 % of nanoparticles. Results indicated that the presence of nanoparticles have no effect on the pool boiling heat transfer coefficient for the copper tube. Variations of surface excess temperature for the copper tube were higher in comparison with that of the other tubes tested

Nucleate pool boiling heat transfer of binary nano mixtures under atmospheric pressure around a smooth horizontal cylinder

Influence of Al2O3 nanoparticles on nucleate pool boiling heat transfer of diluted binary water-glycerol mixtures has been experimentally measured up to heat flux 91 kW/m2 at diluted volume fractions of 1% to 5% of glycerol into pure water at volumetric concentrations 0.5%, 1% and 1.5% of Al2O3 nanoparticles. Obtained results indicate that presence of nanoparticles into the mixtures result in increasing the pool boiling heat transfer coefficient values and also result in decreasing the wall superheat temperature of surface. Increased values of heat transfer are increased with increasing the volume fractions of Al2O3 too. Generally, it is concurred that Al2O3 nanoparticles typically enhance the pool boiling heat transfer coefficient of binary water-glycerol mixture in comparison with absence of nanoparticles circumstances, up to 25% at 1.5% Al2O3. Additionally, new simple semi - mathematical model has been proposed for a rough estimating of enhanced values with uncertainty about 8%

A review on the heat and mass transfer phenomena in nanofluid coolants with special focus on automotive applications

Engineered suspensions of nanosized particles (nanofluids) are characterized by superior thermal properties. Due to the increasing need for ultrahigh performance cooling in many industries, nanofluids have been widely investigated as next-generation coolants. However, the multiscale nature of nanofluids implies nontrivial relations between their design characteristics and the resulting thermo-physical properties, which are far from being fully understood. This pronounced sensitivity is the main reason for some contradictory results among both experimental evidence and theoretical considerations presented in the literature. In this Review, the role of fundamental heat and mass transfer mechanisms governing thermo-physical properties of nanofluids is assessed, from both experimental and theoretical point of view. Starting from the characteristic nanoscale transport phenomena occurring at the particle-fluid interface, a comprehensive review of the influence of geometrical (particle shape, size and volume concentration), physical (temperature) and chemical (particle material, pH and surfactant concentration in the base fluid) parameters on the nanofluid properties was carried out. Particular focus was devoted to highlight the advantages of using nanofluids as coolants for automotive heat exchangers, and a number of design guidelines was suggested for balancing thermal conductivity and viscosity enhancement in nanofluids. This Review may contribute to a more rational design of the thermo-physical properties of particle suspensions, therefore easing the translation of nanofluid technology from small-scale research laboratories to large-scale industrial applications

Intensification of heat exchanger performance utilizing nanofluids

Heat exchangers are widely utilized in different thermal systems for diverse industrial aspects. The selection of HEx depends on the thermal efficiency, operating load, size, flexibility in operation, compatibility with working fluids, better temperature and flow controls, and comparatively low capital and maintenance costs. Heat transfer intensification of heat exchangers can be fulfilled using passive, active, or combined approaches. Utilizing nanofluids as working fluids for heat exchangers have evolved recently. The performance of heat exchangers employed different nanofluids depends mainly on the characteristics and improvement of thermophysical properties. Regarding the unique behavior of different nanofluids, researchers have attended noteworthy progress. The current study reviews and summarizes the recent implementations carried out on utilizing nanofluids in different types of heat exchangers, including plate heat exchangers, double-pipe heat exchangers, shell and tube heat exchangers, and cross-flow heat exchangers. The results showed that nanofluids with enhanced thermal conductivity, although accompanied by a considerable decrease in the heat capacity and raising viscosity, has resulted in performance enhancement of different heat exchangers types. So, the performance evaluation criterion that combines the thermal enhancement and increases the pumping power for any type of heat exchangers is requisite to evaluate the overall performance properly. The challenges and opportunities for future work of heat transfer and fluid flow for different types of heat exchangers utilizing nanofluids are discussed and presented

The Construction of Narratives of Sexual Orientation in Persian-Speaking Communities in the Context of Seeking Asylum in Turkey

Various studies show that bi asylum seekers’ claims are far fewer than lesbian and gay ones. In this research, as the first substantial empirical study on bi asylum seekers in any country and also the first substantial empirical study on bisexuality in Iran, I demonstrate how the dominant homonormative narrative of sexual orientation is constructed in interactions among asylum seekers, activists, aid providers and asylum authorities. Based on interviews with sixteen Iranian non-monosexual and monosexual SOGI-based asylum seekers, one Iranian activist and five Turkish activists and aid providers in Turkey, analysis of Persian Twitter debates and reviews of the previous studies, I show how the narratives of (in)stability, (in)authenticity, (un)belonging and, consequently, (un)deservingness result in bi invisibility and bi negativity and form a vicious cycle of bi erasure in the asylum processes. As discussions around asylum have been central in the Persian debates on SOGI after the criminalisation of same sex sexual conduct following the revolution of 1979, bi negativity in the asylum process has contributed to reproducing the dichotomy of hamjinsgaraa, or the real homosexual, and hamjinsbaaz, or the pseudo-homosexual, as the key concepts of sexual orientation in the Persian language. I also discuss how, due to globalisation, English media and social media play an important role in shaping the contemporary Persian understanding of sexual orientation. I argue that in such a context, not only Persian bi asylum stories but also Persian bi stories, in general, become less tellable and, even if they are told, are often not heard, understood and recognised. However, I also show while sometimes Iranian LGBTQ asylum seekers may feel pressured to perform according to the acceptable norms, in other circumstances, they may not only feel safe enough to tell stories closer to how they define their SOGIs but also question the dominant narrative and advocate for their rights