Forced Convective and Nucleate Flow Boiling Heat Transfer to Alumnia Nanofluids

A large number of experiments have been performed to quantify the forced convective and nucleate flow boiling heat transfer coefficient of Al2O3 water based nanofluid. The employed test loop provides conditions to investigate the influence of operating parameters such as heat flux, flow mass flux and volumetric concentration of nanofluids (0.5, 1 and 1.5%). Results demonstrate that two heat transfer regions are observed namely forced convective and nucleate boiling region. Investigating on the operating parameters illustrated that with increasing the heat flux and flow rate of nanofluid, heat transfer coefficient of nanofluid dramatically increases. In contrast, with increasing the volumetric concentration of nanofluid, controversial condition is observed such that increases the heat transfer coefficient in forced convective region is reported while reduction of heat transfer coefficient is seen for nucleate boiling zone. Obtained results were then compared to Chen and also Gungor-Winterton well-known correlations. Results of this comparison show that experimental data are in a good agreement with those of obtained by correlations

Liquid chemical looping gasification

Combustion of fossil fuel for energy production is not a sustainable method since it releases CO2, particulate materials and greenhouse gases such as NOx into the atmosphere, which causes environmental pollution and global warming. Additionally, fossil fuel resources are limited, thus reliance on fossil fuels is not sustainable. To address this, special attention has recently been paid to renewable energy resources as alternatives for fossil fuels. However, it requires the development of new processes, or to integrate systems to produce energy through clean technologies aimed at the reduction of carbon dioxide emissions. One promising method is to convert fossil fuels, or biomass, to synthetic fuel referred to as “syngas”. Gasification is an established method for producing syngas from a carbonaceous fuel. The conventional gasification pathways employ air to supply the required oxygen for the reactions, however, due to the presence of the nitrogen in the gaseous products, the quality of the syngas (molar ratio of H2: CO) is relatively low. Thus, a new process for the production of syngas has been developed, referred to as a “chemical looping gasification” process, which uses solid metal oxide as the oxygen carrier. This process prevents direct contact between the feedstock and the air, addressing the challenge of the presence of nitrogen in the product. However, there are some disadvantages associated with the use of solid metal oxides, such as sintering, breakage of the particle, agglomeration and the deposition of the carbon on the oxygen carrier particles. Therefore, one potential solution to address the aforementioned challenges is to use a liquid metal oxide as an oxygen carrier instead of solid particles in a new process referred to as Liquid Chemical Looping Gasification (LCLG). To assess the LCLG system, a thermodynamic model was developed to simulate the reactions occurring in a chemical looping gasification system with a liquid metal, such as copper oxide, as the oxygen carrier. To identify other suitable oxygen carriers, a thermodynamic model and a selection procedure were also developed to assess the chemical performance of the system with various metal oxides. Copper, lead, antimony and bismuth oxides were potential options. Amongst them, lead oxide was assessed for integration of the system with a supercritical steam turbine cycle for the co-production of work and syngas. Bismuth oxide was thermodynamically and experimentally assessed for the gasification of biomass, coal and natural gas. To validate the developed models and to demonstrate the liquid chemical looping process, a series of experiments were conducted using a thermo-gravimetric analyser. Experiments were performed to assess the reduction and oxidation reactions of bismuth oxide with a graphitic carbon and air by measuring the mass change of the samples in the nitrogen and the air environments. The activation energy and reaction constant for the reduction and oxidation reactions were measured experimentally. The results obtained with the thermodynamic models for the bismuth oxide were in good agreement with those obtained with the experiments.Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 201

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.

Accurate improvement of a mathematical correlation for estimating diffusion coefficient in gaseous hydrocarbons

Accuracy of Riazi-Whitson mathematical correlation for estimating the molecular diffusion coefficient in gaseous hydrocarbons has been improved, which decreases the absolute average deviation related to the experimental data using About 486 experimental data points that have been collected from latest existing researches. Likewise, re-optimizing, and statistical calculations have been done to synchronize data to avoid unexpected deviations. As shown in present work, deviation values for results of improved correlation from experimental data are less in compare to Riazi-Whitson original correlation. The absolute average deviations for obtained values of improved correlation are about 9.71%, which is about 14% for original mentioned correlation. The input parameters are molecular weight, critical properties, and acentric factors of components in the system; mixture molar density; low-pressure gas viscosity and actual viscosity. The last three properties are calculable by proper correlations in chemical handbooks

Corrigendum to “Experimental studies on the effect of water contaminants in convective boiling heat transfer” [Ain Shams Eng. J. 5 (2) (2014) 553–568]

Refers toMohammad Mohsen Sarafraz, Faramarz HormoziExperimental studies on the effect of water contaminants in convective boiling heat transferAin Shams Engineering Journal, Volume 5, Issue 2, June 2014, Pages 553-56

Experimental studies o

Experimental investigations on the influences of different contaminants to deionized water have been conducted under the sub-cooled flow boiling heat transfer inside the vertical annulus. Many experiments have been performed to investigate the influence of different operating parameters on the flow boiling heat transfer coefficient in the upward flow of contaminated water under the atmospheric pressure. The experimental apparatus provides the particular conditions to investigate the influence of heat flux (up to 132 kW/m2), flow rate (1.5–3.5 l/min), sub-cooling level (Max. 30 °C), and concentration of contaminants (1–5% by volume). According to the results, with increasing the heat flux and flow rate, the flow boiling heat transfer coefficient and rate of bubble formation significantly increase. Results also demonstrated that adding contaminants to the deionized water causes the flow boiling heat transfer coefficient to be deteriorated. Likewise, sub-cooling level may only influence on the onset of nucleate boiling and heat flux corresponding to beginning of nucleate boiling phenomenon which is called inception heat flux