Geometrical investigation of microchannel with two trapezoidal blocks subjected to laminar convective flows with and without boiling

Microchannels are important devices to improve the heat exchange in several engineering applications as heat, ventilation and air conditioning, microelectronic cooling, power generation systems and others. The present work performs a numerical study of a microchannel with two trapezoidal blocks subjected to laminar flows, aiming to analyze the influence of the boiling process on the geometric configuration of the microchannel. Constructal Design and Exhaustive Search are used for the geometrical evaluation of the blocks. The Mixture multi-phase model and the Lee phase change model were both employed for the numerical simulation of the boiling process. In this study, the influence of the height and higher width of the first block (H11/L11) over the heat transfer rate and pressure drop for different magnitudes of the ratio between the lower width and higher width (L12/L11) was investigated. It is considered water in monophase cases and water/vapor mixture for multiphase flow. Two different Reynolds numbers (ReH = 0.1 and 10.0) were investigated. Results indicated that, for the present thermal conditions, the consideration of boiling flows were not significant for prediction of optimal configurations. Results also showed that in the cases where the boiling process was enabled, the multi-objective performance was higher than in the cases without boiling, especially for ReH = 0.1.

Analysis of Transient Boiling Processes during Steel Quenching in Water PAG Solutions to Decrease Distortion

The paper discusses results of testing standard cylindrical probe 12.5 mm diameter in water polymer solutions which was additionally instrumented with a surface thermocouple. It is shown that central thermocouple cannot depict many physical phenomena taking place during quenching in polymer solutions such as shoulder formation, self- regulated thermal process establishing, surface temperature transient from film boiling to nucleate boiling process. Moreover, it is shown that experimental data depicted by central thermocouple cannot be used for solving inverse problem to analyze quenching process in liquid media. Along with analyzing film and nucleate boiling processes during quenching, the paper discusses the possibility of quality quench process control via using sonar system. It is established an equation for evaluating duration of transient nucleate boiling process. As an example, the cooling characteristics of fresh and old polyalkylene glycol (PAG) polymer solutions are analyzed. It is shown that with passing time the critical heat flux density of polymer decreases and inverse solubility effect disappears. That is while the method and apparatus were developed to control in industrial condition the quality of quenched steel parts during hardening in liquid media.

The effect of the boiling process on the Oxalic acid content of some vegetables in the Syrian local market

Oxalic acid HOOC-COOH (OA) is the first in the homologous series of dicarboxylic acids. It is one of the most common acids present in vegetable world1, it is one of the abundant organic compound acts as an anti-nutrient present in most vegetables in various quantities. It is found as salts of insoluble complexes with divalent cations, minerals and trace elements. Oxalates react with calcium to precipitate calcium oxalate and accumulation of oxalates in the body prevents the absorption and utilization of calcium; which in turn causes calcium imbalance, rickets and osteomalacia. In the present study oxalate content of various vegetables commonly available in local market of Syria were determined and effect of boiling on oxalate content of selected vegetable were investigated. Most of the samples analyzed were contained more than 100mg/100g on dry weigh basis. The higher value of total oxalate content was found in Parsley (1466.82 mg/100g); spinach and Cabbage contain (478.7, 191.08 mg/100g). Boiling has shown reduction in total oxalate content and least reduction was obtained in Parsely leaves (28.33%) and highest reduction was obtained from Spinach (40.00%)

Extension of the Process Window in Laser Chemical Machining by Temperature-Dependent Reduction of the Electrolyte Viscosity

The laser chemical process is a material-removing machining process in the micro range. The process is based on a laser-assisted etching process between an electrolyte and a metallic workpiece. Local overheating causes a laser-induced electrolyte boiling process, which limits the laser chemical process window. In order to reduce the laser-induced electrolyte boiling process and thus expand the process window, the laser chemical process is carried out at different electrolyte start temperatures and thus different electrolyte viscosities and surface tensions. The experimental investigations were carried out on Titanium Grade 1 with the electrolytes phosphoric acid and sulfuric acid at different electrolyte temperatures and laser powers to determine the limits of the process window by evaluating the properties of the removal cavities. As a result, the process window is extended at lower electrolyte viscosities. Thereby, the electrolyte viscosities have no influence on the geometric shape of the removal. The extension of the process window is attributed to the fact that a reduction in electrolyte viscosity results in a less pronounced formation of the boiling process, the bubble diameters decrease, and the shielding effect of the bubbles is reduced.

Burnout Investigation of Small Diameter Tubes Immersed in Nanofluids

This paper deals with research into pool boiling critical heat flux (CHF) of water–Al2O3, water–TiO2 and water–Cu nanofluids on horizontal stainless steel tubes. The experiments were conducted under atmospheric pressure. Nanoparticles were tested at concentrations of 0.001%, 0.01%, 0.1% and 1% by weight. Ultrasonic vibration was used in order to stabilize the dispersion of the nanoparticles. Although dispersants were not used to stabilize the suspension, the solutions tested showed satisfactory stability. Experimental measurements were performed with stainless steel tubes of three outside diameters: 1.6, 3 and 5 mm. Enhancement of CHF was observed to be independent of the concentration and material of the nanoparticles and tube diameter, with simultaneous heat transfer degradation. Built up during the boiling process, nanolayers improve substantially the heating surface wettability. A correlation is suggested for the CHF prediction during pool boiling of nanofluids.