Forced and mixed convection experiments in a confined vertical backward facing step at low-Prandtl number

In this paper, we present experimental results for a non-isothermal vertical confined backward facing step conducted with a low-Prandtl number fluid. The eutectic alloy gallium–indium–tin is used as the working fluid. We conducted experiments for different Reynolds and Richardson numbers covering both forced and mixed convection regimes. Time-averaged velocity profiles were measured at six streamwise positions along the test section center-plane with so-called permanent magnet probes. The local Nusselt number was measured in streamwise and spanwise directions along the heating plate mounted right after the step. We further ran RANS simulations of the experiment to study the qualitative influence of assuming a constant specific heat flux thermal boundary condition for the experiment heating plate. The measured velocity profiles show the expected behavior for both studied convection regimes, while the measured streamwise local Nusselt number profiles do not. This is explained by how the heating plate thermal boundary condition is defined. We performed an order of magnitude estimate to estimate the forced- to mixed convection transition onset. The estimate shows good agreement with the experimental data, although further measurements are needed to further validate the estimated transition threshold. The measurement of fluctuating quantities remains an open task to be addressed in future experiments, since the permanent magnet probe measurement equation needs further adjustments. Graphical Abstract

Dynamics of bubble growth under a heated substrate

This paper investigates the growth dynamics of a vapor-gas bubble pressed against a heating plate by the buoyancy force. The shadow method was used to capture images, which were then automatically processed to calculate the size of the bubble. As expected, the bubble dynamics significantly depends on the heating power. It was found that the ratio of bubble diameter to bubble height increases as it grows.

Study on Fixed-Point Growth of Thermal Bubble with Micro-Planar Induction Heater

Background: The thermal bubble-driven micro actuators have advantages of simple structure and low working voltage, which have broad prospects in the field of micro-fluidic systems. Methods: This paper presents a new type of micro-planar induction heater which can realize the fixed-point growth of thermal bubbles by adding some active cavities. The micro-planar induction heater is composed of a metal heating plate, a glass substrate and a planar coil. Results: In the experiments, an alternating current of 80kHz was applied to the micro-planar induction heater, both the heating time and the interruption time were 1 s controlled by PLC. A CCD camera was used to record the generation process of thermal bubbles, including nucleation, growth and shrinkage. The experimental results show that thermal bubbles can grow and contract periodically at the position of the cavities when the cavities diameter is 50μm and 90μm, respectively. The ideal thickness of the heating plate is between 6μm and 13μm. Conclusion:: The fixed-point growth of the thermal bubble with a micro-planar induction heater has been studied. This kind fixed-point growth of thermal bubbles can be used in micro actuators such as micro ejectors, micro mixers and micro pumps.

Physico-Chemical and Microbial Properties of Stored Mushroom Slices

Button mushroom (AgaricusbisporusL.) is extensively produced and consumed in the world. They are more perishable due to their high moisture content. Due to its short shelf-life, the mushroom is usually dehydrated for preservation. Hot air dried mushrooms result in losses in nutrients, colour degradation and deformation in structure. To overcome these problems, freeze-drying of mushroom slices was investigated. White button mushrooms after cleaning were vertically cut into 2, 4, 6 and 8 mm thick slices. Sliced mushrooms were frozen at −20 °C and then subjected to the freeze-drying at various heating plate temperatures of 10, 20, 30 and 40 °C. The effect of slice thickness and heating plate temperature on physicochemical properties like rehydration, porosity, firmness, water activity, colour, ascorbic acid, protein and microbial properties like total bacterial, yeast and mould were evaluated during the storage. Increase in the storage period resulted in decrease in porosity (73.25%), colour L* value (48.12), firmness (0.98 N), rehydration ratio (4.04), ascorbic acid content (14.47 mg/100 g) and protein content (19.15%), whereas the water activity (0.412) increased with the storage period. This may be due to the absorption of moisture during storage. Microbial analysis indicated by yeast count, mould count and total plate count was nil during the first three weeks of storage, whereas in the fourth week negligible growth was observed. So it is concluded that this may be due to the low water activity of stored mushroom slices.

Preventive Detection Method for Leakage of Sheet Tobacco Dryer

Content Sheet Tobacco Dryer is an important and key equipment in the tobacco making workshop of cigarette factory, its function is mainly to expand and dry cut tobacco, and the drying process is mainly carried out by the sheet heating plate in the drum through heat conduction, while the energy of the sheet heating plate mainly comes from the steam inside, and there is a risk of leakage through continuous operation of the sheet and its accessories, once leakage occurs, it will cause quality accidents of tobacco products, and leakage can be well prevented and eliminated through regular leakage detection.

Effect of FSW Heating Base Temperature on Tensile Strength and Hardness of AA 1100 Welds

The research objective was to determine the effect of heating base temperature on tensile strength and hardness of AA 1100 welds in Friction Stir Welding (FSW). The research methodology includes preparing work pieces of size 150 mm x 100 mm x 3.6 mm from aluminium alloy AA1100 series, making work piece clamps that are suitable for the milling machine used, preparing heating plates 500 Watt for FSW, preparing tools from AISI-H13 material with a shoulder diameter of 20 mm and pin size of M5 x 3.4 mm for FSW, the implementation of FSW with a rotating speed of 1750 rpm and translation speed of 10 mm/minute, preparing hardness test specimens, preparing tensile test specimens refers to ASTM E8-13a, and data analysis of hardness test and tensile test results. The FSW results show that the hardness value increases with the increase in the width of the heating plate linearly for a temperature of 200oC from 10 mm to 30 mm which indicates better conditions, meanwhile decreases at a temperature of 175oC for heating plate width from 10 mm to 20 mm, but increases to 30 mm which is different for the temperature of 250oC and temperature of 300oC which have increased from 10 mm to 20 mm, but decreases towards 30 mm, and than the correlation between AA 1100 tensile strength and surface hardness of 3 heating plate widths is shown with the function of tensile strength, s (MPa) = -0.9699 x surface hardness (HV) + 102.01.