VNUHCM Journal of Engineering and Technology

Large-Scale Fabrication of Polyethylene Glycol-Poly(Methyl Methacrylate) Blend with Nanosponge-Porous Structure for High Performance Bio-Triboelectric Nanogenerator

2022-09-18T21:08:57+00:00

In this work, blends of polyethylene glycol (PEG) and poly(methyl methacrylate) (PMMA) with nanosponge-like porous structure are fabricated by a solution phase separation method, subsequently the nanosponge-porous blends are also applied for a high performance triboelectric nanogenerator (TENG). The features of the porous structure are controlled by varying polymer concentrations and PEG/PMMA ratios. A TENG device made of porous PEG-PMMA blend and convex-poly(dimethyl siloxane) (c-PDMS) can generate an instantaneous output power of 3.2 mW. TENG can not only serve as a supply power to light several light emitting diodes (LEDs) on but demonstrate high potential applications as self-powered monitoring healthcare sensors.

Application of blade element theory on horizontal axis wind turbines to research a novel dual rotor wind turbine

2022-10-11T03:44:38+00:00

This research paper applies the blade element momentum theory on a horizontal axis wind turbine to study a 2-stage wind turbine with an independent rotating shaft, a type of small-scale wind turbine that has never been studied. The article also includes the Prandtl loss in the theory of the blade element momentum method to calculate the wind turbine so that the calculated power and efficiency are close to the actual efficiency instead of the consideration of ideal conditions. These theories have been around for a long time, but their applicability is still very high besides the use of modern computational tools such as computational fluid dynamics. Calculation results in the study are achieved by applying basic theories, then comparing with simulation results from Qblade software, a software that is commonly used in studies to calculate small and large-scale horizontal axis wind turbines and gives an error of less than 10%. This method is to ensure the objectivity and authenticity of the article. The proposed method in this study can be used to calculate various blade profiles of wind turbines. The paper aims to use the CL/CD ratio corresponding to a certain angle of attack as a specific case to optimize the calculation process, giving the problem can be automated.

Effect of marble powder content on compressive strength and water absorption of high-strength concrete

2022-10-13T01:57:58+00:00

This paper presents the effect of marble powder content on compressive strength and water absorption of high-strength concrete to expand the utilization of such waste in the construction industry and to reduce the Portland cement production which negatively affects the environment. Mixture proportion of reference concrete without marble powder was designed as per TCVN 10306:2014 with a designed compressive strength at least of 60 MPa and slump of 16 ± 2 cm. To evaluate the effect of marble powder content on compressive strength and water absorption of hardened concrete, the Portland cement was replaced by the marble powder at levels of 0, 5, 10, 15, and 20% by mass. Experimental results showed that the marble powder significantly affected the engineering properties of fresh and hardened concretes, in detail: the replacement of Portland cement by the marble powder from 0 to 20% increased the slump of fresh concrete from 16.0 to 20.5 cm, and the void volume of hardened concrete at the age of 28 days from 2.66 to 4.79%, resulting in the reduction of compressive strength by 2.48–18.60% and the increase in water absorption by 1.59–3.79% when comprared with the reference concrete with 0% marble powder. However, the value of compressive strength at the age of 28 days of hardened concrete using 5–20% marble powder reached 60.94–73.01 MPa, ensuring the requirement in terms of compressive strength of high-strength concrete. In conclusion, the utilization of marble powder as the Portland cement replacement in a range from 5–20% was feasible in making high-strength concrete with compressive strength of above 60 MPa.

Investigating the effects of ingredient proportions on the texture of Vietnamese sausage using mixture experiment design

2022-11-10T21:13:55+00:00

In this study, the effect of different ingredient proportions on the textural and hedonic characteristics of Vietnamese sausage was investigated. Vietnamese sausage is a widely popular traditional food of Vietnam, yet its characteristics are rarely investigated, especially the texture and hedonic properties. Vietnamese sausage’s texture was heavily influenced by three main ingredients: lean meat, lard and starch. In order to study the interactive effects of these three ingredients on texture as well as liking, eight samples with different proportions of these three main ingredients were prepared based on the mixture design approach. The textural characteristics (including hardness, cohesiveness, springiness, chewiness and gumminess) were determined using the texture profile analysis method, while a consumer panel (N = 70) evaluated their texture liking score. Surprisingly, all the texture characteristics were statistically significant difference. However, cohesiveness had a small variance between samples, signalling that this attribute is not important in describing the texture of Vietnamese sausage. To model the effect of ingredients, response surface regression with mixture model was carried out. The results showed that Scheffe’s special cubic model had a good fit for hardness (R2 = 0.946), chewiness (R2 = 0.902) while Scheffe’s quadratic model had a good fit for liking score (R2 = 0.967). The lean meat was found to be the ingredient with the largest effect on increasing the textural charactertistics as well as the liking score. Interestingly, upon inspecting the correlation between texture and liking score, the PCA map of both showed a similar structure. Finally, optimal values of the main ingredients for Vietnamese sausage formulations based on hedonic (> 6.5 liking score) were 4% - 8% starch, 70% - 76% lean meat and 18% - 26% lard. The analysis of consumers’ liking scores suggested that springiness is the main driver of liking for Vietnamese sausage products.

Determination of the efficiency of AgNPs/ZIF-8 coating on different substrates

2022-11-19T03:13:07+00:00

Depending on different applications or materials that integrate with the substrate as well as the transduction method used in the biosensors, different materials of the substrate are considered. This research focuses on selecting the appropriate substrate in designing biosensors, detecting microorganisms in the environment. In this study, the glass slide (glass), Polyethylen plastic (PE plastic), and the cellulose paper (cellulose acetate (CA) & cellulose nitrate (CN)) are investigated substrates for coating AgNPs/ZIF-8 – material used as an optical signal amplification in further steps, using structural analysis techniques – Scanning Electron Microscopy (SEM) for morphology characterization and the Energy Dispersive Spectrometer (EDS) for optical characterization. A morphology characterization with SEM showed that cellulose paper is a better substrate in comparing with the other substrates (glass, PE), because the sensity of distribution on CN was the highest (85-90%) when it coated with AgNPs/ZIF-8. According to EDS analysis, the ratios of Ag in mixture on CN substrate (15.38±0.39% mass) is slightly higher than CA substrate (13.58±0.39% mass); and about 53 times higher than glass substrate (0.37±0.13% mass) and PE plastic substrate (0.29±0.08%). Therefore, cellulose paper (CA) will be suggested to select for further research as a new material with cost (inexpensive) and effectiveness in coating AgNPs/ZIF-8.

Influence of the louver angle on the performance of the air-conditioning outdoor units in high-rise apartment buildings

2022-11-19T03:19:33+00:00

The split-type air conditioners are widely used in high-rise apartment buildings in the major urban areas, especially Ho Chi Minh City - Vietnam, because of its convenience. In the apartments with limited space, the installation of outdoor units not in accordance with technical guidelines will affect the performance of the air conditioning system and the aesthetics of the apartment building. The aim of this study is to propose the technical room in apartments for properly installing outdoor units of air conditioning systems. The CFD method is utilized through Ansys Fluent software to determine the inlet air temperature of condensers and COP corresponding to the louver angle of 0o, 10o, 20o, 30o và 40o. The results obtained from the simulations show that increasing the louver angle results in rising the inlet air temperature of condensers and reducing COP. The average temperature of the air which entering the condensers does not change significantly when the louver angle increases from 0o to 30o. When the louver angle is more than 30o, the inlet air temperature of outdoor units exceeds the continuous operating temperature of 48oC. To maintain the high performance of the air conditioner during operation, the louver angle is adjusted as small as possible and limited to a value of about 30o.

Study of correlation between ink trapping and color difference in overprint

2022-11-19T04:15:40+00:00

The ink trapping value is one of the important parameters affecting the appearance of secondary colors in overprint. Usually, the ink trapping parameter is traditionally calculated based on the solid density values of the primary colors and the overprint color. These density values are measured by the complementary color filter of the color final ink layer, and these ink trapping values can be calculated using the Preucil, Ritz, or Brunner formulas. Furthermore, the density measurement is more suitable for testing the color printing and not for overlapping assessment because these density values are measured by the complementary color filter of the second color ink. The ink has a specific transmittance, and light is not only absorbed but also scattered inside the ink layer, so the total density of the overlapping colors will be less accurate. As a result, the color measurement method is used to describe the effect of ink trapping of the second ink layer on the first layer of ink. The main idea is to use the color difference value to evaluate the ink trapping ability. In this paper, the author has quantitatively analyzed the correlation between the percentage value of ink trapping and the color difference parameter ΔEab*. The studied results show that the ΔEab* value has a linear correlation with the ink trapping value calculated according to the traditional methods based on density values. This result is also aimed at the fluctuant tolerance of ink trapping ratio during four-color printing to achieve the standard color value quickly.