Issues: Kỹ thuật và Công nghệ cho Phát triển bền vững Vol 33.5 (11/2023)
1. Effects of Hybrid Diffuser in Axial-Flow Jet Engine Combustor

Xuan-Truong Le, Van-Minh Le, Phuong-Nam Nguyen, Cong-Truong Dinh*, Trong-Nghia Hoang

It is believed that the turbine engine plays a vital role in the performance of aircraft. Most jet engines nowadays use the axial compressor. In axial-flow compressors, the rising pressure through each stage is dependent on the axial flow velocity. A high axial velocity is essential to achieve the design pressure with the minimum number of stages. Thus, before the combustion can proceed, the air velocity must be reduced to about 20% of the compressor outlet velocity. This depletion is accomplished by fitting a diffuser between the compressor outlet and the upstream end of the liner. Throughout much research into diffuser performance, it has been shown that the operation depends particularly on the flow. Besides, there are several problems that could result in the loss of its efficiency. This study will focus on increasing the diffuser performance of a hybrid type one via pressure-recovery coefficient Cp and loss coefficient λ

Article Code:22034

# Jet engine combustion, Hybrid diffuser, RANS analysis, Diffuser performance

Page: 1-8

Field: Mechanical Engineering
2. Effect of scanning methods on the cracking, microstructure, microhardness of Inconel 625 Nickel - based superalloy parts formed by Direct Laser Metal Depositon

Duong.VanNguy, Trinh.QuangHung, Doan.TatKhoa*

To reduce the occurrence of cracks in the Inconel 625 nickel-based superalloy during the Direct Laser Metal Deposition (DLMD) process, this study simulated the temperature and stress fields of thin-walled parts. The model was used to determine the effect of scanning methods (single direction and reverse direction) on the final stress distribution, and compared the differences in residual stress distribution within the thin-walled part. The results showed that with the single direction scanning method, the residual stress at both ends of the thin-walled part was relatively high while the stress at the middle was smaller, with a stress difference between the maximum and minimum of about 900 MPa. In contrast, with the reverse direction scanning method, the residual stress in the thin-walled part was distributed relatively evenly, with a stress difference of about 300 MPa between both ends and the center. The experimental results showed that with the single direction scanning method, cracks occurred at both ends and in the middle of the thin-walled part, whereas with the reverse direction scanning method, warping and cracks phenomena were eliminated. The microstructure of the Inconel 625 in the forming layer is characterized by a columnar crystal structure that has a small length and grows perpendicularly to the scanning direction. This growth is continuous between the forming layers. In both cases, the microhardness increases with the height of the formed layers; the microhardness values in the left, right, and middle regions are relatively uniform, the microhardness measurement values range from 420 to 450 HV.

Article Code:23025

# Direct laser metal deposition, scanning method, thin-wall, residual stress, crack

Page: 9-18

Field: Mechanical Engineering
3. Removal of methylene blue intensified ozonation using a high-performance rotating reactor

Phuong Thao Nguyen*, Minh Viet Trinh, Thi Doan Pham, Van Tuyen Trinh, Thi Thom Dang, Linh Phuong Phung, Tuan Minh Nguyen

The advanced oxidation process (AOPs) was commonly used in textile dyeing wastewater treatment due to its ability to rapidly degrade dyed compounds. However, its disadvantage is the limited dispersion of ozone in wastewater. To minimize the disadvantage, it is necessary to improve the gas-liquid phase contact to maximize the dispersion of ozone in the wastewater body. Therefore, this study investigated the methylene blue (MB) treatment efficiency in textile dyeing wastewater by performing the ozonation process using a high-performance rotating reactor (HP2R) and compared it with the conventional system. The effect of basic operation parameters such as initial pH, initial methylene blue concentration (Co), rotational speed (ω), and the liquid flow rate (QL) on the decolorization efficiency (η) was evaluated. The results showed that the η of the ozonation using the HP2R reached 98% (pH 8) after only 5 minutes, which was 1.8 times higher than that (54%) of conventional ozonation at the identical period. The decolorization efficiency increased with increasing rotational speed (from 82.0 to 92.5% as ω increased from 300 rpm to 1200 rpm), decreasing liquid flow rate (from 98.0 to 74.9% as QL increased from 0.1 to 0.4 l/min) and initial concentration of MB (from 98.0 to 88.5% as Co increased from 50 to 200 mg/l). These results show that the combined ozonation in the high-gravity technology can be widely applied to various dyeing wastewater treatment processes in general.

Article Code:23041

# Rotating packed bed, ozonation, decolorization, methylene blue, textile dyeing wastewater, HP2R.

Page: 19-25

Field: Environmental Science and Technology
4. Utilizing Coffee Husk Biochar as an Effective Adsorbent for Ammonium Removal in Groundwater

Tien Vinh Nguyen*, Van Phu Pham, Le Minh Tran, Dai Quyet Truong

This study investigated the performance of a novel biochar derived from coffee husks (BCFH) for ammonium removal in the aqueous solution. To enhance the performance of the BCFH, it was also activated by NaOH to generate BCFH-NaOH material. Several batch experiments were conducted with the synthetic solution to determine the adsorption properties of the biochars. At the initial NH4 + concentration of 50 mg/L, the optimal dosage for both materials was 10 g/L, while the ideal pH range was 5-8. The equilibration adsorption time on both materials is within 30 minutes, indicating their high practical applicability. The pseudo-second-order kinetic was applied successfully to describe the adsorption kinetics (R2 >0.999). The isotherms can be defined by both Langmuir and Freundlich models, showing that ammonium removal by biochar is a complex process. BCFH-NaOH showed better performance, with the maximum adsorption capacity reaching 9.97 mg-NH4 + /g, compared to 6.64 mg-NH4 + /g of BFCH. Finally, BCFH-NaOH was tested with a practical groundwater sample (Co = 11.5 mg-NH4 + /L), achieving a sorption efficiency of up to 80 % while eliminating most of the hardness. These results show that the new coffee husks biochars can be applied as low-cost, environmentally friendly adsorbents for ammonium removal.

Article Code:23046

# Agricultural waste, coffee husks biochar, ammonium removal, groundwater

Page: 26-33

Field: Environmental Science and Technology
5. Assessment of Chlorine Residual and Microbiological Parameters in Supply Water of Centralized Supply Water Companies in Vietnam

Nguyen Phuong Hang , Do Phuong Hien , Le Thai Ha , Do Vu Khanh Huyen , Nguyen Thi Quynh Mai , Luu Minh Loan , Nguyen Thi Ha*

In this study, the free chlorine residual and microbiological parameters in supply water of centralized supply water companies were assessed with a total of 1,612 samples in the period of 2020 and 2022. The results showed that 334 samples did not meet the permitted limit QCVN 01-1:2018/BYT for free chlorine residual (0.2-1.0 mg/L), of which, is mostly less than the lower limit (around 80%). The reason is due to the inaccurately used chloramine dose, mainly quantified without adjusting for actual output quality and distribution system. Some companies even periodically disinfect water 1-3 times/week. In many cases, the water samples at the companies’ storage tanks have high free chlorine residual, about 2 times greater than upper limit (>2.0 mg/L). Regarding microbiological parameters, for total coliforms about 40-50% surveyed provinces have water samples that were non-compliance with the acceptable quality standard for QCVN 01-1:2018/BYT with total of 102, 57 and 105 samples. For those water samples, free chlorine residual found also lower than required limit (<0.06 mg/L). Apart from total coliforms and E. coli, Pseudomonas aeruginosa (Ps. Aeruginosa) was also detected in water samples in some provinces and cities with levels exceeding the allowable standards from several times to dozens of times. In addition, the number of provinces/cities where Ps. aeruginosa was detected in supply water also increased over the years but insignificantly. Water samples that did not meet the standard are mostly from water supply companies with a capacity of <1,000 m3/day. Correlation analysis by regression coefficient R2 and Pearson correlation coefficient showed that there was a negative correlation between free chlorine residual and microbiological parameters (total coliforms, E.coli), but the correlation was low and non-linear

Article Code:23054

# Keywords: supply water, free chlorine residual, microbiological parameters, total coliforms, E.coli, Ps. aeruginosa

Page: 34-41

Field: Environmental Science and Technology
6. Characteristics of Microplastics in Sediment at Danang Beaches - Vietnam

Do Van Manh*, Dang Thi Thom, Bui Van Hoi, Duong Tuan Manh, Le Xuan Thanh Thao, Nguyen Duy Thanh, Loc Van Ky, Ha Trong Hao, Tran Thi Hang

Microplastics (MPs) has been recently attracted the attention of many researchers due to their non-degradable and existence for a long time in the environment. MPs are considered as an alarming pollution issue in environment such as their occurence in water, sediment, and organism. In this research, the characteristics of MPs such as their concentration, size, shape and composition of the polymers in the shoreline sediments at the two layers (0- 5 cm and 5 -10 cm) collected from seven beaches on Danang city were investigated by the Fourier-transform infrared (µ-FTIR) method. Consequently, the average concentration of MPs was found at 5565 ± 2359 items 〖kg〗^(-1) dry weight (d.w.) in all sediment two layers. The upper layer of beach sediment (0-5cm) has the majority of MPs with average abundance of 7679 ± 3363 items 〖kg〗^(-1)d.w. MPs had a wide range of sizes from 22.4 μm to 2797.2 μm with an average of 93.4 ± 18.8 μm in sampling sites. In addition, the range size from 20 to 150 μm was the most dominance in both layers.The morphology of MPs was found in the sediment with the most diversity fragment. The variation of the polymer types of the MPs in two sampling layers was determined. Polyamide (PA) was the main polymer type found in both sediment layers while polyether sulfone (PES) was observed only 4/7 sampling beaches.These results showed the diversity of the MPs in the two sediment layers of the seven beaches in Danang city and it is necessary to study on MPs pollution in sediment on beaches of Vietnam in future.

Article Code:23040

# Microplastics (MPs), Danang beaches, morphology, sediment, polymer

Page: 42-48

Field: Environmental Science and Technology
7. Stability and Hopf bifurcation analysis of a phytoplankton- zooplankton model under temperature factor and stage-structure population of phytoplankton

Nguyen Phuong Thuy*, Cao Thi Phuong, Van Duc An, Nguyen Duc Anh

In this paper, we built a predator-prey model to simulate and study the dynamics of zooplankton and phytoplankton populations under the temperature impact, in which the stage structure is considered in the zooplankton population. Our model is an ordinary differential system of three nonlinear equations with some parameters as temperature-dependent functions and uses the generalized Holling response function. The non-negative and boundedness of the model solutions have been proven. The behaviors of our system are shown by the local stability conditions of the equilibria, especially the co-existence case. The stage transformation of zooplankton was studied through the Hopf bifurcation results of varying the temperature. The analysis and simulation results indicate that the ideal temperature for the co-existence is about 12-21 degrees Celsius. The zooplankton's transformation decreases when the temperature increases, leading to an imbalance in the system. Besides that, we also provided simulation figures to illustrate the found theoretical results.

Article Code:23034

# phytoplankton-zooplankton system, predator-prey model, stage-structure population, water temperature, stability analysis, Hopf bifurcation

Page: 49-56

Field: Applied Mathematics and Informatics
8. Evaluating the energy efficiency and environmental impact of a multi-chamber brick kiln in Vietnam

Pham Thai Son, Truong Tuan Ngoc, Nguyen Van Thu, Nguyen Xuan Quang*

Brick production is an essential component of the construction industry, contributing significantly to the development of infrastructure and housing worldwide. This study evaluates the energy efficiency and environmental impact of a multi-chamber brick kiln in Vietnam. The study was conducted through a detailed field survey of the kiln, which included measurements of energy consumption and pollutant emissions. The results show that the kiln has a moderate level of energy efficiency, as indicated by the specific energy consumption of 2,035.1 kJ / kg output brick. However, the kiln also produces pollutants, including SOx, CO, and NOx. The study provides recommendations for improving the kiln's energy efficiency based on the results of the energy analysis. Overall, this study highlights the importance of improving the energy efficiency as well as the environmental performance of a MCBK in Vietnam and provides valuable insights for policy-makers and industry stakeholders.

Article Code:23058

# Energy efficiency, Specific Energy Consumption (SEC), Energy analysis, Brick kiln, Pollutant Emission, Environmental impact.

Page: 57-64

Field: Heat Engineering and Refrigeration
9. Study on Decision Support Tool towards Circular Economy Practice - A Case Study for Electronics Companies

Nguyen Thi Anh Tuyet*, Tran Thanh Chi, Tran Duc Nghiep

This study is a continuation of our previous research on the impact of business organization factors on circular economy (CE) practices towards the development of a decision support tool to facilitate the adoption, implementation, development and strategy of CE activities in the Vietnamese industry. The tool help to quickly assess the status of CE practice in the enterprises and make a structural chart according to the CE maturity models. Having a positive direction in the management organization and application of CE theory, the electronics companies are illustrated as a case study for the application of the tool. As the results, one organization form (namely, the System) aligning with three business models (namely, Resource Models, Design Models, Lifetime extention Models) and five supporting processes (namely, Digitization and Datafication, Return Logistics, Competences, Technical Infrastruture, Setting up Processes, Quality Monitoring) are proposed for visualization of strategic interventions and recommendations for the electronics industry on business sustainability, competitiveness, alignment between their business objectives, priorities, and key performance indicators towards CE practice.

Article Code:23044

# circular economy (CE), decision support tool, electronics industry

Page: 65-73

Field: Environmental Science and Technology