Hasil untuk "Low temperature engineering. Cryogenic engineering. Refrigeration"

Giovanni Tretola, Konstantina Vogiatzaki

Abstract Cryogenic fluids are crucial in applications such as rockets, cryosurgery and energy storage, where they can come in contact with surfaces. Thus, their impact dynamics are of interest. Experiments under cryogenic conditions are very expensive and not always accurate, mainly due to limitations of equipment operating in very low temperatures. Although simulation tools can provide useful insights, currently very few commercial and open-source software tailored for ultra low temperature conditions exist. In this work we present a novel numerical framework used to provide insight into the impact dynamics of cryogenic droplets with solid surfaces. Our aim is to explore whatever conclusions for droplet spreading dynamics from the current literature for droplets at non-cryogenic conditions can be applied to cryogenic droplets as well. We explore different impacting conditions, varying the initial impact velocity, of cryogenic and non-cryogenic cases, while maintaining the same Weber, Ohnesorge and Reynolds numbers between cryogenic and non-cryogenic cases. The impact on a solid surface is investigated first for a water droplet and then for a liquid oxygen droplet moving into gaseous nitrogen. For the latter, the ambient temperature and pressure are below the oxygen critical point, limiting the investigation at a sub-critical regime. The algebraic volume of fluid method with adaptive mesh refinement is employed. Numerical treatments to improve the interface description are also implemented. The simulations have been performed in OpenFOAM with a newly developed code. The results obtained are analysed both qualitatively and quantitatively, comparing the droplet morphology evolution for the two fluids. Differences are observed mainly in the receding stage, once the droplet has reached the maximum spreading, with the receding stage of the cryogenic case characterised by a faster dynamic.

Guo Weichen, Wang Zeng, Zhu Xuejin et al.

A large-scale scientific facility uses constant-temperature air conditioning (CTAC) to control the air temperature fluctuation at an ultrahigh precision, i.e., ≤±0.1 ℃, which implies that the temperature of the chiller water must also be maintained at an ultrahigh precision level. Traditional CTACs depend on electric heating to maintain the chilled water temperature. However, such methods usually fail to address the issue of high-frequency oscillations and typically are not applied to ultrahigh-precision control. In this study, by conducting a reduced-scale experiment, we first validated the feasibility of two water chillers, one using a plate heat exchanger and another using a mixed water pump, to provide chilled water at an ultrahigh precision. Simulations using Modelica models based on these two approaches were established and experimentally verified. Finally, the steady-state and dynamic performances of these two systems were compared. Both approaches can achieve ±0.1 ℃ temperature fluctuation control when the hardware meets specific criteria, with the plate heat exchanger approach exhibiting superior steady-state performance. Under both schemes the root mean square error (RMSE) for the entire time period is below 0.1 ℃. The settling times for the plate heat exchanger and mixed water pump approaches are 5 000 s and 600 s, respectively. The mixed water pump approach exhibits better dynamic performance. Both plate heat exchanger and mixed water pump approaches are capable of actively dampening high-frequency oscillations in the water supply temperature, with damping coefficients of 0.07 and 0.4, respectively.

Thi Thu Hang Tran, Kieu Hiep Le

Abstract In this work, a two-dimensional computational fluid dynamic (CFD) model is developed to describe the drying process of a packed bed made of spherical particles. The volumetrical evaporation rate inside the bed is computed from the pressure difference between the particle surface and the airflow. By using the thermal equilibrium assumption, the heat conservation equation is derived. The CFD model is solved in the COMSOL Multiphysics environment. The obtained results indicate remarkable maldistributions of temperature and moisture content. These maldistributions can be explained by the impact of lateral edges on thermo-hydraulic behavior. Additionally, the impact of particle diameter, air velocity, and bed width on the spatial-temporal moisture content and temperature distribution is investigated. It shows that the CFD model can be simplified to the receding front drying model for a bed made of small particles. Furthermore, by changing the thermal boundary conditions at the lateral edges, the influence of the heating mode at the lateral edges on the drying behavior is explored. The results indicate that contact heating at the bed wall can help to accelerate the drying process significantly.

Vandanababu Talakayala, Prashant Dahiwale, Sanjay Mate

Secret voting in democratic countries using computational intelligence and Blockchain Technology, the vote is a fundamental right in democracy to elect people’s representatives at various levels. Manual voting is tedious and error prone. E-voting systems replaced the manual voting systems to overcome illegal voting and malpractices. Due to growing cybercrimes, the existing e-voting systems are not ideal and face many challenges like authentication, privacy, data integrity, etc. This paper presents computational intelligence and Blockchain technology in developing secret e-voting systems. This paper addresses various issues not addressed by traditional and e-voting systems and proposes new voting using computational intelligence techniques and blockchain technology.

Aashish Dhiman, Pooja Varma

There are several kinds of compulsive usage of “a mobile phone” by youngsters around the world, which can be called mobile phone addiction/misuse. The more specific area of mobile usage is “WhatsApp’s addiction/misuse” which has prompted health officials around the world to consider this quickly expanding issue. The research study aimed to determine WhatsApp usage patterns among primary educators and students, as well as the influence of those patterns on their personal lives. From December 1, 2021, to May 1, 2022, A cross-sectional study was undertaken among primary educators and students of the Meerut region. The information was gathered using a standardized questionnaire. The sociodemographic profile, usage pattern, and impact are all included in the proforma. The overuse of WhatsApp has an adverse influence as well as an extreme effect on study time, educational achievement, and relaxation. Educators utilize WhatsApp groups for academic purposes, which disrupts and demolish their personal lives even after they have finished their professional work. WhatsApp users have enhanced their social lives in the virtual world. The findings of this research study are limited to the specific region and not generalized to other sectors and regions of the world. Further research can be carried out with more sample size considering different variables.

Hua Jiang, Tatsuki Watanabe, Chihiro Watanabe et al.

Gauri Ghai, Ritesh Raj, Ravneet Kaur

Abstract : Education is a powerful tool that has the potential to improve the social and economic condition of a person in a developing country like India. The greatest challenge for the Government is the accomplishment of quality education in inclusive and accessible arrangements for persons with disabilities. The teaching techniques adopted in traditional classrooms aren't usually designed to cater to the need of visually impaired students. Visually impaired students are usually held back from pursuing STEM (Science Technology Engineering and Maths) education and are encouraged to take up humanities and commerce. The lack of resources is mostly responsible for holding back visually impaired students from pursuing Science along with other factors such as the incompetence and attitude of the facilitators. In this work, an inclusive science laboratory for visually impaired students is envisaged using assistive technology that can facilitate them in performing lab experiments. Assistive technology plays a crucial role in the shift of the education system for visually impaired students to an inclusive model. Low cost, easy to use and store, hardware modules with talkable features has been designed to measure temperature, time, to detect contrast and color using Arduino UNO. With the help of these modules, a visually impaired student can be assisted to perform laboratory experiments effortlessly, which otherwise is not made accessible to them. Keywords: Arduino, assistive technology, Inclusive science laboratory, visually impaired.

Du Lin, Zhou Liyang, Chen Qi et al.

The uneven distribution of refrigerants in parallel flow microchannel heat exchangers is one of the reasons that limit their further promotion and application. When the parallel flow microchannel heat exchanger is used as an evaporator, the refrigerant at the inlet of the evaporator is in a vapor-liquid two-phase state, which causes an uneven distribution of vapor and liquid refrigerant in the evaporator. In this study, a two-phase R134a refrigerant was used as the working fluid, and a numerical simulation model which was verified by previous experimental data was proposed. Four schemes to improve the refrigerant distribution characteristics by changing the protrusion depth of different flat tubes are proposed. Numerical simulation models were used for the calculation. When the mass flow rate is 100 kg/(m2?s) and the refrigerant quality is 0.4, it is found by changing the protrusion depth of different flat tubes in the header, the liquid phase refrigerant distribution characteristics can be improved by 29.4%–52.4%.

Natthawut Ruangtrakoon, Tongchana Thongtip

Ziwei Deng, Tianbao Qian, F. Hang

Hydrogels have drawn extensive attention due to their unique physical and biological properties. However, the relatively low mechanical strength and poor processability of hydrogels limit their applications. Especially, the emerging 3D printing technology for nontoxic hydrogels requires proper formability and controllable mechanical behaviors. In this study, a new strategy to construct a novel double-network biocompatible hydrogel from poly(ethylene glycol) diacrylate (PEGDA) and short-chain chitosan (CS) via ionic-covalent cross-linking is by a two-step method involving UV curing followed by immersion in an anionic solution. The CS-based ionic network and PEGDA-based covalent network as well as the hydrogen bonds between them jointly induce excellent mechanical properties, which can be regulated by changing the PEGDA/CS content and ionic cross-linking time. Compared with conventional hydrogels, this mechanically optimized hydrogel exhibits a superior elastic modulus (3.84 ± 0.4 MPa), higher tensile strength (7.23 ± 0.2 MPa), and higher tensile strain (162 ± 7%). Notably, its excellent printing capability through the citrate anionic solution adjustment enables 3D printing with precision, flexibility, and a complex inner structure by extrusion in air at room temperature. In addition, a number of citrate ions existed in the ionic network, giving the hydrogels good electrical conductivity. Therefore, this printable, conductive, and tough hydrogel exhibits potential for vascular engineering, cartilage tissue engineering, and wearable device applications.

P. A. Taylor, Haofu Huang, K. Kiick et al.

Elastin-like polypeptides (ELP) have been widely used in the biomaterials community due to their controllable, thermoresponsive properties and biocompatibility. Motivated by our previous work on the effect of tryptophan (W) substitutions on the LCST-like transitions of short ELPs, we studied a series of short ELPs containing tyrosine (Y) and/or phenylalanine (F) guest residues with only 5 or 6 pentapeptide repeat units. A combination of experiments and molecular dynamics (MD) simulations illustrated that the substitution of F with Y guest residues impacted the transition temperature (Tt) of short ELPs when conjugated to collagen-like-peptides (CLP), with a reduction in the transition temperature observed only after substitution of at least two residues. Placement of the Y residues near the N-terminal end of the ELP, away from the tethering point to the CLP, resulted in a lower Tt than that observed for peptides with the Y residues near the tethering point. Atomistic and coarse-grained MD simulations indicated an increase in intra- and inter- peptide hydrogen bonds in systems containing Y guest residues that are suggested to enhance the ability of the peptides to coacervate, with a concomitantly lower Tt. Simulations also revealed that the placement of Y-containing pentads near the N-terminus (i.e., away from CLP tethering point) versus C-terminus of the ELP led to more π-π stacking interactions at low temperatures, in agreement with our experimental observations of a lower Tt. Overall, this study provides mechanistic insights into the driving forces for the LCST-like transitions of ELPs and offers additional means for tuning the Tt of short ELPs for biomedical applications such as on-demand drug delivery and tissue engineering.

A. Mills, V. Kadirkamanathan

Purpose This paper proposes new methods of fault detection for fuel systems in order to improve system availability. Novel fault systems are required for environmentally friendly lean burn combustion, but can carry high risk failure modes particularly through their control valves. The purpose of the developed technology is the rapid detection of these failure modes, such as valve sticking or impending sticking, and therefore to reduce this risk. However, sensing valve state is challenging due to hot environmental temperatures, which results in a low reliability for conventional position sensing. Design/methodology/approach Starting with the business needs elicited from stakeholders, a quality functional deployment process is performed to derive sensing system requirements. The process acknowledges the difference between test-bed and in-service aerospace needs through weightings on requirements and maps these customer requirements to systems performance metrics. The design of the system must therefore optimise the sensor suite, on- and off-board signal processing and acquisition strategy. Findings Against this systems engineering process, two sensing strategies are outlined which illustrate the span of solutions, from conventional gas path sensing with advanced signal processing to novel non-invasive sensing concepts. While conventional sensing may be feasible within a test cell, the constraints of aerospace in-service operation may necessitate more novel alternatives. Acoustic emission (detecting very high frequency surface vibration waves) sensing technology is evaluated to provide a non-invasive, remote and high temperature tolerant solution. Through this comparison, the considerations for the end-to-end system design are highlighted to be critical to sensor deployment success in-service. Practical implications The paper provides insight into different means of addressing the important problem of monitoring faults in combustor systems in gas turbines. By casting of the complex design problem within a systems engineering framework, the outline of a toolset for solution evaluation is provided. Originality/value The paper provides three areas of significant contributions: a diversity of methods to diagnosing fuel system malfunctions by measuring changes fuel flow distributions, through novel means, and the combustor exit temperature profiles (cause and effect); the use of analytical methods to support the selection (types and quantities) and placement of sensors to ensure adequate state awareness while minimising their impact on the engine system cost and weight; and an end-to-end data processing approach to provide optimised information for the engine maintainers allowing informed decision-making.

J. Jayasinghe, A. Samarasekara, D. Amarasinghe

Cotton is a natural resource that almost consists of 95% of cellulose and it is considered as the purest form of the naturally occurring cellulose. In the past recent years, cotton consumption demand in textile industry increased than the production. In textile engineering cotton blended with various other synthetic fibers such as polyester, nylon and lycra. Therefore, the fabric recycling methods are quite complicated due to mixture/blend of materials in garment waste. In this study, method was developed to identify the amount of cotton present in the cotton/polyester blend based on Fourier transformed infrared (FTIR) second-order derivative spectroscopic method. Microcrystalline cellulose (MCC) was extracted by using the recycle cotton waste. MCC indicates high economic value and remarkable physical properties like specific surface chemistry, biodegradability, low toxicity, renewability and low CO2 emissions into the atmosphere during their production cycle. The study discussed the properties including; morphological features and size (Scanning electron microscopy (SEM)), chemical functionality (Fourier transformed infrared (FTIR) spectroscopy), degree of crystallinity (X-ray diffraction (XRD)) and thermal properties (Thermogravimetric analysis (TGA)). The yield of the MCC was 42% while length, crystallinity index and thermal degradation starting temperature recorded as 20-60µm, 58% and 315°C respectively.

K. Alali, F. Lebsir, Sondes Amri et al.

The production of solketal and conversion of glycerol takes a major importance in the field of the sustainability of the biodiesel industry. The synthesis of (2,2-dimethyl-1,3-dioxolan-4-yl)methanol by the acetalization of glycerol with acetone successfully applied out using various Algerian acid activated clays (maghnia-H+) under autogenous pressure and without solvent. The acid catalyst clays are prepared by an easy technique by activation with the available and low-cost Maghnia clay. The purified Maghnia clay named ALC and the resulting series of acid-activated clays AL1, AL2, AL3, and AL4 are characterized by X-ray Fluorescence (XRF) investigation, N2-adorption/desorption Brunauer–Emmett–Teller  (BET) surface area, X-rays Diffraction (XRD), Fourier Transform Infra Red (FT-IR) spectroscopy, SEM microscopy and the cation exchange capacity (CEC) with copper bisethylenediamine complex method, in order to study the effect of activation at the acid and the catalytic behaviour in the acetalization reaction. The results show a high catalytic activity whose that the yield of solketal production interest reached 95 % at a temperature of 40 °C for a reaction time of 48 hours with full selectivity and glycerol conversion reaching up to 89 %. A mechanistic is proposed to explain the chemoselective of solketal production. These results indicate the potential of this Algerian acid activated clays catalysts for the acetalization of glycerol for an environmentally benign process. Copyright © 2018 BCREC Group. All rights reservedReceived: 28th March 2018; Revised: 17th October 2018; Accepted: 30th October 2018; Available online: 25th January 2019; Published regularly: April 2019How to Cite: Alali, K., Lebsir, F., Amri, S., Rahmouni, A., Srasra, E., Besbes, N. (2019). Algerian Acid Activated Clays as Efficient Catalysts for a Green Synthesis of Solketal by Chemoselective Acetalization of Glycerol with Acetone. Bulletin of Chemical Reaction Engineering & Catalysis, 14 (1): 130-141 (doi:10.9767/bcrec.14.1.2445.130-141)Permalink/DOI: https://doi.org/10.9767/bcrec.14.1.2445.130-141

Ö. Poyraz, M. C. Kuşhan

Laser powder bed fusion (LPBF) is a powder bed additive manufacturing (AM) process used for the production of three dimensional (3D) parts from a wide range of powder materials; it is known with different commercial names, such as selective laser melting (SLM), selective laser sintering (SLS) or direct metal laser sintering (DMLS) [1]. It expands its sectorial utilization by offering good mechanical properties, design freedom [2], easy transition from design to manufacturing, post-processing ability, and low material consumption [3]. Regardless of the various advantages offered by LPBF, remaining challenges such as surface quality [3], residual stresses, distortions [4], or the use of support structures prevent the wider acceptance of this process. LPBF AM uses a laser beam to selectively melt the metal powders by scanning cross sections on the surface of a powder bed layer by layer into an object that has a desired 3D shape based on a computer-aided design (CAD) model [5]. After each cross-section is scanned through a mirror system and solidifies with the help of blowing inert gas, the powder bed is lowered by one layer of thickness, a new layer of material is spread on top with a re-coater, and the process is repeated until the part is complete [4]. In this respect, heat transfer mechanisms include phase change, conduction, convection, and radiation (Fig. 1). As a result of the above-mentioned phenomenon, occurring thermal gradients cause cyclic thermal expansions, which exceed the elastic strain of the material and generate plastic strains, especially at high temperatures. These cumulated strains can generate internal stresses (also known as residual stresses) in the part [6] and cause distortions, which may lead failure by cracking [7] or layer delamination [8]. To eliminate the risk of cyclic thermal expansions and the resultant problems of residual stresses and distortions, several measures can be taken. In this regard, to check residual stresses, inspection techniques can be employed such as neutron diffractometry [9] or X-ray diffraction [10], and distortions with dimensional measurement systems [11] can be used. However, due to the rapid nature of additive manufacturing, these techniques are not Residual Stress-induced Distortions in Laser Powder Bed Additive Manufacturing of Nickel-based Superalloys Poyraz, Ö. − Kuşhan, M.C. Özgür Poyraz1,* Melih Cemal Kuşhan2 1TEI, Tusaş Engine Industries Inc., Turkey 2Eskişehir Osmangazi University, Faculty of Engineering, Department of Mechanical Engineering, Turkey

Jin Ying, Zhou Feng, Li Cuicui et al.

The influence of working fluids on the performance of a cooling system is crucial and the properties of working fluids depend on the contribution sum of the different groups. Therefore, it is essential to analyze the group contribution of working fluids on system performance, which is an important guide for a suitable working fluid match. In this study, the group contribution method was used in the actual cycle of a liquid pump-driven free cooling loop according to the arrangement and combination of the molecular groups of 15 working fluids. The physical properties of the working fluids were investigated using REFPROP when the evaporation temperature was 25 ℃, the condensation temperature was 15 ℃, and the mass flow rate was 2 700 m3/h. The actual cycle of the liquid pump-driven free cooling loop is used to calculate the refrigeration capacity and energy efficiency ratio. The results show that when the working fluid is separated by a monoatomic group, the larger the number of C and H atoms, the greater the cooling capacity. When the working medium is separated by a polyatomic group, the greater the number of H atoms in the polyatomic group composed of the two atoms of C and H, the greater the amount of cooling.

Ji Tianwei, Tao Leren, Yu Zhongyang et al.

Because of the requirement of annual operation, an air source heat pump water heater has complex and variable working conditions. Therefore, there are higher requirements for air source heat pump water heater system control. Based on the flexible adjustment characteristics of the electronic expansion valve, this study proposes a simple control method of the fixed discharge superheated temperature. Meanwhile, the control methods of a fixed valve opening and fixed superheated temperature were used to conduct experimental research and analyze their internal process. When the ambient temperature is 22 ℃，the experimental results show that the discharge temperature dramatically decreased under the control methods of a fixed valve opening; however, its coefficient of performance (COP) is the lowest and its compression risk with liquid is high. Although the COP is the highest under the control method of a fixed superheated temperature, the discharge temperature is also the highest. Under the control method of a fixed discharge superheated temperature, its COP is slightly lower than that of the fixed superheated temperature control method. However, the discharge temperature is effectively reduced by nearly 7 K on average. Meanwhile, compared to the fixed valve opening, its average COP increased 4.9% and the risk of compressor suction with a large amount of liquid refrigerant can be avoided. Therefore, this method effectively combines the advantage of the other two methods.

S. Khalil, Wei Sun

V. Eijsink, Sigrid Gåseidnes, T. Borchert et al.