Research

Jump to: Review

24 pages, 15328 KiB

Open AccessArticle

Detailed Simulations of a Three-Stage Supercritical Carbon Dioxide Axial Compressor with a Focus on the Shrouded Stator Cavities Flow

by Saugat Ghimire and Mark Turner

Processes 2023, 11(5), 1358; https://doi.org/10.3390/pr11051358 - 28 Apr 2023

Cited by 1 | Viewed by 919

Abstract

This paper describes the findings of detailed simulations performed to investigate the impact of seal teeth cavity leakage flow on the aerodynamic and thermal performance of a three-stage supercritical CO

_{2}

axial compressor. The study compares a shrouded stator configuration (with cavities) to [...] Read more.

This paper describes the findings of detailed simulations performed to investigate the impact of seal teeth cavity leakage flow on the aerodynamic and thermal performance of a three-stage supercritical CO

_{2}

axial compressor. The study compares a shrouded stator configuration (with cavities) to a cantilevered stator configuration (without cavities) to highlight their differences. High-fidelity computational fluid dynamics simulations were performed using non-linear harmonic (NLH) and mixing plane assumptions, considering various possible rotor/stator interface configurations for mixing plane calculations. The key performance parameters for each case were compared, and the best-performing configuration selected for further analysis. The individual stage performance parameters are also examined and compared between the cantilevered and shrouded configurations. It was observed that in the shrouded case, the leakage flow enters the cavity downstream of the stator trailing edge and gets entrained into the primary flow upstream of the stator, leading to boundary layer changes at the hub and degradation of stator and downstream rotor performance. Vortical flow structures were also observed in the stator wells, which tended to change the flow angles around the region, thereby affecting mixing and velocity distribution, resulting in a slight deterioration of compressor performance. Additionally, the study examines windage heating due to shear work from rotating walls, including the seal teeth surface. The amount of shear work done on the leakage flow and the corresponding rise in fluid temperature were quantified, tabulated, and further compared with a simple analytical model, showing good agreement between them and, hence, validating the numerical approach used. Full article

(This article belongs to the Special Issue New Advances in Heat Transfer and Fluid Flow)

► Show Figures

Figure 1

21 pages, 16188 KiB

Open AccessFeature PaperArticle

Influence of Gravity on Passively Cooled Heat Sink Using Experimental Data and Finite Element Analysis

by George-Gabriel Chiriac, Cătălin Gabriel Dumitraș, Dragoș Florin Chitariu, Petrică Vizureanu and Andrei Victor Sandu

Processes 2023, 11(3), 896; https://doi.org/10.3390/pr11030896 - 16 Mar 2023

Viewed by 1192

Abstract

This paper studies the effect of gravity orientation on a heat sink, used to passively cool a thick film resistor, by changing the assembly orientation. Using the same geometry and boundary conditions as in the experimental setup, finite element simulations were conducted to [...] Read more.

This paper studies the effect of gravity orientation on a heat sink, used to passively cool a thick film resistor, by changing the assembly orientation. Using the same geometry and boundary conditions as in the experimental setup, finite element simulations were conducted to evaluate the accuracy of Siemens Flotherm XT 2021.2 simulation software. In order to determine the influence of heat sink orientation, experimental measurements were performed on the resistor and heat sink temperature using thermocouples. Siemens Simcenter Flotherm XT 2021.2 software (Siemens, Munich, Germany) was used to perform finite element simulation. The influence of the heat sink position was evaluated on two setups, one where the resistor is placed directly on the heat sink using screws, and the second one, where a thermal pad was placed between the resistor and the heat sink. Screws were to clamp the parts in both cases. In total, four experiments and simulations were performed with two assemblies with two different gravity orientations for each assembly. In all the cases, the heat sink was placed on a wooden structure to prevent heat transfer through conduction, due to poor thermal conductivity of wood, and to allow unrestricted air flow underneath and around the heat sink. The first simulation was then calibrated for the first scenario, and the rest of the simulations were made using the calibrated one. No other changes in boundary conditions were made. Temperature measurements show an improved cooling when the air speed between the heat sink fins is enhanced due to natural hot air movement generated by the gravity. Gravity has an influence on the cooling regardless of the presence or absence of a thermal interface material. Measured temperatures were reduced up to 8.2 °C due to the rotation of the heatsink. Finite element analysis shows similar temperature values to the measured ones in all the scenarios. Full article

(This article belongs to the Special Issue New Advances in Heat Transfer and Fluid Flow)

► Show Figures

Figure 1

16 pages, 4516 KiB

Open AccessArticle

Boiling Heat Transfer Characteristics of Porous Microchannel with Pore-Forming Agent

by Qinhui Lei, Donghui Zhang, Lei Feng, Jijin Mao and Daifen Chen

Processes 2023, 11(2), 617; https://doi.org/10.3390/pr11020617 - 17 Feb 2023

Cited by 1 | Viewed by 1100

Abstract

Traditional microchannel needs to face the flow-reversal difficulty in high heat fluxes due to limited space. It results in large pressure and temperature fluctuation. Porous microchannels arouse more interest to provide a new solution to this problem. Flow boiling experiments in porous microchannels [...] Read more.

Traditional microchannel needs to face the flow-reversal difficulty in high heat fluxes due to limited space. It results in large pressure and temperature fluctuation. Porous microchannels arouse more interest to provide a new solution to this problem. Flow boiling experiments in porous microchannels with PFA were investigated. Porous microchannels were sintered by 10 μm (or 30 μm) spherical copper particles with pore-forming agent (Na₂CO₃, 60–90 μm). Porous microchannels were composed of 23 parallel porous microchannels with 600 μm in width and 1200 μm in depth.The addition of PFA (pore-forming agent) could increase the sample porosity. For Q10 series, sample porosities increase from 20.4% to 52.9% with the PFA percentage change from 0% to 40%, while for the Q30 series they increase from 26.6% to 47.5%. Experimental results showed the boiling heat transfer coefficient (HTC) reached the maximum at the moderate porosity for both Q10 and Q30 series. Too large or too small porosity would degrade boiling heat transfer performance. It demonstrated that there existed an optimal range of PFA content for sintered microchannels. PFA content has a minor effect on the average pressure drop and would not cause the rapid increase in flow resistance. Visual observation disclosed that the sample porosity would affect the pressure instability significantly. The sample with moderate porosity showed periodic pressure fluctuation and could establish rhythmical boiling. Particle size also exerted a certain influence on the boiling heat transfer performance. Q30 series could achieve higher HTC and CHF (Critical heat flux) than Q10 series. This is attributed to the larger ratio of layer-thickness-to-particle-size (δ/d) for Q10-series samples. Full article

(This article belongs to the Special Issue New Advances in Heat Transfer and Fluid Flow)

► Show Figures

Figure 1

15 pages, 6053 KiB

Open AccessArticle

Numerical Analysis of the Free-Falling Process of a Water Droplet at Different Temperatures

by Yuchao Song, Yafei Zhang and Hongtao Gao

Processes 2023, 11(1), 258; https://doi.org/10.3390/pr11010258 - 13 Jan 2023

Cited by 1 | Viewed by 2502

Abstract

The collision behavior and ice formation of a water droplet are affected by its falling process. In this paper, the two-phase flow of air and a water droplet at a specific temperature is adopted to investigate the processes of falling and freezing of [...] Read more.

The collision behavior and ice formation of a water droplet are affected by its falling process. In this paper, the two-phase flow of air and a water droplet at a specific temperature is adopted to investigate the processes of falling and freezing of a single water droplet. To track the air–water droplet interface and the temperature distribution, the level-set method and the non-isothermal flow coupling method are used, and the freezing model is added into the water’s control equations. The numerical results indicated that with the initial temperature at 283.15 K and the spherical shape, the water droplet changes to the shape of a straw hat at 293.15 K and a drum at 293.15 K but an oval face in freezing temperatures at 0.10 s. There is an obvious drop in the downward velocity when the water droplet falls in mild temperatures at 0.09 s. The downward velocity of the water droplet in air at sub-zero temperatures has a continuous increase during the time span from 0 s to 0.10 s. There is also an obvious difference when the water droplet impinges on the solid bottom. Lastly, the freezing of sessile water droplets attached on the horizontal surface is helpful to reveal the unique phase change process of water droplets in cold air. Full article

(This article belongs to the Special Issue New Advances in Heat Transfer and Fluid Flow)

► Show Figures

Figure 1

16 pages, 10186 KiB

Open AccessArticle

Numerical Study of Inclination Effect of the Floating Solar Still Fitted with a Baffle in 3D Double Diffusive Natural Convection

by Mohammed A. Almeshaal and Chemseddine Maatki

Processes 2022, 10(8), 1607; https://doi.org/10.3390/pr10081607 - 13 Aug 2022

Cited by 1 | Viewed by 1143

Abstract

A three-dimensional computational study of double-diffusive natural convection was conducted to explore the impact of tilt on the thermal and solutal performance of a floating pyramidal solar still filled with an air-steam mixture. In the present work, the still is cooled from the [...] Read more.

A three-dimensional computational study of double-diffusive natural convection was conducted to explore the impact of tilt on the thermal and solutal performance of a floating pyramidal solar still filled with an air-steam mixture. In the present work, the still is cooled from the upper walls and is maintained at a low vapor concentration. The bottom wall of the still is maintained at a hot temperature and high concentration. Four different models of baffles placed in the upper region of the solar still have been studied. The mathematical formulation of the equations governing the problem is based on the vector current potential -vorticity formalism. The numerical method of finite volumes is used. The effect of Rayleigh and tilt angle of the floating solar still on the flow structure, iso-temperatures, iso-concentrations, and heat and mass transfer rates were examined. The most relevant results of this study are (i) an uncooled air-vapor mixture outlet was observed during tilting for the solar still equipped with a small, flat baffle, (ii) triangular and curvilinear baffle configurations are suitable to guide the air-vapor mixture towards the cold walls during the tilting of the solar still floating on the sea, and (iii) the triangular baffle configuration is the most relevant design, enhancing thermal and solutal performance by 20%. Full article

(This article belongs to the Special Issue New Advances in Heat Transfer and Fluid Flow)

► Show Figures

Figure 1

15 pages, 16124 KiB

Open AccessEditor’s ChoiceArticle

Shear Strength of Adhesive Bonding of Plastics Intended for High Temperature Plastic Radiators

by Ilya Astrouski, Tereza Kudelova, Josef Kalivoda and Miroslav Raudensky

Processes 2022, 10(5), 806; https://doi.org/10.3390/pr10050806 - 20 Apr 2022

Cited by 3 | Viewed by 3927

Abstract

The use of adhesive joints has increased in recent decades due to their competitive features in comparison with other joining methods. They can be used in specific applications where there is no possibility to use alternative connection techniques. Adhesive bonding was used to [...] Read more.

The use of adhesive joints has increased in recent decades due to their competitive features in comparison with other joining methods. They can be used in specific applications where there is no possibility to use alternative connection techniques. Adhesive bonding was used to assemble the prototype of a high-temperature car radiator (operated up to 125 °C) with a total of 12,240 plastic tubes. This work aims to estimate the shear strength of different adhesives intended for bonding the plastics used to assemble the above-mentioned high-temperature radiator. Fourteen commercial adhesives were tested with one thermoset plastic (G11 glass fabric epoxy sheets) and two glass-reinforced thermoplastics (polyamide PA66-GF30 and polyphenylene sulfide PPS-GF40). Tests were conducted according EN 1465 to determine tensile lap-shear strength of bonding. Testing showed that only 4 of the 14 adhesives tested exhibit substantial bonding strength at temperatures above 120 °C and only one is resistant at 180 °C. The AS60/AW60 adhesive showed the best results for all three substrates: 1.6 MPa for epoxy sheets and PA66-GF, and 1.4 MPa for PPS-GF40. Additionally, the influence of the surface treatment with cold plasma was evaluated on a clean and activated bonding surface, causing a 30% increase in the shear strength. Full article

(This article belongs to the Special Issue New Advances in Heat Transfer and Fluid Flow)

► Show Figures

Figure 1

14 pages, 2295 KiB

Open AccessArticle

Implementation of Heat Flux Measuring Methods for Heat Transfer Coefficient Determination of In Situ Construction

by Marian Flimel, Darina Duplakova and Enes Sukic

Processes 2021, 9(11), 1970; https://doi.org/10.3390/pr9111970 - 04 Nov 2021

Cited by 1 | Viewed by 1930

Abstract

Subjectively, to verify the human perception of the state of satisfaction with the environment it is necessary to use objective methods. One of these methods is the heat flux measuring method. This paper points out the risk factors that affect the heat transfer [...] Read more.

Subjectively, to verify the human perception of the state of satisfaction with the environment it is necessary to use objective methods. One of these methods is the heat flux measuring method. This paper points out the risk factors that affect the heat transfer coefficient H through building structures that are necessary to determine the projected heat input of the building. At the operation stage, the aforementioned structures are affected by environmental factors (noise, artificial lighting, heat sources). This changes the suggested value H_c to the real value H_r, which is documented by the measurements. The rate of change of the H value is given by the correction “K”. According to the measurements the value obtained can be corrected from 0.08 to 0.25. The final values of the heat transfer coefficient were generalized in the equation and the value of the building energy category within the energy certification of buildings was determined. The result is a methodology for the optimal determination of H values for hazard prevention. Full article

(This article belongs to the Special Issue New Advances in Heat Transfer and Fluid Flow)

► Show Figures

Figure 1

Review

Jump to: Research

20 pages, 757 KiB

Open AccessReview

Modeling Strategies for Crude Oil-Induced Fouling in Heat Exchangers: A Review

by Obaid ur Rehman, Marappa Gounder Ramasamy, Nor Erniza Mohammad Rozali, Shuhaimi Mahadzir, Ali Shaan Manzoor Ghumman and Abdul Hannan Qureshi

Processes 2023, 11(4), 1036; https://doi.org/10.3390/pr11041036 - 29 Mar 2023

Cited by 2 | Viewed by 1587

Abstract

Semi-empirical fouling models have proven more effective in predicting the fouling behavior of crude oils in heat exchangers. These models have aided refineries in optimizing operating conditions to minimize or eliminate fouling in preheat exchangers. Despite their complexity, the models continue to improve [...] Read more.

Semi-empirical fouling models have proven more effective in predicting the fouling behavior of crude oils in heat exchangers. These models have aided refineries in optimizing operating conditions to minimize or eliminate fouling in preheat exchangers. Despite their complexity, the models continue to improve in approximating real behavior by taking into account previously neglected aspects. This paper summarizes these findings from various studies along with highlighting different factors which were considered to enhance the predictability of the models. A critical analysis is presented to emphasize that activation energy in the deposition term varies depending on the physical processes involved and may not conform to the precise definition of activation energy. Two primary modeling approaches for crude oil fouling have emerged, i.e., deterministic and threshold models. Threshold models have gained more attention due to their fewer adjustable parameters. The stability or compatibility of crude oils has a substantial impact on asphaltene deposition, which is a major contributor to fouling. However, incorporating this factor into fouling models has received little attention. The inclusion of parameters for inorganic fraction and ageing has increased predictability by accurately estimating the fouling thickness. The use of CFD to analyze fouling mechanisms is promising, particularly for complex geometries. The dynamic and moving boundary modeling approach has potential to broaden the applicability of fouling models. Full article

(This article belongs to the Special Issue New Advances in Heat Transfer and Fluid Flow)

► Show Figures

Graphical abstract

Journal Menu

Journal Browser

New Advances in Heat Transfer and Fluid Flow

Share This Special Issue

Special Issue Editors

Special Issue Information

Keywords

Published Papers (8 papers)

Research

Review

Further Information

Guidelines

MDPI Initiatives

Follow MDPI