| 1. |
- Moosavi, Amin, et al.
(författare)
-
A comparative study on thermo-fluid characteristics of free and wall-bounded cross-flow heat exchangers
- 2023
-
Ingår i: Thermal Science and Engineering Progress. - : Elsevier. - 2451-9057 .- 2451-9049. ; 40
-
Tidskriftsartikel (refereegranskat)abstract
- In recent years, wall-bounded cross-flow heat exchangers have gained significant attention for battery cooling applications. Due to similarities in geometry, these systems are often evaluated based on the heat and flow knowledge of free cross-flow heat exchangers. To determine the reliability of this assumption, this study performs a numerical comparison of the thermo-fluid behavior of wall-bounded and free cross-flow heat exchangers. Both heat exchangers have similar dimensions, with transverse and longitudinal pitch ratios of 2.074 and 1.037, respectively, and are investigated at a Reynolds number of 40000 using the Unsteady Reynolds-Averaged Navier–Stokes (URANS) method. It is observed that the transition model provides the most accurate predictions of the flow field when compared to available experimental data. The results suggest that for wall-bounded heat exchangers with an aspect ratio of 2 or larger, the flow behavior in the central flow region resembles that of a free heat exchanger, but with varying magnitudes due to the increase in velocity in the core region to counterbalance the reduction near the walls. The area-averaged mean Nusselt number from 2D and 3D models for free heat exchangers shows no significant difference compared to wall-bounded heat exchangers. However, there are considerable differences in the local Nusselt number distributions in the angular and spanwise directions. Overall, it is determined that certain conditions must be satisfied to ensure that applying the thermo-fluid characteristics of a free cross-flow heat exchanger to wall-bounded cross-flow heat exchangers in battery thermal management systems is accurate.
|
|
| 2. |
- Alam, Md Tabrez, et al.
(författare)
-
A comparative analysis on charging performance of triplex-tube heat exchanger under various configurations of composite phase change material
- 2024
-
Ingår i: Thermal Science and Engineering Progress. - : Elsevier Ltd. - 2451-9049. ; 51
-
Tidskriftsartikel (refereegranskat)abstract
- In present work, the melting performance of triplex-tube latent heat thermal energy storage (LHTES) unit was numerically studied using equal volumes of PCM and metal foam composite PCM (CPCM) in various arrangements. For the n-eicosane (as PCM), the study was conducted at the fixed Rayleigh number (Ra) = 4.08x107, Prandtl number (Pr) = 62.9, and Stefan number (Ste) = 0.14. The results showed that positioning the metal foam on the bottom side and distributing segmented CPCM with alternating PCM zones effectively improved the system performance. Moreover, this also prevents the overheating of thermal layers in the LHTES unit. While the model labelled M2 exhibited the highest economic efficiency among all isotropic models, its low dimensionless thermal energy storage (TES) density (i.e., q’ ∼ 0.6) led this study to focus on models falling under the category having a TES density of ∼ 0.8. Compared to a pure PCM model, the configurations under equal volume ratio category demonstrated up to ∼ four times higher TES rate (p’) and the significant reduction of ∼ 75 % in melting time. The optimized isotropic model achieved the highest TES rate per unit cost with peak value of ∼ 3 at a price ratio (N) of 1. Lastly, the testing of metal foam anisotropy on the chosen design showed a substantial increase in melting/heat storage rates. The largest drop of ∼ 33 % in the total melting time was noticed for model M2 as compared to isotropic case.
|
|
| 3. |
- Arjmandi, H., et al.
(författare)
-
Geometric optimization of a double pipe heat exchanger with combined vortex generator and twisted tape : A CFD and response surface methodology (RSM) study
- 2020
-
Ingår i: Thermal Science and Engineering Progress. - : Elsevier. - 2451-9049. ; 18
-
Tidskriftsartikel (refereegranskat)abstract
- In this research, a numerical investigation is done on the effect of employing the new combined vortex generators, the twisted tape turbulator and Al2O3-H2O nanofluid as the involved base fluid. Such study is carried out on the behavior of the heat transfer rate and the pressure drop of a double pipe heat exchanger. Accordingly, the response surface methodology (RSM) grounded on the central composite design (CCD) is used for acquiring the optimized geometry of the combined vortex generator and twisted tape turbulator. In order to have the maximum Nusselt number and minimum friction factor, twenty cases with different pitches ratio Pil=0.09-0.18, angles (θ=0-30°) and Reynolds numbers (Re = 5000-20000) are examined. The Results show that the pitch ratio has a predominant effect on the Nusselt number and the friction factor, which causes an efficiency increase up to five times compared to the original one. In addition, by decreasing the angle of the vortex generators in the new combined turbulator, both Nusselt number and the friction factor are increased.
|
|
| 4. |
- Darbandi, Tayebeh, et al.
(författare)
-
CFD modeling of the forces in the wet scrubber acting on particulate matter released from biomass combustion
- 2021
-
Ingår i: Thermal Science and Engineering Progress. - : Elsevier. - 2451-9049. ; 25
-
Tidskriftsartikel (refereegranskat)abstract
- The flue gas from biomass combustion contains particulate matter, which is a considerable precarious constituent cause of serious health issues. The wet flue gas cleaning method is one of the most efficient solutions for small-scale boilers (≈100 kW) and small particles. In this study, the forces on particulate matter in a wet flue gas cleaning process using an absorption solution have been studied with the implementation of compiled user-defined function code in Ansys Fluent 19.2®. The forces governing the wet cleaning process as well as the corresponding conditions of the system have also been studied. Drag, buoyancy, diffusiophoresis, and thermophoresis forces have been analyzed as the most important forces acting on particulate matters. Simulations have been conducted for velocities, particle sizes, temperatures, and water vapor mass fractions within the same range as experiments in order to acquire trends for particle collection for these variables.Moreover, the influence of diffusiophoresis force was compared to that of the thermophoresis force under different conditions. It was unveiled that the diffusiophoresis force had a significant effect on nanoparticle collection. The impact of diffusiophoresis is increased by the ascending gradient of temperature as well as water vapor mass fraction. Simulations declare that the thermophoresis force effect is small compared to the diffusiophoresis force effect in the particle collection process. Thereby, one could conclude that the diffusiophoresis force governs the collection of particulate matter in the wet scrubber method. The model validation is confirmed by comparing the results with previous empirical models.
|
|
| 5. |
- Darbandi, Tayebeh, et al.
(författare)
-
Effect of operation conditions on particulate matter removal by a packed-bed wet scrubber for a small-scale biofuel boiler
- 2024
-
Ingår i: Thermal Science and Engineering Progress. - : Elsevier. - 2451-9049. ; 47
-
Tidskriftsartikel (refereegranskat)abstract
- In 2013 the EU’s Clean Air Policy Package was established, aiming to reduce air pollution to half by 2030 compared to the level in 2005. Small-scale (<500 kW)biofuel boilers play a key role in particulate matter emission, and exposure to particulate matter even in the short term can cause different diseases. With the aim of reducing particulate matter emission in Europe, this study presents an approach to improve the removal of particulate matter emitted by small-scale boilers. A biofuel combustion boiler was equipped with a packed-bed wet scrubber, and the flue gas emitted through combustion was cleaned through the wet scrubber using a saltwater mixture. The performance of a packed-bed wet scrubber was investigated under different operating conditions. The effect of the salt concentration of the absorption solution, the temperature of the absorption solution fed to the absorber, and the height of the packed-bed material on the particle collection efficiency were measured. The operating conditions were selected based on the results obtained in a previous computational fluid dynamic simulation study. The results obtained in the present study show that an absorption solution temperature of 30 °C and an absorption solution concentration of 75 % with a full height of the packed-bed material lead to the best performance in the system. Totally keeping the absorption solution temperature as low as possible, increasing the absorption solution concentration, and raising the packed-bed material height could improve the particle collection efficiency by enhancing the effect of the diffusiophoresis and thermophoresis forces and the contact time between the flue gas and solution.
|
|
| 6. |
- Ghazanfari Holagh, Shahriyar, et al.
(författare)
-
An experimental investigation on bubbles departure characteristics during sub-cooled flow boiling in a vertical U-shaped channel utilizing high-speed photography
- 2021
-
Ingår i: Thermal Science and Engineering Progress. - : Elsevier BV. - 2451-9049. ; 22
-
Tidskriftsartikel (refereegranskat)abstract
- Classified as a passive heat transfer enhancement technique, U-shaped channels are commonly encountered with applications associated with boiling heat transfer such as air conditioning systems, evaporators, and boilers. On the other hand, understanding heat transfer in flow boiling is heavily dependent upon bubbles dynamic behavior, which is influenced by flow and geometrical conditions. In this paper, bubbles departure characteristics are experimentally studied in upward sub-cooled flow boiling of distilled water in a vertical U-shaped channel. The influence of flow conditions, embracing heat flux, mass flux, and inlet sub-cooling on bubbles characteristics, encompassing departure diameter, growth and waiting times, and nucleation frequency, is investigated through conducting 68 experiments. All the experiments are carried out at atmospheric pressure over a Nichrome heating surface installed on the outer wall of the channel, with heat flux, mass flux, and inlet flow temperature in the ranges of 26.1–61.5 kW.m-2, 114–255kg.m-2s-1, and 1 to 8 °C. A high-speed camera is utilized to capture bubbles growth process and departure instance. The results reveal that as wall heat flux increases and mass flux and inlet sub-cooling decrease, bubbles departure diameter and frequency rise, while waiting time declines. Also, lower growth times are detected when wall heat flux and mass flux increase and inlet sub-cooling declines. Two new correlations are developed to predict present and previously published experimental data of departure diameter and nucleation frequency with mean standard deviations of 18.0% and 18.5%, correspondingly.
|
|
| 7. |
- Liu, Zhan, et al.
(författare)
-
An ultralow-temperature cascade refrigeration unit with natural refrigerant pair R290-R170 : Performance evaluation under different ambient and freezing temperatures
- 2023
-
Ingår i: Thermal Science and Engineering Progress. - 2451-9049. ; 46
-
Tidskriftsartikel (refereegranskat)abstract
- The global demand for ultralow-temperature (ULT) refrigeration units gets greatly promoted, for storage, transportation, and distribution of COVID-19 vaccines. In this work, a ULT freezer is developed with a cascade refrigeration system (CRS) utilizing environmentally friendly refrigerants R290 and R170. The performance of the ULT freezer is experimentally evaluated under different ambient temperatures Tamb and freezing temperatures Tfreezing. The result shows that once the refrigeration system starts, the freezer enters a pull-down period and then reaches stable or periodic on-off operation. The monitored temperatures present drastic variations in the low-temperature cycle (LTC) and show a relatively stable start-up process in the high-temperature cycle (HTC). The monitored temperature rises when Tamb increases from 16 °C to 32 °C. The increasing Tamb brings about a larger temperature drop crossing the pre-cooled condenser, cascade heat exchanger, and high-temperature condenser, and a smaller temperature reduction through the anti-condensation. As Tfreezing decreases from −60 °C to −86 °C, the suction/discharge gas temperatures increase in the low-temperature compressor, while the other monitored temperatures reduce. The largest temperature non-uniformity in the freezer is 9.19 °C, and the lowest wall temperature can reach −90.52 °C. With Tamb ranging from 16 °C to 32 °C, the power consumption of the freezer increases from 896 W to 912 W. When Tfreezing varies from −60 °C to −86 °C, the CRS's consumed power reduces from 804 W to 904 W. The present freezer can easily obtain low temperatures e.g., −81 °C, and reach a lower temperature, such as −86 °C with proper improvements to reduce cold loss.
|
|
| 8. |
- Liu, Zhan, et al.
(författare)
-
Investigation on the pressurized discharge performance from a liquid oxygen tank under different injected gas temperatures
- 2022
-
Ingår i: Thermal Science and Engineering Progress. - : Elsevier BV. - 2451-9049. ; 32
-
Tidskriftsartikel (refereegranskat)abstract
- Accurate prediction on the pressurized discharge performance is significant to the safety operation of cryogenic propellant system. In the present study, a two-dimensional numerical model is established to simulate the fuel outflow with high-temperature gas injection. Both the environmental heat invasion and interfacial phase change are detailedly considered. The volume of fluid method is used to predict the distribution of the liquid-vapor interface, and the low Re k-ε turbulent model is adopted to simulate the pressurized discharge of liquid oxygen. The liquid hydrogen discharge tests, under the gas hydrogen injection, are selected to validate the developed numerical model, and the fluid temperature of the symmetry axis of the liquid hydrogen tank is selected as the comparison parameter. It shows that the present numerical model has good prediction accuracy with calculation deviations being less than 20%. Based on the developed numerical model, the effect of the injected gas temperature on the pressurized discharge of liquid oxygen is investigated and analyzed. Some valuable conclusions are achieved. The present work could strengthen the researchers’ understanding on the thermodynamic behavior during pressurized discharge and might supply some technique supports for the design and optimization of cryogenic propellant systems.
|
|
| 9. |
- Roberto Caetano, N., et al.
(författare)
-
Assessment of mathematical models for prediction of thermal radiation heat loss from laminar and turbulent jet non-premixed flames
- 2018
-
Ingår i: Thermal Science and Engineering Progress. - : Elsevier Ltd. - 2451-9049. ; 7, s. 241-247
-
Tidskriftsartikel (refereegranskat)abstract
- Radiation plays an important role in several processes, being of particular interest to energy efficiency and safety of staff and facilities, mainly in the aerospace industry. In this context, along the last years mathematical models have been developed and reported in the literature aiming to obtain reliable predictions of thermal radiation in combustion applications. Some simplified models consider that thermal radiation emmited by a flame is mainly governed by the flame temperature, while other ones also account for the contribution of the combustion products. On the other hand, more detailed models include both flame geometry and composition. Many efforts have been made by several scientists in order to develop these models, however, there is no validation applied in different operating conditions found in the literature. Thus, the novelty brought by this work consists in an assessment on the comparison between the experimental data of thermal radiation emitted by jet non-premixed flames and the results obtained by calculations applying these models on several flame conditions, encompassing a wide range of applications: laminar and turbulent flames, buoyancy and momentum-driven flames, low-carbon and high-carbon fuels. Such assessments are important to assist combustion system designers on selecting the most adequate thermal radiation model during the project of a combustion system or process. The results found in the current investigation pointed out to a good agreement between experimental data and predictions obtained by detailed models, which consider flame geometry and radiative properties. On the other hand, simplified models must be avoided if accurate predictions of radiation are being sought, despite this, they can be employed as engineering tools for risk analysis, once, in general, they provided higher predictions when compared to the experiments, resulting in a safety factor to engineers and designers.
|
|
| 10. |
- Sun, Jie, et al.
(författare)
-
Thermomechanical performances of sandwich panels with multi-layer multi-row lightening holes : Comparative study on corrugated-core and X-core
- 2023
-
Ingår i: Thermal Science and Engineering Progress. - 2451-9049. ; 43
-
Tidskriftsartikel (refereegranskat)abstract
- In the present study, corrugated-core and X-core sandwich panels with multi-layer and multi-row lightening holes are designed from the perspective of extending the thermal short-circuit path. The thermal insulation performance and load-bearing capacity of the integrated thermal protection structure are investigated and enhanced by sequential thermal–mechanical coupling method. For the corrugated-core sandwich structure, heat proofing effect of schemes altering the quantity of lightening holes along the vertical and lateral directions is relatively similar. Compared to a solid corrugated panel, the maximum temperature of the bottom panel is reduced by up to 86.7 K after arranging the lightening holes. Under the joint effect of temperature load and aerodynamic pressure load, the equivalent stress of double-layer lightening holes at the bolted joints is slightly above the material yield strength. X-panel with three kinds of lightening holes decreases the maximum temperature by 54 K, 60 K and 76 K, respectively, compared to that without lightening holes. Increasing the number of lightening holes along the thickness direction has a noticeable effect on the insulation performance within the safety limits. Special X-shaped structure enhances the structural stability, which has a maximum deformation of merely 0.29 mm. Overall temperature of the X panel is lower than that of the corrugated plate by 39–63 K and has better uniformity of the temperature distribution on the bottom panel. These findings enlighten that passive thermal protection technologies could focus on the direction of setting multiple barriers along the direction of temperature transfer.
|
|
| 11. |
- Terekhov, V. I., et al.
(författare)
-
Intensification of heat transfer behind the backward-facing step using tabs
- 2022
-
Ingår i: Thermal Science and Engineering Progress. - : Elsevier BV. - 2451-9049. ; 35
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of tab size and location on the flow structure, distribution of pressures on the surface, and heat transfer in the separation region behind the backward-facing step at Reynolds number Re = 4000 was experimentally investigated. The effect of tabs on the distribution of the local pressure and heat transfer coefficients in the longitudinal and transversal directions was studied. The presence of tabs significantly intensifies the heat transfer directly behind the separation point and brings the region of maximum heat transfer closer to the step. There is a strong uneven distribution of pressure coefficients and Nusselt numbers in the transverse direction due to the formation of vortical wake. The results of measurements are compared with the case of using two-dimensional obstacles in the form of solid ribs; the features of the development of the flow and heat transfer behind 3D tabs are analyzed. It is shown that the main difference in the installation of two-dimensional and three-dimensional obstacles is observed mainly in the immediate vicinity of the flow separation point at X/H < 6.
|
|
| 12. |
- Vakkada Ramachandran, Abhilash, et al.
(författare)
-
Numerical heat transfer study of a space environmental testing facility using COMSOL Multiphysics
- 2022
-
Ingår i: Thermal Science and Engineering Progress. - : Elsevier. - 2451-9049. ; 29
-
Tidskriftsartikel (refereegranskat)abstract
- Environmental chambers are used to test the expected performance of space instrumentation and to investigate certain processes which are relevant in space or other planetary environments. In this study, a computational model of an existing Martian experimental facility is investigated numerically using COMSOL Multiphysics. For this purpose, we simulate the near surface water cycle under Martian temperature and pressure experimental conditions as tested inside the chamber and we compare the simulations with the experimental data. The model shows good agreement with experiments on the equilibration time scales and thermal gradients. Due to the imposibility to place sensors at multiple locations inside the chamber, we use the model to extrapolate the one-point relative humidity of the experimental data to each grid points in the simulation. This model gives an understanding of the gradient in atmospheric water relative humidity to which the experimental samples such as deliquescent salts and Martian regolith simulants are exposed at different time intervals. The of the performance of HABIT instrument during the tests, of the ESA/IKI ExoMars 2022 robotic mission to Mars, when compared with the model shows the existence of an extra internal heating source of about 1 W which can be attributed to the hydration and deliquescence of the salts exposed to Martian conditions when in contact with atmospheric moisture. In addition, the presented model is used to predict the thermal gradients and understand the time response when the chamber is heated in vacuum conditions. Our analysis shows that for thermal vacuum tests, the chamber will take about 2.5 h to reach the test temperature of 420 K.
|
|
| 13. |
- Zaini, Ilman Nuran, et al.
(författare)
-
A pilot-scale test of plasma torch application for decarbonising the steel reheating furnaces
- 2023
-
Ingår i: THERMAL SCIENCE AND ENGINEERING PROGRESS. - : Elsevier BV. - 2451-9049. ; 40
-
Tidskriftsartikel (refereegranskat)abstract
- The decarbonisation of the Swedish iron and steel industry is crucial in achieving Sweden's target to achieve zero net emissions of greenhouse gases (GHG) by 2045. Direct electrification of industrial furnaces could be an important milestone in decarbonising the iron and steel plants. In this study, pilot-scale trials were performed to investigate the possibility of plasma torch application for steel reheating furnaces. A 250 kW DC plasma torch was used to heat the furnace from room to the operating temperature of 1200 degrees C. Different plasma carrier gases were then used to study their impact on the plasma torch efficiency, furnace temperature profile, NOX emission, and steel oxidation. The results show that the furnace could be heated at a relatively uniform temperature and reasonable time. The combination of air and LPG in the plasma generator provides the most uniform temperature distribution and highest plasma torch efficiency, but it generates the highest NOX emission. N2 as plasma gas resulted in notably poorer temperature distribution and lower plasma torch efficiency; however, it can suppress the oxide formations. Meanwhile, CO2 as plasma gas could be a promising option among the studied gas mixtures as it can provide a good heating performance with a low NOX formation. In summary, the current study has proved that it is practical and functionally possible to heat steel using plasma technology.
|
|
