Applied Thermal Engineering最新文献

{"title":"Experimental study and optimization analysis of start control strategy for the transcritical carbon dioxide heat pump","authors":"","doi":"10.1016/j.applthermaleng.2024.124344","DOIUrl":"10.1016/j.applthermaleng.2024.124344","url":null,"abstract":"<div><p>Transcritical carbon dioxide heat pump (TCHP) water heaters hold great promise for widespread adoption in the field of sustainable energy. Due to the high discharge temperature and pressure, inappropriate control strategies can easily lead to the shutdown of the system during the start-up phase. However, the current research has focused on control strategies for the stable operation of TCHP system, without experimental research on the control strategies for the start-up stage. In this study, a TCHP system was constructed to explore the optimal initial opening degree of the electronic expansion valve (EEV) using experimental methods, and the EEV control rules and compressor frequency rising rules in the start-up phase were optimized. Furthermore, the changing characteristics of key parameters under different strategies were analyzed. The results demonstrate that the stability of the system during the start-up phase is maximized when the initial EEV opening degree is set to 300. Furthermore, by employing a compressor frequency rising rule of running at 50 r/s for 60 s, 60 r/s for 60 s, and 90 r/s for 60 s, the total power fluctuation is minimized, resulting in a total power in the three stages of 1073, 1686, and 2152 W, respectively. Additionally, when targeting a discharge pressure range of 8.5–––9.0 MPa controlled by the EEV, the maximum discharge pressure at a water temperature of 60 ℃ is 9.8 MPa, with the EEV opening degree falling within the range of 200–––450. The results are of significant reference value for determining the initial EEV opening degree and the target value of the discharge pressure during the start-up phase of TCHP systems. The optimized start control strategy effectively improves the TCHP system stability during the start-up phase.</p></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142150896","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Heat transfer enhancement of solar collector tube enhanced by swirling flow","authors":"","doi":"10.1016/j.applthermaleng.2024.124346","DOIUrl":"10.1016/j.applthermaleng.2024.124346","url":null,"abstract":"<div><p>Heat transfer capability was one of the key factors that restricted the collecting efficiency of the parabolic trough collector tube. In this paper, a swirl-enhanced solar collector tube with a cyclone inserted at the inlet of the metal tube was purposed to improve the heat transfer capability of the collector tube. The cyclone induced a swirling flow and improved the convection inside the tube, thereby enhancing the heat transfer capacity of the tube. The advantage of the cyclone tube was not changing the structure and processing technology of the original heat collector tube. A numerical model was established to study the flow and heat transfer characteristics of the cyclone tube using Ansys CFX software. The results demonstrated that the swirling flow was over a distance exceeding 1 m and the fluctuations in turbulent kinetic energy was within a distance of approximately 0.2 m. The heat transfer capacity was significantly enhanced within this 0.2 m region and the maximum normalized Nusselt number reached 2.81. Finally, the influences of the blade length and the blade numbers on the heat transfer capability were researched. Results showed that cyclone with short blades and more blades resulted in better enhancing effects.</p></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142150893","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Experimental study on the heat transfer characteristics of flat-plate micro heat pipe arrays with grooved porous wick structure and porous copper foam inserts","authors":"","doi":"10.1016/j.applthermaleng.2024.124251","DOIUrl":"10.1016/j.applthermaleng.2024.124251","url":null,"abstract":"<div><p>The high-speed development of 5G technology and electronic components has provided an opportunity for micro heat pipe arrays (MHPAs). This study proposes a grooved multi-hole wick structure heat pipe (MHPA-CFW) with an MHPA micro-fin structure injected with copper foam to enhance the heat transfer performance. The study investigates how the heat transfer capability of MHPA-CFW is affected by the pore density and width of copper foam. It also examines its ability to function against gravity at various working inclinations. Experimental findings demonstrate that the MHPA-CFW exhibits superior heat transfer capability compared with that of MHPA. Under vertical operation, the heat transfer capability increases as the pore density rises at the low heat flux. However, it initially improves and then weakens with an increase in the pore density when the heat flux exceeds 3.75 <!--> <!-->W/cm². The heat transfer capability deteriorates as the copper foam width increases. A 4#MHPA-CFW (95PPI, 1.0 mm) was chosen for the multi-orientation experiment. Results indicate that it significantly enhances the heat transfer capability by overcoming the effects of gravity when the working inclination angle changes from 90° to −10°. These results provide a reference for improving heat transfer and expanding heat pipe applications in electronic heat dissipation.</p></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2024-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142150881","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Spray and flame characteristics of an ultra-compact combustor for gas turbines","authors":"","doi":"10.1016/j.applthermaleng.2024.124356","DOIUrl":"10.1016/j.applthermaleng.2024.124356","url":null,"abstract":"<div><p>Ultra-compact combustors have received much attention in the development of gas turbines for transportation because of their advantages of compactness, low emissions, and cost. There is an urgent need for a more detailed investigation of the fuel arrangement, ignition process, and flame characteristics in the near-wall region. This study experimentally investigated the effects of the first nozzle position closest to the cavity/mainstream interface on the spray and flame characteristics in an ultra-compact combustor based on a radial flame stabilizer and a circumferential cavity. On this basis, four different nozzle positions were designed. Detailed experimental studies on the fuel injection position of the near-circumferential stabilizer concerning the fuel jet trajectory, droplet size distribution, lean light-off (LLO)/lean blow-out (LBO) limit, ignition process, and flame distribution characteristics were carried out via a CCD camera, a high-speed camera, and a laser particle sizer. Compared with the injection position farthest from the cavity, within the experimental range, the fuel injection position closest to the cavity increased the maximum jet penetration depth by 58 %, increased the average SMD by 127 %, and decreased the FAR of LLO by 76 %. On the basis of the obtained fuel droplet particle size distribution and flame kernel propagation path, a correlation analysis of the fuel droplet motion path, flow field characteristics, and flame kernel propagation path was carried out. The mechanism of the influence of different nozzle positions on the fuel distribution and ignition process was revealed. In addition, the closer the fuel nozzle was, the more uniformly the flame was distributed in the circumferential direction, which could effectively improve the combustor compactness, but simultaneously produce the problem of high wall temperature.</p></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2024-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142150951","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Straight ultra-thin vapor chambers tested under different modes for different vapor duct thicknesses","authors":"","doi":"10.1016/j.applthermaleng.2024.124353","DOIUrl":"10.1016/j.applthermaleng.2024.124353","url":null,"abstract":"<div><p>This study aims to demonstrate, through careful temperature measurements and infrared images, that tests for a vapor chamber (VC) under a VC mode or a heat pipe (HP) mode, reach very different thermal performances due to different severities for water accumulation at the condenser end. Both modes have been frequently adopted in the literature with the difference overlooked. Experiments are conducted for 100 × 20 mm² straight ultra-thin vapor chambers (UTVCs) with a 0.17 mm or a 0.12 mm vapor duct thickness and a total thickness of 0.45 mm or 0.4 mm, respectively. Three different charges, an over-charge, a charge with the charge ratio slightly larger than 1.0, and an under-charge, are prepared for each vapor duct thickness. Severe water accumulation over the condenser is observed under the HP mode, yielding drastic temperature drops therein. Under the HP mode the maximum heat transfer rate (<em>Q</em>_max) drops to about only 3–4 W with vapor duct thickness (<em>h</em>) = 0.17 mm and fails at actual vapor input ∼3 W with <em>h</em> = 0.12 mm. Water accumulation cannot be totally removed in the HP mode when the UTVC is placed vertically, although slight improvement on the thermal performance can be achieved with the assistance of gravity. Under a HP mode, the minimum vapor chamber resistance (<em>R</em>_min) ranges between 0.7–1.0 K/W, while under a VC mode <em>R</em>_min is 0.14–0.29 K/W. <em>Q</em>_max appears slightly reduced for the thinner vapor duct thickness due to the larger vapor resistance.</p></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2024-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142150897","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Experimental study on a pump-driven CO2 two-phase thermosyphon loop","authors":"","doi":"10.1016/j.applthermaleng.2024.124324","DOIUrl":"10.1016/j.applthermaleng.2024.124324","url":null,"abstract":"<div><p>In order to better understanding the internal operating principles of liquid pump-driven two-phase thermosyphon loop (LPTPTL) and promote the application of environmentally friendly working fluids, a LPTPTL using CO₂ as the working fluid was studied through experiment. Both the operating mechanisms and performance of the CO₂ LPTPTL was investigated. It was found that the impact of the pump on the two-phase thermosyphon loop (TPTL) varies significantly across different operation stages. During the oscillatory operation stage, activating the liquid pump eliminated the geyser boiling in the loop and made the TPTL to transition from oscillatory to stable operation. During the normal operation stage, the pump power had little effect on the total thermal resistance of the TPTL. While the system’s EER (Energy Efficiency Ratio) significantly decreased with the increasing pump power. During the overload operation stage, activating the liquid pump helped alleviate overheating or subcooling in the loop. With the pump power increasing from 3.0 W to 18.8 W, the heat transfer limit of the TPTL increased from 1800 W to 3300 W, while the system’s EER decreased from 600 to 176. This study proves the feasibility of CO₂ LPTPTL, and provides theoretical guidance for its real application.</p></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2024-09-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142150956","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Investigation of irreversible losses in subsonic compressor cascade flow field: A study on viscous dissipation and temperature gradient term in entropy production rate","authors":"","doi":"10.1016/j.applthermaleng.2024.124312","DOIUrl":"10.1016/j.applthermaleng.2024.124312","url":null,"abstract":"<div><p>The entropy generation rate is a widely employed loss characterization approach in the design and optimization of fluid machinery. This approach is utilized to quantitatively determine various types of losses in the flow field, and it is considered that the temperature gradient term in the entropy generation rate can characterize irreversible losses. This research paper aims to address the question of whether the temperature gradient term in entropy production rate can represent the irreversible losses in a flow field. By employing the Reynolds-Averaged Navier-Stokes (RANS) numerical simulation method, the flow field of a subsonic compressor cascade, both with and without wall heating, was investigated. Statistical analysis was conducted to examine the contributions of viscous dissipation, the temperature gradient term in entropy production rate, wall shear stress work, and global power loss. The study reveals the distribution differences of viscous dissipation and the temperature gradient term in entropy production rate within the separated flow region. The research results demonstrate that, under wall heating conditions, viscous dissipation increased by approximately 45%, and the ratio of the temperature gradient term to global power loss increased from 4% to 125%, exceeding the mechanical energy loss in the flow field. The distribution of the temperature gradient term within the separated flow region cannot be explained by irreversible losses, and it exhibits significant discrepancies with the distribution of viscous dissipation losses. Therefore, the temperature gradient term in entropy production rate cannot represent the local irreversible losses, whereas viscous dissipation serves as an accurate measure of local irreversible losses. The research results provide theoretical support for accurately determining the irreversible losses in the flow field.</p></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2024-09-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142150895","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Numerical investigation of the influence of heat-generating components on the heat dissipation in a tower server","authors":"","doi":"10.1016/j.applthermaleng.2024.124313","DOIUrl":"10.1016/j.applthermaleng.2024.124313","url":null,"abstract":"<div><p>Many of today’s servers rely on high-power electronic components. During continuous operation, elevated temperatures can lead to sluggish performance and system instability. Therefore, servers urgently require safe and reliable heat dissipation systems. In this work, we focus on a highly scalable tower server as our research subject, exploring its maximum configuration within the designated range. We aim to enhance the server’s thermal performance through a parametric investigation of factors such as the server air outlet, the FAR in air outlet, and the layout of GPUs. The results demonstrate that narrowing the air outlet can effectively reduce the temperature of GPU-2 by 2.83 °C. Further analysis reveals that an optimal FAR of 0.74 for the air outlet leads to a temperature decrease of 1.67 °C for GPU-2 compared to a FAR of 0.24. Moreover, adjusting the position of GPU-2, specifically employing the VLO-L71.16-1 structure with the air outlet positioned on the GPU-1 side, yields optimal heat dissipation performance, resulting in a remarkable temperature decrease of 16.63 °C for GPU-2. Additionally, it was observed that GPU-2 in the base case approaches its limiting temperature. By optimizing the structure to VLO-L71.16-1, the study managed to reduce fan airflow while maintaining GPU-2 within safe operating temperatures. Specifically, the optimal structure achieves approximately 35 % airflow savings when GPU-2 reaches its limiting temperature. This research provides valuable insights for the exploration and design of novel server cooling systems.</p></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2024-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142150955","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Comparison between conduction models and models including the energy balance along the flow, for the simulation of U-tube borehole heat exchangers","authors":"","doi":"10.1016/j.applthermaleng.2024.124311","DOIUrl":"10.1016/j.applthermaleng.2024.124311","url":null,"abstract":"<div><p>Most ground-coupled heat pumps exchange heat with the ground by means of a borehole-heat-exchanger (BHE) field. The time evolution of the fluid temperature at the outlet of the BHE field, employed for the design of the heat pump, is often determined starting from that of the mean temperature of the surface between the BHEs and the ground, evaluated by means of a dimensionless function called <em>g-function</em>. In order to obtain an accurate thermal response to peak loads, this method must be coupled with a short-term simulation tool. Simulation models that yield accurately the time evolution of either the outlet fluid temperature or the mean fluid temperature both in the short and in the long term are also available. The simplest of these models, called here conduction models, represent the fluid by a solid that receives or generates heat. Models that include the energy balance for the flow along the pipes, called here complete models, have also been proposed. Complete models are the most accurate, but can hardly be applied for long-term simulations. In this paper, the results of finite-element simulations of U-tube BHES performed by conduction models are compared with those obtained by complete models, implemented through the COMSOL Pipe Flow Module. It is shown that there is an excellent agreement between the models in the short term, while complete models yield slightly higher values of the mean fluid temperature in the medium and long term. It is also shown that one can obtain by a conduction model the same time evolution of the mean fluid temperature that would be yielded by a complete model, replacing the real 2D BHE thermal resistance, <em>R_b</em>_2D, with a virtual one, equal to the asymptotic value of the 3D thermal resistance yielded by the complete model, <em>R_bPF</em>. For BHEs with length 100 m, diameter 152 mm, grout thermal conductivity 1.6 W/(m K), ground thermal conductivity 1.8 W/(m K) and flow rate 14 L per minute, the ratio <em>R_bPF</em>/<em>R_b</em>_2D is, for instance, 1.032 for a single U-tube BHE with shank spacing <em>s</em> = 94 mm, and 1.090 for a double U-tube BHE with <em>s</em> = 85 mm. Dimensionless correlations yielding the value of <em>R_bPF</em>/<em>R_b</em>_2D for any U-tube BHE will be provided in a future paper.</p></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2024-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S1359431124019793/pdfft?md5=f0641e332766d8c496f83b13f658e1d6&pid=1-s2.0-S1359431124019793-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142150898","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Optimization of glass spray tempering parameters based on response surface methodology and economic analysis","authors":"","doi":"10.1016/j.applthermaleng.2024.124297","DOIUrl":"10.1016/j.applthermaleng.2024.124297","url":null,"abstract":"<div><p>Glass curtain walls have gained significant popularity as building enclosure structures, owing to their exceptional performance. Consequently, it becomes imperative to reduce energy consumption during the glass tempering process to ensure sustainable development within the construction industry. In this study, an experimental design was conducted using the response surface methodology (RSM). The particle count and cooling energy consumption were selected as the response value, while the influencing factors included four process parameters, namely, the spray distance (<em>H</em>), mist load fraction (<em>f</em>), spray pressure (<em>p</em>), and final cooling temperature (<em>T</em>_z). The second order model fitting of the RSM was used to obtain the polynomial regression equation between each response and each factor. Under the optimized conditions of <em>H</em> = 200 mm, <em>f</em> = 1.03, <em>p</em> = 0.5 MPa, and <em>T</em>_z = 150 °C, the number of fractured glass particles was found to be 234, and the cooling energy consumption was 0.00048 kW·h. Further analysis indicated that under these spray conditions, the net present value was 523.90 k$, and the dynamic payback period was 1.1 years. Compared to traditional air-cooled tempering, spray tempering demonstrated superior economic performance.</p></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2024-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142150952","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}