701 research outputs found
Uniformity of Supply Air in the Plenum for Under-Floor Air Distribution Ventilation in a Circular Conference Room: A CFD Study
Underfloor air distribution (UFAD) systems are increasingly used for their advantages in improving energy savings, indoor air quality, and thermal comfort. In UFAD systems, an underfloor plenum delivers conditioned air to the air supply diffusers. The distribution of internal air velocity and static pressure in plenums determines the uniformity of the airflow to the occupied zones. As a result, the plenum has a detrimental effect on the characteristics of the supply air and, thus, the resulting indoor air quality and thermal comfort. Nevertheless, most existing studies on underfloor plenums focused on small-scale plenums with a single internal air duct. Large plenums and multiple air ducts in UFAD equipped in large premises are underexplored. In this study, a circular underfloor plenum with a large scale (radius of 15 m, height difference of 0.9−2.9 m) and 503 under-seat diffusers in a conference room was studied using computational fluid dynamics (CFD) simulation (ANSYS Fluent (16.0)). The distributions of airflow velocity and static pressure inside the plenum were analyzed and compared to one concentrated air supply mode and three uniform air supply modes. Based on the air velocity at the center of under-seat diffusers, the outgoing airflow uniformity from the diffusers under four cases was evaluated by the index of air velocity uniformity. The results showed that the multiple supply ducts with bottom air outlets yielded the best uniformity of supply air. The findings of this paper are expected to provide a technical basis for realizing the optimal design of the UFAD system in terms of uniformity of supply airpublishedVersio
Revisiting the Ocean Color Algorithms for Particulate Organic Carbon and Chlorophyll-a Concentrations in the Ross Sea
The Ross Sea is the most productive marginal sea in the Southern Ocean and plays an important role in carbon cycling. However, limited sampling of Chlorophyll-a (Chl) and particulate organic carbon (POC) concentrations from research expeditions constrains our understanding of the biogeochemical processes there. Satellites provide a useful tool for synoptic mapping of surface water properties on regional and global scales, yet the general applicability of the published algorithms in the Ross Sea is poorly known. Based on the data collected from 18 cruises in the past 20 years, we analyzed both the NASA standard and locally developed Chl and POC algorithms applicable to the Ross Sea. Our results show that Chl and POC are markedly underestimated using the NASA standard algorithms, with root mean square difference (RMSD) of 4.72 mg m−3 and 218.0 mg m−3, and mean bias of −3.48 mg m−3 and −159.1 mg m−3, for a wide range of Chl (0.42–16.3 mg m−3) and POC (46.8–812 mg m−3). Similar poor performances were also found for other algorithms applicable in the Ross Sea. We locally tuned both Chl and POC algorithms, and found that the Rrs667-based approach showed the most robust performances in retrieving both Chl and POC, with improved RMSD of 2.86 mg m−3 and 129.7 mg m−3, and limited biases. Our results show that the algal bloom signals in the Ross Sea in terms of Chl and POC are significantly greater than previously determined. More field observations will further constrain the locally tuned algorithms
Residual Stress Analyses in a Pipe Welding Simulation: 3D Pipe Versus Axi-symmetric Models
AbstractThis paper numerically studied the residual stress in a butt-welded steel pipe. A comparison of 3D pipe and axi-symmetric finite element model under the condition of same welding simulation parameters was carried out. The results showed that axi- symmetric model share similar residual stress distribution with 3D model in the condition of same heat source shape parameters. However, the stress values of the two concerned models were quite different. Meanwhile the scale of welding pool for 3D model was almost twice bigger than that of axi-symmetric model. Both welding experiment and simulation results of 3D model showed that peak temperature of welding pool along the welding path increased during the welding process, and welding pool width and depth also increased with the moving of heat source
A review of research on acoustic detection of heat exchanger tube
Leakage in heat exchanger tubes can result in unreliable products and dangerous situations, which could cause great economic losses. Along with fast development of modern acoustic detection technology, using acoustic signals to detect leakage in heat exchange tube has been gradually accepted and considered with great potential by both industrial and research societies. In order to further advance the development of acoustic signal detection technology and investigate better methods for leakage detection in heat exchange tube, in this paper, firstly, we conduct a short overview of the theory of acoustic signal detection on heat exchanger tube, which had already been continuously developed for a few decades by researchers worldwide. Thereafter, we further expound the advantages and limitations of acoustic signal detection technology on heat exchanger tube in four aspects: 1) principles of acoustic signal detection, 2) characteristics of sound wave propagation in heat exchanger tube, 3) methods of leakage detection, and 4) leakage localization in heat exchanger tube
RLPlanner: Reinforcement Learning based Floorplanning for Chiplets with Fast Thermal Analysis
Chiplet-based systems have gained significant attention in recent years due
to their low cost and competitive performance. As the complexity and
compactness of a chiplet-based system increase, careful consideration must be
given to microbump assignments, interconnect delays, and thermal limitations
during the floorplanning stage. This paper introduces RLPlanner, an efficient
early-stage floorplanning tool for chiplet-based systems with a novel fast
thermal evaluation method. RLPlanner employs advanced reinforcement learning to
jointly minimize total wirelength and temperature. To alleviate the
time-consuming thermal calculations, RLPlanner incorporates the developed fast
thermal evaluation method to expedite the iterations and optimizations.
Comprehensive experiments demonstrate that our proposed fast thermal evaluation
method achieves a mean absolute error (MAE) of 0.25 K and delivers over 120x
speed-up compared to the open-source thermal solver HotSpot. When integrated
with our fast thermal evaluation method, RLPlanner achieves an average
improvement of 20.28\% in minimizing the target objective (a combination of
wirelength and temperature), within a similar running time, compared to the
classic simulated annealing method with HotSpot
Green Building Rating Systems and Construction Waste in High Density Urban Environment: The Case Study of Hong Kong
Hong Kong, as many other countries, is currently facing a waste management crisis with the shortage of reclamation sites and landfill space. Examination of construction waste management (CWM) criteria within Hong Kong’s BEAM Plus is limited and lacking. In this paper, CWM criteria were assessed and a case study was conducted on a recent project, pursuing BEAM Plus, to assess the effectiveness of CWM criteria to facilitate waste reduction. The findings revealed that the overall impact of BEAM Plus on construction waste reduction is negligible. The case study showed that the reasons material/waste-related credits are not commonly attempted is due to the lack of minimum thresholds and a low weighting relative to credits in other categories. In the case study, waste generated per constructed floor area was 0.21 tons/m2. This paper also makes recommendations to improve CWM criteria in BEAM Plus in order to promote a more sustainable building industry
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