Thermal Modeling of Remote Radio Head Units

2015 ◽  
Author(s):  
Manasa Sahini ◽  
Betsegaw Gebrehiwot ◽  
Dereje Agonafer ◽  
Rocky Colapietro
Keyword(s):  
Natural Convection ◽  
Hot Spots ◽  
Thermal Modeling ◽  
Air Flow ◽  
Inlet Temperature ◽  
Fixed Amount ◽  
A Cell ◽  
Computational Fluid Dynamics Cfd ◽  
Convection Cooling ◽  
Cell Tower

Thermal modeling of concealed Remote Radio Head (RRH) units which are placed on a cell tower is the main interest of this paper. RRH units which dissipate fixed amount of heat are modeled in higher ambient temperature. The effect of creating an enclosure on the open air assembly of RRH units is studied. The aim of this study is to analyze if concealment of the RRH units is possible under natural convection for cooling under boundary conditions with inlet temperature 55°C, solar loading and wind. Also, the study has been made to investigate if stacking of one, two, or three concealed sections is possible under natural convection cooling process. Various configurations were modeled and analyzed using a computational fluid dynamics (CFD) tool. Different temperature profiles are reported. An enclosure has been created and the operating temperatures of the enclosed model and an open model are compared. After studying the air flow pattern in the model, specific design modifications, like placing baffles on top of each RRH unit, are suggested for proper air flow management thereby facilitating efficient thermal management inside the enclosure. Also, addition of baffles helped in removing the hot spots in the model. Stacking concealed sections poses a challenge since hot exhaust air from a lower section may enter the air inlets of top sections. Thereby, higher surface temperatures on RRH units in the upper sections are observed. Orientation of the upper section has been changed to address this issue. Results show that with proper airflow management and arrangement of sections, it is possible to have three sections one on top of the other.

Fundamental Issues and Recent Advancements in Analysis of Aircraft Brake Natural Convective Cooling

1998 ◽  
Vol 120 (4) ◽  
pp. 840-857 ◽  
Author(s):  
M. P. Dyko ◽  
K. Vafai
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Flow Field ◽  
Three Dimensional ◽  
Convective Cooling ◽  
Cooling Flow ◽  
Physical Mechanisms ◽  
Braking System ◽  
Flow And Heat Transfer ◽  
Convection Cooling

A heightened awareness of the importance of natural convective cooling as a driving factor in design and thermal management of aircraft braking systems has emerged in recent years. As a result, increased attention is being devoted to understanding the buoyancy-driven flow and heat transfer occurring within the complex air passageways formed by the wheel and brake components, including the interaction of the internal and external flow fields. Through application of contemporary computational methods in conjunction with thorough experimentation, robust numerical simulations of these three-dimensional processes have been developed and validated. This has provided insight into the fundamental physical mechanisms underlying the flow and yielded the tools necessary for efficient optimization of the cooling process to improve overall thermal performance. In the present work, a brief overview of aircraft brake thermal considerations and formulation of the convection cooling problem are provided. This is followed by a review of studies of natural convection within closed and open-ended annuli and the closely related investigation of inboard and outboard subdomains of the braking system. Relevant studies of natural convection in open rectangular cavities are also discussed. Both experimental and numerical results obtained to date are addressed, with emphasis given to the characteristics of the flow field and the effects of changes in geometric parameters on flow and heat transfer. Findings of a concurrent numerical and experimental investigation of natural convection within the wheel and brake assembly are presented. These results provide, for the first time, a description of the three-dimensional aircraft braking system cooling flow field.

Construction Ventilation Scheme Optimization of Underground Main Powerhouse Based on CFD

2013 ◽  
Vol 368-370 ◽  
pp. 619-623
Author(s):  
Zhen Liu ◽  
Xiao Ling Wang ◽  
Ai Li Zhang
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Flow Field ◽  
Air Flow ◽  
Scheme Optimization ◽  
Pressure Distributions ◽  
Air Volume ◽  
Computational Fluid Dynamics Cfd ◽  
Traditional Construction ◽  
Ventilation Scheme

For the purpose of avoiding the deficiency of the traditional construction ventilation, the ventilation of the underground main powerhouse is simulated by the computational fluid dynamics (CFD) to optimize ventilation parameters. A 3D unsteady RNG k-ε model is performed for construction ventilation in the underground main powerhouse. The air-flow field and CO diffusion in the main powerhouse are simulated and analyzed. The two construction ventilation schemes are modelled for the main powerhouse. The optimized ventilation scheme is obtained by comparing the air volume and pressure distributions of the different ventilation schemes.

Highly conserved gsc1 gene of Pneumocystis jirovecii in patients with or without prior exposure to Echinocandins

2021 ◽  
Author(s):  
Pierre L. Bonnet ◽  
Solène Le Gal ◽  
Claire V. Hoffmann ◽  
Florent Morio ◽  
Fouleymata Diabira ◽  
...  
Keyword(s):  
Hot Spots ◽  
Selection Pressure ◽  
Gene Diversity ◽  
Prior Exposure ◽  
Cell Wall Component ◽  
Synonymous Mutations ◽  
Significant Difference ◽  
A Cell ◽  
Patient Groups ◽  
Noncompetitive Inhibitors

Echinocandins are noncompetitive inhibitors of the GSC1 subunit of the enzymatic complex involved in synthesis of 1,3-beta-D-glucan, a cell wall component of most fungi, including Pneumocystis spp. Echinocandins are widely used for treating systemic candidiasis and rarely used for treating Pneumocystis pneumonia. Consequently, data on P. jirovecii gsc1 gene diversity are still scarce, compared to the homologous fks1 gene of Candida spp. In this study, we analyzed P. jirovecii gsc1 gene diversity and the putative selection pressure of echinocandins on P. jirovecii. Gsc1 gene sequences of P. jirovecii specimens from two patient groups were compared. One group of 27 patients had prior exposure to echinocandins whereas the second group of 24 patients did not, at the time of P. jirovecii infection diagnoses. Two portions of P. jirovecii gsc1 gene, HS1 and HS2, homologous to hot spots described in Candida spp., were sequenced. Three SNPs at positions 2204, 2243, and 2303 close to the HS1 region and another SNP at position 4540 more distant from the HS2 region were identified. These SNPs represent synonymous mutations. Three gsc1 HS1 alleles, A, B, and C, and two gsc1 HS2 alleles, a and b, and four haplotypes, Ca, Cb, Aa, and Ba, were defined, without significant difference in haplotype distribution in both patient groups ( p = 0.57). Considering the identical diversity of P. jirovecii gsc1 gene and the detection of synonymous mutations in both patient groups, no selection pressure of echinocandins among P. jirovecii microorganisms can be pointed out so far.

Impact of Severe Temperature Distortion on Turbine Efficiency

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Paul F. Beard ◽  
Andy Smith ◽  
Thomas Povey
Keyword(s):  
Computational Study ◽  
Measurement Techniques ◽  
Inlet Temperature ◽  
Turbine Efficiency ◽  
Computational Fluid Dynamics Cfd ◽  
External Flows ◽  
Torque Transducer ◽  
Formed Part ◽  
Low Uncertainty ◽  
The Eu

This paper presents an experimental and computational study of the effect of severe inlet temperature distortion (hot streaks) on the efficiency of the MT1 HP turbine, which is a highly-loaded unshrouded transonic design. The experiments were performed in the Oxford Turbine Research Facility (OTRF) (formerly the TTF at QinetiQ Farnborough): an engine scale, short duration, rotating transonic facility, in which M, Re, Tgas/Twall and N/T01 are matched to engine conditions. The research formed part of the EU Turbine Aero-Thermal External Flows (TATEF II) program. An advanced second generation temperature distortion simulator was developed for this investigation, which allows both radial and circumferential temperature profiles to be simulated. A pronounced profile was used for this study. The system was novel in that it was designed to be compatible with an efficiency measurement system which was also developed for this study. To achieve low uncertainty (bias and precision errors of approximately 1.5% and 0.2% respectively, to 95% confidence), the mass flow rate of the hot and cold streams used to simulate temperature distortion were independently metered upstream of the turbine nozzle using traceable measurement techniques. Turbine power was measured directly with an accurate torque transducer. The efficiency of the test turbine was evaluated experimentally for a uniform inlet temperature condition, and with pronounced temperature distortion. Mechanisms for observed changes in the turbine exit flow field and efficiency are discussed. The data are compared in terms of flow structure to full stage computational fluid dynamics (CFD) performed using the Rolls Royce Hydra code.

scholarly journals Real-Time Anticipation and Prevention of Hot Spots by Monitoring the Dynamic Conductance of Photovoltaic Panels

2021 ◽  
Author(s):  
William Lamb ◽  
Dallon Asnes ◽  
Jonathan Kupfer ◽  
Emma Lickey ◽  
Jeremy Bakken ◽  
...  
Keyword(s):  
Real Time ◽  
Hot Spots ◽  
Structural Damage ◽  
Reverse Bias ◽  
Control Method ◽  
Physical Damage ◽  
Operating Current ◽  
A Cell ◽  
Real Time Simulations ◽  
Dynamic Conductance

<div>Hot spotting in photovoltaic (PV) panels causes physical damage, power loss, reduced lifetime reliability, and increased manufacturing costs. The problem arises routinely in defect-free standard panels; any string of cells that receives uneven illumination can develop hot spots, and the temperature rise often exceeds 100°C in conventional silicon panels despite on-panel bypass diodes, the standard mitigation technique. Bypass diodes limit the power dissipated in a cell subjected to reverse bias, but they do not prevent hot spots from forming. An alternative control method has been suggested by Kernahan [1] that senses in real time the dynamic conductance |dI/dV| of a string of cells and adjusts its operating current so that a partially shaded cell is never forced into reverse bias. We start by exploring the behavior of individual illuminated PV cells when externally forced into reverse bias. We observe that cells can suffer significant heating and structural damage, with desoldering of cell-tabbing and discolorations on the front cell surface. Then we test PV panels and confirm Kernahan’s proposed panel-level solution that anticipates and prevents hot spots in real time. Simulations of cells and panels confirm our experimental observations and provide insights into both the operation of Kernahan’s method and panel performance.</div>

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