Modeling of laminar forced convection in spherical- pebble packed beds

Yaser Hadad,Khosrow Jafarpur 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.2

There are many parameters that have significant effects on forced convection heat transfer in packed beds, including Reynolds and Prandtl numbers of flow, porosity, pebble geometry, local flow conditions, wall and end effects. In addition, there have been many experimental investigations on forced convection heat transfer in packed beds and each have studied the effect of some of these parameters. Yet, there is not a reliable correlation that includes the effect of main parameters; at the same time, the prediction of precise correct limits for very low and high Reynolds numbers is off hand. In this article a general well-known model of convection heat transfer from isothermal bodies, next to some previous reliable experimental data has been used as a basis for a more comprehensive and accurate correlation to calculate the laminar constant temperature pebble-fluid forced convection heat transfer in a homogeneous saturated bed with spherical pebbles. Finally, for corroboration, the present results are compared with previous works and show a very good agreement for laminar flows at any Prandtl number and all porosities.

Seismic assessment of Nitinol Belleville Elastic Nonlinear (NI-BELL-E-N) structural system

Alireza Asgari Hadad,Bahram M. Shahrooz 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.43 No.3

Nibellen structural system is a novel resilient bracing system based on the application of Bellville disks and Nitinol rods. The cyclic behavior of Nibellen assembly was obtained, and the design equations were developed based on the available literature. Seismic performance of the system was then studied analytically. Two groups of buildings with different lateral force resisting systems were designed and studied: one group with the Nibellen system, and the other with the special concentrically braced frame system. Each building group consisted of 5-, 10-, and 15-story buildings. The Design-Base-Event (DBE) and Maximum Considered Event (MCE) were considered as the seismic hazard, and a suite of seven ground motions were scaled accordingly for response history analyses. Finally, the resiliency of the buildings was studied by obtaining the functionality curve of the buildings before and after the seismic event. The construction cost of the 5-story building with Nibellen bracing system increased but the post-earthquake cost decreased significantly. The application of Nibellen system in the 10- and 15-story buildings reduced both the construction and repair costs, considerably. Resiliency of all the buildings was improved when Nibellen system was used as the lateral force resisting system.

ANALOG COMPUTING FOR A NEW NUCLEAR REACTOR DYNAMIC MODEL BASED ON A TIME-DEPENDENT SECOND ORDER FORM OF THE NEUTRON TRANSPORT EQUATION

Pirouzmand, Ahmad,Hadad, Kamal,Suh, Kune Y. Korean Nuclear Society 2011 Nuclear Engineering and Technology Vol.43 No.3

This paper considers the concept of analog computing based on a cellular neural network (CNN) paradigm to simulate nuclear reactor dynamics using a time-dependent second order form of the neutron transport equation. Instead of solving nuclear reactor dynamic equations numerically, which is time-consuming and suffers from such weaknesses as vulnerability to transient phenomena, accumulation of round-off errors and floating-point overflows, use is made of a new method based on a cellular neural network. The state-of-the-art shows the CNN as being an alternative solution to the conventional numerical computation method. Indeed CNN is an analog computing paradigm that performs ultra-fast calculations and provides accurate results. In this study use is made of the CNN model to simulate the space-time response of scalar flux distribution in steady state and transient conditions. The CNN model also is used to simulate step perturbation in the core. The accuracy and capability of the CNN model are examined in 2D Cartesian geometry for two fixed source problems, a mini-BWR assembly, and a TWIGL Seed/Blanket problem. We also use the CNN model concurrently for a typical small PWR assembly to simulate the effect of temperature feedback, poisons, and control rods on the scalar flux distribution.

Conceptual design of a high neutron flux research reactor core with low enriched uranium fuel and low plutonium production

Rahimi, Ghasem,Nematollahi, MohammadReza,Hadad, Kamal,Rabiee, Ataollah Korean Nuclear Society 2020 Nuclear Engineering and Technology Vol.52 No.3

Research reactors for radioisotope production, fuel and material testing and research activities are designed, constructed and operated based on the society's needs. In this study, neutronic and thermal hydraulic design of a high neutron flux research reactor core for radioisotope production is presented. Main parameters including core excess reactivity, reactivity variations, power and flux distribution during the cycle, axial and radial power peaking factors (PPF), Pu₂₃₉ production and minimum DNBR are calculated by nuclear deterministic codes. Core calculations performed by deterministic codes are validated with Monte Carlo code. Comparison of the neutronic parameters obtained from deterministic and Monte Carlo codes indicates good agreement. Finally, subchannel analysis performed for the hot channel to evaluate the maximum fuel and clad temperatures. The results show that the average thermal neutron flux at the beginning of cycle (BOC) is 1.0811 × 10¹⁴ n/㎠-s and at the end of cycle (EOC) is 1.229 × 10¹⁴ n/㎠-s. Total Plutonium (Pu₂₃₉) production at the EOC evaluated to be 0.9487 Kg with 83.64% grade when LEU (UO₂ with 3.7% enrichment) used as fuel. This designed reactor which uses LEU fuel and has high neutron flux and low plutonium production could be used for peaceful nuclear activities based on nuclear non-proliferation treaty concepts.

Safety margin and fuel cycle period enhancements of VVER-1000 nuclear reactor using water/silver nanofl uid

Hassan Saadati,KAMAL HADAD,Ataollah Rabiee 한국원자력학회 2018 Nuclear Engineering and Technology Vol.50 No.5

In this study, the effects of selecting water/silver nanofluid as both a coolant and a reactivity controllerduring the first operating cycle of a light water nuclear reactor are investigated. To achieve this, coupledneutronicethermo-hydraulic analysis is employed to simulate the reactor core. A detailed VVER1000/446reactor core is modeled in monte carlo code (MCNP), and the model is verified using the porous mediaapproach. Results show that the maximum required level of silver nanoparticles is 1.3 Vol.% at thebeginning of the cycle; this value drops to zero at the end of cycle. Due to substitution of water/boric acidwith water/Ag nanofluid, reactor operation time at maximum power extends to 357.3 days, and theenergy generation increases by about 27.3%. The higher negative coolant temperature coefficient ofreactivity in the presence of nanofluid in comparison with the water/boric acid indicates that the reactoris inherently safer. Considering the safety margins in the presence of the nanofluid, minimum departurefrom nucleate boiling ratio is calculated to be 2.16 (recommendation is 1.75).

Effect of Various Nitrogen Fertilizer Treatments on Vegetative Growth, Yield , Oil Content, and Oil Chemical Composition of Pumpkin (Cucurbita pepo var styriaca)

Mahmood Danaee,Babak Khalili Hadad,Abbas Yadollahi 한국원예학회 2006 한국원예학회 기타간행물 Vol.- No.-

ANALOG COMPUTING FOR A NEW NUCLEAR REACTOR DYNAMIC MODEL BASED ON A TIME-DEPENDENT SECOND ORDER FORM OF THE NEUTRON TRANSPORT EQUATION

AHMAD PIROUZMAND,KAMAL HADAD,서균렬 한국원자력학회 2011 Nuclear Engineering and Technology Vol.43 No.3

This paper considers the concept of analog computing based on a cellular neural network (CNN) paradigm to simulate nuclear reactor dynamics using a time-dependent second order form of the neutron transport equation. Instead of solving nuclear reactor dynamic equations numerically, which is time-consuming and suffers from such weaknesses as vulnerability to transient phenomena, accumulation of round-off errors and floating-point overflows, use is made of a new method based on a cellular neural network. The state-of-the-art shows the CNN as being an alternative solution to the conventional numerical computation method. Indeed CNN is an analog computing paradigm that performs ultra-fast calculations and provides accurate results. In this study use is made of the CNN model to simulate the space-time response of scalar flux distribution in steady state and transient conditions. The CNN model also is used to simulate step perturbation in the core. The accuracy and capability of the CNN model are examined in 2D Cartesian geometry for two fixed source problems, a mini-BWR assembly, and a TWIGL Seed/Blanket problem. We also use the CNN model concurrently for a typical small PWR assembly to simulate the effect of temperature feedback, poisons, and control rods on the scalar flux distribution.

Age-dependent root canal instrumentation techniques: a comprehensive narrative review

Solomonov Michael,Kim Hyeon-Cheol,Hadad Avi,Levy Dan Henry,Ben Itzhak Joe,Levinson Oleg,Azizi Hadas 대한치과보존학회 2020 Restorative Dentistry & Endodontics Vol.45 No.2

The aim of this article was to review age-dependent clinical recommendations for appropriate root canal instrumentation techniques. A comprehensive narrative review of canal morphology, the structural characteristics of dentin, and endodontic outcomes at different ages was undertaken instead of a systematic review. An electronic literature search was carried out, including the Medline (Ovid), PubMed, and Web of Science databases. The searches used controlled vocabulary and free-text terms, as follows: ‘age-related root canal treatment,’ ‘age-related instrumentation,’ ‘age-related chemo-mechanical preparation,’ ‘age-related endodontic clinical recommendations,’ ‘root canal instrumentation at different ages,’ ‘geriatric root canal treatment,’ and ‘pediatric root canal treatment.’ Due to the lack of literature with practical age-based clinical recommendations for an appropriate root canal instrumentation technique, a narrative review was conducted to suggest a clinical algorithm for choosing the most appropriate instrumentation technique during root canal treatment. Based on the evidence found through the narrative review, an age-related clinical algorithm for choosing appropriate instrumentation during root canal treatment was proposed. Age affects the morphology of the root canal system and the structural characteristics of dentin. The clinician’s awareness of root canal morphology and dentin characteristics can influence the choice of instruments for root canal treatment.

Two-Phase Flow Field Simulation of Horizontal Steam Generators

Ataollah Rabiee,Amir Hossein Kamalinia,KAMAL HADAD 한국원자력학회 2017 Nuclear Engineering and Technology Vol.49 No.1

The analysis of steam generators as an interface between primary and secondary circuitsin light water nuclear power plants is crucial in terms of safety and design issues. VVER-1000 nuclear power plants use horizontal steam generators which demand a detailedthermal hydraulics investigation in order to predict their behavior during normal andtransient operational conditions. Two phase flow field simulation on adjacent tube bundlesis important in obtaining logical numerical results. However, the complexity of the tubebundles, due to geometry and arrangement, makes it complicated. Employment of porousmedia is suggested to simplify numerical modeling. This study presents the use of porousmedia to simulate the tube bundles within a general-purpose computational fluid dynamicscode. Solved governing equations are generalized phase continuity, momentum,and energy equations. Boundary conditions, as one of the main challenges in thisnumerical analysis, are optimized. The model has been verified and tuned by simpletwo-dimensional geometry. It is shown that the obtained vapor volume fraction near thecold and hot collectors predict the experimental results more accurately than in previousstudies.

Age-dependent root canal instrumentation techniques: a comprehensive narrative review

Solomonov, Michael,Kim, Hyeon-Cheol,Hadad, Avi,Levy, Dan Henry,Itzhak, Joe Ben,Levinson, Oleg,Azizi, Hadas The Korean Academy of Conservative Dentistry 2020 Restorative Dentistry & Endodontics Vol.45 No.1

The aim of this article was to review age-dependent clinical recommendations for appropriate root canal instrumentation techniques. A comprehensive narrative review of canal morphology, the structural characteristics of dentin, and endodontic outcomes at different ages was undertaken instead of a systematic review. An electronic literature search was carried out, including the Medline (Ovid), PubMed, and Web of Science databases. The searches used controlled vocabulary and free-text terms, as follows: 'age-related root canal treatment,' 'age-related instrumentation,' 'age-related chemo-mechanical preparation,' 'age-related endodontic clinical recommendations,' 'root canal instrumentation at different ages,' 'geriatric root canal treatment,' and 'pediatric root canal treatment.' Due to the lack of literature with practical age-based clinical recommendations for an appropriate root canal instrumentation technique, a narrative review was conducted to suggest a clinical algorithm for choosing the most appropriate instrumentation technique during root canal treatment. Based on the evidence found through the narrative review, an age-related clinical algorithm for choosing appropriate instrumentation during root canal treatment was proposed. Age affects the morphology of the root canal system and the structural characteristics of dentin. The clinician's awareness of root canal morphology and dentin characteristics can influence the choice of instruments for root canal treatment.