Head Of Distribution Research Articles

Experimental and Numerical Analysis of Laminar and Low Turbulent Flow Distributions in Inlet Dividing Header of Shell and Tube Heat Exchanger

Flow distribution headers play a major role in heat exchangers. The selection of header diameter, branch pipe diameter, branch pipe spacing etc. is based on the designer's experience and general guide lines. The proper selection of the header dimensions will yield uniform flow distribution in heat exchangers, which in turn will enhance the heat exchanger efficiency. In this work, the flow distribution in branch pipes and the pressure variation across the branch pipes in laminar and low turbulence region is studied with two models of the inlet dividing headers. When the numerical analysis has been applied, its inability to predict the no flow condition through the branch pipes is revealed. The results are presented in the form of flow rate ratio through branch pipes and nondimensional coefficients across branch pipes which are useful to apply the existing mathematical models for the present experimental setup.

Comparative sensitivity study of the RBMK-1500 reactor one group distribution header blockage accident model

The article presents comparative sensitivity study of the Ignalina NPP RBMK-1500 reactor one group distribution header complete blockage accident model. The accident model was developed by RELAP5 thermal-hydraulic code and the accident scenario is one of the scenarios analyzed in the RBMK reactor safety analysis report. The sensitivity study comprised of the Fourier amplitude sensitivity test and the random sample based sensitivity measures (correlation coefficients and standardized regression coefficients). Two types of the model output were investigated: maximum temperature and dynamic temperature change during the progression of the accident. In addition, the effect of the input parameter distribution of different truncation levels and the effect of double standard deviation to the sensitivity results were studied.

Elimination of non-uniform, extra-device flow effects in membrane adsorbers

Commercial use of membrane adsorbers in the biotechnology industry is increasing. Here the system time lag created by membrane adsorber peripherals and the membrane adsorber flow distribution headers has been modeled using an anion exchange membrane and bovine serum albumin (BSA). The system time lag was modeled as a zero order and first order time lag. The zero and first order time lags have been removed from the breakthrough curve. The method used does not involve fitting a mathematical expression to the breakthrough curve. Further no assumptions are made regarding the shape of the breakthrough curve in the absence of the time lag. The method has been used to calculate the Langmuir isotherm parameters. The membrane capacity was found to be twice as large as the capacity determined after removal of the time lag. The Langmuir constant was five times as large for the system without accounting for the time lag. Errors in fitting isotherm parameters can significantly impact frontal analysis and membrane adsorber scale-up. The Langmuir isotherm calculated under dynamic conditions with the system time lag removed, was in agreement with the static adsorption isotherm.

Quantifying uncertainties in the estimation of safety parameters by using bootstrapped artificial neural networks

For licensing purposes, safety cases of Nuclear Power Plants (NPPs) must be presented at the Regulatory Authority with the necessary confidence on the models used to describe the plant safety behavior. In principle, this requires the repetition of a large number of model runs to account for the uncertainties inherent in the model description of the true plant behavior. The present paper propounds the use of bootstrapped Artificial Neural Networks (ANNs) for performing the numerous model output calculations needed for estimating safety margins with appropriate confidence intervals. Account is given both to the uncertainties inherent in the plant model and to those introduced by the ANN regression models used for performing the repeated safety parameter evaluations. The proposed framework of analysis is first illustrated with reference to a simple analytical model and then to the estimation of the safety margin on the maximum fuel cladding temperature reached during a complete group distribution header blockage scenario in a RBMK-1500 nuclear reactor. The results are compared with those obtained by a traditional parametric approach.

Thermal-Hydraulic Analysis of Coolant Flow Decrease in Fuel Channels of Smolensk-3 RBMK during GDH Blockage Event

One of the transients that have received considerable attention in the safety evaluation of RBMK reactors is the partial break of a group distribution header (GDH). The coolant flow rate blockage in one GDH might lead to excessive heat-up of the pressure tubes and can result in multiple fuel channels (FC) ruptures. In this work, the GDH flow blockage transient has been studied considering the Smolensk-3 RBMK NPP (nuclear power plant). In the RBMK, each GDH distributes coolant to 40–43 FC. To investigate the behavior of each FC belonging to the damaged GDH and to have a more realistic trend, one (affected) GDH has been schematized with its forty-two FC, one by one. The calculations were performed using the 0-D NK (neutron kinetic) model of the RELAP5-3.3 stand-alone code. The results show that, during the event, the mass flow rate is disturbed differently according to the power distribution established for each FC in the schematization. The start time of the oscillations in mass flow rate depends strongly on the attributed power to each FC. It was also observed that, during the event, the fuel channels at higher thermal power values tend to undergo first cladding rupture leaving the reactor to scram and safeguarding all the other FCs connected to the affected GDH.

Evaluation of pipe whip impacts on neighboring piping and walls of the Ignalina Nuclear Power Plant

Stress corrosion cracks have been discovered in Group Distribution Headers (GDH) at the Ignalina and Chernobyl Nuclear Power Plants. This increases the probability that a guillotine pipe break can occur that creates a whipping pipe (GDH) with the potential to damage surrounding structures—i.e. adjacent GDH and its attached piping or adjacent reinforced concrete compartment wall. The GDH is the most important component for reactor safety in case of an accident. Emergency Core Cooling System (ECCS) piping is connected to the GDH piping such that, during an accident, coolant passes from the ECSS into the GDH. Presented in this paper is the transient analysis of a Group Distribution Header following a guillotine break at the blind end of the header. Using a very conservative force loading function, the transient response of a whipping RBMK-1500 GDH along with neighboring concrete walls and pipelines is obtained using finite element methodology. The results of the study, assuming that the impacted GDH does not suffer stress corrosion cracking, indicate that the structural integrity of the compartment should be maintained and failure should not propagate from GDH to GDH.

Two-phase split of refrigerants at a T-junction

The present study experimentally investigated the two-phase flow split of refrigerants at a T-junction. As geometric parameters, the direction of the inlet or branch tube and the tube diameter ratio of branch to inlet tube were chosen. As inlet flow parameters, the inlet mass flux and quality were varied from 100 to 700 kg m −2 s −1 and from 0.1 to 0.9, respectively, for the condition of distribution header of a multi-pass evaporator in the general refrigeration system. All experiments were performed for R-22, R-134a, and R-410A. The measured data were compared with the values predicted by the models developed for air–water or steam–water mixture in the literature. We propose a modified model for application to the reduced T-junction and vertical orientation of tubes. Among the geometric parameters, the branch tube direction showed the largest sensitivity to the mass flow rate ratio for the gas phase, while the inlet quality showed the largest sensitivity to the mass flow rate ratio among the inlet flow parameters.

Best estimate analysis of group distribution header blockage events in RBMK-1500 reactors

Abstract The analysis of Group Distribution Header (GDH) blockage events shows that the integrity of several fuel channels could be violated. A best estimate analysis of GDH blockage events in the RBMK-1500 reactor (Large Channel Type Water-cooled Graphite-moderated Reactor) of the Ignalina Nuclear Power Plant is performed. Uncertainties of the initial and boundary conditions as well as ATHLET code models were taken into account during the simulation. The analysis is performed employing the code ATHLET Mod. 1.2 Cycle D and the package SUSA 3.5. In this paper the ATHLET code model of Ignalina NPP, event scenarios and results of the analysis are presented. Analysis results show that GDH blockage events do not lead to severe consequences.

Simulation of Ignalina NPP accident localisation system behaviour employing the RALOC4 code in the case of group distribution header rupture

The response of the RBMK Accident Localisation System (ALS) to a medium break LOCA (group distribution header (GDH) rupture) is analysed employing the RALOC4 code. The analysis employs a best estimate mass/energy source and considers both short and long-term (up to 24 h) responses of the ALS. The main long-term energy sources and sinks are taken into account and modelled in detail in this analysis. The technical systems connected to the ALS are taken into account and modelled in detail in this analysis in order to achieve correct mass and energy balances. The analysis results demonstrate that the pressures in the ALS compartments are below the maximum allowed design pressures in the case of GDH rupture.

Analysis of potential waterhammer at the Ignalina NPP using thermal–hydraulic and structural analysis codes

The RBMK (Russian acronym for ‘channeled large power reactor’)-1500 reactors at the Ignalina nuclear power plant (NPP) have a series of check valves in the main circulation circuit (MCC) that serve the coolant distribution in the fuel channels. In the case of a hypothetical guillotine break of pipelines upstream of the group distribution headers (GDH), the check valves and adjusted piping integrity is a key issue for the reactor safety during the rapid closure of check valve. An analysis of the waterhammer effect (i.e. the pressure pulse generated by the valves slamming closed) is needed. The thermal–hydraulic and structural analysis of waterhammer effects following the guillotine break of pipelines at the Ignalina NPP with RBMK-1500 reactors was conducted by employing the RELAP5 and PipePlus codes. Results of the analysis demonstrated that the maximum values of the pressure pulses generated by the check valve closure following the hypothetical accidents remain far below the value of pressure of the hydraulic tests, which are performed at the NPP and the risk of failure of the check valves or associated pipelines is low. Sensitivity analysis of pressure pulse dependencies on calculation time step and check valve closure time was performed. Results of RELAP5 calculations are benchmarked against waterhammer transient data obtained by employing structural mechanics code BOS fluids.

Care and Feeding of Steam-Injection EOR Projects

Steam-enhanced recovery methods have been the overwhelming EOR champions since their inception in the mid-1960`s. About 6 of every 10 EOR barrels produced worldwide are the result of some steam process. Historically most well known in the San Joaquin Valley of California, large steam projects exist in countries around the world, including Venezuela, Canada, Colombia, Indonesia, China, and the CIS. Therefore, one would think that most of the basic problems, such as effective steam-distribution piping systems and accurate methods of metering steam into wells, would have been solved years ago. Unfortunately, this is not the case. In fact, this technology has been woefully lacking compared with its relative importance. This paper summarizes current efforts by the industry to improve metering and distribution of quality steam.

Fusion reactor blanket with Li17Pb83 eutectic

The article contains some features of using Li17-Pb83 eutectic as a breeder for ITER/OTR fusion reactor. Described blanket design options aim to reduce electromagnetic loads or relieve eutectic/channel interaction. Eutectic channel stress analysis confirms design feasibility. Channel temperature behaviour is analyzed for loss of blanket cooling system power and rupture of a distribution header accidents. First wall and blanket failure rates were evaluated. The results of neutron power density distribution and tritium breeding ration estimation are presented. Polonium concentration dynamics is estimated for accidental conditions. Some guide-lines for future work and design progress are advised.

A device for simultaneous tightening of the primary threaded fastening of high-pressure vessels

The Irkutsk Scientific-Research Institute for Chemical Machinery together with the Angarsk Petroleum Organic Synthesis Production Union has developed and built a device for tightening the primary fastening of high-pressure columns. The device consists of 16 hydraulic jacks located on a platform, distribution headers, and a pump station. Finds that the use of this device reduces the labor costs and the time for tightening (1 h instead of 8 with the use of the traditional methods and means for tightening) and provides the specified tightening force with uniform distribution of it over all the studs of the gate, which improves the tightness of the joint and increases the operating reliability of the apparatus as a whole.

Artificial lung design: tubular membrane units.

The overall design of tubular membrane oxygenators is considered for three blood conditions: that of a normal adult, haemodiluted adult and new-born. Variations in blood viscosity and oxygen transfer due to the Fahraeus-Lindquist effect are taken into account as well as fabrication variables, including blood header length, potted tube length and packing density of the tubes. For a laminar rectilinear flow, 50 mm Hg≤pressure drop≤200 mm Hg, and practical fabrication parameters, there exists a range of tube diameters from 150 μm to 200 μm which give a minimum priming volume and small blood distribution (header) area. The analysis indicates that, with current construction techniques, low-pressure loss oxygenators are not feasible for adult total-bypass requirements. Such units can be practicable if transfer rates are increased with secondary mixing of the blood. For example, a threefold increase in the transfet rate reduces priming volume and header area by 50% of the unmixed flow values.

Recarbonation With Liquid Carbon Dioxide

pressor often give a great deal of trouble, resulting in frequent interruptions of service because of needed repairs and requiring relatively large amounts of time and money for maintenance. Undesirable irregularities in the quality of the carbon dioxide produced, and, hence, in the treatment of the water, may also occur. In the modern carbon dioxide plant, the compressor is the first instead of, as formerly, the last unit in the producer line. Since the compressor handles only clean air and the entire system is under pressure, combustion is complete, making scrubbing and drying unnecessary. This arrangement considerably simplifies the problem of carbon dioxide production. The conventional softening plant requires a relatively large recarbonation basin area. The gas produced has a carbon dioxide value of approximately 13 per cent, the balance being principally atmospheric nitrogen. The distribution header in such a basin is