Maximum Thermal Flux Research Articles

Current design of disk chopper time-of-flight spectrometer at KAERI

HANARO is a 30 MW multi-purpose research reactor located at the Korea Atomic Energy Research Institute (KAERI) with a maximum thermal flux of 5.4 × 1014 n/cm2/s. It reached first criticality in 1995. As part of its present cold neutron project, the KAERI selected disk chopper time-of-flight (DC-TOF) spectrometer as one of the day-one instruments. In this report, we present the current design of our DC-TOF. In order to optimize the design parameters of DC-TOF and its guide layout, we made full use of two Monte-Carlo simulation codes, VITESS and McStas. We have also optimized technical parameters using analytical tools, whenever possible.

The application of auto-temperature-controlled ventilation embankment in Qinghai-Tibet Railway

Auto-temperature-controlled ventilation embankment is an effective engineering measure for “cooling roadbed”. Practice proves that this new method can sufficiently make use of natural cold energy. It has the advantages of higher efficiency, better cooling effect and feasibility in engineering practice, and wider application in various environment, etc. And also, it is comparatively cheap in project cost. Through practice in the field for half a year, the testing results show that, with the application of auto-temperature-controlled system, the artificial permafrost table has been raised by 65 cm. The artificial permafrost table was basically at the embankment bottom, and the action of freeze-thaw circle on engineering stability was effectively avoided. In the month with highest ground temperature, in the scope with 1–4 m in depth, including the majority of the embankment and the upper part in the original seasonal layer, the ground temperature decreased by 0.7°C. Through thermal flux calculation in the original seasonal layer, in the month with the maximum thermal flux coming into permafrost, it is found that the thermal flux reduces nearly by half. Coming into the cooling period for nearly a month, the ground temperature in entire auto-temperature-controlled embankment is close to zero, and the foundation is at negative temperature. But in a large region in the embankment and foundation the ground temperature was over 0°C and varied from 0°C to0.39°C in ordinary ventilation embankment.

Evaluation of divertor conceptual designs for a fusion power plant

In the frame of the preliminary study of plants suitable for the energy production from the fusion power, particular emphasis has been given on the divertor studies. Since a significant percentage of the power generated from the fusion process is absorbed in the divertor, the thermal efficiency of the power conversion cycle requires a high coolant outlet temperature of the divertor, leading to solutions that are different from those adopted for the present experimental fusion plants. Therefore, copper alloys having extremely high thermal conductivity, cannot be used as structural material for this kind of devices. The most suitable coolants to be used in the divertor are water, helium and liquid metals. A conceptual design study has been developed for each of these three fluids, with the aim to evaluate the maximum allowable thermal flux at the divertor target plate and the R&D requirements for each solution. While a water-cooled divertor can be designed with a limited R&D effort, the development of helium or liquid metal cooled divertors requires a more engaging R&D program.

Safety assessment of hydrogen disposal on vents and flare stacks at high flow rates

We compare the point source and solid flame models for assessing the thermal flux levels from hydrogen vent flares. Substantial disagreement exists between the solid flame approach and the point source model close to the base of the flare stack. In this region, the solid flame model is more reliable and may result in higher estimates of the maximum thermal flux from the flare stack. We use the solid flame model to determine restrictions on vent heights and the location of buildings.

Signature of coronal holes and streamers in the interplanetary space

The properties of different solar wind streams depend on the large scale structure of the coronal magnetic field. We present average values and distributions of bulk parameters (density, velocity, temperature, mass flux, momentum, and kinetic and thermal energy, ratio of thermal and magnetic pressure, as well as the helium abundance) as observed on board the Prognoz 7 satellite in different types of the solar wind streams. Maximum mass flux is recorded in the streams emanating from the coronal streamers while maximum thermal and kinetic energy fluxes are observed in the streams from the coronal holes. The momentum fluxes are equal in both types of streams. The maximum ratio of thermal and magnetic pressure is observed in heliospheric current sheet. The helium abundance in streams from coronal holes is higher than in streams from streamers, and its dependences on density and mass flux are different in different types of the streams. Also, the dynamics of α-particle velocity and temperature relative to protons in streams from coronal holes and streamers is discussed.

Wall-rock alteration and hydrothermal flow paths about the Ann-Mason porphyry copper deposit, Nevada; a 6-km vertical reconstruction

Wall-rock alteration and hydrothermal flow paths about the Ann-Mason porphyry copper deposit, Nevada; a 6-km vertical reconstruction

A neutronic study on the concept of using a fast reactor core for high thermal flux reactors

The concept of using a fast reactor core for high thermal flux reactors was studied by means of a one-dimensional nuclear analysis. Reactor configurations were investigated to obtain high thermal flux under design constraints on the total reactor power and peak power density. Graphite and heavy water were compared as the reflector material, and oxide and metallic fuels were also compared. The power density necessary for a maximum thermal flux of 10 16 n/cm 2 s was evaluted and compared with a conventional heavy-water-cooled high-flux reactor. The results of the analysis showed that this flux level can be attained in the present reactor at a lower power density than in a conventional high-flux reactor.

Optimum distribution of water-wall thickness in a transwall

In this communication, a transient analysis of a transwall for an air-conditioned room is presented. An analytical expression for the thermal flux entering the air-conditioned room through direct and indirect gain is derived in terms of the physical properties of the transwall as well as the climatic parameters. The water temperatures and the flux entering the room are computed on an hourly basis for a number of days for the typical cold climatic conditions of Srinagar. On the basis of the numerical results, it is observed that: (i) steady-state conditions are acheived after the third day; and (ii) the maximum thermal flux is achieved for δL = δL w1/ δL w = 1.

Longitudinal propagation of a normal phase along a superconducting wire and its transient heat evacuation to a normal helium bath

The longitudinal destruction of the superconducting state along a wire by an electrical subcritical current can occur if a strong enough thermal disturbance appears somewhere along the wire. The longitudinal expansion velocity of the normal phase along the wire is then strongly dependent on the different heat production and evacuation processes. As for a wire in a superfluid helium bath, a steady boundary thermal conductance across the wire wall and the normal helium bath can be deduced by adjusting the theoretical data with the experimental data. For the temperature range considered in this paper, the steady boundary thermal conductance seems to be independent of the helium bath temperature but not of the wire surface morphology. It is also shown that the experimental and theoretical data are in strong disagreement unless a transient term in the heat transferred across the wire wall and the liquid He I separating interface is introduced in the theoretical model. A transient heat transfer coefficient is defined, and its dependence on the different wire characteristics is investigated. An empirical relationship between the transient heat transfer coefficient and the wire characteristics is deduced for a given bath temperature. The transient heat transfer coefficient is shown to depend on the maximum thermal flux released into the bath across the wire wall and not on the wire surface morphology.

Fertigungstechnische Probleme beim Einwalzen und Schweißen von Rohren in Rohrböden bei Wärmeaustauschern

AbstractProduction problems in the rolling‐in and welding of tubes in the tube plates of heat exchangers. One of the principal problems besetting the construction of equipment is the mutual sealing of pressurized spaces. These sealing problems governed design for many years and remained virtually stagnant for decades. New chemical processes involving maximum thermal flux densities compelled engineers to produce new designs. Further problems were those of high and low‐temperature corrosion and attack by erosion which required mastering by design measures. The historical development of design constitutes the basis of the paper. The following topics are considered: (1) Rolling‐in and welding techniques; (2) automated welding in nuclear power plant construction (demands placed on seam tube/deposit welding; special demands on production techniques); (3) quality assurance (quality planning, quality control, checking measures, destructive testing, procedures adopted in case of deviations, quality analysis, documentation).

Criteria for the onset of flux-limited thermal conduction in laser-induced compression

The conditions under which flux limitation of thermal conductivity begins to affect laser-induced compression by restricting the energy flow to the ablation zone are considered. On the assumption that the maximum thermal flux is given by Fm = α (1/4 ne ve ) kT, a simple analytic model is used to show that flux limiting commences when the ratio of the critical radius to the ablation radius rc/ra ⪆ (α/16)[(8 AM)/(πmZ)]½. The laser power at which this occurs varies as α3/λ2. Computer modelling is used to check the validity of these predictions.

Can internal heat contribute to the high surface temperature of Venus?

It is shown that current observational data on conditions at the Venusian surface are adequate to exclude the possibility that thermal energy from a hot interior contributes to the high surface temperature of the planet. The maximum energy flux conducted from the interior is estimated by assigning a maximum thermal conductivity and a minimum thickness to the crust. It is found that the crust must be at least 10 km thick and that the maximum thermal flux for this thickness is about 6 millionths of a calorie per sq cm/sec. The relative importance of this internal energy source is assessed by comparing it with the amount of solar energy deposited at the surface. The result demonstrates that the absorbed solar energy is at least one and probably two orders of magnitude higher than the minimum flux conducted from the interior. It is concluded that a very efficient atmospheric trapping mechanism (the greenhouse effect) is operating on Venus.