One-dimensional Homogeneous Model Research Articles

Two-phase pressure drop study for cryosurgical probes using one-dimensional homogeneous model

Cryosurgery is an effective medical treatment approach for treating solid cancerous malignancy, as it is a minimally invasive treatment therapy. The main aim of cryosurgery is to use extreme cold to destroy abnormal tissues while minimizing damage to healthy surrounding tissue. Recent technological advancements in cryogenics have attracted the attention of many researchers to study the low-temperature cryosurgical devices, generally termed cryoprobes. Saturated Liquid Nitrogen (LN2) from pressurized dewar is fed to the cryoprobe through a transfer hose. The fluid evaporates as it flows downstream because of various heat loads and experiences pressure drop. In this paper, a two-phase pressure drop solver is presented following a simplified one-dimensional analysis to estimate pressure losses occurring throughout the system. A qualitative discussion on the contribution of various pressure drop components is provided. It is observed that the major pressure loss occurs along the length of the cryoprobe tubes. The effect of the cryoprobe tube dimensions on the pressure drop is also studied. It is concluded that the miniaturized probe design demands higher system inlet pressure.

Numerical Investigation on Two-Phase Flow Heat Transfer Performance and Instability with Discrete Heat Sources in Parallel Channels

With the rapid development of integrated circuit technology, the heat flux of electronic chips has been sharply improved. Therefore, heat dissipation becomes the key technology for the safety and reliability of the electronic equipment. In addition, the electronic chips are distributed discretely and used periodically in most applications. Based these problems, the characteristics of the heat transfer performance of flow boiling in parallel channels with discrete heat source distribution are investigated by a VOF model. Meanwhile, the two-phase flow instability in parallel channels with discrete heat source distribution is analyzed based on a one-dimensional homogeneous model. The results indicate that the two-phase flow pattern in discrete heat source distribution is more complicated than that in continuous heat source distribution. It is necessary to optimize the relative position of the discrete heat sources, which will affect the heat transfer performance. In addition, compared with the continuous heat source, the flow stability of discrete heat sources is better with higher and lower inlet subcooling. With a constant sum of heating power, the greater the heating power near the outlet, the better the flow stability.

NON-STATIONARY SURFACE TEMPERATURE FIELD LAYER OF METAL WITH PERIODIC ENERGY ACTION ON SURFACE

Under the influence of temperature fluctuations, the properties of metals can change. Thermocyclic treatment of metals, in particular steels, requires accurate detection of patterns of non-stationary temperature field in the treated metal layer. An expression was obtained for the deviation of the temperature from the value of its instantaneous equilibrium distribution for a one-dimensional homogeneous model of finite length under conditions of periodic energy action on its active surface. This solution was applied to the low carbon steel sample.

Investigation on heat transfer in line chill-down process with various cryogenic fluids

This paper focuses on the transient process of the pipe cooling by the internal flow of cryogenic fluid, which is a so-called cryogenic line chill-down process. Due to the increasing use of cryogenic fluid in various industries, the heat transfer characteristics during the line chill-down process are followed with great interest. One of the biggest concern is that there are no universal heat transfer correlations for simulating the chill-down process. This research aims to extend the quenching database with liquid oxygen and predict the cryogenic line chill-down process with a one-dimensional homogeneous model. The line chill-down experiments are performed by liquid oxygen with the mass flux range from 15.9 kg/m2-s to 75.9 kg/m2-s. A 7 m long stainless steel 316 horizontal tube is used as the test section. The empirical correlations for heat transfer coefficient of single-phase vapor convection and film boiling are suggested based on the chill-down experimental data of liquid oxygen, liquid argon, and liquid nitrogen. The line chill-down process is simulated by applying the empirical correlations in a one-dimensional homogeneous model. The feasibility of the dynamic simulation model is verified in the mass flux up to 868 kg/m2-s by simulating the chill-down experimental data in the literature. Moreover, the characteristics of the critical heat flux, critical heat flux temperature, and minimum heat flux temperature are also investigated by comparing various experimental data and the empirical correlations. This study provides not only the open experimental data with liquid oxygen, which is rarely found in the literature but also the numerical simulation method, which predicts the line chill-down time within ± 10% error.

Energy conversion efficiency from low-head water to high-pressure gas

Low-water-head hydropower is usually viewed as useless because of its inefficiency. The Low-Water-Head Hydropower Project can automatically transmute low-water-head hydropower into high-pressure gas power, which will solve the problem of the under-utilization of low-water-head hydropower. Considering the under-utilization of low-water-head hydropower because of its inefficiency, we propose a less intrusive and more efficient solution: the Low-Water-Head Hydropower Project with an automatic pump, which can transmute the low-water-head hydropower into high-pressure gas power. The energy-transfer process from water to air has not been investigated in previous studies. The goal of this study is to improve the energy conversion efficiency of the project. The goal of our study is to improve the energy conversion efficiency. The energy-transfer process from water to air has not been a focus in previous studies. Hence, a full-scale experiment was conducted, and the formula for the energy conversion efficiency η was deduced. Energy balance equations based on the one-dimensional homogeneous model from the Bernoulli equation were established. Through the energy balance equation, the percentages of energy loss of different forms were determined. Wider and higher outlet pipes have higher η values. From an engineering perspective, the frictional head loss in all cases is so small that the frictional head loss caused by sidewall friction can be neglected. The change in temperature does not practically affect the sidewall friction effect. These conclusions can be applied in engineering applications.

Equivalent homogeneous model of D31-mode longitudinal piezoelectric transducers

This article focuses on modelling of D31-mode longitudinal piezoelectric transducers. A simple equivalent one-dimensional homogeneous model of D31-mode longitudinal piezoelectric transducers is proposed in this article. Homogeneous properties of the model are derived by a simple analytical mixing method based on the operation principle of D31-mode longitudinal piezoelectric transducers. Compared with other models in the literature, the proposed homogeneous model can consider passive layers in D31-mode longitudinal piezoelectric transducers for more accurate predictions in either static or dynamic behaviour. The proposed model is validated by a three-dimensional finite element model. Besides, based on the homogeneous model and borrowing the network theory, an exact equivalent circuit is formulated. A more straightforward form of the equivalent circuit can further facilitate analysis and modelling of D31-mode longitudinal piezoelectric transducers. Also, the proposed homogeneous model is wrapped into a transfer matrix form. The formulated transfer matrix of D31-mode longitudinal piezoelectric transducers can be used with the transfer matrix method to facilitate the calculations, when D31-mode longitudinal piezoelectric transducers are connected with numerous mediums in the operation direction. The effectiveness of the equivalent circuit and the transfer matrix is also verified.

ИССЛЕДОВАНИЕ УСТОЙЧИВОСТИ РАСХОДА ТЕПЛОНОСИТЕЛЯ В ДВУХКОНТУРНОЙ АЭС С РЕАКТОРОМ ВВЭР СКД

The coolant flow rate stability in a two-circuit APP with a fast breeder reactor cooled by supercritical pressure steam is numerically analyzed. The investigation is done using the D-decomposition method in the plane of the stability-determining parameters based on a one-dimensional homogeneous model of heat and mass transfer processes in the APP circulation loop. The D-decomposition boundary is constructed using the methodology of numerical computation of the transfer function contained in the characteristic equation of the mathematical model. The flow rate stability in the first closed circuit of the APP, in the second circuit of the steam generator and in the parallel channels of the shield fuel assemblies of the reactor core is analyzed, accounting for the variation of energy release over different fuel assembly groups. The coolant flow rate stability in the nominal regime is found to be provided with a margin. Keywords: reactor core, coolant circulation loop, stability region, steam generator, supercritical steam pressure, flexible regulation mode of the turbine, coolant, thermal-hydraulic instability, shield fuel assembly.

Qualitative and quantitative investigation of the propagation noise in various reactor systems

The space-dependent neutron noise, induced by propagating perturbations (propagation noise for short) is investigated in a one-dimensional homogeneous model of various reactor systems. By using two-group theory, the noise in both the fast and the thermal group is calculated. The purpose is to investigate the dependence of the properties of the space-dependent fast and thermal propagation noise on the static neutron spectrum as well as on the presence of the fluctuations of several cross sections. The motivation for this study arose in connection with recent work on neutron noise in molten salt reactors (MSR) with propagating fuel of various compositions. Some new features of the induced noise were observed, but it was not clear whether these were due to the propagating perturbation alone, or to the propagation of the fuel and hence that of the delayed neutron precursors. The present study serves to clarify the significance of the spectral properties of the different cores through calculating the propagation noise in four different reactor systems, as well as considering the influence of the perturbation of the various cross sections. By comparing the results with those obtained in MSR, the effect of the moving fuel on the propagation noise is clarified. It is shown that in fast systems the noise in the fast group is much larger than in the thermal group and hence can gain diagnostic importance. It is also shown that the co-existence of several cross section fluctuations leads to qualitatively and quantitatively new characteristics of the noise, hence it is important to model the effect of e.g. temperature fluctuations of the coolant in a proper way.

Simulation of the Cyclic Operation of a PSA-based SEWGS Process for Hydrogen Production with CO2 Capture

A dynamic one-dimensional homogeneous model for multiple bed Sorption Enhanced Water Gas Shift (SEWGS) system has been developed in this work. The SEWGS system under consideration is based on a Pressure Swing Adsorption (PSA) process which operates in a cyclic manner. During the reaction/adsorption step, CO2 produced by Water Gas Shift (WGS) reaction is simultaneously adsorbed on a highly CO2-selective solid adsorbent and removed from the gas phase, enhancing the WGS reaction toward higher reaction conversion and hydrogen production. The periodic adsorption and desorption of CO2 is induced by a pressure swing cycle, and the cyclic capacity can be amplified by purging with steam. Simulation results enable tracking the operation of the system over sequence of steps. As it is expected, high levels of CO conversion and CO2 capture ratio are achieved by enhancing the equilibrium reaction of WGS with adsorbents. Moreover there is no need to reheat the hydrogen product before it enters the gas turbine due to operability of SEWGS system at high temperature of approximately 400°C. Hydrogen production undergoes repeating fluctuations over cycle time which is associated with using part of the H2 product for repressurization step.

Effects of physical properties on one-dimensional downward smoldering of char: Numerical analysis

Smoldering combustion in a packed bed of carbonaceous material is a very complex process, where numerous physical and chemical parameters are involved. This study was conducted to examine the impact of several physical parameters on the behavior of natural downward smoldering. For that purpose, a one-dimensional homogeneous model has been developed. Due to the fact that drying, pyrolysis or oxidative degradation occurs significantly faster than carbon oxidation, only the latter phenomenon was taken into account. The model was evaluated by comparison of numerical simulation results with experimental observations. Sensitivity analysis calculations of different physical properties of the bed material with respect to smoldering time, smoldering front velocity and front temperature suggest that in future experiments special attention should be devoted to accurate determination of bed shrinkage, bulk carbon density, mean void size, oxygen diffusivity in fuel bed.

Generation of superthermal electrons interacting with waves in lower-hybrid range of frequency revisited

The problem of quasilinear diffusion of plasma electrons, resonantly interacting with waves in lower-hybrid range of frequency launched from the exterior, is examined within a self-consistent one-dimensional homogeneous model. An analytical solution is obtained, which allows the derivation of a simple formula for the plasma current in terms of the parameters characterizing the spectral distribution of the RF power source. The major outcome is a dramatic sensitivity of the plasma current to the presence of a small, high-N/sub /// component in the RF power source spectral distribution, in agreement with previous numerical calculations.

DISCUSSION PAPER. COLLECTIVE ION ACCELERATION VIA THE TWO‐STREAM INSTABILITY*

Microinstabilities associated with a cold, low $nu$/$gamma$, intense relativistic electron beam passing through a cold underdense ion background are studied. A one-dimensional homogeneous model is assumed. A restriction was made to the relativistic electron-ion longitudinal two-stream instability. (MOW)