Experimental Investigation of the Transient Pool Boiling Heat Transfer On the Quenching of Vertical Rodlet in Water

Quenching is an important phenomenon in the evaluation of an emergency core cooling system following a hypothetical loss of coolant accident (LOCA) in a nuclear reactor. In the present study, an experimental apparatus is designed and constructed with the purpose of conducting high-temperature transient pool boiling quenching experiments for zirconium (Zr-4) cylindrical test samples. Three thermocouples are inserted in the test sample to investigate the effect of axial distance on the minimum film boiling temperature. The Zr-4 rodlet is heated up to a temperature well above the minimum film boiling temperature (up to 600?), and then plunged vertically in a quiescent pool of subcooled water. A data acquisition system is used to record the temperature of the embedded thermocouples with time. Data reduction is performed by an inverse heat conduction code to calculate the surface temperature and corresponding surface heat flux. A visualization study with a high-speed camera is conducted to record the quenching behavior on the test sample. It is found that the minimum film boiling temperature decreases with the axial distance, while the CHF temperature is relatively insensitive to the axial distance. The film boiling heat transfer coefficient decreases with surface temperature, and seems to be independent of axial distance. The quench front is observed to originate from the bottom and move upwards. It is found that the quench front velocity remains nearly constant in the lower region of the test sample, and significantly increases in the upper region.

Heat and Mass Transfer Modeling to Predict Temperature Distribution during Potato Frying after Pre-Treatment with Pulsed Electric Field

Based on unsteady state heat conduction, a mathematical model has been developed to describe the simultaneous heat and moisture transfer during potato frying. For the first time, the equation was solved using both enthalpy and Variable Space Network (VSN) methods, based on a moving interface defined by the boiling temperature of water in a potato disc during frying. Two separate regions of the potato disc namely fried (crust) and unfried (core), were considered as heat transfer domains. A variable boiling temperature of the water in potato discs was required as an input parameter for the model as the water is evaporated during frying, resulting in an increase in the soluble solid concentration of the potato sample. Pulsed electric field (PEF) pretreatment prior to frying had no significant effect on the measured moisture content, thermal conductivity or frying time compared to potatoes that did not receive a PEF pretreatment. However, a PEF pretreatment at 1.1 kV/cm and 56 kJ/kg reduced the temperature variation in the experimentally measured potato center by up to 30%. The proposed heat and moisture transfer model based on unsteady state heat conduction successfully predicted the experimental measurements, especially when the equation was solved using the enthalpy method.

EXPERIMENTAL STUDIES OF THE RELATIONSHIP BETWEEN THE BOILING TEMPERATURE AND THE FLASH TEMPERATURE OF MIXED HYDROCARBON FUELS

В работе экспериментально показано, что по мере испарения смесевой горючей жидкости при одновременном повышении плотности и снижении упругости пара в многокомпонентных взаиморастворимых композициях температура кипения повышается. В этом случае и температура вспышки смесевой горючей жидкости также будет повышаться. Так, при проливах горючих жидкостей происходит довольно быстрое обеднение легкими фракциями, упругость пара при заданной температуре существенно снижается, а температуры кипения и вспышки, соответственно, повышаются. Полученные в работе зависимости температур кипения и вспышки испытанных смесевых горючих жидкостей характерны и для других различных многокомпонентных жидких композиций. Эти зависимости могут учитываться при разработке планов предотвращения и ликвидации аварий в случае их проливов. Based on the experiments it is shown that as the flammable liquid mixtures evaporate, while increasing density and decreasing vapor tension in multicomponent compositions-soluble, the boiling temperature increases. In this case, the flash point of the mixed combustible liquid will also increase. Thus, in the case of spills of flammable liquids there is a fairly rapid depletion of light fractions, the vapor tension at a given temperature reduces significantly, and the boiling and flash temperatures increase accordingly. The dependences of the boiling and flash temperatures of the tested mixed combustible liquids obtained in this work are also typical for other various multicomponent liquid compositions. These dependencies can be taken into account when developing plans for the prevention and elimination of emergencies caused by their spills.

Prediction of the Minimum Film Boiling Temperature of Quenching Vertical Rods in Water Using Random Forest Machine Learning Algorithm

A great amount of research is focused, nowadays, on experimental, theoretical, and numerical analysis of transient pool boiling. Knowing the minimum film boiling temperature (Tmin) for rods with different substrate materials that are quenched in distilled water pools at various system pressures is known to be a complex and highly non-linear process. This work aims to develop a new correlation to predict the Tmin in the above process: Random forest machine learning technique is applied to predict the Tmin. The approach trains a machine learning algorithm using a set of experimental data collected from the literature. Several parameters such as liquid subcooling temperature (Tsub), fluid to the substrate material thermophysical properties (βf/βw), and system saturated pressure (Psat) are collected and used as inputs, whereas Tmin is measured and used as the output. Computational results show that the algorithm achieves superior results compared to other correlations reported in the literature.

Magnetic anisotropy on demand exploiting high-pressure as remote control: an ab initio proof-of-concept

Lanthanide based single molecule magnets have recently become very promising systems for creating single molecule device working at high temperature (nitrogen boiling temperature). However, the variation of direction of the...

Inducing nano-confined crystallization in PLLA and PET by elastic melt stretching

Cold crystallization of pre-melt stretched PLLA and PET permits growth of nano-confined crystals with entanglement mesh size in undisrupted chain networking. Such PLLA and PET are ductile, transparent, rigid at the water-boiling temperature.

Viscosity of Ionic Liquids: Application of the Eyring’s Theory and a Committee Machine Intelligent System

Accurate determination of the physicochemical characteristics of ionic liquids (ILs), especially viscosity, at widespread operating conditions is of a vital role for various fields. In this study, the viscosity of pure ILs is modeled using three approaches: (I) a simple group contribution method based on temperature, pressure, boiling temperature, acentric factor, molecular weight, critical temperature, critical pressure, and critical volume; (II) a model based on thermodynamic properties, pressure, and temperature; and (III) a model based on chemical structure, pressure, and temperature. Furthermore, Eyring’s absolute rate theory is used to predict viscosity based on boiling temperature and temperature. To develop Model (I), a simple correlation was applied, while for Models (II) and (III), smart approaches such as multilayer perceptron networks optimized by a Levenberg–Marquardt algorithm (MLP-LMA) and Bayesian Regularization (MLP-BR), decision tree (DT), and least square support vector machine optimized by bat algorithm (BAT-LSSVM) were utilized to establish robust and accurate predictive paradigms. These approaches were implemented using a large database consisting of 2813 experimental viscosity points from 45 different ILs under an extensive range of pressure and temperature. Afterward, the four most accurate models were selected to construct a committee machine intelligent system (CMIS). Eyring’s theory’s results to predict the viscosity demonstrated that although the theory is not precise, its simplicity is still beneficial. The proposed CMIS model provides the most precise responses with an absolute average relative deviation (AARD) of less than 4% for predicting the viscosity of ILs based on Model (II) and (III). Lastly, the applicability domain of the CMIS model and the quality of experimental data were assessed through the Leverage statistical method. It is concluded that intelligent-based predictive models are powerful alternatives for time-consuming and expensive experimental processes of the ILs viscosity measurement.