The Effect of the Crucible on the Temperature Distribution for the Growth of a Large Size AlN Single Crystal

The appropriate distribution of temperature in the growth system is critical for obtaining a large size high quality aluminum nitride (AlN) single crystal by the physical vapor transport (PVT) method. As the crystal size increases, the influence of the crucible on the temperature distribution inside the growth chamber becomes greater. In order to optimize the field of temperature and study the specific effects of various parts of the crucible on the large size AlN single crystal growth system, this study carried out a series of numerical simulations of the temperature field of two crucibles of different materials and put forward the concept of a composite crucible, which combines different materials in the crucible parts. Four composite crucible models were established with different proportions and positions of tantalum carbide (TaC) parts and graphite parts in the crucible. Calculations reveal that different parts of the crucible have different effects on the internal temperature distribution. The axial temperature gradient at the crystal was mainly governed by the crucible wall, whereas the temperature gradient was determined by the integrated effect of the crucible lid and the crucible wall in the radial direction. One type of composite crucible was chosen to minimize the thermal stress in grown AlN crystal, which is applicable to the growth of large sized AlN crystals in the future; it can also be used to grow AlN single crystals at present as well.

Influence of Different Heater Structures on the Temperature Field of AlN Crystal Growth by Resistance Heating

Based on the actual hot zone structure of an AlN crystal growth resistance furnace, the global numerical simulation on the heat transfer process in the AlN crystal growth was performed. The influence of different heater structures on the growth of AlN crystals was investigated. It was found that the top heater can effectively reduce the axial temperature gradient, and the side heater 2 has a similar effect on the axial gradient, but the effect feedback is slightly weaker. The axial temperature gradient tends to increase when the bottom heater is added to the furnace, and the adjustable range of the axial temperature gradient of the side 1 heater + bottom heater mode is the largest. Our work will provide important reference values for AlN crystal growth by the resistance method.

Simulation of heat transfer processes during the growth of crystals of the NiFeGaCo alloy

Long crystals of NiFeGaCo alloy with shape memory effect, including magnetically controlled ones, were obtained by the methods of Czochralski and Stepanov. A strong influence on the properties of crystals of dendritic formations, especially noticeable in the initial part of the crystal, has been revealed. In order to optimize the growth experiments, the heat transfer process in the thermal growth zone was simulated. It is shown that the formation of dendrites is due to a change in heat transfer during growth, which leads to an increase in the axial temperature gradient near the crystallization front as the crystal grows. This fits into the framework of the classical concepts of the transition from dendritic growth to normal growth.

Investigation of the Freezing Phenomenon in Vials Using an Infrared Camera

The freezing phenomenon has a dramatic impact on the quality of freeze-dried products. Several freezing models applied to solutions in vials have been proposed to predict the resulting product morphology and describe heat transfer mechanisms. However, there is a lack of detailed experimental observations of the freezing phenomenon in vials in the literature. Thus, the present work offers new experimental observations of the freezing phenomenon in vials by infrared (IR) thermography. IR imaging allowed each vial’s whole axial temperature profile to be collected during freezing, providing significant insights into the process. Spontaneous nucleation and vacuum-induced surface freezing (VISF), as a controlled nucleation technique, are investigated. Batches having vials in direct contact with the shelf (exchanging heat mainly through conduction) as well as suspended (exchanging heat mainly through natural convection and radiation) were tested. The study used three solutions: sucrose 5%, mannitol 5%, and dextran 10%. SEM images coupled with an automated image segmentation technique were also performed to examine possible correlations between the freezing observations and the resulting pore size distributions. IR thermography was found to be a promising tool for experimentally predicting the resulting product morphology in-line.

Experimental Study on Axial Temperature Profile of Jet Fire of Oil-Filled Equipment in Substation

With the widespread use of substations around the world, oil jet fire accidents from transformer oil-filled equipment in substations caused by faults have occurred from time to time. In this paper, a series of transformer oil jet fire experiments are carried out by changing the external heat source (30 cm and 40 cm) and the inner diameter of the container (5 cm, 8 cm and 10 cm) to study the axial centerline temperature distribution of the transformer oil jet fire plume of the transformer oil-filled equipment in the substation. The experiment uses K-type thermocouple, electronic balance and CCD to measure and assess the temperature distribution of the axial centerline of the fire plume of the transformer oil jet. The result demonstrates that the axial centerline temperature of the fire plume increases with the external heat release rate and the inner diameter of the container. In addition, a novel axial temperature distribution prediction model of the transformer oil jet fire plume is established. This model can effectively predict the oil jet fire plume temperature of transformer oil- filling equipment in substations, and provide help for substation fire control.

Tilt Pad Bearing Distributed Pad Inlet Temperature with Machine Learning -Part I: Static and Dynamic Characteristics

Uncertainty in mixing coefficients MC for estimating pad leading edge film temperature in tilt pad journal bearings, reduces the reliability of predicted characteristics. A 3D Hybrid Between Pad (HBP) model, utilizing CFD and machine learning ML, is developed to provide the radial and axial temperature distributions at the leading-edge. This provides a ML derived, 2D film temperature distribution in place of a single uniform temperature. This has a significant influence on predicted journal temperature, dynamic coefficients, and Morton Effect response. An innovative Finite-Volume-Method (FVM) solver significantly increases computational speed, while maintaining comparable accuracy with CFD. Part I provides methodology and simulation results for static and dynamic characteristics, while Part II applies this to Morton Effect response.

A Study on Radial and Axial Temperature Effects on the Growth of Bulk Single Crystal of SixGe1-x in Bridgman Setting

A Study on Radial and Axial Temperature Effects on the Growth of Bulk Single Crystal of SixGe1-x in Bridgman Setting