Design of Heating Coils Based on Space-Filling Fractal Curves for Highly Uniform Temperature Distribution

Heating coils utilize the concept of resistive heating to convert electrical energy into thermal energy. Uniform heating of the target area is the key performance indicator for heating coil design. Highly uniform distribution of temperature can be achieved by using a dense metal distribution in the area under consideration, however, this increases the cost of production significantly. A low-cost and efficient heating coil should have excellent temperature uniformity while having minimum metal consumption. In this work, space-filling fractal curves, such as Peano curve, Hilbert curve and Moore curve of various orders, have been studied as geometries for heating coils. In order to compare them in an effective way, the area of the geometries has been held constant at 30 mm × 30 mm and a constant power of 2 W has been maintained across all the geometries. Further, the thickness of the metal coils and their widths have been kept constant for all geometries. Finite Element Analysis (FEA) results show Hilbert and Moore curves of order-4, and Peano curve of order-3 outperform the typical double-spiral heater in terms of temperature uniformity and metal coil length.

Predicting Evaporator Vessel Base Thicknesses From Inspected Heating Coils

The Highly Active Liquid Effluent and Storage plant at Sellafield, UK, currently uses three evaporators to reduce the volume of active liquor stored within the facility before being vitrified for long term storage. This liquor is highly corrosive and the lifetime of the evaporators is potentially limited by the corrosion loss from the heating elements, comprising an external jacket and a number of internal coils, all heated by low pressure steam. Inspection of the heating coils inside the evaporators is possible and measurement data is available of their thicknesses by depth at various inspection intervals. This inspection data has been combined with operational data and thermal models for the heating elements. Our theoretical understanding from laboratory measurements suggests that corrosion is related to temperature through an Arrhenius relationship. As such we have been able to develop a predictive model for the thickness profiles and remaining useful life of the uninspected components. This model is a non-linear mixed effects (multilevel) model and has undergone significant developmental work to account for a number of practical data issues. This paper will briefly outline the various components of the model, whilst discussing issues relevant to any statistical model such as complexities of data collection, approaches to handling correlated data, selecting appropriate model formulations and data transformations. The inclusion of uncertainties in prediction via Monte-Carlo simulation will also be discussed.

A Novel Hybrid Heating Method for Elevated Temperature Mechanical Testing of Miniature Specimens

The lack of robust testing systems to generate uniform elevated temperatures on specimens in material tests is hindering the advancement of small specimen testing technology (SSTT). The purpose of this study is to develop a novel hybrid heating method combining coil heating and electric-resistance specimen heating to uniformly heat micro specimens in material tests. In a hybrid heating process, two heating coils are used to heat the local temperatures on the specimen ends, and electric current is conducted through the specimen to generate Joule heat and compensate the heat transfer effects of natural convection and radiation around the specimen center area. In this way, a highly uniform temperature distribution can be generated on the specimen between the heating coils. In this study, Thermal-Electrical and Transient Thermal FEA simulations are applied to analyze the temperature distributions and preheating times on the micro specimens under coil heating, electric-resistance specimen heating, and hybrid heating respectively. According to the simulation results, it can be concluded that hybrid heating method can provide the ability to generate highly uniform elevated temperature conditions on different micro tubular specimens with short preheating times.