Heat insulation is the process of blocking the transfer of thermal energy between objects at different temperatures. Heat transfer occurs due to conduction, convection, or radiation, as well as any combination of these three mechanisms. Fibrous insulations can completely suppress the convective mode of heat transfer for most applications, and also help to reduce the conductive and radiative modes to some extent. In this study, an attempt has been made to computationally predict the effects of microstructural parameters (e.g., fiber diameter, fiber orientation and porosity) on the insulation performance of fibrous materials. The flexible simulation method developed in this work can potentially be used to custom-design optimal multi-component fibrous insulation media for different applications. With regards to modeling conductive heat transfer, a computationally-feasible simulation method is developed that allows one to predict the effects of each microstructural parameter on the transfer of heat across a fibrous insulation. This was achieved by combining analytical calculations for conduction through interstitial fluid (e.g., air) with numerical simulations for conduction through fibrous structures. With regards to modeling radiative heat transfer, both Monte Carlo Ray Tracing and Electromagnetic Wave Theory were implemented for our simulations. The modeling methods developed in this work are flexible to allow simulating the performance of media made up of different combinations of fibers with different materials or dimensions at different operating temperatures. For example, our simulations demonstrate that fiber diameter plays an important role in blocking radiation heat transfer. In particular, it was shown that there exists an optimum fiber diameter for which maximum insulation against radiative transfer is achieved. The optimum fiber diameter is different for fibers made of different materials and also depends on the mean temperature of the media. The contributions of conduction and radiation heat transfer predicted using the above techniques are combined to define a total thermal resistance value for media with different microstructures. Such a capability can be of great interest for design and optimization of the overall performance of fibrous media for different applications.

This report discusses the use of micro-fabrication techniques for creating experimental test sections containing trees of micro-finned conducting pathways, also referred to as constructal trees, for cooling a heat generating substrate. These trees are made of copper and contain branches that bifurcate at 90° angles to form constructal patterns. The patterns for the finalized test sections were created using photolithography techniques, and copper was deposited via thermal evaporation onto a 1 cm² substrate to create the trees. Certain test section design parameters were varied including the geometric complexity of the constructal trees, the volume of copper used between tree complexities, choice of material for the substrate, and the height, or thickness, of the trees. Also described in this report is an experimental methodology and testing apparatus designed to assess the cooling performance of the test sections. This methodology includes using controlled uniform heating applied to the bottom of each test section, while cooled nitrogen is impinged on the tip of the constructal tree to create a heat sink. / text

abstract: Granular material can be found in many industries and undergo process steps like drying, transportation, coating, chemical, and physical conversions. Understanding and optimizing such processes can save energy as well as material costs, leading to improved products. Silica beads are one such granular material encountered in many industries as a catalyst support material. The present research aims to obtain a fundamental understanding of the hydrodynamics and heat transfer mechanisms in silica beads. Studies are carried out using a hopper discharge bin and a rotary drum, which are some of the most common process equipment found in various industries. Two types of micro-glass beads with distinct size distributions are used to fill the hopper in two possible packing arrangements with varying mass ratios. For the well-mixed configuration, the fine particles clustered at the hopper bottom towards the end of the discharge. For the layered configuration, the coarse particles packed at the hopper bottom discharge first, opening a channel for the fine particles on the top. Also, parameters such as wall roughness (WR) and particle roughness (PR) are studied by etching the particles. The discharge rate is found to increase with WR, and found to be proportional to (Root mean square of PR)^(-0.58). Furthermore, the drum is used to study the conduction and convection heat transfer behavior of the particle bed with varying process conditions. A new non-invasive temperature measurement technique is developed using infrared thermography, which replaced the traditional thermocouples, to record the temperatures of the particles and the drum wall. This setup is used to understand the flow regimes of the particle bed inside the drum and the heat transfer mechanisms with varying process conditions. The conduction heat transfer rate is found to increase with decreasing particle size, decreasing fill level, and increasing rotation speed. The convection heat transfer rate increased with increasing fill level and decreasing particle size, and rotation speed had no significant effect. Due to the complexities in these systems, it is not always possible to conduct experiments, therefore, heat transfer models in Discrete Element Method codes (MFIX-DEM: open-source code, and EDEM: commercial code) are adopted, validated, and the effects of model parameters are studied using these codes. / Dissertation/Thesis / Doctoral Dissertation Chemical Engineering 2020

The current research investigates the use of solid-embedded thermocouples for determining accurate transient temperature measurements within a solid medium, with emphasis on measurements intended for use in inverse heat conduction problems. Metal casting experiments have been conducted to collect internal mold temperatures to be used, through inverse conduction methods, to estimate the heat exchange between a casting and mold. Inverse conduction methods require accurate temperature measurements for valid boundary estimates. Therefore, various sources of thermocouple measurement uncertainty are examined and some suggestions for uncertainty reduction are presented. Thermocouple installation induced bias uncertainties in experimental temperature data are dynamically corrected through the development and implementation of an embedded thermocouple correction (ETC) transfer function. Comparisons of experimental data to dynamically adjusted data, as well as the inverse conduction estimates for heat flux from each data set, are presented and discussed.

The heat input to the tool has been investigated for friction stir welding (FSW) of aluminum alloy AL 7075-T7351 over a wide range of process operating parameters using a combined experimental/numerical approach. In a statistical Design of Experiments fashion, 54 experimental welds (bead-on-plate) were performed at 27 different parameter combinations. Measured outputs during each of the welds included forces in all three coordinate directions and internal temperature of the rotating tool at three locations near the tool/workpiece interface. The heat input to the tool was also identified for each weld using infrared imaging temperature measurement techniques and the portion of the total mechanical power entering the tool was calculated. These values were subsequently analyzed to identify the effect of process operating parameters. Two-dimensional, axisymmetric numerical heat conduction models of the tool were then produced and the approximate spatial distribution of the heat input to the tool along the tool/workpiece interface was identified. Experimental values for the heat input to the tool ranged from 155 W to 200 W, comprising 2.8% to 5.1% of the total mechanical power. Regression equations developed for the two values show that each is a function of the process operating parameters. Heat conduction models of the tool show that the approximate spatial distribution of the heat input to the tool along the tool/workpiece interface is one where the heat input is distributed non-uniformly along the interface, with 1% entering the tool at the pin, 20% entering at the base of the pin, and the remainder entering the flat portion of the shoulder. This distribution was valid for the majority of process operating parameter combinations tested. The maximum predicted temperature for the simulations occurred in the pin. This result was verified by the experimental tool temperature measurements. Insights gained into the FSW process from the combined experimental/numerical investigation were then discussed.

A model is proposed to predict the heat spreading behaviour experienced by laminate materials when heated over only a part of the domain, which is broken up into two regions, known as the heated and fin regions. The 2D, steady-state, two-region fin model is unique in its treatment of multilayer conduction heat transfer, giving the exact solution in the heat-spreading layer only, in both Cartesian and cylindrical coordinates. The experimentally and numerically validated two region fin model can help designers to assess improved heat transfer rates for laminate pouches for use to encapsulate supercooled salt hydrate phase change materials for long-term heat storage. Waste aseptic cartons (e.g. Tetra Brik) are a potentially useful resource for making laminate heat storage pouches since value-added end-uses are largely absent in Canada and in many other countries. The model is also useful for assessing improved temperature uniformity in heat spreading devices with applied heat fluxes.

The master Thesis deals with indirect air heating in air handling units. In the theoretical part of the thesis the categories of heat exchangers are defined according to their positioning in ventilation system, used material and type of heat transfer fluid. To the issue of calculating heat exchanges through heat exchangers and description of different kinds of regulation of primary heat transfer fluid is dedicated a separate chapter. The experimental part of the thesis deals with determining performance of current air heat exchanger at set thermal gradient with various heat transfer fluids. In the calculating part of the Thesis, based on measured values, are suggested two possible solutions for use of technological waste heat. Final evaluation of particular solutions was based on the criterion of efficiency usage and implementation investment costs.

Viele Anwendungen der Hochtemperatur-Supraleitung arbeiten vorteilhaft im Temperaturbereich zwischen 30 - 50 K. Für diesen Temperaturbereich existieren nur wenige geeignete Kältemaschinen mit kleiner Kälteleistung (1-2 W) u. gutem Wirkungsgrad. Neon ist aufgrund seiner Stoffeigenschaften ein hervorragendes Kältemittel für diesen Temperaturbereich, wie z.B. anhand einer realisierten Joule-Thomson (JT) Demonstrationsanlage deutlich wird. Als Ergebnis einer Prozessanalyse wird ein Kreislauf vorgestellt, der speziell den Eigenschaften von Neon angepasst ist. Durch die Überlagerung von Wärmeübertragung u. arbeitsleistender Expansion sowie der Einbeziehung einer JT-Stufe kann auch mit wenig effizienten Komponenten ein vergleichsweise hoher Gütegrad erreicht werden. Durch die Integration von Wärmeübertragerflächen in eine Kolbenexpansionsmaschine wird ein neues Konzept vorgeschlagen, um Kälte in einem großen Temperaturbereich in vielen Expansionsschritten zu erzeugen, ohne dafür viele Expander zu verwenden. Diese Einheit wird als Wärmeübertrager-Expander (WE) bezeichnet. Mit einem Arbeitsraum in konischer Grundform wird der Wärmeübergangskoeffizient günstig gestaltet u. die Wärmeübergangsfläche vergrößert. Mehrere Versuchsmaschinen wurden untersucht. Anhand der Versuche konnten die wesentlichen Verlustquellen u. Problembereiche identifiziert werden. Es wurde im Rahmen der Versuchsbedingungen nachgewiesen, dass für das vorgesehene Druckverhältnis eine nahe isotherme Expansion u. Kompression möglich ist. Es werden Möglichkeiten zur Verringerung der Längswärmeleitung vorgestellt. Zwei Simulationsprogramme wurden verwendet. Mit Hilfe des Wärmeübertrager-Programms wurden die Wärmeübertragungsvorgänge unter Berücksichtigung der Längswärmeleitung simuliert. Hierbei geht die Expansionsarbeit als stationäre Wärmesenke ein. Der im Ergebnis vorliegende stationäre Temperaturverlauf ist die Grundlage für die Berechnung der Expansionsarbeit unter Berücksichtigung der Realgaseigenschaften im Expander-Programm. Für die Neon-Tieftemperaturvariante wurde eine Grundvariante des WE definiert. Anhand dieser wurde mit Hilfe der Programme der Einfluss verschiedener Parameter auf Kälteleistung u. Gütegrad untersucht. Der WE wird als Teil des beschriebenen Prozesses mit einer JT-Stufe betrachtet. Die Kälteleistung weist sowohl in Abhängigkeit vom Massestrom als auch vom Hub ein Maximum auf. Der Shuttle-Verlust verschiebt durch Wärmetransport mittels des Kolbens die effektive Kälteleistung zu kleineren Hüben. Die durch die Güte (NTU) des JT-Wärmeübertragers bestimmte Eintrittstemperatur des Niederdruckstroms in den WE hat einen großen Einfluss auf die Kälteleistung. Mit steigender Eintrittstemperatur steigen der NTU-Wert für den Arbeitsraum u. somit auch die Kälteleistung. Das Maximum der Kälteleistung stimmt nicht mit dem Optimum für den Gütegrad überein. Der Gütegrad strebt mit sinkenden Masseströmen einem Optimum zu. Durch den zunehmenden Einfluss der Längswärmeleitung u. begrenzt durch die Minimalfüllung der Maschine aufgrund des Schadraumes ergibt sich ein Optimum. Der Einfluss des Massestroms ist entscheidend. Als untergeordnete Größen beeinflussen die Eintrittstemperatur des Niederdruckstroms u. der Hub den optimalen Gütegrad. Der Einfluss der Längswärmeleitung auf Kälteleistung u. Gütegrad wird exemplarisch anhand von vergleichenden Rechnungen gezeigt. Konkret kann für einen Eintrittsdruck von 200 bar, einen Austrittsdruck von 60 bar bei einer Eintrittstemperatur des Niederdruckstroms von 80 K für die Grundvariante eine maximale effektive Kälteleistung von 1,3 W mit einem Massestrom von 0,22 g/ s bei einem Hub von ca. 17 mm ausgewiesen werden. Der effektive Gütegrad für diese Bedingungen beträgt ca. 14%. Kommerzielle Split-Stirlingkühler erreichen bei 42 K einstufig Gütegrade von ca. 7%. Mit der vorgeschlagenen Konfiguration wird ein Konzept vorgestellt, das trotz technologisch offener Fragen das Gütegradniveau bekannter Kryokühler übertreffen kann. / Many applications of high temperature superconductivity are working advantageously within a temperature range between 30 K and 50 K. But for this temperature range only few suitable cryocooler with small refrigerating capacity (1-2 W) and good efficiency exist.Due to its properties Neon is an excellent refrigerant for this temperature level as an example with realised Joule-Thomson plant shows. A process analysis results in the presented cycle which is especially adapted to the properties of Neon. By combination of heat exchange and work extracting expansion and integration of a Joule-Thomson stage a high efficiency could be reached in spite of less efficient components.By arranging heat exchanger surfaces into a piston expansion machine a new concept is suggested to produce refrigeration in a large temperature range with a lot of expansion steps with reduced number of expanders. This unit is referred hereinafter to as heat exchanger-expander.The conical shaped working space results in an increase of the heat transfer coefficient and the heat transfer area.Several test machines were investigated. By means of testing the main loss sources and critical zones could be identified. The test results prove the opportunity of a near isothermal expansion and compression for the specified pressure ratio.Options to reduce the axial heat conduction are presented.Two simulation programs were utilised. Using the heat exchanger program the heat transfer is simulated in consideration of the axial heat conduction. Thereby the expansion work is considered as a stationary heat sink. The resulting stationary temperature pattern is the base for the expansion work calculation using the real gas properties in the expander program. Referring to the defined basic neon low temperature application the influence of different parameters on refrigerating capacity and efficiency was researched with the programs. The heat exchanger-expander is part of the described process with a Joule-Thomson stage. The refrigerating capacity shows a maximum depending as well from the mass flow as from the stroke. In result of the shuttle loss smaller strokes lead to better capacity due to heat transport with the piston.The inlet temperature of the low pressure flow influenced by the quality (NTU) of the Joule-Thomson heat exchanger has a large influence on the refrigerating capacity. With increasing inlet temperature the number of transfer units (NTU) for the fluid in the working volume increases and so the refrigerating capacity, too. The location of refrigerating capacity maximum and efficiency optimum is different. While decreasing mass flow efficiency is increasing to an optimum caused by the increased influence of axial heat conduction but limited by the minimum charge of the machine due to the dead space. The influence of the mass flow is dominating. As lower range values the inlet temperature of the low pressure flow and the stroke are influencing the optimal efficiency. The influence of axial heat conduction on refrigerating capacity and efficiency is shown using comparing calculations.For an inlet pressure of 200 bar, an outlet pressure of 60 bar, an inlet temperature of the low pressure flow of 80 K, a mass flow of 0,22 g/ s and a stroke of about 17 mm for the basic version of heat exchanger-expander a maximal effective refrigerating capacity of 1,3 We could be shown. The effective efficiency therefore is 14 %. Current commercial split Stirling cryocooler reach with single stage operation efficiencies of about 7 % at 42 K. The suggested configuration represents a concept that could be able to master the efficiency level of known cryocooler.