Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2011. / Please refer to full text to view abstract.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The optimal design of a heat exchanger for a specified heat transfer, pressure drop and set of ambient conditions entails minimising space, weight, material usage and overall cost. However, the variables which influence the performance as well as the overall cost of a heat exchanger are not related in a simple way and it is not obvious which variables play the most important roles (Perry & Green, 1997:11-44). Air cooled heat exchangers (ACHEs) are normally designed in three stages, by different experts in the field, and with the aid of specially designed software. This project combines these thermal, mechanical and cost estimation processes into a MS Excel model which makes it easier to see the influence that design parameters have on the overall cost of the heat exchanger. A thermal model was created to design an API 661 (2006) ACHE. The results from this model compared well with those of HTRI Xchanger Suite 6.0 software, with HTRI being more conservative in its design mode. A mechanical design model was then developed, which uses as inputs the outputs of the thermal design. The output from this mechanical design model is the minimum material thicknesses based on the stress criteria of Appendix 13 of ASME VIII div 1 (2007) Boiler and Pressure Vessel Code. An experiment on a finned tube bundle was performed in a wind tunnel facility to determine performance characteristics and compare these to existing correlations in literature. The results showed that both the heat transfer coefficient (h) and loss coefficient (Eu) correlations proposed by Ganguli et al. (1985) closely predict the measured data, and were consequently used in the thermal design model. During this experiment it was also shown that the tube bundle reached 8 % - 9 % of its allowable internal fouling factor, due to rust build up inside the tubes, and in a testing period of only nine days. The thermal and mechanical models were then combined with a cost estimation process to perform both a thermal and mechanical parametric study. The thermal study showed that to obtain an optimal solution, the design must attempt to maximise the length, increase the width rather than the number of bays, make use of two bundles per bay with fewer but larger fans and employ a large number of tube rows with the least number of tube passes. These guidelines were used to create an initial design; Excel Solver was then applied to locate the optimum combination of bundle length and width that result in the minimum heat exchanger cost. Two mechanical considerations were investigated, both requiring additional welding and thus increased welding cost. Firstly the use of stay plates result in reduced required plate thicknesses according to the stress criteria since it provides additional stiffness in the header box design. Secondly the use of more (but smaller) nozzles as opposed to less (but larger) nozzles was also considered. The mechanical parametric study showed no specific trends, but both considerations should still be checked as it can be cost beneficial in a specific design. / AFRIKAANSE OPSOMMING: Optimale ontwerp van ’n warmteoordraer vir ’n gespesifiseerde warmteoordrag, drukval en stel van omgewingstoestande behels die minimalisering van ruimte, gewig, materiaalverbruik en algehele koste. Die veranderlikes wat egter die werkverrigting, sowel as die algehele koste, van ’n warmteoordraer beïnvloed, hou nie in ’n eenvoudige sin met mekaar verband nie, en dit is nie vanselfsprekend watter veranderlikes die belangrikste rolle speel nie (Perry & Green, 1997:11-44). Lugverkoelde warmteoordraers (air-cooled heat exchangers of ACHEs) word normaalweg in drie fases ontwerp deur verskillende kundiges in die veld en met behulp van spesiaal ontwerpte programmatuur. Hierdie studie kombineer dié termiese, meganiese en kosteberamingsprosesse in ’n MS Excel-model, wat dit makliker maak om van te stel wat die invloed wat ontwerpparameters op die algehele koste van die hitteruiler is. ’n Termiese model is geskep om ’n “API 661 (2006) ACHE” te ontwerp. Die resultate van hierdie model het goed vergelyk met dié van die HTRI Xchanger Suite 6.0-program, met HTRI meer konserwatiew in die ontwerp af. Na die termiese model geskep is, is ’n meganieseontwerp-model ontwikkel, wat as insette die uitsette van die termiese ontwerp gebruik het. Die uitset van hierdie meganieseontwerp-model is die minimum materiaaldikte gebaseer op die spanningskriteria van Bylae 13 van “ASME VIII div 1 (2007) Boiler and Pressure Vessel Code.” Daar is ’n eksperiment op ’n vinbuisbundel in ’n windtonnelfasiliteit uitgevoer om werkverrigtingskarakteristieke te bepaal en dit met bestaande korrelasies in die literatuur te vergelyk. Die resultate het getoon dat sowel die warmteoordragskoëffisiënt (h) en die verlieskoeffisient (Eu) korrelasies, voorgestel deur Ganguli et al. (1985), die data wat gemeet is akkuraat voorspel, en gevolglik is die korrelasies in die termieseontwerp-model gebruik. Gedurende die eksperiment is ook getoon dat die buisbundel 8 % - 9 % van sy toelaatbare interne-aanpakkingfaktor bereik het vanweë roesopbou binne-in die buise, en dit in ’n toetsingtydperk van slegs nege dae. Die termiese en meganiese modelle was toe gekombineer met ’n kosteberamingsproses om ’n termiese sowel as ’n meganiese parametriese studie uit te voer. Die termiese studie het getoon dat, om ’n optimale oplossing te verkry, die ontwerp moet poog om die lengte te maksimeer; die wydte eerder as die aantal strate (bays) te vermeerder; van twee bundels per straat gebruik te maak met minder, maar groter waaiers; en ’n groot aantal buisrye met die kleinste hoeveelheid buisdeurvloeiweë in te span. Hierdie riglyne is gebruik in ’n aanvanklike ontwerp, waarna die Excel Solver gebruik is om die optimale kombinasie van bundellengte en –wydte vas te stel met die oog op die laagste moontlike warmteoordraerkoste. Twee meganiese oorwegings is ondersoek wat albei addisionele sweiswerk sou vereis en dus tot verhoogde sweiskoste sou lei. Eerstens lei die gebruik van ankerplate (stay plates) tot ’n vermindering in die vereiste plaatdiktes volgens die spanningskriteria, aangesien dit addisionele stewigheid in die spruitstukhouerontwerp bied. Tweedens is die gebruik van meer (maar kleiner) spuitstukke teenoor minder (maar groter) spuitstukke ook oorweeg. Die meganiese parametriese studie het geen spesifieke voorkeurneigings getoon nie, maar altwee oorgewings moet nog getoets word want dit kan koste voordelig word in 'n spesifieke ontwerp.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: High temperature heat sources are becoming an ever-increasing imperative in the process industry for the production of plastics, ammonia and fertilisers, hydrogen, coal-toliquid fuel and process heat. Currently, high temperature reactor (HTR) technology is capable of producing helium temperatures in excess of 950°C; however, at these temperatures, tritium, which is a radioactive contaminant found in the helium coolant stream, is able to diffuse though the steel retaining wall of the helium-to-steam heat exchanger. To circumvent this radioactivity problem, regulations require an intermediate heat exchange loop between the helium and the process heat streams. In this paper, the use of a uniquely designed sodium-charged heat pipe heat exchanger is considered, and has the distinct advantage of having almost zero exergy loss as it eliminates the intermediate heat exchange circuit. In order to investigate this novel heat pipe heat exchanger concept, a special intermediate-temperature (± 240°C) experimental heat pipe heat exchanger (HPHE) was designed. This experimental HPHE uses Dowtherm A as working fluid and has two glass windows to enable visual observation of the boiling and condensation two-phase flow processes. A high temperature air-burner supply simulates the high temperature stream, and the cold stream is provided by water from a constant-heat supply tank. This experimental apparatus can be used to evaluate the validity of steady-state and start-up transient theoretical models that have been developed. This paper will highlight the special design aspects of this HPHE, the theoretical model and the solution algorithm described. Experimental results will be compared with the theoretically calculated results. The theoretical model will then be used to predict the performance of a high temperature (sodium working fluid at 850°C) HPHE will be undertaken and conclusions and recommendation made. / AFRIKAANSE OPSOMMING: Hoë temperatuur hitte bronne is besig om ‘n toenemende noodsaaklikheid te raak in die proses industrie vir die vervaardiging van plastieke, ammoniak, kunsmis, waterstof, steenkool-tot-vloeibare brandstof en proses hitte. Huidige hoë temperatuur reaktor tegnologie is in staat om helium te verhit tot temperature hoër as 950°C, maar by sulke hoë temperature is die vorming van tritium, wat ‘n radioaktiewe produk is, in die helium verkoeling stroom wat deur die reaktor vloei, ‘n probleem. Die tritium is in staat om deur die staal wand van ‘n enkel fase warmte uitruiler te diffundeer. Om hierdie radioaktiewe probleem te uitoorlê, stel huidige regulasies voor dat ‘n oorgangs hitte uitruil lus gebruik raak tussen die helium en proses strome van die reaktor stelsel. In hierdie tesis word ‘n unieke natrium gevulde hitte pyp warmte uitruiler nagevors, hierdie ontwerp het die voordeel dat dit geen “exergy” verlies het omdat dit nie ‘n oorgangs hitte uitruil lus benodig nie. Hierdie unieke konsep was nagevors deur ‘n spesiale oorgangs temperatuur (± 230°C) eksperimentiële hitte pyp warmte uitruiler te ontwerp. Hierdie eksperimentiële hitte pyp warmte uitruiler gebruik Dowtherm A as oordrags medium tussen die warm en koue strome en het twee glas venters waardeur die kook en kondensasie van die oorgangs medium dop gehou kan word. ‘n Hoë temperatuur verbrander simuleer die warm stroom deur die reaktor en die koue stroom word gesimuleer deur koue water. Die eksperimentiële opstelling sal gebruik word om die tyd afhangklike en tyd onafhangklike teoretiese wiskundige modele te valideer. Hierdie tesis sal die spesiale ontwerp aspekte van die hitte pyp warmte uitruiler, teoretiese modelle en oplos algoritme te bespreek. Eksperimentiele resultate sal met die teoretiese resultate vergelyk word en dan sal die teoretiese modelle gebruik word om ‘n natrium gevulde warmte uitruiler te simuleer. Gevolgtrekkings en aanbevelings sal in die lig van die resultate verskaf word.

Thesis (MEng) -- Stellenbosch University, 2014. / ENGLISH ABSTRACT: This project investigates aspects of a novel inherently safe nuclear power steam supply system as safety is of paramount importance. The system envisaged has unique features namely: a) a two-phase flow flash-tube type natural circulating primary loop (also the secondary radioactive particle containment); b) a twophase flow thermosyphon heat pipe type heat exchanger secondary loop is used to transfer heat from the primary loop to the steam generators, thereby physically separating the two flow streams from one another; c) a natural convection air cooled condenser for the removal of the reactor’s residual heat; d) a unique core using TRISO type fuel (acting as the primary radioactive particle containment) with life of at least 8.9 years; e) a steel containment vessel acting as a tertiary radioactive product containment; f) a concrete containing structure with air vents to allow air to pass over the main steel containment vessel for cooling purposes in the case of an emergency, and for the removal of parasitic heat during operation. In particular the primary and secondary loops of the proposed system are investigated. This is done by design, construction and testing of a small scale experimental set-up of the primary and secondary loops as well as the development of theoretical models for the two loops. A literature survey focusing on nuclear technology, thermosyphon loops, natural circulating loop instabilities, heat pipes, and two-phase flow modelling is presented to give a brief overview of the technologies as well as tools used in the work undertaken. Observations of the inside flow behaviour of the primary loop experimental set-up were made possible by windows providing many insights into the inner workings, such as plume formation and geysering. The transient response of the secondary heat pipe loop start-up is also investigated. A thermal resistance theoretical model was developed for the secondary loop using heat transfer formulae from theory as well as experimentally semiempirical correlated formula. Different states of operation of the secondary loop were observed during testing with the theoretical model of the condensing regime correlating well, two-phase regime correlating acceptably and liquid regime correlating poorly to experimental results and thus were modelled using an experimentally determined overall heat transfer coefficient. The secondary loop model of the liquid regime is coupled with the primary loop theoretical model to predict the system’s performance. A homogeneous, one-dimensional, simple theoretical model for the primary loop was derived and computer simulated. The results did not compare well with experimental results for single phase flow and failed to capture the onset of two-phase flow. The assumptions of one dimensional model with a unidirectional flow, a hydrostatic pressure problem, a constant volumetric flow rate and the inability of the implementation of the code to handle expansion are noted as some of the flaws in the theoretical model. The following recommendations are made: a more advanced design of the pressuriser should be incorporated into the experiment; the secondary loop’s theoretical model should be characterised under a broader set of operating conditions; the computer program can be used as the basis for further research and implementation of alternative solution algorithms and models. / AFRIKKANSE OPSOMMING: Hierdie projek ondersoek aspekte van ’n ongewone, essensieel veilige kernkrag stoomtoevoer-stelsel, omdat veiligheid van kardinale belang is. Die stelsel wat voorgestel is, het unieke eienskappe, naamlik: a) ’n twee-fasevloei flits-buistipe natuurlik sirkulerende primêre lus (wat ook die sekondêre inperking van radioaktiewe materiaal bevat); b) ’n twee-fasevloei termo-heweleffek sekondêre lus hitte-pyp hitte-uitruiler word gebruik om die hitte vanaf die primêre lus oor te dra na die stoomkragopwekkers en daardeur word die twee strome se vloei fisies geskei van mekaar; c) ’n natuurlike konveksie lugverkoelde kondensor word gebruik vir die verwydering van die reaktors se oortollige hitte; d) ’n unieke kern gebruik TRISO-tipe brandstof (wat as die primêre inperking van radioaktiewe materiaal optree) met ’n lewe van minstens 8.9 jaar; e) ’n inperkingshouer van staal wat optree as ’n tersiêre radioaktiewe produkhouer; f) ’n betonstruktuur met lugventilasie om toe te laat dat lug oor die hoof staalhouer vloei vir verkoeling in ’n noodgeval, en vir die verwydering van parasitiese hitte tydens werking. Hoofsaaklik word die primêre en sekondêre lusse van die voorgestelde stelsel ondersoek. Dit word gedoen deur die ontwerp, konstruksie en die toets van ’n eksperimentele opstelling van die primêre en sekondêre lusse op klein skaal, sowel as die ontwikkeling van teoretiese modelle vir die twee lusse. ’n Literatuurstudie wat fokus op kerntegnologie, termo-heweleffeklusse, natuurlik sirkulerende lus instabiliteit, hitte-pype, en twee-fase vloeimodellering word aangebied om ’n kort oorsig te gee van die tegnologie, sowel as gereedskap gebruik in die werk wat onderneem is. Om die interne vloeigedrag van die primêre lus se eksperimentele opstelling waar te neem, word daar gebruik gemaak van vensters wat dien as ’n manier om die innerlike werking van die proses soos pluimvorming en die kook van die water in die warmwaterkolom te toon. Die oorgangsreaksie van die sekondêre hittepyplus aanvangs is ook ondersoek. ’n Teoretiese termiese weerstandmodel is ontwikkel vir die sekondêre lus met behulp van hitte-oordragformules waarvoor hitte-oordragteorie gebruik is, wat met eksperimentele semi-empiriese formules gekorreleer is. Verskillende toestande van die sekondêre lus se werking is waargeneem gedurende die toetse. Die teoretiese model het goed met die kondensasiestaat gekorreleer, terwyl by die twee-fasewerkswyse aanvaarbare korrellasies aangetref is en die uiteindelike vloeitoestand swakker gekorrelleer het met eksperimentele resultate en dus gemodelleer is met behulp van die NTU-effektiwiteitsmetode. Die sekondêre lusmodel van die vloeistoftoestand is gekoppel met die primêre lus teoretiese model om die werking van die stelsels te voorspel. ’n Homogene een-dimensionele eenvoudige teoretiese model van die primêre lus is afgelei en ’n rekenaar simulasie is uitgevoer. Die resultate vergelyk nie goed met die eksperimentele resultate vir enkelfasevloei en kon nie die aanvang van twee-fasevloei beskryf nie. Die aannemings van ’n een-dimensionele model met eenrigting vloei, ’n hidrostatiese druk probleem, ’n konstant volumetries vloeitempo en die onvermoë van die implementering van die kode om uitbreiding te hanteer is bekend as ’n paar van die foute in die teoretiese model. Die volgende aanbevelings word gemaak: ’n meer gevorderde ontwerp van drukreëlaar moet in die eksperiment ingesluit word; die sekondêre lus se teoretiese model moet gekenmerk word onder ’n wyer stel bedryfsomstandighede, en die rekenaar program kan gebruik word as die basis vir verdere navorsing en die implementering van alternatiewe algoritmes en modelle.

Superconductors present great potential for weight reduction and increased power delivery when compared to traditional copper power delivery systems, but current systems require cryogenic cooling systems. Traditional superconductor cooling systems consist of helium cooled by helical heat exchangers made of Oxygen Free High thermal Conductivity (OFHC) copper tube. The helium is cooled by bulky heat exchangers consisting of OFHC copper coils wrapped around a cryogenic cooler heat sink for heat transfer into the working fluid. Metal foams have recently been studied in a variety of heat transfer applications, and could greatly reduce the weight of heat exchanger modules in superconductor cooling systems while simultaneously providing increased heat transfer effectiveness. Aluminum and Copper foams have been available for several years, but more recently, graphite foams, such as PocoFoam™, have been developed which have particularly good heat transfer characteristics. Using Computational Fluid Dynamics (CFD) to model a cryogenic heat exchanger application, this study examines the effectiveness and pressure drop of several metal foam heat exchangers, and compares their performance with the traditional helical coil design for superconductor cooling applications. The CFD simulation results show that a heat exchanger with the same heat sink contact area as existing helical heat exchangers weighs up to 95 percent less and can be up to 25 percent more effective, depending on system conditions such as pressure, cryogenic cooler temperature and helium inlet temperature. Aluminum and copper foam heat exchangers had comparable weight to the PocoFoam heat exchanger, but were significantly less effective than the helical or PocoFoam heat exchanger models.

Concevoir des dispositifs thermiques plus compacts, nécessitant moins de masse de matière, produisant moins de pertes de charge et présentant un rendement thermique accru représente un enjeu clé pour des performances améliorées à un coût moindre. La présente thèse étudie le potentiel et la validité de l’optimisation topologique en tant qu’outil CFD viable permettant de générer des designs thermiques optimaux par rapport aux approches conventionnelles telles que l’optimisation de forme et paramétrique. La première partie de la thèse présente une étude expérimentale de structures bi matériaux arborescentes optimales obtenues par optimisation topologique. Le problème mathématique d’optimisation topologique est formulé et implémenté dans OpenFOAM®. Il est appliqué au problème d’optimisation de la conduction thermique dans une configuration de type volume-vers-point. Des mesures thermiques expérimentales sont effectuées sur les structures optimisées, en utilisant la thermographie infrarouge afin de quantifier leurs performances de transfert de chaleur et ainsi validé les performances des structures optimales déterminées par le code d’optimisation topologique développé. La deuxième partie de la thèse présente une technique bi-objectif innovante d’optimisation topologique des systèmes de transferts de chaleur conjugués (CHT, Conjugate Heat Transfer) en régimes d’écoulement laminaires. Pour cela, le problème est développé mathématiquement et implémenté dans le solveur OpenFOAM® basé sur une méthode directe par volumes finis. La fonction objectif est formulée par la pondération linéaire de deux fonctions objectifs, l’une pour la réduction de la perte de charge et l’autre pour l’augmentation du transfert de chaleur. Ceci représente une cible très difficile du point de vue numérique en raison de la concurrence entre les deux objectifs (minimisation de la perte de charge et maximisation de la puissance thermique récupérable). Des designs non intuitifs, mais optimaux au sens de Pareto, ont été obtenus, analysés, discutés et justifiés à l’aide de diverses méthodes d’analyses numériques globale et locale. De plus, une configuration identique à une optimisation par une méthode Lattice Boltzmann issue de la bibliographie a été optimisée en utilisant le solveur OpenFOAM® développé. L’objectif, en complément de la comparaison des solutions optimales, est également d’initier un cas de référence pour les futures études dans ce domaine de recherche et d’innovation de façon à pouvoir pleinement comparer les solutions optimales obtenues par différences méthodes et différents solveurs. Enfin, les différents points expérimentaux et numériques mis en lumière et illustrés dans cette thèse démontrent l’importance de la méthodologie et potentiel très important de l’optimisation topologique pour la conception de systèmes thermiques industriels plus performants. / Designing thermal devices that are more compact with less mass, less frictional losses and increased thermal efficiency is a key requirement for enhanced performances at a lower cost. The present PhD thesis investigates the potential and validity of topology optimization numerical method as a viable CFD tool to generate optimal thermal designs as compared to conventional approaches like shape and parametric optimization. The first part of the thesis presents an experimental investigation of topology optimized tree-like structures made of two materials. The topolgy optimization mathematical problem is formulated and implemented in OpenFOAM®. It is applied to the topolgy optimization problem of volume-to-point heat removal. Experimental thermal measurements are carried out, on the optimal structures, using infrared thermography in order to quantify their heat transfer performances and thus validate the performances of the optimal structures determined by the developed topology optimization code. The second part of the thesis presents an innovative bi-objective optimization technique for topology optimization of Conjugate Heat Transfer (CHT) systems under laminar flow regimes. For that purpose, an inequality constrained bi-objective topology optimization problem is developed mathematically and implemented inside the Finite Volume based OpenFOAM® solver. The objective function is formulated by linear combination of two objective functions for pressure drop reduction and heat transfer enhancement which is numerically a very challenging task due to a competition between the two objectives (minimization of pressure drop and maximization of recoverable thermal power). Non-intuitive Pareto-optimal designs were obtained, analyzed, discussed and justified with the help of various global and local numerical analysis methods. Additionally, a recent Lattice Boltzmann topology optimization problem form the literature was solved using the developed OpenFOAM® solver. The objective, in addition to the comparison of the optimal solutions, is also to initiate a case of reference for future studies in this field of research and innovation so as to be able to fully compare the optimal solutions obtained by different and different methods. solvers. Finally, the various experimental and numerical findings highlighted and illustrated in this PhD thesis, demonstrate the importance of the methodology and immense potential behind topology optimization method for designing efficient industrial thermal systems.

<div>Enhancements of gas turbine engines efficiency are critical for the development of the next generation of clean and efficient aircraft. With the increase in combustion temperatures, cooling of the turbine blades poses one of the most important thermal management issues. The current and most adopted solution is to flow cooling air bled from the compressor through channels inside turbine blades. Fuel preheating, meant to increase combustion efficiency, could be used to cool such air flow in fuel-air heat exchangers. However, when fuel thermodynamic states approach supercritical pressures and temperatures, large amplitude oscillations have been known to occur with catastrophic hardware failures. For this reason, the use of supercritical fuels in fuel-air heat exchangers has been avoided, thereby reducing the fuel's cooling potential and the overall efficiency of the aircraft. Engine manufacturers desire a model capable of predicting the onset of such disruptive thermoacoustic oscillations. To this goal, we study theoretically and numerically transcritical thermoacoustic oscillations, i.e., thermoacoustic instabilities manifesting themselves when a fluid is heated close to its critical point, where abrupt changes of thermodynamic properties appear. Details of this work will be on the development of a transcritical thermoacoustic theory and on numerical results from linear stability analysis and high-fidelity Navier-Stokes simulations. Meeting the needs of industry and with the intent of pushing technological and scientific barriers, we propose to exploit such powerful oscillations for energy conversion through the use of the first-ever-built transcritical thermoacoustic engine.</div>

Se ha desarrollado y construido una infraestructura experimental orientada a la validación de modelos de intercambiadores compactos de aletas y tubos y sistemas de refrigeración con sobrealimentación de líquido. El objetivo ha sido la obtención de datos experimentales fiables, con condiciones geométricas y de contorno exactamente definidas, para poder compararlos inequívocamente con resultados de simulaciones numéricas. Se presentan los modelos matemáticos, objetivo de la validación, y una descripción detallada del circuito de aire, del refrigerante líquido, y del refrigerante de cambio de fase, que integran la infraestructura.Estos tres circuitos están encargados de asegurar condiciones estables y controladas para los prototipos ensayados y para el sistema de refrigeración con sobrealimentación de líquido, en un amplio rango de temperaturas, flujos másicos y potencias. El diseño permite el ensayo de prototipos de intercambiadores de calor con diferentes geometrías y dimensiones. Se presentan detalladamente los instrumentos de medida con sus precisiones, montaje, se describen también los componentes y los parámetros de la unidad de adquisición de datos.Especial atención se ha dedicado a la calibración de los instrumentos de medida como parte esencial del proceso de preparación de los ensayos. Se describe el proceso de estimación de las incertidumbres sistemáticas de los sensores calibrados. Se expone en detalle la formulación y la metodología adoptada para el análisis de incertidumbre de los resultados experimentales.El procesamiento y el análisis de los datos experimentales se ha realizado en forma automática con un código computacional especialmente desarrollado, encargado de calcular los resultados a partir de las variablas medidas, de llevar a cabo el análisis de incertidumbres detallado, y de comparar los resultados numéricos y experimentales.Se presentan resultados experimentales obtenidos con la infraestructura experimental desarrollada. Se presentan estudios detallados de intercambiadores de calor compactos en condiciones de enfriamiento de aire, utilizando refrigerante líquido y de cambio de fase. Se presentan también resultados del estudio experimental del sistema de refrigeración con sobrealimentación de líquido. Los resultados han sido comprobados y verificados a través de balances energéticos en todos los componentes, donde la misma magnitud física ha sido evaluada de mediciones independientes. Con el objetivo de permitir el uso mas general de los resultados experimentales se presentan también los datos crudos de las variables medidas durante los ensayos.Se ha propuesto una metodología de validación para el modelo de intercambiadores compactos, basada en comparaciones sistemáticas de resultados numéricos y experimentales. Estas comparaciones han sido analizadas en términos estadísticos con el objetivo de cuantificar las diferencias observadas y dar una evaluación global de las prestaciones del modelo numérico en las condiciones ensayadas. La metodología propuesta para la validación del modelo de intercambiadores compactos puede ser utilizada como base para metodologías de validación en general. / Experimental infrastructures intended for validation of compact heat exchanger models, and models of liquid overfeed refrigeration systems have been developed and constructed. The aim has been the obtaining of reliable experimental data from tests at exactly defined geometrical and boundary conditions, permitting the unequivocal comparisons with numerical simulation results. The mathematical models are presented and detailed description of the airhandling, the liquid refrigerant, and phase-changing refrigerant circuits integrating the experimental infrastructure is given.These three circuits are encharged to provide stable controlled conditions for the tested prototypes and the liquid overfeed system in the desired range of temperatures, fluid flows, and capacities. The design permits the accommodation of heat exchanger prototypes with different geometry and sizes.Detailed overview of the measuring instruments is presented, with their accuracies and mounting, and the components and parameters of the data acquisition system are described.Special attention has been paid to the calibration of the measuring instruments as an essential part of the test preparation. The process of estimation of the systematic uncertainties in the calibrated sensors measurements is described. The formulation and the methodology adopted for the uncertainty analysis of the experimental results is exposed in detail.The experimental data processing and analysis has been performed automatically with a specially developed program encharged with the calculation of the experimental results from the measured variables, the detailed uncertainty analysis, and the numerical to experimental results comparisons.Experimental results obtained with the developed infrastructure are presented. Detailed studies of compact heat exchangers under cooling conditions, using liquid and phase-changing refrigerants, are performed and presented. Results from the experimental studies of the liquid overfeed refrigeration system are also presented. The results have been checked and verified through energy balance checks for all the components where measurements of the same physical magnitude can be contrasted with independent measurements. In order to give more general use of the obtained experimental data, the raw measured variables during the tests are also presented.An experimental validation methodology for the compact heat exchanger model has been proposed, based on systematic comparisons between numerical and experimental results. The comparisons have been analysed in statistical terms in order to quantify the observed differences and to give global evaluation of the numerical model performance in the tested conditions. The methodology proposed for validation of the heat exchanger model can be used as a basis for validation methodology for numerical models in general.

Accurate forecasting is a real problem at many companies and that includes Alfa Laval in Lund. Alfa Laval experiences problems forecasting for future raw material demand. Management is aware that the forecasting methods used today can be improved or replaced by others. A change could lead to better forecasting accuracy and lower errors which means less inventory, shorter cycle times and better customer service at lower costs. The purpose of this study is to analyze Alfa Laval’s current forecasting models for demand of raw material used for pressed plates, and then determine if other models are better suited for taking into consideration trends and seasonal variation.

Finned-tube heat exchangers are predominantly used in space conditioning systems, as well as other applications requiring heat exchange between two fluids. One important widespread use is in residential air conditioning systems. These residential cooling systems influence the peak demand on the U.S. national electrical system, which occurs on the hot summer afternoons, and thereby sets the requirement for the expensive infrastructure requirement of the nations power plant and electrical distribution system. In addition to this peak demand, these residential air conditioners are major energy users that dominate residential electrical costs and environmental impact. The design of finned-tube heat exchangers requires the selection of over a dozen design parameters by the designer. The refrigerant side flow and heat transfer characteristics inside the tubes have been thoroughly studied. However, the air side flow around the tube bundle and through the fin gaps is much more complex and depends on over a dozen design parameters. Therefore, experimental measurement of the air side performance is needed. First this study built an experimental system and developed methodology for measuring the air side heat transfer and pressure drop characteristics of fin tube heat exchangers. This capability was then used to continue the goal of expanding and clarifying the present knowledge and understanding of air side performance to enable the air conditioner system designer in verifying an optimum fin tube condenser design. In this study eight fin tube heat exchangers were tested over an air flow face velocity range of 5 ?? ft/s (675-1600cfm). The raw data were reduced to the desired heat transfer and friction data, j and f factors. This reduced heat transfer and friction data was plotted versus Reynolds number and compared. The effect of fin spacing, the number of rows and fin enhancement were all investigated. The heat transfer and friction data were also plotted and compared with various correlations available from open literature. The overall accuracy of each correlation to predict experimental data was calculated. Correlations by C.C. Wang (1998b, 1999) showed the best agreement with the data. Wangs correlations (1998b, 1999) were modified to fit the current studys data.