O seguinte trabalho procura estudar problemas de fronteira móvel, conhecidos por problemas de Stefan, bem como aproximar suas soluções. Aplicações de problemas de Stefan encontram-se, por exemplo, na física termal de mudança de estados, presente em diversos fenômenos físicos e químicos naturais e na indústria. Devido a não-linearidade, a maior parte destes problemas não possuem solução analítica conhecida e uma técnica comum para se aproximar soluções é o método de balanceamento integral, inicialmente estudado por Goodman (1958). Este método e suas variações propõem perfis de aproximação no domínio da solução e resolvem uma versão integral da equação diferencial. O problema se resume a resolver uma equação diferencial ordinária no tempo envolvendo a profundidade de penetração do calor e o perfil de aproximação proposto. O trabalho estuda tais métodos para problemas termais clássicos em primeiro lugar, de modo que a extensão para problemas de Stefan seja natural. Refinamentos são apresentados, bem como uma técnica de subdivisão do espaço que resulta num esquema numérico. A técnica de imobilização e fronteira é desenvolvida e aplicada em diversos momentos, a fim de simplificar a utilização dos métodos integrais. / The current work aims to study moving boundary problems, known as Stefan problems, and approximate their solutions. Applications of Stefan problems are found in situations where there is change of physical state, present in several natural and industrial physical and chemical phenomena. Due to their inherent nonlinearity, most of these problems have no known analytic solution and a common technique to approximate solutions is the heat balance integral method, originally studied by Goodman (1958). This method and its variations propose an approximating profile and solve an integral version of the differential equation. The problem is reduced to solving an ordinary differential equation in time involving the depth of heat penetration and the proposed profile. This work studies such classic methods to thermal problems first, in a way that the extension to Stefan problems is natural. Refinements are presented, as well as a technique of subdividing the space domain which results in a numerical scheme. The technique of boundary immobilization is developed and applied at different times in order to simplify the use of these methods.

Master thesis in cooperation with High Voltage Valley (Ludvika) and VB Energi (Ludvika)

With regard to heat stress, the limiting factor inherent in clothing ensembles is the total evaporative resistance. Clothing with higher evaporative resistance impedes the ability to cool by sweat evaporation. Knowing the evaporative resistance provides a means to compare candidate ensembles. Further, a value for evaporative resistance means that a rational method can be used to assess the heat stress exposure. Evaporative resistance of five clothing ensembles (cotton work clothes, cotton coveralls, and three coveralls of particle barrier, liquid barrier and vapor barrier properties) was determined empirically from wear tests during two study phases. For Phase 1, the metabolic rate was held constant at 160 W/m², and three levels of humidity (20, 50, 70% rh) were explored. Fourteen heat-acclimated participants (9 men and 5 women) completed trials for all combinations of clothing ensemble and environment. In the Phase 2 study, the humidity was held constant at 50% rh, and three levels of metabolic rate (114, 176, 250 W/m²) were explored. Fifteen heat-acclimated participants (11 men and 4 women) completed trials for all combinations of clothing ensemble and environment. The data from both phases were analyzed separately using ANOVA. Significant differences were found among ensembles (p<0.0001). The vapor barrier ensemble had the highest resistance at 0.026 kPa m²/W. The liquid barrier was next at 0.018; followed by the particle barrier and cotton coveralls at 0.016. Work clothes was 0.014 kPa m²/W. Vapor and liquid barrier ensembles were found to be significantly different from other ensembles. From the Phase 2 study, evaporative resistances decreased with increased activity and ranged from 0.0024 (cotton coveralls) to 0.0094 (vapor barrier) kPa m²/W. The higher differences were associated with higher total evaporative resistance. The decreased evaporative resistances in Phase 2 can be explained by the pumping action associated with increased work. The relationship of Re,T to the difference of Pair -- Pskin was explored and found Re,T does not remain constant. Environment appeared to influence this relationship.

Η ανταλλαγή θερμότητας μεταξύ ατμόσφαιρας και θάλασσας είναι μια διεργασία πολύ σημαντική για τη δυναμική και τις φυσικές ιδιότητες των δύο μέσων (π.χ. θερμοκρασία) αλλά και σε βάθος χρόνου για το κλίμα ολόκληρου του πλανήτη. Η συνολική ενέργεια που μεταφέρεται από την ατμόσφαιρα στη θάλασσα και αντίστροφα είναι το άθροισμα τεσσάρων επιμέρους συνιστωσών : α) της μικρού μήκους ηλιακής ακτινοβολίας, β) της μεγάλου μήκους υπέρυθρης ακτινοβολίας, γ) της λανθάνουσας θερμότητας και δ) της θερμότητας αγωγιμότητας. Μέσες μηνιαίες τιμές για τις τέσσερις αυτές συνιστώσες από το Ιόνιο και Κρητικό Πέλαγος εξετάζονται για το διάστημα 1958-2007. Οι τιμές προέρχονται από τη Μεσογειακή Βάση Δεδομένων ARPERA και αποτελούν προϊόν διόρθωσης αριθμητικής προσομοίωσης (reanalysis product). Στην παρούσα εργασία παραθέτονται στατιστικά χαρακτηριστικά των χρονοσειρών της κάθε συνιστώσας και στις δύο περιοχές. Από τη μελέτη της ροής θερμότητας και στα δύο Πελάγη διαπιστώθηκαν οι εξής διαφορές : το Κρητικό Πέλαγος εμφανίζει μεγαλύτερες απώλειες θερμότητας σε σχέση με το Ιόνιο καθώς επίσης και μεγαλύτερο δυναμικό αιολικής ενέργειας. / The heat exchange between the atmosphere and the sea is a very important process for the dynamics and physical properties of the two media (e.g. temperature) and long-term climate of the entire planet. The total energy transferred from the atmosphere to the sea and vice versa is the sum of four separate components : a) the short wave solar radiation , b ) the long wave radiation , c ) latent heat and d ) heat conduction . Average monthly prices for these four components of the Ionian and Cretan Sea are examined for the period 1958-2007 . The values ​​come from the Mediterranean Database ARPERA and result correction numerical simulation (reanalysis product). In this thesis I present statistical characteristics of the time series of each component in both regions . From the study of heat flow in both regions we found the following differences: the Cretan Sea shows greater heat loss in relation to the Ionian as well as greater wind potential .

The bacteria Streptomyces venezuelae produce the novel antibiotic jadomycin. The study of growth characteristics and metabolic behavior of the bacteria are necessary to scale up antibiotic production and facilitate further research. In this study, a method for producing consistent inoculum was developed that showed good repeatability when used in growth trials. The rod shaped spores of Streptomyces venezuelae were determined to be approximately 0.8 x 0.2 ?m with a smooth surface type. The effects of temperature and pH on bacterial growth and substrate consumption were examined in a 7 L bioreactor. Of the range of parameters tested (28, 32, 36 °C, and media pH of 5, 7 and 9), 32 °C with a media pH of 7 yielded the highest rate of growth (µmax of 1.43 hours-1 with a lag time of 7.7 hours). The results of all trials showed that free glucose was consumed before the maltose, which was the major sugar substrate in the media. The initiation of exponential bacterial growth occurred after rapid consumption of free glucose. A heat balance analysis was also performed over the bioreactor to identify the heat generated through agitation, losses over the vessel and the heat of metabolism from Streptomyces venezuelae. Under normal operating parameters 33 - 24 % of the heat generated through mixing was lost with the exhaust gas, while 56 - 64 % was lost through the bioreactor wall. The heat of mixing was calculated to be 1.62 J•s-1 while the maximum amount of heat generated by Streptomyces venezuelae metabolism and activity during a growth trial was 2.28 J•s-1 for 60 x 109 CFU?mL-1.

O seguinte trabalho procura estudar problemas de fronteira móvel, conhecidos por problemas de Stefan, bem como aproximar suas soluções. Aplicações de problemas de Stefan encontram-se, por exemplo, na física termal de mudança de estados, presente em diversos fenômenos físicos e químicos naturais e na indústria. Devido a não-linearidade, a maior parte destes problemas não possuem solução analítica conhecida e uma técnica comum para se aproximar soluções é o método de balanceamento integral, inicialmente estudado por Goodman (1958). Este método e suas variações propõem perfis de aproximação no domínio da solução e resolvem uma versão integral da equação diferencial. O problema se resume a resolver uma equação diferencial ordinária no tempo envolvendo a profundidade de penetração do calor e o perfil de aproximação proposto. O trabalho estuda tais métodos para problemas termais clássicos em primeiro lugar, de modo que a extensão para problemas de Stefan seja natural. Refinamentos são apresentados, bem como uma técnica de subdivisão do espaço que resulta num esquema numérico. A técnica de imobilização e fronteira é desenvolvida e aplicada em diversos momentos, a fim de simplificar a utilização dos métodos integrais. / The current work aims to study moving boundary problems, known as Stefan problems, and approximate their solutions. Applications of Stefan problems are found in situations where there is change of physical state, present in several natural and industrial physical and chemical phenomena. Due to their inherent nonlinearity, most of these problems have no known analytic solution and a common technique to approximate solutions is the heat balance integral method, originally studied by Goodman (1958). This method and its variations propose an approximating profile and solve an integral version of the differential equation. The problem is reduced to solving an ordinary differential equation in time involving the depth of heat penetration and the proposed profile. This work studies such classic methods to thermal problems first, in a way that the extension to Stefan problems is natural. Refinements are presented, as well as a technique of subdividing the space domain which results in a numerical scheme. The technique of boundary immobilization is developed and applied at different times in order to simplify the use of these methods.

The main aim of this diploma thesis is design and calculation of steam condensing turbine with given parameters. In the first part is made calculation of heat balance scheme, which contains high and low pressure regeneration and turbine with total of 5 unregulated steam extraction. It is followed by calculation of regulating stage with impulse blading and calculation of stage part of turbine with reaction blades with total of 27 stages divided to 7 cones. Designes of regulating stage and stage part were checked by calculation of tensile and bending stress. In next parts are calculations of compensating piston and turbine seal system, design of radial and thrust bearings and in the last chapter is shown consumption characteristics of turbine. The designed turbine after optimization at nominal condition has power of 55013,02 kW with thermodynamic efficiency of 83,06 %. The reheat factor of turbine is 1,063. The diploma thesis is supplemented by a conceptual sectional drawing of turbine.

Diploma thesis deals with the design of the condensing steam turbine with power output 23.63 MW at 5000 rpm and an efficiency of 84.17% after optimization. The turbine contains one controlled steam extraction and four bleeds. The steam mass flow required by controlled steam extraction is 0-75 t/h of a total mass flow to the turbine 105 t/h. Design of the steam turbine is preceded by calculation of heat balance of the cycle. Then the thermodynamic and strength calculation of regulation stage and reaction staging flow channel are made. Thermodynamic calculation of the flow channel consists of preliminary and detailed calculation. It is detailed calculation that leads to the turbine parameters optimization. The design also includes gland sealing system and balance piston calculation. In addition to the strength calculation there is bearings load calculation included. In the end, the consumption diagram is made, showing the interval by which the turbine can be safely operated. Integrated part of the thesis is conceptual drawing of steam turbine section.

The thesis aims to identify suitable and in the locality available raw materials to a commnon fermentation with sludge from pulp and fodder yeast production in company Biocel Paskov a.s.. Introductory chapter briefly describes the mechanisms of penetration of the sludge itself. The following section deals with origin, chemical composition and properties of biogas. The factors affecting the production of biogas are described. A key part of this thesis is a performance of sludge fermentation test and selected mixed substrate. Acquired knowledge is evaluated and the optimum composition of input raw materials with regard to maximum, but also economic recovery of biogas selected. Further, on the basis of obtained data a rough draft of biogas station is done, icluding its energeic and economic balance.

As the world is becoming aware of the impact of global warming reducing greenhouse gases emissions presents itself as a fundamental issue in order to avoid the environmental collapse and its negative consequences. One of the key points of this challenge it’s to make a responsable use of the energy. In European countries, buildings sector consumes around the 40% of the total energy use. Thus ensuring energy efficiency becomes a vital issue in order to reduce energy usage and its environmental impact. This master thesis reports on the energy audit made in Din Hälsocentral. The energy use of the health center is studied through a heat energy balance from September to May (the months when the local district heating network works) with the aim of suggesting cost-effective energy saving measures.The study combines information provided by Din Hälsocentral, data estimated based on the characteristics of the installations and literature review. The energy balance shows that Din Hälsocentral has a heat energy input 595 MWh. This heat is received by the health center through district heating, solar radiation and internal heat generation while it’s lost through transmission losses, mechanical ventilation losses, infiltration heat losses and tap water heating. To decrease the energy use five saving measures have been suggested: the substitution of the health center windows by more efficient ones, the reduction of the indoor temperature, the replacement of the heat exchangers from the mechanical ventilation system, the installation of an aerothermal heating system in order to replace the district heating supply and the improvement of the roof isolation. The implementantion of those different measures would report heat energy savings between the 4% and the 63%, having payback periods between 0 and 7 years. However, the viability of application of aerothermal heating system in the health center installations as well as its maintenance costs must be studied more deeply.