Modelling the effect of temperature on height increment of Scots pine at high latitudes

Abstract

Dynamic Model of a Small Once-Through Boiler

In this study, a model for the unsteady dynamic behaviour of a once-through counter flow boiler that uses an organic working fluid is presented. The boiler is a compact waste-heat boiler without a furnace and it has a preheater, a vaporiser and a superheater. The relative lengths of the boiler parts vary with the operating conditions since they are all parts of a single tube. The present research is a part of a study on the unsteady dynamics of an organic Rankine cycle power plant and it will be a part of a dynamic process model. The boiler model is presented using a selected example case that uses toluene as the process fluid and flue gas from natural gas combustion as the heat source. The dynamic behaviour of the boiler means transition from the steady initial state towards another steady state that corresponds to the changed process conditions. The solution method chosen was to find such a pressure of the process fluid that the mass of the process fluid in the boiler equals the mass calculated using the mass flows into and out of the boiler during a time step, using the finite difference method. A special method of fast calculation of the thermal properties has been used, because most of the calculation time is spent in calculating the fluid properties. The boiler was divided into elements. The values of the thermodynamic properties and mass flows were calculated in the nodes that connect the elements. Dynamic behaviour was limited to the process fluid and tube wall, and the heat source was regarded as to be steady. The elements that connect the preheater to thevaporiser and the vaporiser to the superheater were treated in a special way that takes into account a flexible change from one part to the other. The model consists of the calculation of the steady state initial distribution of the variables in the nodes, and the calculation of these nodal values in a dynamic state. The initial state of the boiler was received from a steady process model that isnot a part of the boiler model. The known boundary values that may vary during the dynamic calculation were the inlet temperature and mass flow rates of both the heat source and the process fluid. A brief examination of the oscillation around a steady state, the so-called Ledinegg instability, was done. This examination showed that the pressure drop in the boiler is a third degree polynomial of the mass flow rate, and the stability criterion is a second degree polynomial of the enthalpy change in the preheater. The numerical examination showed that oscillations did not exist in the example case. The dynamic boiler model was analysed for linear and step changes of the entering fluid temperatures and flow rates.The problem for verifying the correctness of the achieved results was that there was no possibility o compare them with measurements. This is why the only way was to determine whether the obtained results were intuitively reasonable and the results changed logically when the boundary conditions were changed. The numerical stability was checked in a test run in which there was no change in input values. The differences compared with the initial values were so small that the effects of numerical oscillations were negligible. The heat source side tests showed that the model gives results that are logical in the directions of the changes, and the order of magnitude of the timescale of changes is also as expected. The results of the tests on the process fluid side showed that the model gives reasonable results both on the temperature changes that cause small alterations in the process state and on mass flow rate changes causing very great alterations. The test runs showed that the dynamic model has no problems in calculating cases in which temperature of the entering heat source suddenly goes below that of the tube wall or the process fluid.

Lämmöntalteenottokattilan dynaaminen simulointimalli

Työssä mallinnettiin kombivoimalaitoksen lämmöntalteenottokattila Apros-simulointiohjelmalla. Simulointimalli valmistettiin vastaamaan Helsingin Energian Vuosaari B:n voimalaitoksen lämmöntalteenottokattilaa, joka toimii kahdella painetasolla. Kattila on Foster Wheelerin valmistama. Ennen mallinnuksen aloittamista tutustuttiin laitoksen termodynamiikkaan, jolloin saatiin riittävä teoreettinen tieto koko laitoksen toiminnasta. Kattilan reunaehtoina ovat kaasuturbiiniprosessi ja laitoksen höyrykierto. Kaasuturbiini korvattiin laskentayhtälöillä, jotka antavat alkuarvot mm. savukaasun massavirralle ja lämpötilalle ennen kattilaa kaasuturbiinin tehon funktiona. Kattila liitetään höyrykiertoon tuorehöyry- ja syöttövesilinjasta, jolloin reunaehtoina annetaan lämpötilat ja paineet massavirroille. Valmistettua mallia testattiin ylösajo- ja kuormanmuutostilanteessa. Ylösajotilanteessa saatuja laskentatuloksia verrattiin todellisen laitoksen mittaustuloksiin, jolloin varmistuttiin simulointimallin oikeasta fysikaalisesta toiminnasta. Kuormanmuutostilanteissa kaasuturbiinin tehoa muutettiin ja samalla seurattiin kattilan reagointia muutostilanteessa. Kuormanmuutosmittauksessa varmistettiin vielä, että kattila reagoi kuormanmuutokseen oikealla tavalla, eikä muutos aiheuta kattilan toiminnalle haitallista värähtelyä.

Fractionation of wood hydrolysate by ultrafiltration membranes at high temperature

Ultrafiltration (UF) is already used in pulp and paper industry and its demand is growing because of the required reduction of raw water intake and the separation of useful compounds from process waters. In the pulp and paper industry membranes might be exposed to extreme conditions and, therefore, it is important that the membrane can withstand them. In this study, extractives, hemicelluloses and lignin type compounds were separated from wood hydrolysate in order to be able to utilise the hemicelluloses in the production of biofuel. The performance of different polymeric membranes at different temperatures was studied. Samples were analysed for total organic compounds (TOC), lignin compounds (UV absorption at 280 nm) and sugar. Turbidity, conductivity and pH were also measured. The degree of fouling of the membranes was monitored by measuring the pure water flux before and comparing it with the pure water flux after the filtration of hydrolysate. According to the results, the retention of turbidity was observed to be higher at lower temperature compared to when the filtrations were operated at high temperature (70 °C). Permeate flux increased with elevated process temperature. There was no detrimental effect of temperature on most of the membranes used. Microdyn-Nadir regenerated cellulose membranes (RC) and GE-Osmonics thin film membranes seemed to be applicable in the chosen process conditions. The Polyethersulphone (NF-PES-10 and UH004P) and polysulphone (MPS-36) membranes used were highly fouled, but they showed high retentions for different compounds.

Calculation of the critical crack size for cold form rectangular hollow section tube (CRHS) under bending load at -40º C temperature

To predict the capacity of the structure or the point which is followed by instability, calculation of the critical crack size is important. Structures usually contain several cracks but not necessarily all of these cracks lead to failure or reach the critical size. So, defining the harmful cracks or the crack size which is the most leading one to failure provides criteria for structure’s capacity at elevated temperature. The scope of this thesis was to calculate fracture parameters like stress intensity factor, the J integral and plastic and ultimate capacity of the structure to estimate critical crack size for this specific structure. Several three dimensional (3D) simulations using finite element method by Ansys program and boundary element method by Frank 3D program were carried out to calculate fracture parameters and results with the aid of laboratory tests (loaddisplacement curve, the J resistance curve and yield or ultimate stress) leaded to extract critical size of the crack. Two types of the fracture which is usually affected by temperature, Elastic and Elasti-Plastic fractures were simulated by performing several linear elastic and nonlinear elastic analyses. Geometry details of the weldment; flank angle and toe radius were also studied independently to estimate the location of crack initiation and simulate stress field in early stages of crack extension in structure. In this work also overview of the structure’s capacity in room temperature (20 ºC) was studied. Comparison of the results in different temperature (20 ºC and -40 ºC) provides a threshold of the structure’s behavior within the defined range.

Factors affecting the usability of aspen (Populus tremula) wood dried at different temperature levels

In this dissertation the main aim was to study the usability of aspen wood in the mechanical wood processes, especially the factors that affect the usability of aspen wood, which is dried at different temperature levels. The problematic of varying temperatures from level to another seem to have significant effects on distortions. According to the studies conducted, many practical solutions for drying of aspen timber can be made. European aspen sawn timber should be dried in relatively narrow widths, short lengths, edged and sawn pith free. The results achieved give an interesting view for the distortions of aspen wood between HT drying and heat treatment. The most significant result is that cupping seems to decrease when increasing temperature level from HT drying to heat treatment phase. The difference is significant. Other very obvious result is that bow and crook are increasing between these two temperature levels, bow significantly. Also the modelling gives a good background for this result since cupping is reduced by higher temperatures. It can also be assumed that these distortions can be affected for example by sorting out the timber used to different moisture levels before drying. This could be a very simple solution for practical purposes. From practical point of view, it was also noted during the drying tests performed that the discoloration seem to be no problem for aspen boards dried in temperatures under 150 °C. Altogether, this dissertation covers many interesting points of view of factors affecting distortions of wood in different temperature stages. Aspen as species in use of mechanical wood industries seems to be a species suitable for component production. According to the results, the best yield from aspen timber can be achieved in industry that can utilize relatively short components of sawn wood. Results achieved give a significant indication about the factors affecting distortions of wood at different temperature stages of drying, especially considering European aspen.

Modeling of water/steam circulation in Circulating Fluidized Bed boiler

A distinctive design feature of steam boiler with natural circulation is the presence of the steam drum which plays a role of the separator of vapor from the flow of water-and-steam mixture coming into steam drum from the furnace tubes. Steam drum with unheated downcomer tubes, deducing from it, and riser (screen/furnace tubes) inside the furnace is a closed circulation loop in which movement of water (downcomer tubes) and water-and-steam mixture (riser tubes) is organized. The movement of the working fluid is appears due to occurrence of the natural pressure, determined by the difference in hydrostatic pressure and the mass of water and water-and-steam mixtures in downcomer and riser tubes and called the driving pressure of the natural circulation: S drive = H steam (ρ down + ρ mix) g where: ρ down - density of water in downcomer tubes; ρ mix - density of water in riser tubes; H steam - height of steam content section; g - acceleration of gravity. In steam boilers with natural circulation the circulation rate is usually between 10 and 30. Thus, consumption of water in the circulation circuit “circulation rate times” more than steam output of the boiler. There are two aspects of the design of natural water circulation loops. One is to ensure a sufficient mass flux of circulating water to avoid burnout of evaporator tubes. The other is to avoid tube wall temperature fluctuation and tube vibration due to oscillation of circulation velocity. The design criteria are therefore reduced, in principle, to those of critical heat flux, critical flow rate for burnout, and flow instability. In practical design, however, the circulation velocity and the void fraction at the evaporator tube outlet are used as the design criteria (Seikan I., et. al., 1999). This study has been made with assumption that the heat flux in the furnace of the boiler even all the time. The target of the study was to define the circulation rate of the boiler, thus average heat flux do not change it. I would like to acknowledge professionals from “Foster Wheeler” company for good and comfortable cooperation.

Climate driven changes in temperature, pH and food quality : effects on copepod reproduction

Increased emissions of greenhouse gases into the atmosphere are causing an anthropogenic climate change. The resulting global warming challenges the ability of organisms to adapt to the new temperature conditions. However, warming is not the only major threat. In marine environments, dissolution of carbon dioxide from the atmosphere causes a decrease in surface water pH, the so called ocean acidification. The temperature and acidification effects can interact, and create even larger problems for the marine flora and fauna than either of the effects would cause alone. I have used Baltic calanoid copepods (crustacean zooplankton) as my research object and studied their growth and stress responses using climate predictions projected for the next century. I have studied both direct temperature and pH effects on copepods, and indirect effects via their food: the changing phytoplankton spring bloom composition and toxic cyanobacterium. The main aims of my thesis were: 1) to find out how warming and acidification combined with a toxic cyanobacterium affect copepod reproductive success (egg production, egg viability, egg hatching success, offspring development) and oxidative balance (antioxidant capacity, oxidative damage), and 2) to reveal the possible food quality effects of spring phytoplankton bloom composition dominated by diatoms or dinoflagellates on reproducing copepods (egg production, egg hatching, RNA:DNA ratio). The two copepod genera used, Acartia sp. and Eurytemora affinis are the dominating mesozooplankton taxa (0.2 – 2 mm) in my study area the Gulf of Finland. The 20°C temperature seems to be within the tolerance limits of Acartia spp., because copepods can adapt to the temperature phenotypically by adjusting their body size. Copepods are also able to tolerate a pH decrease of 0.4 from present values, but the combination of warm water and decreased pH causes problems for them. In my studies, the copepod oxidative balance was negatively influenced by the interaction of these two environmental factors, and egg and nauplii production were lower at 20°C and lower pH, than at 20°C and ambient pH. However, presence of toxic cyanobacterium Nodularia spumigena improved the copepod oxidative balance and helped to resist the environmental stress, in question. In addition, adaptive maternal effects seem to be an important adaptation mechanism in a changing environment, but it depends on the condition of the female copepod and her diet how much she can invest in her offspring. I did not find systematic food quality difference between diatoms and dinoflagellates. There are both good and bad diatom and dinoflagellate species. Instead, the dominating species in the phytoplankton bloom composition has a central role in determining the food quality, although copepods aim at obtaining as a balanced diet as possible by foraging on several species. If the dominating species is of poor quality it can cause stress when ingested, or lead to non-optimal foraging if rejected. My thesis demonstrates that climate change induced water temperature and pH changes can cause problems to Baltic Sea copepod communities. However, their resilience depends substantially on their diet, and therefore the response of phytoplankton to the environmental changes. As copepods are an important link in pelagic food webs, their future success can have far reaching consequences, for example on fish stocks.

Power cycling lifetime estimation of IGBT power modules based on chip temperature modeling

In this doctoral thesis, methods to estimate the expected power cycling life of power semiconductor modules based on chip temperature modeling are developed. Frequency converters operate under dynamic loads in most electric drives. The varying loads cause thermal expansion and contraction, which stresses the internal boundaries between the material layers in the power module. Eventually, the stress wears out the semiconductor modules. The wear-out cannot be detected by traditional temperature or current measurements inside the frequency converter. Therefore, it is important to develop a method to predict the end of the converter lifetime. The thesis concentrates on power-cycling-related failures of insulated gate bipolar transistors. Two types of power modules are discussed: a direct bonded copper (DBC) sandwich structure with and without a baseplate. Most common failure mechanisms are reviewed, and methods to improve the power cycling lifetime of the power modules are presented. Power cycling curves are determined for a module with a lead-free solder by accelerated power cycling tests. A lifetime model is selected and the parameters are updated based on the power cycling test results. According to the measurements, the factor of improvement in the power cycling lifetime of modern IGBT power modules is greater than 10 during the last decade. Also, it is noticed that a 10 C increase in the chip temperature cycle amplitude decreases the lifetime by 40%. A thermal model for the chip temperature estimation is developed. The model is based on power loss estimation of the chip from the output current of the frequency converter. The model is verified with a purpose-built test equipment, which allows simultaneous measurement and simulation of the chip temperature with an arbitrary load waveform. The measurement system is shown to be convenient for studying the thermal behavior of the chip. It is found that the thermal model has a 5 C accuracy in the temperature estimation. The temperature cycles that the power semiconductor chip has experienced are counted by the rainflow algorithm. The counted cycles are compared with the experimentally verified power cycling curves to estimate the life consumption based on the mission profile of the drive. The methods are validated by the lifetime estimation of a power module in a direct-driven wind turbine. The estimated lifetime of the IGBT power module in a direct-driven wind turbine is 15 000 years, if the turbine is located in south-eastern Finland.

Surface transformation hardening of carbon steel with high power fiber laser

This study investigated the surface hardening of steels via experimental tests using a multi-kilowatt fiber laser as the laser source. The influence of laser power and laser power density on the hardening effect was investigated. The microhardness analysis of various laser hardened steels was done. A thermodynamic model was developed to evaluate the thermal process of the surface treatment of a wide thin steel plate with a Gaussian laser beam. The effect of laser linear oscillation hardening (LLOS) of steel was examined. An as-rolled ferritic-pearlitic steel and a tempered martensitic steel with 0.37 wt% C content were hardened under various laser power levels and laser power densities. The optimum power density that produced the maximum hardness was found to be dependent on the laser power. The effect of laser power density on the produced hardness was revealed. The surface hardness, hardened depth and required laser power density were compared between the samples. Fiber laser was briefly compared with high power diode laser in hardening medium-carbon steel. Microhardness (HV0.01) test was done on seven different laser hardened steels, including rolled steel, quenched and tempered steel, soft annealed alloyed steel and conventionally through-hardened steel consisting of different carbon and alloy contents. The surface hardness and hardened depth were compared among the samples. The effect of grain size on surface hardness of ferritic-pearlitic steel and pearlitic-cementite steel was evaluated. In-grain indentation was done to measure the hardness of pearlitic and cementite structures. The macrohardness of the base material was found to be related to the microhardness of the softer phase structure. The measured microhardness values were compared with the conventional macrohardness (HV5) results. A thermodynamic model was developed to calculate the temperature cycle, Ac1 and Ac3 boundaries, homogenization time and cooling rate. The equations were numerically solved with an error of less than 10-8. The temperature distributions for various thicknesses were compared under different laser traverse speed. The lag of the was verified by experiments done on six different steels. The calculated thermal cycle and hardened depth were compared with measured data. Correction coefficients were applied to the model for AISI 4340 steel. AISI 4340 steel was hardened by laser linear oscillation hardening (LLOS). Equations were derived to calculate the overlapped width of adjacent tracks and the number of overlapped scans in the center of the scanned track. The effect of oscillation frequency on the hardened depth was investigated by microscopic evaluation and hardness measurement. The homogeneity of hardness and hardened depth with different processing parameters were investigated. The hardness profiles were compared with the results obtained with conventional single-track hardening. LLOS was proved to be well suitable for surface hardening in a relatively large rectangular area with considerable depth of hardening. Compared with conventional single-track scanning, LLOS produced notably smaller hardened depths while at 40 and 100 Hz LLOS resulted in higher hardness within a depth of about 0.6 mm.

Reliability of SMD interconnections on flexible low-temperature substrates with inkjet-printed conductors

julkaisumaa: NLD

Modeling of temperature regimes in a furnace of bubbling fluidized bed boiler

The work is mainly focused on the technology of bubbling fluidized bed combustion. Heat transfer and hydrodynamics of the process were examined in the work in detail. Special emphasis was placed on the process of heat exchange in a freeboard zone of bubbling fluidized bed boiler. Operating mode of bubbling fluidized bed boiler depends on many parameters. To assess the influence of some parameters on a temperature regime inside the furnace a simplified method of zonal modeling was used in the work. Thus, effects of bed material fineness, excess air ratio and changes in boiler load were studied. Besides the technology of combustion in bubbling fluidized bed, other common technologies of solid fuels combustion were reviewed. In addition, brief survey of most widely used types of solid fuel was performed in the work.

Track of HSMS Sophia tracing the extent of navigable water along the main northern ice between Spitzbergen and Greenland September 1868 : also showing the nature of the ice and temperature and depth of the sea

Kartta kuuluu A. E. Nordenskiöldin kokoelmaan

Bumblebees in a Changing Climate: Evaluating the Effects of Temperature on Queen Performance

Bumblebees are a very essential group of pollinating insects, but their populations have declined drastically during the past decades. We need to understand why their numbers are decreasing and what can be done to reverse this trend. Climate change-related phenomena, such as changes in the overwintering temperatures and spring conditions, are among the most prominent threats to bumblebees. Queens have a special role in the lifecycle of bumblebees because they overwinter and start new colonies the next year. Their successful performance: survival, overwintering ability, longevity, immune competence, and nest establishing capability in spring, is highly important for bumblebee populations. However, the effects of climate change on bumblebee queen performance remain unknown. The main objective of this thesis was to assess how temperature affects the performance of bumblebee queens during and after overwintering. The effects of warm temperature predicted by climate change scenarios on queen survival and stress-tolerance were studied by a four-month artificial diapause of bumblebee queens at two temperatures (9°C and 1.8°C). Bumblebee colonies were also reared in a laboratory and factors affecting colony characteristics were examined. In addition, queen performance during spring was studied in a starvation experiment using two temperatures (15°C as normal; 24°C as warmer than average) and queens collected from nature right after their emergence. My research revealed how temperature affects queen performance, and queen size was found to be an important factor determining the direction of some of these effects. We found a 0.4g weight threshold for bumblebee queens to be able to survive overwintering. In addition, during mild winters, larger queens have a higher chance than smaller ones to survive through winter and also to cope with immunological stresses after overwintering. During cold conditions, which are normal in the current climatic situation, this advantage disappears. In the spring starvation experiment, the starved queens survived approximately eight days longer in 15°C than in 24°C, which means that starvation risk rises significantly with increasing spring temperature, in a situation where food is scarce due to for example frost damage or asynchrony between bumblebees and their important food plants. These results could mean that in the future climate, larger queens are better able to survive the winter, initiate their nests and start rearing their offspring. This may be problematic, because I also detected two alternative strategies of colony development that differ between large and small queens; larger queens start to lay eggs earlier at nest initiation, their colonies mature later, they produce more workers, and they have a more strongly male biased sex allocation compared with smaller queens. If larger queens have a greater change of producing offspring after a mild winter, this could lead to a significant decline in the total production of new queens at a population level. Thus, it seems that queen size could act as one mechanism regulating the population level outcomes in different temperatures. The new information presented in my thesis reinforces that basic research, monitoring, and local species conservation of bumblebees both in Finland and globally must be increased to ensure that this highly important pollinator group survives in the face of climate change.