Microchannel heat exchangers present many advantages, such as reduced size, high thermal efficiency and low fluid inventory; and are increasingly being used for heat transfer in a wide variety of applications including heat pumps, automotive air conditioners and for cooling of electronics.However, the fundamentals of fluid flow and heat transfer in microscalegeometries are not yet fully understood. The aim of this thesis is to contribute to a better understanding of the underlying physical phenomena in single-phase and specially flow boiling heat transfer of refrigerants in small channels. For this purpose, well-characterized heat transfer experiments have been performed in uniformly heated, single, circular, vertical channels ranging from 0.64 to 1.70 mm in diameter and using R-134a, R-22 and R-245fa as working fluids. Furthermore, flow visualization tests have been carried out to clarify the relation between the two-phase flow behavior and the boiling heat transfer characteristics. Single-phase flow experiments with subcooled liquid refrigerant have confirmed that conventional macroscale theory on single-phase flow and heat transfer is valid for circular channels as small as 640μm in diameter. Through high-speed flow boiling visualization of R-134a under non adiabatic conditions seven flow patterns have been observed: isolated bubbly flow, confined bubbly flow, slug flow, churn flow, slug-annular flow, annular flow, and mist flow. Two-phase flow pattern observations are presented in the form of flow pattern maps. Annular-type flow patterns are dominant for vapor qualities above 0.2. Onset of nucleate boiling and subcooled flow boiling heat transfer of R-134a has been investigated. The wall superheat needed to initiate boiling was found as large as 18 ºC. The experimental heat transfer coefficients have been compared to predictions from subcooled flow boiling correlationsav ailable in the literature showing poor agreement. Saturated flow boiling heat transfer experiments have been performed with the 640 μm diameter test section. The heat transfer coefficient has been found to increase with heat flux and system pressure and not to change with vapor quality or mass flux when the quality is less than ∼0.5. For vapor qualities above this value, the heat transfer coefficient decreases with vapor quality. This deterioration of the heat transfer coefficient is believed to be caused by the occurrence of intermittent dryout in this vapor quality range. The experimental database, consisting of 1027 data points, has been compared against predictions from correlations available in the literature. The best results are obtained with the correlations by Liu and Winterton (1991) and by Bertsch et al. (2009). However, better design tools to correctly predict the flow boiling heat transfer coefficient in small geometries need to be developed. Dryout incipience and critical heat flux (CHF) have been investigated in detail. CHF data is compared to existing macro and microscale correlations. The comparison shows best agreement with the classical Katto and Ohno (1984) correlation, developed for conventional large tubes. / QC 20101101

<!-- --> In the wake of the economic growth of the Chinese market the past couple of decades, the energy consumption has surged. One of the biggest consequences of the increased energy consumption is a massive increase in CO2 emission. In fact, China has overtaken the U.S. as the biggest emitter of CO2. In light of this energy-saving technology gets more important to implement. District heating is one of the solutions used with success in parts of China where heating is required. In this paper, an energy recovery technology has been examined for two climate zones in China namely a mechanical ventilation system using a flat-plate counter-flow heat exchanger. Beijing is located in a cold zone while Hong Kong is located in a zone with hot summers and mild winters. Cooling load calculations were conducted manually using the RTS - method developed by ASHRAE and heating load calculations were conducted for Beijing using Swedish guidelines stated in BBR. Further, the energy recovery unit (VM1) that was provided by Systemair AB was tested using a rig where different outdoor conditions were simulated. This data was then used to evaluate the potential for energy recovery in a model apartment located in the two zones. As expected, significant differences were obtained when comparing the performance for the two locations. / Redan avklarad

This work presents a study and implementation of the simulation of residual stresses in castings. The objects of study are a cast iron truck Hub part (provided by the company Volvo 3P) and an optimized version of the Hub resulting from the application of a topology optimization process. The models are solved through an uncoupled thermo-mechanical solidification analysis, performed both in the FE commercial software Abaqus and the FD commercial software Magmasoft and the results are compared. First, a thermal analysis is carried out where the casting is cooled down from a super-heated temperature to room temperature. The thermal history obtained, is then used as an external force to calculate the residual stresses by means of a quasi-static mechanical analysis, using a J2-plasticity model. The simulation procedures are explained through a simplified model of the Hub and then applied to the geometries of interest. A results comparison between the original Hub and its optimized version is also presented. The theoretical base is given in this work as well as detailed implementation procedures. The results shows that the part subjected to the topology optimization process develop less residual stresses than its original version.

This project deals with the potential of membrane stratified solar ponds which consist of two water layers, where one is a salt solution here, and a separating translucent membrane. An experimental pond was set up to study the thermal behaviour of such collector systems. The input is mainly solar radiation, sometimes when the ambient temperatures are higher than the pond temperatures also heat from the environment is transferred into the pond. The measured temperatures of the pond, the ambient temperature, the global radiation and wind speed were the basis data for thermal calculations which showed that the pond was working well as a solar collector and thermal storage system all in one. Heat was not extracted from the pond however, only the losses to the environment were studied. It was found out that the pond temperatures were higher than the ambient temperature over the whole measurement period of 12 days, and insulation and pollution problems as well as future prospects and suggestions for further studies are discussed at the end of this paper.

Nowadays, lighting represents 20% of the global electricity consumption. Light can be produced using different technologies but more than 100 years after its invention, the incandescent bulb is still the most sold and one of the more used light sources. Of the total energy input in an incandescent bulb more than 90% is lost as heat while less than 10% is converted into visible light. However, there are alternative technologies which use up to 85% less energy for conventional lighting and there are even more efficient light sources for other purposes that if they replace completely all incandescent lamps over the world could reduce dramatically the global electricity consumption and greenhouse gases emissions. One may identify these alternative technologies mainly as LEDs and discharge lamps, but are they the unique alternatives? This thesis is focused on a new lighting technology whose name is LightLab and which is based on the field emission and cathodoluminescence concepts. This technology is under the research and development stage but prototypes have already achieved energy savings over 85% compared to incandescent lamps with a great color performance and with the advantage that it does not use mercury or other hazardous substances compared with discharge lamps. Thus, in the first part of the project all technologies and last improvements are studied while the second part analyses the market applications possibilities for the LightLab lamp considering the environmental perspective regulations and comparing the lamp with the other light sources. The result is that despite there are still some unknown parameters that need to be developed or improved, the lamp has a great potential for different applications fields.

<p>This work presents a study and implementation of the simulation of residual stresses in castings. The objects of study are a cast iron truck Hub part (provided by the company Volvo 3P) and an optimized version of the Hub resulting from the application of a topology optimization process. The models are solved through an uncoupled thermo-mechanical solidification analysis, performed both in the FE commercial software Abaqus and the FD commercial software Magmasoft and the results are compared. First, a thermal analysis is carried out where the casting is cooled down from a super-heated temperature to room temperature. The thermal history obtained, is then used as an external force to calculate the residual stresses by means of a quasi-static mechanical analysis, using a J2-plasticity model. The simulation procedures are explained through a simplified model of the Hub and then applied to the geometries of interest. A results comparison between the original Hub and its optimized version is also presented. The theoretical base is given in this work as well as detailed implementation procedures. The results shows that the part subjected to the topology optimization process develop less residual stresses than its original version.</p>

<p>Oxygen-diluted Combustion (OdC) technology has evolved from the concept of Excess Enthalpy Combustion and is characterized by reactants of low oxygen concentration and high temperature. Recent advances in this technology have demonstrated significant energy savings, high and uniform thermal field, low pollution, and the possibility for downsizing the equipment for a range of furnace applications. Moreover, the technology has shown promise for wider applications in various processes and power industries.</p><p>The objectives of this thesis are to analyze the thermodynamic aspects of this novel combustion technology and to quantify the enhancement in efficiency and heat transfer inside a furnace in order to explore the potentials for reduced thermodynamic irreversibility of a combustion process and reduced energy consumption in an industrial furnace. Therefore, theoretical and experimental investigations were carried out.</p><p>The 2nd law of thermodynamics analyses of OdC systems have been carried out for cases in which the oxidizer is either oxygen (Flameless-oxy-fuel) or air (High Temperature Air Combustion, HiTAC). The analyses demonstrate the possibilities of reducing thermodynamic irreversibility of combustion by considering an oxygen-diluted combustion process that utilizes both gas- and/or heat-recirculation. Furthermore, the results showed that an oxygen-diluted combustion system that utilizes oxygen as an oxidizer, in place of air, results in higher 1st and 2nd law efficiencies.</p><p>Mathematical models for heat regenerators were developed to be designing tools for maximized heat recovery. These models were verified by heat performance experiments carried out on various heat regenerators.</p><p>Furthermore, experiments were performed in a semi-industrial test furnace. It was equipped with various regenerative burning systems to establish combustion and heat transfer conditions prevailing in an industrial furnace operating based on HiTAC. The tests were carried out at seven firing configurations, two conventional and five HiTAC configurations, for direct and indirect heating systems.</p><p>Measurements of energy balance were performed on the test furnace at various configurations in order to obtain the 1st law efficiency. Moreover, local measurements of temperature, gas composition, and heat fluxes in the semi-industrial test furnace were performed to find out the main characteristics of HiTAC flame and the effects of these characteristics on the heating potential, i.e., useful heating in the furnace. In the case of HiTAC, these measurements showed uniformities of chemistry, temperature, temperature fluctuation, and heat fluxes profiles. The values of fluctuations in temperature were small. The high speed jets of the fuel and air penetrated deep into the furnace. The fuel gradually disappeared while intermediate species gradually appeared in relatively high concentrations and at broader regions inside the furnace. These findings indicate: a large reaction zone, low specific combustion intensity in the flame, low specific fuel energy release, and high heat release from this large flame. In addition to the thermodynamic limitations to the maximum temperature of the Oxygen-diluted Combustion, the low specific energy release of the fuel and the high heat release from the flame to its surroundings cause this uniform and relatively moderate temperature profile in a HiTAC flame, consequently suppressing thermal-NO formation.</p><p>Heat flux and energy balance measurements showed that heating potential is significantly increased in the case of HiTAC compared to that in the conventional case, implying much more energy savings than the apparent heat recovery from the heat regenerators, and consequently much less pollutants emissions. Therefore, it is certain that this large HiTAC flame emits more thermal radiation to its surroundings than the conventional flame does, in spite of the moderate-uniform temperature profile of the flame. This intense heat flux was more uniform in all HiTAC configurations, including the indirect heating configuration, than that of the conventional-air combustion configuration.</p>

This thesis investigates the possibility of using an unglazed flat-plate solar collector as a cooling radiator. The solar collector will be connected to the condenser of a heat pump and used as cooler during nighttime. Daytime the solar collector will be connected to the evaporator of the heat pump and used as heat source. The two widely differing fields of application make special demands on the solar collector. The task is given by the heat pump manufacturer Thermia and the main objective is to find out whether a solar collector should be used as a cooler or not. The performance of the solar collector under varying environmental conditions is investigated using COMSOL Multiphysics 3.3. Only the cooling properties are investigated here. The performance of the solar collector as a heat exchanger is estimated using the effectiveness-NTU method, and the solar collector is found to be a good heat exchanger at low wind speeds. The heat transfer coefficients of the convection and radiation are determined for varying temperature and wind speeds. The convective heat transfer coefficient is lowered by tubes above the absorber plate and for a high convective heat transfer rate the solar collector surface should be smooth. For a high radiative heat transfer rate the surface needs to have a high emissivity. The cooling rate is higher from a warm surface than from a cold and since no temperature change of the heat carrier is necessary the solar collector should be kept at a high temperature. To increase the cooling rate alterations need to be made to the solar collector that makes its heating performance deteriorate. A solar collector that can be used for cooling is not an efficient solar collector.

<p>As a part of the fight against the global warming the energy production needs to be more efficient and redirected towards sustainable options. One alternative is cogeneration, which means that electricity and heat is produced in one plant. The purpose with this survey is to examine if there are any commercial available combined heat and power techniques, based on combustion of solid moist biomass, which are suitable to small-scale applications. The technique must be able to produce between 2 and 10 MW thermal and the heat demand is a Swedish district-heating system. When already published reports had been studied, the Organic Rankine Cycle (ORC) was chosen as the most suitable technique. The possibility of using the ORC to generate electricity from the district-heating return flow was considered simultaneously. The chosen ORC-technique was then evaluated in Excel. The first aspect to be examined was how the performance of a combined heat and power plant was affected by variations in the supply line temperature. It showed that the performance reaches top levels when the temperature is low. The second part contains an optimisation, in a techno-economical perspective, of the ratio between cogeneration and separate heat production for district-heating systems with heat demands below 50 GWh/year. The most profitable combined heat and power plant generates 45 % of the installed power in a 50 GWh system. The profit is, however, too low to justify any construction plans. The conclusion was that there are no economical reasons to choose combined heat and power based on an organic rankine cycle in Sweden today.</p>

<p>Detta är ett examensarbete som genomförts hos Göteborg Energi AB och syftar till att utreda omkryogen uppgradering av biogas med fördel kan ske genom att producera nödvändig kyla medvärmedriven absorptionskylmaskin. Göteborg Energi är en av tre parter som tillsammans ska bygga enbiogasanläggning i Lidköping som ska vara i drift 2010. Anläggningen ska producera 30 GWhflytande biogas per år.</p><p>Arbetet utreder om det är fördelaktigt ur ekonomiskt, energimässigt och miljömässigt perspektiv attuppgradera biogas med kryogen teknik med värmeproducerad kyla. En jämförelse görs först medkryogen teknik där kylan är producerad med el och sen med andra uppgraderingstekniker. Som stödhar två olika processimuleringsprogram används, Hysys och DESIGN II.</p><p>Resultatet visar att energianvändningen ökar då värmedriven kyla används i jämförelse med kylaproducerad med el. 0,47 kW/Nm3 rågas för kryo med absorptionskyla och 0,29 kW/Nm3 rågas medel. Om det finns avsättning för spillvärmen kan energianvändningen i uppgraderingen minska till 0,29kW/Nm3 rågas och 0,15 kW/Nm3 rågas för systemet med värmedriven respektive eldriven kyla. Ijämförelse med andra uppgraderingstekniker ligger 0,47 kW/Nm3 bland de teknikerna med högstenergianvändning medans 0,29 kW/Nm3 placerar sig bland de teknikerna med lägstenergianvändning.</p><p>Resultat visar att klimatpåverkan från uppgraderingen, som kommer av metanslip och elanvändningen,minskar marginellt om kylan produceras med värme istället för el. Resultatet varierar mycket beroendepå hur koldioxidutsläppen från marginalelen beräknas. I jämförelse med andra uppgraderingsteknikerligger kryo lägre än de flesta andra. Undantaget är COOAB-tekniken som är överlägset bäst tack varalågt metanslip och liten elanvändning.</p><p>Ekonomisk jämförelse med andra uppgraderingstekniker visar att kostnaden för energianvändningenligger i samma nivå som övriga uppgraderingstekniker i jämförelsen, ca 0,03 kr/kWh uppgraderad gas.Om det finns avsättning för spillvärmen sjunker kostnaden till 0,024 och 0,02 kr/kWh uppgraderad gasför kryoteknik med kyla ifrån värme respektive el.</p><p>Min slutsats är att utnyttjande av spillvärmen är av stor vikt för att få god ekonomi och lågenergianvändning med kryogen uppgradering. En marginellt förbättrad miljöprestanda kan erhållas omnödvändig kyla produceras med värme istället för el då kryogen uppgradering används. Annars är detalltid mer fördelaktigt att använda el för att producera nödvändig kyla.</p> / <p>This is a master thesis that has been carried out at Göteborg Energi AB. It refers to investigate ifcryogenic upgrading of biogas with advantage can be done by producing necessary cold with a heatdriven absorption cooling machine. Göteborg Energi is one of three actors that together will build abiogas plant in Lidköping that will be up and running in 2010. The plant will produce 30 GWhliquefied biogas annually.</p><p>This thesis investigastes whether it is advantageous, to upgrade biogas with heat driven cooling, in aperspective of economy, energy use and environment. It compares cryogenic upgrading with coldproduced by electricity, but also by other techniques. Two different process simulation softwares havebeen used as support to this thesis; Hysys and DESIGN II.</p><p>The result shows that energy usage increases when the necessary cold is produced with heat instead ofelectricity; 0,47 kW/Nm3 rawgas for cryo upgrade with absorptions cooling and 0,29 kW/Nm3 rawgaswith cold produced by electricity. If it’s possible to use the waste heat to warm the digester, the energyconsumption for the upgrading can be reduced to 0,29 kW/Nm3 for the system with heat-driven cold,and 0,15 kW/Nm3 rawgas for cold produced by electricity. In comparison with other techniques forupgrading, 0,47 kW/Nm3 rawgas is a high value while 0,29 kW/Nm3 rawgas is among the lowestvalues for energy use.</p><p>The impact on the climate emerges from the use of electricity and when methane slips out from theupgrading plant. The result shows that the impact on the climate is slightly decreased for cryogenicupgrading when the cold is produced with a heat driven absorption machine instead of electricity. Theresult varies a lot due to how one calculate the emission of carbon dioxide from the electricity on themargin. In comparison with other upgrading techniques, the climate impact from cryogenic upgradingis less, other than the COOAB-technique that is superior because of its low methane slip and lowdemand of electricity.</p><p>An economical comparison shows that the cost for energy usage is about the same for cryogenic as forother techniques; approximately 0,03 SEK/kWh upgraded gas. If one can utilize the waste heat, thecost would be decreased to 0,024 and 0,02 SEK/kWh upgraded gas for the system with cryogenicupgrading with cooling from absorption machine respectively cooling produced with electricity.</p><p>My conclusion is that the utilization of the waste heat is essential if one wishes to get good economyand low energy use for the upgrading of biogas with cryogenic methods. A slightly increasedenvironmental improvement can be received if one change the cold production from electricity to heat,otherwise it is always more advantageous to use electricity for cryogenic methods.</p>