Technological developments in the area of high power LED light sources have enabled their utilization in general illumination applications. Along with this advancement comes the need for progressive thermal management strategies in order to ensure device performance and reliability. Minimizing an LED's junction temperature is done by minimizing the total system's thermal resistance. For actively cooled systems, this may essentially be achieved by simultaneously engineering the conduction through the heat sink and creating a well-designed flow pattern over suitable convective surface area. While such systems are routinely used in cooling microelectronics, their use in LED lighting systems encounter additional constraints which must be accounted for in the design of the cooling system. These are typically driven by the size, shape, and building codes involved with the lighting industry, and thus influence the design of drop-in replacement LED fixtures. Employing LED systems for customary down-lighting applications may require shrouded radial fin heat sinks to increase the heat transfer while reducing the space requirement for active cooling. Most lighting is already in some form of housing, and the ability to concurrently optimize these housings for thermal and optical performance could accelerate the widespread implementation of cost-efficient, environmentally-friendly solid-state lighting. In response, this research investigated the use of conical, cylindrical, square, and pyramidal shrouds with pin/radial fin heat sink designs for the thermal management of high power LED sources. Numerical simulations using FLUENT were executed in order to account for details of the air flow, pressure drop, and pumping power, as well as the heat transfer and temperature distributions throughout the system. The LEDs were modeled as a distributed heat source of 25 - 75 W on a central portion of the various heat sinks. Combinations of device junction temperature and pumping power were used to assess the performance of shrouded heat sink designs for their use in air-cooled, down-lighting LED fixtures.

A nanofluid is a new heat transfer fluid produced by mixing a base fluid and solid nano sized particles. This fluid has great potential in heat transfer applications, because of its increased thermal conductivity and even increased Nusselt number due to higher thermal conductivity, Brownian motion of nanoparticles, and other various effects on heat transfer phenomenon. In this work, the first aim is to predict convective heat transfer of nanofluids. A numerical code is created and run to obtain results in a pipe with two different boundary conditions, constant wall temperature and constant wall heat flux. The results for laminar flow for thermally developing region in a pipe are obtained for Al2O3/water nanofluid with different volumetric fraction and particle sizes with local temperature dependent conductivity approach. Various effects that influence nanofluid heat transfer enhancement are investigated. As a result, a better heat transfer performance is obtained for all cases, compared to pure water. The important parameters that have impact on nanofluid heat transfer are particle diameter of the nanoparticles, nanoparticle volumetric fraction, Peclet number, and viscous dissipation. Next, a heat transfer performance evaluation methodology is proposed considering increased pumping power of nanofluids. Two different criteria are selected for two boundary conditions at constant pumping power. These are heat transfer rate ratio of the nanofluid and the base fluid for constant wall temperature boundary condition and difference between wall temperature of the pipe at the exit and inlet mean temperature of the fluid ratio for constant wall heat flux case. Three important parameters that influence the heat transfer performance of nanofluids are extracted from a parametric study. Lastly, optimum particle size and volumetric fraction values are obtained depending on Graetz number, Nusselt number, heat transfer fluid temperature, and nanofluid type.

A nanofluid is a new heat transfer fluid produced by mixing a base fluid and solid nano sized particles. This fluid has great potential in heat transfer applications, because of its increased thermal conductivity and even increased Nusselt number due to higher thermal conductivity, Brownian motion of nanoparticles, and other various effects on heat transfer phenomenon. In this work, the first aim is to predict convective heat transfer of nanofluids. A numerical code is created and run to obtain results in a pipe with two different boundary conditions, constant wall temperature and constant wall heat flux. The results for laminar flow for thermally developing region in a pipe are obtained for Al2O3/water nanofluid with different volumetric fraction and particle sizes with local temperature dependent conductivity approach. Various effects that influence nanofluid heat transfer enhancement are investigated. As a result, a better heat transfer performance is obtained for all cases, compared to pure water. The important parameters that have impact on nanofluid heat transfer are particle diameter of the nanoparticles, nanoparticle volumetric fraction, Peclet number, and viscous dissipation. Next, a heat transfer performance evaluation methodology is proposed considering increased pumping power of nanofluids. Two different criteria are selected for two boundary conditions at constant pumping power. These are heat transfer rate ratio of the nanofluid and the base fluid for constant wall temperature boundary condition and difference between wall temperature of the pipe at the exit and inlet mean temperature of the fluid ratio for constant wall heat flux case. Three important parameters that influence the heat transfer performance of nanofluids are extracted from a parametric study. Lastly, optimum particle size and volumetric fraction values are obtained depending on Graetz number, Nusselt number, heat transfer fluid temperature, and nanofluid type.

Refrigerant management is crucial in the attempts to slow climate change. Emissions from the refrigeration sector are primarily due to poor management and unsafe destruction of refrigerants currently in circulation. Safe refrigerant management and improving system operating efficiency can result in a reduction of emissions. Ice rinks are some of the most energy-intensive public buildings, providing both heating and cooling. The major share of energy in an ice rink is the refrigeration system, which consumes about 43%. There are more than 360 ice rinks in Sweden as of 2018 and the most common type of refrigeration system is an indirect system. With the push for natural fluids, aqua ammonia is becoming a more appealing option as a secondary fluid in ice rinks because of its minimal negative impact on the environment and favorable thermophysical properties. The main drawbacks of the fluid are its toxic characteristics and material compatibility. However, since the first use in 2007, there has been an increase to 34 of the total ice rinks in Sweden that have aqua ammonia as a secondary fluid.  Thermophysical properties are used to calculate refrigeration design parameters, including secondary fluid concentration and pumping power required. The properties of aqua ammonia have not been experimentally tested within this century to the extent presented in this thesis. Existing data is either derived from measured values taken several decades ago or has been calculated. The novelty of this thesis project stems from the unique and more accurate results measured through laboratory work and from the ability to determine the impact of the newly measured values in ice rink refrigeration design. A total of 11 varying concentrations of aqua ammonia were tested for density, dynamic viscosity, specific heat capacity, thermal conductivity, and corrosion of 7 metal specimens. The solutions tested ranged from 2 wt-% to 30 wt-%, correlating to freezing points from -2C to -84C. The measurements for density resulted in values similar to reference values, ranging in a difference of only 0.3% to 1.7%. Dynamic viscosity results followed nearly the same trend as references with changing temperature and solution concentration, with values varying from 0.8% to 17% different than references. Specific heat capacity measurements proved significantly different than reference values. The trend is opposite of the reference, leading to drastically different values, especially at lower temperatures and higher solution concentrations. The difference in values ranges from 0.1% to 28%. Thermal conductivity results show similar trends, but higher values than expected. The difference between measured values and reference values range from 0.1% to 13%. Corrosion results show that copper and brass have the highest corrosion rates of 16.2 mm/yr and 1.84 mm/yr, respectively. The most compatible specimen was stainless steel, followed by carbon steel, with maximum corrosion rates of 0.041 mm/yr and 0.11 mm/yr, respectively. Brass connections commonly used in industry were also tested and resulted in corrosion rates ranging from 69.6 g/yr to 112 g/yr, which accounts for about 1% and 1.5% of the connections’ total weight lost per year. Compiling the laboratory measurements taken during the completion of this thesis project results in a more complete and accurate list of thermophysical properties for aqua ammonia that has never existed before.  These updated thermophysical properties for aqua ammonia, along with measured properties for other secondary fluids, were used to calculate operational parameters in a hypothetical ice rink refrigeration system. The results show that aqua ammonia is favorable with high COP and low pumping power, and therefore low pressure drop. Ammonia is most comparable to CaCl2 and K-formate for most results. The changes in calculated COP between old reference data and new measured data were less than a 1% decrease when plotting versus the temperature of the ice surface and with a set pump control (T) for cooling capacities of 200kW and 300kW. The change in heat transfer coefficients was more significant, with a range of about a 9% to 27% decrease in either the U-pipe under the rink floor or in a plate of the heat exchanger. Even though these heat transfer coefficient values are lower than previously calculated, the required pumping power is also lower using updated properties: 40% lower at a secondary fluid temperature of -10C. Even though the change in heat transfer coefficients is larger with experimental values, the impact on COP is minimal.  The takeaway from this project is that aqua ammonia is a favorable secondary fluid compared to calcium chloride and ethylene glycol, the two most commonly used secondary fluids in ice rink refrigeration. A system using aqua ammonia would have a 45% and 47% lower pumping power requirement compared to calcium chloride and ethylene glycol, respectively. The system would also have a 4.7% and 11.6% higher COP when compared to systems with calcium chloride and ethylene glycol, respectively. The significantly lower pumping power will lower total energy demand of the ice rink, thus decreasing operation costs. / Köldmediehantering är avgörande i försöken att sakta ner klimatförändringen. Utsläppen från kylsektorn beror främst på dålig hantering och osäker destruktion av köldmedier som för närvarande är i omlopp. Säkrare hantering av köldmedium och förbättrad systemdriftseffektivitet kan leda till ett minskat utsläpp. Ishallar är några av de mest energiintensiva offentliga byggnaderna som ger både uppvärmning och kylning. Den största andelen energi i en ishall är kylsystemet som förbrukar cirka 43%. Det finns mer än 360 isbanor i Sverige från och med 2018 och den vanligaste typen av kylsystem är ett indirekt system. Med trycket på naturliga vätskor blir ammoniakvatten ett mer tilltalande alternativ som en köldbärare i ishallar på grund av dess minimala negativa påverkan på miljön och gynnsamma termofysikaliska egenskaper. Köldbärares främsta nackdelar är dess toxiska karaktär och materialkompatibilitet. Sedan den första användningen 2007 har det dock skett en ökning till 34 av de totala ishallar i Sverige som har ammoniakvatten som köldbärare.  Termofysikaliska egenskaper används för att beräkna parametrar för kyldesign, inklusive köldbärares koncentration och pumpeffekten som krävs. Ammoniakvattens egenskaper har inte testats experimentellt under detta sekel i den utsträckning som presenteras i detta exjobb. Befintliga data härleds antingen från uppmätta värden som tagits för flera decennier sedan eller har beräknats. Nyheten härrör i detta exjobbsprojekt från de unika och mer exakta resultat som mätts genom laboratoriearbetet och från förmågan att bestämma effekten av de nyligen uppmätta värdena i kylskåpsdesign. Totalt 11 olika koncentrationer av ammoniakvatten testades med avseende på densitet, dynamisk viskositet, specifik värmekapacitet, värmeledningsförmåga och korrosion av 7 metallprover. De testade lösningarna varierade från 2 vikt-% till 30 vikt-%, korrelerade med fryspunkter från -2 ° C till -84 ° C. Mätningarna för densitet resulterade i värden som liknar referensvärdena, med en skillnad på endast 0,3% till 1,7%. Dynamiska viskositetsresultat följde nästan samma trend som referenser med förändrad temperatur och lösningskoncentration, med värden som varierade från 0,8% till 17% annorlunda än referenser. Specifika värmekapacitetsmätningar visade sig vara väsentligt annorlunda än referensvärden. Trenden är motsatt referensen, vilket leder till drastiskt olika värden, särskilt vid lägre temperaturer och högre koncentrationer. Skillnaden i värden varierar från 0,1% till 28%. Värmeledningsförmåga visar liknande trender, men högre värden än förväntat. Skillnaden mellan uppmätta värden och referensvärden sträcker sig från 0,1% till 13%. Korrosionsresultat visar att koppar och mässing har de högsta korrosionshastigheterna på 16,2 mm / år respektive 1,84 mm / år. Det mest kompatibla exemplet var rostfritt stål, följt av kolstål, med maximala korrosionshastigheter på 0,041 mm / år respektive 0,11 mm / år. Mässinganslutningar som vanligen används i industrin testades också och resulterade i korrosionshastigheter från 69,6 g / år till 112 g / år, vilket motsvarar för cirka 1% och 1,5% av anslutningarnas totala viktförlust per år. Att sammanställa laboratoriemätningarna som gjorts under slutförandet av detta projekt resulterar i en mer fullständig och noggrann lista över termofysikaliska egenskaper för ammoniakvatten som aldrig funnits tidigare.  Dessa uppdaterade termofysikaliska egenskaper för ammoniakvatten, tillsammans med uppmätta egenskaper för andra köldbärare, användes för att beräkna driftsparametrar i ett hypotetiskt kylsystem. Resultaten visar att ammoniakvatten är gynnsam med hög COP och en låg pumpeffekt och därmed ett lågt tryckfall. Ammoniakvatten är mest jämförbart med CaCl2 och K-formiat för de flesta resultat. Förändringarna i beräknad COP mellan gamla referensdata och nya uppmätta data var mindre än 1% minskning vid planering jämfört med isytans temperatur och med en inställd pumpkontroll (T ) för kylkapacitet på 200 kW och 300 kW. Förändringen i värmeövergångstal var mer signifikant, med ett intervall på cirka 9% till 27% minskning i antingen U-röret under golvet eller i en platta på värmeväxlaren. Även om dessa värmeövergångstal är lägre än tidigare beräknat, är den erforderliga pumpeffekten också lägre med hjälp av uppdaterade egenskaper: 40% lägre vid en köldbärarestemperatur på -10 ° C. Även om förändringen i värmeövergångstal är större med experimentella värden, är påverkan på COP minimal.  Slutsatser från detta projekt är att ammoniakvatten är en lämplig köldbärare jämfört med kalciumklorid och etylenglykol, de två vanligaste köldbärare i ishallskylning. Ett system som använder ammoniakvatten skulle ha ett pumpeffektbehov på 45% respektive 47% jämfört med kalciumklorid respektive etylenglykol. Systemet skulle också ha en 4,7% och 11,6% högre COP jämfört med system med kalciumklorid respektive etylenglykol. Den betydligt lägre pumpeffekten kommer att sänka det totala energibehovet för ishallar, vilket minskar driftskostnaderna.