Graphite foams have high bulk thermal conductivity and low density, making them an excellent material for heat exchanger applications. This research focused on the characterization of graphite foams under various processing conditions (different foaming pressures and particle additions), specifically studying the effects of porosity on the thermal properties. The characterization of the foams included measuring cell sizes, percent open porosity, number of cells per square inch, bulk density, Archimedes density, compression strength, thermal conductivity, thermal resistance, and permeability. Several relationships between the structure and properties were established, and a recommendation for the processing conditions of graphite foams for the use in heat exchangers was determined. / Master of Science

Rapporten behandlar och utvärderar tre olika isolermaterial, Polyisocyanurat (PIR), grafitcellplast och mineralull, vid tilläggsisolering av miljonprogrammets byggnationer.  Stora delar av miljonprogrammet är nu i behov av upprustning. Samhällets skärpta krav gällande energiförbrukning gör att nya rationella metoder och material krävs för att tillgodose ställda krav. Att tilläggsisolera är en del i denna upprustning, och eftersom valet av isolermaterial ofta faller på gamla beprövade metoder och materialval, såsom mineralull, syftar denna rapport till att öka kunskapen om alternativa, mer högpresterande isolermaterial. Isolermaterialens egenskaper tas först upp och behandlas i en generell jämförelse där ekonomiska och tekniska aspekter beaktas. För att konkretisera och påvisa utfallet i ett specifikt fall genomförs en studie för ett referensprojekt, kvarteret Hundlokan, som ägs och förvaltas av Fastighets AB Förvaltaren. I studien undersöks tre olika alternativ för vart och ett av materialen vid tilläggsisolering utvändigt av Hundlokans fasader. Samtliga alternativ ställs sedan mot varandra och utvärderas med hjälp av: fukt-, U-värdes-, energi-, kostnads- och LCC-beräkningar (livscykelkostnad). Enklare fuktberäkningar som påvisar relativ fuktighet (RF), ånghalt och temperatur i väggens olika skikt genomförs. Resultatet visar att alla alternativ anses vara möjliga att tillämpa utan att fuktproblem ska behöva uppstå. Mer avancerade beräkningar bör genomföras vid projektering. Energiberäkningarna för de olika alternativen och även ursprungsfallet görs i ”VIP-energy” för att möjliggöra en realistisk jämförelse där skillnaderna i transmissionsförluster ställs mot varandra. I kostnadsberäkningarna påvisas skillnaderna i produktionskostnaderna för de olika alternativen. Dessa tillsammans med energibesparingen i form av minskade transmissionsförluster ligger sedan till grund för LCC-beräkningarna. Då stora ytor av fasaden i kv. Hundlokan upptas av fönster och indragna balkonger som skapar köldbryggor görs med ökad isolertjocklek ingen stor energibesparing i form av minskade transmissionsförluster. Initialkostnaderna för de tjockare isoleralternativen blir för höga för att möjliggöra återbetalning inom rimlig tidsram. Slutsatsen blir att tilläggsisolering med alternativa material till mineralull kan vara lönsamt och bör alltid undersökas i ombyggnadsprojekt. I det specifika fallet kvarteret Hundlokan är tilläggsisolering med 10 cm PIR det mest lönsamma alternativet. / This report treats and evaluates three different types of insulation materials: Polyisocyanurate (PIR), graphite foam and mineral wool, at additional insulation of houses from the Swedish “millionprogram”. Large parts of the houses from the millionprogram are now in need of restoration. The stricter rules laid down by the society regarding the use of energy, demands new, rational methods and materials to satisfy the regulations. Additional insulation is a step in meeting the energy regulatory requirements, and since the choice of insulation often is limited to traditional out tried methods and choices of materials, such as mineral wool, this report will explore the alternative, high-performance insulation materials. The insulation material’s qualities will be treated in a general comparisment where economical and technical aspects will be covered. In order to concretize and demonstrate the outcome in a specific case, a case study will be executed for the neighborhood Hundlokan owned and managed by Fastighets AB Förvaltaren. In the case study, three different alternatives will be examined, for each and every material at the additional insulation, outwardly at Hundlokan’s facades. All these alternatives are compared with each other and evaluated with regards to moister, u-value, energy, costs and LCC- calculations (Life cycle analysis). Simpler moisture calculations are implemented demonstrating the relative humidity (RF), steam level and temperature in the walls different layers. The results of the moisture calculations demonstrate that all alternatives seem possible to apply without the risk of the occurrence of any moisture problems. But more advanced moisture calculations are recommended to be carried out for restoration projects. Energy calculations regarding the different alternatives and the current state will be performed with “VIP-energy” in order to enable a realistic comparisment between the differences at transmission losses. Differences are shown within the cost’s calculations in production costs for the different alternatives. These along together with the energy savings in terms of less transmission losses are bases for the LCC-calculations. A large surface of the facade is covered by windows and recessed balconies which create thermal bridges, increased thickness of the isolation results in no larger energy savings in terms of decreased transmission losses.  The initial costs for the thicker isolation alternatives will be high in order to enable repayment within a reasonable time frame. The conclusion is that adding insulation with alternative materials than mineral wool can be profitable and should always be examined in reconstruction projects. For the specific case, Hundlokan additional insulation with 10 cm PIR is the most profitable option.

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.

This work investigated a novel vapor chamber for efficient heat spreading and heat removal. A vapor chamber acting as a heat spreader enables for more uniform temperature distribution along the surface of the device being cooled. First, a vapor chamber was studied and compared with the traditional copper heat spreader. The thickness of vapor chamber was kept 1.35 mm which was considered to be ultra-thin vapor chamber. Then, a new geometrical model having graphite foam in vapor space was proposed where the graphite foam material was incorporated in vapor space as square cubes. The effects of incorporating graphite foam in vapor space were compared to the vapor chamber without the embedded graphite foam to investigate the heat transfer performance improvements of vapor chamber by the high thermal conductivity graphite foam. Finally, the effects of various vapor chamber thicknesses were studied through numerical simulations. It was found that thinner vapor chamber (1.35 mm thickness) had better heat transfer performance than thicker vapor chamber (5 mm thickness) because of the extreme high effective thermal conductivities of ultra-thin vapor chamber. Furthermore, the effect of graphite foam on thermal performance improvement was very minor for ultra-thin vapor chamber, but significant for thick vapor chamber. The GF could help reduce the junction temperature by 15-30% in the 5-mm thick vapor chamber. Use of GF embedded vapor chamber could achieve 250-400 Watt per Centimeter square local heat removal for power electronics. The application of this is not only limited to electronic devices but actuator and avionics cooling in aircrafts, thermal management of electronics in directed energy weapon systems, battery thermal management for electric and hybrid vehicles, smart phones cooling, thus covering a wide gamut of heat flux applications.