Energy shortages around the world necessitated research into alternative energy sources especially for domestic applications to reduce the load on conventional energy sources. This resulted in research done on the possibility of integrating solar energy with an aqua-ammonia diffusion absorption cycle specifically for domestic applications. The bubble pump can be seen as the heart of the diffusion absorption cycle, since it is responsible, in the absence of a mechanical pump, to circulate the fluid and to desorb the refrigerant (ammonia) from the mixture. It is thus of paramount importance to ensure that the bubble pump is designed efficiently. Various bubble pump simulation models have been developed over the years, but it was found that none of the existing models served as a good basis for application-specific design. Most of the models constrained too many parameters from the outset which made the investigation of the effects of certain parameters on the bubble pump’s performance impossible. According to the research, no bubble pump model investigated the effect of such a wide variety of factors including tube diameter, heat flux, mass flux, generator heat input and system pressure on the bubble pump’s lift height. A simulation model for a bubble pump for integration with a solar-driven aqua-ammonia diffusion absorption cycle was developed. It serves as a versatile design model to optimise the bubble pump for a large variety of conditions as well as changes in parameters. It was achieved by constraining the bubble pump dimensions and parameters as little as possible. A unique feature of this model was the fact that the bubble pump tube was divided into segments of known quality which made the length of the pipe completely dependent on the flow inside the pipe. It also made the demarcation of the flow development inside the tube easier. The model attempted to incorporate the most appropriate correlations for pressurised two-phase aqua-ammonia flow. The most appropriate void fraction correlation was found to be Abstract The design and optimisation of a bubble pump for an aqua-ammonia diffusion absorption heat pump the Rouhani-Axelsson (Rouhani I) correlation. It was mainly due to its exclusive use of thermophysical properties and the vapour quality. The most appropriate heat transfer coefficient that predicted the most realistic wall temperature, was the correlation from Riviera and Best (1999) which was the only correlation found in the literature developed with aqua-ammonia in mind. It was found that the published correlation could not reproduce their experimental results, and a modification of their correlation was made after which the simulation model’s results correlated well with the experimental values of Riviera and Best (1999). The main goal of the simulation model was to determine the height that the bubble pump was capable of lifting at the slug to churn flow transition under various conditions. The effect of varying a variety of parameters on the bubble pump lift height was also investigated. The results from Shelton & White Stewart (2002) were compared to the outputs of the simulation model, and it was found that their constraining of the submergence ratio limited their outputs, and that their heat inputs under different conditions was a bit optimistic. The simulation model’s outputs correlated well at higher tube diameters with the results from Shelton & White Stewart (2002), but at the lower diameters which was used in their study it was impossible to compare data, since their diameters was already in mini flow and micro flow regions. The temperatures also correlated well, all within 2% of the results from Shelton & White Stewart (2002). It was found that there couldn’t be just one set of optimised conditions and values for the bubble pump, but that each cycle with differing specifications and operating conditions would yield a unique set of optimised parameters. It was for that reason very important not to constrain parameters beforehand without investigating its effect on the bubble pump first. / Thesis (MIng (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2013.

Energy shortages around the world necessitated research into alternative energy sources especially for domestic applications to reduce the load on conventional energy sources. This resulted in research done on the possibility of integrating solar energy with an aqua-ammonia diffusion absorption cycle specifically for domestic applications. The bubble pump can be seen as the heart of the diffusion absorption cycle, since it is responsible, in the absence of a mechanical pump, to circulate the fluid and to desorb the refrigerant (ammonia) from the mixture. It is thus of paramount importance to ensure that the bubble pump is designed efficiently. Various bubble pump simulation models have been developed over the years, but it was found that none of the existing models served as a good basis for application-specific design. Most of the models constrained too many parameters from the outset which made the investigation of the effects of certain parameters on the bubble pump’s performance impossible. According to the research, no bubble pump model investigated the effect of such a wide variety of factors including tube diameter, heat flux, mass flux, generator heat input and system pressure on the bubble pump’s lift height. A simulation model for a bubble pump for integration with a solar-driven aqua-ammonia diffusion absorption cycle was developed. It serves as a versatile design model to optimise the bubble pump for a large variety of conditions as well as changes in parameters. It was achieved by constraining the bubble pump dimensions and parameters as little as possible. A unique feature of this model was the fact that the bubble pump tube was divided into segments of known quality which made the length of the pipe completely dependent on the flow inside the pipe. It also made the demarcation of the flow development inside the tube easier. The model attempted to incorporate the most appropriate correlations for pressurised two-phase aqua-ammonia flow. The most appropriate void fraction correlation was found to be Abstract The design and optimisation of a bubble pump for an aqua-ammonia diffusion absorption heat pump the Rouhani-Axelsson (Rouhani I) correlation. It was mainly due to its exclusive use of thermophysical properties and the vapour quality. The most appropriate heat transfer coefficient that predicted the most realistic wall temperature, was the correlation from Riviera and Best (1999) which was the only correlation found in the literature developed with aqua-ammonia in mind. It was found that the published correlation could not reproduce their experimental results, and a modification of their correlation was made after which the simulation model’s results correlated well with the experimental values of Riviera and Best (1999). The main goal of the simulation model was to determine the height that the bubble pump was capable of lifting at the slug to churn flow transition under various conditions. The effect of varying a variety of parameters on the bubble pump lift height was also investigated. The results from Shelton & White Stewart (2002) were compared to the outputs of the simulation model, and it was found that their constraining of the submergence ratio limited their outputs, and that their heat inputs under different conditions was a bit optimistic. The simulation model’s outputs correlated well at higher tube diameters with the results from Shelton & White Stewart (2002), but at the lower diameters which was used in their study it was impossible to compare data, since their diameters was already in mini flow and micro flow regions. The temperatures also correlated well, all within 2% of the results from Shelton & White Stewart (2002). It was found that there couldn’t be just one set of optimised conditions and values for the bubble pump, but that each cycle with differing specifications and operating conditions would yield a unique set of optimised parameters. It was for that reason very important not to constrain parameters beforehand without investigating its effect on the bubble pump first. / Thesis (MIng (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2013.

Several steps are followed in order to evaluate the cycle as the title suggests. The diffusion absorption refrigerator (DAR) cycle performance is evaluated when using helium or hydrogen as auxiliary gas. A slight increase in COP is found when using helium, but it is not sufficient to justify the cost. A secondary simulation of an alternate dual-pressure cycle using a pump is done as feasibility comparison with the same parameters as the diffusion cycle. It was found that the second cycle is not acceptable due to high evaporator temperatures needed to ensure liquid enters the pump instead of partially evaporated solution. This would greatly increase the work input required for what essentially becomes a compressor. Optimisation of the DAR is evaluated by simulating the use of a rectification column and the effects of different design points on overall performance. Meteorological data for Potchefstroom, South Africa is used to perform a yearly analysis on the simulated cycle and to specify a suitable design point. The use of a radiative cooling system as heat sink for the system is then investigated and incorporated into the system model. Finally, the performance characteristics of the simulated DAR cycle are discussed, verified and compared with available data from similar research. It is shown that a 40% solution aqua-ammonia-hydrogen cycle driven by 526 kW of solar thermal energy at 130°C and a system pressure of 1.5 MPa can easily achieve a COP over 0.4 with an air-cooled absorber at 40°C and a water-cooled condenser at 35°C. A 231 kW refrigeration capacity at an average evaporator temperature of –20°C is achieved, satisfying the requirements for a domestic refrigeration system. / Thesis (MIng (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2013.

Several steps are followed in order to evaluate the cycle as the title suggests. The diffusion absorption refrigerator (DAR) cycle performance is evaluated when using helium or hydrogen as auxiliary gas. A slight increase in COP is found when using helium, but it is not sufficient to justify the cost. A secondary simulation of an alternate dual-pressure cycle using a pump is done as feasibility comparison with the same parameters as the diffusion cycle. It was found that the second cycle is not acceptable due to high evaporator temperatures needed to ensure liquid enters the pump instead of partially evaporated solution. This would greatly increase the work input required for what essentially becomes a compressor. Optimisation of the DAR is evaluated by simulating the use of a rectification column and the effects of different design points on overall performance. Meteorological data for Potchefstroom, South Africa is used to perform a yearly analysis on the simulated cycle and to specify a suitable design point. The use of a radiative cooling system as heat sink for the system is then investigated and incorporated into the system model. Finally, the performance characteristics of the simulated DAR cycle are discussed, verified and compared with available data from similar research. It is shown that a 40% solution aqua-ammonia-hydrogen cycle driven by 526 kW of solar thermal energy at 130°C and a system pressure of 1.5 MPa can easily achieve a COP over 0.4 with an air-cooled absorber at 40°C and a water-cooled condenser at 35°C. A 231 kW refrigeration capacity at an average evaporator temperature of –20°C is achieved, satisfying the requirements for a domestic refrigeration system. / Thesis (MIng (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2013.

The transition from fluorinated gases to natural refrigerants could be key to reducing the impacts of climate change. Ice rinks are energy-intensive buildings, with large heating and cooling demands. The pumping power required to move the secondary refrigerant typically accounts for a sizable amount of the energy use of the refrigeration system. The use of aqua ammonia as a secondary fluid shows promising results, with pumping power use of about half that required of ethylene glycol, environmental friendliness, and low corrosivity to steel components. Aquaammonia is still novel but is currently in usein 34 Swedish ice rinks. This thesis addresses questions regarding evaporation rates, performance, material compatibility, safety, and regulations of aqua ammonia in ice rink systems. Laboratory tests were performed to assess aqua ammonia evaporation rates during storage and operations. Long-duration concentration change, in well-sealed and well-stored containers, indicated low levels of evaporation for all tested concentrations samples. Short-term concentration in open-air conditions, indicated rapid rates of evaporation, with nearly full evaporation of all ammonia concentration occurring within only 90seconds of open-air exposure. Testing of sample-mixtures containing contamination by substances aquaammonia was likely to encounter during retrofit replacement situations determined that aquaammonia and calcium chloride produce flakey sedimentation. Additionally, lower concentrations of aquaammonia are slightly more prone to becoming basic when mixed with the tested substances, such as calcium chloride. Historical data of systems operating with aquaammonia were analyzed for energy performance. While pumping requirements typically account for 10-20% of the energy for refrigeration, the pumps of the rinks studied with aqua ammonia accounted for only 1.2 to 4.2%. However, data availability and system configuration anomalies suggest additional analyses are required. Furthermore, best operating, maintenance, and safety practices were analyzed and global regulatory restrictions were examined. Surveying of manufacturer material compatibility information found copper and brass to be incompatible with aqua ammonia, while steel and carbon steel are recommended. Various plastics were addressed by the manufacturers, notably PVC was found to be acceptable for use with aqua ammonia. A cost comparison between aqua ammonia and calcium chloride found aqua ammonia to require less expensive equipment. Finally, aqua ammoniawas determined to fall outside of the classification of refrigerants in several international refrigeration codes. Various additional safety regulations guiding personal protective equipment, exposure times, transportation, storage, and disposal regulations were catalogued as part of this work. In summary, aqua ammoniawas found to be a safe substance with performance that matches theoretical energy savings. Pumping requirements were reduced from 10-20% to approximately 1-5% of overall refrigeration system energy use. Necessary safety precautions were found to be much less stringent than high concentrations of ammonia and aqua ammonia was ascertained to fall outside of refrigeration codes in Europe, Canada, and the United States of America. / Övergången från fluorerade gaser till naturliga köldmedier kan vara nyckeln till att minska effekterna av klimatförändringen. Isbanor är energikrävande byggnader med stora värme-och kylbehov. Den pumpeffekt som krävs för att pumpa köldbärare står vanligtvis för en stor mängd energianvändning i kylsystemet. Användningen av ammoniakvatten som köldbärare visar lovande resultat, med användning av pumpeffekt på ungefär hälften som krävs av etylenglykol, miljövänlighet och låg korrosion för stålkomponenter. Ammoniakvattenär fortfarande ny men används för närvarande i 34 svenska isbanor. Detta exjobb behandlar frågor om avdunstningshastigheter, energiprestanda, materialkompatibilitet, säkerhet och föreskrifter för ammoniakvatten i isbanasystem. Laboratorietester utfördes för att bedöma avdunstningshastigheter för ammoniakvatten under lagring och drift. Långvarig koncentrationsförändring, i väl tillslutna och välförvarade behållare, indikerade låga nivåer av avdunstning för alla testade koncentrationsprover. En kortvarig koncentration under friluftsförhållanden indikerade snabba avdunstningshastigheter, med nästan full avdunstning av all ammoniakkoncentration inom endast 90 sekunder efter exponering. Testning av olika ammoniakvatten lösningar som innehåller föroreningar skulle sannolikt påträffas vid byte av köldbärare. Dessutom är lägre koncentrationer av ammoniakvatten lite mer benägna att bli basiska när de blandas med de testade ämnena. Historiska data för system som arbetar med ammoniakvatten analyserades med avseende på energiprestanda. Medan pumpeffekten vanligtvis står för 10-20% av kylenergin, pumparna för de studerade isbanorna med ammoniakvatten behövde bara för 1,2 till 4,2%av kylenergi. Datatillgänglighet och systemkonfigurationsavvikelser föreslår dock att ytterligare analyser krävs. Dessutom analyserades bästa metoder för drift, underhållning och säkerhet och globala regleringsbegränsningar. Kartläggning av tillverkarens materialkompatibilitetsinformation visade att koppar och mässing var oförenliga med ammoniakvatten, medan stål och kolstål rekommenderas. Olika plast och packning materialbehandlades, särskilt PVC var acceptabelt för användning med ammoniakvatten. En kostnadsjämförelse mellan ammoniakvatten och kalciumklorid köldbärare visade att ammoniakvatten krävde billigare utrustning. Slutligen visades det att ammoniakvatten faller utanför klassificeringen av köldmedier i flera internationella kylnormer. Olika ytterligare säkerhetsreglersom styr personlig skyddsutrustning, exponeringstider, transport, lagring och bortskaffande föreskrifter katalogiserades som en del av detta arbete. Sammanfattningsvis visade ammoniakvatten vara ett säkert ämne med prestanda som matchar teoretiska energibesparingar. Pumpeffekten minskade mellan 10-20% och 1-5% av den totala energianvändningen i kylsystemet. Nödvändiga säkerhetsåtgärder visade sig vara mycket mindre stränga än att höga koncentrationer av ammoniak och ammoniakvatten konstaterades falla utanför kylnormeri Europa, Kanada och USA.

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.