Browsing by Author "Solomon Teklemariam (PhD)"

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    Investigation of Exhaust Gases Driven Absorption Cooling System Case Study on Gambella, General Cargo Ship
    (Addis Ababa University, 2025-06) Beniam Getasetegn; Solomon Teklemariam (PhD)
    In shipping transportation emission reduction has been a great concern for the last decades own to various reasons. Due to increment of oil prices, shipbuilders have been inspired to rise the vessel’s overall fuel efficiency. Currently, these situations are initiated by emission controlled areas as well as taxation of CO2. Recovering waste heat from low grade energy through vapor absorption refrigeration system is a promising way to improve engine efficiency and fuel consumption. In this thesis, utilization of exhaust gas from marine engines as a heat input to vapor absorption system is examined using marine vessel Gambella as a case study ship. The absorption cycle uses H2O−LiBr solution as a circulating fluid. An exhaust gas analysis is computed based on six months of engine performance data and then thermodynamic analysis is computed and simulation analysis is performed using Excel for vapor absorption system. This thesis focuses on performance enhancement of single effect vapor absorption system. By adding mixing chamber, flash gas removal and liquid suction heat exchanger into a single stage system, system performance is raised. Thermodynamic analysis is computed to compare the increment of performance on proposed cycle with ordinary and combined cycle. Simulation result shows that a proposed cycle COP is increased considerably by 38.23% and 3% relative to ordinary cycle and combined cycle respectively. Adding of vapor mixing chamber and flash gas removal accounts 35.23% increment on system performance and the remaining 3% is accounted by liquid suction heat exchanger. From the results the proposed cycle also considerably increased the cooling effect in an evaporator as well as an overall efficiency of marine diesel engine of the case study ship between 4 – 9%. Hence, introducing vapor mixing chamber and liquid suction heat exchanger to an ordinary cycle is a novel enhancement. Environmentally, utilizing the absorption system throughout sailing will diminish fuel utilization by 82.5 ton/year with fuel cost saving by 57,188.18 $/year and this results a payback period of 7 years for investment cost. This, in turn, decreasing emissions of NOX, SOX as well as CO2 by cost effectiveness of 2.88 $/kg, 18.86 $/kg as well as 0.054 $/kg respectively and also reduces about 349.55 and 418.11 tons of CO2e in 100years and 20 years using well to wake approach respectively.
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    Numerical Simulation and Performance Investigation of Bubble Pump Refrigerator
    (Addis Abab University, 2023-10) Henok Habte; Solomon Teklemariam (PhD)
    Approximately 30% of the primary energy consumed worldwide is used for refrigeration. In light of the global search for sustainable energy sources and energy-efficient methods of operation, solar-powered bubble pump refrigeration systems have gained traction as an alternative means of satisfying cooling requirements. Diffusion absorption refrigerators, sometimes referred to as bubble pump refrigerators, are driven by low-grade energy sources such as solar, waste heat, and recovery heat and do not require any mechanical moving components. However, in comparison to other cooling options, this system's coefficient of performance (COP) has been low. To increase the system's efficiency, more research on the effects of various parameters is required. The objective of this study is to enhance understanding of the behavior of the system through an examination of the impact of several critical factors. Using the programs ASPEN PLUS and EES, a thorough numerical simulation was conducted after a thermodynamic and system model was created. Every simulation was run with a standard total pressure of 25 bars. The model was used to forecast how different factors, such as generator heat, concentration of the refrigerant in a rich solution, and refrigerant purity, would affect the system's performance. The significant impact of refrigerant purity at the rectifier's outlet on coefficient of performance (COP) was one of the key finding. It was discovered that the COP rose from 0.15 to 0.36 as the purity improved from 0.950 to 0.999. It was also noted that a generator temperature of 200oC at 240W of thermal input was optimal at 25 bars of total system pressure. Additional heat rises did not appear to have a noticeable impact on the performance of the system. The one thing that makes this research stand out is the study of the effect of hydrogen on the COP of the system. It was observed that both heat absorbed at the evaporator (Qevap) and COP increased steadily and with similar degree of increments as hydrogen mass fraction increased from 0.5 to 0.95. This is due to the higher reduction of the partial of the refrigerant at evaporator inlet causing the refrigerant to lower its temperature further. Generally speaking, with more research done, the bubble pump refrigeration holds a lot of potential to take the place of traditional cooling technologies.
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    Numerical Simulation and Performance Investigation of Bubble Pump Refrigerator
    (Addis Ababa University, 2023-10) Henok Habte; Solomon Teklemariam (PhD)
    Approximately 30% of the primary energy consumed worldwide is used for refrigeration. In light of the global search for sustainable energy sources and energy-efficient methods of operation, solar-powered bubble pump refrigeration systems have gained traction as an alternative means of satisfying cooling requirements. Diffusion absorption refrigerators, sometimes referred to as bubble pump refrigerators, are driven by low-grade energy sources such as solar, waste heat, and recovery heat and do not require any mechanical moving components. However, in comparison to other cooling options, this system's coefficient of performance (COP) has been low. To increase the system's efficiency, more research on the effects of various parameters is required. The objective of this study is to enhance understanding of the behavior of the system through an examination of the impact of several critical factors. Using the programs ASPEN PLUS and EES, a thorough numerical simulation was conducted after a thermodynamic and system model was created. Every simulation was run with a standard total pressure of 25 bars. The model was used to forecast how different factors, such as generator heat, concentration of the refrigerant in a rich solution, and refrigerant purity, would affect the system's performance. The significant impact of refrigerant purity at the rectifier's outlet on coefficient of performance (COP) was one of the key finding. It was discovered that the COP rose from 0.15 to 0.36 as the purity improved from 0.950 to 0.999. It was also noted that a generator temperature of 200oC at 240W of thermal input was optimal at 25 bars of total system pressure. Additional heat rises did not appear to have a noticeable impact on the performance of the system. The one thing that makes this research stand out is the study of the effect of hydrogen on the COP of the system. It was observed that both heat absorbed at the evaporator (Qevap) and COP increased steadily and with similar degree of increments as hydrogen mass fraction increased from 0.5 to 0.95. This is due to the higher reduction of the partial of the refrigerant at evaporator inlet causing the refrigerant to lower its temperature further. Generally speaking, with more research done, the bubble pump refrigeration holds a lot of potential to take the place of traditional cooling technologies.