Refrigeration systems employing the NH3-H2O absorption cycle provide cooling using a thermal energy input. This cycle relies on the zeotropic nature of the refrigerant - absorbent pair: because of the difference in boiling temperatures between NH3 and H2O, they can be separated through selective boiling in the desorber. Desorbers with counter-current flow of the solution and generated vapor enable efficient heat and mass transfer between the two phases, reducing the absorbent content in the generated vapor. Flow visualization experiments at temperatures, concentrations and pressures representative of operating conditions are necessary to understand the heat and mass transfer processes and flow regime characteristics within the component. In this study, a Flooded Column desorber, which accomplishes desorption of the refrigerant vapor through a combination of falling-film and pool boiling, was fabricated and tested. Refrigerant-rich solution enters the top of the component and fills a column, which is heated by an adjacent heated microchannel array. The vapor generated within the component is removed from the top of the component, while the dilute solution drains from the bottom. Flow visualization experiments showed that the Flooded Column desorber operated most stably in a partially flooded condition, with a pool-boiling region below a falling-film region. It was found that the liquid column level was dependent on operating conditions, and that the pool-boiling region exhibits aggressive mixing between the vapor and solution phases. Heat transfer coefficients were calculated from the data for the pool-boiling region, and were compared with the predictions of several mixture pool-boiling correlations from the literature. The correlations from the literature were in general unable to predict the data from this study adequately. It was found that the Flooded Column desorber yielded higher heat transfer coefficients within the pool-boiling region than those predicted by these correlations. Therefore, modifications to existing mixture boiling correlations are suggested based on the findings of this study. The resulting modified correlation predicts 33 of the 35 data points from this study within ±40%, with an average absolute error of 19%.

This thesis covers the modelling of a Heat Recovery Steam Generator (HRSG) in a Combined Cycle Power Plant(CCPP). This kind of power plant has become more and more utilized because of its high efficiency and low emissions. The HRSG plays a central role in the generation of steam using the exhaust heat from the gas turbine. The purpose of the thesis was to develop efficient dynamic models for the physical components in the HRSG using the modelling and simulation software Dymola. The models are then to be used for simulations of a complete CCPP.The main application is to use the complete model to introduce various disturbances and study their consequences inthe different components in the CCPP by analyzing the simulation results. The thesis is a part of an ongoingdevelopment process for the dynamic simulation capabilities offered by the Solution department at SIT AB. First, there is a theoretical explanation of the CCPP components and control system included in the scope of this thesis. Then the development method is described and the top-down approach that was used is explained. The structure and equations used are reported for each of the developed models and a functional description is given. Inorder to ensure that the HRSG model would function in a complete CCPP model, adaptations were made and tuning was performed on the existing surrounding component models in the CCPP. Static verifications of the models are performed by comparison to Siemens in-house software for static calculations. Dynamic verification was partially done, but work remains to guarantee the validity in a wide operating range. As a result of this thesis efficient models for the drum boiler and its control system have been developed. An operational model of a complete CCPP has been built. This was done integrating the developed models during the work with this thesis together with adaptations of already developed models. Steady state for the CCPP model is achieved during simulation and various disturbances can then be introduced and studied. Simulation time for a typical test case is longer than the time limit that has been set, mainly because of the gas turbine model. When using linear functions to approximate the gas turbine start-up curves instead, the simulation finishes within the set simulation time limit of 5 minutes for a typical test case.

The purpose of this report is to investigate the possibilities with drain water heat recovery (DWHR) in residential buildings. Information and relevant theory has been collected and summarized in this report. Calculations have been done for given scenarios to evaluate profits. DWHR heat exchangers use simple technology and have long life-time. The heat exchanger is connected to outgoing drainage pipe and incoming cold-water supply so countercurrent flow is accomplished. This makes it possible to increase the temperature of the incoming cold-water and thereby decrease the amount of energy used to heat water. There are mainly two types of models on the markets, vertically and horizontally heat exchangers. DWHR can be cost-effective if installed during new constructions or renovation, otherwise installation costs can be quite expensive. An installation of a DWHR-unit means no increasing risks of bacteria growth (legionella). Approximately 20 % of the energy used to heat hot-water can be counted as internal heat gain, with a DWHR heat exchanger the amount increases which will result in less energy consumed in the room heating system. More development of existing models is required to reduce the prices and spread information. A big advantage with DWHR is that the energy need for heating water is quite constant during the whole year compared to other demands, for example room-heating. Results from calculations in this report show that a reduction of 43 % of the heating demand for hot-water could be made in a normal family house and 17 % reduction could be made in a residential building with fifty apartments. / Syftet med arbetet är att undersöka möjligheterna med att återvinna värme från spillvatten i bostäder. Fakta och relevant teori inom området har samlats ihop och sammanfattats i denna rapport. Egna beräkningar har gjorts för att utvärdera hur mycket det är möjligt att återvinna. Tekniken för spillvattenvärmeväxling är enkel och växlarna håller i regel länge och kräver inget underhåll. En spillvattenvärmeväxlare kopplas in så att motströmsvärmeväxling uppnås. En växlare ansluts till utgående spillvattenledning och inkommande kallvattenledning. Ett problem är att de större växlarna för flerbostadshus kan vara platskrävanade och dyra. En installation av en växlare lämpar sig bäst vid nybyggnation för både småhus och flerbostadshus. Vid renoveringar av miljonprogrammen som uppfördes på 1960–70-tal finns det goda möjligheter att installera spillvattenvärmeväxlare då man genom exempelvis en stamrenovering gör ingrepp på befintliga ledningar, detta kan minska installationskostnaderna. Det finns inga tillkommande risker för legionellabakterier med spillvattenvärmeväxlare. Mer utveckling borde ske inom området så att nya modeller tillkommer. För nuvarande är den vertikala växlaren liten och passar bäst i småhus medan den horisontella växlaren passar bättre vid större anläggningar, med utveckling kan modellerna anpassas så de kan fungera oavsett användningsområde. I småhus bör man i första hand titta på andra åtgärder att för att minska energiförbrukningen, exempelvis driftoptimering, tätning av fönster, tilläggsisolering av vind m.m. En spillvattenvärmeväxlare kan istället vara ett alternativ för ett lågenergihus eller passivhus där vanliga åtgärder redan vidtagits. Ungefär 20 % av energiåtgången för tappvarmvatten kan tillgodoräknas som internvärme, med en installerad spillvattenvärmeväxlare ökar denna del vilket är bra då mindre effekt krävs till värmesystemet. En stor fördel som kan ses med spillvattenvärmeväxling är att tappvarmvattenförbrukningen är relativt konstant under året till skillnad från exempelvis värmebehovet. Utifrån givna scenarion visade beräkningarna i denna rapport att 43 % kunde besparas i småhus och 17 % i flerbostadshus.

Limited worldwide energy supplies demand the improved utilization of thermal energy, which is the dominant form of all primary energy sources used today. Large quantities of waste heat are routinely exhausted wherever thermo-mechanical energy conversion occurs, providing an opportunity to improve utilization. Two waste-heat-driven cycles are analyzed: an absorption/compression cascade cooling cycle and a coupled Rankine/compression cycle. The absorption/compression cascade provides an environmentally-sound option for a common approach to thermal energy recovery: the use of absorption cycles for cooling applications. To achieve cooling at temperatures below 0ºC, ammonia-water is the overwhelming choice for the working fluid. However, concerns about the toxicity and flammability of ammonia sometimes limit its application in sensitive arenas. In this study, a lithium bromide-water absorption cycle is coupled with a carbon dioxide vapor compression cycle to realize the benefits of high-lift cooling without the concerns associated with ammonia. This cycle utilizes a waste heat stream at temperatures as low as 150°C to provide cooling at -40°C. The topping absorption cycle achieves a coefficient of performance (COP) of about 0.77, while the bottoming cycle achieves a COP of about 2.2. The coupled Rankine/compression cycle provides a mechanical expansion and compression approach to achieve thermally activated cooling, again driven by waste heat. The power produced in the turbine of the Rankine cycle is directly coupled to the compressor of a vapor-compression cooling cycle to generate cooling to be utilized for space-conditioning. The refrigerant R245fa is used throughout the cycle. Even with low grade waste heat sources, a Rankine cycle efficiency of about 11-12 percent can be achieved. When coupled to the bottoming compression cycle with a COP of about 2.7, this yields an overall waste heat to cooling conversion efficiency of about 32 percent at nominal conditions.

The diffusion absorption refrigeration (DAR) cycle is a promising technology for fully thermally driven cooling. It is well suited to applications in medicine refrigeration and air-conditioning in off-grid settings. However, design and engineering knowhow for the technology is limited; therefore, system development has historically been an iterative and expensive process. Additionally, conventional system designs require high-grade energy input for operation, and are unsuitable for low-temperature solar- or waste-heat activated applications. In the present effort, component- and system-level DAR engineering analyses are performed. Detailed bubble-pump generator (BPG) component models are developed, and are validated experimentally and with direct simulations. Investigations into the BPG focus on the Taylor flow pattern in the intermediate Bond number regime, which has not yet been thoroughly characterized in the literature, and has numerous industry applications, including nuclear fuel processing and well dewatering. A coupling-fluid heated BPG design is also investigated experimentally for low-source-temperature operation. Phase-change simulation methodologies are developed to rigorously study the continuously developing flow pattern in this BPG configuration. Detailed component-level models are also formulated for all of the other DAR heat and mass exchangers, and are integrated to yield a complete system-level model. Results from these modeling studies are applied to develop a novel fully passive low-source-temperature (110 - 130°C) DAR system that delivers refrigeration grade cooling. This design achieves operation at target conditions through the use of alternate working fluids (NH3-NaSCN-He), the coupling-fluid heated BPG, and a novel absorber configuration. The complete DAR system is demonstrated experimentally, and evaluated over a range of operating conditions. Experimental results are applied to assess and refine component- and system- level models.

This research project was about the combined organic Rankine cycle which extracted energy from the exhaust gas of a diesel engine. There was a study about significant properties of suitable working fluids. The chosen working fluid, R134a, was used to operate at the dry condition when it exited the steam piston engine. Furthermore, R134a is environmentally friendly with low environmental impact. It was also compatible with sealing materials. There were calibrations for the components of the combined Rankine cycle. The efficiency of the heat exchanger converting exhaust heat from the diesel engine to vaporize R134a was 89%. The average efficiency of the generator was 50%. The hydraulic pump used for the combined Rankine cycle showed a transporting problem, as vapor-lock occurred when the pump ran for about 1 minute. The output of the combined Rankine cycle was normalized to compensate for the parasitic losses of a virtual vane pump used in hydraulic systems for the 6 liter diesel engines. There were three different vane pump widths from different pumps to compare frictional loss. The pump with the smallest vane width presented the least frictional mean effective pressure (fmep) (0.26 kPa) when scaled with the displacement of the GMC Sierra 6 liter diesel engine. The power output of the Rankine cycle was scaled to brake mean effective pressure (bmep) to compare with the frictional mean effective pressure. The maximum bmep was at 0.071 kPa when diesel engine had rotational speed at 2190 RPM. The power outputs of the organic Rankine compensated partially the frictional loss of the vane pumps in the 6 liter diesel engine. By using R134a, the condensing pressure was 0.8 MPa; hence, the power outputs from steam engine were limited. Therefore, refrigerants with lower condensing pressure were needed. There were proposal for improvement of the organic Rankine by substituting R134a by R123 (0.1 MPa), R21 (0.2 MPa), and R114 (0.25 MPa) . / text

This thesis was concerned with the proof of concept for mid-grade, 250-500oC, industrial waste heat recovery using a thermally regenerative electrochemical system. Proposed thermally regenerative electrochemical systems are limited to high operating temperatures (> 900oC) and suffer from poor conversion efficiencies (< 20%). As such, a single chamber design that is free of moving parts was presented in this work. The concept for this novel regenerative system relies on gravity and a liquid medium to convey dissolved sodium hydride in a hydride-borohydride solution from cold to hot regions in a continuous circuit. Such a liquid transport medium could allow for operation below 500oC while stabilizing the hydride from thermal decomposition. Investigations on this system were carried out using a custom pressure differential thermal analyzer that was able to operate above temperatures of 700oC and pressures of 2.2MPa. The results of the experiments provided valuable information concerning the phase diagrams of various hydride-borohydride mixtures. The eutectic composition of the NaH-KBH4 system was found to be 43 mole% NaH. The corresponding eutectic temperature (503oC) was determined using the differential cooling curves. Appreciable NaH decomposition was noticed in mixtures above 59.0 mole% NaH. Mixtures up to 42.5 mole% KH in KBH4 were also investigated. The eutectic composition of the KH-KBH4 binary system was determined by extrapolating the liquidus curve to intersect the solidus curve. The KH-KBH4 eutectic temperature was found to be 390oC at 66 mole% KH. The experimental work successfully demonstrates that thermally unstable hydrides can be obtained in the liquid phase below their melting points, under moderate pressures, when mixed with alkali borohydrides. This significantly lowers the achievable operating temperature of the thermally regenerative electrochemical systems currently proposed. The use of the single chamber design with a hydride-borohydride liquid medium offers numerous advantages including: reduced maintenance, reduced operating temperature, reduced system weight, reduced parasitic losses, increased voltage, and increased reliability. The viability for mid-grade industrial waste heat recovery requires construction of a prototype which optimizes power outputs and explores the hydrodynamic transport of material. / Thesis (Master, Mining Engineering) -- Queen's University, 2009-09-24 14:33:22.627

Combined Cycle power plants have recently become a serious alternative for standard coal- and oil-fired power plants because of their high thermal efficiency, environmentally friendly operation, and short time to construct. The combined cycle plant is an integration of the gas turbine and the steam turbine, combining many of the advantages of both thermodynamic cycles using a single fuel. By recovering the heat energy in the gas turbine exhaust and using it to generate steam, the combined cycle leverages the conversion of the fuel energy at a very high efficiency. The heat recovery steam generator forms the backbone of combined cycle plants, providing the link between the gas turbine and the steam turbine. The design of HRSG has historically largely been completed using thermodynamic principles related to the steam path, without much regard to the gas-side of the system. An effort has been made using resources at both UK and Vogt Power International to use computational fluid dynamics (CFD) analysis of the gas-side flow path of the HRSG as an integral tool in the design process. This thesis focuses on how CFD analysis can be used to assess the impact of the gas-side flow on the HRSG performance and identify design modifications to improve the performance. An effort is also made to explore the software capabilities to make the simulation an efficient and accurate.

Thesis (M.S.)--Mississippi State University. Department of Mechanical Engineering. / Title from title screen. Includes bibliographical references.

European industries have realized that a reduction of primary energy usage is not only a European requirement but can also be of great economic interest. Especially both energy and resource intensive industries like the pulp and paper industry will benefit. Industrial excess heat as a by-product of industrial processes needing energy has a great potential to be a key factor in reducing primary energy usage. Both excess heat utilization and heat integration are potential ways for Kraft pulp mills to increase their energy efficiency, to decrease their primary energy use and thus green-house gas emission, and to support the pulp and paper industry to achieve sustainability goals and meet EU regulations. This thesis examines the total excess heat potential in the Swedish Kraft pulp industry through pinch analysis and optimization on a modelled average Swedish Kraft pulp mill (FRAM). Different excess heat recovery technologies (EHRTs) are identified based on their applicability and are evaluated regarding their environmental and economic benefits for the Swedish pulp industry by using the energy price and carbon scenarios tool (ENPAC tool). An excess heat potential in the Swedish Kraft pulp mill industry of 2,03 TWh at 60°C, and 3,53 TWh at 25°C is found in this study. Heat delivery to the district heating network (DH), cooling delivery to the district cooling network (DC), electricity generation with a condensing turbine (CT), phase-change material engine (PCM) and organic Rankine cycle (ORC) are identified as suitable excess heat recovery technologies for Swedish Kraft pulp mills. A payback time calculation in this study found the condensing turbine as the EHRT to be of highest economic benefit in 2018 (less than 3 years). With predicted future energy prices of the years 2030, 2040 and 2050 all considered recovery technologies become economically feasible (payback time of less than 3 years). The CT and combinations of CT with DH and DC are furthermore the recovery technologies with the highest CO2 savings of 100.000 t/a in 2018. All in all, this study suggests investing in a CT, or combinations of it with DH and DC, to create the greatest economic and environmental benefits in 2018. With future price changes on the energy market and an uncertain future energy demand an investment in combinations of recovery technologies generating both heat, cooling and electricity is found to be the most sustainable choice.