| 1. |
- Alanne, Kari, et al.
(author)
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Thermo-economic analysis of a micro-cogeneration system based on a rotary steam engine (RSE)
- 2012
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In: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 44, s. 11-20
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Journal article (peer-reviewed)abstract
- A rotary steam engine (RSE) is a simple, small, quiet and lubricant-free option for micro-cogeneration. It is capable of exploiting versatile thermal sources and steam temperatures of 150 to 180 ºC, which allow operational pressures less than 10 bar for electrical power ranges of 1 to 20 kWe. An RSE can be easily integrated in commercially available biomass-fired household boilers. In this paper, we characterize the boiler-integrated RSE micro-cogeneration system and specify a two-control-volume thermodynamic model to conduct performance analyses in residential applications. Our computational analysis suggests that an RSE integrated with a 17 kWth pellet-fuelled boiler can obtain an electrical output of 1.925 kWe, in the design temperature of 150 ºC, the electrical efficiency being 9% (LHV) and the thermal efficiency 77% (LHV). In a single-family house inFinland, the above system would operate up to 1274 h/a, meeting 31% of the house’s electrical demand. The amount of electricity delivered into the grid is 989 kWh/a. An economic analysis suggests that incremental costs not exceeding € 1,500 are justifiable at payback periods less than five years, when compared to standard boilers.
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| 2. |
- Araoz, Joseph Adhemar, 1982-, et al.
(author)
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Non-ideal Stirling engine thermodynamic model suitable for the integration into overall energy systems
- 2014
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In: Applied Thermal Engineering. - : Elsevier. - 1359-4311 .- 1873-5606. ; 73:1, s. 203-219
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Journal article (peer-reviewed)abstract
- The reliability of modelling and simulation of energy systems strongly depends on the prediction accuracy of each system component. This is the case of Stirling engine-based systems, where an accurate modelling of the engine performance is very important to understand the overall system behaviour. In this sense, many Stirling engine analyses with different approaches have been already developed. However, there is a lack of Stirling engine models suitable for the integration into overall system simulations. In this context, this paper aims to develop a rigorous Stirling engine model that could be easily integrated into combined heat and power schemes for the overall techno-economic analysis of these systems. The model developed considers a Stirling engine with adiabatic working spaces, isothermal heat exchangers, dead volumes, and imperfect regeneration. Additionally, it considers mechanical pumping losses due to friction, limited heat transfer and thermal losses on the heat exchangers. The predicted efficiency and power output were compared with the numerical model and the experimental work reported by the NASA Lewis Research Centre for the GPU-3 Stirling engine. This showed average absolute errors around ±4% for the brake power, and ±5% for the brake efficiency at different frequencies. However, the model also showed large errors (±15%) for these calculations at higher frequencies and low pressures. Additional results include the calculation of the cyclic expansion and compression work; the pressure drop and heat flow through the heat exchangers; the conductive, shuttle effect and regenerator thermal losses; the temperature and mass flow distribution along the system; and the power output and efficiency of the engine.
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| 3. |
- Björk, Erik, et al.
(author)
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A thermographic study of the on-off behavior of an all-refrigerator
- 2010
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In: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 30:14-15, s. 1974-1984
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Journal article (peer-reviewed)abstract
- In this work a thermographic camera is used to observe the temperature distribution of a household refrigerator cooling system operating at on off cycling conditions. This technique offers an alternative method to analyze the cooling system compared to conventional thermocouples. In particular it is interesting to view the overall picture of how the refrigerant charge is distributed over the cooling system at transient conditions. In addition, four sources of energy losses were identified and discussed. Out of these losses, two would have been difficult to find using conventional thermocouple temperature measurements. (C) 2010 Elsevier Ltd. All rights reserved.
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| 4. |
- Cardozo, Evelyn, et al.
(author)
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Integration of a wood pellet burner and a Stirling engine to produce residential heat and power
- 2014
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In: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 73:1, s. 669-678
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Journal article (peer-reviewed)abstract
- The integration a Stirling engine with a pellet burner is a promising alternative to produce heat and power for residential use. In this context, this study is focused on the experimental evaluation of the integration of a 20 kWth wood pellet burner and a 1 kWe Stirling engine. The thermal power not absorbed by the engine is used to produce hot water. The evaluation highlights the effects of pellet type, combustion chamber length and cycling operation on the Stirling engine temperatures and thermal power absorbed. The results show that the position of the Stirling engine is highly relevant in order to utilize as much as possible of the radiative heat from the burner. Within this study, only a 5 cm distance change between the Stirling engine and the pellet burner could result in an increase of almost 100 °C in the hot side of the engine. However, at a larger distance, the temperature of the hot side is almost unchanged suggesting dominating convective heat transfer from the hot flue gas. Ash accumulation decreases the temperature of the hot side of the engine after some cycles of operation when a commercial pellet burner is integrated. The temperature ratio, which is the relation between the minimum and maximum temperatures of the engine, decreases when using Ø8 mm wood pellets in comparison to Ø6 mm pellets due to higher measured temperatures on the hot side of the engine. Therefore, the amount of heat supplied to the engine is increased for Ø8 mm wood pellets. The effectiveness of the engine regenerator is increased at higher pressures. The relation between temperature of the hot side end and thermal power absorbed by the Stirling engine is nearly linear between 500 °C and 660 °C. Higher pressure inside the Stirling engine has a positive effect on the thermal power output. Both the chemical and thermal losses increase somewhat when integrating a Stirling engine in comparison to a stand-alone boiler for only heat production. The overall efficiency of the pellets fired Stirling engine system reached 72%.
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| 5. |
- Chen, Jianyong, et al.
(author)
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Investigation of ejectors in refrigeration system : Optimum performance evaluation and ejector area ratios perspectives
- 2014
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In: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 64:1-2, s. 182-191
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Journal article (peer-reviewed)abstract
- This paper presents an ejector model to determine the optimum performance as well as obtaining the design area ratio of an ejector in a refrigeration system. Working fluid properties and auxiliary dynamic equations are used to model the processes in the ejector. The normal compression shock in the mixing chamber is considered. Experimental data from literature are used to validate the model, and the agreement with the model at optimum operating conditions is very good. The deviation between the model and the experimental data at non-optimum conditions is slightly larger. A study of working conditions for refrigerants R123 and R141b indicates that the condenser temperature has more influence than the generator and evaporator temperatures on the area ratio and the entrainment ratio in the ejector. Furthermore, area ratios need to keep up the pace with the variation of entrainment ratio as operating conditions are changed. A variable-geometry ejector seems a very promising alternative to ensure that the ejector refrigeration system operates at its optimum conditions. Ejector efficiencies play a very important role in the present model, and the influence of the efficiencies on the ejector performance is investigated. This ejector model may be used for parametric analysis and optimum performance evaluation as well as ejector design.
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| 6. |
- Chen, Jianyong, et al.
(author)
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Parametric analysis of ejector working characteristics in the refrigeration system
- 2014
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In: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 69:1-2, s. 130-142
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Journal article (peer-reviewed)abstract
- A detailed investigation of ejector working characteristics in terms of refrigeration efficiency, ejector entrainment ratio, and irreversibilities in each ejector component (nozzle, mixing chamber and diffuser) is carried out by using R141b, R245fa and R600a as the working fluids. The aim of this paper is to generalize the interactions and relationships of various ejector parameters to get better understanding of the ejector working characteristics in the refrigeration system. External and internal ejector parameters are studied separately. The operating conditions and ejector component efficiencies have significant influence on the ejector behavior, and different refrigerants perform distinctively different in the ejector refrigeration system. However, effects of superheat of the three working fluids are negligible. The irreversibility related to the shock process dominates in the diffuser and plays an important role in the ejector performance. Further attention is paid on an analysis of quantifying the ejector component efficiencies based on published test data. Correlations are established to estimate the ejector efficiency and to show how ejector parameters interact.
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| 7. |
- Furberg, Richard, et al.
(author)
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Boiling heat transfer on a dendritic and micro-porous surface in R134a and FC-72
- 2011
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In: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 31:16, s. 3595-3603
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Journal article (peer-reviewed)abstract
- A visualization study was conducted with the aim of deepening the understanding of the boiling mechanism in a dendritic and micro-porous copper structure for enhanced boiling heat transfer. The unique structure has earlier been shown to enhance heat transfer in pool boiling applications as well as in convective boiling in both small and large channels. Pool boiling tests were conducted in R134a and in the dielectric fluid FC-72 and were visualized with a high speed imaging system. Data on bubble size, bubble frequency density, heat transfer coefficient and the latent and sensible heat flux contributions were collected and calculated at heat flux varying between 2 and 15 W/cm(2). The enhanced surface produces smaller bubbles and sustains a high bubble frequency density in both fluids, even at low heat flux. An enhanced latent heat transfer mechanism of up to 10 times, compared to that of a plain reference surface, is the main reason for the improved boiling heat transfer performance on the enhanced surface. The data also suggests that the high nucleation bubble frequency density leads to increased bubble pumping action and thus enhancing single-phase convection of up to 6 times. The results in this study highlight the importance of both two and single-phase heat transfer within the porous structure.
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| 8. |
- Gong, Shengjie, et al.
(author)
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An experimental study on the effect of liquid film thickness on bubble dynamics
- 2013
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In: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 51:1-2, s. 459-467
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Journal article (peer-reviewed)abstract
- Experiments were conducted to investigate the boiling phenomenon in various liquid layers on a silicon heater surface with an artificial cavity. Deionized water is employed as working liquid. The emphasis is placed on how the liquid layer thickness affects bubble behaviour and liquid layer integrity for nucleate boiling under the isolated bubble regime. The experimental results show that for boiling in a liquid layer of ∼7.5 mm, the bubble dynamics reproduce the typical pool boiling characteristics with the averaged maximum diameter of 3.2 mm for the isolated bubbles growing on the cavity. As the water layer thickness decreases to the level comparable with the bubble departure diameter, the bubble is found to remain on the heater surface for an extended period, with a dry spot forming under the bubble but rewetted after the bubble rupture occurs. Further reducing the liquid layer thickness, an irreversible dry spot appears, suggesting a minimum rewettable thickness ranging from 1.2 mm to 1.9 mm corresponding to heat flux of 26 kW/m2 to 52 kW/m2. The void measured in the cavity confirms that it is dry inside the artificial cavity at high heat flux.
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| 9. |
- Gong, Shengjie, et al.
(author)
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Simulation and validation of the dynamics of liquid films evaporating on horizontal heater surfaces
- 2012
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In: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 48, s. 486-494
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Journal article (peer-reviewed)abstract
- In this study a non-linear governing equation based on lubrication theory is employed to model the thinning process of an evaporating liquid film and ultimately predict the critical thickness of the film rupture under impacts of various forces resulting from mass loss, surface tension, gravity, vapor recoil and thermo-capillary. It is found that the thinning process in the experiment is well reproduced by the simulation. The film rupture is caught by the simulation as well, but it underestimates the measured critical thickness at the film rupture. The reason may be that the water wettability of the heater surfaces is not taken into account in the model. Thus, the minimum free energy criterion is used to obtain a correlation which combines the contact angle (reflection of wettability) with the critical thickness from the simulation. The critical thicknesses predicted by the correlation have a good agreement with the experimental data (the maximum deviation is less than 10%).
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| 10. |
- Grip, Carl-Erik, et al.
(author)
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Process integration. Tests and application of different tools on an integrated steelmaking site
- 2013
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In: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 53:2, s. 366-372
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Journal article (peer-reviewed)abstract
- The energy network in Lulea consists of the steel plant, heat and power production and district heating. Global system studies are necessary to avoid sub-optimization and to deliver energy and/or material efficiency. SSAB began work with global simulation models in 1978. After that several more specialized process integration tools have been tested and used: Mathematical programming using an MILP method, exergy analysis and Pinch analysis. Experiences and examples of results with the different methods are given and discussed. Mathematical programming has been useful to study problems involving the total system with streams of different types of energy and material and reaction between them. Exergy is useful to describe energy problems involving different types of energy, e.g. systematic analysis of rest energies. Pinch analysis has been used especially on local systems with streams of heat energy and heat exchange between them.
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