| 1. |
- Björk, Erik T.
(author)
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A simple technique for refrigerant mass measurement
- 2005
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In: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 25:8-9, s. 1115-1125
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Journal article (peer-reviewed)abstract
- A simple technique for refrigerant mass measurement is described and evaluated. First, quick-closing valves trap the refrigerant in the section under consideration. Then, the refrigerant is expanded into a tank, thus reaching a superheated state. Finally the mass is calculated by p-nu-T relationship. The technique was implemented on a domestic refrigerator and was computer automated (no need for manual intervention). Preliminary (1) data are reported of the charge distribution during an on-off cycle.
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| 2. |
- Björk, Erik T., et al.
(author)
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Refrigerant mass charge distribution in a domestic refrigerator. Part I : Transient conditions
- 2006
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In: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 26:8-9, s. 829-837
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Journal article (peer-reviewed)abstract
- Experimental results are presented of the refrigerant mass charge distribution in a steadily cycling domestic refrigerator. In detail it is shown how the charge is displaced at compressor start-up and shut-down. At start-Lip it was found that the charge was temporarily displaced towards the condenser before returning to a steady state distribution in the latter part of the on-period. As a result, initially the evaporator was starved with a lowered evaporation temperature and a peak 10 degrees C superheat. The superheat disappeared within 3 min as the evaporator was gradually refilled with refrigerant. At shut-down the pressure equalised within 3 min as refrigerant was pushed into the evaporator from the condenser. The losses due to charge displacements were estimated to 11% (capacity) and 9% (efficiency). Possible ways to reduce the losses are discussed.
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| 3. |
- Björk, Erik T., et al.
(author)
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Refrigerant mass charge distribution in a domestic refrigerator. Part II : Steady state conditions
- 2006
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In: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 26:8-9, s. 866-871
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Journal article (peer-reviewed)abstract
- Experimental results are presented of the refrigerant mass charge distribution in a steady state operating domestic refrigerator at varied thermal loads. It was found that the charge decreased in the evaporator and increased in the condenser and compressor upon increased thermal load. No subcooling or superheat was observed over the range of capacities tested (74-145 W). The combination of a low side accumulator and an expansion device with high capacity (short capillary tube) explained this. The study suggests that a capillary tube throttled cooling system, with a floating condensation temperature, can handle large load variations without becoming destabilised (superheat or subcooling) just like a more sophisticated thermostatic expansion device control system.
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| 4. |
- Chen, Yang, et al.
(author)
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A comparative study of the carbon dioxide transcritical power cycle compared with an organic rankine cycle with R123 as working fluid in waste heat recovery
- 2006
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In: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 26:17-18, s. 2142-2147
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Journal article (peer-reviewed)abstract
- The organic rankine cycle (ORC) as a bottoming cycle1The expression "bottoming cycle" refers to the power cycle that uses waste industrial heat for power generation by supplementing heat from any fossil fuel.1 to convert low-grade waste heat into useful work has been widely investigated for many years. The CO2 transcritical power cycle, on the other hand, is scarcely treated in the open literature. A CO2 transcritical power cycle (CO2 TPC) shows a higher potential than an ORC when taking the behavior of the heat source and the heat transfer between heat source and working fluid in the main heat exchanger into account. This is mainly due to better temperature glide matching between heat source and working fluid. The CO2 cycle also shows no pinch limitation in the heat exchanger. This study treats the performance of the CO2 transcritical power cycle utilizing energy from low-grade waste heat to produce useful work in comparison to an ORC using R123 as working fluid. Due to the temperature gradients for the heat source and heat sink the thermodynamic mean temperature has been used as a reference temperature when comparing both cycles. The thermodynamic models have been developed in EES2EES - Engineering equation solver. The thermodynamic properties for carbon dioxide in EES are calculated by the fundamental equation of state developed by R. Span and W. Wagner, A new equation of state for carbon dioxide covering the fluid region form the triple-point temperature to 1100 K at pressures up to 800 MPa, J. Phys. Chem. Ref. Data, Vol. 25, No. 6, 1996. http://www.fchart.com/ees/ees.shtml.2 The relative efficiencies have been calculated for both cycles. The results obtained show that when utilizing the low-grade waste heat with the same thermodynamic mean heat rejection temperature, a transcritical carbon dioxide power system gives a slightly higher power output than the organic rankine cycle.
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| 5. |
- Chen, Yang, et al.
(author)
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Theoretical research of carbon dioxide power cycle application in automobile industry to reduce vehicle's fuel consumption
- 2005
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In: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 25:14-15, s. 2041-2053
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Journal article (peer-reviewed)abstract
- The current work discusses means to utilize low-grade small-scale energy in vehicle exhaust gases, to reduce the vehicle's fuel consumption and to make it run more environmental friendly. To utilize the energy in the exhaust gas, a CO2 bottoming system in the vehicle's engine system is proposed. Several basic cycles-according to the different design concepts-are presented, and the efficiencies are calculated using Engineering Equation Solver (EES).1 Several thermodynamic models in EES show that after system optimization, in CO2 Transcritical power cycle with a gas heater pressure of 130 bars and 200 °C expansion inlet temperature, about 20% of energy in the exhaust gas can be converted into useful work. Increasing the pressure in the gas heater to 300 bars and with same expansion inlet temperature, about 12% of exhaust gas energy can be converted. When raising the pressure both in the gas cooler and in the gas heater, the cycle runs completely above the critical point, and the efficiency is about 19%. Besides, in the CO2 combined cycle, the system COP is 2.322 and about 5% of exhaust gas energy can be converted.
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| 6. |
- Ji, Xiaoyan, et al.
(author)
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Thermodynamic properties for humid gases from 298 to 573 K and up to 200 bar
- 2006
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In: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 26:2-3, s. 251-258
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Journal article (peer-reviewed)abstract
- For the needs of process design, the model proposed in our previous papers was extended to calculate the thermodynamic properties of humidity, heat capacity, molar volume, partial pressure of water vapour, enthalpy and entropy for humid gases (nitrogen, oxygen, air or a nitrogen-oxygen mixture). The comparison with other models from 300 to 473 K and I to 100 bar shows that the results calculated with different models are consistent within 50 bar and 400 K; out of this range, there is some difference. Meanwhile, mole ratios of nitrogen to oxygen in the saturated humid air were calculated from 323 to 523 K and 50 to 250 bar. It is found that the mole ratio of nitrogen to oxygen keeps almost constant, and the effect of the slight changes in the ratio of nitrogen to oxygen on the humidity, enthalpy and entropy of humid air is small enough to be neglected. Moreover, the enthalpy of dry air was predicted, and the comparison with other models again proved the reasonable assumptions and prediction capability of the new model
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| 7. |
- Larsson, Mikael, et al.
(author)
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Development of a method for analysing energy, environmental and economic efficiency for an integrated steel plant
- 2006
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In: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 26:13, s. 1353-1361
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Journal article (peer-reviewed)abstract
- The steel industry has faced several challenges during the years. There has always been an aspiration towards higher economic profitability for the system. During the mid 1970s and 1980s the energy crises caused a dramatic rise in energy costs, which led to an increased awareness in energy conservation. In recent years, climate change issues have become more important for the industry. The operating practises for an industrial system are often affected by external restrictions concerning the economical, energy and environmental efficiency of the system. There are a large number of ways to increase the system efficiency, e.g. installation of new process equipment, and practice changes. However, industrial systems such as an integrated steel plant consist of a system of several processes connected together with product and by-product interactions, where changes in one unit may result in changes throughout the total system. A process integration method focusing on the total integrated steel plant system by a simultaneous approach is adopted. An optimisation model is developed and used to study the effect of changes in the existing material and energy system. Applications of the model on the energy and material system have been made. The model can be used to analyse energy, environmental and economic aspects making it a powerful complement as a decision making tool. Conclusions about energy, environmental and economic effects are presented. © 2005 Elsevier Ltd. All rights reserved.
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| 8. |
- Lazzaretto, Andrea, et al.
(author)
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Prediction of performance and emissions of a two-shaft gas turbine from experimental data
- 2008
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In: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 28:17-18, s. 2405-2415
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Journal article (peer-reviewed)abstract
- Precise performance evaluation at design and off-design operations is needed for a correct management of power plants. This need is particularly strong in gas turbine power plants, which can quickly react to load variations and are very sensitive to ambient conditions. The paper aims at presenting a simple tool to determine the values of the thermodynamic quantities in each point of the plant and the overall plant performances of a real gas turbine plant. Starting from experimental data, a zero-dimensional model is developed, which properly considers the effect of ambient conditions and water injection for pollutant abatement at different load settings under the action of the control system. In particular, semi-empirical correlations for pollutant emissions taken from the literature are adapted by tuning their coefficients on the experimental data, in order to predict carbon monoxide and nitrogen oxide pollution. Such a tool can be useful to manage the energetic, economic and environmental aspects of plant operation.
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| 9. |
- Mwaba, MG, et al.
(author)
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A semi-empirical correlation for crystallization fouling on heat exchange surfaces
- 2006
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In: Applied Thermal Engineering. - Oxford : Pergamon Press. - 1359-4311 .- 1873-5606. ; 26:4, s. 440-447
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Journal article (peer-reviewed)abstract
- Crystallization fouling experiments are reported in this paper. In general the results show four distinct time regions: a region where the fouling thermal resistance is zero, a region where the fouling thermal resistance is negative, a region where the fouling resistance increases steadily and a region where the fouling thermal resistance remains constant. Each of these regions can be matched with different development phases in the crystallization fouling process: nucleation phase (regions 1 and 2), growth phase and asymptotic phase. Overall the fouling curves exhibit an S-curve, characteristic of the logistic curve. A new correlation based on the solution of the logistic equation is formulated. The correlation parameters are evaluated and related to the crystallization parameters. The results of this work can find application in predicting the evolution of the fouling scale layer in heat exchangers that are in operation. The predictions can assist heat exchanger operators to plan cleaning schedules.
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| 10. |
- Palm, Björn E.
(author)
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Refrigeration systems with minimum charge of refrigerant
- 2007
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In: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 27:10, s. 1693-1701
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Journal article (peer-reviewed)abstract
- Concern for the environmental effects of HFC-refrigerants as well as the use of flammable refrigerants has resulted in a need of decreasing the refrigerant charge in refrigeration and heat pump systems. This paper discusses the possibility of such reductions, both at the systems- and the component level. It is shown that a move towards indirect systems, using secondary refrigerants, on both the cold and the hot side of the system may result in considerable reduction of charge. However, this reduction may come at the cost of slightly reduced system performance, which in itself is detrimental from an environmental point of view. At the component level, it may be shown that the main contents of refrigerant is usually contained in the heat exchangers. By selecting compact designs the charge may be reduced to extremely low levels. Specifically, mini-channel heat exchangers can be used for reaching low charge. With proper selection of heat exchangers, the system performance should not be influenced by the reduction of charge. For indirect systems, the amount of refrigerant solved in the compressor oil may be comparable to the amount in the (compact) heat exchangers. A possible solution to reduce this amount is to use compressors with less oil. With components selected for minimum charge, the system design may be different than what is usual. Instead of a high pressure receiver and a thermostatic expansion valve, a capillary tube may be used in combination with a minimal low pressure receiver, similar to the system design used in household refrigerators.
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