| 11. |
- Högberg, Marine, 1962, et al.
(författare)
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Calculation methods for comparing the performance of pure and mixed working fluids in heat pump applications
- 1993
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Ingår i: International Journal of Refrigeration. ; 16:6, s. 403-413
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Tidskriftsartikel (refereegranskat)abstract
- Three methods for comparing cycle performance of working fluids, pure as well as non-azeotropic mixtures, are investigated for two applications and for two mixture pairs, HCFC22-CFC114 and HCFC22-HCFC142b, and their pure components. The methods differ in the way of calculating the heat exchange processes. They assume, respectively, equal minimum approach temperatures, equal mean temperature differences and equal heat transfer areas. Changes of coefficient of performance (COP) with composition are explained for all methods. It is shown that transport properties must be taken into account when making rigorous comparisons between working fluids. To predict the relations between fluids with high accuracy, one must use the method with equal heat transfer areas. By the method with equal mean temperature differences, the COP can be estimated with the same accuracy for mixtures as for pure fluids, and can be used for rough estimations of the COP level with different fluids. The method of equal minimum approach temperatures should be avoided for non-azeotropic mixtures.
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| 12. |
- Högberg, Marine, 1962, et al.
(författare)
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Energy aspects in CFC-developments
- 1990
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Ingår i: Presented at Workshop on Concepts for Energy Savings in Heat Pumps and Refrigeration Systems, KTH, Stockholm August 29-31, 1990. ; , s. 13-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In the search for substitutes for teday's CFC fluids in electrically driven heat pumps the aspect of any changes in the electricity consumption is, of course, crucial. Reliable data on this aspect can only be achieved from full-scale experimental plants. However, in order to identify new fluids of interest, theoretical system simulations must be carried out in parallel with experimental projects. In such simulations the optimal equipment design for each new fluid can also be identified. In this paper some results from heat pump cycle calculations with different CFC substitutes are presented. From these results conclusions are drawn on the possible impact on the electricity consumption in future heat pump systems. A sensitivity analysis on some of the most important uncertainty factors in system simulations with new fluids is also presented.
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| 13. |
- Högberg, Marine, 1962, et al.
(författare)
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Impact of uncertainties on estimations of heat pump cycle performance
- 1996
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Ingår i: International Journal of Refrigeration. ; 19:1, s. 34-42
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Tidskriftsartikel (refereegranskat)abstract
- Sensitivity analysis is used to show how uncertainties in basic factors, such as heat transfer, pressure drop,compressor efficiency, and thermophysical properties, influence the result of heat pump cycle performanceestimations. By comparing the results of this analysis with uncertainty levels of estimations and experimental determinations, it is established to what extent improvements in accuracy are needed. The investigation was carried out for several different applications and, as working fluids, both pure substances and non-azeotropic mixtures were examined. It was found that evaporation heat transfer and compressor efficiency are two areas where improvements are needed. It is also shown that estimates using very accurate, substance-specific, equations of state differ from those using more general types by up to 1 % for COP and 2% for capacity.
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| 14. |
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| 15. |
- Linden, M. Mc., et al.
(författare)
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The need for, and availability of, working fluid property data: Results from Annexes XIII and XVIII
- 1993
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Ingår i: Presented at The 4th International Energy Agency Heat Pupm Coference Maastrict, The Netherlands, April 26-29.1993.
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Konferensbidrag (refereegranskat)abstract
- In these days of transition to new, more environmentally friendly working fluids, there is a definite need for good data and models of basic thermodynamic and transport properties of both pure compounds and mixtures to be used for cycle calculations and equipment redesign.Two annexes of the IEA Program on Advanced Heat Pumps have dealt with such data, namely Annex XIII-State and Transport Properties of High Temperature Working Fluids andNonazeotropic Mixtures and Annex XVIII-Thermophysical Properties of the Environmentally Acceptable Refrigerants. In this paper, highlights of these two annexes are presented.A sensitivity analysis (from Annex XIII) gives an estimate of how accurately these basic data need to be known to reach a certain accuracy in heat pump coefficient of performance (COP) and heating or cooling capacity calculations. This analysis points out the importance of measured property data. Other projects to be highlighted are a comparison of equations of state with experimental density, vapor pressure, and heat capacity data for mixtures (XIII), a survey of current research on the properties of the "new" refrigerants (XVIII), and an evaluation of equations of state for R134a and R123 which will lead to an international bulletin for the properties of these two alternative refrigerants (XVIII).
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| 16. |
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| 17. |
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| 18. |
- Melin, Peter, 1964, et al.
(författare)
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Flow boiling heat transfer and pressure drop for zeotropic mixtures in a horizontal tube
- 1994
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Ingår i: Presented at IIR International Conference, Padua, September 21-23, 1994. ; , s. 8-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Flow boiling heat transfer and pressure drop have been measured in a horizontal tube. The mediums used have been three mixtures of HCFC22 and HCFCI42b, two mixtures of propane and n-butane, and the pure substances HCFC22, HCFCI42b, propane and n-butane. The experimental facility was constructed to resemble a direct expansion evaporator typical for larger heat pumps. The evaporator is 5 metres long and divided into 10 half-metre sections. The results of the measurements show a large decrease in heat transfer during vaporization of mixtures, as compared to the predicted heat transfer using the thermodynamic properties of the mixtures in correlations working well for the pure constituents. The decrease for 50/50% mixtures was about 27- 32% and for 20/80% mixtures 19-24%. The measured heat transfer and pressure drop have been compared with existing correlations from literature (20 for heat transfer and 12 for pressure drop). The correlation most accurately predicting the measured data for pure substances in this paper was the correlation of Klimenko. Including the Thome-Shakir mixture boiling correction factor, the Klimenko correlation also predicted the mixture data with good agreement. For pressure drop, a number of correlations predicted the data well both for pure substances and for mixtures.
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| 19. |
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| 20. |
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