| 1. |
- Granryd, Eric G.
(författare)
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Hydrocarbons as refrigerants - an overview
- 2001
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Ingår i: International journal of refrigeration. - 0140-7007 .- 1879-2081. ; 24:1, s. 15-24
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Tidskriftsartikel (refereegranskat)abstract
- Possibilities and problems of using hydrocarbons as working fluids in refrigerating equipment are discussed. An overview of safety standards is given. Different hydrocarbon alternatives are listed and characteristics in terms of thermodynamic cycles as well as heat transfer are shown. The general conclusion is that hydrocarbons offer interesting refrigerant alternatives for energy efficient and environmentally friendly refrigerating equipment and heat pumps. However, safety precautions due to flammability must be seriously taken into account. For some applications this can be done without adding noticeably to the total installation cost, but not in the general case.
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| 2. |
- Navarro, E., et al.
(författare)
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A phenomenological model for analyzing reciprocating compressors
- 2007
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Ingår i: International journal of refrigeration. - : Elsevier BV. - 0140-7007 .- 1879-2081. ; 30:7, s. 1254-1265
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Tidskriftsartikel (refereegranskat)abstract
- A new model for hermetic reciprocating compressors is presented. This model is able to predict compressor efficiency and volumetric efficiency in terms of a certain number of parameters (10) representing the main sources of losses inside the compressor. The model provides users with helpful information about the way in which the compressor is designed and working. A statistical fitting procedure based on the Monte Carlo method was developed for its adjustment. The model can predict compressor performance at most points with a maximum deviation of 3%. A possible gas condensation on cold spots inside the cylinder during the last part of the compression stroke was also evaluated.
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| 3. |
- Navarro, E., et al.
(författare)
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Performance analysis of a series of hermetic reciprocating compressors working with R290 (propane) and R407C
- 2007
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Ingår i: International journal of refrigeration. - : Elsevier BV. - 0140-7007 .- 1879-2081. ; 30:7, s. 1244-1253
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a series of compressors with different capacities and geometries working with propane as refrigerant are analyzed in terms of the compressor model developed by [E. Navarro, E. Granryd, J.F. Urchueguia, J.M. Corberan, A phenomenological model for analyzing reciprocating compressors, International Journal of Refrigeration, in this issue, doi:10.1016/j.irefrig.2007.02.006]. The relative influence of the diverse compressor losses is estimated as a function of the operating conditions. In addition, a comparison study between propane and R407C was carried out for one compressor and the observed differences were analyzed in terms of the compressor model. This study was also useful to verify the model's goodness with the aim of predicting the compressor performance with an untested refrigerant.
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| 4. |
- Shao, D. W., et al.
(författare)
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Flow pattern, heat transfer and pressure drop in flow condensation part I : Pure and azeotropic refrigerants
- 2000
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Ingår i: HVAC & R RESEARCH. - : Informa UK Limited. - 1078-9669 .- 1938-5587. ; 6:2, s. 175-195
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Tidskriftsartikel (refereegranskat)abstract
- This study concerns the flow pattern, heat transfer, and pressure drop for flow condensation. The experimental results are recorded in tests with a smooth horizontal tube of 6 mm inner diameter and 2 to 10 m long. This manuscript, which is part I of a two part series, focuses on pure and azeotropic fluids. Part II describes results with non-azeotropic refrigerant mixtures. A flow pattern map by Tandon et al. (1982) roughly predicts flow patterns associated with pure and azeotropic fluids in this work. However, the Froude number is found to be a good additional indicator to identify transition between annular and wavy flows. The transition occurs mostly at Fr = 15 to 20 for both pure and azeotropic fluids. In the case of pure and azeotropic fluids, the hear transfer coefficient was found to be independent of the mass flux in wavy flow regions, but increased with an increasing mass flux in the annular flow regions. For pure and azeotropic fluids, a modified Tandon et al. correlation agreed best with experimental data from tests with R-12, R-22, R-134a, and R-502. For the local pressure drop it is correlated within +/-15% by using the Lockhart-Martinelli parameters. The experimental data for pure and azeotropic refrigerants can be predicted by using a correlation for overall pressure drop.
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| 5. |
- Shao, D. W., et al.
(författare)
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Flow pattern, heat transfer and pressure drop in flow condensation part II : Zeotropic refrigerants mixtures (NARMs)
- 2000
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Ingår i: HVAC & R RESEARCH. - : Informa UK Limited. - 1078-9669 .- 1938-5587. ; 6:2, s. 197-209
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Tidskriftsartikel (refereegranskat)abstract
- This paper, which is parr II of a study on flow condensation is focused on zeotropic (or non-azeotropic) refrigerant mixtures (NARMs) In the experiments, condensation in a horizontal tube of inner diameter 6 mm and 10 m length were studied with fluids R-404A, R-407C, and three mixtures of R-32 and R-134a. A flow pattern map by Tandon et al. (1982) roughly predicts flow patterns associated with NARMs studied in this work. Most tests recorded are in the annular or semi annular flow region. The Froude number is, however, found to be an additional indicator to identify transition between annular and wavy flows. The transition in the experiments occurs mostly at Fr = 15 to 20 for the fluids tested. For NARMs with a small temperature glide (e.g. R-404A), as observed in the case of pure and azeotropic fluids, the hear transfer coefficient is independent of the mass flux in wavy flow regions, and increases with an increasing mass flux in annular flow regions. For other NARMs tested, the hear transfer coefficient (starting from a lower level) always increases with an increasing mass flux within the tested ranges. The heat transfer data from the tests with R-404A, R-407C, and R-32/R-134a mixtures can be predicted reasonably well by a modified Tandon et al. (1985b, 1995) equation with a correction proposed by Granryd (1989)for NARMs. The classical correlations for the pressure drop do nor work well. Instead, the data for local pressure drop are correlated within +/-15% by means of the same correlation as for the pure and azeotropic fluids. A simple correlation for the overall pressure drop based on the experimental data for pure and azeotropic fluids is good also for R-404A (with a small glide), but overpredicts the pressure drop (by up to 50%)for NARMs with glide, such as R-407C.
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