| 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. |
- Isaksson, Ove, et al.
(författare)
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Pressure-viscosity coefficient of a refrigerant-oil mixture : [Coefficient pression-viscositéd'un mélange frigorigène-huile]
- 1993
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Ingår i: International journal of refrigeration. - 0140-7007 .- 1879-2081. ; 16:2, s. 139-142
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Tidskriftsartikel (refereegranskat)abstract
- A coaxial cylinder viscosimeter has been used to determine the pressure-viscosity coefficient of a pure refrigeration oil and of a mixture of refrigerant and oil at gauge pressures up to 15 MPa. The test fluid, Gargoyle Arctic oil 300, is a naphthenic-base oil. The refrigerant was R22, chlorodifluoromethane, which is a commercially important refrigerant. In a gap apparatus the refrigerant-oil mixture has been visually inspected at different pressures. Two different mechanisms are involved in the refrigerant-oil mixture: the change in solubility with pressure and the change in viscosity with refrigerant concentration. If the mixture is pressurized with excess refrigerant available then the concentration of refrigerant will increase with increasing pressure and therefore the viscosity will decrease. If the concentration is kept at a constant level then the viscosity will increase with pressure. The results from the cylinder viscosimeter showed that the viscosity increase with pressure for the mixture was almost the same as for the pure oil
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| 3. |
- Belman-Flores, J. M., et al.
(författare)
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Experimental study of R1234yf as a drop-in replacement for R134a in a domestic refrigerator
- 2017
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Ingår i: International journal of refrigeration. - : ELSEVIER SCI LTD. - 0140-7007 .- 1879-2081. ; 81, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents an experimental study for three identical domestic refrigerators using R1234yf as a drop-in replacement for R134a. An alternative methodology was proposed to estimate the optimal mass charge for R1234yf; with the use of such methodology, new evidences were sought on the thermal behavior of the refrigerator compartments as well as at the heat exchangers. Additionally, energy performance for both refrigerants was measured, and, finally, a TEWI analysis was conducted. For the type of refrigerator evaluated, results showed that R1234yf presented an average (for the 3 refrigerators) of 0.4 degrees C for the fresh food compartment, and 1.2 degrees C for the freezer, among different charges with respect to R134a. The optimal charge for R1234yf was 92.2 g, which is about 7.8% lower than the one for R134a, which represents a small increase of 4% in energy consumption in comparison to R134a. Finally, the TEWI analysis for the R1234yf was 1.07% higher than the R134a.
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| 4. |
- Bengtsson, Peder, 1968-, et al.
(författare)
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A household dishwasher heated by a heat pump system using an energy storage unit with water as the heat source
- 2015
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Ingår i: International journal of refrigeration. - : Elsevier. - 0140-7007 .- 1879-2081. ; 49, s. 19-27
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Tidskriftsartikel (refereegranskat)abstract
- Electricity usage by a household dishwasher can be reduced by using a heat pump system to heat the dishwasher cabinet, dishware and washing water. The evaporator obtains the energy from an energy storage unit which consists of a container filled with water which freezes to ice. The majority of the heat transfer from the energy storage to the evaporator occurs when ice is created in the energy storage unit. A transient simulation model of a dishwasher with a heat pump system was developed and compared to an experimental setup with good agreement. A simulation study of the compressor cylinder volume and the compressor operating time was performed. The results showed a 24% reduction in total electricity use compared to a dishwasher cycle using a traditional electric element.
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| 5. |
- Bengtsson, Peder, 1968-, et al.
(författare)
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Study of using a capillary tube in a heat pump dishwasher with transient heating
- 2016
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Ingår i: International journal of refrigeration. - : Elsevier. - 0140-7007 .- 1879-2081. ; 67, s. 1-9
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Tidskriftsartikel (refereegranskat)abstract
- For competitive purposes, manufacturers of household appliances need to produce appliances that use less electricity. One way of doing this for a dishwasher is to add a heat pump system. Previous studies using R134a as refrigerant have shown that the addition of a heat pump can reduce total electricity consumption by about 24%. This paper reports on the use of a capillary tube in a heat pump dishwasher during the transient heating period. Working with an available compressor, the mass of R600a and the length of a 0.9 mm capillary tube were varied in order to find the configuration with the lowest electricity consumption. Three methods of calculating the length of the capillary tube were used to determine five lengths for evaluation. The results show that using a single capillary tube throughout the transient heating period yields similar electricity consumption to a variable expansion device which occurred by switching the capillary tube between two or three different lengths during the heating period.
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| 6. |
- Björk, Erik T., et al.
(författare)
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Flow boiling heat transfer at low flux conditions in a domestic refrigerator evaporator
- 2008
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Ingår i: International journal of refrigeration. - : Elsevier BV. - 0140-7007 .- 1879-2081. ; 31:6, s. 1021-1032
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the flow boiling heat transfer in a typical domestic refrigerator evaporator with horizontal flow, frequent bends and a non-circular cross-section. The mass flux was varied between 21 and 43 kg/m(2) s, the heat flux between 1 and 5 kW/m(2) and the vapour quality between 0.2 and 0.8. In spite of a predicted stratified to wavy-stratified flow pattern complete tube perimeter wetting was believed to occur except for the lowest mass flux and for positions upstream of the first bend. it was concluded that the bends helped wetting the tube perimeter. The experimental data revealed heat transfer coefficients higher than predicted with conventional correlations. This was suggested to be explained by thin film evaporation at a perimeter repeatedly wetted by liquid slugs. A simple correlation based on the pure convective part of the Shah correlation [3] was derived from the experimental data. The mean deviation of this was 16.9% compared to Shah's 54.7%.
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| 7. |
- Björk, Erik T., et al.
(författare)
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Performance of a domestic refrigerator under influence of varied expansion device capacity, refrigerant charge and ambient temperature
- 2006
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Ingår i: International journal of refrigeration. - : Elsevier BV. - 0140-7007 .- 1879-2081. ; 29:5, s. 789-798
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports experimental results of an on/off cycling domestic refrigerator at varied expansion device capacity (EDC), quantity of charge and ambient temperature. It was found that the energy consumption is insensitive to varied EDC and charge within a wide range of settings. For the charge this is explained by the low side accumulator, which buffers over- and undercharge. It was also found that the optimum charge increased at lower ambient temperature. The paper describes an experimental procedure on how to determine the capillary tube length and the quantity of charge for a domestic refrigerator/freezer. This procedure is recommended since it takes different thermal masses and loads into consideration and since the potential for energy saving with a more sophisticated method appears to be limited.
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| 8. |
- Caramaschi, Matteo, et al.
(författare)
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Natural refrigerant mixtures in low-charge heat pumps: An analysis of the potential for performance enhancements
- 2024
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Ingår i: International journal of refrigeration. - : Elsevier BV. - 0140-7007 .- 1879-2081. ; 165, s. 70-83
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Tidskriftsartikel (refereegranskat)abstract
- The study investigated the characteristics of different natural refrigerants and their mixtures in a residential heat pump with low refrigerant charge. Three main evaluation criteria were utilized for comparing different mixtures: Coefficient of Performance (COP), Volumetric Heating Capacity (VHC), and a newly proposed indicator, the heating capacity at charge limit. Propane was used as a reference refrigerant. It was found that some mixtures significantly improved both COP and the heating capacity at charge limit while maintaining similar volumetric heating capacity and operating conditions. Alternative multi-criteria decision-making techniques were adopted to rank the best refrigerant mixtures. Mixtures rich in Dimethyl Ether (DME), such as DME-CO2 [0.96-0.04] and DME-Propylene [0.75-0.25] were found consistently among the best options. Those were followed by Propylene-rich mixtures such as Propylene-CO2, Propylene-Isobutane and Propylene-Butane. The levelized cost of heat (LCOH) could be improved by up to 12 %. To accelerate the transition to natural refrigerants, without compromises on efficiency and costs, further research and certification activities on non-fluorinated refrigerants based on Dimethyl Ether (R-E170), CO2 (R-744) and Propylene (R-1270) are recommended.
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| 9. |
- Chen, Jianyong, et al.
(författare)
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Screening of working fluids for the ejector refrigeration system
- 2014
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Ingår i: International journal of refrigeration. - : Elsevier BV. - 0140-7007 .- 1879-2081. ; 47, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- For an ejector refrigeration system, the working fluid significantly influences the ejector behavior and system performance as well as ejector design. There are three categories of working fluids: wet fluids, dry fluids and isentropic fluids. Four wet fluids (R134a, R152a, R290 and R430A), four dry fluids (R245fa, R600, R600a and R1234ze) and one isentropic fluid (R436B) are selected in the paper. Special consideration is paid to the superheat of the ejector primary flow. This superheat is needed not only for wet fluids, but also for dry fluids and isentropic fluids at some cases, to eliminate droplets inside the ejector. A minimum superheat is found, and it is dependent on the used working fluid and the operating temperatures as well as the ejector nozzle efficiency. The comparison among these nine candidates indicates that R600 is a good candidate for the ejector refrigeration system due to a relatively high COP and its low environmental impact.
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| 10. |
- Claesson, Joachim
(författare)
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Correction of Logarithmic Mean Temperature Difference in a compact brazed plate evaporator assuming heat flux governed flow boiling heat transfer coefficient
- 2005
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Ingår i: International journal of refrigeration. - : Elsevier BV. - 0140-7007 .- 1879-2081. ; 28:4, s. 573-578
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Tidskriftsartikel (refereegranskat)abstract
- The heat transfer in heat exchangers is commonly calculated using the concept of Logarithmic Mean Temperature Difference (LMTD). As is well known this approach is only valid for counter-current and co-current heat exchanger configurations. For other configurations, corrections for the deviation from pure counter-current are introduced. From any standard text book in heat transfer it may be found that the LMTD approach may also be used if condensation and evaporation occurs in the heat exchanger. The purpose of the present paper is to investigate if the LMTD approach can be used in a compact brazed plate evaporator. It will be shown through integration of the governing equations that the LMTD approach indeed may be used for practical cases, even though deviations occur at small logarithmic mean temperature differences. The article presents suggestions on the correction factor (F) needed under some simplified assumptions in a compact brazed plate heat exchanger operating as an evaporator for heat pump and refrigeration applications.
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