| 1. |
- Abdi, Amir, et al.
(författare)
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Experimental investigation of thermo-physical properties of n-octadecane and n-eicosane
- 2020
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Ingår i: International Journal of Heat and Mass Transfer. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0017-9310 .- 1879-2189. ; 161
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Tidskriftsartikel (refereegranskat)abstract
- Reliable knowledge of phase change materials (PCM) thermo-physical properties is essential to model and design latent thermal energy storage (LTES) systems. This study aims to conduct a methodological measurement of thermo-physical properties, including latent enthalpy, isobaric specific heat, thermal conductivity and dynamic viscosity, of two n-alkanes, n-octadecane and n-eicosane. The enthalpy and isobaric specific heat of the materials are measured via differential scanning calorimetry (DSC) technique, using a pDSC evo7 from Setaram Instrumentation with a sample mass of 628.4 mg. The influence of the scanning rates, varying from 0.5 K/min to 0.025 K/min, in dynamic continuous mode within temperature range of 10-65 degrees C is investigated. The thermal conductivity and the dynamic viscosity are measured via Hot Disk TPS-2500S instrument and Brookfield rotational viscometer, respectively, up to 70 degrees C. The thermal analysis results via the pDSC show that the isothermal condition can be approached at a very low scanning rate, however at the cost of a higher noise level. A trade-off is observed for n-octadecane, achieving the lowest deviation of 0.7% in latent heat measurement at 0.05 K/min, as compared to the American Petroleum Table values. For n-eicosane, the lowest deviation of 1.2% is seen at the lowest scanning rate of 0.025 K/min. The thermal conductivity measured values show good agreements with a number of documented literature studies in the solid phase, within deviations of 2%. Larger deviations of 5-16% are found for the measurement in the liquid phase. The viscosity values also show a good agreement with the literature values with maximum deviations of 2.9% and 6.3%, with respect to the values of American Petroleum Tables, for n-octadecane and n-eicosane, respectively. The good agreements achieved in measurements establish the reliable thermo-physical properties contributing to the future simulations and designs.
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| 2. |
- Gunasekara, Saman Nimali, 1982-, et al.
(författare)
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Thermal conductivity measurement of erythritol, xylitol, and their blends for phase change material design : A methodological study
- 2019
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Ingår i: International Journal of Energy Research. - : John Wiley & Sons. - 0363-907X .- 1099-114X. ; 43:5, s. 1785-1801
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Tidskriftsartikel (refereegranskat)abstract
- This work presents and discusses a detailed thermal conductivity assessment of erythritol, xylitol, and their blends: 25 mol% erythritol and 80 mol% erythritol using the transient plane source (TPS) method with a Hot Disk Thermal Constants Analyzer TPS‐2500S. Thereby, the thermal conductivities of xylitol, 25 mol% erythritol, 80 mol% erythritol, and erythritol were here found for respectively in the solid state to be 0.373, 0.394, 0.535, and 0.589 W m−1 K−1 and in the liquid state to be 0.433, 0.402, 0.363, and 0.321 W m−1 K−1. These obtained results are comprehensively and critically analyzed as compared to available literature data on the same materials, in the phase change materials (PCMs) design context. This study clearly indicates that these thermal conductivity data in literature have considerable discrepancies between the literature sources and as compared to the data obtained in the present investigation. Primary reasons for these disparities are identified here as the lack of sufficiently transparent and repeatable data and procedure reporting, and relevant standards in this context. To exemplify the significance of such transparent and repeatable data reporting in thermal conductivity evaluations in the PCM design context, here focused on the TPS method, a comprehensive measurement validation is discussed along various residual plots obtained for varying input parameters (ie, the heating power and time). Clearly, the variations in the input parameters give rise to various thermal conductivity results, where choosing the most coherent result requires a sequence of efforts per material, because there are no universally valid conditions. Transparent and repeatable data and procedure reporting are the key to achieve comparable thermal conductivity results, which are essential for the correct design of thermal energy storage systems using PCMs.
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| 3. |
- Gunasekara, Saman Nimali, 1982-, et al.
(författare)
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Thermal Conductivity Measurement of Erythritol, Xylitol and Their Blends for Phase Change Materials Design : a Methodological Study
- 2018
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Ingår i: The 14th International Conference on Energy Storage. - Adana, Turkey : IEA ECES. - 9789754872187 ; , s. 364-378
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Konferensbidrag (refereegranskat)abstract
- This work presents and discusses a detailed thermal conductivity assessment of erythritol, xylitol and their blends: 25 mol% erythritol and 80 mol% erythritol using the Transient Plane Source (TPS) method with a Hot Disk Thermal Constants Analyzer TPS-2500S. Their thermal conductivities were here found to be respectively: 0.59; 0.37; 0.39 and 0.54 W/(m·K) in the solid state, and to be 0.32; 0.43; 0.40 and 0.36 W/(m·K) in the liquid state. These obtained results are comprehensively and critically analyzed as compared to available literature data on the same materials, in the phase change materials (PCMs) design context. This study clearly indicates that the literature has considerable discrepancies among their presented thermal conductivities, and also as compared to the values found through the present investigation. Primary reason for these disparities are identified here as the lack of sufficiently transparent and repeatable data and procedure reporting, and relevant standards in this context. To exemplify the significance of such transparent and repeatable data reporting in thermal conductivity evaluations in the PCM design context, here focused on the TPS method, a comprehensive measurement validation is discussed along various residual plots obtained for varying input parameters (i.e., the heating power and time). Clearly, the variations in the input parameters give rise to various thermal conductivity results, where choosing the most coherent result requires a sequence of efforts per material, but there are no universally valid conditions. Transparent and repeatable data and procedure reporting is the key to achieve comparable thermal conductivity results, which are essential for the correct design of thermal energy storage systems using PCMs.
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| 4. |
- Ignatowicz, Monika, 1983-, et al.
(författare)
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Alternative alcohol blends as secondary fluids for ground source heat pumps
- 2016
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Ingår i: Refrigeration Science and Technology. - : International Institute of Refrigeration. - 9782362150180 ; , s. 610-617
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Konferensbidrag (refereegranskat)abstract
- The most common secondary fluid used for the borehole heat exchangers in Sweden is an aqueous solution of ethyl alcohol (EA) due to its relatively good thermophysical properties and low toxicity. Commercially available ethyl alcohol based fluids in Sweden contain up to 10 wt-% denaturing agents in form of propyl alcohol (PA) and n-butyl alcohol (BA). The aim of this paper was to investigate the performance of the existing ethyl alcohol blend containing two denaturing agents and alternative alcohol blends in terms of the pressure drop and heat transfer in the BHE and comparison with ethyl alcohol based secondary fluid. Experimental results showed that the presence of these denaturing agents improves thermophysical properties such as specific heat capacity, thermal conductivity and dynamic viscosity when added in small concentration. EA18 + PA1.6 + BA0.4 and EA18.4 + PA1.6 present the best characteristics in terms of the heat transfer and pressure drop. Both blends are giving higher heat transfer coefficient by 9.4 % (EA18 + PA1.6 + BA0.4) and 8.11 % (EA18.4 + PA1.6) than pure EA20. Both blends are giving as well lower pressure drop than EA20 by up to 2.7 % (EA18 + PA1.6 + BA0.4) and 3 % (EA18.4 + PA1.6). EA18 + PA1.6 + BA0.4 gives 1.4 % higher heat transfer coefficient and EA18.4 + PA1.6 gives lower pressure drop by up to 0.4 % when these two blends are compared.
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| 5. |
- Ignatowicz, Monika, 1983-, et al.
(författare)
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Alternative formate salts as low temperature secondary fluids
- 2017
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Ingår i: 5Th Iir International Conference On Thermophysical Properties And Transfer Processes Of Refrigerants (Tptpr). - : INT INST REFRIGERATION. ; , s. 443-450
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Konferensbidrag (refereegranskat)abstract
- Potassium organic salts like formates and acetates are known as environmentally friendly secondary fluids. The most important advantages of salts compared to aqueous solutions of alcohols and glycols are good thermophysical properties, low toxicity and non-flammability. The purpose of this work is to investigate properties of different formate salt based secondary fluids like: lithium formate, ammonium formate and sodium formate at low temperatures in order to propose new blends of formate salts that could be used as secondary fluids for low temperature applications. Studies showed that different alkali metal ions like sodium, lithium or ammonium are affecting the solubility level, freezing point, thermal conductivity, dynamic viscosity and specific heat capacity in different way. Among examined formate salts, ammonium formate showed the best performance by giving the lowest freezing point as well as the highest specific heat capacity and highest thermal conductivity and similar dynamic viscosity. Lithium formate salts had the highest dynamic viscosity among all samples and despite high specific heat capacity and thermal conductivity values these salts cannot be recommended for low temperature applications. 30 wt-% sodium formate and 36 wt-% lithium formate were recrystallizing at lower temperatures than 0 degrees C when fast cooling rate was applied. Thus, the possible application for these salts is rather limited to higher temperatures only. As seen, different type of cation group in the formate salt can result in different properties, thus, further studies to investigate ammonium formate as well as different acetate salts are recommended.
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| 6. |
- Ignatowicz, Monika, 1983-, et al.
(författare)
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Cesium and ammonium salts as low temperature secondary fluids
- 2019
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Ingår i: Refrigeration Science and Technology. - : International Institute of Refrigeration. - 9782362150357 ; , s. 2568-2575
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Konferensbidrag (refereegranskat)abstract
- Potassium formate and potassium acetate, as well as their blends are known as environmentally friendly secondary fluids with good thermophysical properties. The aim of this work was to investigate properties of cesium formate, cesium acetate and ammonium acetate solutions. Results showed that various alkali metal ions such as potassium, sodium, cesium or ammonium are affecting the freezing point, thermal conductivity, viscosity and specific heat capacity in different ways. Among examined salts, ammonium formate showed the best performance by giving the highest specific heat capacity and highest thermal conductivity and the lowest dynamic viscosity compared to potassium formate and other salts. Cesium formate solutions had the lowest viscosity among all tested salts. This study shows that both cesium formate and sodium formate could be used as different additives to enhance different properties of potassium formate and potassium acetate secondary based fluids.
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| 7. |
- Ignatowicz, Monika, 1983-
(författare)
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Corrosion prevention methods in indirect systems with secondary refrigerants
- 2010
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Secondary refrigerants are aqueous solutions of organic or inorganic salts used in indirect refrigeration systems to transfer heat. Water is known for its corrosive character and secondary refrigerants based on aqueous solutions have the same tendency. The most important corrosion factors are: type of secondary refrigerant, fluid velocity, pH, concentration, temperature, dissolved oxygen and scaling behaviour. Nevertheless, it is possible to minimize corrosion problems. There are several aspects which need to be taken into the consideration while working with the secondary refrigerants e.g. design of system, selection of secondary refrigerant, corrosion inhibitors and compatible materials used in the installation. The methods of system cleaning, refrigerant charging and deaeration procedures are also extremely important. The purpose of this paper is to present corrosion problems and provide a list important aspects related to designing, preparing and maintaining of indirect systems. Moreover, it introduces the traditional and alternative methods of corrosion protection of indirect systems with secondary refrigerants.
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| 8. |
- Ignatowicz, Monika, 1983-, et al.
(författare)
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Different ethyl alcohol secondary fluids used for GSHP in Europe
- 2017
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Konferensbidrag (refereegranskat)abstract
- The most common secondary fluid used for the borehole heat exchangers in Sweden is aqueous solution of ethyl alcohol (EA). Commercially available ethyl alcohol based fluids in Sweden and other European countries contain various denaturing agents. Ethyl alcohol based secondary fluids in Sweden are distributed as ethyl alcohol concentrate, including up to 12 wt-% denaturing agents in form of propyl alcohol (PA) and n-butyl alcohol (BA). In other European countries, like Switzerland and Finland, the commercial products containing a mixture of methyl ethyl ketone and methyl isobutyl ketone (up to 4.5 vol-%) are used for GSHP application. The chemical character of these denaturing agents can in different ways affect the thermophysical properties. Therefore, the aim of this paper was to investigate the performance of commercially available alcohol blends in Europe in terms of pressure drop and heat transfer in the BHE. The results show that the most commonly used product in Sweden (EA18+PA1.6+BA0.4) presents the best characteristics in terms of higher heat transfer (up to 10 %) and lower pressure drop (up to 2.7 %) among different commercial products found in Europe. Another commercial product used in Switzerland showed second best performance in terms of higher heat transfer (up to 5 %) and lower pressure drop (up to 2 %). Moreover, other products containing higher concentrations of denaturing agents presented the worst performance in terms of lower heat transfer (up to 8 %) and higher pressure drop (up to 1 %) than EA20.
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| 9. |
- Ignatowicz, Monika, 1983-, et al.
(författare)
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Ethyl alcohol based secondary fluid : Effect of corrosion inhibitors on thermophysical properties
- 2016
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Ingår i: Refrigeration Science and Technology. - : International Institute of Refrigeration. - 9782362150180 ; , s. 602-609
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Konferensbidrag (refereegranskat)abstract
- Currently available commercial ethyl alcohol (EA) based secondary fluids in Sweden and other Nordic countries contain up to 10 wt-% denaturing agents (in concentrate alcohol) in form of propyl alcohol and n-butyl alcohol but no corrosion inhibitors. These studies were initiated due to a growing need for providing any protection against corrosion and extending the lifetime of the system. A literature search has been made to find the compatible corrosion inhibitors that can effectively protect the system. Afterwards, measurements have been performed to investigate the effect of these corrosion inhibitors on the thermophysical properties of the base fluid. Results showed that the different corrosion inhibitors can affect the thermophysical properties even when added in small concentrations. The presences of corrosion inhibitor had a positive effect and decrease the freezing point. Additionally, the presence of corrosion inhibitor in 30 wt-% ethyl alcohol samples had no significant effect on the dynamic viscosity and only EA25 + 0.01 SG (sodium gluconate) sample showed lower dynamic viscosity value by up to 10 %. The corrosion inhibitors had negative effect on the thermal conductivity in the full temperature range. EA25 and EA30 samples containing sodium gluconate, benzotriazole and sodium molybdate had higher specific heat capacity than the pure solutions. This study showed that both benzotriazole and 2-mercaptobenzothiazole seem to be the most promising corrosion inhibitor for ethyl alcohol based secondary fluids.
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| 10. |
- Ignatowicz, Monika, 1983-, et al.
(författare)
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Experimental investigation of thermophysical properties of ethylene glycol based secondary fluids
- 2023
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Ingår i: International journal of refrigeration. - : Elsevier BV. - 0140-7007 .- 1879-2081. ; 155, s. 137-153
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Tidskriftsartikel (refereegranskat)abstract
- Aqueous solutions of ethylene glycol are commonly used as secondary fluids in different indirect refrigeration systems and heat pumps as well as nanofluids. A very extensive literature review has been done, including more than 90 references published from 1905 to 2023. Despite the wide application and importance, especially in the energy sector, ethylene glycol solutions seem to be less investigated in low temperature ranges and more research is required to improve the quality and quantity of available data. The novelty of this paper is to investigate the most important thermophysical properties of ethylene glycol solutions in low temperatures. In this study a different approach was made and solutions having a specific freezing point temperature (between -5 and -50 ºC) rather than specific concentration were investigates in temperature ranges applicable for different cooling applications. The concentrations giving a certain freezing point temperature seemed to deviate in some cases with 1–2 wt-% between different sources. Nevertheless, the density results were in rather good agreement with all reference data. The viscosity results were lower by up to ±10% compared to reference values. Additionally, the obtained experimental results for thermal conductivity were higher by up to 12% compared to ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) data. The specific heat capacity results were higher by up to 14.6% and 5.4% than current reference data. There is a high probability that the current ASHRAE data for specific heat are actually indirectly calculated values from thermal conductivity data and not validated using differential scanning calorimetry techniques.
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