Heat transfer performance of CO2, ethane and their azeotropic mixture under supercritical conditions

Kravanja, Gregor; Zajc, Gašper; Knez, Željko; Škerget, Mojca; Marčič, Simon; Knez, Maša

doi:10.1016/j.energy.2018.03.146

Cited by 25 publications

(7 citation statements)

References 36 publications

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“…Currently, only two CO2-based azeotropic refrigerants, CO2/R170 and CO2/R41, have been reported and analyzed in the literature. Studies have shown that these two mixed refrigerants can significantly improve the performance of heat pump water heater systems, reduce the discharge temperature and compression ratio of the compressor, and extend the service life of the compressor [70][71][72] . Among them, the COP and exergy efficiency of the CO2/R170 cycle were found to be 31.3% and 30.6% higher than those of the R134a cycle, respectively [70] , while the COP of the CO2/R170 cycle exceeded 50% when the evaporation temperature was above 0 ℃ and the operating cost is greatly reduced [72] .…”

Section: Research On Co2-based Mixed Refrigerantsmentioning

confidence: 99%

Research progress and applications of transcritical carbon dioxide heat pumps: A review

Mei,

Liu,

Liu

2023

Clean Energ. Sci. Tech.

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Heat pump technology is an energy-saving technology that can efficiently utilize low-grade energy. It has broad application prospects in building heating, industrial waste heat utilization, new energy and other fields. However, the refrigerants used in traditional heat pump systems have serious negative impacts on the environment, and there is an urgent need to find a safe, environmentally friendly, and efficient alternative refrigerant. As a natural refrigerant, CO2 has good physical and chemical properties and is very suitable as a working fluid in transcritical cycles, showing great advantages in the field of heat pump technology. At present, research on CO2 heat pumps has made certain progress, but there are few reviews of the research status and development trends of CO2 heat pumps in different applications. Therefore, this article systematically summarizes the latest research results of transcritical CO2 heat pumps in different application fields, pointing out the difficulties such as high pressure and low operating efficiency in system design and operation. It also summarizes the latest optimization research on system components, cycle structure, mixed refrigerants and control strategies. The results show that each optimization method can significantly improve system performance, among which mixed refrigerant is the simplest optimization method. Finally, the outlook for CO2 heat pump technology is put forward. With policy support and technological advancement, more comprehensive, energy-saving, and intelligent CO2 heat pump technology will continue to develop and innovate.

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Section: Research On Co2-based Mixed Refrigerantsmentioning

confidence: 99%

Research progress and applications of transcritical carbon dioxide heat pumps: A review

Mei,

Liu,

Liu

2023

Clean Energ. Sci. Tech.

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“…At the same region, HTC also decreases with qw increasing, but the HTC will be influenced a little by qw if bulk temperature (Tb) be far from Tpc. Mixed SC-CO2 and ethane as a working fluid has been proposed by Kravanja et al [16] for cooling the heat transfer through a coiled pipe. One of the important conclusions was the mixture's higher efficiency in cooling the system compared to pure coolants.…”

Section: Introductionmentioning

confidence: 99%

Convection Heat Transfer Analysis with Flow Resistance for Mini-Helically Coiled Tubes at Supercritical Pressures Experimentally

Jaddoa¹

2021

IJHT

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This paper analyzes the effect of fluid flow characteristics on the convection heat transfer for mini-helically coiled tubes (HCT) using supercritical carbon dioxide (CO2) as a natural refrigerant. Two experimental cases have studied in this work for mini-helically coiled tubes at different diameters with different coil pitches for analyzing the convection heat transfer with flow resistance. In the first case, the inner tube diameter, coil diameter and coil pitch were 5 mm, 200 mm and 10 mm respectively, while 10 mm, 100 mm and 5 mm were for the second case. Moreover, this work has also investigated the influence of frictional pressure drop, heat flux, friction factor and mass flux on dimensionless exergy destruction. The work environments were 300-500 K as an inlet temperatures range, 200-2000 Kg / (m2. s) as a mass heat fluxes range, 50,000-500,000 as a Reynolds number (Re) range and 50-200 Kw/m2 as an inner heat fluxes range. As a result, a large effect has been observed for dimensionless exergy destruction compared with the flow friction of CO2 which induced by heat transfer irreversibility. On the other point of view, a good sensitivity of optimal Re with the tube dimeter and mass flux also noticed compared with the heat flux. At a suitable range for Re, smallest and best exergy destruction also noticed for the tube diameters. A correlation has for the optimal Reynolds number as function of main dimensionless parameters related to wall heat flux, mass flux, fluid properties and geometric dimensions is proposed. Characteristics of the fluid flow had influenced significantly by mass and heat fluxes. In the future, the collected experimental data can be employed in order to design and improve the refrigeration conditioning performance for exchangers and other systems such as heat pumps.

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“…Nowadays, usage of supercritical fluids in various applications including refrigeration engineering, nuclear engineering, and aerospace engineering is very popular . More attention is primarily focused on carbon dioxide, water, refrigerants, and hydrocarbon fuels, particularly for water and carbon dioxide in the view of the heat transfer. In addition, there are also studies on thermodynamic analysis .…”

Section: Introductionmentioning

confidence: 99%

“…Similarly, this situation can be diminished and even removed by the higher operating pressures.KEYWORDS buoyancy, operating pressure, secondary flow, supercritical n-decane, thermal boundary layer, turbulence intensity 1 | INTRODUCTION Nowadays, usage of supercritical fluids in various applications including refrigeration engineering, nuclear engineering, and aerospace engineering is very popular. 1,2 More attention is primarily focused on carbon dioxide, water, refrigerants, and hydrocarbon fuels, 3-6 particularly for water 7-9 and carbon dioxide [10][11][12][13][14][15] in the view of the heat transfer. In addition, there are also studies on thermodynamic analysis.…”

mentioning

confidence: 99%

Turbulent heat transfer characteristics of supercritical n ‐decane in a vertical tube under various operating pressures

Sun

Sundén

et al. 2019

Int J Energy Res

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Summary To explore the effect of the operating pressure on the flow and thermal characteristics in a vertical tube with supercritical n‐decane, the inner wall temperature along the streamwise direction, the applicability of empirical correlations and buoyancy criteria are studied firstly. The mechanisms in views of density distribution, velocity field, turbulence intensity, the thickness of the thermal boundary layer, and secondary flow are then analyzed. It is observed that the buoyancy is helpful for the phenomenon of heat transfer deterioration at lower operating pressures but higher operating pressures can diminish this tendency. According to this reason, the empirical correlation proposed by Bae and Kim is suitable for the higher operating pressures but cannot well predict the occurrence of heat transfer deterioration. However, it can be evaluated by the buoyancy criterion Gr/Re2 = 0.01 qualitatively. The decrease of turbulence intensity, the thickened thermal boundary layer, and secondary flow generation make contributions to the heat transfer deterioration in particular. Similarly, this situation can be diminished and even removed by the higher operating pressures.

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Heat transfer performance of CO2, ethane and their azeotropic mixture under supercritical conditions

Cited by 25 publications

References 36 publications

Research progress and applications of transcritical carbon dioxide heat pumps: A review

Research progress and applications of transcritical carbon dioxide heat pumps: A review

Convection Heat Transfer Analysis with Flow Resistance for Mini-Helically Coiled Tubes at Supercritical Pressures Experimentally

Turbulent heat transfer characteristics of supercritical n ‐decane in a vertical tube under various operating pressures

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