Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
Results
Showing 1 to 13 of 13 for “"R744"”.
-
Primary refrigeration system commissioning based on a transcritical 2- stage R744 cycle
… into the use of carbon dioxide as a refrigerant (R744) and describes the development of a two-stage trans-critical cooling system that is intended to be used as a chiller for the detectors at CERN's Large Hadron Collider (LHC). It then goes on to describe the steps taken to prepare the system for …
-
The performance of a reversible R744 vapor compression system with an internal heat exchanger in continuous frosting/ defrosting cycles
Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2024-08-01
-
Design, Testing And Controls For Air Source Heat Pump System In Cold Climates Using Natural & Conventional Refrigerants
… be a good alternative to the HFC refrigerants. R744 has zero ozone depletion potential (ODP) and a global warming potential (GWP) of 1 which is almost thousand times lower than the HFC refrigerants.</p> <p>In this study, air source heat pump systems with natural refrigerant and conventional …
-
Experimental and Analytical Investigation of a Two-Phase Ejector Used for Expansion Work Recovery in a Transcritical R744 Air-Conditioning System
… of the transcritical carbon dioxide (CO2, R744) refrigeration cycle, the supercritical heat rejection pressure can be used to maximize the system performance. In addition, large throttling losses make R744 a suitable fluid for expansion work recovery. This study presents experimental and …
-
Comparative Life Cycle Assessment of CFC-replacement Compounds in Different Technical Applications
… (R290), isobutane (R600a), carbon dioxide (R744), pentafluorodimethyl ether (E125), 1,1,1’,1’-tetrafluorodimethyl ether (E134), hepta-fluoropropyl methyl ether (E7000), methyl nonafluorobutyl ether (E7100), ethyl nonafluorobutyl ether (E7200), and 1,1-difluoroethane (R152a). The data …
-
Potentials for COP increase in vapor compression systems
… investigated for R410A and transcritical R744. Experiments were carried out in a limited range of operating conditions but an experimentally validated model was used to extrapolate trends. As the relative size of the HXs was increased, a maximum COP of 9.5 (without fans power) was …
-
Role of internal heat exchanger in air conditioning systems
… potential substitution of refrigerants (R134a, R744 and R1234yf among them). It provide extra heat transfer between the high temperature liquid from the condenser and the cold vapor from the evaporator, which can lower the inlet quality to the evaporator and potentially increase system capacity …
-
Vortex control of two-phase refrigerant flow in nozzles and its application in ejector vapor compression cycles
… the influence of vortex control on transcritical R744 ejector and cycle performance has been experimentally investigated. Vortex control was applied to ejectors with different geometric parameters. The performance of ejector and ejector cycle with vortex control was compared with those of the …
-
Commercial Electric Vehicle Cabin Heating System Modelling and Optimization
… substantial environmental benefits. The use of R744 demonstrated strong heating potential but would require a complete system redesign to accommodate transcritical operation. Optimization of the orifice diameter yielded an average system COP improvement of approximately 2 %, and the inclusion of …
-
Flash gas bypass concept utilizing low pressure refrigerants
… As the advantages of flash gas removal in R744 systems are observed, it is of scientific interest to elaborate the same approach in R134a or similar low pressure refrigerant A/C systems. The main reason for this is the fact that lower pressure fluids are more affected by pressure drop, …
-
Scuffing and wear of engineering materials under different lubrication regimes in the presence of environmentally friendly refrigerants
… as water, air, and ammonia, carbon dioxide (CO2, R744) is an attractive and possibly the most viable candidate. Although, CO2 is a non-flammable and non toxic natural refrigerant (being not the case for Hydrocarbons and Ammonia), one of the main drawbacks related to its implementation as a …
-
Experimental and numerical investigation of the design and control of vapor-compression systems with integration of two-phase ejectors for performance enhancement through expansion work recovery
… high throttling loss, such as transcritical CO2 (R744) systems, should use the ejector to directly supplement compressor power using the pressure increase provided by the ejector, while systems using lower-pressure refrigerants should use the ejector to improve the performance of the evaporator by …
-
Non-equilibrium effects on in-tube condensation from superheated vapor
… from R134a, R32, R1234ze(E), R410A, as well as R744 condensing at mass fluxes from 100 to 200 kg m-2 s-1 and heat flux from 5 to 25 kW m-2, showing that most experimental data are within 15% of the model predictions. As for the effects of non-equilibrium on condenser design, there is an obvious …