Module 47 December 2012


1. What is the approximate current average concentration of CO2 the earth’s atmosphere?


A 360ppm B 370ppm C 380ppm D 390ppm E 400ppm


2. What conditions define the critical point of CO2


A -78.5°C and 0.52MPa B -56.6°C and 0.52MPa C -56.6°C and 7.36MPa D 31.1°C and 0.52MPa E 31.1°C and 7.36MPa


3. If CO2 was at a temperature of 0°C and a pressure of 10MPa, what state would it be in?


A A point where it may co-exist as solid, liquid and gas B Gas C Liquid D Solid E Supercritical fluid


4. Which one of these is most likely to apply specifically to a transcritical CO2


refrigeration cycle?


A It works both above and below the critical point B The transport of liquid is critical to operation C The transfer of heat is critical D The whole cycle is above the critical point E The whole cycle is below the critical point


5. Considering the article and the diagrams, which one of these statements about the cycles in a R134a subcritical cycle compared to a CO2


transcritical cycle is most likely to be correct?


A If the outlet from the expansion device stays at a constant enthalpy but the evaporator pressure rises, the potential for evaporator heat transfer increases in both cycles


B The heat rejection process in the transcritical process takes place at six to eight times the pressure of that of the subcritical process, and at a significantly higher temperature


C The heat rejection process for both cycles is dependent on condensation


D The compression process for the transcritical system can accept liquid at the entry to the compressor, whereas the subcritical system can not


E The compressor is likely to have smaller refrigerant volume flowrate in the R134a system compared to the CO2 for similar loads


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