التقييم البيئي و الحراري لاستخدام R 744 كوسيط تبريد طبيعي بديل

الملخص EN

The aim of this research is reconsidering the using of carbon dioxide as refrigerant in vapour compression cycles instead of the traditional industrial refrigerants which have several environmental bad effects.

In this research, the properties of this chosen refrigerant were studied and compared with the other used refrigerants and then the positive and negative side for these properties was mentioned and the possible applications for this refrigerant.

One of these applications was chosen which is the heat pump used for providing domestic hot water, and through equations studying and making a computer program by using EES program to simulate this heat pump cycle working on carbon dioxide.

This simulation helped in determines the parameters for this cycle according to changed conditions.

Later the written program was developed to design the heat exchanger between the refrigerant and the water and study the best dimensions for having best result, so for heat exchanger (gas cooler) double-wall counter-current flow with capacity of 3[kW] the results were refrigerant pipe Diameter di =6 , the air gap d1-do =0.2 mm, water path Di -d2=1.75 mm, and heat transfer coefficient Ua =0.229 [W/m2.^ ].

for pressure value for refrigerant =100 bar , hot water temperature = 60°C , feed water = 15°C the length for the gas cooler =42.5 m, approach temperature =10°C, evaporation temperature = 5°C, and the Overall compressor efficiency =0.6 , the resulted COP = 3.534, and due to the properties of Transcritical circuit for CO2 the problem of pinch point effect can be solved by correct choice for both gas cooler pressure and its length, and with this we can get much design and investment benefit.

There are many methods for improving the efficiency of carbon dioxide Transcritical cycles that can be applied with a lot of benefit, as example adding an internal heat exchanger WAe [0.1,0.2] to cycle raise its COP to value exceed 4 for the same above condition.

In addition to that the using for multi stage compression is very useful, especially if we could get a work from the expanding process by many methods mentioned in the research.