Carbon Dioxide As Natural Refrigerant - Research Paper Example

Carbon Dioxide As Natural Refrigerant Refrigeration is one of the peak demands of the modern world. It is vital in preserving and storing food items for longer periods. However, the environmental impact of the product used for refrigeration is worse. People acknowledged the poisonous nature of the refrigerant products and demanded more energy efficient products. Many refrigerants have been introduced. However, each refrigerant has some negative impacts on the environment. Research shows that refrigerants are responsible for the ozone depletion. However, research shows that the power consumed by the old refrigerants reduced to about half within the past two decades. “Carbon dioxide (CO2) is a naturally found gas that can replace the old refrigerants and remain environmentally responsible”. Carbon dioxide (CO2) is the natural constituent of the air and makes no damage to the Ozone. On the other hand, it can be controlled by developing green technology. Carbon dioxide (CO2) is considered as the natural refrigerant due to its tendency to boil to gas a lower temperature of -78.5o C. It is a colorless, odorless and tasteless gas. It melts at -56.6oC and remains solid at -78.5o C. Carbon dioxide (CO2) has high solubility is water, ethanol and acetone. It can be easily transported and better thermo physical properties as compared to other refrigerants. Carbon dioxide (CO2) is inflammable but used as a fire extinguisher (Pearson, 1140-1148). The table shows the toxicity and flammability of different refrigerants, while one column classifies the Refrigerants. Refrigerants are classifies as CFC (Chloroflourouscarbon), HFC (Hydroflourouscarbon), HCFC (Hydrochloroflourouscarbon) and Natural refrigerants. Carbon dioxide (CO2) and NH3 are the natural refrigerants. In comparison with other available refrigerants, carbon dioxide (CO2) has about three to four times more vapor pressure. Thus, the system manufactured to utilize carbon dioxide (CO2) as refrigerants should use material with more thickness so that the hoses, heat exchangers and receivers can hold the pressure. On the other hand, due to having higher volumetric heat capacity, the charge magnitude of carbon dioxide (CO2) decreases. The system becomes less damaging in case of shattering on explosion due to having large volumetric heat capacity. Carbon dioxide (CO2) is named as R744, while R717 is ammonia (NH3). More volumetric heat capacity reduces the size of compressor, tubes and heat exchangers. Below is the comparison chart showing carbon dioxide (CO2) has large volumetric heat capacity as compared to other refrigerants. Below is the comparison chart showing that the vapor pressure of carbon dioxide (CO2) is the highest as compared to other refrigerants. Below is the comparison of the molecular mass and Density of different refrigerants. The table shows that only R717 (NH3 has less mass than air while carbon dioxide (CO2) has the mass more than air but less as compared to the other refrigerants (Padalkar, A. D., 261-271). Below is the comparison of properties of different commercially used refrigerants. Carbon dioxide (CO2) has the least surface tension at saturation temperature as compared to other refrigerants, while NH3 has the highest. As compared to other refrigerants, carbon dioxide (CO2) has about 60-70% more heat transfer coefficient (except NH3). The higher the vapor density of the refrigerants, the higher will be its heat absorbing capacity. Below is the chart showing the surface tension at the saturation temperature. Surface tension is the property that is important to determine fluid’s wetting properties. The lower the surface tension, the better will be the wetting of the tube and better heat transfer can be achieved. On the other hand, less amount of heat energy will be required to produce the gas bubbles from liquid bubbles due to less surface tension. The process also increases that gas bubble in the evaporator’s downstream tube that impact the temperature transfer coefficient (Padalkar, A. D., 261-271). Vapor Compression Cycle Compression and evaporation are the two main processes that are taking place in any refrigeration system. The critical temperature evaluates whether the refrigerant is suitable for the operation or not as it determines critical point of the refrigerant by showing the heat rejection point of the refrigerants. The commercially utilized refrigerants have 2 to 3 times more critical temperature as compared to the ambient temperature (Padalkar, A. D., 261-271). While considering regular subcritical vapor compression cycle, refrigerant phase change processes evolve as heat rejection and absorption. While in carbon dioxide (CO2), the heat rejection process can not be considered as the heat phase change process, as the ambient temperature of carbon dioxide (CO2) remains more than 31oC (Padalkar, A. D., 261-271). Environmental Impact of Carbon Dioxide (CO2) Based Refregration System The environental impact of a refrigerant can be calculated by viewing Ozone Deplition Potention (ODP) and Global Warming Potention (GWP). R22 has the highest ODP, whule R12 has the highest GWP of about 10600. Carbon dioxide (CO2) has zero ODP values while the GWP of carbon dioxide (CO2) is about 1 (Acul, et. al, 1-10). Considering the values, carbon dioxide (CO2) can be considered as the best Refrigerant as compared to conventional refrigerants. However, NH3 has the GWP values less than 1 but other propeties of the carbon dioxide (CO2) are better than NH3. Below is the chart that presents ODP and GDP values of different refrigerants available. Cost The cost of the carbon dioxide (CO2) as the refrigerant is the least as compared to other refrigerants. R407c costs about 10, 68 €/Kg, while R07 costs about 19, 53 €/Kg. the most used conventional refrigerant R134a has cost of about 9, 38 €/Kg, while R744- CO2 costs the lowest about 0, 52 €/Kg. R717 NH3 costs about 1, 3 €/Kg. Below is the table of the cost of some the conventional and natural refrigerants (Acul, et. Al, 1-10). Comparison of Thermo physical Properties of CO2 with other Refrigerants CO2 has the lowest value dynamic viscosity. It has the highest value of thermal conductivity as compared to the conventional refrigerants but lower value than NH3. CO2 has the highest value of volumetric Capacity as compared to all the available refrigerants. It has the highest value of Specific heat capacity as compared to the conventional refrigerants but Specific heat capacity of NH3 is more than CO2. CO2 has the highest value of gas phase density as compared to all the available refrigerants. It is more than 3 times of the highest gas phase density of conventional refrigerants and 30 times more than the gas phase density of NH3. The liquid phase density of the CO2 is least as compared to the compared to conventional refrigerants but more than NH3. CO2 has the highest critical pressure as compared to the conventional refrigerants but lower than the NH3. CO2 has the lowest critical temperature. While comparing all the thermo physical properties of CO2 with conventional and natural refrigerants, CO2 has the best properties to replace the conventional refrigerants (Acul, et. al, 1-10). System Design The basic components of the CO2 based refrigeration system remain same as in the conventional refrigeration system but due to the high vapor pressure. The material utilized to design the hoses, tubes, compressors, heat exchangers and radiators should have more thickness as compared in the conventional system, however, composite material with better thermal and pressure properties can be utilized to lower the price of the system. The system can be utilized in the split units for homes and offices. In the similar way, CO2 based system can replace the industrial refrigeration systems. Conclusion CO2 based refrigeration system has the capacity to provide refrigeration without damaging the environment. The system is the most secure system for homes and offices. CO2 has the best thermal properties as compared to the natural refrigerants. The system based on CO2 refrigeration is cost efficient, energy efficient and proved to be much effective as compared to the conventional refrigerants. Works Cited Padalkar, A. S., and A. D. Kadam. "Carbon Dioxide as Natural Refrigerant."International Journal of Applied Engineering Research, Dindigul 1.2 (2010). Print Acül, Hasan, Canbaz, Hatice, Kasap, Fatih And Erbil, Selim. “CO2 Cooling Systems, CO2 Unit Coolers/Evaporators, CO2 Gas Coolers”. Friterm Technical Data Page Friterm A.Ş. R&D Department, 2010. Print Pearson, Andy. "Carbon dioxide—new uses for an old refrigerant." international Journal of Refrigeration 28.8 (2005), Print Read More