Why is R245fa used in many low-temperature waste heat recovery projects?
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This post was last edited by sdwfsgyykai on 2018-5-4 at 12:00. I studied n-pentane, isopentane, R123, R141b, and R245fa – several working fluids used at normal temperatures – and found that their boiling points are similar. However, the heat of vaporization of n-pentane and isopentane is almost twice that of R245fa; moreover, these two fluids have a low GWP or no GWP at all, while R245fa has a GWP of 950. So why is R245fa still used for recovering low-temperature waste heat (where the temperature of the waste heat stream is between 100° and 200°)? Is this cheap? Or is it some other reason?
Same question! I only know that R245FA is used in small ORC cycles, where the cycle efficiency is very low, less than 10%, whereas isopentane is used in larger ORC cycle systems, resulting in a higher cycle efficiency.
Because 1. alkanes are flammable and explosive, whereas refrigerant substances do not pose such a risk； 2. Since alkane-based working fluids have high specific heat and high specific latent heat, they are often used in medium- to high-temperature heat sources after the risks associated with leaks have been addressed (as medium- to high-temperature heat sources generally generate a large amount of heat and are on a large scale); refrigerant-based working fluids are usually used in medium- to low-temperature heat sources (though this is not absolute).