Environmentally Safe Refrigerants

The solution of this example is too extensive to provide herein. It is best undertaken in Exercise 19.8. In one solution, obtained by students at the Georgia Institute of Technology, using gasoline as the fuel, the entire vehicle weighs 1,750 kg and carries 74 L of fuel. Its fuel cell operates at 3 bar, provides =111 kW, has an efficiency of 43%, current density = 473 mA/cm and area = 450,000 cm. Its overall system efficiency is 8.10 km/L, overall fuel efficiency is 35.4%, and the total cost of the power train is 24,700, far in excess of the cost of a conventional gasoline engine. Note that the cost of the fuel cell is 13,300, with a mass of 25.1 kg.  

It has been estimated that one chlorine atom can destroy 10,000 molecules of ozone. Bromine also reacts with ozone, but fluorine does not. In 1995, Molina and Rowland, together with Paul Crutzen, who showed in 1970 that nitrogen oxides also reacted with ozone, received the 1 million Nobel Prize in Chemistry for their discovery of the depletion of the ozone layer, which the Nobel committee termed the Achilles heel of the universe. 

The R-12 must be replaced because it can release chlorine atoms, which deplete ozone in the stratosphere. Accordingly, a new refrigerant must be selected. Hopefully, one can be found that will not require any major changes to the current equipment or its operation. Possible candidates are fluorinated paraffin hydrocarbons of the general formulas and However, it should be noted that the 

The problem is to select a suitable new refrigerant. To accomplish this, the following steps are to be taken using a process simulation program. 

Examine the vapor pressures, toxidties, and flammability characteristics of all HFC refrigerant candidates and select one that appears to be in the range that will permit use of the current equipment. 

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Note that several CFC refrigerants are included, although they are being phased-out and replaced by more environmentally safe refrigerants. These are left in the table at this time because they have been such common/prominent refrigerants in industrial applications. 

Duvedi, A. Achenie, L. E. K, 1996, Designing environmentally safe refrigerants using mathematical programming, Chemical Engineering Science, 15, 3727-3739. 

Recall that butane is used in lighters and in torches. Isobutane is used as both an environmentally-safe refrigerant and a propellant in products such as shaving gel, as shown in Figure 21.9. In addition to these applications, both butane and isobutane are used as raw materials for many chemical processes. 

Acoustic refrigeration units have some real advantages they have no moving parts (except the speaker drivers) and they are environmentally safe. Presently the sound-fridge is neither as cheap nor as efficient as conventional cooling devices, but Garrett believes that the unit can be made competitive within several years. ... 

Many of today s automobile and truck air conditioners can use hydrocarbon refrigerant mixtures containing 2-methylpropane that are environmentally safe. 

To do so could bring about a major crisis for civilization. How, without refrigeration, could we ensure safe and adequate food supplies to urban areas, or delivery of heat-sensitive medical supplies A return to old-fashioned refrigerants would also be fraught with environmental hazards. So the solution is not simple. 

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