Membranes Metric units

Finally, a few words on units. Because a great deal of modem membrane technology originated in the United States, the US engineering units—gallons, cubic feet, and pounds per square inch—are widely used in the membrane industry. Unlike the creators of the Pascal, I am not a worshipper of mindless uniformity. Metric units are used when appropriate, but US engineering units are used when they are the industry standard. 

Potentiometry is the measurement of the potential at an electrode or membrane electrode, so the detector response is in units of volts. The potentio-metric response tends to be slow, so potentiometry is used infrequently in analysis.47 One example is the use of a polymeric membrane impregnated with ionophores for the selective detection of potassium, sodium, ammonium, and calcium 48 In process chromatography, potentiometry may be used to monitor selected ions or pH as these values change over the course of the gradient. 

As previously reported, membrane contactors present interesting advantages with respect to traditional units. Moreover, they well respond to the main targets of the process intensification, such as to develop systems of production with lower equipment-size/production-capacity ratio, lower energy consumption, lower waste production, higher efficiency. In order to better identify the potentialities of membrane contactors in this logic, they have been recently compared to traditional devices for the sparkling-water production in terms of new defined indexes [24]. In particular, the comparison has been made at parity of plant capacity and quality of final product. The metrics used for the comparison between membranes and traditional units are ... 

Membrane operations are well known for their modularity, compactness and flexibility, therefore they can be eonsidered as new operations developed in the logie of proeess intensifieation. Reeently, new metrics for comparing membrane performanees with those of eonventional units have been introduced. These new metries take into aeeount the size, weight, flexibility, yield and modularity... 

Table 23.1. Electrocatalyst cycle and metrics [44]. (Reproduced from United States Department of Energy. DOE cell component accelerated stress test protocols for PEM fuel cells electrocatalysts, supports, membranes, and membrane electrode assemblies. 2007. With permission from DOE.)...

The unit of toughness is a very important parameter used in fracture mechanics. Toughness, K, is the property of a material to absorb energy, hi the U.S. Customary system, this unit is expressed as ksiVin. When using the metric SI system, many people use MPa An, mainly because it is closer in value to the U.S. Customary unit. The m denotes meters. The critical value of the mode stress intensity, Kj, at which fracture occurs is a function of the maximum uniform membrane stress. In the SI system, stress is usually denoted as MPa (N/mm ). Since the stress unit MPa is 1.0 N/mm, the unit for toughness becomes... 

---