calculations can be used with membrane manufacturer's specific ion flux constants to estimate the concentrations of

particular ions in the product water.

Symbols:

Qs

= The salt flow

= The salt flux constant for the ion under consideration across the membrane

Ks

used

A

= The area of membrane

Cion feed/brine average

= One half the sum of the feed concentration and the reject brine concentration of

the ion under consideration (Mg+ + in this example)

Cion product

= The concentration in the product of the ion under consideration (Mg+ + in this

example)

Given:

-4

The salt flux constant for this membrane Ks = 2.8 x 10 gallons per square foot-hour

The membrane area A, = 1,000 square feet

The feed water contains 204.4 grains per gallon of magnesium Mg ++.

The product water contains 0.3 grains per gallon of magnesium Mg+ +.

Qs = KsA (Cion feed/brine average Cion product)

-4

Qs = (2.8 x 10 gallons per square foot-hour)

(1,000 square feet)

(204.4 grains per gallon Mg+ + -0.3 grains per gallon Mg++)

= 57 grains Mg+ + per hour

however, a limiting efficiency of conversion of heat energy to mechanical or electrical energy. No heat machine can

operate at this best efficiency, but it does allow a rough estimate of the value of lower grades of steam.

Symbols:

TH =

Temperature in degrees Rankine of steam source. Higher temperature in degrees

Rankine (degrees Rankine equal degrees Fahrenheit plus 460 degrees)

TL =

Temperature in degrees Rankine of the cooling sink. Lower or discharge

temperature in degrees Fahrenheit

emax =

Maximum possible second law efficiency (maximum percent of the heat available

that can be converted theoretically into work)

emax =

(TH - TL)/TH X 100

Given:

The steam temperature drop available is 264 degrees Fahrenheit to 68 degrees Fahrenheit.

(See problem A-2.)

emax = (724 degrees Rankine - 528 degrees Rankine)/724 degrees Rankine x 100

emax = 27 percent

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