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Membrane Performance
Performance of the reverse osmosis membrane element is affected by two key factors, temperature of the
feed water and the net driving pressure across the element. These two factors must be taken into account
before comparing or evaluating the performance of the membrane element of a reverse osmosis system.
The higher the temperature will provide more the product flow and a lower temperature will provide less
product flow. All reverse osmosis membrane elements and systems are rated at 77º Fahrenheit
(25ºCelsius).
To find the membrane permeate rate at different temperatures follow these steps:
1) Find the Temperature Correction Factor (TFC) from the table below.
2) Divide the rated permeate flow at 77º F by the TFC.
The result is the permeate flow at the desired temperature.
Example Question
: If a thin-film membrane permeate rate at 77 degrees Fahrenheit = 100 gallons/day.
What is the permeate rate at 59 degrees Fahrenheit?
Answer:
Temperature correction factor (from table above) = 1.47permeate flow at 59 degrees Fahrenheit =
100÷1.47 = 68.03 gallons (us)/day.
Net Pressure Correction
The membranes used in the systems referred to in these instructions are rated with water at 60 psi
pressure and a temperature of 25 degrees Celsius. To calculate your expected production rate, first
establish your expected production at a given temperature as explained above. This will be called
Temperature Correct Flow (TCF).
Multiply TCF by the membranes rated pressure, for these membranes this is 60psi. Then divide by your
water pressure supply (WPS). Expected production rate will = (TCF * 60) / WPS
Feed Water
Temperature
Correction
ºC
ºF
Factor
5
41.0
2.58
6
42.8
2.38
7
44.6
2.22
8
46.4
2.11
9
48.2
2.00
10
50.0
1.89
11
51.8
1.78
12
53.6
1.68
13
55.4
1.61
Feed Water
Temperature
Correction
ºC
ºF
Factor
5
41.0
2.58
6
42.8
2.38
7
44.6
2.22
8
46.4
2.11
9
48.2
2.00
10
50.0
1.89
11
51.8
1.78
12
53.6
1.68
13
55.4
1.61
Feed Water
Temperature
Correction
ºC
ºF
Factor
5
41.0
2.58
6
42.8
2.38
7
44.6
2.22
8
46.4
2.11
9
48.2
2.00
10
50.0
1.89
11
51.8
1.78
12
53.6
1.68
13
55.4
1.61
