Found the link below.
Monday, March 29, 2010
Wednesday, March 24, 2010
GAS COMPRESSOR PERFORMANCE
| THEORY & FORMULAE |
Performance of Polytropic Compressors
Compressors are gas movers. It is a mechanical device that increases the pressure of a gas by reducing its volume. Compression of a gas naturally increases its temperature. There are two basic types of compressors: the reciprcating compressor which is well suited for high pressures and low flow rates, and the centrifugal compressor which is preferred for low pressures and high rates.Compressors are rated in height of compression head developed. From the point of view of thermodynamics, real compression processes are polytropic processes, which lie somewhat between adiabatic and isothermal compression. The polytropic head and discharge temperature are given from the following expressions (from which horsepower can be derived):
where
H = polytropic head
Z = average compressibility factor
R = universal gas constant
P1 = suction gas pressure
P2 = discharge gas pressure
Rc = compression ratio = P2/P1
T1 = suction gas temperature
T2 = discharge gas temperature
Mw = molecular weight of gas
n = polytropic exponent = Cp/Cv
Cp = gas specific heat at constant pressure
Cv = gas specific heat at constant volume
Friday, March 19, 2010
AIR-COOLED HEAT EXCHANGER DESIGN
THEORY & FORMULAE
The calculator here is based on the correlations presented by Smith and Brown, and the series of equations presented by Blackwell to fit the graphs and tables of Smith and Brown. In brief, the method begins with the first equation, hinges on the iterative solution of the second equation below, and ultimately leads to the third equation, as described by Coker:
where
R = number of tube rows
U = overall heat transfer coefficient
Q = exchager duty (heat load)
Ci's = correlation constants
t1 = air outlet temperature
t2 = air inlet temperature
T1 = process fluid outlet temperature
T2 = process fluid inlet temperature
Af = face area of bundle
Vf = face velocity of air
W = tube bundle width
L = tube width
Sizing of Air-Cooled Heat Exchanger
Heat exchangers are systems that transfer heat between fluid mediums. The fluids or gases in a heat exchanger can be mixed or the energy transference can go through a conductive wall that keeps them separate. Heat exchangers are found in car radiators, furnaces, refrigerators, air conditioning, space heating, refining and chemical processing systems. Air-cooled heat exchangers typically have rectangular bundles containg several rows of tubes. The hot fluid enters at the top of the bundle, while air is blown by fans vertically upwards across the tube bank, i.e. counter current flow.The calculator here is based on the correlations presented by Smith and Brown, and the series of equations presented by Blackwell to fit the graphs and tables of Smith and Brown. In brief, the method begins with the first equation, hinges on the iterative solution of the second equation below, and ultimately leads to the third equation, as described by Coker:
where
R = number of tube rows
U = overall heat transfer coefficient
Q = exchager duty (heat load)
Ci's = correlation constants
t1 = air outlet temperature
t2 = air inlet temperature
T1 = process fluid outlet temperature
T2 = process fluid inlet temperature
Af = face area of bundle
Vf = face velocity of air
W = tube bundle width
L = tube width
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