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ACA Series selection

Compressed Air

Using The Graphs

Normally air compressors have airflow rates based upon the horsepower. Rotary Screw compressors normally discharge air at 180 o f - 200 o f, prior to after-cooling. Recipro- cating compressors normally discharge air at 250 o f - 275 o f, prior to after-cooling. Compressors are rated in CFM or cubic feet per minute of free air at inlet conditions. For practical pur- pose we will use sea level at 68 o f and 36% relative humidity as a norm. Altitude, differing ambient conditions with respect to temperature and humidity will all affect heat exchanger performance to a degree. Moisture content in air actually increases the Btu/hr load requirement for cooling air by adding an additional condensing load to the gas load requirement. As air rapidly cools, moisture in the compressed air stream will condense and separate into droplets, the more humidity pres- ent the more condensation will occur. The performance curves provided are for air. How- ever, gases other than air may be applied to this cooler with respect to compatibility by applying a correction factor. Please take time to check the operating specifications thoroughly for material compatibility, pressure, and size before applying an American Industrial heat exchanger into your system. Sizing Terms Approach Temperature is the desired outlet temperature of the compressed gas minus the inlet ambient air temperature of the external air flowing over the coil. SCFM (Standard Cubic Feet per Minute) A cubic foot of air at 68 o f, 14.696 psia, & 36% relative hu- midity, per minute. CFM (Cubic Feet per Minute) Air at inlet atmospheric conditions. ACFM (Actual Cubic Feet per Minute) Air at current pressure, temperature, & humidity conditions without reference to a standard. If the heat load (Btu/hr) is unknown a value can be calculated based upon system operational requirements. To properly calculate the heat load (Btu/hr) to be rejected, several items must be known with certainty (see below). • Flow rate SCFM (standard cubic feet pr minute) • Type of gas and its makeup. • System inlet pressure to the heat exchanger. • Ambient temperature where the heat exchanger will be located (hotest condition). • Temperature of the gas at the heat exchanger inlet. • Temperature of the gas desired at heat exchanger outlet. • Maximum acceptable pressure loss or cooled gas. American Industrial has created a quick reference chart for selecting ACA heat exchangers for Rotary Screw compressors (see page 214) [This chart offers basic infor- mation based upon compressor horsepower and average airflow rates. To properly use the chart, select the compressor horsepower at the left or the air flow rate. Next select the approach to ambient that is desired. Where the two columns intersect is shown the proper ACA model number.] To Determine the Heat Load Using The Chart

American Industrial provides performance graphs for ease of model selection. The following calculation examples (page 213), illustrate formulas to determine model selection sizes. It should be noted that there are some assumptions made when applying the basic principles for calculation in the formula. Altitude, humidity, materials, pressures, etc... all contribute to the final selection. Contact American Industrial for more detailed calculation. The selection process is important, many consider- ations should be made when selecting a heat exchanger. Once the proper Fs requirement is calculated, it is time to apply the data to the graph and make a selection. Selection 1) Find the Flow rate in SCFM located at the bottom of the graph. Follow the graph line up until it matches the calculated Fs from your calculations. If the point falls just above one of the model graphed lines, select the next larger size. If the point is on a line select it as your choice. 2) Check carefully the pressure differential. Units with operat- ing pressures from 70+ psig will have no greater than 2.0 psid within the published flow range. For lower inlet pressure see the pressure drop curves for more detail. 3) Calculate a Nozzle size using the nozzle size calculation to verify your selection has the proper port sizes for your required inlet pressure.

Formula: Nozzle Calculation

All numbers in equation are constants except for SCFM and (d) "density".

Nozzle Size = (SCFM x 4.512) (270,000 x d) .7854

x 144

Example: Flow rate = 200 SCFM Pressure = 15 psig Density = (d) from Compressed Air Density Graph

(200 x 4.512) (270,000 x .14) .7854

x 144 = 2.09" or (2" Nozzle)

Compressed Air Density @ 140F

0.4 0.6

0.2

0.1

.05

200

0.3 1

100

Inlet Pressure PSIG

note: AIHTI reserves the right to make reasonable design changes without notice.

230

355 American Industrial Drive LaCrosse, VA 23950

tel: 434-757-1800

fax: 434-757-1810

email: sales@aihti.com

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