1 4 th Integrated Seminar

2 Determining the Tower Capability  Characteristic Curve Method It can be performed using the Demand Curve tab, along with appropriate data supplied by the manufacturer and field test data.  Performance Curve Method It can be performed using the Mechanical Draft Performance Curve tab, along with a set of performance curves supplied by the tower manufacturer or rebuilder and field test data.

3 Cooling Tower Demand Curves  It is the numerical solution of the Merkel integral over the wide range of L/G values.  Use in designing cooling towers.  Apply for analysis of test data.  Evaluate for the prediction of cooling tower performance.  Plot with the thermal demand, KaV/L, and L/G.  Contain the values of KaV/L, cooling ranges and approaches

4 Limitations on use of Demand Curve Actual tower performance may deviate from predicted at water loading and air velocities. The followings affect it. a)At very low water loadings b)At very high water loadings c)At very high air velocities d)Changing the airflow due to air-side resistance

5 Cooling Tower Characteristic Curves To analyze the thermal performance capability of a specified cooling tower. This equation is used for each demand curve. where, KaV/L = Tower characteristic, C = Constant related to the cooling tower design, L/G = Liquid and Gas ratio, and m or slope = Exponent related to the cooling tower design

6 Illustration of Tower Demand Curve, Characteristic Curve and Design Point Fig (1) – Tower Curve Descriptions

7 Constructing the Demand and Characteristic Curves Use the following data.  Wet bulb temperature = 75°F  Hot water temperature (T 1 ) = 100°F  Cold water temperature (T 2 ) = 80°F  Temperature range = 20°F  Approach = 5°F  L/G ratio = Needs.  To construct the demand and characteristic curves of a specified cooling tower  To plot the performance curve.

8 Solving the Requirements by using Merkel Equation T,°Fh water h air h w - h a T 2 = 80 T (20) = 82 T (20) = 88 T (20) = 92 T (20) = 98 T 1 = h 1 = 39.1 h (0.8662)(20) = h (0.8662)(20) = h (0.8662)(20) = h (0.8662)(20) = h 2 =

9 Checking Merkel Result by using CTI Toolkit v3.0 Software

10 Creating the Demand Curve with CTI Toolkit v3.0 Software Procedures  Enter the values of wet bulb temperature, range and altitude.  Put in the fill or tower coefficients C and slope (m).  Define the design point.  Click on “Recalculate” brings up the appropriate group of demand curves. DEMONSTRATE THE SOLVING PROCEDURES IN OTHER WINDOW DIALOG BOX DETAILEDLY.

11 Data Entering Dialog Box

12 Result Dialog Box after clicking the Recalculate Tab

13 The Complete Work Sheet Dialog Box Characteristic Curve Demand Curve KaV/L Line L/G Line Design Point

14 Constructing the Performance Curve of the Cooling Tower by using CTI Toolkit v3.0 Software Steps  Recalculate the approach temperature by changing the WBT again and again.  Record each approach temperature.  Then, calculate the CWT corresponding to the WBT and approach.  Plot CWT versus WBT.

15 Plotting the Tower Performance Curve Fig (2) – Off-Design Performance Curve

16 Conclusion  The performance curves are used to determine the cooling tower capability.  Tower demand curves are a graphical worksheet that facilities cooling tower calculations.  A set of performance curves of the standardized cooling towers is supplied by the tower manufacturers and companies.  Generally, it is experimentally determined by measuring field test data.

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