Research Papers: Gas Turbines: Industrial & Cogeneration

Gas Turbine Power Augmentation: Parametric Study Relating to Fog Droplet Size and Its Influence on Evaporative Efficiency

[+] Author and Article Information
Mustapha Chaker

 Bechtel Corporation, Houston, TXmchaker@bechtel.com

Cyrus B. Meher-Homji

 Bechtel Corporation, Houston, TXcmeherho@bechtel.com

The number of nozzles is a function of the nozzle flow rate, gas turbine airflow rate, and the design DBT and RH utilized.

The rationale for the selection of this distance is provided in Sec. 4 and is essentially that the rate of growth of droplet size diminishes after around 8–10 cm—see Sec. 4).

The response time is the time taken for the droplet to attain airflow velocity.

Typical airflow velocities in gas turbine ducts when the fog nozzles are located after the filters.

This value is typical for heavy duty gas turbines.

It is true that with poor drainage system design, the agglomerated droplets may be of larger size and have the potential to erode blades over time.

This can be accentuated with compressor fouling degradation.

This avoids problems with wetting of the silencers, excessive drainage, and also the washing of accumulated dirt into the compressor. Of course, the duct geometry and dimensions must offer an adequate residence time for evaporation for this location.

J. Eng. Gas Turbines Power 133(9), 092001 (Apr 20, 2011) (10 pages) doi:10.1115/1.4002883 History: Received August 24, 2010; Revised September 01, 2010; Published April 20, 2011; Online April 20, 2011

Several gas turbine power augmentation techniques are available to counter the detrimental drop in power and thermal efficiency that occur at high ambient temperatures. Inlet fogging and wet compression are two common and relatively simple techniques. This paper addresses the influence and importance of droplet size on evaporative cooling performance and efficiency. Spray nozzles used for inlet fogging and wet compression include impaction pin, swirl jet, air assisted, and swirl flash nozzle designs. The evaporation efficiency of the atomized droplets from these nozzles depends on the droplet size, size distribution, and spray plume shape. Droplets size varies with nozzle type, configuration, operating conditions, and nozzle manifold location in the gas turbine inlet duct and are affected by airflow velocity, residence time, coalescence effects, and water carryover. The proper selection of nozzle type, nozzle manifold location, and nozzle distribution are of cardinal importance to avoid large droplets and under-/oversaturated areas, which would affect compressor mechanical and aerodynamic efficiency. Analytical and numerical studies are compared with experimental results. This paper provides a comprehensive treatment of parameters affecting droplet size and will be of value to gas turbine fog system designers and users.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 2

Wind tunnel section showing the Malvern Spraytec measurement system for nozzle testing under airflow conditions

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Figure 1

Typical fog nozzle array

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Figure 3

Typical plume shape from ((a)–(d)) impaction-pin nozzles and ((d) and (e)) swirl-jet nozzles

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Figure 4

Droplet sizes measurement locations in the plume

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Figure 5

Effect of airflow velocity on droplet sizes DV90: solid line and D32: dashed line. (a) and (b) Impaction pin and (c) and (d) swirl jet.

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Figure 6

Effect of measurement distance on droplet size at 207 bars (3000 psi) pressure: (a) impaction-pin type and (b) swirl-jet type

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Figure 7

Effect of ambient humidity on droplet size at different axial distances from the nozzle at 138 bars (2000 psi) pressure

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Figure 8

Effect of flow rate on droplet size

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Figure 9

Effect of water temperature on droplet size for different operating pressures

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Figure 10

Effect of water temperature on droplet size

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Figure 11

Effect of plume width on droplet size as function of airflow velocity (measurement taken at 20 cm from nozzle orifice)

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Figure 12

Cumulative volume showing total injected water, unevaporated water, and evaporated water for ambient conditions of ((a)–(d)) 45°C(113°F) with 5% RH and ((e) and (f)) 15°C(59°F) with 80% RH. Residence time is 1 s.

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Figure 13

Picture taken at operating pressure: 207 bars; distance of measurement: 7.2 cm; and airflow velocity: 4.1 m/s

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Figure 14

Vortex ingestion into axial compressor bellmouth from water pooled on the floor



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