**9. References**

94 Efficiency, Performance and Robustness of Gas Turbines

*I*

*Qh*

*Qcc*

*S*

η

*eff* ε

Subscripts

*a* dry air *c* with cooling *cc* cooling coil *ch* chiller *comb* combustion *comp* compressor *eff* effective *el* electricity *f* fuel *g* gas *nc* no cooling *o* ambient *t* turbine *v* vapor

ω

 exergy destruction, kW *k* specific heats ratio. *m* mass flow rate, kg s-1 *ma* air mass flow rate, kg/s

*Po* atmospheric pressure, kPa *PR* pressure ratio = *P2/P1*

*P* pressure, kPa *PGR* power gain ratio

heat rate, kW

entropy, kJ/K

*T* Temperature, K

*t* time, s

*x* quality. *W* power, kW

Greek symbols

efficiency

*mcw* chilled water mass flow rate, kg/s *mr* refrigerant mass flow rate, kg/s *mw* condensate water rate, kg/s NCV net calorific value, kJ kg-1

*Qe r*, chiller evaporator cooling capacity, kW

*U* overall heat transfer coefficient, kW/m2K

effectiveness, according to subscripts

specific humidity (also, humidity ratio),according to subscripts, kg/kgdry air

cooling coil thermal capacity, kW

*TEC* thermal efficiency change factor


**4** 

**Energy and Exergy Analysis of Reverse Brayton** 

The output of Gas turbine (GT) power plants operating in the arid and semiarid zones is affected by weather conditions where the warm air at the compressor intake decreases the air density and hence reduces the net output power far below the ISO standard (15 oC and 60% relative humidity). The power degradation reaches an average of 7% for an increase in temperature by only 10oC above the 15 oC ISO standard. Furthermore; in hot summer days the plants are overloaded due to the increase in demand at peak periods, to meet the extensive use of air-conditioning and refrigeration equipment. The current techniques to cool the air at the compressor intake may be classified into two categories; direct methods employing evaporative cooling and indirect methods, where two loops refrigeration machines are used. Erickson (2003) reviewed the relative merits, advantages and disadvantages of the two approaches; Cortes and Willems (2003), and Darmadhkari and Andrepont (2004) examined the

current inlet air cooling technology and its economic impact on the energy market.

increased the daily power output by 6.77% versus 2.5% for spray water cooling.

In direct cooling methods water is sprayed at the compressor inlet bell mouth either through flexuous media (cellulose fiber) or fogging (droplets size in the order of 20 micron) into the air stream, Ameri *et al*. (2004). All spray cooling systems lower the intake temperature close to the ambient wet bulb temperature; therefore the use of the spray cooling is inefficient in coastal areas with high air humidity. Ameri *et al*. (2004) reported 13% power improvement for air relative humidity below 15% and dry bulb temperature between 31oC and 39oC. In addition to the effect of the ambient air humidity, the successful use of the direct method depends on the spray nozzles characteristics, Meher-Homji *et al* (2002) and droplets size, Bettocchi *et al*. (1995) and Meher-Homji and Mee, (1999). In evaporative cooling there is, to some extent, water droplets carry over problem, addressed by Tillman *et al* (2005), which is hazardous for compressor blades. Therefore, evaporative cooling methods are of limited use in humid coastal areas. Alhazmy *et al* (2006) studied two types of direct cooling methods: direct mechanical refrigeration and evaporative water spray cooler, for hot and humid weather. They calculated the performance improvement for ranges of ambient temperature and relative humidity, and their results indicated that the direct mechanical refrigeration

**1. Introduction** 

**Refrigerator for Gas Turbine Power Boosting** 

Rahim K. Jassim1, Majed M. Alhazmy2 and Galal M. Zaki2

*2Department of Thermal Engineering and Desalination Technology,* 

*1Department of Mechanical Engineering Technology, Yanbu Industrial College, Yanbu Industrial City* 

*King Abdulaziz University, Jeddah* 

 *Saudi Arabia* 

