## 1 Introduction  
In power plants, water is used to remove heat from a wide variety of sources. In cooling application, water is withdrawn from underground, nearby lakes, rivers, and ocean and is diverted and circulated to absorb heat from a wide variety of sources, and then it is discharged back to its original source. Since the discharged water is highly contaminated and its temperature is high, it can cause severe environmental problems. For example, it increases the temperature of our rivers, lakes, and ocean waters, harming marine lives, degrading aquatic ecosystems, etc. For thermal power plants in areas lacking ample water, fresh water must be delivered from far-away places which consumes energy and adds to the cost. Power plants utilizing water for cooling are also vulnerable to power disruptions due to shutdowns or curtailments during times of drought and extreme heat. In addition, water is corrosive, and as it flows, it corrodes the walls of the pipes, the turbine blades, etc. In addition, in arid regions, water is a sparse and valuable commodity, and water losses during fluid circulation can present a significant economic liability and burden on the ecosystem. A few recent studies point to the use and storage of CO\({}_{2}\) in various applications (see [1; 2; 3]). Air cooling (throughout this paper we use the term 'air' for 'dry air') of thermal power plants has been used in a few isolated instances [4; 5; 6; 7]. With air cooling, the exhaust vapor-liquid steam from the turbine generator is circulated through a series of finned tubes in a condenser and is cooled down by a stream of ambient air blown by fans over the tubes. Although air is environmentally preferred and a useful alternative for power plant cooling where water is not available, due to its low overall heat transfer rate per unit surface area, air cooling has many disadvantages. The low overall heat transfer rate per unit surface area requires an increase in steam condensation temperature and associated saturation pressure. This leads to higher steam turbine back pressure which decreases the turbine output and reduces the overall plant efficiency. The low overall heat transfer rate per unit surface area requires relatively larger modules with significant heat transfer enhancements to achieve similar performance levels to water cooling systems, even at higher initial temperature differences. This leads to higher energy costs for cooling fans and higher capital costs. The effectiveness of air cooling depends on the ambient air temperature and humidity. At higher ambient air temperatures, there is a decrease in the rate of thermal energy from the steam to the air. Thus, power plants in hot and arid areas require higher fan work and have lower plant efficiency. Many studies in geothermal heat mining (see [8; 9; 10; 11; 12; 13; 14; 15; 16; 17]) have reported that CO\({}_{2}\) is a better geothermal heat extraction fluid than water. Following these studies, in this paper, we evaluate and compare the thermophysical properties of both CO\({}_{2}\) and air to explore the use of CO\({}_{2}\) as the cooling fluid for thermal power plant applications. The critical temperature and pressure of CO\({}_{2}\) are 31.04 \({}^{\circ}\)C and 7.382 MPa, and thus a low temperature flow of supercritical CO\({}_{2}\) can be created. Flow rates for a given driving force are proportional to the ratio of the density of the fluid to its viscosity, \(m\propto\rho/u_{\
u}\). The sensible heat carried by mass flow is proportional to the specific heat of the fluid. The density of supercritical CO\({}_{2}\) is \(\rho=636\) kg/m\({}^{3}\), and its viscosity is \(\mu=50.623\) uPa-s and \(c_{p}=1.08\) kJ/kg-K, while for water, these values are 998.80 kg/m\({}^{3}\) and 1084.0 uPa-s, 4.18 kJ/kg, and for air, at 0.1 MPa, the density is 1.16 kg/m\({}^{3}\), viscosity is 18.55 uPa-s, and \(c_{p}=1.06\) kJ/kg-K. The sensible heat carried by CO\({}_{2}\) is about 4 times more than that by water and 215 times more than air.