Comparison between Heat Pipes based condenser and Conventional condenser of Power Plant

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Abstract This paper explores the feasibility of using heat pipes for steam condensation and heat pipe based condenser. The concept of heat pipes for steam condensation is newly proposed and studied herewith. . CFD analysis and Experimental studies carried on the single heat pipe for steam condensation. Experimental setup and results of heat pipes based steam condenser presented . Properties like Effectiveness, heat transfer surface area, exergy analysis for the conventional condenser made of simple copper tubes and heat pipe based condenser are compared


INTRODUCTION
Improving the energy efficiency and miniaturization are continual processes in industrial world and power sector has no exception. At present, the major of dependence for electric power is on thermal power generation. Nevertheless, as compared to other industrial sectors, especially electronic industry the miniaturization of major subcomponents of thermal power station is minimal. Reports on improvement in thermodynamic energy efficiency and exergy efficiency among thermal power generation components like boiler, turbine ,condenser etc. are very little. In this work, the design modification of condenser has been proposed and also the advantages of the proposed condenser has been compared with the conventional condenser. The proposal of condenser modification is presented with the help of a case study which is described below.

Case Study
A 210 MW thermal power plant operating in India was considered. This plant is a base load plant, operates on Rankine cycle with reheating. The plant is equipped with different sub components like Boiler (consisting of pulverized coal firing burners, super heater, re heater, economizer etc.), 3 stage Steam turbine (High pressure turbine, Intermediate Pressure Turbine, Low Pressure Turbine ) , Condenser etc . Feed water is pumped by Boiler feed pump into the boiler and the boiler converts this water into super-heated steam and streams this super-heated steam into the turbine. The steam exhaust of the turbine will be dumped into condenser. Condenser converts this steam into water which again fed into the boiler as feed water.
Condenser converts the steam into water with help of cooling water flowing through the condenser tubes. During this process, the heat energy from the steam transfers from the steam to cooling water due to which there will be temperature rise in the cooling water. This visible temperature rise indicates that, the heat transfer mechanism, employed for the purpose condensing the steam is single phase mechanism. Because of this single phase mechanism a large heat transfer area is required to handle the steam exited from the turbine resulting large number of condenser tubes. This paper describes the technology for improvement of efficiency and the miniaturization of this condenser by improving the heat transfer mechanism. It is proposed a two phase heat transfer mechanism in condenser which enhances the heat transfer capability and improves the effectiveness of condenser. The introduction of this two phase heat transfer mechanism is achieved by using heat pipes in place of conventional condenser tubes.

Description of Heat Pipe
Heat pipe is a man-made heat transfer device which transports large quantities of heat with minimum temperature gradient without any additional power between the two temperatures limits [1]. It consists of three different sections namely evaporator, adiabatic and condenser and a working fluid inside the heat pipe. The heat energy to be transferred will be streamed on the evaporator section of heat pipe. The working fluid present in the heat pipes will absorb the heat energy and converts into vapour (change of phase).This vapour will migrate from the hotter portion of heat pipe to the cooler section of heat pipe which is condenser portion of the heat pipe. In this section vapour condenses back to liquid by releasing absorbed heat energy to the cooling media present at peripheral area of condenser section of the heat pipe. The condensed heat pipe liquid drops back to vapour section by gravitational force or through wick. Due, to the latent heat of evaporation of working fluid inside heat pipe, considerable quantities of heat energy will be transported by this heat pipe. The evaporator and condenser sections of a heat pipe function independently, needing only common liquid. Amir Faghri [2] reported in his text book the details of heat pipe and also wide applications of heat pipes. These heat pipes were utilized to upgrade the design of the condenser in thermal power plants.

3.a Literature Review on the Application of heat pipes
In 1981, Littwin and McCurely [3] reported that usage of HPHE (Heat exchanger made by heat pipes) for steam generation and for preheating of combustion air in fossil fuel fired power plants. Vasiliev et al (1984) [4] described the usage of HPHE for waste heat recovery systems. Hong Zhang , Jun Zhuang [5] in 2003 narrated the application of heat pipes for different industrial uages. L.L Vasiliev in 2005 [6] described the application of Heat pipes in modern heat exchangers and indicated the use of heat pipes in thermal power plants. But, the heat transfer Industries have not explored the condensation of steam using the heat pipes or heat pipe based condenser., in spite of excellent heat transfer capabilities of heat pipes. This paper address the usage of heat pipe for steam condensation and also heat pipe based condenser.

CONCEPT OF THE PROPOSED HEAT PIPE BASED CONDENSER
The mechanism of steam condensation using heat pipe is presented in the Fig. 2.The steam incidents on the heat pipe evaporator surface at 46 °C. The evaporator will be heaving the water (as working fluid inside the heat pipe) at a pressure of 0.07 bar. At this pressure the boiling temperature of the water is 39.02 °C. Therefore the ∆T will be (46-39.02) 6.98 °C. For 0.07 bar, ∆Tchf is equal to 14 ºC, which is greater than ∆T in the present case. Hence nucleate boiling will occur.

Fig 2. Proposed concept steam condensation
So the vapors from the evaporator regions enters the condenser portion of heat pipe. This portion is maintained at a surface temperature of 27 ºC with the help of inlet cooling water. So, the vapors which reached the top portion of the heat pipe will condense on side surface of the heat pipe by releasing heat gained at evaporator section to the cooling water. The condensate will flow down due to gravity. The cycle repeats as the process go on.

4.a CFD Analysis of the proposed heat Pipe
Computational fluid dynamic analysis is carried out to know the working of the fluid inside heat pipe. For the analysis, exact boundary conditions similar to experimental set up are applied for CFD analysis. The analysis is carried out on a single heat pipe as shown in   Table 1.

Case Study
The details of Condenser chosen for this case study are presented in Table 2. A suitable heat pipe is designed to suit the requirement and its specifications are presented in Table 3. The thermodynamics details of the designed heat pipe are presented in the Table 4. A condenser using the above designed heat pipe is proposed. The details of the proposed condenser using the specially designed heat pipes are presented in Table 4.  2),the heat pipe condenser can be considered as liquid-coupled, indirect-transfertype exchanger system. The analysis procedure adopted from the [9] as liquid-coupled, indirecttransfer-type exchanger . Hence it can be concluded that Heat pipe based condenser is more effective than conventional condenser.

6.b
Heat Transfer per unit area The Table 6 clearly brings out the comparison of heat transfer area of the conventional and heat pipe based condenser.
Heat transfer Load on the condenser = 260 MW Hence it can be concluded that Heat pipe based condenser is more suitable than conventional condenser from the point of view of Exergy.

EXPERIMENTAL SET UP AND FABRICATION PROCESS
The heat pipe lower portion is enclosed with a jacket in which steam is injected for condensation purposes. Top portion is enclosed with another jacket which acts like a cooling water jacket. The portion of heat pipe enclosed for steam condensation acts as evaporator of the heat pipe and the portion which is enclosed by cold water jacket as condenser of the heat pipe. The inlet and out let temperatures are measured with the digital thermometers implanted at the inlet and outlet openings. Steam with different temperatures is allowed to enter steam jacket from opening and this steam is condensed and condensate is exited from tap provided. Cold water allowed to enter the cold water jacket bottom opening and allowed to exit from the top opening.
Experiments were carried out on single heat pipe as shown in

EXPERIMENTAL RESULTS
The output of mini boiler and fed into the condenser built by heat pipes. The heat pipe based condenser converts the fed steam into condensate and the resulting condensate flowing outside shown in Fig 12 Condensate outflow Figure. 12 : Flow of Condensate It is hereby concluded that the heat pipe based condenser is capable of converting the steam into condensate. The outflow of condensate from the tank clearly indicates that the heat pipes are converting the steam continuously. Hence it can concluded that the heat pipes placed inside the condenser are capable of converting steam into the water.

Performance of Heat Pipe based Condenser
After reaching the steady state conditions, the readings were taken and presented in Table  The