ANALYSIS OF CONDENSER OPERATION
- 1. ANALYSIS OF CONDENSER OPERATION PRESENTED BY : SUMIT WADEWALE : MECHANICAL ENGINEERING : ROLL NO : 629 SUB: APPLIED THERMODYNAMICS -I BAJAJ INSTITUTE OF TECHNOLOGY, WARDHA
- 2. VACUUM CREATION When steam condenses in a closed vessel, the vapour phase of working substance (water) changes to liquid phase, and thus its specific volume reduces to more than one thousand times. Due to change in specific volume, the absolute pressure in the condenser falls below the atmospheric pressure and high vacuum is created.
- 3. This lower pressure in the condenser permits maximum expansion of steam in the turbine, and more work is developed. The minimum pressure that can be attained depends on the temperature of condensate and air present in the condenser. The term vacuum means the pressures below the atmospheric pressure. The vacuum in the condenser is generally measured in mm of mercury (Hg). The vacuum is the negative gauge pressure and is equal to the differences of barometric pressure and absolute pressure in the condenser.
- 5. The absolute pressure in the condenser = atmospheric pressure – vacuum gauge pressure = barometer reading – vacuum gauge reading The vacuum is usually referred to a standard atmospheric pressure as 101.325 kPa or 760 mm of Hg, i.e.
- 6. At any barometric reading other than standard reading of 760 mm of Hg, the vacuum gauge reading is corrected to standard barometric reading as corrected in mm of Hg = Standard barometer reading – (Actual barometer reading – vacuum gauge reading ) The absolute pressure in condenser can be determined as Pabs = 760 mm – corrected vacuum in mm of Hg
- 7. DALTONS LAW OF PARTIAL PRESSURE For a mixture of non reactive gases, the total (mixture) is given by Where Pi is the pressure of ith gas component at the mixture temperature T and volume V.
- 8. According to Dalton’s law, the total pressure of a non- reactive mixture is equal to sum of partial of its components, if each component would occupy the same volume alone at the mixture temperature. the condenser has a mixture of wet steam and air. The total pressure p in the condenser is the sum of partial pressure of steam, Psat and air Pa. The saturation pressure of steam Psat can be obtained from the steam table at condensate (saturation) temperature. According to Dalton’s law, P = psat + pa or pa = p - psat
- 9. With the help of partial pressure of air, the mass of air can be determined as, Where, V is the volume of condenser, Tsat is the condensate temp and Ra is characteristic gas constant of air which is equal to 287 J/KgK
- 10. In the steam condenser, a mixture of steam and air is present. Therefore, the absolute pressure in the condenser is the sum of partial pressures of steam and air. The presence of air in the condenser disturbs the vacuum is less than that could be attained in the condenser, if only steam is present. If no airt is present in the condenser then absolute pressure bin the condenser is the saturation pressure of steam and thus the maximum vacuum would be attained.
- 11. Where pg is the actual vacuum = barometric pressure – absolute pressure in condenser = patm – p Maximum possible vacuum Pg, max = barometric pressure – sat. pressure of steam corresponding to condensate temperature = patm - psat The vacuum efficiency is defined as the ratio of actual vacuum to the maximum possible vacuum.
- 12. SOURCES OF AIR IN THE CONDENSER All types of condensers require air extraction pump to remove the air present in the condenser. The main sources of air present in the condenser are the following: the ambient air leaks to the condenser chamber at the joints and glands which are internally under pressure lower than that of ambient. It can be reduced by taking utmost care while designing and making vacuum joints. another source of air is dissolved air with feed water. The dissolved air in the feed water enters into the boiler and it travels with steam into the condenser. Its quantity depends upon the quality of feed water. In case of jet condenser, some air comes in with the injected water in which it is dissolved.
- 13. EFFECT OF AIR LEAKAGE INTO CONDENSER The presence of air in the condenser is a far serious concern. It affects the performance of the condenser to a great extent, thereby, the performance of steam power plant. The presence of air into the condenser puts the following effects: the presence of air lowers the vacuum in the condenser. Thus the back pressure of plant increases, and consequently, the work output of the turbine reduces.
- 14. the presence of air also lowers the partial pressure of steam and hence lower saturation temperature. The steam with lower saturation temperature has higher latent heat. A large quantity of cooling water is required to get the desired result in the condenser. Air forms the film adjacent to the tube surface in the condenser. Air has very poor thermal conductivity. Hence, the rate of heat transfer from vapour to cooling medium is reduced. The presence of air in the condenser corrodes to the metal surfaces. Therefore, the life of condenser is reduced.
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