A DESK TOP STUDY ON THE APPLICATION OF EVAPORATIVE CONDENSERS FOR SUBCRITICAL CO_2 CONDENSING

摘要

Ammonia can be condensed at 30℃ in an evaporative condenser with entering air wet bulb temperature ofrn24℃. We show that an evaporative condenser for subcritical CO_2 condensing at 30℃, i.e. 1.1 K below therncritical point, can be designed for a wet bulb of 24℃. Average climate conditions in much of Europe,rnincluding the warmer climates in Spain, Italy, Greece and Turkey, are suitable for evaporative condensers torncondense subcritical CO_2 at 30℃. Canada, large parts of the USA and China, and most of Australia belowrnthe tropic of Capricorn also have climates suitable for the application of evaporative condensers to subcriticalrnCO_2 condensing. The thermodynamic and transport properties of subcritical CO_2 at 30℃ changernsignificantly with temperature. We show the effect this has on CO_2 temperature profile, heat transfer andrnpressure loss for a particular design.rnThe benefits of applying evaporative condensing techniques for the condensation of subcritical CO_2 arernexamined. They are lower design pressures compared to transcritical operations, lower energy consumption,rnlower running and operating costs. Hot gas defrosting would also become a standard feature of subcriticalrnCO_2 refrigeration plant operations.rnIt is concluded that the use of evaporative condensers for CO_2 in temperate and many subtropical climatesrnwould make CO_2 refrigeration as ubiquitous as any chemical refrigerant and would compete successfullyrnwith ammonia when it needs to be used in an indirect application such as the heating and cooling of officernbuildings and hospitals for example.