Numerical Research On Air Distribution Of Air Conditioning System For Construction Platform Of Large LNG Carrier Cargo Tank

LNG carrier is a special ship built for the transportation of liquefied natural gas with-163 oC. Some difficulties exist in the respect of ship building technology. One is to control indoor environment during the process of cargo tank building. Invar, a cryogenic material, which used for the containment system of LNG cargo tank is easy to corrode in a damp environment, thus the relative humidity and temperature of LNG cargo tank under construction have to be conditioned. The capacity of LNG cargo tank is over 50,000 m3, which belongs to a large space. The uniform of air distribution is always a key point in the ventilation and air conditioning system designing for large spaces. Therefore, to explore the problem of indoor environmental control during LNG cargo tank construction in the typical coastal climate condition has some practical significance for projects.A relative integrated ventilation and air conditioning system design for the construction platform of LNG cargo tank was proposed in this paper. Then, air distribution characteristics of the construction platform in summer and winter were studied numerically. The effects of air supply angles on the distribution characteristics of temperature, relative humidity and gaseous pollutant in the occupied zone were discussed specifically, and also the effects on air exchange efficiency, heat removal efficiency(energy utilization coefficient) and contaminant removal efficiency were discussed. Next, a comprehensive evaluation method of air distribution for the construction platform was put forward through literature research, which based on the evaluation system of air distribution for stadiums proposed by Tsinghua University. Further, all designed scenarios in summer and winter were evaluated using the proposed comprehensive evaluation method of air distribution at the purpose of guiding practical engineering application. The results showed that(1) The ventilation method of bottom supply and upper return could create huge air circulations in the space between the third floor and ninth floor of the construction platform, thus the difference of temperature and relative humidity at every floor were small relatively.(2) In summer, at the similar conditions of position, air supply velocity and temperature difference, air supply angle were shown to have little influence on air exchange efficiency, heat removal efficiency and contaminant removal efficiency.(3) However in winter, air exchange efficiency, heat removal efficiency and contaminant removal efficiency were shown to be affected greatly by air supply angle but were not positively related with air supply angle.(4) The comprehensive evaluation method of air distribution, which combines the strengths of lumped indexes and local indexes, could not only evaluate overall air distribution but also reflect environmental parameters at each spatial point. It could help designers to choose optimal air distributions.The study was one exploration to the environment control problem during the process of building cargo tanks for LNG carrier. The study could also provide references for the building technology of LNG Floating Production Storage and Offloading(LNG-FPSO), LRG carrier etc.