Control of Heat Transfer and Defrostings with Fluidized Beds

点击翻译按钮获取中文摘要

In the cases where conventional finned-tube heat exchangers are used as evaporators in heat pump systems and LNG-gasification systems, moisture in humid air freezes and forms a thick frost layr on the fin surfaces, which reduces the heat transfer, increases the pressure loss, and finally results in choking of the evaporatores. Thus development of frost-free evaporators is an important and urgent research subject. The present research project has been performed to study heat and mass transfer characteristics of impinging jet-type fluidized bed and its defrosting characteristics. The obtained results are useful to establish a fluidized-bed heat exchanger which is effective for defrosting.Results of the Joint ResearchIn Tohoku University, the following experimental studies were performed :(1) Study on local heat transfer and frosting characteristics of cold tubes in single-phase impinging jets.(2) Study on defrosting mechanism of a very shallow fluidized bed, measurement of particle's con … More tact frequency onto the tube surface, and observation of the behavior of particles on the tube surface.(3) Study on heat transfer characteristics of cold tubes under defrosting by particle impingement.In Hokkaido University the following experimental studies were performed :(1) Study on heat transfer charactersistics of impinging-jet type fluidized ged. Especially the effect of fluidizing particles on heat transfer in a powder-mixed fluidized bed.(2) Study on freezing and continuous production characteristics of liquid ice by use of the fluidized bed.(3) Study on frosting characteristics of a vertical cooled plate and a horizontal cooled tube array immersed in a fluidized bed.(4) Study on melting heat transfer characteristics of a horizontal cooled tube array immersed in liquid ice.In Technical University, Vienna, theoretical study on formation process of particle-gas jets and their impingement onto tube surface was performed especially for the cornice-type distributor, utilized in Tohoku University.By joining these results of the above-mentioned studies, an potimum design method for impinging-jet type fluidized bed has been established. Also the heat-transfer and defrosting characteristics and the control theory for them were clarified, which is useful for practical applicatios. Less