An important feature of small multitubes flow-through boilers is that they must be designed to be produced according to regulations such as a maximum working pressure of 1MPa and a maximum surface area of 10m2. Within these regulations, more compact and effective boilers are being designed and developed. At present, a design which has achieved a maximum equivalent steam generating rate of 2ton/h and a relatively high heat flux has been developed for industrial use. These results have been achieved due to advances in heat transfer techniques. However, several problems remain to be solved in order to make the separator and upper header, which maintain the steam dryness fraction, more compact and effective. The problems for creating a two-phase flow vapor-liquid process in this boiler are mentioned.
