Vol 105, No 2 (2016)

Testing of platefinned surfaces with interrupted rectangular channels allowed defining the range of the change of current estimations values of a rational enhancement of the convective heat exchange (RECH) Qi = 2,11…2,15...2,78 in the range of the values of criterion Rei = 600…1000...4400 and fin thickness ratio (/d)i = 0,071 … 0,083 ... 0,061. The experiment proved the rationality of the energy saving management of channels operation under conditions of the initial zone of hydrodynamic and thermal stabilization of the flow along with the scale control (/d - variable) of generable vortexes in the thin wall layer at weak diffusion towards the flow core that provided a high increase of the heat transfer coefficient at a moderate increase of aerodynamic resistance. A maximal value of RECH estimation 2,78 at Re = 4400 and (/d) = 0.061 was defined. The results of researches were analyzed in terms of physical mechanisms of the RECH process. Keywords: highdrag fin frontal profile; wall layer; flow core; parameters - fin thickness ratio, degree of channel section narrowing; vortex zone of separation; zone of reattachment.

A mathematical description of the process of a substance phase state change at freezing of any body is presented. It is shown that the duration of the process is defined by the position of the interface between frozen and not frozen parts of the body that is not evidently specified and is displaced in time. The subfreezing is considered as a process of interrupted freezing that is used in many technologies of foodstuffs cold treatment. The analytical solution of the body freezing problem was obtained by Stefan when admitting a great intensity of external heat that should be confirmed experimentally in respect to a concrete technology. An experimental research of the meat subfreezing process at the contact with a freezing plate was carried out. A tolerable matching of results obtained by analytical and experimental methods was established. This allows calculating the thickness of the subfrozen layer or the duration of the subfreezing process as well as defining the temperature field in the body for any moment of time. The possibility of using Stefan’s mathematical model assumes a principal character when the solutions of heat conductivity problems are used as intermediate results for the solutions of other tasks that are more complicated, for example, giving proof of the storage conditions of subfrozen NOR/DFD meat taking into account the quantity of water frozen out. Keywords: meat subfreezing, phase state change at freezing, Stefan’ problem, freezing plate