In this work an unsteady phase transformation mode for droplets that are slipping in humid air was numerically simulated. Initial slipping for droplet of 150 micrometre diameter is defined by Reynolds criterion values of 0, 5, 10, 20, 40 and 80. Warming droplet energy state is evaluated by balance method according to average heat flow density values in distinguished Fourier criterion time intervals at condensing and unsteady evaporation modes. At numerical experiment a balance control of heat flow on droplet surface was carried out, when allowable imbalance is defined by less than hundredth percentage point. A bright water slipping in humid gas impact for their heat transfer in condensation phase transformation mode was based on. This impact reveals due to reactivation of leaded heat to central layers as well as an equal droplet warming and duration grow of condensing mode.DOI: http://dx.doi.org/10.5755/j01.mech.21.5.12167

The phase transformations of water droplets in the humid air flow for water injection into the flue gas in biofuel combustion technology under typical boundary conditions have been simulated. The numerical study was performed in two stages. The first one defines the influence of radiation on the thermal state of the water droplets and on the cycle of phase transformation modes. It is shown that the influence of radiation in a flue gas flow of 150℃→200℃ temperature on the thermal state of quantitatively injected water droplets is not significant, but it induces qualitative changes in the temperature field and influences phase transformations cycle of the droplets. In the second step, the cycling of the droplet phase transformation modes for water injection into the exhaust flue gas prior to a condensing economiser under typical boundary conditions was numerically investigated. It was justified that for efficient cooling and humidification of the flue gas before the condensing economiser it is necessary to inject water heated above the dew-point temperature by dispersing it into fine droplets.

Subcooled flow boiling of distilled water was investigated in a vertical annular minichannel with smooth and surface-modified heated tubes. Copper and stainless-steel substrates were tested with ZnO and ZnO/PMHS coatings; Al₂O₃ was additionally tested on stainless steel. A simplified one-dimensional cylindrical model provided local effective heat transfer coefficients, and modified surfaces were compared pointwise with smooth references at matched operating conditions and axial positions. A modification was considered favourable only when the heat transfer coefficient increased without an increase in wall temperature. ZnO on stainless steel was the only modification meeting this criterion at both nominal mass flow rates: the mean pointwise coefficient increased by 44.2% at 7 kg/h and 42.9% at 10 kg/h, while mean wall temperature decreased by 36.9 and 32.8 K, respectively. Al₂O₃ and ZnO/PMHS on stainless steel reduced the coefficient and increased wall temperature, whereas copper modifications showed no robust improvement relative to the designated references. A separate model-sensitivity assessment did not alter the qualitative ranking. ZnO-modified stainless steel was therefore the best-performing configuration within the tested matrix; no broader superiority is claimed beyond the present geometry, fluid, flow rates, and heat-flux range.

This article presents a heat transfer model that is based on by heat conductivity theory in slipping droplet. Strong and liner receding liquid circulation cases were analysed. According to received simulation results of thermal state by slipping droplet, it can be state that according to strong circulation model a calculated droplet thermal state in weak slipping case is close to liner receding modelling results, while a droplet thermal state is bright different from strong circulation modelling results for intensive droplet slipping case according to liner recieding circulation model. Therefore, it is recommended to apply a strong liquid circulation model for all droplet slipping cases.DOI: http://dx.doi.org/10.5755/j01.mech.22.2.13314