Impact of freezing temperature (Tfr) of Al2O3 and molecular diameter (H2O)d on thermal enhancement in magnetized and radiative nanofluid with mixed convection

The dynamics of nanofluid by considering the role of imposed Lorentz forces, thermal radiations and velocity slip effects over a vertically convectively heated surface is a topic of huge interest. Therefore, the said study is conducted for Al2O3-H2O nanofluid. Mathematical modelling of the problem is done via nanofluid effective correlations comprising the influences of freezing temperature, molecular diameter and similarity transformations. The results for multiple parameters are plotted and provide comprehensive discussion. From the analysis, it is examined that Al2O3-H2O nanofluid motion drops by strengthening Lorentz forces. The temperature in the nanofluid (Al2O3-H2O) is improved by inducing viscous dissipation effects (Ec number), surface convection (Biot number) and thermal radiations (Rd). Moreover, the shear stresses at the surface decreased due to higher magnetic field effects and rises due to velocity slip. A significant rise in Local Nusselt number is observed due to thermal radiations and Biot effects. Finally, enhanced heat transport mechanism in Al2O3-H2O is examined than a conventional liquid. Therefore, nanofluids are better for industrial applications and the uses of conventional liquids are limited due to low thermal conductivity.

The Piston Effect inside a microchannel with Carbon Dioxide near Critical conditions

Heat transfer near the critical condition of Carbon Dioxide due to thermo-acoustic waves in a 100-µm high microchannel was numerically studied. The temperature at a point farthest away from the heated surface was compared between computational fluid dynamics (CFD) models and a pure conduction model. The comparison revealed that the CFD model predicted a temperature increase furthest from the surface much faster than the time constant required for such increase purely by conduction. It is believed that another heat transfer process, termed the piston effect (PE), which is associated with pressure waves in the fluid, was responsible for this increase. Explicit unsteady methodology in the fluid model indicated that propagation of pressure waves due to a rapid expansion of the boundary layer and the associate change in the fluid density distribution resulted in this temperature raise. It was confirmed that natural convection wasn’t responsible for the temperature increase under quiescent conditions. In addition, it was discovered that the PE is significant for certain forced convection conditions.

Defining patterns of heat transfer through the fire-protected fabric to wood

Under the thermal action on wood when applying a protective screen made from fire-retardant fabric, the process of temperature transfer is natural. It has been proven that depending on the thermal properties of the coating of fire-proof fabric, this could lead to varying degrees of heat transfer. Therefore, it becomes necessary to study the conditions for establishing low thermal conductivity and establishing a mechanism that inhibits heat transfer to wood. Given this, a mathematical model has been built of the process of heat transfer to wood when it is protected by a screen made of fire-proof fabric. According to the experimental data on determining the temperature on the non-heated surface of the fabric and the resulting dependences, the density of the heat flow transmitted to wood through fire-proof fabric was determined. Thus, with an increase in the temperature, the density of the heat flow to the surface of the wood through a protective screen made of fire-proof protected coating based on "Firewall-Attic" increases to a value above 16 kW/m2, which is not sufficient for ignition of wood. Instead, the density of the heat flow through the protective screen of fire-proof fabric protected by the "Firewall-Wood"-based coating did not exceed 14 kW/m2. This makes it possible to argue about the compliance of the detected mechanism of formation of heat-insulating properties in the protection of wood and the practical attractiveness of the proposed technological solutions. Thus, the peculiarities of inhibition of the process of heat transfer to wood through a protective screen made of fire-proof fabric under the action of a radiation panel imply the formation of a heat-insulating layer of coked cellular material when decomposing the coating. Thus, on the surface of the fire-proof fabric, a temperature above 280 °C was achieved and, on an untreated surface of the fabric, it did not exceed 220 °C, which is insufficient for the ignition of wood.

Determination of the heat transfer coefficient of a rotary film evaporator with a heating film-forming element

A model of a rotary film evaporator with a film-forming element with a reflective heated surface has been developed. This will allow stabilizing the hydraulic movement of the cut wave flow due to the reflective surface of the geometric shape for the forced direction of the cut raw material to the heating surface. Autonomous heating of the reflective surface additionally provides a temperature effect in the conditions of movement of particles of raw materials after cutting. The analysis of the experimental and theoretical parameters of heat transfer made it possible to substantiate the criterion equation for determining the heat transfer coefficient of an evaporator with the proposed film-forming element and a reflective heated surface for calculating the coefficient from the working surface to the raw material. The resulting equation takes into account the influence of the vertical component of the motion of the raw material film, centrifugal movement during the rotation of the film-forming element, mixing of the boiling film of the raw material with steam bubbles, and the geometric characteristics of the film-forming blade on the hydrodynamic flow of the raw material. The calculation of the rotary-film evaporator was carried out using the criterion equation and the obtained useful heat exchange surface – 0.75 m2. The specific metal consumption in a rotary film evaporator with a film-forming element having a reflective surface is 57 kg/m2, compared to the vacuum evaporator traditionally used in canning industries (410 kg/m2), which is 7.1 times less. The duration of the temperature effect on the raw material is also reduced: a rotary film evaporator – 200 s and 3600 s in a traditional apparatus. The data obtained will be useful for the design of rotary-film devices of different geometric parameters using articulated blades with a reflective plate.