Vol 25, No 1 (2016)

This paper describes application of SiC ceramic foam to distillation. The investigated foam SiC ceramic packing and smooth SiC ceramic packing parameters in geometrical characteristics are similar to the Mellapale structured packing parameters. The hydrodynamic performance parameters including pressure drop for dry and wet packing, flood velocity, and liquid hold-up, which are determined in a plexiglas tower of a 100-mm internal diameter. The mass transfer efficiency is measured in another glass tower of a 100-mm internal diameter by total reflux experiments, using a mixture of n-heptane and cyclohexane at atmospheric pressure. The experimental results show that the foam SiC ceramic structured packing has a higher dry and wet pressure drop, higher liquid hold-up, higher mass transfer efficiency, and unchanged flood velocity, comparing with a smooth SiC ceramic structured packing with the same shape. Comparison of the experimental data on the separation efficiency and relative pressure drop was performed for foam/smooth SiC ceramic and metal Mellapak structured packings.

The dynamics of growth and interaction of vapor bubbles in droplets of pure water and LiBr water solution on a horizontal wall were investigated in a wide superheating range. The growth rates of bubbles were determined both in a distillate droplet and in a salt solution droplet. The bubble growth rate in a pure water droplet at the final stage is somewhat lower than in pool boiling. The bubble growth rate in a salt solution is substantially lower than for pure water. Due to the bubble density maldistribution, the vapor flow density is appreciably higher at the droplet edges than on the droplet axis. Collective behavior of the bubbles possesses both stochastic character and elements of self-organization. The thermal measurements were carried out by means of high-speed video and blowup thermal imager.

A physical model and a mathematical model of heat transfer in the conditions of inhomogeneous (with a solid inclusion—a carbon particle) liquid droplet evaporation while moving through high-temperature (800–1500 K) gases are formulated. Numerical investigations were performed using, as an example, a spherical inhomogeneous water droplet during heating in the air medium. The most probable mechanism of phase transitions in a water–carbon particle–heated air system is considered (the initial droplet size, radius, varied in the range from 0.5 mm to 1.5 mm, the inclusion radius was 0.1–1 mm). It has been found that in certain conditions, besides water evaporation from the outer (free) droplet surface, intensive vaporization is possible at the liquid–solid inclusion interface. Conditions of realization of these phase transitions in inhomogeneous water droplet–high-temperature gas medium systems are identified.

Heat transfer with vapor condensation inside a longitudinally finned tube is numerically studied. The proposed model considers vapor condensation on two initial flow areas, namely, annular and rivulet. The model allows prediction of pressure difference along the tube length, vapor velocity profiles in the central channel and an interfin groove, and also a velocity profile in the condensate rivulet at the bottom of the interfin channel, local heat transfer coefficients at different fin points, and average heat transfer coefficients over tube section and length. The calculations showed that in the case of vapor condensation in longitudinally finned tubes of a small diameter it is of fundamental importance to divide the flow tube section into a central channel and interfin channels. The governing vapor velocities in these channels may differ by more than an order of magnitude. The reduced vapor velocity, used in engineering calculations, does not reflect the character of dynamic vapor impact on a condensate film on the most part of the heat transfer surface. For tubes with relatively large fins the proposed model describes vapor condensation almost completely,meanwhile, the mass vapor quality by the time of filling of the grooves reaches 0.01–0.05. The highest heat transfer intensification was obtained for “sharp fins” with a high value of the fin head curvature. Comparison of results of calculation by the model with results of the known experiments on water vapor condensation yields a good qualitative and quantitative agreement for low vapor velocities at the channel inlet (under 30 m/s). The wall thermal conductivity coefficient value affects significantly the condensation efficiency.

In this work, an assessment of the effect of distribution uniformity over water use efficiency is shown. The experimental study took place in Sebha region, southern Libya, characterized by arid climate and interested a barley field. The results of water irrigation in the sprinkler irrigation system with respect to the operating pressure (P) and raiser height of sprinkler (H) are reported with respect to distribution uniformity and water use efficiency. The main objective of irrigation is to apply the optimum amount of water to the crop root zone that is needed for its growth and maturation, and it is, hence, important for to check the uniformity of irrigation systems in order to adjust the operating parameters involved. To assess uniformity, the coefficient of uniformity (CU), the low quarter distribution uniformity (DU), and the coefficient of variation (CV) were considered, while the grain yield (GY), the crop height (CH) and the water use efficiency (WUE) weremeasured in order to find the best solution in terms of operating conditions. The highest values reached by the uniformity parameters with varying the operating conditions defined the best operating practices under which the irrigation system works efficiently: the results demonstrated that the maximum values for CU and DU, 91.37% and 0.85, respectively, were obtained at the highest P and H, and under the same conditions, also grain yield, plants height and WUE recorded the highest values: 5.50 t·ha⁻¹, 63.49 cm and 0.75 kg·m⁻³, respectively. The results emerged in this work can be useful for similar arid regions like Sebha region, in order to solve the problems related to water scarcity and water use efficiency.

A new equation of state (IR EOS) recently reported for liquids and gases has been utilized to predict the densities of some energy carriers at different temperatures, pressures. The ability of IR EOS is examined by comparing its results with experimental data for some energy carriers in homogeneous gas, homogeneous liquid and gas–liquid transition region from low to very high pressures. The IR EOS gives excellent results in homogenous gas and homogeneous liquid region while its predictions in gas–liquid transition have more deviations. The average absolute deviation between calculated and experimental densities for 968 data points of 12 energy carriers is 0.33% over the entire range of data with a maximum pressure of 1000 MPa.