Improving heat and mass transfer rates through continuous drop-wise condensation

Drop-wise condensation (DWC) has been the focus of scientific research in vapor condensation technologies since the 20th century. Improvement of condensation rate in DWC is limited by the maximum droplet a condensation surface could sustain and the frequency of droplet shedding. Furthermore, The presence of non-condensable gases (NCG) reduces the condensation rate significantly. Here, we present continuous drop-wise condensation to overcome the need of hydrophobic surfaces while yet maintaining micron-sized droplets. By shifting focus from surface treatment to the force required to sweep off a droplet, we were able to utilize stagnation pressure of jet impingement to tune the shed droplet size. The results show that droplet size being shed can be tuned effectively by tuning the jet parameters. our experimental observations showed that the effect of NCG is greatly alleviated by utilizing this technique. An improvement by multiple folds in mass transfer compactness factor compared to state-of-the-art dehumidification technology was possible.

MULTI-FACTOR HEAT EXCHANGER DESIGN MODELS

Compressed air is widely used in enterprises, and it is possible to reduce air consumption on pneumatic devices by heating. Most often, heating is carried out in shell-and-tube heat exchangers. To increase the area of heat exchange between the heating medium and the air, finned tubes are used, which can significantly reduce the volume occupied by the heater. The design of the heater is influenced by many factors, and the importance of the influence of each of them can differ significantly. It is advisable to use the overall characteristic in the form of a compactness factor, which shows the ratio of the heat exchange area to the volume of the heater. The work developed a method for determining the optimal design of heaters by such a parameter as the compactness factor. The obtained regression equations make it possible to determine the influence of such factors as the number of rows of tubes across the flow and the length of one tube on the volume occupied by the heat exchanger and the compactness factor. According to Fisher's criterion, the equations of the model are adequate to the true dependence with a confidence level of 95%. Most of all, the volume of the heat exchanger and the compactness are affected by the number of tubes transverse to the air flow. Changing the length of one tube does not fundamentally affect the obtained values of the output parameters. With an increase in the length of one tube and their number across the flow, it is possible to achieve the highest values of the compactness coefficient, the dependence of which on the main factors has a pronounced maximum. Using the developed technique, it is possible, in a fairly simple formulation, to analyze the value of the compactness factor for various combinations of the above factors and to optimize the design of the heater.

Charged compact star in f(R, T) gravity in Tolman–Kuchowicz spacetime

In this current study, our main focus is on modeling the specific charged compact star SAX J 1808.4-3658 (M = 0.88 $$M_{\odot }$$ M ⊙ , R = 8.9 km) within the framework of $$f(R,\,T)$$ f ( R , T ) modified gravity theory using the metric potentials proposed by Tolman–Kuchowicz (Tolman in Phys Rev 55:364, 1939; Kuchowicz in Acta Phys Pol 33:541, 1968) and the interior spacetime is matched to the exterior Reissner–Nordström line element at the surface of the star. Tolman–Kuchowicz metric potentials provide a singularity-free solution which satisfies the stability criteria. Here we have used the simplified phenomenological MIT bag model equation of state (EoS) to solve the Einstein–Maxwell field equations where the density profile ($$\rho $$ ρ ) is related to the radial pressure ($$p_{\mathrm{r}}$$ p r ) as $$p_{\mathrm{r}}(r) = (\rho - 4B_{\mathrm{g}})/3$$ p r ( r ) = ( ρ - 4 B g ) / 3 . Furthermore, to derive the values of the unknown constants $$a,\, b,\, B,\, C$$ a , b , B , C and the bag constant $$B_{\mathrm{g}}$$ B g , we match our interior spacetime to the exterior Reissner–Nordström line element at the surface of stellar system. In addition, to check the physical validity and stability of our suggested model we evaluate some important properties, such as effective energy density, effective pressures, radial and transverse sound velocities, relativistic adiabatic index, all energy conditions, compactness factor and surface redshift. It is depicted from our current study that all our derived results lie within the physically accepted regime which shows the viability of our present model in the context of $$f(R,\,T)$$ f ( R , T ) modified gravity.

Anisotropic strange quintessence stars in f(R,G) gravity

This paper is devoted to formulate a new model of quintessence anisotropic compact stars in the modified [Formula: see text] gravity. Dynamical equations in modified theory consisting of anisotropic fluid along with quintessence field have been evaluated by adopting analytical solution of Krori–Barua. In order to determine the unknown constraints of Krori–Barua metric observational data of different stars, [Formula: see text]-[Formula: see text], [Formula: see text], [Formula: see text]-[Formula: see text] has been taken into account. To solve the dynamical equations Starobinsky-like model, [Formula: see text] of modified gravity has been used. The outcome of the results depicts that all the examined celestial bodies are free from central singularity and are physically stable. Different physical parameters, such as energy density, energy conditions, evolution of quintessence and compactness factor, have been reviewed in detail.

Anisotropic solution for compact objects in f(𝒢,𝒯) gravity

In this paper, we consider a new solution to discuss the physical aspects of anisotropic compact celestial bodies in the background of [Formula: see text] theory. We take static spherically symmetric metric to describe the internal region of the stellar objects and apply the embedding class-I method to get the metric solution corresponding to a specific [Formula: see text] model. By matching the interior and exterior geometries at the boundary, we find the values of unknown constants. We check the stability and viability of the resulting solution through various parameters that include energy bounds, causality condition, Herrera’s condition, role of adiabatic index, redshift and compactness factor. The graphical interpretation is done for some particular compact star candidates, i.e. LMC X-4, Cen X-3, 4U 1820-30 and Vela X-1. We conclude that our model provides physically acceptable structure of the considered compact objects and is also stable.

An anisotropic model for represent compact stars

Starting from a perfect fluid solution we constructed a generalization with anisotropic pressures and regular geometry as well as the pressures, the density and the speed of sound, these are also positive and monotonic decreasing functions. The speed of sound is lower than the speed of light, that is to say, the condition of causality is not broken. The model satisfies all the energy conditions and the radial [Formula: see text] and tangential [Formula: see text] speeds and complies with [Formula: see text] because of this the solution is stable according to the stability criteria related with the concept of cracking. The maximum value of the compactness factor [Formula: see text] which is lower than the Buchdahl limit and associated to neutron stars. In a complementary manner, we realize an analysis of the behavior of a star with a mass of [Formula: see text], with a fixed value of the anisotropy parameter and different compactness values, giving as a result that their central density [Formula: see text] and the superficial density [Formula: see text], the maximum values match the value of greater compactness of the model with a stellar radius of 6506.921 m.

Influence of extruder screws speed and process temperature on the extrudate shape changes of the maize-spelt blends

The objective of the study was examination of changes in the shape factors of extruded products, which occur as a result of different settings of the extrusion process variables. Samples analysed included products created by means of the extrusion process from a mixture of spelt flour and cornmeal, with the share of spelt at 70 to 100%. The samples were made with the use of a co-rotating twin screw extruder. Two speeds of extruder screw rotation (300 and 350 rpm) as well as two levels of temperature (120 and 140°C) were set during the investigation. The samples obtained were photographed in a light box, following which they underwent an image analysis with the use of specialist vision software. Four shape-related factors were determined: area, elongation factor, Heywood circularity factor and compactness factor. It was determined that the product shape changed significantly depending on the share of spelt flour in the mixture. Moreover, it was observed that change in the screw rotation speed within the analysed range may cause material changes in the shape of particular extrudates.

Geometric Design of Scroll Expanders Optimized for Small Organic Rankine Cycles

The application of organic Rankine cycles (ORCs) for small scale power generation is inhibited by a lack of suitable expansion devices. Thermodynamic and mechanistic considerations suggest that scroll machines are advantageous in kilowatt-scale ORC equipment, however, a method of independently selecting a geometric design optimized for high-volume-ratio ORC scroll expanders is needed. The generalized 8-dimensional planar curve framework (Gravesen and Henriksen, 2001, “The Geometry of the Scroll Compressor,” Soc. Ind. Appl. Math., 43, pp. 113–126), previously developed for scroll compressors, is applied to the expansion scroll and its useful domain limits are defined. The set of workable scroll geometries is: (1) established using a generate-and-test algorithm with inclusion based on theoretical viability and engineering criteria, and (2) the corresponding parameter space is related to thermodynamically relevant metrics through an analytic ranking quantity fc (“compactness factor”) equal to the volume ratio divided by the normalized scroll diameter. This method for selecting optimal scroll geometry is described and demonstrated using a 3 kWe ORC specification as an example. Workable scroll geometry identification is achieved at a rate greater than 3 s−1 with standard desktop computing, whereas the originally undefined 8-D parameter space yields an arbitrarily low success rate for determining valid scroll mating pairs. For the test case, a maximum isentropic expansion efficiency of 85% is found by examining a subset of candidates selected the for compactness factor (volume expansion ratio per diameter), which is shown to correlate with the modeled isentropic efficiency (R2 = 0.88). The rapid computationally efficient generation and selection of complex validated scroll geometries ranked by physically meaningful properties is demonstrated. This procedure represents an essential preliminary qualification for intensive modeling and prototyping efforts necessary to generate new high performance scroll expander designs for kilowatt scale ORC systems.

RELATIVISTIC STRANGE STARS WITH ANISOTROPY

We study a compact star comprising strange matter content in the presence of pressure anisotropy. Considering strange matter with equation of state p = (ρ-4B)/3, where B is Bag parameter, we analyze the effect of pressure anisotropy on the Bag parameter for a compact star described by Vaidya–Tikekar metric. The values of B inside and on surface of the star are determined for different anisotropy parameter α. It is found that in the vicinity of the center of a compact star, B parameter is almost constant. However, away from the center B varies with the radial distance and finally at the surface B attains a value independent of the anisotropy. It is also noted that for some values of α, B remains constant throughout the star. Given α and spheriodicity a, B is found to be decreasing with the increase in compactness factor. The models admitting B increasing with α for a given spheriodicity parameter (a) and compactness are also found.