Papers by Keyword: Mass Transfer

Abstract: Biodiesel represents a renewable alternative fuel that reduces dependence on petroleum and lowers greenhouse gas emissions. In this study, biodiesel was produced from castor oil via alkaline transesterification to investigate the influence of temperature on mass transfer between the immiscible oil and alcohol phases. A series of transesterification experiments were carried out using methanol and a homogeneous alkaline catalyst (1.12 wt% KOH). The temperature was varied at 35 °C, 50°C, and 65°C to evaluate its influence on the mass transfer rate between the oil and alcohol phases. The molar ratio of methanol to oil was maintained at 14.12:1, and each experiment was conducted for a reaction time of 60 minutes. Increasing temperature significantly enhanced interfacial diffusion, reduced viscosity, and increased miscibility between the two phases. The intersection of TG and FAME curves occurred earlier at higher temperatures, at 65 °C, triglyceride (TG) conversion reached 92% within 10 min and approximately 99% after 60 min, while slower conversions were observed at 35 °C and 50 °C. Product composition and FAME yield were evaluated by GC-MS examination at the Ministry of Industry and Minerals' Industrial Research and Development Authority. Overall, the study highlights that optimized temperature conditions minimize mass transfer limitations, improves phase interaction and conversion efficiency also shortens the total reaction time supporting the creation of an effective and sustainable method of producing biodiesel process from renewable castor oil feedstock.

Abstract: This study presents an analytical and numerical approach to thermosolutal mixed convection in a vertical rectangular cavity containing a Newtonian fluid of Prandtl number, Pr = 7. The vertical walls are mobile and subject to constant heat and mass fluxes, while the horizontal walls are considered impermeable and adiabatic. The mathematical model is based on the Navier-Stokes equations, as well as the conservation of energy and concentration equations. An analytical solution, based on the parallel flow approximation, has been developed for elongated cavities (A >> 1). At the same time, the governing equations were solved numerically using the finite-difference method. The results show that the analytical solution is in good agreement with the numerical one for all the considered parameters. Rayleigh number and Peclet number growth play roles in enhancing mixed convection, thus influencing the overall flow and heat transfer characteristics.

Abstract: Throughout this study, the Lewis number influence on double-diffusive natural convection inside a rectangular cavity horizontally disposed, filled with Copper nanoparticles dispersed in water, heated and salted by constant thermal and solutal fluxes on the side walls while the horizontal ones are assumed thermally adiabatic and solutally impermeable, is studied analytically (parallel flow approximation) and numerically (finite difference method) for a large range of the aspect ratio, 1 ≤ A ≤ 16, the Lewis number, 10-3 ≤ Le ≤ 103, and the nanoparticles volume fractions, φ = 0 and 0.05. The results revealed that the numerical and analytical outcomes showed a good agreement. Both the aspect ratio and the Lewis number have a range responsible for variations in heat and mass transfer rates, A ≤ 12 and 10-2 ≤ Le ≤ 10 for Nusselt number and Le ≥ 10-2 for Sherwood number. The results obtained by examining the interest of using nanofluids in the considered configuration were against all expectations, that they led to a degradation of the rates of heat and mass transfers with the increase in the nanoparticle volume fraction.

Abstract: During high-pressure torsion (HPT), the sample positioned between the plungers of the experimental setup is resistant to fracturing, allowing the HPT process to be sustained almost indefinitely. Despite this, relaxation processes taking place within the sample during HPT lead swiftly to the establishment of a steady state. Factors such as hardness, grain size, the scale of second-phase precipitates, electrical conductivity, lattice spacing, among others, rapidly reach a saturation point, albeit after varying revolutions of the plunger. For instance, in the scenario of HPT involving a binary solid solution accompanied by secondary phase particles that act as sources of dissolved atoms, a dynamic equilibrium and competition emerge between the formation and decomposition of a supersaturated solid solution. Consequently, a specific equilibrium state is achieved with a designated concentration (c_ss) of the second component within the solid solution. This equilibrium state is independent of the initial one (referred to as equifinality). The steady-state concentration c_ss can be identified on the solubility limit line (solvus) of the second component in the phase diagram at an effective temperature T_eff. In copper alloys, the value of T_eff grows as the activation enthalpy for the volume diffusion of the second component increases. This amplification signifies a rise in defect concentration and an activation-driven character of mass transfer during HPT.

Abstract: Sanitary ware, including toilets, washbasins, and bathtub, plays a crucial role in maintaining hygiene and sanitation in various settings. The drying process is a critical stage in the manufacturing of ceramic sanitary ware, as it influences product quality, production efficiency, and energy consumption. Then, the purpose of this work is to investigate the drying of sanitary ware at low temperature by experiments and empirical mathematical models. The idea is to accurately predict moisture loss of the ceramic parts under different operational conditions. Results of the drying kinetics have shown that higher temperatures and lower air relative humidity accelerate the drying process. Also, no cracks or fissures were observed as a result of drying sanitary ware at low temperatures and the two-term model provides the best fit for the dimensionless average moisture content as a function of the time. These findings contribute to a better understanding of the drying process and support the optimization of sanitary ware manufacturing.

Abstract: Liquid-solid mass and heat (by analogy) transfer at the bottom of a cylindrical stirred vessel were studied by using the well-known electrochemical technique. Variables studied included the impeller geometry and its rotational speed. Results revealed that the radial flow impeller is preferable over the axial flow one in terms of mass transfer enhancement, additionally, increasing the impeller rotational speed led to an increase in the mass transfer coefficient. Results were correlated by dimensionless equations. Application of these equations in the design and operation of an improved catalytic biochemical reactor suitable for conducting diffusion-controlled immobilized cell (or enzyme) reactions was highlighted. These equations can serve in predicting the corrosion rate and corrosion allowance required to calculate the bottom thickness of the agitated vessel in its design stage. Furthermore, these equations can be used in estimating the heat lost from the tank bottom, accordingly, design an effective cooling jacket surrounding the agitated vessel bottom in case of exothermic biochemical reactions to avoid thermal degradation of the biomass.

Abstract: In order to contribute for a better understanding of the moisture diffusion in infrared (IR) drying of residual seeds from passion fruit processing, the effective moisture diffusivity (D_eff) in the particles was determined from experimental drying kinetics using two different approaches, in which it is considered either as a constant parameter during the process or as dependent on moisture ratio (XR). Experiments were conducted with the seeds arranged in a single layer and exposed to three IR source temperature levels (50, 65 and 80°C). The IR source was set at a distance of 15 cm from the samples. The average effective moisture diffusivity was in the range from 2.76 x 10^-11 to 11.03 x 10^-11 m² s^-1. The activation energy for IR drying was 53.3 kJ/mol. Results of D_eff as a function of XR, obtained using the slope method, indicated that at higher IR source temperatures the vapor diffusion is the main mechanism of moisture transport, while at lowest drying temperature, the process is controlled by both liquid and vapor diffusion.

Abstract: Investigations of the influence of the parameters of mechanical effects on the temperature and mass of electrode metal droplets during electric arc surfacing with electrode materials of various chemical composition and type have been carried out. The main regularities of the process of droplet transfer during melting of a strip electrode with the introduction of control mechanical impacts have been established. The optimal range of the oscillation frequency of the strip electrode end is 40 ÷ 80 Hz, in which the average droplet diameter decreases to 1.3 ÷ 1.5 mm, and the mass to 0.08 ÷ 0.1 g. As a result of the research, it was found that, during electric arc surfacing with a strip electrode, changing the parameters of mechanical control impacts on the strip end allows not only to control the drop transfer frequency, but also to reduce the size and temperature of the electrode metal droplets, ensuring a decrease in heat input into the base metal and the formation of a favorable structure of the deposited weld metal.

Abstract: This work is part of the European project MOTION (Interreg 2 Seas Mers Zeeën), which aims to develop an exoskeleton for children with cerebral palsy (CP). The developed exoskeleton is equipped with a smart garment in order to detect the stress (e.g. physical, physiological) during the rehabilitation. Five different sensors, i.e. electrocardiogram (ECG), respiratory rate (RR), pressure, galvanic skin response (GSR) and textile heat fluxmeter (THF), are integrated into this smart garment for stress detection. This paper focuses on the development of the textile heat fluxmeter. Several researchers used heat fluxmeters in physiological studies to measure the body heat exchanges with the environment. However, the non-permeability of such fluxmeter gives inaccurate measurements in wet condition. Innovative flexible textile heat fluxmeter may detect, analyze, and monitor the heat and mass transfers with minimum disturbance due to its porosity. Moreover, it is desirable to have flexible sensors when they need to be in contact with the human body, in which the flexibility and non-irritability requirements are of utmost importance.

Abstract: In the work, a variant of mathematical modeling of the solution of the heat transfer problem was developed, analytical analysis of the dependencies of the parameters of technological parameters was carried out to determine the parameters of current pulses that ensure a uniform distribution of current density over the treated surface. A diagram of the stages of constructing a complete mathematical model of the ECDP process (electrochemical dimensional processing) of titanium, aluminum, and their alloys is given. The above equations reflect the theory of mass transfer processes, include the temperature parameter. The limitations of the possibility of carrying out the treatment process are modeled, the peculiarities of formation and development of the gas-liquid layer, changes in its physical properties, and violation of the treatment stability are taken into account. It has been found that to eliminate the processing instability associated with the appearance of turbulence in the electrode reaction zone due to the large gas filling of the interelectrode gap, a series of relationships must be considered DT = f (i, Q, t_imp) to determine optimal parameters of pulse current.