International Journal of Thermofluid Science and Technology

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Open AccessArticle

Hydrodynamics of a two-phase upward flow during boiling at distributed heating centers

by A. I. Andreev and A. E. Semenov

Int. J. Thermofluid Sci. Technol. 2024, 11(3), 110303; https://doi.org/10.36963/IJTST.2024110303 - 8 Jan 2025

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In this paper, the mechanics and hydrodynamics of a two-phase boiling flow were investigated, in which the increase in the vapor content in the flow occurs discretely at local vaporization centers distributed uniformly along the length of a vertical channel (pipe). A stand was developed for conducting a model experiment and a method for measuring the velocity of vapor bubbles in a channel based on dynamic light scattering at gas-liquid interfaces. Experimental studies were conducted and data were obtained showing significant differences in the mechanics of two-phase flow motion during discrete and continuous vaporization. The experimental data show a stepwise dependence when changing the parameters during motion between heat sources distributed along the length of the channel. These experiments were approximated using the Heaviside function, which makes it possible to obtain the distribution of parameters along the length and by the amount of vapor in the flow. Energy dependences are obtained based on the principle of least action taking into account the stepwise nature of the change and it is shown that with a change in the intensity of steam generation, the step function degenerates into a smooth one, due to the predominance of the potential energy of hydrostatic pressure. The patterns of change in hydraulic resistance from the dimensional change in the diameter of the channel (pipe) are shown. A topical issue in the work is also the study of changes in flow parameters between the motion sections and in the steam generation sections. From the point of view of practical application, the study of discrete steam generation on distributed heating centers is relevant for immersion cooling systems of microelectronics and new generations of steam generators. Full article

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Open AccessArticle

Transient Analysis of Conjugate Natural Convection in the Hottest Channel of MTR Nuclear Fuel Type

by Hamed Djalal

Int. J. Thermofluid Sci. Technol. 2024, 11(3), 110302; https://doi.org/10.36963/IJTST.110302 - 20 Dec 2024

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Abstract

A numerical solution of the transient natural convection in the hottest channel of MTR nuclear fuel type is performed in this study by mean of the lumped parameter approach. After employing this approach, the momentum and the energy equations are reduced, to form a lumped parameter model. This model is solved numerically by the Runge-kutta method for a given reactor power according to an iterative process based on the balance between the buoyancy and the friction forces. After these forces are balanced the transient variation of the fuel, coolant and the reactor pool temperatures are carried out and used to evaluate the fuel and the coolant temperatures variation along the channel active length. Finally, the lumped parameter model (LPM) results are validated after we have obtained a good agreement with elsewhere published results of the Relap 5 code system. Full article

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Designing a Vapour-Compression Cascade Refrigeration Setup Aimed at Storing Fresh Plasma

by Olarewaju Oginni, Bukola Bolaji, Olatunde Oyelaran, Adedotun Adetunla and Ang Kiang Long

Int. J. Thermofluid Sci. Technol. 2024, 11(3), 110301; https://doi.org/10.36963/IJTST.2024110301 - 22 Sep 2024

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Abstract

Throughout the duration of the COVID-19 pandemic, human plasma emerged as a primary resource for various therapeutic transfusions, leveraging its protein content as an alternative treatment for infectious ailments. Cascade refrigeration systems, with their capability for ultra-low temperature applications and convenient storage, have emerged as a compelling and highly efficient innovation. This study presents the creation of a portable vapor-compression refrigeration system designed for the handling of blood products at collection points. To capitalize on their superior thermodynamic properties, operational fluid mixtures comprising R410A and R404A were chosen. The system underwent testing both without load and under varying load conditions, with its viability, consistency, and repeatability assessed using animal blood plasma. The process of converting different masses of freshly harvested plasma to refrigerated plasma at -35°C took varying durations, ranging from 120 to 190 minutes. Importantly, the nutritional and biological integrity of the plasma remained unaltered post-freezing. Specific values obtained include pre-albumin levels of 19.2/12.6 mg/dl, albumin levels of 35.2/42.2 g/dl, protein levels of 85.7/82.4 g/dl, fibrinogen levels of 3.30 g/dl, and globulin levels of 36.9 g/dl, respectively. Performance evaluation of the system revealed a cooling effect of 79.5% equating to 186.40 kJ/kg, a coefficient of performance (COP) of 3.57, and an isentropic efficiency of 44.6%. This developed device addresses the challenges posed by heat-sensitive medications in regions with limited power resources, potentially saving countless lives and conserving 3942 MJ of energy, rendering it economically feasible even in affluent nations. Full article

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Int. J. Thermofluid Sci. Technol., Volume 11, Issue 3 (09 2024) – 3 articles

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