Papers by Keyword: Heat Transfer

Abstract: Passive Flow Control in Pipelines is gaining increased importance in the field of fluid transport, particularly in oil and gas applications. This approach relies on the installation of passive devices designed to alter fluid flow paths by generating suppression zones. Among these devices, fins are particularly notable. Hence, the objective of this paper is to provide a numerical investigation into the behavior of laminar flow within a bifurcated backward-facing step (BFS), controlled through the installation of a flexible fin at the lower wall of the enlarged duct part, with varying mechanical stiffness and positioning. The study considers a flow through an expanded conduit, where the fluid enters with a predefined velocity profile and subsequently splits into two sub-conduits. The investigation focuses on examining the influence of fin length (0.5 ≤ L_c/H ≤ 1), position (4 ≤ x₀/H ≤ 7), and elasticity on the elasto-hydrodynamic structure of the flow, including vortex formation, flow separation, the maximum displacement of the flexible fin, and the efficiency of the sub-conduits at the outlet. This analysis is governed by the momentum equations, coupled with solid mechanics equations, using the Arbitrary Lagrangian-Eulerian (ALE) framework. The governing equations are solved using the finite element method, implemented through the simulation and the sliding mesh technique in COMSOL Multiphysics 5.7. The numerical results reveal that installing a flexible or rigid fin within the BFS system significantly impacts the non-isothermal flow behavior within the bifurcation ducts. This configuration effectively allows for flowrate regulation at the BFS outlet, also making it possible to equalize flow rates under specific conditions, particularly when using longer fin that extend halfway across the channel. Moreover, the fin placement on the bottom is important for achieving effective flow rate control and heat transfer, aligning with desired requirements for each branch outlet.

Abstract: Natural gas is selected as transition energy to achieve net zero emissions. Gas pipeline construction is developed in accordance with Sustainable Development Goals on Industry, Innovation & Infrastructure, Clean & Affordable Energy, and Climate Action. The potential risk of the heat transfer process from the pipeline to the ground surface temperature can create a potential hazard that can cause pain/injury to human skin if it exceeds the pain threshold temperature. This study aims to investigate the best method for risk mitigation of heat transfer from gas pipelines to the ground surface, through alternative solutions such as burial deepening options, insulation options, or air cooler at well site options. These options are studied as part of the risk mitigation strategy for the buried high-temperature gas pipeline construction. These risk mitigation options consider technical and economic feasibility studies at the conceptual stage presented in this study to identify the best option to mitigate the potential injury risk to humans. The result with a buried insulated pipeline is the best option for controlling heat transfer compared to the air cooler option. The constructability of burial deepening up to 8 m is not feasible, especially the 6m depth of the groundwater table observed.

Abstract: This article presents the findings of a research on improving the properties of hemp masonry to meet the standard strength of non-load baring concrete blocks and assess its properties as energy conserving construction material according to specifications declared under the Ministerial Announcement of the Ministry of Energy. Production of hemp masonry used finely chopped hemp stalk with bark mixed with Type 1 Portland cement, sand and water to form 7.5 x 7.5 x 10 centimeters blocks. The ratio by weight between hemp and binder was 1:10 and the property was improved using Al₂(SO₄)₃, plasticizers, natural rubber latex and polymer. Compression strength, dry density, water absorption, thermal conductivity coefficient, specific heat value and OTTV were tested. The research found that hemp masonry improved using Al₂(SO₄)₃ at 10% by weight of hemp with polymer was the sample with properties within standard limits of non-load baring concrete blocks. The compression strength achieved was 2.79 MPa, dry density 990 kg/m³, water absorption 351 kg/m³, thermal conductivity coefficient 0.25 w/m°C, specific heat 1.12 kJ/kg°C and the highest OTTV of 45 w/m² was calculated for the southeast wall. This was lower than the minimum standard for masonry of energy conserved office building. Therefore, the masonry produced using hemp stalk with bark has the strength comparable to non-load baring concrete block and has the quality to protect heat from outside which is good for energy conservation construction practice.

Abstract: A cooling tower is a cooling device often used in industries as a heat exchanger, where water is cooled by coming into direct contact with air. This process causes evaporation, which leads to a reduction in the water's temperature. We conducted an experimental study of the effect of the number of holes (80, 120, 185 and 250) on the cooling tower flat plate with variations of inlet temperature (65°C, 75°C and 85°C). This study aims to determine the heat transfer characteristics and how the number of holes and inlet temperature variations affect the performance of multi-story cooling towers. The cooling tower has an overall height of approximately 2.4 m, with each flat plate measuring 0.7 m x 0.5 m and a 15° slope. The results showed that the highest heat transfer rate occurred at 85°C inlet temperature with 250 holes. The largest heat transfer coefficient value occurred at 75°C inlet temperature with 250 holes. Thus, the number of holes significantly influences the heat transfer rate, convection heat transfer coefficient, and temperature difference in the optimization of the cooling tower performance.

Abstract: This study proposes a numerical investigation of turbulent flow and heat transfer properties within an air channel featuring a 7-shaped baffle affixed to the lower wall. The main objective of this computational investigation is to assess how the Reynolds number influences the enhancement of heat transfer across a range of Reynolds values from 18000 to 33000. To solve the governing equations, the QUICK numerical scheme and the SIMPLE discretization algorithm are employed. The numerical results are presented through variations in mean velocity and temperature, as well as profiles of local Nusselt number, friction coefficient, Nusselt number and friction factor. These representations facilitate a comprehensive exploration of the aerodynamic and thermal flow properties.

Abstract: Atherosclerosis occurs due to plaque thickening in arteries, reducing blood flow and oxygen supply to tissues. This study models blood flow in a bifurcated stenosed artery under a uniform magnetic field, analyzing magnetohydrodynamics (MHD) hybrid blood nanofluid flow with heat transfer. Using COMSOL Multiphysics, the laminar and Newtonian flow of a hybrid blood nanofluid with silver (Ag) and gold (Au) nanoparticles is simulated. Results, validated by existing literature, highlight key parameters such as velocity, heat flux, and wall shear stress (WSS). The study shows that Ag and Au nanoparticles improve blood flow, reducing recirculation in stenosed arteries, offering the potential for nanomedicine treatments.

Abstract: The energy issue is necessary today due to the decrease in fossil energy and its impacts on the environment. It is important to use energy effectively. In the air conditioning sector, the energy consumption of air conditioners is the top energy user in buildings. The air conditioner user needs to find the best way to operate the air conditioner. In the present research, the effect of pressure behavior at start-up conditions on the energy consumption and heat transfer process is analyzed. The result shows that the pressure behavior affects the evaporator temperature, specific heat, and thermal conductivity in liquid and vapor conditions. In the first 20-second AC operation, the energy consumption of the AC compressor increases significantly before the compressor work slowly decreases at 40-second operation and remains constant at steady conditions. The negligible heat transfer at the first 20-second AC operation increases steeply for 40 seconds. The heat transfer is steady at 60 seconds of operation and above.

Abstract: The research deals with the determination of the temperature distribution in a two-stage porous catalytic medium when the heat flow passes through. The peculiarity of the proposed model of heat and mass transfer in a porous catalyst is to consider the change in the volume of the spherical particle that makes up the catalyst.A program for calculating the temperature distribution in a two-scale porous structure of a catalyst made of spherical particles that change in volume with time has been developed. It should be noted that the temperature gradient is rather high, and the temperature in the central region of the particle becomes high enough for the process of catalytic reaction initiation only after 3.25 s. The developed program together with analytical and empirical studies allow to find the range of temperature and time of heat treatment at which the given thermophysical characteristics of porous material will be observed.The work will be useful for engineers and scientists studying the problems of thermochemical reactors and heat transfer in catalytic fills.

Abstract: The Cahn-Hilliard equation, known for describing the evolution of interfaces in multicomponent systems, can also be employed to noise reduction in mathematical functions and concentration-dependent heat transfer simulations. This work presents a finite difference method discretization of the Cahn-Hilliard equation and explores its applications. For noise reduction, three different noisy functions are simulated, demonstrating effective recovery of original functions despite significant noise levels. In heat transfer simulations, three initial temperature distributions are explored with concentration-dependent thermal diffusivity. Results show that concentration significantly affects thermal diffusivity and heat propagation, leading to non-uniform temperature distributions. Comparative simulations without concentration influence highlight the distinct impact of concentration on thermal behavior. The study underscores a reliable approach to noise reduction and insight into concentration-dependent heat transfer dynamics.

Abstract: Land use changes can affect the flow of energy in the soil-atmosphere system, impacting the urban heat island (UHI) effect. Since the climate conditions of Campos dos Goytacazes are changing (becoming drier and warmer), the city was chosen as a study area. This research aims to investigate the behavior of surface energy fluxes and their impact on the UHI and discomfort index (DI) by simulating different surface condition scenarios for the warmest day of 2019. The weather research and forecasting model was used to simulate three scenarios: in the first simulation, anthropogenic heat was excluded, and no green roofs were added; in the second simulation, anthropogenic heat was included without green roofs; and in the third simulation, both anthropogenic heat and green roofs were included. The results showed that anthropogenic heat intensifies the UHI and increases the DI. The effect of green roofs covering 50% of the urban area can reduce the nocturnal effects of the UHI caused by anthropogenic heat, but it does not significantly impact the DI.