Papers by Keyword: Heat Transfer

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.

Abstract: Deep learning has achieved great progress in image recognition, segmentation, semantic recognition, and game theory. It also shows potential to solve scientific computing such as simulation problems in engineering. On the other hand, the numerical simulation method requires constitutive modelling, involves a huge computation volume and takes a long time. In this paper, two mirror U-Net models were proposed for the simulation of the heat transfer during the casting process. These models include an upper U-Net branch for the treatment of the geometries of casting, mold, and chill, and a lower U-Net branch for the treatment of the initial temperature field. Their difference is whether the bottoms of upper and lower U-Nets are shared. These two branches tackle the problems involving the input of a geometrical model which consists of three types of materials and the input of an initial or current temperature field image. These models were trained and validated with a big database with hundreds of casting shapes. The prediction results show that the average accuracy reaches 98.8%.

Abstract: Microchannels based on Micro Electromechanical Systems (MEMS) have garnered a great lot of interest over the past 40 years from the fields of microfluidics and biomedicine. In order to address the problem of heat dissipation in incredibly small integrated circuits with up to 790 W/cm² of huge heat dissipation capabilities, Tuckerman et al. [1] first proposed the microchannel heat rejection idea in 1981. These channels are typically at the microscale, with characteristic dimensions on the order of micrometers 10^-6 m or smaller as shown in Figure 1 [2]. These channels often exist at the microscale and have characteristic diameters of micrometres 10^-6 m or less. Microchannels display distinct fluidic behaviour as a result of their small size. Because the flow is normally laminar and the Reynolds number is low, the flow pattern is predictable. Capillary forces and other surface forces become comparatively more important. As a result, fluid behaviour in microchannels is greatly influenced by surface wetting characteristics and channel surface roughness.

Abstract: Studying the temperature regimes affecting the durability of the metal wall of heat exchanger pipes helps identify ways to enhance efficiency in heat exchange processes. One of the key factors determining the temperature regime of the pipe wall is the heat transfer. One of the main factors contributing to an increase in heat transfer is the intensification of heat exchange.

Abstract: Many engineering applications include the heat exchange process between two fluids with distinct temperature gradients separated by solid walls. The machinery used in this operation is known as a heat exchanger. The interaction between exhaust gas and water was modeled in this study using a variety of heat exchanger types. The boundary conditions parameters of the input exhaust gas for the simulation model were established based on the test diesel engine. When the engine is operating at 1200 rpm and 100% load, modeling results show that the heat recovery efficiency of the exhaust gas reaches the maximum value of 65% thanks to the 9-compartment structure and one heat sink in each compartment.

Abstract: In this paper, there is considered MHD boundary layer flow and heat transfer characteristics of Fe-Casson base nanofluid over an exponentially stretching/shrinking surface along the heat source/sink and Newtonian heating effects. In this regard, to develop the system of the governing equations, the one phase model named as Tiwari and Das model is considered with iron nanoparticles. The non-linear governing PDEs are first changed into the system of ODEs using suitable similarity transformations. Later on, the equations are solved numerically by using bvp4c in Matlab software. Effects of certain physical parameters on skin friction coefficient and the local Nusselt number are illustrated graphically. Moreover, the velocity and temperature profiles are examined to observe the influence of various physical parameters such as, Casson, magnetic, suction, radiation, Newtonian heating, heat source/sink and the nanoparticles volume fractions. It is seen that an increase in Casson, magnetic, suction and the nanoparticle volume fractions decrease the velocity profiles for both shrinking and shrinking cases of surface. The temperature profile recedes due to augmentation of Prandlt number and the suction parameter for both stretching/shrinking case while increases with increase in Magnetic, radiation and nanoparticles volume fractions.

Abstract: Thermoelectric technology is one of the fast-developing technologies in the present days due to its excellent heat transfer and heat conversion capabalities. This uses the electromotive force produced by the temperature difference at each end of the device to produce electricity and vice versa. There are various applications developed based on this thermoelectric technology which includes thermoelectric coolers, thermoelectric generators, and thermoelectric air conditioners. This paper provides a comprehensive analysis of thermoelectric (TE) technologies, starting with a complete summary of their working principles explaining the effects like Seebeck, Peltier, and Thomson effects, as well as optimization techniques, applications, semi-conductor materials used, and potential future developments.

Abstract: While light shelves enhance daylight inside buildings in tropical climates, there is a concern that the heat reflected from them will increase the cooling load inside a building. In this study, experiments are conducted under controlled conditions to understand the heat transmission characteristics of light shelves. The total heat reflected by a prototype of a light shelf is compared to the case of a similar setup with a no light shelf. Different materials were tested to evaluate the heat and light transmission. A mirror glass light shelf gave the highest illuminance, whereas an aluminium light shelf transmitted maximum heat. To explain the experimental results, a simulation model was created using the heat balance equation for the light shelf. The Mean square error between the simulation and experimental data is computed to predict the heat transmitted by the light shelf. The simulation model could reasonably replicate the trends obtained in the experimental data. The simulation model helps in controlling the heat transferred by light shelves in tropical climates.