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In this paper, two heated blocks and three flexible baffles that are alternately placed on the upper and bottom sides of a rectangular channel are used to replicate the transient heat and air movement. The novelty of this research is the use of flexible baffles to destruct the thermal boundary layer with maintaining little pressure drop, and thus reducing the required pumping capacity. The finite thickness blocks are subject to a constant heat flux, while the baffles are very thin and deforms depending on the strength of the flow of coolant (air). Finite element method with arbitrary Lagrangian–Eulerian approach is used for solving such deforming domain problem. The problem is inspected transiently by varying the dimensionless time (τ=0.0 to 10) and two salient parameters which are Reynolds number Re=10−500, and baffle elasticity parameter E=105−108. Results show that the flexibility feature of the baffles contributes not only in directing the coolant towards the hot blocks, but also contributes in reducing the skin friction and pressure drop through the channel. At Re=150, the skin friction and pressure drop of the flexible baffles are 13.2% and 16.5%, respectively lesser than the rigid baffles. The improvement of Nusselt number with flexibility parameter is marginal and within a limited low Reynolds number, where the maximal improvement is about 3.4% at Re=150.

In this study, the process of catalytic oxidation of methane considering radiative heat transfer was simulated using FLUENT computational software to study the effect of thermal radiation on the oxidation performance of the simulated device, and to investigate the extent to which radiative heat transfer affects the oxidation performance of the device under different operating conditions. The results show that the extent to which thermal radiation affects the oxidative performance of the equipment increases with increasing inlet temperature. When the intake temperature reaches 900K, its proportion is close to 45 %. At the same time, as the inlet gas temperature increases, the maximum reaction temperature of the oxidation unit is 1154 K, and the methane conversion rate reaches up to 89 %. The main factor affecting the oxidation performance of the unit at this time is radiation heat transfer. The extent to which thermal radiation affects the oxidative performance of the device diminishes with increasing inlet velocity. When the wind speed reaches 2 m/s, the proportion of radiative heat transfer is only 10 %, the maximum reaction temperature of the plant falls to 993 K, and the methane conversion rate drops to 68 %. At this time, the main factor affecting the oxidation performance of the plant is convective heat transfer. The influence of thermal radiation on oxidation performance gradually diminishes with an increase in intake velocity, and the proportion of radiative heat transfer decreases continuously. At methane concentrations above 1 %, the proportion of radiative heat transfer is less than 25 per cent, the maximum reaction temperature of the unit increases to 1087 K, and the methane conversion rises to 88 %. At this point, the main factor affecting the oxidation performance of the plant is convective heat transfer.

Commercial freezers are commonly used the outer wall as a heatsink. This heatsink needs surrounded ambient air for cooling, which is the natural convection mechanism. However, in theory the force convection provides more heat transfer than the natural convection. Therefore, energy consumption of the force convection is generally less than the natural convection. This study aims at testing and comparing the heat transfer between the natural convection and force convection of the heatsink of the commercial freezer. Moreover, this study investigated the potential of energy reduction of the freezer by using the natural convection and the force convection of the heatsink. In this study, the unmodified commercial freezer installed with the wind tunnel over the heatsink of the freezer was made. The necessary parameters such as heatsink surface temperature, cooling air temperature, ambient air temperature, velocity of cooling air, and power consumption of the freezer were collected. The testing conditions were varied the internal heat load of the freezer by using water as 0, 3, and 6 kg, and varied the cooling air velocity as 0, 1, 2, and 3 m/s. The results showed that the convection mechanism was significantly affected by energy consumption. Furthermore, it was clearly found that the heat transfer for the force convection was higher than the natural convection. Moreover, the use of force convection resulted in a lower energy consumption. In particular at the internal heat load of 6 kg, the energy consumption of the force convection decreased by 17.5%, 17.7%, and 20.5% as compared to the natural convection at the cooling air velocity of 1, 2, and 3 m/s, respectively. Based on the results obtained it can be concluded that the force convection for the freezer heatsink can be used to reduce energy consumption, which could be efficiently applied in the future works.

In this work, the effect of acoustic waves on vortex shedding and convective heat transfer of two tandemly arranged cylinders is investigated using experiments and numerical simulations. This paper focuses on the average Reynolds number Re = 200, the sound pressure level ranges from 127dB to145dB, and the sound frequency ranges from 100Hz to 1000Hz. Different acoustic wave frequencies and particle vibration velocity amplitudes were set as the entrance conditions. The average heat transfer in the upstream and downstream cylinders was enhanced due to the increase in the particle velocity amplitude of the fluid around the cylinder by acoustic oscillations. Moreover, with the increase in the acoustic frequency, the flow mixing is enhanced and irregular vortices appeared in the cylindrical wake. With regards to the particle velocity amplitude, the values of the Nusselt number of the two cylinders increase with the increase in particle velocity amplitude. With the increase in the particle velocity amplitude, the forced mixing and heat transfer of the gap flow between the two cylinders are enhanced. The comparison between the experimental and numerical results shows that acoustic waves can enhance convective heat transfer of two tandemly arranged cylinders in the cross-flow.

During the construction of tunnels subjected to high temperatures (here called high-temperature tunnels), ventilation cooling is an essential requirement. A high-temperature section of a construction tunnel on the Sichuan-Tibet Railway was used as a test case to study the heat exchange on both sides of the ventilation duct during active cooling. We used theoretical analysis and numerical simulation to establish a model for calculating the temperatures associated with the ventilation duct, and studied the influence of different factors on the convection heat exchange on the inside and outside the duct during the ventilation cooling process. According to simulation and field measurement results, the airflow temperature inside the duct rose with the distance from the inlet, and the temperature near the duct's wall was higher than the temperature in the center. After analyzing different influencing factors, it was found that duct material and thickness have little effect on the convection heat transfer inside the duct. But the convection heat transfer intensity would rise when the temperature difference between the inside and the outside of the duct increased, and the heat flux (q) through the wall increased by 1.5 W/m2. The average air temperature trend of the ventilation duct section was stable as the ventilation distance increased. It increased linearly as ventilation distance increased. While the effect of ventilation cooling gradually declined, and the overall temperature of the air of the tunnel rose when the ventilation distance increased. As a result, heat exchange along the duct should be fully considered in the design and application of the ventilation cooling process to ensure that the airflow temperature reaching the excavation face at the head of the tunnel meets the operational requirements.

The convection heat transfer in a countercurrent double-tube heat exchanger with various fins in a turbulent flow is investigated. The suitable heating or cooling process of fluids is the effective use of the double-pipe heat exchanger. We use water-aluminum oxide nanofluid and water-titanium dioxide at four concentrations (0.4%, 2%, 4%, 6%) as the cold fluid in the inner tube and water as the hot fluid in the annular space. The single-phase model for nanofluid modeling and the standard k-ε model with scalable wall function for simulating the turbulent flow is utilized. To better examine this novel geometry, its performance is compared with simple and rectangular-finned geometries. The results show that the water aluminum oxide nanofluid has a better convection heat transfer coefficient than water titanium dioxide and pure water. Raising the nanofluid concentration from 0.4% to 6% increases the convection heat transfer coefficient by 12%. Heat exchangers with a rectangular and curved fin have 81% and 85% better efficiency than the heat exchanger without a fin. The novel geometry causes a smaller pressure drop despite its higher convection heat transfer coefficient. Also, it is shown that with raising the Reynolds number and nanofluid concentration, the pressure drop increases.

Convection heat transfer (CHT) in porous media founds broad significance in the applications of solar collectors, geothermal systems, and biological sciences. In this work, the natural CHT in a porous medium embedded with a rectangular thermal source at the bottom is numerically solved via the lattice Boltzmann method (LBM). The generalized Brinkman-Forchheimer-extended-Darcy model is applied to describe the momentum equation. The numerical solutions obtained by the LBM are verified against the experimental data for the correctness validation of the presented lattice Boltzmann model. Effects of the Darcy number (Da), medium porosity (ε), size of the thermal source, and the aspect ratio of the thermal source on the temperature- and flow-field in the porous medium are systematically investigated. Results show that the increase of Da remarkably enhances the heat exchange and changes the heat transfer mode from conduction to convection. The existence of the thermal source sidewall has a suppression effect on the heat exchange along the top wall of the thermal source, and this suppression effect is pronounced when the CHT is weak.

In the present case study, the thermal performance of fins for a novel axial finned-tube heat exchanger is investigated and predicted using machine learning regression technique. The effects of variation in the fin spacing, fin thickness, material, and the convective heat transfer coefficient on the overall efficiency and total effectiveness have been analyzed and commented upon. The k-Nearest Neighbor (k-NN), a machine learning algorithm, is used for regression analysis to predict the thermal performance outputs and the results showed high prediction accuracies. The k-NN algorithm is robust and precise which can be used by thermal system design engineers for predicting output variables. The temperature profiles of various geometries have been depicted and compared in the results. It was concluded that the efficiency is increasing with fin thickness & decreasing with fin spacing and the maximum efficiency ηmax=0.99975 is achieved at δ∗=0.1&t∗=0.0133 having h=5W/m2.K for copper material. The effectiveness is increasing with fin spacing & fin thickness and the maximum effectiveness εmax=122.766 is for δ∗=8&t∗=0.4 having h=5W/m2.K.

In the present paper, the experimental system under consideration is a rotating cylinder of 50 mm diameter placed in still air. The numerical calculations are carried out by using a finite volume method based computational fluid dynamics solver FLUENT. The results of the heat transfer are characterized in terms of the non-dimensional parameters: Nusselt number (Nu), Reynolds number (Re), and Grashof number (Gr). The experimental measurements are carried out for Reynolds number range of 1880–6220 and Grashof numbers range of 14,285–714,285, while the numerical calculations are carried out for Reynolds number range of 0–100,000 and Grashof numbers range of 100–1,000,000. The effects of rotation on the heat transfer characteristics are presented in terms of the isotherm patterns, streamlines, local and the average Nusselt numbers. The results correlated as: Nu = 0.022Re0.821 which compares very well with the data available for air in published works.

Non-Darcian forced convection heat transfer over a horizontal flat plate in a porous medium of spherical particles has been studied experimentally. With air as the working fluid, the effects of particle diameter and particles materials of different thermal conductivities were examined. The heat transfer measurements were obtained by heating the test plate under the condition of constant heat flux. The experiments have been made for Reynolds numbers ranging from 105 to 106 based on the test plate length. The porous media used in the experiments were made of glass, rock, and steel covering a wide range of solid thermal conductivity. Particles diameters of 2.7 mm, 4.2 mm, 5.6 mm, 8.1 mm, and 11 mm for rock material and 11 mm particle diameter for glass and steel materials were used. It was found that higher heat transfer coefficients were obtained with larger particle size and higher particle thermal conductivity.