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In the present paper, numerical computations have been carried out to investigate the mixed convection developing within a cavity ventilated by injection / suction of a cold jet of isothermal air, interacting with the external environment through two openings arranged in the middle of the left and right vertical walls. The remaining portions of the left vertical wall are subjected to a constant heat flux, while, the remaining walls of the cavity are perfectly insulated. The combined effects of the basic parameters namely the Reynolds number, 20≤Re≤3000, the walls emissivity, 0≤ε ≤ 0.85, and the imposed external flow mode (injection or suction) on the flow characteristics and heat transfer are examined. The results revealed that, for both modes of ventilation, the contribution of radiation to the total heat transfer is significant even for a predominant forced convection regime particularly for high values of wall emissivity. [ABSTRACT FROM AUTHOR]

The paper presents the finite element modeling of the spatial heat transfer to identify the temperature and the heat flux distributions both in the linear and point thermal bridges in various up-to-date wall systems. The paper considers the spatial heat transfer in the corner zone of the brickwork fragment. The ANSYS finite element program is used for the numerical simulation of the temperature fields and thermal fluxes for the brickwork connection with a hollow-core slab and a balcony slab. The influence of hollow cores in the floor slab is considered in relation to the temperature behavior along the inner surface of the brickwork fragment. To eliminate the negative effect from thermal bridging, it is suggested to increase the temperature on this inner surface. The brickwork thermal properties are investigated herein. [ABSTRACT FROM AUTHOR]

This study investigates heat transmission and thermal performance factor characteristics in a tube with coil wire and twisted tape inserts using air as the working fluid. This study investigates heat transmission and thermal performance factor characteristics in a tube with coil wire and twisted tape inserts using air as the working fluid. The goal of this research is to improve forced convection heat transfer in tubes with and without swirl inserts and coil wire inserts for air Reynolds numbers ranging from 10.328×103 to 11.769×103. The impacts of different parameters of heat transfer are considered in this work with heat flux are constant conditions of 600 W/m2 and 800 W/m2 with using the coil wire and twisted tapes with three ratios (y/w = 3, 4 and 5). The test section is a horizontal annular passage with outer diameter 10 cm. The results showed that using coil wire inserts to improve heat transfer coefficient factors in tubes resulted in local heat transfer coefficient percentages of (5.1%) to (7.8%) with heat flux are constant conditions of 600 W/m2 and 800 W/m2, respectively. While tube with swirl inserts provide local heat transfer coefficient percentages of (3.6% to 6.1%) for heat fluxes (600) W/m2 and (800) W/m2, respectively. The obtained results demonstrate that as the twisted ratio (y/w) decreases, the mean Nusselt number and heat transfer coefficient in the tube with twisted tape and coil wire rise. Experimental results is shown, heat transfer coefficient for the coil wire when compared with that of swirl inserts tube were ranged between (10.6%) to (16.5%) and (11.5%) to (17.3%) for the heat flux (600) W/m2. [ABSTRACT FROM AUTHOR]

The paper dealt with an experimental investigation for mini vertical tube through study the transfer of CO2 heat convection at supercritical pressures. The dimensions of tube were 4mm and 10mm for diameter and length respectively. Many parameters have been measured to investigate the heat transfer convection which are; coefficients of heat transfer, temperatures of fluid bulk, temperatures of wall, rate of mass flow, temperature of inlet and flux of heat. The collected results showed that the heat transfer by convection has been affected by CO2 heat buoyancy and thermos-physical characteristic. On the other hand, the proportional relationship between heat transfer by convection and mass flow rate not fixed sometimes when the mini tube being empty. Moreover, the main influences on the heat transfer by convection were due to temperature of the inlet, flux of the heat and rate of the mass flow. [ABSTRACT FROM AUTHOR]

Liquid metal heat transfer systems are a technically attractive option to increase the efficiency of CSP plants. Sodium as heat transfer medium is promising especially due to high heat transfer rates. In this paper, basic considerations are made to match the requirements of a small-scale loop with sodium as heat transfer medium. The setup of the test facility KArlsruhe ReceIver test FAcility (KARIFA) to heat up this loop with a 20 kW IR laser is described. The loop is planned as an integrated design using an additive manufacturing process. Different technologies like selective laser melting (SLM) are established processes to realize an integrated design and to bring together components in one part. Some variations must be implemented to adapt these processes to liquid metal loops. The high heat fluxes also demand a flow simulation to ensure an efficient and safe operation. A Reynolds-averaged Navier-Stokes (RANS) steady state simulation was performed to show the surface and duct temperatures as well as dimensionless values to analyse the characteristics of the sodium flow. [ABSTRACT FROM AUTHOR]

This paper presents the numerical analysis on the impact of downstream edge angle of chamfered rectangular transverse rib on the thermal performance of solar air heater (SAH). A two-dimensional CFD simulation study is carried out to determine the influence of downstream edge inclination angle of chamfered rectangular rib on the thermal and flow characteristics of SAH. The analysis is carried out under constant heat flux conditions for varying flow Reynolds number of 9000 and 19000. The ribs are modified on its rear edge where the angle of the edge is varied from 45° to 135°. The angle of inclination of downstream edge of transverse rib has a significant effect on heat transfer characteristics of SAH system. The friction factor is not significantly affected by the downstream inclination angle considered in the analysis. The Nusselt number enhancement is about 1.85 times for the downstream edge angle of 135° as compared to that of 1.09 for 45° angle. [ABSTRACT FROM AUTHOR]

The most important direction of the medium-speed diesel engines development is to increase their power values. The forcing diesel engines by increasing the mean effective pressure leads to an increase in the thermal factor of the engine parts. High temperatures of the cylinder cover fire deck and the cylinder liner working surface cause thermal fatigue cracks in these parts as well as piston scuffing. Thus, the development of both new methods of intensifying heat transfer in cooling gallery and new methods for determining the engine parts thermal state is needed to decrease the thermal factor of the cylinder covers and liners. In this case, the controlled coolant boiling can be used as an effective method for local cooling. This paper presents the developed method for determining the temperature field of diesel engine taking into account the coolant boiling as well as the results of calculating the thermal state of the D500 medium speed diesel engine. Based on the results obtained, the thermal factor of the main engine parts was estimated. It is noted that the boiling is fully developed in some regions of the cooling system while the transition to the film boiling is not carried out since the heat fluxes do not reach critical values and there are no stagnant flow zones. The recommendations for normalization of the thermal state of the cylinder cover for forced working processes are formulated. [ABSTRACT FROM AUTHOR]

The paper presents the solution of laminar forced convection in a square duct recessed in thermal insulation. It was assumed that the heated walls have a constant temperature, while on the boundary in contact with the insulation an adiabatic wall was established, and the axial heat conduction in the fluid was neglected. The relationship between the Nusselt number and the ratio of the adiabatic wall height to the height of the square duct, which can be used as a main parameter in the design of micro-heat exchangers, was determined in this work. The paper also presents sample temperature fields and heatlines for selected Nusselt numbers. [ABSTRACT FROM AUTHOR]

The prediction of critical heat flux (CHF) phenomenon at atmospheric pressure was carried out using computational fluid dynamics (CFD) methods. Heat transfer experiments of flow boiling will be validated at the University of West Bohemia, where an experimental apparatus is built. The test section consists of one 3000 mm long resistance heated fuel rod imitator (HRI) with an outer diameter of 9.1 mm placed in an annular tube. Several spacer grids are used on the experimental device to hold the heated rod imitator in its position while improving the internal heat transfer. All simulations presented in this paper started with the same inlet conditions, while the heating input gradually increased until the two-phase flow reached a steady state. The successfully predicted CHF happened through a liquid sublayer dryout under very high vapor volume fractions (93+ %) which led to complete thermal isolation of the HRI. Thanks to the results of the CFD simulations, the temperature measuring system on the experimental loop could be optimized. [ABSTRACT FROM AUTHOR]

The effect of the water operating pressure on the external heat losses value of the shell-and-tube heat exchanger by using the heat loss recovery systems based on the Rankine steam cycle has been analyzed in the present paper. A comparative analysis of the effectiveness of insulating various sections of the outer surface of the heat exchanger casing was also carried out. The choice of the heat exchanger was determined by the design simplicity, the ability to withstand high pressures and temperatures, as well as by the fact that its design makes it easier to carry out thermal insulation. The analysis of the heat transfer processes in regenerative HE was conducted on the basis of the equations contained in the ANSYS Fluent package. When modeling heat exchange processes, the following boundary conditions have been adopted: the hot air temperature at the inlet Th is equal to 600 °C (the first option) and 800 °C (the second option); the water temperature at the inlet Tw is 16 °C; the ambient temperature Ta is 20 °C. The heat transfer coefficient α between the environment and outer surface of the HE is considered as constant. The obtained results revealed that heat losses significantly decrease only when the first section is insulated in 25% of the casing surface. After isolating 50% of the casing surface, the heat losses amount remained largely unchanged. It can also be concluded that with an increase in excess water pressure, the heat losses value decreases from ∼40% to ∼8% (at the inlet gas temperature of 800 °C) and from ∼34% to ∼7% (at the inlet gas temperature of 600 °C), when the casing surface insulating degree changes from 0% to 100% and water pressure varies from 1 to 150 atmospheres, correspondingly. This is due to the fact that the water pressure increase results in increasing the boiling point and the liquid water heating area with a high heat capacity. The latter increases the heat flux perceived by the water from the hot gas, and therefore leads to the external heat loss decrease. [ABSTRACT FROM AUTHOR]

Solar air heaters generally exhibit lower levels of thermal performance due to thermal losses and poor heat transfer characteristics of air. One of the commonly used techniques for performance improvement is to enhance turbulence levels in the flowing air stream. This paper presents the computational fluid dynamics analysis on the influence of trapezoidal rib shape factor and notch on the overall thermal behavior of solar air heater at constant heat flux conditions. The simulation is conducted for different Reynolds number varying from 11000 to 25000. The rib shape factor is varied as 1.71-8.85 for a fixed rib height value of 1.4 mm. The results reveal that lower values of shape factor improve heat transfer by about 13.1% for the rib shape factor of 2.42 while lower values of shape factor produce increased pressure drop by about 31% on an average for the rib shape factor of 1.71. The presence of notches create additional peak Nusselt number locations which however is negated by the presence of entrapped smaller eddies which effectively result in marginal improvement in heat transfer relative to the notchless rib irrespective of the geometry of notch. It is concluded that the suitable design modification of notches is essential to overcome the hot spots in order to take advantage of the concept of notch on ribs to achieve improved thermal characteristics. [ABSTRACT FROM AUTHOR]

This paper describes the thermal analysis of building block used for passive cooling application. For this purpose, a concrete block with cavities, drilled near the outer wall, is filled with micro encapsulated Phase Change Material (PCM). The commercially available PCM, HS 29 is used for this analysis. The micro encapsulated PCM filled in the cavities and during the heating cycle, The PCM absorbs latent heat and melts. This will prevent the heat entry into the living space and hence cool the space. The thermal performance of the brick is analyzed by Ansys-Fluent 14.5. The two-dimensional numerical analysis has been carried out using finite element analysis by seeing heat and mass transfer in the PCM. The effectiveness of PCM in the building bricks has been estimated by relating three different brick types, viz, normal solid bricks with air filled in the cylindrical cavity and bricks with PCM filled in the cylindrical cavity. In this case, the PCM filling holes are offset from center of the brick towards the exposed surface to reduce the re-entry of heat during solidification cycle. From the analysis is found that brick filled with PCM is more effective for reduction in heat flux while using for passive cooling application of buildings. [ABSTRACT FROM AUTHOR]

In the Fire Safety Engineering subject, one of the basic phenomena is fire spread on around an object that close to heat source because of the heat transfer process. At high temperature, radiation thermal have a significant effect on an exposed object. There are 3 kinds of characteristic of radiation, which are reflection, absorption, and transmission. Their characteristics are more convenient to learn if there are experiment tools or learning facilities that used radiation to be the main process. Therefore, this research has the objective of designing and built experimental tools used that process and it refers to radiometer. The radiometer is used to study the radiative heat transfer phenomenon in which heat flux emitted from a heat source is measured by using a heat flux sensor as the measurement instruments. Compared to existing radiometer apparatus, the design of this radiometer has some advantages like multiaxis features, user-friendly, portable, and low-cost manufacture. There are some additional features in radiometer likes variation of measurement range in x, y, and z-axis, measurement of view factor, measurement of tilt plane to acknowledge convection effect to heat transfer process, and using flat radiant heater. In this paper, the outcome is the design of a radiometer that can measure heat flux of thermal radiation and suits the study literature. [ABSTRACT FROM AUTHOR]

In this paper, based on the obtained for the first time analytical solution to the problem of heat conduction in an anisotropic plate with sinks of thermal energy, unsteady heat transfer under the influence of heat fluxes distributed along its boundaries is investigated. Using the obtained solution, the temperature field distributions were studied subject to changes in the components and the orientation angles of the principal axes of the thermal conductivity tensor. It was shown that in the presence of thermal energy sinks inside the plate, temperature fields are localized and limited by limiting isotherms as the time increases. This makes it practically possible to concentrate the high-temperature region in the vicinity of boundary heat fluxes, leaving the peripheral sections of the plate cold. [ABSTRACT FROM AUTHOR]

The recent advancements in electronic devices to increase its processing speed, performance, reliability and to decrease its form factor has significantly increased the heat generation within the system exponentially. The higher heat flux generation and reduced surface area to dissipate the heat due to the reduced form factor of the device has critical effects on the user’s health as well for products reliability and performance thus creating a need for a more compact and efficient device to tackle the thermal management challenges in the electronic components. Due to its compact size and enhanced heat transfer characteristics, Microchannel heat sinks (MCHS) proves to be an effective solution for complex thermal management problems. In this paper, comprehensive study of articles focused on MCHS from the current decade have been studied in order to further increase the performance of the MCHS and also to develop the novel techniques to synchronize the MCHS with other heat exchangers to solve evolving complex thermal challenges faced by the Industry today such as 5G devices, High powered LEDs, Automotive electronics and Medical electronics. [ABSTRACT FROM AUTHOR]

The paper deals with the issue of heat transfer in the structure of fibre insulators under low air pressure (close to a vacuum). In the course of studying the behaviour of fibrous insulators suitable for the production of vacuum insulating panels, it was found that the dependence of thermal conductivity at a vacuum on temperature is significantly affected by the orientation of the fibres, relative to the direction of the heat flux. This makes it possible to better describe the arrangement of the fibre structure of the thermal insulators, and can be applied to the study of heat exchange through the fibre structures under normal pressure. [ABSTRACT FROM AUTHOR]

This paper proposes an approach of calculation of permissible heat fluxes of heat pipe. Simulation algorithms and their program realization are developed with the use of MATCAD. Permissible heat fluxes in the heat pipe are determined accounting operating conditions and properties of capillary-porous materials. This approach allows us to compare heat transfer characteristics of the heat pipe by using different materials and coolant. By employing simulation data heat pipes with mesh wick and groove wick are designed. [ABSTRACT FROM AUTHOR]

This paper examines the thermal properties of thermal insulation coating applied to the building materials surfaces. The main objective is to determine the insulation coating impact on the heat flux transfer. The heat flux is modelled in terms of the heat transfer coefficient on the surface of a solid body. The thermal conductivity and heat transfer coefficient are obtained from the solution of the inverse heat conduction problem in 3D, based on the temperature measurements. The real temperature evolution is perturbed due to intrinsic properties of the measuring apparatus. We correct this situation via modelling a thermocouple function. Afterwards the determination procedure of the heat flux transfer parameters is a standard solution of the inverse problem based on the minimization of discrepancy between corrected measured data and computed temperature data. [ABSTRACT FROM AUTHOR]

The paper presents the problem of heat transfer enhancement with the application of multilayer metal mesh structures during boiling of ethyl alcohol at ambient pressure. The preparation of samples involved sintering fine copper meshes with the copper base in the reduction atmosphere in order to prevent oxidation of the samples. The experiments included testing up to 4 layers of copper meshes. Significant augmentation of boiling heat transfer is possible, however, considerable number of meshes actually hinders heat transfer conditions and leads to the reduction in the heat flux transferred from the heater surface. [ABSTRACT FROM AUTHOR]

In this paper, the effect of Magnetohydrodynamic (MHD) towards the flow and heat transfer for the upper - convected Maxwell (UCM) fluid over a stretching/shrinking sheet with prescribed heat flux (PHF) is considered. The governing equations are transformed into a set of ordinary differential equations (ODEs) by using the similarity transformation. Shooting technique is applied to solve the transform ODEs. Numerical solutions of the local temperature, reduced skin friction coefficient, velocity and temperature profiles are obtained. The features of the flow and heat transfer characteristics for various values of the Prandtl number Pr, the magnetic parameter M, the suction parameter S,thestretching/shrinking parameter S and the Maxwell parameter β are analyzed and discussed. [ABSTRACT FROM AUTHOR]

In this paper, the effect of Magnetohydrodynamic (MHD) towards the flow and heat transfer for the upper - convected Maxwell (UCM) fluid over a stretching/shrinking sheet with prescribed heat flux (PHF) is considered. The governing equations are transformed into a set of ordinary differential equations (ODEs) by using the similarity transformation. Shooting technique is applied to solve the transform ODEs. Numerical solutions of the local temperature, reduced skin friction coefficient, velocity and temperature profiles are obtained. The features of the flow and heat transfer characteristics for various values of the Prandtl number Pr, the magnetic parameter M, the suction parameter S,thestretching/shrinking parameter ε andthe Maxwell parameter β are analyzed and discussed. [ABSTRACT FROM AUTHOR]

In the present paper, detailed state-to-state model of vibrational-chemical kinetic and transport processes is applied to study fluid dynamics and heat transfer in a non-equilibrium flow of a five-component mixture containing CO2 molecules and products of their dissociation near the surface of the Mars Sample Return Orbiter. For several test cases, vibrational distributions, chemical composition, specific vibrational energy profiles as well as the transport coefficients and different contributions to the heat flux are calculated along the stagnation line. For a non-catalytic surface, the role of thermal diffusion process is found to be important. Prandtl and Schmidt numbers are calculated along the stagnation line, and their influence on the diffusion velocities and heat flux is evaluated. [ABSTRACT FROM AUTHOR]

In the present paper, the influence of self-diffusion of vibrationally excited states on the fluid dynamics and surface heat transfer in an axisymmetric Mach 7.2 air flow past a sphere-cone is discussed. Two models for state-to-state transport properties are considered: a simplified model using the Eucken's relation for thermal conductivity and Fick's law for diffusion velocities with the constant Lewis number, and a rigorous kinetic theory based model for the calculation of state-specific thermal conductivity, diffusion and thermal diffusion coefficients. The simplified model is applied for the flowfield simulation to avoid high computational costs. For the application of the accurate kinetic theory approach, a post-processing procedure is used. Inclusion of self-diffusion results in an increase in the surface heat flux of up to 6.5% upstream of a shoulder region. Thermal conductivity is found to be the primary contributor to surface heat flux; the influence of mass and thermal diffusion is found to be negligible. Self-diffusion has a considerably greater influence in decreasing heat flux in the downstream regions far from stagnation point. [ABSTRACT FROM AUTHOR]