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Heat gain in buildings occurs due to heat transfer through the building fabric or envelope, especially the walls and roof. The purpose of this paper is to identify and recommend the suitable wall materials for better thermal performance in buildings in warm and hot climatic zones of India. As India lies between the tropic of cancer and the equator, the solar radiation from the sun falls more on the walls than the roofs of the buildings. Thus, it is imperative to protect the walls from heat gain to promote thermal comfort in naturally ventilated buildings and reduce the energy loads due to artificial cooling systems in air-conditioned buildings.

In this paper, an investigation of heat flow characteristics in steady-state and the transient state for five different uninsulated wall structures using computational fluid dynamics (CFD) software has been carried out. The climate conditions at Madurai, India have been considered for this study.

The findings of the study revealed that aerated autoclaved concrete (AAC) and hollow clay blocks (HCB) for external walls in naturally ventilated buildings in warm climatic regions could improve the building’s thermal performance index and reduce peak indoor operative temperature by about 6°C–7°C. The results of steady-state and transient state analysis were found to be in good agreement with the results of the reviewed literature.

Over the past few decades, only very few architects and builders have been successful in influencing their clients to accept alternate materials such as AAC blocks, HCB, stabilized earth blocks, adobe blocks, fly-ash bricks as an alternate to conventional bricks in an attempt of highlighting their benefits, such as; materials that are easily available, more energy-efficient, can withstand the extreme weather conditions, promote thermal comfort and cost-effective. This paper provides strong evidence that AAC and HCB blocks are the most appropriate materials for improving the thermal performance of envelope walls in regions where the outdoor temperatures are above 40°C.

This paper has made an attempt to identify the appropriate wall materials for effective thermal performance in warm and hot climates. A comparative analysis between five different wall types under the existing solar conditions has been analyzed using CFD simulation study in steady-state and transient conditions under summer conditions and the appropriate wall materials have been suggested. There has been no attempt carried out so far to analyze the thermal performance of different walls using 24 h transient approach in CFD.

The conception of a heat function, just like the stream function used in a laminar two dimensional incompressible flow field visualization, has been introduced to visualize the convective heat transfer or the flow of energy around a sphere when the sphere is either being cooled or heated by a stream of fluid flowing around it. The heat function is developed in a spherical polar coordinate and is used to generate the heat lines around the sphere. The heat lines essentially show the magnitude and direction of energy transfer around the sphere with and without the existence of a finite radial velocity at the surface. The steady state hydrodynamic field around the sphere is numerically obtained up to a maximum Reynolds number of 100 and the corresponding thermal field has been obtained by solving the steady state energy equation. The field properties thus obtained are utilized to form the heat function, which becomes an effective tool for visualization of convective heat transfer.

Volumetric air receivers experience high thermal stress as a consequence of the intense radiation flux they are exposed to when used for heat and/or power generation. This study aims to propose a proper design that is required for the absorber and its holder to ensure efficient heat transfer between the fluid and solid phases and to avoid system failure due to thermal stress.

The design and modeling processes are applied to both the absorber and its holder. A multi-channel explicit geometry design and a discrete model is applied to the absorber to investigate the conjugate heat transfer and thermo-mechanical stress levels present in the steady-state condition. The discrete model is used to calibrate the initial state of the continuum model that is then used to investigate the transient operating states representing cloud-passing events.

The steady-state results constitute promising findings for operating the system at the desired airflow temperature of 700°C. In addition, we identified regions with high temperatures and high-stress values. Furthermore, the transient state model is capable of capturing the heat transfer and fluid dynamics phenomena, allowing the boundaries to be checked under normal operating conditions.

Thermal stress analysis of the absorber and the steady/transient-state thermal analysis of the absorber/holder were conducted. Steady-state heat transfer in the explicit model was used to calibrate the initial steady-state of the continuum model.

The purpose of this study is to validate whether the local thermal equilibrium for unsteady state is an appropriate assumption for the porous media with closed pores. It also compares the transient temperatures between the pore scale and volume averaged approaches to prove that the volume averaged method is an appropriate technique for the heat transfer in closed-cell porous media. The interfacial heat transfer coefficient for the closed-cell porous media is also discussed in details.

The governing equations for the pore scale and continuum domains are given. They are solved numerically for the pore scale and volume-averaged domains. The results are compared and discussion was done. The performed discussions and explanations are supported with figure and graphics.

A local thermal non-equilibrium exits for the closed-cell porous media in which voids are filled with water during the unsteady heat transfer process. Local thermal non-equilibrium condition exists in the cells under high temperature gradient and it disappears when the heat transfer process becomes steady-state. Although a local thermal equilibrium exists in the porous media in which the voids are filled with air, a finite value for heat transfer coefficient is found. The thermal diffusivity of air and solid phase are close to each other and hence a local thermal equilibrium exists.

The study is done only for the closed-cell porous media and for Rayleigh number till 10⁵. Two common working fluids as water and air are considered.

There are many applications of porous media with closed pores particularly in the industry, such as the closed-cell metal foam or the closed cells in porous materials such as foods and plastic-based insulation material. The obtained results are important for transient heat transfer in closed-cell porous materials.

The obtained results are important from the transient application of heat transfer in the closed-cell material existing in nature and industry.

The authors’ literature survey shows that it is the first time the closed-cell porous media is discussed from local thermal non-equilibrium point of view and it is proved that the local thermal non-equilibrium can exist in the closed-cell porous media. Hence, two equations as solid and fluid equations should be used for unsteady heat transfer in a closed-cell porous medium.

The purpose of this paper is to investigate the effect of changes to fundamental components of concrete; cement type, water/cementitious (w/c) ratio, aggregate size and age, on thermo-mechanical properties. Understanding the heat transfer properties of construction materials will enable a reduction in energy expenditure and associated CO₂ emissions, contributing to a more sustainable built environment.

Concrete specimens were subject to steady-state heat transfer test methods to determine thermal conductivity and specific heat values. Pore volume of specimens was determined using water displacement method.

Cement type CEM I produced the lowest thermal conductivity values by a maximum of 30 per cent, cement type group CEM I corresponded to higher pore volumes and lower densities than cement type group CEM II. Specific heat was higher in specimens containing CEM II compared to CEM I, with cement type being the dominant factor that determines the specific heat capacity. The w/c ratio 0.55 provided lowest thermal conductivity values of the w/c ratio specimens, however, w/c ratio had no impact on the specific heat of concrete. Cement type was the most dominant component of concrete of the properties tested.

The paper presents knowledge of the thermal performance of concrete with easily achieved changes to concrete mix design, which can be used alone or combined for maximum effect. Steady-state heat transfer techniques in a low moisture environment combined with pore volume testing, provides originality to the study of the behaviour of cement replacements as previous research has mainly been based on transient techniques. The use of steady-state heat transfer experimentation allows important thermal properties, thermal conductivity and specific heat to be calculated.

Empirical rules and experimental evidence are not capable of dealing with both geometric complexity and nonlinearities to design a sufficient accurate, reliable and affordable electrical device. To minimize this gap and to achieve an high performance level in the industry design of an electromagnetic device two CAD packages (electromagnetic CAD package and thermal CAD package) working in parallel processing should be used. In this paper these two packages have been used separately. The finite element technique is used to solve the heat conduction problem in complex devices of arbitrary shape with imposed boundary conditions. As an application example, the steady‐state temperature distribution will be produced for an high voltage cross‐linked polyethylene insulated power cable. The results are discussed and the importance of such a study as an aid to improve the life expectancy of high voltage power cables is pointed out. Finally, several conclusions are suggested to increase the power cable current transmission capacity.

The purpose of this paper is to validate an assumption of what to use as an effective (steady state) heat transfer coefficient of thermal conductivity for the honeycomb core sandwiched by Fiberglass face sheets composite. A one-dimensional model based on Fourier law is developed. The results are validated experimentally.

The results were obtained from the one-dimensional mathematical model of an overall or effective heat conductivity of the Honeycomb composite panel. These results were validated experimentally by applying heat flux on the specimen under controlled environment. The surface temperatures at different voltages were recorded and analysed. The skin of the sandwich composite material used in the investigation was Fiberglass sheet with a thickness of 0.5 mm at the bottom and 1.0 mm at the top surface. Both skins have a stacking sequence of zero degrees. Due to the presence of air cells in the core (Honeycomb), the model considers the conduction, convection and radiation heat transfer, across the thickness of the panel, combined as an effective conduction mode, whose value may be predicted by using the coefficient of thermal conductivity of the air based on the average temperature difference between the two skins. The experimental results for the heat transfer through the thickness of the panel provide validation of this assumption/prediction. Both infrared thermography and conventional temperature measurement techniques (thermocouples) were used to collect the data.

The heat transfer experiment and mathematical modeling were conducted. The data obtained were analyzed, and it was found that the effective thermal conductivity was temperature-dependent as expected. The effective thermal conductivity of the honeycomb panel was close to that of air, and its value could be predicted if the panel surface temperatures were known. It was also found that as temperature raised the variation between experimental and predicted effective air conduction raised up. This is because there was an increase in molecular diffusion and vibration. Therefore, the convection heat transfer increased at high temperatures and the air became an insulator.

Honeycomb composite panels have excellent physical and thermal properties that influence their performance. This study provides an appropriate method in determining thermal conductivity, which is one of the critical thermal properties of porous composite material. This paper also gives useful and practical data to industries that use or manufacture honeycomb composite panels.

The purpose of this paper is to carry out numerical modeling of single-blow transient analysis using FLUENT porous media model for estimation of heat transfer and pressure drop characteristics of offset and wavy fins.

A computational fluid dynamics program FLUENT has been used to predict the design data in terms of j and f factors for plate-fin heat exchanger wavy and offset strip fins, which are widely used in aerospace applications.

The suitable design data in terms of Colburn j and Fanning friction f factors is generated and presented correlations for wavy fins covering the laminar, transition and turbulent flow regimes.

The correlations for the friction factor f and Colburn factor j have been found to be good by comparing with other references. The correlations can be used by the heat exchanger designers and can reduce the number of tests and modification of the prototype to a minimum for similar applications and types of fins.

The study aims to highlight the behaviour of one-dimensional and two-dimensional fin models under the natural room conditions, considering the different values of dimensionless Biot number (Bi). The effect of convection and radiation on the heat transfer process has also been demonstrated using the meshless local Petrov–Galerkin (MLPG) approach.

It is true that MLPG method is time-consuming and expensive in terms of man-hours, as it is in the developing stage, but with the advent of computationally fast new-generation computers, there is a big possibility of the development of MLPG software, which will not only reduce the computational time and cost but also enhance the accuracy and precision in the results. Bi values of 0.01 and 0.10 have been taken for the experimental investigation of one-dimensional and two-dimensional rectangular fin models. The numerical simulation results obtained by the analytical method, benchmark numerical method and the MLPG method for both the models have been compared with that of the experimental investigation results for validation and found to be in good agreement. Performance of the fin has also been demonstrated.

The experimental and numerical investigations have been conducted for one-dimensional and two-dimensional linear and nonlinear fin models of rectangular shape. MLPG is used as a potential numerical method. Effect of radiation is also, implemented successfully. Results are found to be in good agreement with analytical solution, when one-dimensional steady problem is solved; however, two-dimensional results obtained by the MLPG method are compared with that of the finite element method and found that the proposed method is as accurate as the established method. It is also found that for higher Bi, the one-dimensional model is not appropriate, as it does not demonstrate the appreciated error; hence, a two-dimensional model is required to predict the performance of a fin. Radiative fin illustrates more heat transfer than the pure convective fin. The performance parameters show that as the Bi increases, the performance of fin decreases because of high thermal resistance.

Though, best of the efforts have been put to showcase the behaviour of one-dimensional and two-dimensional fins under nonlinear conditions, at different Bi values, yet lot more is to be demonstrated. Nonlinearity, in the present paper, is exhibited by using the thermal and material properties as the function of temperature, but can be further demonstrated with their dependency on the area. Additionally, this paper can be made more elaborative by extending the research for transient problems, with different fin profiles. Natural convection model is adopted in the present study but it can also be studied by using forced convection model.

Fins are the most commonly used medium to enhance heat transfer from a hot primary surface. Heat transfer in its natural condition is nonlinear and hence been demonstrated. The outcome is practically viable, as it is applicable at large to the broad areas like automobile, aerospace and electronic and electrical devices.

As per the literature survey, lot of work has been done on fins using different numerical methods; but to the best of authors’ knowledge, this study is first in the area of nonlinear heat transfer of fins using dimensionless Bi by the truly meshfree MLPG method.

The objective of present research is to characterize the unsteady thermal behavior of a square enclosure filled with water-Al₂O₃ nanofluids in the presence of oriented magnetic fields. The purpose this paper is to study the effect of pertinent parameters on the transient natural convection in the enclosure.

In this research, an in-house implicit finite volume code based on the SIMPLE algorithm is utilized for numerical calculations. To ensure the accuracy of results, comparisons are also made with previous works in literature. In this study, a constant strength magnetic field is concerned and for Rayleigh numbers of Ra=103, 104 and 105 the effect of magnetic field orientation with respect to the case of zero inclination on the thermal performance of cavity is investigated at Hartmann number range of Ha=15-90. In the present work, the nano-particle volume fractions range from φ=0-0.06.

Results show that when Rayleigh number is Ra=103, the inclination angle, solid particles and Hartmann number has no effect on the transient behavior. It is shown that during the time advancement to steady condition, the heat transfer rate relative to zero inclination angle, may reach to a maximum value. This relative maximum heat transfer increases as the inclination angle increases and decreases as the solid volume fraction increases. The effect of increase in Hartmann number is to decrease this maximum value at Rayleigh number of Ra=104 and at Rayleigh number of Ra=105, depending on the Hartmann number, this value may increase or decrease. It is also found that an increase in Hartmann number leads to delay the appearance of the relative maximum value of heat transfer. Results show that this maximum value is of more significance at zero solid volume fraction when inclination angle is 90 degrees and Hartmann number is Ha=60.

Limited works could be found in the literature regarding the idea of using nanofluids as the working fluid in an enclosure in the presence of magnetic field. In these works, the steady state thermal behavior of enclosures subjected to fixed magnetic fields is concerned. In the present work, the unsteady thermal behavior is concerned and the effect of magnetic field orientation angles on transient heat transfer performance of the enclosure at different Rayleigh and Hartmann numbers and solid volume fractions is explored.