The aim of this work is to determine the radiative thermal exchange in 2D closed diode cavities in which a natural convective flow is established. The distinction between heat transfer by natural convection and radiation is necessary for these cavities, considering their particular geometry. The hot and cold walls of the cavity have the same size (height H) and are at the origin of the natural 2D convective flow. Being at a distance L, varying according to the treated case (shape factor A = L/H) and remaining always vertical, they are maintained isotherm with an imposed difference of temperature ΔT. The four other walls of the cavity have a very high thermal conductive resistance (i.e., adiabatic). The upper and lower walls are inclined in relation to the horizontal with an angle slope α that can be positive or negative. Thus, the lateral walls of the cavity have a parallelogram shape in most of the cases. The configurations of the cavities corresponding to various combinations of ΔT, α and A = L/H parameters give very different natural flows being able either to favor the convection or, on the contrary, to decrease it (convective diode effect). According to the treated case, it entails sensi-tive differences of natural convection and radiation contributions. In this survey, we put the emphasis on the radiative aspect. We present detailed calculations based on radiosity method coupled with thermal measurements obtained experimentally. The results of this work put in evidence the importance of radiation in the global exchange. These cavities can be used in several engineering domains. However, this work consists in adapting their use in solar energy techniques like building and flate-plate solar collectors.

The intervention on historic buildings through building energy retrofitting has become one of the current challenges of improving energy efficiency. Nonetheless, this building typology presents certain complexities. Among them, one of the most relevant is the protection on their façades due to the historical and/or artistic values of a given façade and, therefore, the addition of external thermal insulation is restricted. However, at the same time, in several of those buildings indoor surfaces do not present that architectural value, and then internal thermal insulation becomes a promising strategy for improving their thermal performance. Nevertheless, its application must be carefully evaluated to avoid possible pathologies caused by moisture problems. This paper aims to identify constructive solutions for interior insulation of walls free from moisture problems. For this purpose, a comprehensive analysis of a series of constructive solutions based on internal insulation has been carried out through hygrothermal simulations. The results show how the application of water-repellent impregnation becomes essential to guaranteeing the integrity of the envelope. In addition, the combination of insulations with or without inner membranes, such as smart vapor retarders or vapor diffusion barriers, has been evaluated detecting the solutions that best fit the objective. Finally, taking advantage of the great potential of 2D simulation tools, the post-processing of the data has been performed to apply the wood decay model, and thus assess the behavior of a very conflictive point in this type of intervention, i.e., the wooden beam-ends. The results in this critical point have shown how the application of the proposed constructive solutions becomes essential to guarantee the integrity of the element and how the application of traditional solutions could lead to a hazard that must be avoided.

Airtightness is a major issue in architectural design and it has a significant impact on the energy performance of buildings. Moreover, the energy behaviour of built heritage is due, to its singular characteristics, still a great unknown. The aim of this study is to establish a better knowledge of the airtightness of historical buildings, based on an in depth field study using blower-door tests. A set of 37 enclosures were analyzed inside eight buildings located in historical areas of a Spanish city with a significant built heritage. They were constructed between 1882 and 1919 and include diverse construction typologies applied for many building uses such as residential, cultural, educational, administrative and emblematic. The results indicate lower values compared to other previous airtightness studies of historical buildings. The average air change rate was found to be n₅₀ = 9.03 h⁻¹ and the airtightness of the enclosures presented a wide range of between 0.68 and 37.12 h⁻¹. Three main levels of airtightness were identified with two thirds of the tested samples belonging to the intermediate level between 3–20 h⁻¹. To conclude, several correlations have been developed which provide a method to estimate air leakage and could serve as a basis for energy performance studies of these kinds of building.

Films are used in a wide range of electronic and mechanical technologies. An analytical solution is developed in this paper in order to investigate the effect of films on the thermal behavior at the vicinity of a static or moving rough interface. The roughness is modeled by multiple circular contacts which are assumed identical and regularly distributed over the interface according to a square net. The governing equations are solved by using the finite complex Fourier transform and the finite cosine Fourier transform. The developed solution is explicit and allows to calculate the three-dimensional steady-state temperature regardless of the velocity and the ratio of the real contact area to the apparent one. Thus, this solution can be also used for other applications such as the moving laser beam. The comparisons performed show a good agreement of our results with available models. We study the effects of: thermal properties of materials, the relative size of micro-contacts, the film thickness and the velocity, on the thermal behavior of the body.