convection

Purpose of the work

Condensation risks in wooden building components are mainly caused by water vapor penetrating the cross section of the component through airflow. Even small pressure differentials result in a lot more vapor flowing through a joint of only a few millimeters than that which would migrate by diffusion through many more undisturbed square meters of area.

Heat and mass transfers in building materials influence the thermal properties and performances ofthe materials more especially as they are porous. This paper deals with the case of various porousbuilding materials (Aerated Autoclaved Concrete, Hemp Concrete and Vertically Perforated Brick)studied by an experimental approach. A cell of exchange makes it possible to impose on a sample,gradients of temperature and relative humidity variables as function of time. The performances ofthese materials are thus deduced from the evolution of T and %RH in several positions.

This work lies within the concept of positive energy buildings. The aim is to develop an activemanagement of local free energy (solar, air and earth) inside the envelops by convection heat transfer and by the use of phase change materials (PCMs) in order to store or release heat when needed. A 1D RC network simulation tool has been developed for different standard fronts including a solar air collector and a double skin faade (south frontage), leading to the thermal simulation of a room with different configurations, with or without PCMs integration and for ventilated envelops.

This paper studies in three-dimension the coupled convective and radiative heat transfer rate from awindow surface with adjacent venetian blind using a commercial CFD code. For this study the window surface was modeled as an isothermal vertical flat plate. The flow patterns (temperature and velocity fields) and convective heat transfer coefficient were investigated for different blade angles (00, 450, -450, 800). Comparisons were made with experimental and other theoretical research.

This paper presents an analytical model for predicting the air flow and velocity in an open vertical air channel due to natural convection. It can be used in the study of ventilated windows and double-faade systems, which are arousing interest as an energy-efficient means of providing fresh air, daylight and solar radiation to rooms. Unlike most previous work in this field, it proceeds from known surface temperatures instead of known surface heat flux.

A comparative study between experiments and numerical simulations in the developingzone of a non-isothermal plane vertical jet is presented. Low velocity airflow, in aiding mixedconvection regime, discharging from a large rectangular nozzle in a quiescent medium at a highertemperature is considered (Re = 4220).The "Reynolds-Averaged" Navier-Stokes equations (RANS) are solved with two codes, the CFD code Fluent and the Aquilon code, including different turbulence models.

The present study is directed toward an accurate analysis on the transport of sensible heat overa realistically shaped human body model by way of a coupled convection-radiation simulation technique. A low-Reynolds-number type k- e turbulence model is employed to obtain the convective heat flux distribution with greater accuracy. Configuration factors over the complex geometry are accurately calculated using a Monte-Carlo method incorporating symmetrization procedures.

In the case of moderate climates, convective and radiative heat exchanges are the main avenues for heat losses on a human body. When using a dummy it is sometimes difficult to have a good estimation of the heat transfer coefficients for convection and/or radiation and especially to determine the part of each mode. It is now quite easy to calculate radiative transfer with accuracy. The approach proposed here, is to find a better estimation of the local radiative heat transfer through modeling and to discuss the value of local radiative coefficients in different situations.

This paper presents a number of advantages (both practical and thermodynamic) of ceiling heating systems compared to under-floor heating. It is estimated that the heat flux from ceiling heating is approximately the same as under-floor heating: the larger exposed surface of the ceiling, and the lower thermal resistance between the water in the pipes and the ceiling surface, compensate for the lower convective heat flux from the ceiling. Using the same water temperature in the pipes, the total heat flux from ceiling heating will be similar to that of under-floor heating.

Natural convection, which arises around an occupant by his own metabolic heat, plays an important role in convection heat dissipation of the body in a room environment. The present research aimed at to know how local airflow penetrates through the natural convection layer, how it is perceived at a body surface, and finally causes sensations of warmth and air motion. As a basic study of it, horizontal local airflow was directed at the representative two locations on subjects surfaces, which are the back of the neck and the left side of the ankle.