convection

In order to obtain means for determining realistic convective heat transfer coefficients, a hierarchy of interacting and interdependent calculation methods have been developed by the authors. Both higher and lower level models have been used to develop and verify an 'intermediate level' computer code, which formed the basis for generating input convective heat transfer data for dynamic building models. The contribution considers the computation of convective heat exchange within three-dimensional, rectangular enclosures when buoyancy effects are significant.

This paper presents a numerical study of instationary three-dimensional flows. Three methods, a semi-implicit one and two explicit ones were compared and tested on typical flow configurations (lid driven cavity, natural convection and mixed convection in a cavity). These methods were then applied to a problem of ventilation in a paint-booth. The semi-implicit method proved to have a higher accuracy. The explicit method of the M.A.C. type turned out to be more advantageous in calculation time.

Measurements reported in this paper demonstrate the increase in heat transfer due to convective air flow that can occur in wood-frame walls containing air-permeable mineral wool insulation with air spaces in contact with both sides. The effect of this air interchange between the air spaces increases with increasing temperature difference, air space height and air permeability of the insulation. Use of mid-height blocking and higher density insulation thus resulted in some reduction in the heat flow through the insulation, although convective effects were still significant.

Theoretical relationships have been developed to describe the heat transfer by combined fluid conduction-convection through air-permeable insulation with vertical air spaces adjacent to both surfaces. The fluid conduction-convection is shown to be a function of fluid properties, air flow coefficient of the insulation, insulation height and thickness, and temperature difference. A correlation in terms of dimensionless groups has been derived. Results of measurements on a 4-ft high insulation specimen over a temperature difference range from 30 to 90F were in agreement with the theory.

This paper reports the results of measurements of inside surface temperatures on a basic double window arrangement consisting of two sheets of glass surrounded by insulated construction. Principal variables were air space width, height, and overall temperature difference. Carefully controlled natural convection conditions were provided on the warm side, with forced convection on the cold side. Results were also obtained for the average surface to surface thermal conductance of each configuration.

This paper discusses the flow of air around ideal (cubic) structures on plane surfaces subjected to a turbulent boundary layer wind. These winds are shown to follow a power-law variation with height, while winds significantly effected by thermal stratification follow a log-linear distribution. Discussion of stagnation zones, flow separation, and pressure changes is included, with possible effects upon air quality and infiltration. Also discussed are variations in building design and addition of neighboring buildings, both which produce very complex winds, yet to be quantized.

Describes the influence on heat resistance of an insulated wall of workmanship and forced convection. Compares experimental investigations on cross-bar walls with calculated values. Examples show the influence on heat resistance of insulation installation, air-flow along the insulation and air-flow through the insulation. Concludes that air-tightness of the vapour barrier and partly of the inside board are of great importance.

Gives equations and charts for the calculation of heat and moisture flow due to natural convection through openings in vertical partitions separating spaces at different air conditions. Finds that heat and moisture transfer coefficients depend on the Grashof number and to some extent on the ratio of opening height to thickness. Also gives chart and equations for flow across an opening in a horizontal partition when the higher density air is above the opening.

Discusses in theoretical terms complexity of interactions of weather-driven air infiltration by 1) wind and 2) convection induced by indoor/outdoor temperature difference. Notes implications for practice of this complexity such as near impossibility of achieving accurate computer models. Treats flow through a single crack. Illustrates diagrammatically and discusses nature of the interaction of the 2 effects for several idealised examples. In an appendix proves mathematically the subadditivity of the effects for a wide class of situations.