Many situations are encountered where it is desired to reduce the overall heat transfer between two radiating surfaces. The task is accomplished by placing radiation shields between the emitting surfaces. The shields are thin opaque partitions arranged in the direction perpendicular to the propagation of radiated heat, and made of materials of very low absorptivity and high reflectivity (thin sheets [...]
Contrary to the common belief that addition of insulating material on a surface always brings about a decrease in the heat transfer rate, there are instances when the addition of insulation to the outside surfaces of cylindrical or spherical walls (geometries which have non-constant cross-sectional areas) does not reduce the heat loss. In fact, under certain circumstances, it actually increases [...]
The radiative heat exchange between two systems (surfaces) is generally calculated from the simplified equation- The factor hr is called the coefficient of radiant heat transfer from solid to solid and is expressed in W/m2-deg temperature difference between the enclosed and enclosing surfaces. The value of hr can be calculated from the heat flux equation for any configuration. For example, [...]
In many engineering situations, means are often sought to improve heat dissipation from a surface to its surroundings. The Newton-Rikhman relation Q = hA (t - ta) reveals that the convective heat flow can be enhanced by increasing the film coefficient h, the surface area A and the temperature difference (f - ta). The convective coefficient is a function of [...]
When two dissimilar metals are joined together at two points to form a closed loop and a temperature difference exists between the junctions, an electrical potential is set up between the junctions. Such an arrangement is known as thermocouple and is frequently used for the measurement of temperature. Measurement of temperature by a thermocouple is an important application of the [...]
In this article we will discuss about the empirical correlations for free and forced convection. Bulk Temperature and Mean Film Temperature: The physical properties (µ, k, ρ, cp) of a fluid are temperature dependent. Undoubtedly the accuracy of the results obtained by using theoretical relations and the dimensionless empirical correlations would depend upon the temperature chosen for the evaluation of [...]