Natural convection windows

Heat transfer by natural convection across an enclosed space, called an enclosure or, sometimes, a cavity, occurs in many real situations, see [34] to [67]. For example, the heat transfet between the panes of glass in a double pane window, the heat transfer between the collector plate and the glass cover in a solar collector and in many electronic and electrical systems basically involves natural convective flow across an enclosure. 

Examine natural conveclion from finned surfaces, and determine the optimum fin spacing, B Analyze natural convection inside enclosures such as double-pane windows, and... 

Gases are nearly transparent to radiatioo, and thus heat transfer through a gas layer is by simultaneous convection (or conduction, if the gas is quiescent) and radiation. Natural convection heat transfer coefficients are typically very low compared to those for forced convection. Therefore, radiation is usually disregarded in forced convection problems, but it must be considered in natural convection problems that involve a gas. This is especially the case for surfaces with high emissivities. For example, about half of the heat transfer through the air. space of a double-pane window is by radiation, The total rate of heat transfer is determined by adding the convection and radiation components,... 

Consider a l.2-m-high and 2-m-wide glass window with a thickness of 6 nun, thermal conductivity k = 0.78 W/m C, and emissivity e = 0.9. The room and the walls that face the window are maintained at 25°C, and the average temperature of the inner surface of the window is measured to be 5°C. If the temperature of Ihe outdoors is -5 C, determine (a) the convection heat transfer coefficient on Ihe inner surface of the window, (b) the rate of total heat transfer through the window, and (c) the combined natural convection and radiation beat transfer coefficient on the outer... 

S8C Someone claims that the air space in a double-pane window enhances the heat transfer from a house because of the natural convection currents that occur in the air space and recommends that the double-pane window be replaced by a single sheet of glass whose thickness is equal to the sum of the thicknesses of the two glasses of the double-pane window to save energy. Do you agree with this claim ... 

Natural convection in enclosed spaces. Free convection in enclosed spaces occurs in a number of processing applications. One example is in an enclosed double window in which two layers of glass are separated by a layer of air for energy conservation. The flow phenomena inside these enclosed spaces are complex since a number of diflerent types of flow patterns can occur. At low Grashof numbers the heat transfer is mainly by conduction across the fluid layer. As the Grashof number is increased, different flow regimes are encountered. 

Natural Convection Heat Loss in Double Window. A vertical double plate-glass... 

During natural convection, the initial temperature of 22 °C reaches 34-35 °C. As reported in [9], the ageing phenomena in the battery accelerate at elevated temperatures and the cycle life of the cell decreases. At setting 1 and 2 of the ventilator, the temperature increase is limited to 5-6 °C. Based on these temperature evolutions and produced power losses, the heat transfer coefficient is 13.7, 44.4, and 57.1 W/m °C at natural convection, position 1 and position 2, respectively. Following these results, we can conclude that the heat transfer coefficient 44.4 W/m K is required, which represents with position 1 of the ventilator, to keep the battery cell within the appropriate temperature window. 

Dilution ventilation utilises natural convection through open doors, windows, roof ventilators etc. or assisted ventilation by roof fans or blowers which draw or blow in fresh air to dilute the contaminant. With both of these systems the problem of providing make-up air at the proper temperature, especially during the winter months, has to be consider. ... 

There are two main classifications of convection, forced and natural. Forced convection is fluid motion that is a result of forced input, such as a fan or pump. Natural convection is a result of density gradients in the flow which cause motion. In forced convection, there is also often a component of natural convection, but this is typically dominated by the forced convection effects. The density gradients in the flow, which are the genesis of natural convection, can be caused by either temperature or solutal buoyancy effects. Temperature effects are simply a result of the density-temperature relationship for a fluid. These effects can be illustrated by imagining a window in a warm apartment on a cold winter day (see Figure 5.41). At the inside surface of the window, the air in the room is cooled by the window and increases in density, sinks down along the window, and causes an uncomfortable draft. 

Figure 5.41 Schematic of natural convection flowing from a cold window.

Neither of these designs permits replenishment of the electrolyte layer (other than by natural convection and diffusion), and therefore they cannot be used when large amounts of material are transformed, e.g., in metal deposition, though they are ideal for studies of adsorption and processes involving restructuring. When solution replacement is required, a flow system must be used, and a possible cell design is shown schematically in Figure 8. Here, a narrow band electrode is used which defines the thickness of the electrolyte layer since the windows are fixed on either side of it. 

In this paper we present for the first time a test that combines heat extraction and heat injection pulses in one experiment. It is expected that differences in the ground thermal conductivity, when different data windows are used to obtain an estimate, can be related to advection and convection of ground water. The real ground conductivity should be derived from the experimental data where the response is close to or lower than the natural ground temperature, minimizing effects of advection and convection. First results, for a case of no ground water flow, show that estimates of ground thermal conductivity are very comparable for the different data windows. 

---