Latent heat transport

Latent heat transport and microconvection by departing bubbles. The... 

The latent heat transport accounts for only 2% of the total heat flux in this case. However, it was observed by several investigators that the total heat transfer rate is proportional to this value, <7, lenl, because it is proportional to the bubble volume and the number of bubbles that cause intense agitation of the liquid layer close to the surface. This agitation, termed microconvection, together with the liquid-vapor exchange, were considered to be the key to excellent characteristics of boiling heat transfer (Forster and Greif, 1959). 

The boiling number (Bo) is the ratio of vapor velocity away from the heating surface to flow velocity parallel to the surface, V The vapor velocity is evaluated on the basis of heat transfer by latent heat transport. 

Figure 4 The main processes contributing to the heat conductivity of snow, kr k conduction through the network of interconnected ice crystals. k2=conduction through the air in the pore spaces, k3=latent heat transport across pore spaces due to ice condensation/sublimation cycles during metamorphism. k4=air convection in the pore space.

Latent heat transport. Here, the vapor being transported from the surface into the bulk fluid transports heat from the surface in the form of latent heat. This process is particularly important when heat fluxes are high. It may also play a very important role when the situation is such as to promote microlayer evaporation (e.g., at very low pressures). 

FIGURE 15.46 Relative contributions of latent heat transport, natural convection, and enhanced convection in the saturated pool boiling of water at atmospheric pressure (from Paul et al. [97], with permission from ASME). 

Significant amounts of condensables as load to the vacuum system can be an important consideration in the design and selection of the vacuum pump. Vacuum system suppliers must be provided condensable data in order to properly design the vacuum system. Information required include molecular weight, vapor pressure, specific heat, latent heat, transport properties, and solubility in water. 

Correlations for Boiling Heat Transfer Nucleate boiling is a complex phenomenon. Several mechanisms have been proposed to explain the boiling process, such as latent heat transport, microconvection, vapor-liquid exchange, wake flow, enhanced convection, and microlayer evaporation, details of which can be found in Ginoux (1978). 

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