Niisselt number

Niisselt number correlations for cross (low over tube banks for A/ > 16 and... 

Variation of local Niisselt number with length for the re-entrant, square-edged, and bell-mouth inlets in the transition region. 

In heat convection analysis, ii is often convenient to express the heat transfer coefficient in a nondimensionali7ed form in terms of the dimensionless Niisselt number, defined as... 

As a drop evaporates, the Niisselt number gets smaller and approaches 2,0, To simplify the analysis, assume Nu = 2,0, The drops injected into warm air soon reach the wet-bulb temperature. Heat transferred to a drop ... 

When the gas is motionless, the free convection is desoibed by three dimensionless numbers the Niisselt number, the Grashof (Gr) number, and the Prandtl (Pr) number ... 

The Niisselt number is expressed in terms of the other two dimensionless numbers ... 

As said already in Part 2.3, considerable work has been done on the subject of heat transfer through a solid and a fluid, especially for evaluation of heat transfer systems [2], and various dimensionless numbers have been established, whatever the nature of the fluid motion. In any case, either with a motionless or a stirred fluid, the Niisselt number expressed in Equation 2.29, appears as the most important parameter. 

There is a free convection, and following Section 2.3.2, we have to evaluate the Niisselt number through the Grashof and Prandtl numbers. There is the following ... 

This is the case of a square rubber sheet 1 cm thick with 10-cm sides, initially at 160°C, immersed in stirred air at 20°C on both sides, in a vertical position. The Reynold s number should be used and evaluated, and from the valne obtained for this number, it is possible to calculate the Niisselt number. 

Various studies have been undertaken to resolve experimentally the problem of a fluid circulating in a tube [2]. The other problem of heat convection between the external surface of a cylinder and the fluid is quite different. The method to be followed is based on the relationship between two dimensionless numbers, the Niisselt (Nu) number and the Reynold (Re) number. 

As the diameter of the polymer sheath varies within a wide range, depending on the final use of the film, the values of the Niisselt and of the Reynolds numbers also vary largely. This is the reason why, as examples, two very different values are selected for the coefficient of heat convection hj, = 0.5 and 0.05, expressed in cal/cmVs/deg. 

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