NTU method

The Number of Transfer Units ( NTU) is a dimensionless parameter and belongs to the field of heat transfer.

The benefits of NTU is to design a heat exchanger or recalculate an existing device. The NTU method simplifies the interpretation or Nachrechnungsprozess considerably since it eliminates complex calculations in more complicated flow patterns.

Inferring can be NTU, where you initially for the transferred without loss of heat flow, the formula for the fluid ( with: mass flow, heat capacity, temperature difference ) and the formula for the transfer area ( with: heat transfer coefficient k, transfer area A, logarithmic temperature difference) noted that according to the conservation of energy both must be the same:

Now it converts this equation into the relationship between temperature difference and logarithmic temperature difference, since the latter does not follow in the heat exchangers of the co-or counter -current principle, is difficult to determine:

In the literature, the expression (often ) also referred to as the heat capacity flow. This expression refers to the NTU for the heat transfer. The NTU for the mass transfer is calculated as follows:

Here is the mass transfer coefficient with the unit.

To work with NTU one needs so-called NTU charts that are available for common types of flow in the literature. On the basis of known mass flows and fluid temperatures can be read from the graph, the NTU. Underestimation of the heat transfer coefficient U is the heat transfer surface can be determined.

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