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Eficácia - Método NTU

1955
  • W. M. Kays
  • A. L. London
Trocador de calor utilizado em termodinâmica para análise de eficácia pelo método NTU.

(Imagem gerada apenas para fins ilustrativos)

The Effectiveness-NTU método is used in heat exchanger analysis when fluid inlet temperatures are known, but outlet temperatures are not. Effectiveness ([latex]\epsilon[/latex]) is the ratio of actual heat transfer to the maximum possible heat transfer. The Number of Transfer Units (NTU) is a dimensionless measure of the heat exchanger’s size, defined as [latex]NTU = \frac{UA}{C_{min}}[/latex].

O método Effectiveness-NTU oferece uma alternativa poderosa ao LMTD method, especially in situations where iterating to find outlet temperatures would be cumbersome. The core of the method lies in three dimensionless parameters: effectiveness ([latex]\epsilon[/latex]), the number of transfer units (NTU), and the heat capacity rate ratio ([latex]C_r = C_{min}/C_{max}[/latex]). The maximum possible heat transfer rate, [latex]Q_{max}[/latex], occurs in a hypothetical infinitely long counter-flow heat exchanger, where the fluid with the smaller heat capacity rate ([latex]C_{min}[/latex]) undergoes the maximum possible temperature change, [latex]\Delta T_{max} = T_{h,in} – T_{c,in}[/latex]. Thus, [latex]Q_{max} = C_{min}(T_{h,in} – T_{c,in})[/latex]. The actual heat transfer is then simply [latex]Q = \epsilon Q_{max}[/latex]. The key is that effectiveness ([latex]\epsilon[/latex]) can be expressed as a function of only NTU and [latex]C_r[/latex] for a given flow arrangement. For example, for a parallel-flow exchanger, the relationship is [latex]\epsilon = \frac{1 – \exp[-NTU(1+C_r)]}{1+C_r}[/latex]. These relationships have been derived and charted for numerous common heat exchanger configurations, allowing engineers to quickly determine the performance of a given exchanger or to size a new one without knowing the outlet temperatures beforehand. This method is particularly useful in design and optimization studies where the impact of changing the exchanger’s size (and thus NTU) on its performance (effectiveness) is being investigated.

UNESCO Nomenclature: 3328
Termodinâmica

Tipo

Sistema abstrato

Interrupção

Incremental

Uso

Uso generalizado

Precursores

  • Método LMTD para análise de trocadores de calor
  • conceito de números adimensionais em mecânica dos fluidos e transferência de calor (por exemplo, Reynolds, números de Prandtl)
  • avanços na termodinâmica e na dinâmica dos fluidos durante o início do século XX

Aplicações

  • análise de regeneradores de turbinas a gás
  • Projeto de trocadores de calor compactos onde as temperaturas de saída são difíceis de prever.
  • Avaliação do desempenho de sistemas de refrigeração eletrônica
  • design de radiador automotivo
  • sistemas de gerenciamento térmico aeroespacial

Patentes:

NA

Ideias de Inovação Potencial

  • integration of NTU-based models into machine learning algorithms for predictive maintenance of industrial heat exchangers
  • development of modular heat exchanger systems where units (NTUs) can be added or removed to match heat load demands
  • ntu-optimized microchannel heat sinks for high-power density electronics and laser diodes
  • software tools that automatically generate ntu-effectiveness curves for novel 3d-printed heat exchanger geometries
  • dynamic ntu modeling for transient analysis of waste heat recovery systems in hybrid vehicles
  • application of the ntu method to biological systems, such as modeling heat exchange in animal circulatory systems
  • ntu-based performance guarantees for commercial heat exchanger products
  • creation of advanced composite materials with tunable thermal conductivity to actively control a heat exchanger’s ntu value
  • use of the ntu method to design thermal storage systems coupled with heat exchangers
  • development of educational software that visualizes the relationship between ntu, effectiveness, and flow configuration
Relacionado a: eficácia, NTU, trocador de calor, transferência de calor, Kays e London, termodinâmica, número adimensional, projeto térmico, trocador de calor compacto, relação de taxa de capacidade.

Contexto histórico

Eficácia - Método NTU

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(Caso a data seja desconhecida ou irrelevante, por exemplo, "mecânica dos fluidos", é fornecida uma estimativa aproximada de seu surgimento notável)

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