Smoke Plume Mass Flow
Calculate the mass flow of a fire's smoke plume by the Heskestad correlation, ṁ = 0.071·Q̇_c^(1/3)·z^(5/3), from the convective part of the heat release rate Q̇_c (kW) and the height above the fire base z (m). The result, in kg/s, is the amount of hot gases and smoke rising and accumulating, governing the design of smoke control and exhaust systems (mechanical or natural) that keep a smoke-free layer for safe evacuation. The flow grows strongly with height. Enter the convective heat fraction and the height.
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Vazão da pluma de fumaça (Heskestad)
Num incêndio, os gases quentes e a fumaça sobem em forma de pluma, arrastando (por entranhamento) o ar frio ao redor à medida que sobem — por isso a pluma fica mais larga e com mais massa quanto mais alto se mede. A correlação de Heskestad para a vazão mássica da pluma na zona acima das chamas é ṁ = 0,071·Q̇_c^(1/3)·z^(5/3), onde Q̇_c é a parcela convectiva da taxa de liberação de calor (tipicamente ~70% da HRR total, pois parte do calor sai por radiação, em kW) e z é a altura acima da base do fogo (m). O resultado, em kg/s, é a quantidade de fumaça e gases que chega àquela altura e se acumula no teto, formando a camada de fumaça que desce progressivamente. Esse é o cálculo-chave do controle de fumaça: para manter uma camada livre acima das cabeças das pessoas durante a evacuação (e para os bombeiros enxergarem), os sistemas de exaustão — mecânica (ventiladores) ou natural (aberturas no topo) — precisam extrair fumaça na mesma taxa em que a pluma a produz na altura da camada de projeto. Como a vazão cresce fortemente com a altura (expoente 5/3), átrios e pavilhões altos geram plumas enormes, exigindo sistemas de exaustão potentes. Dimensionar isso corretamente é o que garante visibilidade e ar respirável nas rotas de fuga. Informe a parcela convectiva do calor e a altura.
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