Transient heat transfer to a forced flow of supercritical helium at 4.2 K
1986; Elsevier BV; Volume: 26; Issue: 5 Linguagem: Inglês
10.1016/0011-2275(86)90006-8
ISSN1879-2235
Autores Tópico(s)Subcritical and Supercritical Water Processes
ResumoThe transient heat transfer coefficient of supercritical helium flowing through a rectangular copper tube with a hydraulic diameter of 5 mm has been measured. The conditions of the flow were: inlet bulk temperature of the fluid was 4.2 K pressures from 3 to 10 bar and Reynolds numbers between 1.5 × 104 and 2 × 105. The tube was heated on four sides with heat fluxes up to 9800 W m−2. From the experiments it followed that during the first tens of milliseconds the heat transfer is determined by the heat conduction in the boundary layer of the supercritical helium flow. The heat transfer coefficient can be described by h = 0.5(Π λ p Cp/t)12. Although the helium properties λ p and Cp are a strong function of pressure and temperature, it was remarkable that the temperature increase during a heat pulse was almost the same at different flow pressures. After analysing the data an empirical relation, h =b ṁ0.75 (tt/t)case1n, was derived, which predicts the heat transfer coefficient at a given mass flow, ṁ, to within 10% during 0.1 s. The constants b, n and tt are related to the mass flow, ṁ, and the pressure of the fluid.
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