Influence of wall material on nucleate pool boiling of liquid nitrogen

Abstract

The wall material thermal conductivity k is one of the surface characteristics that influences the pool boiling heat transfer coefficient (HTC). It is believed that growth rates of vapor bubbles and their frequency are mechanisms affected by the thermal conductivity. In order to investigate this effect, different surface materials (copper, aluminum, stainless steel) are tested in a horizontal surface geometry. From a physical point of view, the redistribution of local heat fluxes between the free surface (wet by the liquid) and the spot covered with nucleation centers is hindered in the case of low values of k. But the wall material k affects the nucleate boiling curve only in the case of a very limited number of nucleation sites. Previous experiments in fact concluded that for a rough surface that has a larger number of vapor generating centers, the wall thermal conductivity does not significantly affect the boiling HTC; therefore the tested surfaces are mechanically polished to avoid any roughness effect. In this paper, nucleate pool boiling curves of saturated nitrogen under ambient pressure are experimentally obtained on a horizontal flat surface and the effect of three different wall materials is evaluated. Hysteresis behaviour has been observed for the copper and aluminum surfaces, while the results for stainless steel are contradictory. The critical heat flux (CHF) is also compared and analyzed by taking into account the thermal effusivity of the different materials. Finally, experimental results are compared against the most common empirical correlations for nucleate pool boiling heat transfer.

Thermal analysis of marine structural steel EH36 subject to non-spreading cryogenic spills. Part I: experimental study

“…One of the parameters that may affect heat flux to the liquid pool is surface roughness. The effect of surface roughness on the boiling curve of liquid nitrogen has not been sufficiently studied in the literature (Bombardieri and Manfletti 2016), especially for steel-LN 2 pool boiling. The top surface of the steel plate in contact with the liquid nitrogen was polished for all specimens (see Figure 9) except for PLATE#1-RP.…”

Measurement of the onset of nucleate boiling in liquid xenon

“…In this situation, the bulk fluid is held at or below saturation temperature and only the boiling surface reaches superheated temperatures, as opposed to in a LXe bubble chamber where the entire bulk fluid is superheated [14]. The onset of boiling is highly dependent on parameters such as the surface orientation, the material roughness and the amount of subcooling [15,16]. In LXe, the study by Haruyama [17] finds Δ𝑇 wall,ONB to be between approximately 3.8 and 18 K on a thin platinum wire, depending on hysteresis effects.…”

Measurement of the onset of nucleate boiling in liquid xenon

“…The accepted phenomenological model of nucleation boiling describes the superheating as the temperature in excess of saturation allowing the local vapor pressure at the nucleation sites to overcome the surface tension [12]. The onset of boiling is highly dependent on parameters such as the surface orientation, the material roughness and the amount of subcooling [13,14]. In water this value is generally accepted to be less than 5 • K. In LXe, the study by Haruyama [15] finds ∆T wall,ON B to be between approximately 3.8 and 18 • K on a thin platinum wire, depending on hysteresis effects.…”