Test Specification of A1-2 Test for OECD-ATLAS Project

According to Sateesh et al., the model for boiling on non-horizontal surfaces should consider microlayer evaporation and transient conduction owing to the sliding of bubbles, as shown in Eq. (1) q_tot = (q_me+q_tc)x_st +(q_mes+q_tcs)x_s + q_nc, (1)where q_tot is the total heat flux, q_me and q_tc are the microlayer evaporation and transient conduction heat flux from a stationary bubble, q_mes and q_tcs are the microlayer evaporation and transient conduction heat flux owing to the sliding bubbles, q_nc is the natural convection heat flux, x_st and x_s are constants determined by the area ratio parameter R defined as the ratio of area available per nucleation site to the projected area of the bubble at departure. In a model of wall heat flux partitioning, the microlayer evaporation from sliding bubbles q_mes can be defined by four sub-models, i.e., the bubble departure diameter d_d , bubble lift-off diameter d₁ , bubble departure frequency f, and active nucleation site density n_b, as shown in Eq. (2) q_mes=1/6, (2) where is density of the vapour, and h_fg is the specific latent heat. Among these sub-models, this paper focuses on the bubble lift-off diameter. Situ et al. stated that the bubble lift-off diameter, which is the bubble size when a bubble detaches from the heater surface, can be different from the bubble departure size, which is the bubble size when a bubble detaches from the nucleation site. There have been a number of works performed on the departure and lift-off diameters of the bubbles generated on non-horizontal surfaces: Schomann, Luke and Gonfleo, Luke (study on the horizontal tube) Cornwell and Schuller, Situ et al., and Cho et al. (study on the vertical surface). Although there are many useful models to predict the departure and lift-off diameters of the bubbles generated on non-horizontal surfaces, the previous researchers did not deal with the bubble lift-off diameter model applicable on a horizontal tube. The boiling phenomena on the outside a horizontal tube is widely seen in many applications. Therefore, the objective of this research is to study the bubble lift-off size generated on a horizontal tube in a natural convective boiling flow