Effect of inclination angle onthe pool boiling heat transfer of ultra-light copper foams.pdf

ORIGINAL Effect of inclination angle on the pool boiling heat transfer of ultra-light copper foams Yongping Yang ? Xianbing Ji ? Jinliang Xu Received: 8 October 2009 / Accepted: 23 May 2010 / Published online: 5 June 2010  Springer-Verlag 2010 Abstract Effect of inclination angles on the pool boiling heat transfer on ultra-light copper foam covers was studied using acetone as the working fluid. The inclination angle was from 0 to 90. It is found that copper foam covers decrease the surface superheat at the onset of nucleate boiling and extend the operation ranges of surface superheats and heat fluxes, significantly. Boiling curves are crossed between low and high inclination angles. Heat transfer coefficients are increased, attain maximum values, and then are decreased with continuous increases in heat fluxes. The thermal performance is very insensitive to inclination angles at low pool liquid temperatures. The thermal performance is better for the saturation pool boiling heat transfer at small surface superheats, but it is better for the subcooled pool boiling heat transfer at high surface superheats. The Nusselt number is well correlated using the 812 data points, with the maximum error of 20%. List of symbols a0, a1 and a2 Empirically determined constants for temperature distribution in copper block ANG The parameter describing the effect of inclination angles Bo Bond number Cpf Specific heat of liquid J kg -1 K-1 df Copper ligament diameter mm dp Pore diameter of copper foam mm F The F number, defined as d/dp g Gravity force acceleration m s-2 h Heat transfer coefficient W m-2 K-1 hfg Latent heat of evaporation J kg -1 ke Effective thermal conductivity for copper foam solid–liquid system W m-1 K-1 kf Thermal conductivity of liquid W m -1 K-1 ks Thermal conductivity of solid copper W m-1 K-1 l Ligament length of a unit cell m mg Mass flux of vapor phase kg m -2 s-1 Nu The Nusselt number ppi The number of pores per unit length of foam cell q Heat flux at the ba