Lattice Boltzmann modeling of boiling heat transfer: The boiling curve and the effects of wettability

A hybrid thermal lattice Boltzmann (LB) model is presented to simulate thermal multiphase flows with phase change based on an improved pseudopotential LB approach [Q. Li, K. H. Luo, and X. J. Li, Phys. Rev. E 87, 053301 (2013)]. The present model does not suffer from the spurious term caused by the forcing-term effect, which was encountered in some previous thermal LB models for liquid-vapor phase change. Using the model, the liquid-vapor boiling process is simulated. The boiling curve together with the three boiling stages (nucleate boiling, transition boiling, and film boiling) is numerically reproduced in the LB community for the first time. The numerical results show that the basic features and the fundamental characteristics of boiling heat transfer are well captured, such as the severe fluctuation of transient heat flux in the transition boiling and the feature that the maximum heat transfer coefficient lies at a lower wall superheat than that of the maximum heat flux. Furthermore, the effects of the heating surface wettability on boiling heat transfer are investigated. It is found that an increase in contact angle promotes the onset of boiling but reduces the critical heat flux, and makes the boiling process enter into the film boiling regime at a lower wall superheat, which is consistent with the findings from experimental studies.

💡 Research Summary

The paper introduces a hybrid thermal lattice Boltzmann (LB) framework designed to simulate multiphase flows with phase change while eliminating the spurious term that has plagued earlier thermal LB models. Building on the improved pseudopotential approach proposed by Li, Luo, and Li (Phys. Rev. E 87, 053301, 2013), the authors separate the evolution of density/velocity fields (handled by the conventional LB collision–streaming scheme) from the temperature field (governed by a dedicated energy equation). By coupling these two fields through an energy‑conserving formulation rather than inserting a forcing term directly into the thermal equation, the model avoids artificial source terms and preserves thermodynamic consistency.

The authors first validate the model by simulating the classic boiling process on a heated wall under zero‑gravity conditions. By gradually increasing the wall superheat (ΔT) they obtain the full boiling curve, reproducing the three canonical boiling regimes for the first time within the LB community: nucleate boiling (NB), transition boiling (TB), and film boiling (FB). In the NB regime, the average heat flux (q) rises nearly linearly with ΔT, reflecting stable bubble nucleation and departure. As ΔT approaches the critical point, the system enters the TB regime, where q exhibits large, rapid fluctuations and the heat‑transfer coefficient (h) reaches a maximum at a lower ΔT than the peak heat flux. This reproduces the experimentally observed “heat‑transfer coefficient peak before the critical heat flux” phenomenon and confirms that the model captures the unstable interfacial dynamics characteristic of transition boiling. Further increase of ΔT leads to the formation of a continuous vapor film (FB), causing a decline in q due to thermal insulation by the vapor layer.

A second major contribution is the systematic investigation of surface wettability on boiling performance. By adjusting a virtual surface force that imposes a prescribed contact angle (θ), the authors explore a range from hydrophilic (θ≈30°) to hydrophobic (θ≈110°) conditions. The simulations reveal that larger contact angles promote earlier onset of nucleate boiling (lower ΔT required for bubble formation) but simultaneously reduce the critical heat flux (CHF) and cause the transition to film boiling at a lower superheat. These trends align closely with experimental findings, confirming that the model correctly incorporates the influence of wettability on bubble dynamics, coalescence, and vapor‑film formation.

From a numerical standpoint, the hybrid scheme demonstrates robust stability even in the presence of steep density and temperature gradients at the liquid–vapor interface. The collision operator and the force‑energy coupling suppress non‑physical pressure oscillations that often destabilize conventional thermal LB methods. Long‑time simulations (several thousand time steps) show convergence of averaged heat‑transfer metrics, while transient spikes in q during TB are interpreted as genuine physical fluctuations rather than numerical artifacts.

In summary, the paper delivers a thermodynamically consistent, spurious‑term‑free thermal LB model capable of quantitatively reproducing the full boiling curve and elucidating the role of surface wettability. The work bridges a critical gap in LB research, offering a powerful tool for predictive simulation of boiling heat transfer in engineering applications such as high‑performance heat exchangers, nuclear reactor cooling, and electronic device thermal management.