A Numerical Study of Pulsating Heat Pipe Performance

Abstract

A pulsating heat pipe (PHP), also known as an oscillating heat pipe (OHP), is a passive thermal transport device which consists of a single meandering microchannel making multiple passes each through an evaporator and condenser. With a sufficient number of such passes, intermittent boiling of liquid slugs within each evaporator pass perturbs flow in adjacent channels leaving the device in a perpetually unstable state of oscillation. A PHP is thus distinguished operationally from a loop thermosyphon by having a motive force other than buoyancy and the ability to operate in all gravitational orientations. The most successful PHP models to date track liquid slug motion, sensible heating of the slugs, and mass transfer between liquid slugs and vapor plugs due to evaporation and condensation. However, the predictive capabilities of PHP models remain poor and the numbers assigned to evaporation and condensation heat transfer coefficients are generally not well justified by any realistic physical process. The current study applies methods consistent with state of the art prediction methods in microchannel boiling, to obtain results which predict the PHP’s heat transfer performance and the effect of gravitational orientation on performance.

Physical principles and state-of-the-art of modeling of the pulsating heat pipe: A review

“…In an alternative approach, d'Entremont and Thome [59,60] assume the vapor to always remain at saturation. During the volume variation at oscillations, vapor density ρ sat changes and they find a new vapor temperature by inverting the ρ sat (T ) curve.…”

“…The slope of evaporating film was introduced by Thome et al [105] for the flow boiling description and applied later to the PHP modeling [60,[106][107][108]. By combining Eqs.…”

“…An obvious limitation of the FEC model is its inability to describe accurately the film shape and thus the mass exchange that may impact the PHP dynamics. For multi-branch PHP modeling, d'Entremont and Thome [60], Nemati and Shafii [129] used the wedge film evaporation model with the variable film thickness δ = δ(x, t) defined by the local evaporation (sec. 2.3.4).…”

“…where ω 0 is given by Eqs. (60). The parameters α c and α e characterize the film condensation in the condenser and film evaporation in the evaporator, respectively.…”

“…sec. 2.3.6) was developed by d'Entremont and Thome [59,60]. The 4th order Runge-Kutta method was used for the time stepping.…”