1d Homogeneous Modeling of Microchannel Two-phase Flow with Distributed Liquid Water Injection from Walls

This paper presents a theoretical model and a numerical simulation of a liquid-gas two-phase flow within a microchannel (50 500 2 m m cm μ μ × × ) equipped with distributed liquid water injection through the side walls. The modeling and solution of the conservation equations provide pressure drop as a function of inlet velocity. The influence of different parameters involving water injection is investigated, such as the quantity of water that is injected and the profile that is used to inject it. The numerical results show that for small water injection rates (1 10 / min) L μ − the air flow velocity and pressure drop are not significantly perturbed by the presence of liquid water. But if water injection becomes important (10 100 / min) L μ − larger pressure drops are observed. The influence of inlet pressure is also investigated. The model predictions are compared with experimental results obtained from testing a set of microchannels with a varying number of water injection slots on the side walls. Pressure drop distribution data from these experiments are consistent with model predictions. INTRODUCTION Two-phase flow in microchannels has recently attracted attention because of its wide applicability to technologies such as MEMS, integrated circuits cooling [1], chemical process engineering, medical/genetic engineering and bioengineering among others. For example, gas-liquid flow and transport is a subject of increasing importance in low-temperature Proton Exchange Membrane (PEM) fuel cells [2]. A good way to improve their performance is to use microchannels (0.05 – 1 mm) in the anode and cathode gas delivery systems [3], because this reduces species transport resistances within the channels. However, microchannels substantially complicate the issue of water management [4-6], particularly on the cathode side, where oxygen is consumed and water produced. This aspect is still poorly understood and needs to be investigated. The present paper describes a theoretical model and a numerical simulation of a liquid-gas two-phase flow within a microchannel (50 500 2 m m cm μ μ × × ) equipped with distributed liquid water injection through the side walls. The modeling and solution of the conservation equations provide pressure drop as a function of inlet velocity. The influence of different parameters involving water injection is investigated, such as the quantity of water that is injected and the profile that is used to inject it. The numerical results show that for small water injection rates (1 10 /min) L μ − the air flow velocity and pressure drop are not significantly perturbed by the presence of liquid water. The influence of the inlet pressure is also investigated. The model predictions are compared with experimental results obtained from testing a set of microchannels with a varying number of water injection slots on the side walls. Pressure drop distribution data from these experiments are consistent with model predictions. PROBLEM STATEMENT We consider a rectangular microchannel of 500 microns width, 50 microns depth and 2 centimeters length. An air flow is setup at the inlet of the channel. Between the inlet and the outlet liquid water is injected into the flow. The liquid water enters the gas channel through a uniform distribution of slots along the side walls. In other words we are considering a bicomponent (air/water) two-phase (gas/liquid) flow inside a rectangular channel. We consider a one-dimensional formulation of this problem, so the liquid water injection is treated as if water was created in the core of the flow (as a source term in the equations). The flow is pressure driven (Poiseuille flow) so the value of the stagnation pressure at the inlet of the channel is an important parameter.