PHYSICAL EFFECTS OF VARIABLE FLUID PROPERTIES ON GASEOUS SLIP-FLOW THROUGH A MICRO-CHANNEL HEAT SINK

Rajan Kumar

doi:10.18186/thermal.888496

Abstract

Physical effects induced in micro-convective gaseous slip-flow due to variation in fluid properties are numerically examined in this paper. The problem is particularly simulated for slip-flow through a micro-channel heat sink (MCHS) having constant heat flux supplied from the wall under hydrodynamically and thermally fully developed flow (FDF) conditions. It is observed that the Nusselt number (Nu) for slip-flow is significantly higher than the no-slip-flow condition and Nu is significantly affected due to variable fluid properties (VFP). Four different cases of VFP are studied in order to investigate their effects individually. Pressure and temperature dependent density (ρ(p, T)) variation flattens the axial velocity profile in radial direction (u(r)) profile which promotes faster-moving particles close to the wall which considerably enhances Nu. The incorporation of temperature-dependent viscosity (μ(T)) variation marginally enhances Nu along the flow. Incorporation of temperature-dependent thermal conductivity (k(T)) variation highly augments Nu due to higher ρ and higher k fluid near to the wall and the incorporation of temperature-dependent specific heat at constant pressure (Cp(T)) variation reduces Nu due to lower k fluid near to the wall. The investigation also shows that the pressure drop significantly deviates from no-slip to slip condition. Furthermore, the effects of VFP on the gauge static pressure drop (Δpg) and slip velocity are also examined. The incorporation of μ(T) and k(T) variations trivially affects the Δpg and slip velocity. However, the incorporation of Cp(T) variation significantly affects the Δpg and slip velocity.

Highlights

Gas micro-convection is an important active research area in transport phenomena since it is the basis for a broad range of miniaturized high-performance applications like Micro-Electro-Mechanical Systems (MEMS) and Nano-Electro-Mechanical Systems (NEMS)
The microscale gas flow regimes can be classified into different categories according to the value of Knudsen number (Kn), which can be expressed in terms of Mach number (Ma) and Reynold number (Re) as [2, 3]: Kn = γγγγ/2 Ma/Re, where γγ is the ratio of specific heats, Ma is Mach number; Ma = um/c, and Re is Reynolds number; Re = ρm·um·D/μm
Yu and Ameel [10] and Ameel et al [11] analytically studied laminar slip-flow forced convection (FC) in micro-channels for thermally developing flow subjected to constant wall temperature (CWT) and constant wall heat flux (CWHF) boundary conditions (BCs)

Summary

INTRODUCTION

Gas micro-convection is an important active research area in transport phenomena since it is the basis for a broad range of miniaturized high-performance applications like Micro-Electro-Mechanical Systems (MEMS) and Nano-Electro-Mechanical Systems (NEMS). Yu and Ameel [10] and Ameel et al [11] analytically studied laminar slip-flow forced convection (FC) in micro-channels for thermally developing flow subjected to constant wall temperature (CWT) and constant wall heat flux (CWHF) boundary conditions (BCs). Hadjiconstantinou and Simek [14] investigated the CHT characteristics for gaseous flow through a 2dimensional micro and nano-channels under hydrodynamically and thermally FDF conditions Both the slip-flow regime and the transition regime were covered in their research. Zade et al [31] numerically investigated the special effects of VFP on the flow and HT characteristics of simultaneously developing slip-flow in rectangular micro-channels with CWT and CWHF BCs. Kushwaha and Sahu [32] used the 2nd order VS and TJ BCs to solve the momentum and energy equations along with iso-flux thermal BC at the surface of the micro-pipe. It was concluded that the physical effects need to be well considered in the applications of laminar gas microconvection based on large temperature gradients, for example, the design of MCHS, and the flow cannot be generally considered as a constant property flow, as in conventional channels

OBJECTIVE

RESULTS AND DISCUSSION

CONCLUSIONS