Quantitative Visualization of Heat Transfer in Oscillatory and Pulsatile Flows

Abstract

Oscillatory and pulsatile flows arise in a variety of engineering applications as well as in nature. Typical examples include blood flow, breathing, flow in some pipe systems, acoustic systems, etc. Typical engineering applications include enhancement of heat transfer and species transport, chemical species separation, flow control, flow velocity measurement equipment calibration and biomedical applications. Very often these flows are accompanied by heat or mass transfer processes. During the past four decades numerous studies have addressed issues specific for purely oscillatory and modulated or pulsatile flows (oscillatory flow superimposed on a mean steady flow). Recent advances in the study of oscillatory flows were reviewed by Cooper et al. (1993) and Herman (2000). A better understanding of these flows and the accompanying heat transfer processes is essential for the proper design of equipment for such processes and physical situations. Both the experimental study and the computational modeling of oscillatory and pulsatile flows pose specific challenges, which will be addressed in this chapter, with the emphasis on quantitative experimental visualization using holographic interferometry. Experimental visualization of oscillatory and pulsatile flows and heat transfer requires noninvasive measurement techniques, to avoid affecting the investigated process. In this chapter we discuss holographic interferometry (HI) as a powerful tool in the quantitative visualization of oscillatory and pulsatile flows and heat transfer. Two situations will be considered to demonstrate the applications of the method: (i) the study of self-sustained oscillatory flows and the accompanying heat transfer in grooved and communicating channels and the study of (ii) oscillatory flow and heat transfer in the stack region of thermoacoustic refrigerators. In this chapter we introduce holographic interferometry as an experimental technique that simultaneously renders quantitative flow and heat transfer data. We demonstrate that for a certain class of problems HI is superior to conventional flow visualization techniques, such as tracer methods or dye injection, since it can provide not only qualitative but also quantitative insight into certain types of unsteady flows and it does not require the seeding of the flow. Several types of flows and heat transfer processes amenable for quantitative evaluation will be analyzed in the paper. We begin the discussion by introducing the experimental apparatus and technique, followed by the description of the investigated