Introduction

Although the emphasis in this book is on the dynamics of vaporization of liquids in the form of drops and sprays, it is important to note when liquids might better be applied in a form other a spray. Such a situation can develop when miniature devices are of interest. The use of a wall film rather than a spray might provide sufficient surface area of liquid to vaporize at desired rates. Also, other benefits might arise. In this chapter, we discuss a concept of liquid-film combustors that are superior for miniaturization.

Combustion has the potential to provide simultaneously high-power density and high-energy density; these parameters make it more attractive than batteries and fuel cells for applications for which weight is an issue, e.g., flight or mobile power sources. So it is important to study this method of power generation on a small scale. The microgas turbine (combustor volume 0.04 cc), the mini (0.078-cc displacement) and micro (0.0017-cc displacement) rotary engine, the microrocket (0.1-cc combustion chamber), and the micro Swiss-roll burner are examples of such studies. See Dunn-Rankin et al. (2006), Waitz et al. (1998), Fu et al. (2001), Micci and Ketsdever (2000), Lindsay et al. (2001), and Sitzki et al. (2001). These devices are not yet sufficiently efficient to compete with the best batteries; however, the feasibility of internal combustion as a miniature power source has been shown. The major challenge for all miniature-combustor designs is the increasing surface-to-volume (S/V) ratio with decreasing size.