Robert O. Warrington

The Graetz problem extended to slip-flow

Abstract The original problem for thermally developing heat transfer in laminar flow through a circular tube, as formulated by Graetz, did not consider the ‘slip-flow’ condition. This paper extends the original work of Graetz to include the effect of slip-flow, which occurs in gases at low pressures or in microtubes at ordinary pressures. A special technique was developed to evaluate the eigenvalues for the problem. Eigenvalues were evaluated for Knudsen numbers ranging between 0 and 0.12. Simplified relationships were developed to describe the effect of slip-flow on the convection heat transfer coefficient.

Energy scavenging sources for biomedical sensors

Energy scavenging has increasingly become an interesting option for powering electronic devices because of the almost infinite lifetime and the non-dependence on fuels for energy generation. Moreover, the rise of wireless technologies promises new applications in medical monitoring systems, but these still face limitations due to battery lifetime and size. A trade-off of these two factors has typically governed the size, useful life and capabilities of an autonomous system. Energy generation from sources such as motion, light and temperature gradients has been established as commercially viable alternatives to batteries for human-powered flashlights, solar calculators, radio receivers and thermal-powered wristwatches, among others. Research on energy harvesting from human activities has also addressed the feasibility of powering wearable or implantable systems. Biomedical sensors can take advantage of human-based activities as the energy source for energy scavengers. This review describes the state of the art of energy scavenging technologies for powering sensors and instrumentation of physiological variables. After a short description of the human power and the energy generation limits, the different transduction mechanisms, recent developments and challenges faced are reviewed and discussed.

Miniaturization technologies applied to energy systems

An overview of the miniaturization technologies and their application to energy systems is presented. Based on the technologies referred to as MEMS (microelectromechanical systems) or MST (micro systems technologies), silicon based micromachining, deep X-ray lithography and the micro mechanical machining processes (micro drilling, milling, cutting, electrical discharge machining, laser, focused ion beams, etc.) will be discussed in the context of application to fluid flow, heat transfer, fluidics and energy systems. An overview of fundamental research and applications will be made with emphasis on the work in the United States. The collaborative work in progress by the Institute for Micromanufacturing and the Pacific Northwest National Laboratories is highlighted. In particular, the on-going development of a micro HVAC (heating, ventilating and air conditioning) system is given specific attention. Devices and/or systems such as micro heat pumps, heat pipes, evaporators, condensers, heat exchangers, compressors and the like will be presented. Advantages, disadvantages and the rationale for miniaturization will be discussed. Current needs and markets will be discussed along with a discussion for future needs.

Evaluation of the eigenvalues for the graetz problem in slip-flow

Abstract A technique was developed for evaluation of the eigenvalues for the Graetz problem extended to slip-flow. The first four eigenvalues for Knudsen numbers of 0.02, 0.04, …, 0.12 were found. By using a least square curve-fit method, simplified relationships between the eigenvalues and Knudsen number were obtained. The efficient and accurate determination of the eigenvalues will lead to better predictions of heat transfer in rarefied gas flows and for gas flows in microtubes.

Experimental Studies of Natural Convection in Partitioned Enclosures With a Trombe Wall Geometry

Natural convection heat transfer was investigated in a scaled test facility of a Trombe wall geometry. A silicone oil was employed as the convecting medium to obtain large Rayleigh numbers (up to 1.5 {times} 10{sup 10}, based on enclosure height) characteristic of a full-scale Trombe wall in a passive solar building. The main objectives were to study the effects of Trombe wall nonisothermality and location on heat transfer, fluid temperature and fluid flow patterns. As expected, Nusselt numbers were slightly larger on the Trombe wall space side than on the living space side. Nusselt numbers increased slightly as the mass transfer gaps in the Trombe wall were increased. The results were verified, for the zero gap case, by comparing with previous studies. Physical understanding of the convection process was enhanced by flow visualization data. The information obtained should be useful to designers in optimizing overall building performance for passive solar heating.

Body motion for powering biomedical devices

Kinetic energy harvesting has been demonstrated as a useful technique for powering portable electronic devices. Body motion can be used to generate energy to power small electronic devices for biomedical applications. These scavengers can recharge batteries, extending their operation lifetime or even replace them. This paper addresses the generation of energy from human activities. An axial flux generator is presented using body motion for powering miniature biomedical devices. This generator presents a gear-shaped planar coil and a multipole NdFeB permanent magnet (PM) ring with an attached eccentric weight. The device generates energy by electromagnetic induction on the planar coil when subject to a changing magnetic flux due to the generator oscillations produced by body motion. A 1.5 cm3 prototype has generated 3.9 µW of power while walking with the generator placed laterally on the ankle.

Rotational energy harvester for body motion

This paper presents a micro-rotational energy harvester topology for extracting electric energy from human body motion at joint locations. This was accomplished using an inertial-based axial flux machine constructed with multiple permanent magnet poles and stacked microfabricated planar coils. Several body locations were tested while walking and running on a motor-driven treadmill. An average power of 472µW was obtained when the 2cm3 device was placed on the ankle while walking at 4mph.

THREE-DIMENSIONAL NUMERICAL MODEL FOR THERMAL ANALYSIS IN X-RAY IRRADIATED PHOTORESISTS

Abstract Three-dimensional X-ray irradiated resist has been modeled numerically, based on the Douglas alternating direction implicit (ADI) scheme and the parallel ‘divide and conquer’ technique, in order to analyze the temperature distribution and the potential temperature rise. This numerical procedure is simple and efficient and can be generalized to the multilayer case, since it converts three-dimensional computations into a sequence of one-dimensional computations and easily overcomes the unknown at the interface between layers. Furthermore, the computational procedure is a domain decomposition algorithm. Numerical results were obtained with regard to the temperature distribution and maximum temperature rise attained in the resist.

The miniaturization technologies: past, present, and future

Microelectromechanical systems (MEMS), micro systems technologies (MST, primarily in Europe) and micromanufacturing are relatively recent phrases that have become synonymous with the design, development and manufacture of very small devices and systems. This paper overviews the history of the major technologies that are utilized in this field. After this brief historical overview of the technologies, a short description of MEMS technologies, is presented. The current status of the MEMS effort worldwide is reviewed with emphasis on the United States, Japan and in the European community with particular emphasis on Germany, the Netherlands and Switzerland. The future for the technology along with technology transfer and management is discussed from the standpoint of market pull. Bulk and surface micromachining of silicon, X-ray micromachining using the LTCA process, and the complementary processes such as laser and focussed ion beam micromachining are reviewed.<<ETX>>

Miniaturized surface-driven electrostatic actuators: design and performance evaluation

A series of miniaturized, surface-driven rotary and linear electrostatic actuators was designed and fabricated. The finite element analysis method was used to aid in the design and analysis of the electrostatic drive mechanism. The actuators, consisting mainly of a copper-coated 200 /spl mu/m-thick glass epoxy stator board and a 34 /spl mu/m-thick carbon-coated polyethylene-terephthalate (PET) film slider, were fabricated using modified printed circuit board techniques. These actuators, able to carry mechanical loads up to 375 times their own weight, can be used as micro conveyers or robots in an automated micromachine assembly environment for a wide range of applications.