This paper presents the system-level and component design of a micro steam turbine power plant-on-a-chip which implements the Rankine cycle for micro power generation. The microfabricated device consists of a steam turbine that drives an integrated micropump and generator. Two-phase flow heat exchangers are also integrated on-chip with the rotating components to form a complete micro heat engine unit, converting heat to electricity. The system-level design includes cycle analysis and overall performance predictions, accounting for the expected performance of miniaturized components, thermal and structural integrity of the microsystem, and system-level trade-offs for optimal overall performance. Operating principles and design studies are also presented for the core component, with emphasis on a multistage, planar, radial microturbine and a spiral groove viscous pump. Design consideration for two-phase flow heat exchangers, microbearings, seals and micro-generators are also presented. Expected power levels range from 1–12 W per chip with energy conversion efficiency in the range of 1–11%. This suggests power density of up to 12 kW/kg for this technology, which is an order of magnitude greater than competing technologies, such as thermoelectrics. This study suggests the viability of a micro Rankine power plant-on-a-chip, but also identifies critical engineering challenges that must be met for practical implementation.

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A previous teaching grant from the National Fluid Power Association provided senior mechanical engineering students a project to design and fabricate a fluid-powered gantry crane. During fabrication, assembly, and testing of the fluid-powered gantry crane, a number of areas for improvement of the student design were identified. Among these were the inclusion of a control system to limit load swing, redesign of the fluid distribution system, redesign to reduce binding between the trolley and crossbar, and heat sink design for cooling of the electrical system. Rather than fixing the deficiencies with a second senior design project, problem-based learning (PBL) exercises were developed to introduce more students to fluid power using the existing gantry crane. The PBL modules were implemented in junior and senior Mechanical Engineering courses including Mechatronics, Fluid Mechanics, and Heat Transfer. After the PBL activities, direct assessment with a common rubric was used to evaluate the quality of problem solutions and student surveys were used to qualitatively assess the effectiveness of the PBL experience. The assessment results indicate that the PBL activities contributed to student learning both on concepts introduced in class and on problem solving skills which required synthesis of material from class.

This paper presents an experimental study of flow evaporation in non-uniform microchannels, demonstrating the ability to provide a stable flow of evaporated fluid for energy conversion and chip cooling applications. Two mechanisms are proposed to stabilize the internal flow evaporation. The first mechanism is to establish a temperature gradient along the channel to separate the room temperature inlet fluid from the steam exit flow. The second mechanism is to change the direction of the surface tension forces acting on the meniscus to fix its position along the channel. To achieve this, shaped channels are formed of contractions and expansions with varied wall angles. The device consists of a silicon wafer with through-etched complex microchannels, that is anodically bonded to a glass wafer on each side. Inlet and exit holes for the fluid are machined in the glass wafers. Water is forced through the chip while it is heated on the exit side of the three layer chip. The qualitative nature of the two-phase flow along the shaped channels is observed through the glass cover wafer, for different flow rates and wall temperatures. The temperature gradient achieved with different thickness of channel walls shows agreement with the modeling results. Also, the benefit of having multiple expansions in the channels was demonstrated. By using these two mechanisms the onset of water evaporation was fixed along the channel. This will lead to the development of adequate two-phase flow micro heat exchangers.

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