N. Damean

Heat transfer in a MEMS for microfluidics

Paper presents an 1D model for the heat transfer in a limited but significant region of an actuator?sensor structure for the determination of fluid and flow characteristics. As an essential step for the design of this structure, the usefulness of the model in the framework of the structure?s functionality is underlined. In the first part of the work, the main heat transfer mechanisms are detailed by qualitative and quantitative evaluations. The 1D model is derived from the heat rate balance of the region we are interested in. In the second part of the work, we compare the data obtained by simulating the 1D model with the experimental data. Also, some full 3D simulations of the fluid flow and heat transfer are made using a commercial software package. Part of these numerical results are compared with the corresponding experimental data. The modeling errors are discussed for both sets of comparisons. Finally, we comment the merits of the 1D model versus the 3D approach. The results obtained herein might be directly used for various thermally based actuators and sensors for flow control and measurement both in micro and macro world.

Poiseuille number for the fully developed laminar flow through hexagonal ducts etched in silicon

This paper focuses on a main subject encountered in the design process of the hexagonal ducts etched in silicon, namely, the achievement of the Poiseuille number Po for the velocity field of the fully developed laminar flow. The particular shape of the duct is determined by silicon technology. This type of duct is the main part of a structure for the determination of fluid and flow parameters. We develop a procedure for obtaining Po versus the aspect ratio of the hexagonal cross section. The validity of this procedure is proven using different shapes of cross sections. We underline the merit of this procedure, namely, its applicability using a commercial software package in a rather straightforward manner. The results presented in this paper might be adapted for many other situations encountered both in micro and macro world where devices containing ducts having various non-circular cross sections are present.

Velocity field of the fully developed laminar flow in a hexagonal duct

The paper presents a study concerning the velocity field of the fully developed laminar flow in a hexagonal duct. This duct is the main part of an actuator–sensor structure used for the determination of fluid and flow parameters. The particular shape of the duct is determined by silicon technology. The central subject detailed herein is the building of an approximative analytical formula for the velocity field inside hexagonal ducts. We detail two approaches for this subject and we discuss their limitations in the practical circumstances by using the CFD-ACE+ software package for the fluid flow simulation. One approach is based on the point-matching method and another one is based on the generalised integral transform method. The both approaches are offering similar credibility, namely the maximum errors produced by using these formulae are, respectively, 5 and 12% for the middle part of the cross-section where the actuators and sensors are usually placed. The second approach is more suitable for flatter ducts or when the designer is interested in a small central region of the cross-section. The simple applicability of the inferred formulae contrasts with the classical and huge time consuming numerical approaches, these formulae being suitable tools in the design process of the structure operating in the micro-world. The results presented in this paper might be adapted for similar structures operating in the macro-world where devices containing ducts having various non-circular cross-sections are present and where the fully developed laminar flow of the incompressible and Newtonian fluids is concerned.

Measurement concepts: from classical transducers to new MEMS

In this paper a formalization of the measurement concept (mc) is presented. Based on this formalization, a classical measurement concept (cmc) supported by classical transducers is derived. Restrictions and inconveniences of the cmc are exposed when the evaluation of more characteristics is concerned (the so-called multi-measurement process). Using a new measurement concept (nmc) developed in this work, the main drawbacks of the cmc can be removed. The core of the nmc is an actuator–sensor structure. Some basic principles regarding the design of this new structure as a MicroElectroMechanical System (MEMS) are also mentioned. Developing a state-space representation of the classical transducer and the new structure, the practical implementations of both concepts are compared and the superiority of the nmc is proven. Finally, the nmc is illustrated with an example concerning the determination of fluid and flow parameters using MEMS.

NEW NUMERICAL ALGORITHM FOR TEMPERATURE MEASUREMENT BASED ON THE VARIATIONAL APPROACH OF AN OPTIMAL CONTROL PROBLEM

A new numerical algorithm to measure temperatures is presented. Using a numerical computer, it reduces the measurement of the unknown temperature to the variational approach of an optimal control problem. Based on this algorithm, a new device for temperature measurement is built. The principal component of the new device is a rod. The variation of the temperature that is produced near one end of the rod is determined using some temperature measurements in the other end of the rod and the new numerical algorithm that is described in this work. At the same time, some possibilities of practical implementation and a collection of simulations are presented.

A study of fluid flow in a MEMS designed for the determination of fluid and flow characteristics

This paper presents a study on the hydrodynamically developed flow in hexagonal ducts, built as a MicroElectroMechanical System (MEMS) for the determination of fluid and flow characteristics. The design and operation of this structure in the framework of the new measurement concept developed previously requires detailed knowledge about the physical phenomena implied, namely about the fluid flow and heat transfer in the structure. Because the main operation of the structure is taking place in the hydrodynamically developed flow, we develop a procedure for obtaining the Poiseuille number Po versus the shape of the duct. Knowledge of this number is a main step for the design and operation of the structure. The procedure developed herein is applied for the hexagonal ducts that are analysed in other papers and a good agreement is noticed. Main features of the procedure are its applicability to any noncircular duct and the possibility to use a commercial software package. Finally, the next steps for the design of this structure are specified.

A new computer method for temperature measurement based on an optimal control problem

Abstract A new computer method to measure extreme temperatures is presented. The method reduces the measurement of the unknown temperature to the solving of an optimal control problem, using a numerical computer. Based on this method, a new device for temperature measurement is built. It consists of a hardware part that includes some standard temperature sensors and it also has a software section. The problem of temperature measurement, according to this new method, is mathematically modelled by means of the one-dimensional heat equation, with boundary and initial conditions, describing the heat transfer through the device. The principal hardware component of the new device is a rod. The variation of the temperature which is produced near one end of the rod is determined using some temperature measurements in the other end of the rod and the new computer method which is described in this work. This device works as an attenuator of high temperatures and as an amplifier of low temperatures. In fact, it realizes an extension of the standard working range of temperature sensors at very high and very low values. The mathematical model of the device and the computer method are explained in detail and some possible practical implementations and a collection of simulations are also presented.