A microchannel heat sink, integrated with pressure and temperature microsensors, is utilized to study single-phase liquid flow forced convection under a uniform heat flux boundary condition. Utilizing a wafer–bond-and-etch-back technology, the heat source, temperature and pressure sensors are encapsulated in a thin composite membrane capping the microchannels, thus allowing experimentally good control of the thermal boundary conditions. A three-dimensional physical model has been constructed to facilitate numerical simulations of the heat flux distribution. The results indicate that upstream the cold working fluid absorbs heat, while, within the current operating conditions, downstream the warmer working fluid releases heat. The Nusselt number is computed numerically and compared with experimental and analytical results. The wall Nusselt number in a microchannel can be estimated using classical analytical solutions only over a limited range of the Reynolds number, Re: both the top and bottom Nusselt numbers approach 4 for Re < 1, while the top and bottom Nusselt numbers approach 0 and 5.3, respectively, for Re > 100. The experimentally estimated Nusselt number for forced convection is highly sensitive to the location of the temperature measurements used in calculating the Nusselt number.

The design, fabrication and characterization of an intergrated thermal microsystem are presented. The system, consisting of thin-film heater elements, an array of microchannels, pressure and temperature microsensor arrays, is designed for studying forced convection heat transfer under well-controlled thermal boundary conditions. Utilizing a wafer bond and etch back technology, the heat source, pressure and temperature sensors are separated from the fluid flow by a membrane only 1.5 µm in thickness, thus allowing experimentally improved approximation of classical boundary conditions, especially the uniform heat flux at the solid/fluid interface. A three-dimensional simulation model is constructed for numerical analysis to complement the experimental characterization of the liquid single-phase flow in this microsystem. Pressure and temperature distributions, for various operating conditions, have been measured and compared with computed profiles. The agreement between the experimental and numerical results confirms that, though not ideal, the heat flux boundary condition is nearly uniform.

A thermal microsystem, integrated with pressure and temperature microsensors, is fabricated to study single-phase liquid flow forced convection under uniform heat flux boundary condition. Standard micromachining techniques were utilized in the fabrication of the integrated microsystem. Utilizing a wafer-bond-and-etch-back technology, the heat source, temperature and pressure sensors are separated from the fluid flow by a 1.5 mum thick composite membrane; thus, allowing experimentally good control of the thermal boundary conditions. A three-dimensional numerical simulation model has been constructed to investigate the heat flux distribution. The results show that upstream the cold working fluid absorbs heat, while downstream the warmer working fluid releases heat. The Nusselt number is calculated based on the computations, which are compared with analytical and experimental results. The wall Nusselt number in a microchannel can only be estimated by conventional analytical solution in a limited Reynolds number range. The estimated Nusselt number for forced convection is found to be highly dependent on the location of the temperature measurements.

While most prior studies on Enterprise Application Integration (EAI) and Web Services adoption have focused on large counterparts, this research recognizes the importance of these technologies, and realizes the difficulties involved in their effective adoption by Small to Medium Sized Enterprises (SMEs). The aim of this paper is to study as to whether the resources constraints (time, finance, and expertise) a real obstacle to emerging integration technologies (EAI and Web Services) adoption in SMEs. The paper initially conceptualizes a model to support the analysis and proposes a research issue for validation. A qualitative multiple case study approach was considered as an appropriate research methodology to test the conceptual model. Findings obtained from the empirical study suggest that: (1) expertise, time and financial constraints is a real obstacle to SMEs’ integration technologies adoption, and these constraints are important influential parameters affecting SMEs’ adoption decision; and (2) SMEs’ resource constraints are closely related to financial and expertise availability, time and expertise flexibility, and manager’s attitude on managing time and financial issues. Based on this, the proposed conceptual model is revised. Finally, concluding section of the paper also outlines limitations and provides future research directions.

A thermal microsystem with integrated heaters, pressure and temperature microsensors, has been fabricated to study local temperature and pressure fluctuations occurring in forced convective boiling in microchannels. The observed two-phase flows can be classified into two patterns: oscillating liquid/vapour interface and liquid burst flow; both leading to unsteady temperature and pressure fields. FFT power spectra of the measured signals are correlated with flow visualizations to analyse the two-phase flow modes. The dominant fluctuation frequency of each flow mode increases with input power; and, under similar conditions, the frequency of the periodically oscillating liquid/vapour interface is higher than the dominant frequency of the liquid bursts. Dimensional analysis is performed to derive empirical correlations for the dimensionless fluctuation frequency, Strouhal number, for both flow patterns.

A microchannel heat sink, integrated with pressure and temperature microsensors, is fabricated to study convective boiling under uniform heat flux boundary condition. Utilizing a wafer bond and etch back technology, the heat source, temperature and pressure sensors are separated from the fluid flow by a membrane only 1.5μm in thickness; thus, allowing good control of the thermal boundary conditions. Temperature and pressure distributions for various power levels and flow rates are measured while, simultaneously, the flow patterns are recorded. Single-phase flow results, compared with numerical simulations, confirm that the heat flux boundary condition is indeed nearly uniform. The sensor arrays, particularly for two-phase flow, provide the spatial and temporal dependence of both the temperature and pressures fields.

A thermal microsystem, integrated with pressure and temperature microsensors, is fabricated to study convective boiling under nearly uniform heat flux boundary condition. The temperature and pressure distribution along the microchannel is measured correspondingly. The pressure increases with input power when two phase flow develops. A pressure peak appears at the location of liquid-vapor interface region. The transient temperature and pressure fluctuation is also measured. The dominant frequencies of the temperature and pressure fluctuation are the same values at the liquid-vapor interface region and this dominant frequencies increase with input power. Simultaneously, the qualitative visualizations of the evolving flow patterns have been correlated with the quantitative temperature and pressure measurements.

Forced convection boiling in microchannels is studied experimentally under the uniform heat flux boundary condition. Several microchannel heat sinks with integrated temperature sensors, spanning two orders of magnitude in height 5-500 mu m, have been fabricated with designed nucleation sites on the bottom surfaces. The microchannels are capped by a glass wafer to monitor bubble activity using video microscopy. Distributed micro heater elements on the device backside are used as the heat source, while the working liquid flow rate is adjusted using a syringe pump. The boiling curves of the device temperature as a function of the input power have been measured for various flow rates. The curves for increasing and decreasing heat flux exhibit a hysteresis loop, while the conditions corresponding to the onset of nucleate boiling and critical heat flux (CHF) are clearly distinguishable. The activity of nucleation sites as well as the ensuing bubble dynamics, from incipience to departure, is found to depend on the channel height. The critical size above which a nucleation site is active, along with three aspects of bubble dynamics, namely growth rate, departure size and release frequency, have been characterized experimentally and proper control parameters have been identified.

The height effect on bubble dynamics in a microchannel is experimentally studied. We reported that the critical size for a nucleation site to be active increases linearly with the channel height. However, once a bubble is formed, its evolution from incipience to departure can also be channel-size dependent. Thus, various microchannel heat sinks have been fabricated, about 5-10 /spl mu/m in height, with integrated temperature sensors utilizing Si-to-glass anodic bonding technology. Nucleation sites have been formed on the microchannels bottom silicon surface in order to ensure regular bubble formation, while the sensors allow continuous monitoring of the wall temperature. The microchannels are capped by a glass wafer; hence, it is possible to record the bubble activity using video equipment. The three aspects of bubble dynamics: growth rate, departure size and release frequency have been characterized experimentally, and proper control parameters have been identified.

Forced convection boiling in microchannels is studied experimentally under uniform heat flux boundary condition. Several microchannel heat sinks, ranging in height between 5 and 20 /spl mu/m, have been fabricated using standard micromachining techniques with nucleation sites varying in size etched at the channels bottom surface. The heat flux was provided by a heater integrated at the device back side, while constant water flow rate was supplied by a syringe pump. Boiling curves of device temperature as a function of the input power have been measured for a variety of conditions. The points corresponding to the onset of nucleate boiling and critical heat flux (CHF) are clearly distinguishable. Furthermore, the boiling curves for increasing and decreasing heat flux exhibit a hysteresis loop. The activity of the nucleation sites is found to depend on the channel height. The critical size, above which nucleation sites are active, increases exponentially with the microchannel height, asymptotically approaching a theoretical value.

The characterization of a micro heat pipe system, integrated with a local heater, temperature and capacitive microsensors is presented. Two liquid charging schemes based on a single hole, requiring vacuum environment, and a pair of holes, utilizing capillary forces are compared. Taking advantage of the great disparity between the dielectric constants of liquids and gases, capacitance sensors are used for void fraction measurements. Since it is difficult to control the phase content of a liquid–gas mixture in a micro heat pipe, a calibration technique based on a traveling water–air interface due to evaporation is introduced. The integrated sensor capacitance for pure water is found to depend on measurement frequency, temperature and ion concentration, exhibiting trends that are different from previous reports. The measured temperature and void fraction distribution along the heat pipes are consistent with the two-phase flow patterns recorded during the microsystem operation.

An integrated microchannel heat sink consisting of shallow, nearly rectangular microchannels has been fabricated using standard micromachining techniques to highlight the effects of the micrometer sized channel shape on the evolving flow patterns and, consequently, on the thermal performance of the microsystem. An integrated heater serves as a local heat source, while an array of micro thermistors is used for temperature distribution measurements. The working fluid, DI water, is pressurized through the microchannels for forced convection heat transfer studies. Boiling curves for different flow rates have been recorded and analyzed based on the visualized flow patterns. Local nucleation, including bubble formation and bubble dynamics, is documented and found to be negligible. Although detected, in contrast with triangular microchannels, annular flow is observed to be unstable. Instead, the dominant flow pattern is an unsteady transition region connecting an upstream vapor zone to a downstream liquid zone with an average location depending on the input power. A physical mechanism based on the force balance across the vapor–liquid interface, and the development of a restoring force, is proposed to explain the flow visualization results.

The design, fabrication and characterization of an integrated microsystem consisting of micro heat pipes, a micro heater, temperature and capacitive microsensors are presented. CMOS-compatible micromachining techniques are utilized to fabricate the micro heat pipe device capped by a nitride layer. In order to allow clear visualization of flow patterns during operation, the process has been modified using a glass wafer to cap the heat pipes. Temperature distributions along the micro heat pipes have been measured using the microsensors located next to the heat pipes. The capacitive microsensors have been used to measure the void-fraction, taking advantage of the large difference between the dielectric constants of the liquid and vapor phases.

An integrated microchannel heat sink consisting of shallow, trapezoidal microchannels has been fabricated using standard micromachining techniques to highlight the effects of the micrometer sized channel shape on the evolving flow patterns and, consequently, on the thermal response of the system. An integrated heater provides the local heat source, while an array of temperature microsensors is used for temperature distribution measurements. DI water, serving as the working fluid, is pressurized through the microchannels for forced heat convection. Temperature plateaus are observed in the boiling curves, corresponding to the latent heat of phase change of the working fluid from liquid to vapor phase. The evolving two-phase flow patterns have been recorded and analyzed using high-speed camera. Bubble formation, growth and detachment at specific nucleation sites have been observed. Annular flow mode has been found to be unstable in trapezoidal channels. Instead, a highly unsteady transition region from upstream vapor phase to downstream liquid phase flow is developed, and the average location of this region depends on the input power.

Abstract A micro heat sink comprising 10 microchannels integrated with a local heater and a temperature microsensor array has been fabricated on a silicon wafer using standard micromachining techniques. A glass wafer was anodically bonded to the silicon wafer in order to cap the trapezoidal microchannels, about 14μm in depth and 120μm in average width. DI water was pressurized through the heat sink serving as the working fluid. Boiling curves of device temperature, at a few locations along the centerline, were measured as a function of the input power. In contrast to previously reported results, the boiling plateau associated with latent heat of phase change from liquid to vapor was detected. The transparent glass ceiling allowed the visualizations of flow phenomena dominated by surface effects. The classical bubble dynamics of bubble formation, growth, and detachment was observed at relatively low input power. However, this mode was completely suppressed at moderate power levels. Further increase of the input power resulted in a clear separation between the upstream vapor and the downstream liquid. The average location of the vapor/liquid interface shifted downstream with the input power, and near the critical heat flux condition the interface was located at the channel outlet. Thus, the added heat resulted in increased quality of the two-phase flow rather than increasing the mixture temperature.

A thermal microsystem, integrated with pressure and temperature microsensors, is fabricated to study convective boiling under uniform heat flux boundary condition. Utilizing a wafer bond and etch back technology, the heat source, temperature and pressure sensors are separated from the fluid flow by a membrane only 1.5 mu m in thickness; thus, allowing experimentally good control of the thermal boundary conditions. Temperature distributions for various input power levels have been measured to obtain the boiling curves. The conditions corresponding to the onset of two phase flow, with boiling plateau, and the critical heat flux (CHF) are clearly distinguishable. Simultaneously, timedependent pressure signals have also been recorded. In single liquid phase flow, the pressure is constant with time. However, in two phase flow, strong pressure fluctuations occur with certain frequencies. The qualitative visualizations of the evolving flow patterns have been correlated with the quantitative temperature and pressure measurements.