Design and fabrication of a cross flow micro heat exchanger

A cross flow micro heat exchanger was designed to maximize heat transfer from a liquid (water-glycol) to a gas (air) for a given frontal area while holding pressure drop across the heat exchanger of each fluid to values characteristic of conventional scale heat exchangers. The predicted performance for these plastic, ceramic, and aluminum micro heat exchangers are compared with each other and to current innovative car radiators. The cross flow micro heat exchanger can transfer more heat/volume or mass than existing heat exchangers within the context of the design constraints specified. This can be important in a wide range of applications (automotive, home heating, and aerospace). The heat exchanger was fabricated by aligning and then bonding together two identical plastic parts that had been molded using the LIGA process. After the heat exchanger was assembled, liquid was pumped through the heat exchanger, and minimal leakage was observed     

地源热泵地热换热器模拟设计软件的研制

为了更好的进行地源热泵地热换热器的设计,且设计时能够方便地使用所需的参数信息,从而有效地利用相关的数学模型进行复杂的计算,采用Delphi 7开发了地源热泵地热换热器模拟设计软件,实现了各种参数的快速准确输入,并在该软件中集成DeSTII软件,对建筑负荷进行动态模拟.该软件能快速的进行模拟计算和设计计算,计算结果根据不同类型在Exoel中分别以表格和曲线图的形式显示,为地热换热器的准确设计提供了有效的数据参考,大大提高了设计的效率和准确性.     

Concentration-dependent viscous mixing in microfluidics: modelings and experiments

In microfluidic mixing, great attention has been devoted to the structural design to enhance mixing efficiency. However, the influence of the variant viscosity in the mixing process is rarely discussed due to the practical challenges originated from the strong and complex couplings between species concentration and other fluid properties such as density, viscosity and diffusion coefficient. In this work, a group of coupling relationships among concentration, density, viscosity, as well as diffusion coefficient are introduced to accurately simulate the mixing process with a viscous flow involved. Compared with the traditional linear approximation, the new approach is more suitable to simulate the concentration-dependent viscous mixing in microfluidics. Furthermore, a planar passive micromixer is designed to validate the coupling approach from both modeling and experiment perspectives. By comparing experimental and numerical results, it turns out that the coupling approach achieves higher accuracy than the traditional linear approximation. In addition, four derived models are experimentally tested and numerically simulated by adopting the new method. The results of each model reach a good agreement between modeling and experiment.     

An optimal analysis of radiated nanomaterial flow with viscous dissipation and heat source

Microsystem Technologies - The present work explores the analytical study of nanofluid flow above a stretching medium with the heat source and viscous dissipation. Additional radiative effects are...     

CFD simulation and optimization of ICEs exhaust heat recovery using different coolants and fin dimensions in heat exchanger

In this paper, finned type heat exchangers with different fin dimensions in the exhaust of a gasoline engine are modeled numerically for improving the exhaust energy recovery. RNG k-ε viscous model is used and the results are compared with available experimental data presented by Lee and Bae (Int J Therm Sci 47:468–478, 2008) where a good agreement is observed. Also, the effect of fin numbers, fin length and three water-based nanofluid coolants (TiO₂, Fe₂O₃ and CuO) on the heat recovery efficiency are investigated in different engine loads. As a main outcome, results show that increasing the fin numbers and using TiO₂-water as cold fluid are the most effective methods for heat recover. Furthermore, an optimization analysis is performed to find the best fins dimensions using response surface methodology.     

Numerical simulation for thermal response test performance in closed-loop vertical ground heat exchanger

In this study, a series of numerical analyses was performed in order to evaluate the performance of full-scale closed-loop vertical ground heat exchangers constructed in Wonju, South Korea. The circulating HDPE pipe, borehole and surrounding ground formation were modeled using FLUENT, a finite-volume method (FVM) program, for analyzing the heat transfer process of the ground heat exchanger system. Two user-defined functions (UDFs) accounting for the difference in the temperature of the circulating inflow an...     

Investigation of lubricant depletion under a continuous heat source using molecular dynamics simulation

Microsystem Technologies - In this study, a model for investigating lubricant depletion in heat assisted magnetic recording slider/disk system was developed using molecular dynamics simulation. The...     

Fouling detection in a heat exchanger: A polynomial fuzzy observer approach

The paper presents new results on state estimation of nonlinear systems based on a fuzzy polynomial Takagi–Sugeno representation. Using sum of squares tools and some matrix properties, conditions to compute the gains of the observers can be obtained easily. Then, the results are applied on the detection of the fouling occurring in a counter flow heat exchanger, which involves many polynomial terms. Simulations and a comparison with previous approaches show the interest of the approach.     

Mathematical theory of compressible,viscous, and heat conducting fluids

We develop a mathematical theory of compressible, viscous, and heat conducting fluids based on the concept of weak solutions and the second law of thermodynamics. We derive suitable a priori estimates and show the weak sequential stability property for the complete Navier–Stokes–Fourier system.     

Comparison and application of DDC algorithms for a heat exchanger

In recent years, several algorithms for Direct Digital Control (DDC) have been proposed in literature. Although some of these, such as PID or cascade controllers, are very commonly used in industrial applications, the more recent ones like optimal state feedback controllers using an observer or parameter adaptive controllers have rarely been applied to a real plant. The primary difficulty behind this application has been perhaps the lack of testing such algorithms on a pilot plant. Moreover, there has been no serious attempt to make a comparative study of the merits of such algorithms for an existing plant under actual operating conditions. In this paper, seven DDC algorithms are applied to the temperature control of a heat exchanger. These algorithms are: PID, cascade, compensation (pole assignment), deadbeat, half-proportional, adaptive and optimal state feedback controller using an observer. The system performance and sensitivity with respect to changes of the plant parameters, disturbances and set point variations are investigated for the heat exchanger using these algorithms. The results indicate that the more sophisticated algorithms, e.g. optimal state feedback, compensation and adaptive controllers, requiring more computer time and memory, yield relatively less improvement when applied to a low-order plant than do the simple algorithms such as PID or cascade. It was deduced that the PID controller with anti-windup is the most suitable one.     

Numerical simulation of a compressible turbulent boundary layer over a conductive wall with line heat source

A conjugated problem of supersonic turbulent flow over a conductive solid wall with an embedded line heat source has been investigated as a model of a separation detector and skin friction gage. The 2-D Navier-Stokes equations for compressible fluid, including a two layer eddy viscosity model, are solved simultaneously with the heat transfer equation for the solid, written in general coordinates. The effect of the interface boundary condition on the stability of the implicit scheme of the flow field has been checked. A careful investigation of the effect of heat source strength, solid and fluid conductivity and Mach and Reynolds numbers on flow and temperature fields has been performed. The results of this investigation may be used to design an optimal gage with a minimum influence on the flow field.     

One-dimensional simulation of nitrogen dielectric barrier discharge driven by a quasi-pulsed power source and its comparison with experiments

Parallel-plate nitrogen dielectric barrier discharge (DBD) driven by a quasi-pulsed power source (60 kHz) is simulated using a fully-implicit 1D self-consistent fluid modeling code. Simulated discharged currents of gap distances (0.5, 0.7 and 1.0 mm) agree very well with measured data; while simulated discharged currents of wider gap distance (1.2 mm) fail to reproduce the measured data. It is found that the discharge mode is homogeneous Townsend-like for the former case; while it is filamentary-like for the latter case based on the experimental observation. These findings demonstrate that previous numerical studies showing mode transition by changing the gap distance may require further investigation.     

A micromachined piezoelectric tactile sensor for an endoscopicgrasper-theory, fabrication and experiments

Present-day commercial endoscopic graspers do not have any built-in sensors, thus, the surgeon does not have the necessary tactile feedback to manipulate the tissue safely. This paper presents the design, fabrication, testing, and experimental results of a micromachined tactile sensor, which can be integrated with the tips of commercial endoscopic graspers. The prototype sensor consists of three layers. The top layer is made of micromachined silicon with a rigid tooth-like structure similar to the present-day endoscopic grasper. The bottom layer is made of flat Plexiglass serving as a substrate. Packaged between the Plexiglass and the silicon is a patterned Polyvinglidene Fluoride (PVDF) film. The proposed sensor exhibits high sensitivity, a large dynamic range, and a high signal-to-noise ratio. Through experimental results, it is shown that the magnitude and position of an applied force can be determined from the magnitude and slope of the output signals from the PVDF sensing elements. Structural analysis is also performed using the finite-element method, and the results are compared with the experimental analysis. The advantages and limitations of this sensor are also reported. A discussion of how the design of the sensor can be integrated with the design of an endoscopic grasper is also presented     

MEMS-based solid propellant microthruster design, simulation, fabrication, and testing

A new design concept of solid propellant microthruster is proposed for micropropulsion applications. Modeling and simulation have been performed before the fabrication of the microthrusters using MEMS technologies. At sea level, the predicted thrust magnitudes range from 0.76 mN to 4.38 mN and the estimated total impulses range from 1.16/spl times/10/sup -4/ N/spl middot/s to 4.37/spl times/10/sup -4/ N/spl middot/s using HTPB/AP/AL as the propellant. In space, the predicted thrust magnitudes range from 9.11 mN to 26.92 mN and the estimated total impulses range from 1.25/spl times/10/sup -3/ N/spl middot/s to 1.70/spl times/10/sup -3/ N/spl middot/s. Single microthruster, microthruster layers and arrays have been successfully fabricated. Preliminary testing for microcombustion is conducted to verify the feasibility of the novel design. Continuous combustion has been achieved after igniting the solid propellant and successful production of thrust has been verified by the microthruster displacement.     

Structural optimization as a harmony of design, fabrication and economy

The main requirements of load-carrying engineering structures are safety, producibility and economy. The role and importance of fabrication constraints and costs is shown in the case of a compression tubular strut, a tubular truss of parallel chords and a welded stiffened square plate. The evaluation of optimal versions of these structures shows that, neglecting the fabrication constraints and costs, the design cannot result in up-to-date solutions.     

Fuzzy model-based fault detection and diagnosis for a pilot heat exchanger

This article addresses the design and real-time implementation of a fuzzy model-based fault detection and diagnosis (FDD) system for a pilot co-current heat exchanger. The design method is based on a three-step procedure which involves the identification of data-driven fuzzy rule-based models, the design of a fuzzy residual generator and the evaluation of the residuals for fault diagnosis using statistical tests. The fuzzy FDD mechanism has been implemented and validated on the real co-current heat exchanger, and has been proven to be efficient in detecting and isolating process, sensor and actuator faults.     

Design, simulation, fabrication, and characterization of a PMMA tunneling sensor based on hot embossing technique

Polymethyl methacrylate (PMMA) was chosen to fabricate highly sensitive tunneling sensors due to its extremely low cost and quick machining by hot embossing. The structure of an all-PMMA-based membrane vertical tunneling sensor platform was synthesized by ANSYS. The system characteristics and feedback system were evaluated with MatLab SimuLink. The first all-PMMA-based membrane tunneling transducers were produced by hot embossing replication with silicon masters. The fabricated tunneling sensors have presented a tunneling barrier height of 0.17 eV, a sensitivity of 26 V/g, and a dynamic range of 1.5 mg, which demonstrated competitive performances with lower cost, lighter weight, and easier fabrication processing.     

Physiological effects of a mouth-borne heat exchanger during heavy exercise in a cold environment

A mouth-borne heat and moisture exchanger (HME) was tested. Nine healthy subjects performed an incremental-load cycle ergometry test to exhaustion, breathing once through the HME and once through a similar device without heat-exchange function (control). HME substantially increased inspired gas temperatures and decreased expired gas temperatures measured at the mouth; at 260 W (pulmonary ventilation (VE) approximately 1001 min-1) these changes amounted to + 15 degrees C and -5 degrees C, respectively. The breathing resistance was increased by HME but remained well within tolerable levels even during severe exercise. This was reflected in the subjective assessments of breathing resistance and breathing discomfort which, at any given workload, were rated similarly in the HME and control conditions. Also, time to exhaustion as well as oxygen uptake and VE at a given workload were unaffected by HME. That even at high pulmonary ventilations HME provided a good heat-exchange function while keeping breathing resistance relatively low suggests HME to be a useful aid for individuals suffering from cold-induced bronchospasm.     

Artificial neural network control of a heat exchanger in a closed flow air circuit

This paper experimentally investigates the control of a heat exchanger in a closed flow air circuit. The temperature inside the test section of the test facility has been maintained at a set value by variation of air flow rate over the heat exchanger tube surface and the water flow inside the heat exchanger tubes. The neural network based control has been implemented in a Labview platform and compared with the PID control. The performance of the controller has been investigated for multiple changes in set points and under externally imposed disturbance. The neural network based control has higher speed of response and the steady-state error for the neural network control has a smaller average value than that of the PID control. The control action based on the neural network technique shows less oscillation in comparison to that of the PID based control. Dual actuations, i.e. both air flow and water flow control, have better performance than that with single actuation, i.e. either air flow or water flow control. Both the ANN and PID based control are equally robust in the presence of externally imposed disturbance.