Pressure drop and optimization meta-models for arbitrary low-height pleated filter shapes and flowrates

Journal of Mechanical Science and Technology - This study delivers equations useful for low-height pleated fibrous filter design: two pressure drop equations and one set of optimum design equations...     

Development of a new simulation model of spin coating process and its application to optimize the 450 mm wafer coating process

A new one-dimensional simulation model to predict the surface coverage and average thickness of coating films obtained from spin coating processes is developed adopting moving mesh technique. The effects of initial profile, dispensed volume, solvent vapor pressure, relative humidity and initial viscosity on the coating film geometry are investigated numerically. The initially dispensed volume, solvent vapor pressure, initial viscosity and wafer rotation speed are found to be effective parameters to control the surface coverage and average film thickness. The relations between spin coating process parameters and the film geometry parameters, surface coverage and average film thickness, are derived from the new model. It is found that the photoresist solution consumption per a given size of chips could be reduced by optimizing the operation parameters.     

Round-robin test on thermal conductivity measurement of ZnO nanofluids and comparison of experimental results with theoretical bounds

Ethylene glycol (EG)-based zinc oxide (ZnO) nanofluids containing no surfactant have been manufactured by one-step pulsed wire evaporation (PWE) method. Round-robin tests on thermal conductivity measurements of three samples of EG-based ZnO nanofluids have been conducted by five participating labs, four using accurate measurement apparatuses developed in house and one using a commercial device. The results have been compared with several theoretical bounds on the effective thermal conductivity of heterogeneous systems. This study convincingly demonstrates that the large enhancements in the thermal conductivities of EG-based ZnO nanofluids tested are beyond the lower and upper bounds calculated using the models of the Maxwell and Nan et al. with and without the interfacial thermal resistance.     

Automated processes of estimating the heating and cooling load for building envelope design optimization

An automated process is developed to perform dynamic energy simulations for several hundreds or thousands of the conditions required to examine the influence of dozens of building envelope design factor changes on the heating and cooling load of a building. The developed process was applied for 10-factor 128-treatment fractional factorial design, it was experimentally confirmed that the simulated preparation period, which took about 1 day to complete via manual operation, took about 10 min using the automated process; this represents a 400-fold increase in speed. It is shown that the processing time savings obtained with the automation process increase exponentially as the number of design factors considered increases. The regression equations between heating and cooling loads and design factors are analyzed with a multi-objective optimization algorithm to obtain the Pareto-front, which is a combination of optimal design factors that can be used to minimize the building heating and cooling loads and to provide building designers with viable alternatives by considering the building energy performance.     

Microfluidics of nano-drug delivery

After a brief review of microfluidics, a bio-MEMS application in terms of nanofluid flow in microchannels is presented. Specifically, the transient 3-D problem of controlled nano-drug delivery in a heated microchannel has been numerically solved to gain new physical insight and to determine suitable geometric and operational system parameters. Computer model accuracy was verified via numerical tests and comparisons with benchmark experimental data sets. The overall design goals of near-uniform nano-drug concentration at the microchannel exit plane and desired mixture fluid temperature were achieved with computer experiments considering different microchannel lengths, nanoparticle diameters, channel flow rates, wall heat flux areas, and nanofluid supply rates.Such micro-systems, featuring controlled transport processes for optimal nano-drug delivery, are important in laboratory-testing of predecessors of implantable smart devices as well as for analyzing pharmaceuticals and performing biomedical precision tasks.     

Automated thermal conductivity measurement algorithm for the transient hot wire method

Even after more than 20 years of research, establishment of a nanofluid thermal conductivity enhancement mechanism is impeded by differences in research results among researchers. Thermal conductivity measurement results may differ considerably depending on the selection of the temperature history range used to estimate thermal conductivity. This range should be selected carefully considering factors such as the hot wire specifications and the applied heat, but comparisons between researchers’ choices have rarely been reported.

To resolve this problem, herein we present an algorithm that estimates test fluid thermal conductivity based upon the inputs of various hot wire specifications, wire resistance history, and applied voltage. We confirm that the proposed algorithm gives more accurate and precise results comparing with the cases of selecting the range based on solely on the determination coefficient R² and is effective in eliminating data affected by the errors. The proposed method for fluid thermal conductivity measurement is robust to differences in measurement conditions including operator skill level, applied voltage, and hot wire specifications. It is expected that the discrepancies noted across the results of different research groups would be greatly reduced by adopting the proposed method.

     

Impact analysis of natural convection on thermal conductivity measurements of nanofluids using the transient hot-wire method

Significant deviations between published results have been reported measuring the effective thermal conductivity of nanofluids with the transient hot-wire method (THWM). This may be attributed to a poor selection of the temperature data range, which should meet the following conditions. The start time should be chosen after the conductive heat flux delay time, while the end time should be selected before a crossover point when natural convection becomes significant. Considering an EG-based 1.06 vol.% ZnO nanofluid, the thermal conductivity was measured to increase by 5.4% over that of the base fluid.     

Model for predicting the critical size of aggregates in nanofluids

Stable suspension of the nanoparticles in the base fluids is inevitable to have the nanofluids be operated properly. Here we report the theoretical model to find the critical size of aggregates in nanofluids for the first time. The concept of relaxation time τ _r is adopted, which reflects the probability of encountering the particles. The hydrodynamic diameter of the aggregates in nanofluids must be kept below the critical size to be stably suspended, which is in good agreement with the experimental results.     

Performance analysis of ammonia absorption GAX cycle for combined cooling and hot water supply modes

An ammonia Generator–Absorber heat eXchange (GAX) absorption cycle with combined cooling and hot water supply modes is developed in this study. This paper proposes new multi-modes GAX cycles which function in three different modes (case 1, case 2 and case 3) of cooling and hot water supply with one hardware (ammonia/water GAX absorption heat pump), and finds the best cycle for performance improvement by the parametric analysis. The key parameters are the outlet temperature of hot water and the split ratio of the solution. It is found that the COP_c values for case 1, case 2 and case 3 are 60%, 42% and 87% of COP_c for case 0, respectively, which is the standard cooling mode for the conventional GAX cycle. From the viewpoints of hot water supply, case 1 gives the best performance. However, during the summer season when the cooling mode is the primary purpose rather than the hot water supply, case 3 is the most desirable cycle. The split ratio of the solution should be carefully determined depending on the primary application of the modified GAX cycle; cooling or hot water supply applications. It is also recommended that the optimum design values of UA_SCA and UA_HCA for case 3 should be less than those for case 1.