Inlet Volume Research Articles

Multi-parameter optimization for micro-channel heat sink under different constraint conditions

This paper, for specific chips geometrics of 10mm∗10mm, the micro-channel heat sink is designed and optimized. Three dimensionless variables are defined as width ratio of chip to channel pitch (N), the width radio of channel to pitch (I) and aspect ratio (αc). The optimal designs of MCHS based on minimum thermal resistance is performed at one or more constraint conditions of fixed inlet volume flow rate, fixed pressure drop and fixed pumping power. Results show the thermal resistance can reach smaller for fixed volume flow rates, but the pressure drop even increased to 350kPa unacceptable in application. Similarly results are found for the fixed pressure drop or pumping power. Multiple constraint conditions are used to optimize channel sizes for a better thermal performance with acceptable pressure drop penalty. An interesting phenomenal is found the best thermal structure can be got of 200ml/min, but not 400ml/min under pressure drop less 50kPa and pumping power less 0.5W, which average temperature of 200ml/min is 308.4K, but 312.17K of 400ml/min. The required flow rate is from 146 to 225ml/min and channel structures are N from 92 to 110, I=0.6 and Hc=350μm under limitations of pressure drop of 30–70kPa and pumping power less 0.5W.

Heat Transfer and Pressure Drop Simulation of CO2-Hydrate Mixture in Tube

The formation of CO2 hydrate during CO2 transportation presents a complex two-phase flow within tube. A two-dimensional CFD model for CO2 hydrate mixture flow in tube is derived based on the Eulerian multiphase flow modeling approach in which the two phases consist of CO2 gas and CO2 hydrate particles. A coupled Eulerian multiphase and nonisothermal flow model without phase-change is developed based on COMSOL Multiphysics built-in application modes. The model couples the mass, momentum, and energy equations for the two phases to solve the temperature and flow characteristics of the CO2 hydrate mixture flow in tube. CO2 hydrate particles are found to settle down during flow even under high velocity operation. The pressure drop increased linearly with inlet volume fraction from 1.29[Formula: see text]kPa for 0.1–5.2[Formula: see text]kPa for 0.5, and the related overall heat transfer coefficients of the CO2 hydrate mixture computed from the model ranged from 980 to 4000[Formula: see text]W/m2K with variation of CO2 hydrate volume fraction.

Determination of gas length for gas-assisted extrusion forming of polymer melt

To determine the optimal gas length for the gas-assisted etrusion forming of melt, numerical investigations about the gas length on the extrudate swell of melt were performed by using the finite element method. Meanwhile, the geometric model of gas-assistd extrusion forming was established. The full slip boundary condition was used as the gas-assisted condition. Numerical results show that the gas length should be shortened with increasing of the inlet volumme flow rate of melt. In addition, under the given inlet volume flow rate of melt, the extrudate swell ratio, X velocity and shear stress of melt greatly decreases with increasing the gas length. Accroding to the numerical results and experiences reported past time, under the inlet volume flow rate of 0.5cm3/s, the optimal gas lenth of gas-assisted extrusion forming is about 10mm.

Research on simulation and experimental of thermal performance of LED array heat sink

This study presents experimental study and numerical simulation on thermal analysis and design of array heat sink under natural convection conditions. Based on computational fluid dynamics (CFD) method, the thermal performances of LED array heat sink have been studied. The numerical results show that both the average convection heat transfer coefficient and the heat resistance decrease with the increase of the number of fins. The heights of the fins have the same effect on LED array thermal performance with the number of fins. The heating power and horizontal air inlet volumes can lead to the decrease of the thermal resistance and the increase of the average convection heat transfer coefficient. And according to the regression analysis method, the average Nusselt criterion correlations were derived. Furthermore, the numerical results are also compared to the experimental dates, this study suggest that the established mathematical models can be predicted the heat transfer characteristics of this type heat sink.

Hydrological modeling of a detention reservoir: flood control and aquifer recharge

ABSTRACT In this paper, we proposed studying a small urban drainage catchment, named Pilot Basin of Mirassol (PBM) in Natal, RN - Brazil whose outlet is a detention and infiltration reservoir (DIR). The rainfall-runoff transformation processes, water accumulation in DIR and the process of infiltration and percolation in the soil profile until the free aquifer were modeled; and, from rainfall event observations, water levels in DIR, free aquifer water level measurements, and also, parameter values determination, it was able to calibrate and modeling these combined processes. The mathematical modeling was carried out from the use of a distributed rainfall-runoff model, and besides, we developed a model to simulate the soil percolation in an unsaturated porous media. Continuous simulation was run over a period of eighteen months in time intervals of one minute. The generated hydrographs were transformed into inlet volumes to the DIR and then, it was carried out water balance in these time intervals, considering infiltration and percolation of water in the soil profile. As a result, we obtain an evaluation on the storage water process in DIR as well as the infiltration of water, redistribution into the soil and the groundwater aquifer recharge, in continuous temporal simulation. We found that the DIR has good performance in order to storage storm water (floods) and contributing to the local aquifer recharge process.

Unsteady-state methanation of carbon dioxide in a fixed-bed recycle reactor — Experimental results for transient flow rate ramps

The utilization of fluctuating renewable electrical energy in chemical processes necessitates the dynamic operation of chemical reactors. One important example is the methanation reactor in the power-to-gas process, where the electrolysis of water is applied for the production of hydrogen, which can be converted into methane via hydrogenation of carbon oxides. The methanation step might be operated dynamically in order to reduce the storage capacity of hydrogen. Therefore, the unsteady-state behavior of the methanation is investigated in the present work. In particular a fixed-bed reactor with product recirculation is considered in terms of the system stability upon dynamic variations of the inlet flow rate. A systematic three-step study based on a steady-state parameter variation as well as load ramps with and without gas recycle was conducted on a lab-scale test facility. Focusing on a reactor system reaching chemical equilibrium, it was found that the reactor behavior is independent of the load change velocity in the investigated range. During the transient variation of the inlet volume flow rate, the temperature response inside the fixed-bed is decelerated compared to the concentration response. The adaption of the product recirculation allows to stabilize the bed temperature, which is unavoidable for a high conversion of carbon dioxide.

Numerical investigation of EHD effects on heat transfer enhancement and flow pattern of R-134a two phase flow

In this paper the effects of electrohydrodynamics (EHD) on heat transfer enhancement and flow pattern of R134a two-phase mixture, flowing in a horizontal tube, were numerically investigated. A uniform DC electric field was applied through a circular stainless steel rod along the centerline of tube, while the tube was considered as a grounded electrode. The simulations, in order to investigate the EHD mechanism, were performed for a constant heat flux 2000 W/m2, voltages between 0 and 5 kV, inlet volume fractions 65% and 85%, mass fluxes from 30 kg/m2s to 50 kg/m2s and electrode diameters between 1.57 mm and 2.4 mm. These flow conditions correspond to stratified flow. The flow regime redistributions under the applied electric field was obtained. The results show that the steady state condition was occurred at the time about 900 ms. According to the results, enhancement ratio is directly proportional to voltage, and it is reversely proportional to electrode diameter, mass flux and inlet volume fraction.

Measurement of Threshold Image Intensities on Difference of Vascular Model: Effect on Computational Fluid Dynamics for Patient-Specific Cerebral Aneurysm

Threshold image intensity for patient vascular models is determined instinctively. In this study, we used the simple method of threshold resolve to evaluate the effect of threshold image intensity level on computational fluid dynamics (CFD) of patient-specific cerebral aneurysm. This investigation involved five patients with internal carotid aneurysms collected in retrospect between August 2010 and October 2012. In 3-dimensional rotational angiography with digital subtraction angiography (DSA) image data, we set five straight line probe across the parent of the internal carotid artery and deliberate the average profile curve of the image intensity along this line. To determine the threshold image intensity level objectively, we calculated the threshold coefficient Cthre using this profile curve. The effect of Cthre value on vascular model configuration and the wall shear stress (WSS) distribution of the aneurysm was evaluated. Result shows for the inlet area and volume of the vascular model decreased and WSS increased according to the Cthre value increase. In one stage, the pattern of WSS distribution changed strangely and the threshold image intensity level can result reflective effects on CFD. This finding necessary to advance a further understanding of problems in image segmentation and solving the patient-specific aneurysm problems.

Energy and cost optimization of shell and tube heat exchanger with helical baffles using Kriging metamodel based on MOGA

In order to overcome the dependence on empirical correlations and to achieve a more accurate results for modeling the computer response, an improved algorithm combing a Kriging response surface and the multi-objective genetic algorithm (MOGA) for the optimization design of shell and tube heat exchanger with helical baffles (STHXsHB) is proposed in this paper. The helical angles β, baffle overlap proportion e and inlet volume flow rate V are considered as optimization parameters, in which the heat transfer rate and total cost are optimized by multi-objective optimization. The results show that compared with the real solutions of CFD simulation, the optimized results illustrated a good agreement within ±3% error. Therefore, the optimization method is verified to be successful. Besides the obtained Pareto-optimal points show that a small helical angle with 15° and the baffle overlap proportion is equal to 0.25 are beneficial to trade off the heat transfer rate and total cost of STHXsHB. Furthermore, the comparison between the optimum STHXsHB and a conventional shell and tube heat exchanger with segmental baffles (STHXsSB) are carried out. The results show that the comprehensive performances of the optimum STHXsHB are better. The evaluation index PEA and PEB increase by 76.5–91.2% and 69.0–84.5%, respectively. Therefore, it can be concluded that employed helical baffles in the STHXs can obtain a better performance. Moreover, this new method can be used to optimize the STHXsHB and the conclusions are benefit in the design of STHXsHB for energy saving and cost reduction.

CO2 Absorption Characteristics in Ammonia Solution inside the Structured Packed Column

Ammonia has proved an alternative and potential solvent for postcombustion CO2 capture. It is of benefit to the reduction of energy consumption for CO2 capture to clarify the CO2 absorption characteristics in ammonia solution. On the basis of the representative elementary volume method and pseudo-single-liquid model, the computational model of CO2 absorption into ammonia solution in the structured packed column of a pilot CCS plant was developed, in which the gas-phase flow was also taken into account. The modeling and computational methods were validated by comparing with the experimental data from two pilot CO2 absorption towers. The CO2 removal efficiency and volumetric overall mass transfer coefficient were obtained at various inlet CO2 volume fractions, gas flow rates, aqueous ammonia solution flow rates and temperatures, and the ammonia mass fractions. The results show that the absorption process is predominated by the liquid film, so the flow rate and ammonia concentration of the aqueous ammonia so...

관 내 물-토사 혼합물의 이상유동 해석

Torrential rainfall in Korea causes the large amount of water and soil mixture flow into drainage pipes. Soil in the mixture is sedimented in drainage pipes and frequently blocks the pipes, results in flooding in a city. In the present study, the effects of inlet velocity, size of soil particle, and volume concentration of soil in the soil and water mixture on the flow characteristics and the soil distribution inside the pipe were numerically investigated by using the two-phase mixture model. The horizontally located pipe, whose length and diameter are 10 m and 0.6 m, was used in this simulation. With increase of inlet mixture velocity, velocity at the upper part of the tube is higher than that at lower part by 14.9%, and the volume fraction of soil from bottom to 0.2 m of tube decreased subsequently by 4.6%. The distribution of mixture velocity and soil volume fraction is getting uniform with increase of the inlet volume fraction of the soil in the mixture. With increase of size of the soil particle, the soil concentration increased subsequently by 6.6% from bottom to 0.2 m of the pipe, which make significant distortions in velocity distribution in tube.

Optimal input experiment design and parameter estimation in core-scale pressure oscillation experiments

Summary This paper considers Pressure Oscillation (PO) experiments for which we find the minimum experiment time that guarantees user-imposed parameter variance upper bounds and honours actuator limits. The parameters permeability and porosity are estimated with a classical least-squares estimation method for which an expression of the covariance matrix of the estimates is calculated. This expression is used to tackle the optimization problem. We study the Dynamic Darcy Cell experiment set-up (Heller et al., 2002) and focus on data generation using square wave actuator signals, which, as we shall prove, deliver shorter experiment times than sinusoidal ones. Parameter identification is achieved using either inlet pressure/outlet pressure measurements (Heller et al., 2002) or actuator position/outlet pressure measurements, where the latter is a novel approach. The solution to the optimization problem reveals that for both measurement methods an optimal excitation frequency, an optimal inlet volume, and an optimal outlet volume exist. We find that under the same parameter variance bounds and actuator constraints, actuator position/outlet pressure measurements result in required experiment times that are a factor fourteen smaller compared to inlet pressure/outlet pressure measurements. This result is analysed in detail and we find that the dominant effect driving this difference originates from an identifiability problem when using inlet–outlet pressure measurements for joint estimation of permeability and porosity. We illustrate our results with numerical simulations, and show excellent agreement with theoretical expectations.

Effect of non-condensable gas on laminar film condensation of steam in horizontal minichannels with different cross-sectional shapes

In the present study, a 3-D numerical simulation of laminar film condensation of steam in the presence of non-condensable gas is performed in horizontal minichannels with six cross-sectional shapes based on the volume of fluid (VOF) method. Mixture of steam and oxygen enters the channel with uniform temperature, while the inlet volume fraction of oxygen increases from 0% to 3%. It is shown that the existence of non-condensable gas results in significant reduction in the mass transfer rate from vapor to liquid along the interface in the axial direction. And then the heat transfer coefficient of condensation with oxygen is demonstrated to decline sharply compared with that of the pure vapor condensation.

Comparative study on AL2O3 nanoparticle addition on cool storage system performance

Adding nanoparticles almost enhance the thermal transport properties in thermal storage system. Nanoparticles could be used in two manners, the first one with Phase Change Material (PCM) as a nucleation agent to help the fast formation of crystals in solidification process. The second manner with Heat Transfer Fluid (HTF) to enhance the rate of heat transfer through the heat transfer process. In the present study a comparison between adding Al2O3 nanoparticles to either distilled water as PCM, and to aqua ethylene glycol solution of 50% wt as a HTF on the performance of cool storage system.A spherical capsule with 85% filling of its internal volume with PCM is used as a tested platform. A set of experiments to study the effect of adding Al2O3 nanoparticles to HTF at different volume fraction concentrations up to 1% for different HTF inlet temperature and volume flow rates on the solidified mass fraction, surface heat flux and complete solidification time, was performed. Comparing the present results with those for nanoparticles with PCM, it could be concluded that adding the nanoparticles to PCM alone is much beneficial to cool storage system than adding it to HTF alone.

Thermodynamic optimisation of the performance of a parabolic trough receiver using synthetic oil–Al2O3 nanofluid

In this paper, results of a thermodynamic analysis using the entropy generation minimisation method for a parabolic trough receiver tube making use of a synthetic oil–Al2O3 nanofluid as a heat transfer fluid are presented. A parabolic trough collector system with a rim angle of 80° and a concentration ratio of 86 was used. The temperature of the nanofluid considered was in the range of 350–600K. The nanofluid thermal physical properties are temperature dependent. The Reynolds number varies from 3,560 to 1,151,000, depending on the temperature considered and volume fraction of nanoparticles in the base fluid. Nanoparticle volume fractions in the range 0⩽ϕ⩽8% were used. The local entropy generation rates due to fluid flow and heat transfer were determined numerically and used for the thermodynamic analysis. The study shows that using nanofluids improves the thermal efficiency of the receiver by up to 7.6%. There is an optimal Reynolds number at each inlet temperature and volume fraction for which the entropy generated is a minimum. The optimal Reynolds number decreases as the volume fraction increases. There is also a Reynolds number at every inlet temperature and volume fraction beyond which use of nanofluids is thermodynamically undesirable.

Experimental study on the performance of a liquid cooling garment with the application of MEPCMS

As a novel working fluid, microencapsulated phase change material suspension (MEPCMS) exhibits obvious superiority in both heat transfer and temperature control compared with traditional ones. In this paper, extensive experimental study on the performance of a liquid cooling garment (LCG) with the application of this novel working fluid was conducted for future space applications. The main task for a LCG is to efficiently collect, transport and dissipate the metabolic heat produced from the human body. In the experiment, a thermal manikin was employed to simulate the human body, and the performance of the LCG with MEPCMS as the working fluid was evaluated by a variety of aspects such as heat dissipation, temperature control, pump power consumption and thermal comfort under both steady state and transient conditions. Experimental results show that the inlet temperature, mass flowrate and volume concentration of the MEPCMS are three key parameters affecting the performance of the LCG, which can be enhanced significantly by a proper combination of these parameters. Otherwise, the performance of the LCG will deteriorate or even be worse than that using water as the working fluid. When the inlet temperature, mass flowrate and volume concentration of the MEPCMS were selected as 11°C, 200g/min and 20% respectively, the heat dissipation of the LCG was enhanced by up to 26% with no obvious increase of the pump power compared with that using water as the working fluid, the temperature distribution in the human body became more uniform, and the capability of the LCG to adapt large heat load change became stronger. This work helps better understand the performance characteristics and contributes greatly to the design of a LCG with the application of the MEPCMS.

Unsteady Unidirectional Flow of Voigt Fluid through the Parallel Microgap Plates with Wall Slip and Given Inlet Volume Flow Rate Variations

Unsteady Unidirectional Flow of Voigt Fluid through the Parallel Microgap Plates with Wall Slip and Given Inlet Volume Flow Rate Variations

Application and Operating Experience of Sintered Metal Fiber Hot Gas Filters for FCC Unit

A long-term test was performed in a Fluid Catalytic Cracking (FCC) hot gas filtration facility using sintered metal candle filters. The operating temperature and pressure were maximum 550°C and 0.28MPa respectively. Specific particles sampling systems were used to measure the particle size and concentration directly at high temperature. The inlet particles concentration ranged from 150 to 165mg/Nm3. The outlet particles concentration was in the range of 0.71-2.77mg/Nm3 in stable operation. The filtration efficiency ranged from 98.23% to 99.55%. The inlet volume median diameters and the outlet volume median diameters of the particles were about 1μm and 2.2μm respectively. The effects of operating parameters including face velocity, gas cleaning pressure and maximum pressure drop were investigated. Operating experience, optimal operating conditions and cleaning strategies were determined. The results show that sintered metal fiber filters are suitable for industrial applications due to the better performance and higher efficiency observed.

The role of initial flow conditions for sibilant fricative production.

Sibilant fricative sound production depends on the geometric and flow properties of the production system. Nevertheless, few studies deal with the potential impact of flow properties other than the inlet volume flow rate on the noise produced. In this work, an experimental study is presented using a replica based on a reconstructed oral cavity for the phoneme /s/. Initial flow conditions upstream from the sibilant groove are altered by varying the method of air supply. Statistical moments of the initial velocity distribution are characterized using hot-film anemometry and related to spectral features of the radiated acoustic pressure. Discrepancies in the dynamic amplitude (≤25%) and negative spectral slope (≤35%) observed at a constant Reynolds number but different initial upstream flow conditions are of the same order of magnitude as those previously reported in humans. This suggests that consideration of the upstream flow conditions is important in the study of sibilant fricative sound production.

Experimental analysis of the fluid–structure interaction in finite-length straight elastic vessels

Numerous bio-mechanical flow problems are characterized by fluid–structure interaction phenomena. To analyze in detail the impact of fluid–structure interaction on the overall flow structure and the wall motion the oscillating laminar flow in an elastic vessel is experimentally investigated by time-resolved particle image velocimetry and pressure measurements. The vessel deformation amplitude is varied between 0.5% and 6% of the vessel diameter at Reynolds number and Womersley number ranges of 300≤Re≤1000 and 5≤Wo≤10. Motivated by Womersley’s fundamental results for rigid and elastic vessels it is the purpose of this study to extend the discussion to vessels of finite length undergoing high dilatation amplitudes and to provide benchmark data for numerical fluid–structure interaction methods. A detailed discussion of the results of the volume flux distribution, static pressure distribution, rate of change of the diameter, and wall-shear stress distribution is given and evidences a significant effect of vessel deformation on the distribution of the flow quantities. The inlet volume flux distribution excited by the piston pump generates an internal pressure distribution determining the vessel deformation which via the temporal derivative of the diameter change generates a delayed volume flux distribution that is superimposed onto the inlet volume flux. The comparison of the results with comparable rigid pipe flows shows variations in the velocity profile amplitude of up to 10% depending on the phase angle. The vessel elasticity leads to a wall-shear stress reduction during forward flow of up to 20%.