Flow Distribution In Channels Research Articles

Bionic optimization for cooling structure of GaN HEMTs inspired by leaf vein structure

Inspired by the leaf vein structure, this article proposes cooling structures with tapered contracting manifold and leaf vein feature, to optimize the cold plate structure for high heat flux gallium nitride high electron mobility transistors (GaN HEMTs). The correlation between the fluid flow distribution in channels and the temperature uniformity of chips is investigated. The performance of the designed Bionic Structures is compared with that of the traditional Parallel Structure in terms of fluid flow characteristics, heat transfer characteristics and comprehensive performance. Results show that the Bionic Structures with tapered contracting manifold and leaf vein feature improve the fluid flow uniformity by up to 44.1 % and the temperature uniformity of chips by up to 65.0 %, while reducing the pressure drop by up to 24.7 % and the convective heat transfer resistance by up to 32.8 %. The comprehensive performance is also significantly improved. This article demonstrates the great potential of bionic cooling structure for breaking through the thermal management limit of high heat flux power chips.

Hydrostructural Phenomena in a Wastewater Screening Channel with an Ascendable Sub-Screen Using the Arbitrary Lagrangian–Eulerian Approach

Wastewater invariably accumulates soluble and insoluble waste and requires treatment at a wastewater treatment plant (WTP) to become reusable. The preliminary screening of insoluble waste occurs through a wastewater screening mechanism (WSM) before entering the WTP. The present study computationally investigates the impact of a WSM, comprising a main screen, sliding sub-screen, and rake, on channel flow distribution, deformation, and stresses. Various sub-screen configurations, fully and partially lowered, are examined. The fluid–structure interaction between sewage water and the WSM was solved using the arbitrary Lagrangian–Eulerian approach. Unlike similar studies in the past which have been conducted in 2D, the present study considers the 3D design and thus captures a greater complexity of the WSM assembly. The velocity distribution inside the channel, structural deformation, and von Mises stresses of WSM components were analyzed for a range of inlet velocities at different stages of the screening process. The results reveal that a fully lowered sub-screen with an inactive rake ensures a uniform flow through the WSM, while a partially lowered sub-screen induces persistent flow separation. Structural analysis reveals significant deformation in the upper mid-region of the sub-screen and fluctuating deformations in the rake, accompanied by elevated von Mises stresses. The study serves as a design guideline for manufacturing and operating a WSM, ensuring the prevention of unfavorable stress and deformation in the WSM and the WTP.

유동 가시화를 이용한 PCHE의 유동분배에 관한 실험적 연구

PCHE, Printed Circuit Heat Exchanger, is widely used for industrial applications with increasing demand in extreme environments. As interest in hydrogen for future fuel is increased, the interest in PCHE is also increased. In this study, we focused on the flow distribution in channels of PCHE. Although flow distribution has been employed a lot of times for decades, there are few reliable studies based on experimental results that can be directly applied in actual industrial fields. Here, we introduce experimental results about flow distribution by flow visualization. Effects of flow rates and the verticality are addressed to clarify the difference in distribution. When the flow rate is low, the flow speed difference between channels is not significantly large. If it becomes larger, the difference becomes large. Moreover, when inlet and outlet pipes are installed at a slight angle, back flow is observed. The speed profile of the tilted case in high flow rate is not easily predicted. Although the tilting angle looks very small, the measured speed profile can be completely different.

Numerical study on the flow maldistribution characteristics of a plate heat exchanger

Flow maldistribution problem in the plate heat exchanger precludes the intended ideal performance. In this study, the flow and temperature distribution impact on flow maldistribution depending on the channel number of the plate heat exchanger were investigated by computational fluid dynamics (CFD) analysis to identify the maldistribution flow effects of the plate heat exchanger and suitable installation location of the measurement device. Channels located at the end of the header are confirmed to have excessive flow, while the flow rate of working fluid in channels near the inlet pipe is relatively low. The channel flow distribution degraded with an increase in Ntot,ch. In plate heat exchangers withNtot,ch = 20, 40, and 60, γf,ch was 18–21.3 %, 24.3–25.9 %, and 29.1–31.2 %, respectively, whenG¯ch = 100–500 kg/(m2·s). A jet flow occurs when the fluid flows from the channel to the outlet header; therefore, the velocity and temperature distribution inside the outlet header is not uniform. However, the mass flux and temperature distribution in the pipe become uniform owing to the swirl flow. Thus, γvm=93.5 %–95.3 % and MATD = 0.26–0.33 °C whenG¯ch = 100–500 kg/(m2·s) at DPL = 10, which indicates that the velocity and temperature distribution of fluids become uniform over that point.

Research on heat transfer and pressure drop performance of plain plate fin-and-tube oil cooler

According to the characteristics of large number of sets and large size differences in the plain plate fin-and-tube oil cooler, a set of heat exchange units including a baffle is selected as the characteristic structure, and the heat transfer and pressure drop characteristics are numerically simulated and experimentally studied. The simulation results are compared with the experimental data to study the effects of changes in shell-side flow rate and plate-fin spacing on the heat transfer and pressure drop characteristics in the oil cooler. The results indicate that as the shell-side flow rate increases, both the heat transfer coefficient and pressure drop increase. When the shell-side flow rate is 1.6 m3/h, the heat transfer effect is the best; when the plate-fin spacing is 4 mm, the channel flow distribution is the most uniform, therefor the heat transfer effect is the best. The relationship curve between shell-side Nu number and Re number of the plain plate fin-and-tube oil cooler is obtained by fitting. It is used to explore the flow field and heat transfer characteristics inside the multi-layer small-spacing plain fin structure, which is instructive for optimizing its internal structure.

Modelling of fluid flow distribution in multichannel ceramic membrane: Application to the filtration of produced water

Multichannel ceramic membranes are considered as one of the most promising process for separating oil and particles from produced water. The aim of this work is to show (i) the influence of the permeability contrast between the support of the membrane and the selective layers and (ii) the impact of fouling on the fluid flow distribution for different ceramic membrane geometries. A theoretical model is developed to simulate the filtration of a simplified produced water (PW) matrix in both circular and square multichannel ceramic membranes.Under several assumptions, the problem can be considered as first two-dimensional. Therefore, the model consists of Darcy's equation for fluid flow in the porous medium coupled with a resistance-in-series model for selective layer fouling. These are solved in the porous medium domain, which consists of a multichannel membrane composed of a large macroporous region (i.e. the support of the membrane) and several small microporous regions (i.e. the selective layers of the channels).The results show that, for filtration with pure water, the contribution of the channels to total permeate flux can be drastically non-homogenous and depends on the permeability ratio between the macroporous and the microporous regions. For membranes with low permeability contrast, the contribution of the inner channels is negligible. For filtration of PW, fouling also significantly influences the pressure fields and spatial distribution of permeate velocity among the channels. It progressively homogenizes the flux in all the channels through the accumulation of suspended matter, which decreases the permeability of the selective layers in the channels filtering the highest fluxes. After a certain time of filtration, all the channels are working at the same flux but at a permeability significantly lower than the initial one. A higher permeability contrast between microporous and macroporous media is thus one of the key parameters impacting, at the beginning, the fluid flow distribution in channels. Then, these initial filtration conditions could contribute to fouling mitigation, by limiting high local fouling velocities induced if local flux exceeds the sustainable flux values in some areas.

NUMERICAL STUDY OF THE EFFECT OF AREA OF MANIFOLD AND INLET/OUTLET FLOW ARRANGEMENT 0N FLOW DISTRIBUTION IN PARALLEL RECTANGULAR MICROCHANNEL COOLING SYSTEM

Parallel microchannels have been widely used in cooling of compact electronic equipment due to large contact area with liquid and availability of large mass of fluid to carry away heat. However, understanding of flow distribution for microchannel parallel system is still unclear and there still lack of studies give a clear pictures to understand the complex flow features which cause the flow maldistribution. Generally, the geometrical structure of the manifold and micro channels play an important role in flow distribution between micro channels, which might affects the heat and mass transfer efficiency, even the performance of micro exchangers. A practical design of exchanger basically involves the selection of an optimized solution, keeping an optimal balance between gain in heat transfer and pressure drop penalty. A parallel microchannels configurations consisting inlet and outlet rectangular manifold were simulated to study flow distribution among the channels were investigated numerically by using Ansys Fluent 14.5. The numerical results was validated using existing experimental data and showed a similar trend with values 1% higher than experimental data. The influence of inlet/outlet manifold area and inlet/outlet arrangement on flow distribution in channels were carried out in this study. Based on the predicted flow non-uniformity value, 𝜙, Z- type flow arrangement exhibits higher value of 𝜙, which is 8%, followed by U-type, 2.6% and the I-type, 2.49%. Thus, a better uniformity of velocity and temperature distributions can be achieved in I-shape flow arrangement. The behavior of the flow distributions inside channels is due to the vortices that occurred at manifold. Besides comparing the pressure drop for case 1(D1) and case 2(D2), it is worth to mention that, as the area of inlet and outlet manifold decrease by 50%, the pressure drop is increasing about 5%. However, the inlet/outlet area of manifold on velocity and fluid temperature distributions was insignificant.

Flow and thermal analyses of regenerative cooling in non-uniform channels for combustion chamber

Regenerative cooling is considered one of the most prospective thermal protection techniques in hypersonic vehicles. However, the non-uniform flow distribution in the cooling channels has the potential to lead the combustion chamber to overheat. In the present study, the regenerative cooling channels designed in a variety of non-uniform patterns are proposed. The conjugated flow and heat transfer behaviors of coolant and solid combustion chamber are numerically investigated. The scaling factor (Ω), i.e., height/width ratio, channel inlet/outlet manifold configuration, and relative angle (ω) of the inlet/outlet tube on flow and heat transfer characteristics are discussed. The numerical prediction is in reasonable agreement with previous numerical and experimental data. Results reveal that the basic configuration (Ω=1) contributes dramatic non-uniform flow in the channels near the inlet tube. The non-uniformity becomes more evident in the case of ω=60°. The scaling factor (Ω) exerts stronger influence on flow distribution in channels and the reformed case of Ω=0.9 for Ch-1–4 gives the best flow uniformity and temperature distribution. The flow distribution is less sensitive to the outlet manifold than the inlet manifold.

Turbulent heat transfer past a sudden expansion with a porous insert using a nonlinear model

ABSTRACTThis work presents numerical investigations for turbulent flow and heat transfer in a backward-facing step with and without porous inserts. Two classes of the model were employed, namely linear and nonlinear turbulence closures. The entire set of transport equations was discretized by means of the control volume method and the system of algebraic equations obtained was relaxed using the SIMPLE (Semi Implicit Pressure-Linked Equations) method. Results were first validated against the experimental data and the simulations follow experimental values and trends. Computations further indicated that when using the porous insert, the size, shape, and length of the recirculating region were drastically reduced in addition to being pushed toward the channel exit, leading eventually to a complete bubble suppression for thicker inserts. A more permeable medium gave better results in quickly suppressing the circulatory motions. By including porous inserts in the channel, turbulence generated due to the shear inside the recirculating region was damped, whereas high levels of k were concentrated within the permeable structure. Large variations for the skin friction factor along the bottom wall were also smoothed out by placing inserts, spanning from a typical distribution for an unobstructed back-step flow to a standard parallel channel flow distribution as the inserts got ticker. On the other hand, at the upper wall, flow pushed toward the top surface gave rise to a sudden increase of the skin friction factor, which was later stabilized downstream the flow. Heat transfer analysis followed showing damping for Nu at the bottom wall as the thickness of the porous substrate was increased. Overall, the thickness of the insert played a dominant role in changing the final flow and heat transfer characteristics rather than the porosity or permeability of the porous material. Finally, this work indicated that the sudden increase of Nu around the reattachment point, known to be undesirable in many practical situations for causing additional thermomechanical loads on the surface, may by avoided by the use of a porous obstacle past the back-step.

Study of core flow distribution for small modular natural circulation lead or lead-alloy cooled fast reactors

Small modular natural circulation lead or lead-alloy cooled fast reactor (LFR) is a potential candidate for LFR development. It has many attractive advantages such as reduced capital costs and inherent safety. The core flow distribution calculation is an important issue for nuclear reactor design, which will provide important input parameters to thermal-hydraulic analysis and safety analysis. The core flow distribution calculation of a natural circulation LFR is different from that of a forced circulation reactor. In a forced circulation reactor, the core flow distribution can be controlled and adjusted by the pump power and the flow distributor, while in a natural circulation reactor, the core flow distribution is automatically adjusted according to the relationship between the local power and the local resistance feature. In this paper, a non-uniform heated parallel channel flow distribution calculation code was developed and the comparison study between the channel method and the CFD method was carried out to assess the exactness of the developed code. The core flow distribution analysis and optimization design for a 10MW natural circulation LFR was conducted using the developed code. A core flow distribution optimization design scheme for a 10MW natural circulation LFR was proposed according to the optimization analysis results.

Effect of Flow Distribution to the Channels on the Thermal Performance of the Multipass Plate Heat Exchangers

Over last two decades, plate heat exchangers (PHEs) have presented themselves as a viable alternative to the conventional shell and tube heat exchangers in the process and power industries. The thermal theory available for plate heat exchangers in the literature largely works on the assumption of equal flow in each channel. However, it is well known that the distribution of fluid from port to channel in PHE is far from being uniform. The present study brings about this port to channel flow distribution effect on the thermal behavior of multipass plate heat exchangers. The variation of the heat transfer coefficient due to flow variation from channel to channel has also been taken into consideration. Heat exchangers with both equal and unequal passes of the fluids have been studied. The results indicate that the flow maldistribution severely affects the performance of plate heat exchangers, and multipassing can act as an important tool to reduce the deterioration in performance due to maldistribution. The results show that with a low number of passes, the increase of velocity of fluid may be counterproductive in terms of heat transfer enhancement. Also, adding plates in order to increase the heat transfer surface may not be effective due to an increase in flow maldistribution. The correlations for 1-1, 1-2, 2-2, and 2-3 pass plate heat exchangers with the maldistribution index as a parameter are also presented.

Experimental and analytical investigations on core flow distribution and pressure distribution in the outlet header of a PHWR

The Indian pressurised heavy water reactor (PHWR) comprises of a number of horizontal channels containing nuclear fuel bundles. The parallel channels are connected to headers at the inlet and outlet through feeder pipes. The flow distribution between the channels of the PHWR is an important aspect of the design of the core and primary heat transport system. A correct determination of the channel flow distribution is required to evaluate the thermal safety margin. The estimation of the design flow rate in the channels is based on the assumption that the pressure in each header is uniform. Moreover, in the reactor core only sixteen channels out of the 306 channels are provided with flow metering elements. An analytical model has been developed to enable a better prediction of the flow distribution between the different channels and the variation of pressure in the outlet header. The flow rates in the channels and the pressure distribution in the outlet header are predicted from the solution of two first order differential equations (pressure-flow equation set) involving the flow rate and the pressure difference across the headers. The outlet header is divided into four basic combining flow manifolds and an iterative procedure has been adopted to satisfy the flow and pressure conditions at each junction point between two successive manifolds by solving the pressure-flow equation set for each manifold. The model adopted for the analytical studies has been validated against experimental data. The experimental studies were carried out on a one-fourth scale model to determine the channel flow distribution in the reactor core and the pressure distribution in the outlet header at different flow rates, with (i) both the steam generating (SG) branches open and (ii) one of the steam generator branches closed. Air was used as the test fluid. The measured flow distribution in the test model has been compared with the theoretically obtained flow distribution. The pressure variations in the outlet header for different modes of pump operation are compared. The analytical results for the flow distribution are in excellent agreement with the experimental data. Analysis is also performed for the prototype reactor header using the validated model for different modes of pump operation. The analytically obtained results are compared with the plant data.

Modelling and measurement of gas flow distribution in corrugated sheet structured packings

A mathematical model and calculation procedure are developed for the gas flow distribution in channels formed between tightly packed, corrugated, unperforated metal sheets. The model is a discrete cell model based on averaged mass, momentum and energy balance equations for each of numerous crossings of gas flow channels, with characteristic friction factors for gas inlet, bulk zone and wall zone as model parameters, which can be easily obtained from pressure drop measurements for each type and size of structured packing. The model enables prediction of velocity profiles leaving an element or packing layer consisting of segments of unperforated, structured packing. It is also suited for perforated packings which under operating (wetted) conditions function as a closed surface packing.