Baffle Holes Research Articles

Experimental and numerical investigation on energy efficiency improvement of methane/propane added of hydrogen-fueled micro power generation

The micro-thermal power generation presents several challenges including reaction instability, large heat loss, and energy conversion. So, a micro-planar with multi-hole baffle for micro power generation is proposed with C3H8/CH4 blended and reaction sensitivity analyzed. Effects of fuel sensitivities, baffle settings, operating conditions on combustion characteristics and performance of thermal are analyzed. Experimental results revealed the thermal performance of H2-fueled combustion with blended CH4 and C3H8 can be improved, while the H2/CH4/air burning obtains a higher improvement by promoting flame anchoring and reducing heat losses. Thermal reflux and high temperature zones can be generated at appropriate baffle positions and hole sizes to enhance the operating micro-combustor performance. Optimized baffles and CH4 blending ratios significantly improved combustor output power and system efficiency. For instance, the maximum mean radiation temperature of 1347 K can be obtained in combustor C8-0.8 at mc = 25 % and mf = 4.08 × 10−5 kg/s. Meanwhile, micro-thermophotovoltaic (MTPV) system equipped with InGaAsSb cell can achieve a 3.4 W electrical power output and a system efficiency of 3.5 %. It provides solutions for recovering energy from exhaust gases and improving energy efficiency to develop efficient and sustainable micro-energy sources.

Numerical heat transfer study of square duct equipped with novel flapped V-baffles

The paper describes a computational study of heat transfer enhancement inside a square duct with V-shaped flapped baffles located repeatedly on the bottom and top walls for fluid flowing with Reynolds numbers (Re) from 3000 to 21,000. The basic goal of this work is to attain the largest relative Nusselt number (Nu/Nu0) whilst maintaining the highest thermal performance to improve energy savings. A finite volume method was used in the computations, along with the Realizable k‒ε turbulent model. The variable baffle parameters considered first in the current simulation were the relative height/blockade ratio (BR = 0.05−0.2) and the flap angle of the baffle hole (β = 0° − 90°), while the fixed parameters included the attack angle (α = 60°), hole diameter ratio (dR = 0.5), and pitch ratio (PR = 0.5). To accomplish this goal, the previously mentioned parameters providing the best thermal performance were investigated further by extending the values of BR to 0.25−0.3, dR to 0.8 and α to 45°−30°. The simulation results indicate that the jet flowing from the flapped hole, as well as the vortices created by the baffle, can boost heat transfer and friction loss in comparison to the plain duct. In comparison, using a flapped baffle with β > 0° results in less friction loss, a greater thermal enhancement factor (TEF), and a higher Nusselt number than using a baffle with no flap. The first investigation disclosed that for BR = 0.2 and β = 20°, the greatest TEF of 2.19 with Nu/Nu0 of 7.9 times are obtained. The extended study, on the other hand, showed that the highest TEF of roughly 2.49 with Nu/Nu0 of 8.4 times are seen for α = 45°, dR = 0.8, BR = 0.25 and β = 20° at lowest Re. Thus, the flapped baffle provides a significant increase in Nu/Nu0 and TEF over the baffle alone.

Flame and heat transfer characteristics of a micro combustor with multihole baffle-induced inflows for a thermo-photovoltaic application

For an effective thermo-photovoltaic application, the inflow effects on the flame and heat transfer characteristics of micro power generators are numerically investigated in a multihole baffled micro combustor. The flow inside the baffle hole is considered as a circular pipe flow. Various inlet profiles of the micro combustor are obtained by varying the baffle thickness corresponding to the length of the baffle hole. The velocity distribution of the flow past the baffle plate attains an M-shaped (also called saddle-back), a parabolic, or a fully developed profile according to the baffle thickness. For a baffle thickness less than the fuel hole diameter, the inflow of the combustion chamber has an M-shaped velocity profile with two off-center peaks. Vortical motions and lobe-shaped flame are promoted by this type of inlet condition. Combustion characteristics, including flame length, combustion efficiency, heat loss ratio, and preheating effect, are comprehensively examined to evaluate the possibility as an thermo-photovoltaic device. The results indicate that a micro combustor with a thin baffle (bt ≤ 0.1Df ) increases the combustion efficiency and wall heat flux. This suggests that the current baffled combustor can be effectively applied in both micro power generation systems and micro thermal emitters.

Numerical investigation on heat transfer performance of molten salt in shell and tube heat exchangers with circularly perforated baffles

The molten-salt heat exchanger is a critical heat transfer device used in concentrated solar power systems. In this paper, molten salt heat-transfer performance characteristics and flow resistances in shell and tube heat exchangers with perforated baffles with a notch height of 0.25D (D is the baffle diameter) are simulated. Four opening schemes that use the same opening area (10% of the baffle area) are designed. The numerical results show that the baffle holes can shrink the molten salt flow dead zone significantly and greatly decrease the flow resistance on the shell side at the cost of a slight reduction in the heat-transfer performance. The comprehensive performance of each scheme after opening is higher than that before opening, and the comprehensive performance of Scheme 4 is the best. Next, a genetic algorithm is used to optimize the Scheme 4 opening diameter. The results show that the heat-flux density on the molten-salt side reaches a maximum of 17327 W/m2 when the opening diameter is 2.24 mm. We find that the opening diameter should be maximized to optimize the comprehensive performance at a given pump power. Finally, the data are compared to other correlations. The deviation decreases gradually as the Reynolds number increases. This is because the turbulence enhancement caused by structural change is not substantial at high Reynolds numbers.

Numerical Investigation of the Effect of Muffler Geometry on Engine Performance

Muffler is a part of an exhaust system fitted to IC engines for damping noise and to convey hot gases from the combustion chamber. Several research efforts have been put into the study of muffler. This is due to their significant effects on noise reduction, fuel consumption, efficiency and life span of engine. Good muffler minimizes noise, back pressure and engine fuel consumption. Currently, the price of petroleum products in the global market is high and very unstable. Therefore, conservation of fuel is very important, particularly to the end user. This study seeks to examine the effects of baffle holes on the fluid flow characteristics and forces on the baffle walls. Three muffler models were designed using Autodesk Investor 2015. ANSYS 16.0 was used as the CFD working tools to predict the flow characteristics and forces on the walls. Samples A, B and C were modeled to have 7, 13 and 26 holes, respectively while the diameter of the holes for samples A, B and C were 50, 37.5 and 25 mm, respectively. Navier-Stokes and energy transport equations govern the three muffler models. Muffler sample A displayed the lowest backpressure of 20.235 Pa, average wall temperature of 986.311 K and best fuel efficiency characteristics. Sample B had the lowest forces on the wall while Muffler C has the least advantage when compared with other models. Muffler sample B gave the optimum design characteristic considering fuel consumption engine efficiency and muffler durability.

Design and Testing of a Denucleation and Decortication Device for Lychee

Abstract. An automatic machine for lychee denucleation and decortication was designed to improve lychee processing efficiency and ensure the integrity of the lychee pulp. The main structure and operating parameters of this machine were determined by theoretical analysis and two orthogonal tests. The effects of the denucleation knife diameter, processing speed, and distance during denucleation and decortication were investigated. The denucleation rate, decortication rate, and juice loss rate were evaluated. The results of the processing tests showed that the denucleation rate was 94% when the diameter of the lychee fruit was between 29 and 33 mm, the diameter of the lychee seed was less than 10 mm, the diameter of the denucleation knife was 6 mm, and the processing speed of the denucleation knife was 0.5 m s-1. The decortication rate was 85% when the diameter of the baffle hole was 26 mm and there were eight grooves in the hole, yielding zero distance between the upper end of the decortication rod and the groove during operation. This machine is designed to perform automatic lychee processing, which includes the functions of denucleation, decortication, and lychee pulp separation. The processing speed of the machine is 600 kg d-1. This enhanced output is ten times greater than the output of conventional processing, and significant production costs are saved. Keywords: Decortication, Denucleation, Lychee, Processing, Pulp.

A study on the flow characteristics of butterfly valve with baffles

In the industry, globe valves, which are commonly used to precise control the flow rate along with opening and closing flow in pipes, are technically and economically limited in valve size due to structural instability related to complex internal flow passage. Butterfly valves, on the other hand, have advantages such as low weight and low manufacturing costs, but it is difficult to control the flow rate at an opening angle of 60°or higher and flow is unstable in the case of butterfly valve. Therefore, the purpose of this study is to have characteristics of flow rate of the globe valve that is used in the industry at the same diameter of pipeline and flow stability due to uniformity of flow through the baffle hole by adding 1/2 baffle to butterfly valve. Hole size of baffles were set at 5, 7 and 9 mm and baffles were set at the rear of the butterfly valve. To verify the method of numerical analysis, the results of experimental study were compared with the results of numerical study. As a results, it is confirmed that characteristics of flow rate of butterfly valve with baffle is similar to globe valve in the case of hole size 5 mm. In addition, flow pattern is to be stable by analyzing turbulence energy. Consequently, when applying baffle to butterfly valve, it is possible to reduce the flow unstability and change the flow rate of butterfly valve.

Numerical Simulation and Design Optimization of Baffle Perforations for Better Noise Reduction

An increasing vehicle population always pressurizes to focus on environmental concerns for reduced noise level and harmful emissions. Even though many qualitatively optimized exhaust systems are developed during last two decades, still researchers focus on noise reduction and emission control. Abundant research and development activities are carried out to get a reasonable back pressure drop along with a significant noise reduction in the muffler. The development in computational coding leads to a realistic prediction of flow and acoustic characteristics inside the muffle. Hence the present research work focuses on computational simulation of muffler with single and multi-chambers separated by baffles along with porous pipes. The present work analyses a conventional single baffle muffler configuration and compares the flow behaviour with multi chambers separated by multiple baffle configurations. The shape of the baffle holes is also optimised to get better acoustic performance based on the transmission losses. The flow behaviour and its details are studied inside the muffler to identify the possibility of design improvements. Among the muffler configurations with single and multiple chambers, the overall pressure losses are calculated and compared to get an optimized design with reasonable sound attenuation.

Flame characteristics depending on recirculating flows in a non-premixed micro combustor with varying baffles

For an efficient micro combustor, the introduction of a bluff body has been a major design factor due to favorable effects for flame holding. To investigate the relation between flame characteristics and recirculation patterns originated from bluff bodies, three kinds of the plate-type baffle and the multi-hole baffle are introduced for a micro combustor. In this regard, various simulations using the Reynolds Stress Model (RSM) and the Eddy Dissipation Concept (EDC) of GRI-Mech 3.0 are performed for such micro combustors. The pseudo flame extinction is proposed to determine the undesirable combustion condition and the global equivalence ratio which is one of the most important variables is changed to explore the reacting flows near the unstable combustion of the baffled micro combustors. From the results, it is ascertained that wall recirculation, center recirculation, and their mixed flows are variously formed depending on the baffle configuration inside the combustor due to the different baffle blockage. These features are largely connected to the extension of flammable range and the spatial development of flame zone which determines the efficient combustion or flame extinction. Under the same operating condition, combustion characteristics of flame length, maximum temperature, and combustion efficiency are comparatively discussed for plate-type baffles and multi-hole baffle. From the probability distributions of the local equivalence ratio, the plate-type baffle shows a unique role according to its location in the micro combustor like inducing the fuel-lean or fuel-rich mixture. And, it is found that the recirculating flows near the fuel stream produce a more effective combustion than those near the air streams. Also, the key features of flame shape and recirculating flows are examined at near the extinction condition and those are carefully compared for the premixed and non-premixed combustors. Finally, the baffle configuration giving the swirling flow structure is discussed and a flame stability diagram is obtained for the baffled micro combustor. So, the overall change of flame pattern and flammable range of the baffled micro combustor is identified depending on the baffle hole size.

Investigation of baffle configuration effect on the performance of exhaust mufflers

Using baffles in exhaust mufflers is known to improve their transmission loss. The baffle cut ratio should affect the muffler performance analogous to a shell-and-tube heat exchanger. To the authors’ knowledge, there is no previous assessment reported in literature of the effects that the baffle cut ratio configuration has on acoustic response and back pressure. This investigation presents a parametric study on the effect of baffle configuration on transmission loss and pressure drop predicted. The effect of (i) the baffle cut ratio and baffle spacing, (ii) the number of baffle holes, and (iii) the hole distribution for their effect on transmission loss was investigated. Results show that decreasing the baffle cut ratio tends to increase the transmission loss at intermediate frequencies by up to 45%. Decreasing the spacing between muffler plates was shown to enhance the muffler transmission loss by 40%. To assess the baffle effect on flow, the OpenFoam CFD libraries were utilized using the thermal baffle approach model. Baffles were found to cause sudden drop in fluid temperature in axial flow direction. The outlet exhaust gases temperature was found to decrease by 15% as the baffle cut ratio changed from 75% to 25%.

Acoustic behaviour analysis and optimal design of a multi-chamber reactive muffler

A two-dimensional analytical approach is developed to study the acoustic behaviour of a multi-chamber reactive muffler. The value of the transmission loss is obtained by matching the acoustic pressure and the particle velocity across the interfaces between different domains in the muffler. The analytical approach is validated by experimental results. Unlike the transfer matrix method, with this approach the acoustic behaviours can be studied above the first cut-off frequency of the muffler. Next, the effects of several structural parameters on the transmission loss value are invetigated, including the radii of the baffle holes, the inlet and the outlet, as well as the lengths and the radii of the expansion chambers. The variations in these parameters lead to quite large changes in the value of the transmission loss of the multi-chamber reactive muffler. Then, these parameters are chosen as the variables for the optimal design of the muffler, where the objective is the average transmission loss value between 1000 Hz and 3000 Hz. The results show that the objective value increases from 23.3 dB to 54.9 dB during optimization. The analytical approach in this paper can be used for analysis and optimization of the multi-chamber reactive muffler to reduce the noise effectively and efficiently in various applications.

Thermal Hydraulic Performance in a Solar Air Heater Channel with Multi V-Type Perforated Baffles

This article presents heat transfer and fluid flow characteristics in a solar air heater (SAH) channel with multi V-type perforated baffles. The flow passage has an aspect ratio of 10. The relative baffle height, relative pitch, relative baffle hole position, flow attack angle, and baffle open area ratio are 0.6, 8.0, 0.42, 60°, and 12%, respectively. The Reynolds numbers considered in the study was in the range of 3000–10,000. The re-normalization group (RNG) k-ε turbulence model has been used for numerical analysis, and the optimum relative baffle width has been investigated considering relative baffle widths of 1.0–7.0.The numerical results are in good agreement with the experimental data for the range considered in the study. Multi V-type perforated baffles are shown to have better thermal performance as compared to other baffle shapes in a rectangular passage. The overall thermal hydraulic performance shows the maximum value at the relative baffle width of 5.0.

NUMERICAL ANALYSIS OF CAVITATION SUSCEPTIBILITY FOR STEAM GENERATOR INTEGRAL PREHEATER TUBES

A new tube degradation mechanism was observed in a recirculating steam generator (SG) with an integral preheater tube at the clearance gap between the tube and the preheater baffle. The general pattern of the damage and material composition in the degraded region suggested that the degradation was cavitation erosion. Cavitation erosion occurs when vapour bubbles exist or form in the flowing liquid and then these bubbles collapse violently in the vicinity of a solid wall. The bubbles collapse when they contact water that is sufficiently subcooled, i.e., below the saturation temperature. In the clearance gap between the tube and the preheater baffle, secondary fluid flow exists due to the pressure difference across the baffle plate. Meanwhile, heat transfer occurs from the primary-side fluid to the secondary-side fluid within this clearance gap, driven by the primary-to-secondary temperature difference. Factors such as the tube position in the baffle hole and fouling may influence the local flow and heat transfer conditions and can cause subcooled boiling that results in cavitation. This paper presents a numerical analysis of flow and heat transfer phenomena to determine the factors contributing to cavitation erosion of tubes in the preheater of a recirculating SG. The analysis used the THIRST code for a 3-dimensional thermalhydraulic simulation of steam generator and the ANSYS Fluent® code for detailed calculations of flow and heat transfer in the clearance gaps. A detailed temperature distribution in the gap was obtained using this analysis to determine the regions where subcooled boiling could occur by comparing the local fluid temperature with its saturation temperature. The susceptibility to cavitation was found to increase with increased inclination (i.e., tilt) and eccentricity (i.e., off-centre) of the tube in the baffle plate gap, and increased fouling on baffle plate surfaces. This methodology could be applied to analyze the cavitation susceptibility for other preheater types with this “tube to baffle plate” gap, as these preheaters might have conditions where boiling followed by the rapid condensation of the steam bubbles are present.

STUDY ON THE CORROSION MECHANISM OF T2 COPPER CONDENSER TUBE UNDER THE HUMID ENVIRONMENT

During the maintenance of two years, T2 copper tube in a heat exchanger has leaked, it can be deduced that the residual water and volatile water vapor would play an important role in leakage. By SEM, OM, stereo microscope observation, it was found that serious corrosion happened on the surface of copper in the gaps constituted by copper tube and stainless steel baffle holes, and perforation occurred in a few locations. Wetting experiments show that the gap formed between the T2 copper tube and the baffle hole wall is small enough that it could produce siphon liquid film, which could connect the copper tube surface and baffle hole. Therefore there is a difference of oxygen supply between the copper tube outer surface and the copper tube in the gap site, the outer surface of copper tube becomes oxygen–rich zone and the copper tube in the gap site oxygen–poor zone. Potential monitoring results show that the potential of the external surface of copper tube with an oxide is higher than that of copper in the gap site leading to a galvanic cell formed between them. The surface of copper in the gap site is anode region and the external copper tube surface is cathode region. The differences of oxygen supply combined the effect of the galvanic cell leads to the severe localized corrosion of copper tube in the gap site.

A Real-Time Directed Routing Protocol Based on Projection of Convex Holes on Underwater Acoustic Networks

The directed routing protocol ends in failure when it faces a situation of the destination node with a very low velocity in a sparse ad hoc network so that none of nodes exist in its forwarding zone. Illuminated by BFDREAM and ZONER, the paper firstly proposes a novelty routing protocol that is fairly immune to forwarding failure through projecting the present source node on the boundaries of convex baffle holes of underwater acoustic networks in deep sea. Compared with DREAM and BFDREAM, the experimental results show our protocol achieves a great improvement in decreasing the propagation delay and reducing quantities of the non-effect information. So the new protocol may have a bright application prospect in deep sea acoustic networks.

An Underwater Acoustic Routing protocol based on Hole Projecton

The directed routing protocol ends in failure when it faces a situation of the destination node with a very low velocity in a sparse ad hoc network so that none of nodes exist in its forwarding zone. Illuminated by BFDREAM and ZONER, the paper firstly proposes a novelty routing protocol that is fairly immune to forwarding failure through projecting the present source node on the boundaries of baffle holes of underwater acoustic networks in deep sea. Compared with DREAM and BFDREAM, the experimental results show our protocol achieves a great improvement in decreasing the propagation delay and reducing quantities of the non-effect information. So the new protocol may have a bright application prospect in deep sea acoustic networks.

Optimization of Six Strand Tundish Based on Flow and Temperature

In this paper the fluid flow and temperature are used together to optimize the 40 tons six strand tundish. Fluid flows in a six strand tundish have been investigated with physical modeling, then steady, three-dimensional temperature fields inside the six strand tundish are obtained. The physical modeling experiments give two optimal integrated tundish structural parameters of baffle holes. From the further study of temperature fields, the tundish should be optimized in the structural parameters of baffle holes in the condition of height 300mm, angel 30° and diameter 20mm.

A Numerical Study on Heat Transfer and Friction in Rectangular Channel with Inclined Perforated Baffles

A three dimensional numerical study has been applied to predict the turbulent fluid flow and heat transfer characteristics for the rectangular channel with different types of baffles. Four different types of the baffles are used. The inclined baffles have the width of 19.8 ㎝, the square diamond type hole having one side length of 2.55 ㎝, and the inclination angle of 5o. Reynolds number is varied between 23,000 and 57,000. The SST k -ω turbulence model is used in the present numerical study. The validity of the numerical results is examined with the experimental data. The numerical results of the flow field depict that the flow patterns around the different baffle type are entirely different and it significantly affects the local heat transfer characteristics. The heat transfer and friction factor depend significantly on the number of baffle holes. It is found that the heat transfer enhancement of baffle type Ⅱ (3 hole baffle) has the best values.

Microfluidic characteristics of a multi-holed baffle plate micro-reactor

As part of a larger project aiming at development of a miniaturized hydrogen generator for small mobile/onboard fuel cell applications, a series of experiments was conducted on a novel micro-reactor to examine the effectiveness of its design in promoting the mixing of reactant agents. The reactor is essentially a tubular vessel fitted with a multi-holed baffle plate mounted on a central tube. The mixing phenomenon within the micro-reactor was studied using the micro-PIV (micro-particle image velocimetry) flow visualization technique. Experiments were conducted on a 1:1 scale replica of the reactor. Results indicate that the application of the multi-holed baffle plate considerably improves the mixing performance of the reactor when compared with a simpler co-axial jet tubular reactor. However, the geometrical characteristics of the baffle plate and central tube are found to have dramatic impacts upon the flow structure and mixing patterns within the reactor. Hence, the optimization of the reactor geometry is required to achieve the desirable mixing performance. For the range of Reynolds numbers studied here, the optimum reactor geometry is achieved when the central tube and baffle holes are of similar diameters and baffle holes are located half way between the stream-wise axis and the reactor wall.

Single- and multi-hole baffles—a heat transfer and fluid flow control for hydrothermal growth

Hydrothermal solution growth is an important technique to grow high-quality single crystals. An autoclave, a closed cylindrical low-carbon steel vessel, is used to grow the large size crystals. A baffle located at the median height divides an autoclave into two chambers. Previous numerical studies indicate that the buoyancy-driven flow within an autoclave is very sensitive to the temperatures on the wall established by the heating. Baffles are required to establish the conditions for growth of high quality single crystals. This paper presents a numerical study of the effects of various baffles on the fluid flow and temperature fields in an industry-size autoclave. A wide range of baffle area openings for a single-hole baffle from 2 to 25%, together with five multi-hole baffles, is investigated. Computational results indicate that changing the baffle hole opening and the number of holes on a baffle are effective ways to control the temperature uniformity in the growing chamber. With a single-hole baffle, a smaller opening leads to a weaker flow field and a more uniform temperature profile. A multi-hole baffle establishes a more uniform temperature in the upper chamber than a single-hole baffle of the same area opening. The number of holes of a multi-hole baffle shows significant effects while the hole arrangements, however, affect the thermal condition only in the near-baffle region.