Lower Baffle Research Articles

Research on a new designed upward turning comb of escalator

Abstract Escalator is an important transportation method for people in their daily life. The comb fixed at the entrance and exit is an important component of the escalator. Its function is to facilitate the transportation of passengers and prevent the escalator from being damaged by foreign matters to a certain extent. In order to avoid harm to passengers caused by the comb, the end of the comb should be made of easily broken material traditionally such as plastic and aluminum to ensure that the object can be released when clamped. This greatly increases the loss of comb and the repair time of maintenance personnel and leaves potential safety hazards. The article researches a new designed upward turning comb of escalator. The device comprises comb plate, mounting base, guide rod, spring, comb teeth, rotating shaft, upper baffle, chute, notch, mounting hole, long hole, guide hole, lower baffle, positioning block and arc push block. Compared with the prior technology, this new comb has the advantages of simple structure, convenient operation, repeated use, difficult to damage.

Joint improvements of radar/infrared stealth for exhaust system of unmanned aircraft based on sorting factor Pareto solution

In order to reduce the radar cross section (RCS) of the unmanned aircraft while suppressing its infrared signature, a comprehensive design method (CDM) based on sorting factor Pareto solution is presented. The physical optics and physical diffraction theory are used to evaluate the electromagnetic scattering characteristics of the aircraft, and the Monte Carlo and ray tracing method are used to evaluate the infrared radiation intensity of the exhaust system. CDM is used to evaluate and screen each individual in each offspring, and the design parameters and sub-models of the aircraft exhaust system are continuously improved. The results show that the exhaust port model, lower baffle and nozzle height are the main factors affecting the RCS indicators, nozzle stages, exhaust port model, lower baffle and outer width make the main contribution to infrared radiation suppression. The presented CDM is efficient and effective in enhancing the radar/infrared integrated stealth performance of the aircraft.

Mixed design of radar/infrared stealth for advanced fighter intake and exhaust system

With the continuous development and enhancement of anti-stealth technology, fighters will be increasingly threatened by joint detection of radar and infrared detectors. To improve the overall stealth performance of the aircraft's intake and exhaust systems, a mixed design approach (MDA) is presented to reduce the aircraft's radar cross-section (RCS) and suppress infrared signature. Full factorial design method is used to establish the aircraft model, taking into account the influencing factors of the air intake model, nozzle stages, exhaust port form, lower baffle, center baffle, lateral baffle and nozzle opening width. The physical optics and physical theory of diffraction are used to solve the electromagnetic scattering characteristics of the target, and the Monte Carlo and ray tracing method are used to solve the infrared radiation signature of the system. After comprehensive evaluation and selection of MDA, the RCS mean index and tail RCS index of the optimized aircraft model have been effectively reduced, and the infrared radiation index has also been greatly improved. MDA is effective and efficient in terms of radar/infrared integrated stealth design for the intake and exhaust systems of advanced fighters.

Effect of the inner-surface baffles on the tangential acoustic mode in the cylindrical combustor

Abstract The combustion instability in a propulsion system is a ubiquitous problem. The radial baffles usually installed on the injector faceplate eliminate the combustion instability (acoustic pressure oscillation) in the propulsion system. In this article, the longitudinal baffles are installed on the inner surface of the combustor wall to control the combustion instabilities. The first-order and second-order tangential modes are induced in the experiments. The effects of the parameters of the baffle on the acoustic pressure oscillation in the cylindrical combustor are investigated. The effect of the combustor nozzle on the tangential modes has been systematically investigated. It is concluded that the eigen-frequency and amplitude of the first-order tangential mode decline with the increase in the longitudinal baffle number and height. For the second-order tangential mode, the eigen-frequency and amplitude monotonically increase until a maximum value (four baffles), subsequently decrease with the increase in the baffle number and height. The combustor without the nozzle obtains a lower frequency than that with the nozzle, especially for the low baffle height in the combustor.

Thermal optimization of shell and tube heat exchanger using porous baffles

In this study, total heat transfer rate and pressure drop along a shell and tube heat exchanger (STHX) with 6 porous baffles are numerically investigated. To study the impacts of segmental porous baffles, three values for the permeability (10−9 m2, 10−12 m2, and 10−15 m2), porosity (0.2, 0.5, and 0.8), and baffle cut (25%, 35%, 50%) were considered, and the output parameters were calculated. Low baffle cuts provided the highest heat transfer; however, it generated a considerable amount of pressure drop as well. Although the porosity of 0.2 was superior in terms of heat transfer, higher pressure drop at lower baffle cut is the obstacle to consider it as the optimum value. The data was then utilized to train an Artificial Neural Network (ANN) to characterize the STHX and perform the sensitivity analysis. Baffle cut had the highest impact on the heat transfer as well as pressure drop while the porosity had the least in both by having 5% contribution. Finally, using genetic algorithm (GA), the optimum values for permeability, porosity, and baffle cut are calculated to gain the maximum heat transfer and minimum pressure drop in the system.

Heat and mass transfer of oils in baffled and finned ducts

This analysis intends to simulate the forced-convection and oil flow characteristics in the turbulent regime (Re = 5000-25000) through rectangular-shaped ducts with staggered, transverse, solid, and flat baffle plates. The study is achieved by using a calculation software based on the finite volume method (FLUENT) with selected SIMPLE, Quick, and k-? model. Two various models of baffled ducts are simulated in this analysis under steady flow conditions. In the first model (Case A), a duct with one upper fin and two lower baffles is examined. However and in the second model (Case B), a duct with two upper fins and one lower baffle is treated. The con?tour plots of stream-function, number of Nusselt, and coefficient of skin friction are addressed. As expected, the heat transfer rates raised in the second case (Case B), due to the presence of the lower second obstacle that directs the entire oil current towards the hot upper part of the second duct at very high velocities, resulting thus in enhanced heat transfer rates, especially in the case of high Reynolds number values.

Heat and mass transfer of oils in baffled and finned ducts

This analysis intends to simulate the forced-convection and oil flow characteristics in the turbulent regime (Re = 5000-25000) through rectangular-shaped ducts with staggered, transverse, solid, and flat baffle plates. The study is achieved by using a calculation software based on the finite volume method (FLUENT) with selected SIMPLE, Quick, and k-? model. Two various models of baffled ducts are simulated in this analysis under steady flow conditions. In the first model (Case A), a duct with one upper fin and two lower baffles is examined. However and in the second model (Case B), a duct with two upper fins and one lower baffle is treated. The con?tour plots of stream-function, number of Nusselt, and coefficient of skin friction are addressed. As expected, the heat transfer rates raised in the second case (Case B), due to the presence of the lower second obstacle that directs the entire oil current towards the hot upper part of the second duct at very high velocities, resulting thus in enhanced heat transfer rates, especially in the case of high Reynolds number values.

A New Device used in Selective Withdrawal from Reservoirs and its Effectiveness Verified in Computational Fluid Dynamics

Water intake with fixed height limits the application of selective withdrawal technology in a certain degree. This study proposes a technological idea to install baffles on water intake. Through the rotation of upper and lower baffle, poor water layer can be blocked. A Computational Fluid Dynamics (CFD) model for the upper baffle on water intake is constructed. The results show that the baffle installed on the upper part of orifice can reduce the withdrawal layer thickness and flow on the upper part of orifice centre. Thereby, the withdrawal flow on lower part can be indirectly increased. While, baffle length and inclining angle are the important factors to influence the withdrawal layer thickness and flow distribution. Therefore, the adjusting range of selective withdrawal can be economically enhanced by installing baffles on water intake.

Theory and Design of Counter Flow Shell-and-Coil Heat Exchanger for CO2Based Solar Water Heater

A shell type helical tube countercurrent flow heat exchanger was designed, fabricated and tested using CO2 refrigerant material. Helical copper tube was immersed in bulk water tank. Hot CO2 was piped to upper coil baffle and cold CO2 was circulated into collector loop through lower baffle. Cold water was made to enter through lower tap and hot water was taken out from upper tap. Both in/out pipes were inserted from the top and coil tubes from upper and lower sides of water tank. Supercritical thermosyphon operation was achieved by evacuated glass tube solar heat collector using CO2 refrigerant. U shaped copper pipes enveloped in aluminum foil were inserted in evacuated glass tubes to transfer heat under thermosiphon principle to upper header connected to inlet baffle of shell type helical coil heat exchanger. Lower header was connected to heat exchanger helical coil outlet baffle. Solar collector heat raised CO2 refrigerant temperature from 35 to 78C giving temperature difference of 43C. Temperature of CO2 refrigerant at exit from heat exchanger was found to be 40C at surrounding ambient temperature of 36C. Heat exchanger raised the inlet water temperature from 26 to 55C under off water tap condition in about 3 hours. Inlet and outlet temperature difference of heat exchanger was measured to be 27C. We believe system efficiency can further increase if we use the system in mild sunshine cold weather regions duplicating geothermal loop.

A review of the advancements made in helical baffles used in shell and tube heat exchangers

This paper provides a review about the major work done on helical baffles to improve the performance of shell and tube heat exchangers. Some of the major factors affecting the performance of shell and tube heat exchanger are discussed. A comparison between segmental baffles and helical baffles is also presented to show that helical baffles are more advantageous than segmental baffles. In most cases, discontinuous, folded, sextant helical baffles, 40° baffle inclination angle as well as low baffle spacing will give the best results when integrated in some combination, whereas continuous helical baffles eliminate dead regions. Moreover, sealing strips are more likely to improve the performance of shell and tube heat exchangers with continuous helical baffles.

Buoyancy-Induced Heat Transfer in a Trapezoidal Enclosure with Offset Baffles

A numerical study has been conducted to examine the effects on heat transfer of mounting two offset baffles onto the upper inclined and lower horizontal surfaces of trapezoidal cavities. Two thermal boundary conditions are considered. In the first, the short left vertical wall is heated while the long right vertical wall is cooled (buoyancy-assisting mode along the upper inclined surface of the cavity). In the second, the long right vertical wall is heated while the short left vertical wall is cooled (buoyancy-opposing mode along the upper inclined surface of the cavity). For both boundary conditions, computations are performed for several offset baffle heights, four Rayleigh number (Ra) values, three Prandtl number (Pr) values, and two baffle positions (Position I and Position II). In Position I, the lower baffle is offset toward the short vertical wall and the upper baffle is offset toward the long vertical wall of the enclosure, whereas in Position II, the lower and upper baffles are offset toward the long and short vertical walls, respectively. Results reveal a decrease in heat transfer in the presence of baffles, with the rate generally increasing with increased baffle height and Pr. At a given baffle height and Ra, Nussett number (Nu) values are lower in the buoyancy-opposing mode. For both boundary conditions, the highest decrease is achieved in fully partitioned enclosures.

Natural Convection in a Trapezoidal Enclosure with Offset Baffles

A numerical investigation has been made of natural convection heat transfer in a trapezoidal enclosure (representing attic spaces) with offset baffles. Two thermal boundary conditions representing summerlike conditions (upper surface heated) and winterlike conditions (upper surface cooled) and two baffle heights are studied. For each boundary condition and baffle height, two baffle positions are considered. In position I, the upper baffle is offset toward the heated vertical wall and the lower baffle is offset toward the symmetry plane of the enclosure, whereas in position II, the upper baffle is offset toward the symmetry plane and the lower baffle is offset toward the heated wall. Rayleigh number values range from 10 3 to 5 × 10 7 for summerlike conditions and from 10 3 to 10 6 for winterlike conditions. Predictions reveal a decrease in heat transfer in the presence of baffles. In winterlike conditions, convection starts to dominate at a Rayleigh number much lower than that in summerlike conditions. The maximum reduction in heat transfer is achieved with long baffles placed in position II for summerlike conditions and in position I for winterlike conditions. Average Nusselt number correlation for both boundary conditions are presented.

Armour Materials for the ITER Plasma Facing Components

The selection of the armour materials for the Plasma Facing Components (PFCs) of the International Thermonuclear Experimental Reactor (ITER) is a trade-off between multiple requirements derived from the unique features of a burning fusion plasma environment. The factors that affect the selection come primarily from the requirements of plasma performance (e.g., minimise impurity contamination in the confined plasma), engineering integrity, component lifetime (e.g., withstand thermal stresses, acceptable erosion, etc.) and safety (minimise tritium and radioactive dust inventories). The current selection in ITER is to use beryllium on the first-wall, upper baffle and on the port limiter surfaces, carbon fibre composites near the strike points of the divertor vertical target and tungsten elsewhere in the divertor and lower baffle modules.This paper provides the background for this selection vis-à-vis the operating parameters expected during normal and off-normal conditions. The reasons for the selection of the specific grades of armour materials are also described. The effects of the neutron irradiation on the properties of Be, W and carbon fibre composites at the expected ITER conditions are briefly reviewed. Critical issues are discussed together with the necessary future R&D.

Buoyancy-induced heat transfer in a vertical enclosure with offset partial vertical dividers

A numerical study has been made of buoyancy-induced flow in a square, externally heated vertical enclosure with two offset baffles or vertical dividers, in order to investigate the effect of baffle height on the flow and heat transfer characteristics. Air is taken to be the working fluid, and the horizontal end walls are assumed to be perfectly conducting. Two baffle positions are considered: in one, the upper baffle is offset toward the hot wall, and the lower baffle toward the cold wall (position A): in the other, the upper baffle is offset toward the cold wall, and the lower baffle toward the hot wall (position B). The effect of baffle conductivity and height on the thermal stratification and heat transfer is investigated. Both factors are found to play an important role, with lower heat transfer at higher baffle conductivities and baffle heights. The nature of thermal stratification between the baffles and in the baffle—near wall region controls the corresponding flow behavior. In position B, strong vertical stratification between the baffles inhibits the crossflow, whereas in position A stratification and correspondingly reduced flow penetration into the baffle—near wall region is noted. These differing flow patterns have important ramifications on the heat transfer.

A vibrofluidized-bed heat exchanger for heat recovery from a hot gas II. Heat-transfer evaluation of a pilot-scale system

The objective of this work is to experimentally evaluate a process for recovering the thermal energy from a hot exhaust gas by direct contact of the gas with a countercurrently flowing vibrofluidized bed of solids. This portion of the two-part paper presents the results of heat-transfer studies on a pilot-scale vibrofluidized-bed heat-exchanger system described in Part I. Based on the phenomenon of spray zone formation observed in Part I together with results from gas-temperature measurements and cold-flow experiments, a model was proposed for the effective convective heat-transfer coefficient between the hot supernatant gas and the vibrofluidized solid. By using a factorial design of experiments, high effective heat-transfer coefficients were obtained with high air and solid flow rates, low baffle heights and high vibrational intensities. Under the ranges of operating conditions investigated, a maximum heat-transfer coefficient of 268 ± 5 W/(m 2·K) was obtained with an effective heat-exchange area of 0.11 m 2. The resulting pressure drop across the gas-deflection baffle is relatively low, being less than 350 Pa. Convective heat-transfer results from a supernatant gas to a flowing vibrofluidized bed of solids represent the only data reported thus far, and have led to a better understanding of the proposed vibrofluidized-bed system for heat-recovery applications.