Duct Losses Research Articles

Modeling of pressure losses in a cylindrical duct with rectangular ribs

AbstractIn order to improve the thermal performance of heat exchangers and air collectors, we insert various forms of artificial roughness, known as ribs, into the useful duct. These ribs promote the creation of turbulent flows and enhance heat transfer by conduction, convection and radiation.However, the introduction of these ribs leads to an increase in pressure drop, requiring higher mechanical power to pump the heat transfer fluid. This experimental study focuses on estimating, using empirical approaches, the pressure losses induced by rectangular ribs with an inclined top. The ribs are made from 0.4 mm galvanized sheet steel.An experimental set-up was designed to measure the head losses generated by the ribs, from the point of entry to the point of exit from the useful duct. Using the dimensional analysis method, correlations were established to evaluate head losses as a function of flow regime and rib geometry and configuration (including different geometries for rib arrangement over the configuration area).

G‘UJUMSOY KONI HAVO UZATISH STVOLIDA HAVO OQIMINI BOSHQARISH SAMARADORLIGINI OSHIRISHDA HAVO PARDASINI QOʻLLASH

On the extraction of gold-bearing ores in mines, the amount of air in the ventilation network of mines increases in proportion to increases in the length of excavations and deepening of the mines. The article deals with issues of managing the air flows into mines, the use of air curtains to reduce external and internal losses to the mine, and aerodynamic resistance. The work describes the use of the main fan and an optimal ventilation scheme in order to increase the efficiency of ventilation in mines with complex ventilation systems, with the view to reducing outdoor air losses in the ventilation duct and ventilation network by determining the optimal values for air flow, air flow rates, and pressure changes with ventilation parameters to ensure ways of effective control and distribution of the air flow.

Variable Refrigerant Flow in Air Conditioning of Buildings: System Configuration and Energy Efficiency

Variable Refrigerant Flow (VRF), also known as Variable Refrigerant Volume (VRV) refers to the ability of an air-conditioning (AC) system to control the amount of refrigerant flowing to multiple evaporators (indoor unit). This study evaluates the VRF system to its core, and how the system is more beneficial in terms of built environment than the traditional air-conditioning system. This type of type of system consists of a number of air handling units (possibly up to 48) connected to a modular external condensing unit. The refrigerant flow in the VRF system is varied using either an inverter-controlled variable speed compressor or multiple compressors of varying capacity in response to changes in the cooling or heating requirement within the air-conditioned space. With the help of these advanced compressor like the twin rotary compressor the metering device can be closed to controls the flow of refrigerant between the indoor and outdoor unit which helps in avoiding the overheating or overcooling of the space. VRF system also helps in covering the duct losses which is impossible to cover in traditional system as VRF system is ductless or minimum duct are used in the process.

Analysis and Improvement of the Suction Performance of Axial Piston Pumps in Swash Plate Design

The article illustrates a systematic investigation of the suction performance of hydrostatic pumps on the example of an axial piston pump in swash plate design. The focus is on pressure losses in the suction duct as well as on losses due to the interaction between the suction flow and the rotating group. The investigations of the suction flow are performed by means of numerical and experimental methods. Also a full cavitation model and a two-way fluid-structure-interaction approach were introduced for the numerical works. The experimental works were used to validate the CFD model. For the improvement of the suction performance two approaches are pursued. The bionic design of the suction duct based on meandering rivers and the suction pressure pulsation reduction by the help of a Helmholtz resonator. As a result of the CFD analysis, regions with the largest total pressure losses were identified. Based on CFD simulation significant improvements of the suction performance were shown due to the two presented measures. By means of the meander shape design the pressure losses reduced by more than 50 % and the pressure ripple was dampened by about 9.5 dB using the integrated Helmholtz resonator.

Open Rotor Engines—Still an Open Question?

A major factor in the continued domination of turbofan engines for economic airline propulsion, is the ability to increase bypass ratios. However, increasing fan diameters to go to ever higher bypass ratios increases nacelle weight, aerodynamic drag and duct losses. By eliminating the need for a fan duct, open rotor engines can effectively in-crease bypass ratios, resulting in a significant savings in fuel consumption. Open rotor engines have been under intermittent development since the 1980s, sub-ject to rising and falling of fuel prices. Technical challenges that continue in their de-ployment include noise reduction, airframe integration and protection from propel-ler/fan blade failure.

Secondary electron emission detectors for neutral beam characterization on C-2W.

Heating, current drive, and partial fueling from neutral beam injection are essential to sustainment of C-2W field-reversed configuration plasmas. C-2W has eight 2.1 MW neutral beams (16.8 MW of total electrical power), capable of providing a beam of 15 keV hydrogen neutrals for 30 ms. To maximize the effectiveness of neutral beam injection, duct losses must be minimized by maintaining beam alignment and optimizing beam current for minimum divergence. Each beam terminates on a vertical and horizontal array of secondary electron emission detectors (nine in the vertical, seven in the horizontal, and sharing one in the middle). The molybdenum detectors are spatially separated to characterize the beam size and alignment. With knowledge of the geometry of the vacuum ducts and horizontal and vertical beam profiles from test stand measurements, the focal length, divergence, and power loss were calculated. Through characterization, the set of neutral beams are optimized to inject up to 12 MW of power into the confinement vessel throughout the plasma discharge.

Characterization of heat transfer enhancement and frictional losses in a two-pass square duct featuring unique combinations of rib turbulators and cylindrical dimples

Transient heat transfer experiments using liquid crystal thermography have been carried out on a two-pass square channel for testing several unique combinations of ribs and cylindrical dimples. Four different rib shapes, viz. 45° angled, V, W and M have been studied. In compound channels, the rib pitch accommodates cylindrical dimples arranged in the shape of the rib, hence following the direction of rib induced secondary flows. For each rib shape, three different configurations – rib alone, dimple alone and rib–dimpled compound cases were studied. The rib-height-to-channel hydraulic diameter ratio was 0.125 and rib-pitch-to-rib-height ratio was 16. The dimple-depth-to-print diameter ratio was 0.3. The experiments were carried out for a wide range of Reynolds number (19,500–69,000), covering a spectrum typically found in both land-based and air-breathing engines. A total of 52 experiments were carried out to measure detailed heat transfer coefficient on the bottom wall of the two-pass channel. A transient liquid crystal thermography technique was used for heat transfer measurement. Static pressure measurements were carried out to measure the overall pressure drop in the two pass channel. From globally averaged Nusselt number and overall pressure drop, thermal-hydraulic performance of the 13 configurations were determined, compared and analyzed. It has been observed that 45° angled and V compound configurations resulted in higher heat transfer augmentation as well as higher thermal hydraulic performance when compared with their corresponding ribs alone and dimples alone configurations.

Minimization of exergy losses in a trapezoidal duct with turbulator, roughness and beveled corners

This research is focused on the study of force convective heat and exergy transfers characteristics of flow through a trapezoidal duct with turbulator. Two vortex generators are located in the duct to enhance the heat transfer rate. The numerical simulations are done for the Reynolds numbers in the range of 400<Re<1600. The conservation of mass, momentum, and energy equations are solved numerically by applying a finite volume approach. The results are presented for the friction factor, Nusselt number, and entropy generations (Friction, thermal and total entropy generations). Finally, the attention is focused on the minimization of exergy losses by using two techniques. These techniques were use of beveled corners and surface roughness for the duct. It was found that the total entropy generation decreases by installing the vortex generators inside the duct. These reductions are 24.9%, 24.4%, 25.8%, and 26.6% for Re=400, 800, 1200, and 1600, respectively. Moreover, the total entropy generation decreases by using beveled corners for duct. These reductions in the total entropy rates are in the vicinity of 10.4%, 9.15%, 8.54%, and 8.1% for Re=400, 800, 1200, and 1600, respectively.

An assessment of distributed propulsion: Part B – Advanced propulsion system architectures for blended wing body aircraft configurations

Studies such as those by NASA predict large performance benefits when integrating Distributed Propulsion (DP) with the Blended Wing Body (BWB) aircraft configuration. This is because the BWB planform geometry is particularly suited to the ingestion of boundary layer air. The present study evaluates the relative benefit of DP through a comparison with an advanced turbofan reference system of the same technology level as in Part A of this two part paper. Fuel savings of 5.3% relative to the reference aircraft have been shown to be achievable, although it was found that the system is particularly sensitive to duct losses.

Experimental Measurements of Pressure Losses in the Inter-Turbine Duct of a Gas Turbine

The paper presents the total pressure experimental measurements carried out at the Romanian Research and Development Institute for Gas Turbines COMOTI in order to determine the total pressure losses in the Inter - Turbine Duct of a two spools gas turbine, as a function of the gas turbine operating regime (mass flow rate) and rotational speed. The Inter - Turbine Duct experimental assembly has been designed, manufactured and tested at COMOTI. The total pressures were measured as a function of the pre-swirling angle, which simulates the influence of the high pressure turbine rotational speed located upstream of the Inter turbine duct in the real gas turbine, as well as for three operational regimes, without the pre-swirlers modules. The results indicate that the total pressure loss along the Inter - Turbine Duct is of maximum 0.9 %. The lowest overall total pressure loss occurs at 0o pre-swirling angle, around 0.8%, while along the ITD struts, the lowest pressure loss is obtained for a 15o pre-swirling, below 0.1%. The influence of the operating regime on the total pressure loss was found to be linearly, the pressure loss increasing with the reduced mass flow rate, between 1% and 1.9% overall, and between about 0.1% and 0.4 % along the struts.

Analysis and Improvement of the Suction Performance of Axial Piston Pumps in Swash Plate Design

The article illustrates a systematic investigation of the suction performance of hydrostatic pumps on the example of an axial piston pump in swash plate design. The focus is on pressure losses in the suction duct as well as on losses due to the interaction between the suction flow and the rotating group. The investigations of the suction flow are performed by means of numerical and experimental methods. Also a full cavitation model and a two-way fluid-structure-interaction approach were introduced for the numerical works. The experimental works were used to validate the CFD model. For the improvement of the suction performance two approaches are pursued. The bionic design of the suction duct based on meandering rivers and the suction pressure pulsation reduction by the help of a Helmholtz resonator. As a result of the CFD analysis, regions with the largest total pressure losses were identified. Based on CFD simulation significant improvements of the suction performance were shown due to the two presented ...

Multidisciplinary Analysis of a Geared Fan Intercooled Core Aero-Engine

The reduction of CO2 emissions is strongly linked with the improvement of engine specific fuel consumption, along with the reduction of engine nacelle drag and weight. One alternative design approach to improving specific fuel consumption is to consider a geared fan combined with an increased overall pressure ratio intercooled core performance cycle. The thermal benefits from intercooling have been well documented in the literature. Nevertheless, there is very little information available in the public domain with respect to design space exploration of such an engine concept when combined with a geared fan. The present work uses a multidisciplinary conceptual design tool to analyze the option of an intercooled core geared fan aero engine for long haul applications with a 2020 entry into service technology level assumption. With minimum mission fuel in mind, the results indicate as optimal values a pressure ratio split exponent of 0.38 and an intercooler mass flow ratio of 1.18 at hot-day top of climb conditions. At ISA midcruise conditions a specific thrust of 86 m/s, a jet velocity ratio of 0.83, an intercooler effectiveness of 56%, and an overall pressure ratio value of 76 are likely to be a good choice. A 70,000 lbf intercooled turbofan engine is large enough to make efficient use of an all-axial compression system, particularly within a geared fan configuration, but intercooling is perhaps more likely to be applied to even larger engines. The proposed optimal jet velocity ratio is actually higher than the value one would expect by using standard analytical expressions, primarily because this design variable affects core efficiency at mid-cruise due to a combination of several different subtle changes to the core cycle and core component efficiencies at this condition. The analytical expressions do not consider changes in core efficiency and the beneficial effect of intercooling on transfer efficiency, nor do they account for losses in the bypass duct and jet pipe, while a relatively detailed engine performance model, such as the one utilized in this study, does. Mission fuel results from a surrogate model are in good agreement with the results obtained from a rubberized-wing aircraft model for some of the design parameters. This indicates that it is possible to replace an aircraft model with specific fuel consumption and weight penalty exchange rates. Nevertheless, drag count exchange rates have to be utilized to properly assess changes in mission fuel for those design parameters that affect nacelle diameter.

Beamline duct monitoring of the TJ-II neutral beam injectors

In the stringent geometry of TJ-II NBI ducts, beam reionization can reduce beam transmission by a significant fraction. The re-emitted gas from direct beam impact areas acts as “seed” gas for reionization losses. In order to monitor and control reionization losses two diagnostics have been commissioned: infrared thermography of the beam path and Fast Ion gauge measurements of the pressure buildup at the duct exit during beam pulses in the absence of magnetic field. An upper limit of 20% for reionization losses in a well-conditioned duct has been obtained from infrared thermography. The gas dynamics has been studied, obtaining the re-emitted gas flow (6–12mbarls−1) and a limit for the characteristic time constant of the emission process (<100ms).

Exergy analysis and operational efficiency of a horizontal ground-source heat pump system operated in a low-energy test house under simulated occupancy conditions

This paper presents data, analyses, measures of performance, and conclusions for a ground-source heat pump (GSHP) providing space conditioning to a 345m2 house whose envelope is made of structural insulated panels. The entire house thermal load with RSI-3.7 (RUS-21) walls, triple-pane windows (U-factor of 1.64Wm−2K (0.29Btuh−1ft−2°F−1)) and solar heat gain coefficient of 0.25, a roof assembly with overall thermal resistance of about RSI-8.8 (RUS-50), and low leakage rates of 0.74 ACH at 50Pa, was satisfied with a 2.16 ton (7.56kW) GSHP unit. Coefficient of performance is calculated on the basis of the total power input (including duct, ground loop, and control power losses). Exergy analysis provides a true measure of how closely actual performance approaches the ideal, and it unequivocally identifies, better than energy analysis does, the sources and causes of lost work — the root cause of system inefficiencies and wasted energy.

Aerodynamic Shape Optimization Using First and Second Order Adjoint and Direct Approaches

This paper focuses on discrete and continuous adjoint approaches and direct differentiation methods that can efficiently be used in aerodynamic shape optimization problems. The advantage of the adjoint approach is the computation of the gradient of the objective function at cost which does not depend upon the number of design variables. An extra advantage of the formulation presented below, for the computation of either first or second order sensitivities, is that the resulting sensitivity expressions are free of field integrals even if the objective function is a field integral. This is demonstrated using three possible objective functions for use in internal aerodynamic problems; the first objective is for inverse design problems where a target pressure distribution along the solid walls must be reproduced; the other two quantify viscous losses in duct or cascade flows, cast as either the reduction in total pressure between the inlet and outlet or the field integral of entropy generation. From the mathematical point of view, the three functions are defined over different parts of the domain or its boundaries, and this strongly affects the adjoint formulation. In the second part of this paper, the same discrete and continuous adjoint formulations are combined with direct differentiation methods to compute the Hessian matrix of the objective function. Although the direct differentiation for the computation of the gradient is time consuming, it may support the adjoint method to calculate the exact Hessian matrix components with the minimum CPU cost. Since, however, the CPU cost is proportional to the number of design variables, a well performing optimization scheme, based on the exactly computed Hessian during the starting cycle and a quasi Newton (BFGS) scheme during the next cycles, is proposed.

Variation in indoor particle number and PM 2.5 concentrations in a radio station surrounded by busy roads before and after an upgrade of the HVAC system

Indoor particle number and PM 2.5 concentrations were investigated in a radio station surrounded by busy roads. Two extensive field measurement campaigns were conducted to determine the critical parameters affecting indoor air quality. The results indicated that indoor particle number and PM 2.5 concentrations were governed by outdoor air, and were significantly affected by the location of air intake and design of HVAC system. Prior to the upgrade of the HVAC system and relocation of the air intake, the indoor median particle number concentration was 7.4×10 3 particles/cm 3 and the median PM 2.5 concentration was 7 μg/m 3. After the relocation of air intake and the redesign of the HVAC system, the indoor particle number concentration was between 2.3×10 3 and 3.4×10 3 particles/cm 3, with a median value of 2.7×10 3 particles/cm 3, and the indoor PM 2.5 concentration was in the range of 3–5 μg/m 3, with a median value of 4 μg/m 3. By relocating the air intake of the HVAC, the outdoor particle number and PM 2.5 concentrations near the air intake were reduced by 35% and 55%, respectively. In addition, with the relocation of air intake and the redesign of the HVAC system, the particle number penetration rate was reduced from 42% to 14%, and the overall filtration efficiency of the HVAC system (relocation of air intake, pre-filter, AHU and particle losses in the air duct) increased from 58% to 86%. For PM 2.5, the penetration rate after the upgrade was approximately 18% and the overall filtration efficiency was 82%. This study demonstrates that by using a comprehensive approach, including the assessment of outdoor conditions and characterisation of ventilation and filtration parameters, satisfactory indoor air quality can be achieved, even for those indoor environments facing challenging outdoor air conditions.

Measuring residential duct efficiency with the short-term coheat test methodology

Assessing the thermal efficiency of a forced-air distribution system is difficult, in large part because of interactions between energy loss mechanisms and other building characteristics. This paper describes short-term coheating, a method of measuring the thermal efficiency of residential heating and cooling distribution systems in situ, and presents the results of a series of studies that utilized the short-term coheat methodology. Short-term coheat tests were conducted in 53 residential buildings including both site-built and manufactured housing. The magnitude of the distribution efficiency, defined as the ratio of the energy required to heat the building if there were no duct losses to the actual heating energy required, ranged from less than 50% for homes with disconnected ducts to more than 90% for well sealed and insulated systems. Duct retrofits were also performed at 20 of the test sites and, following the retrofits, on average, the homes required 16–17% less heating energy. These results show that residential distribution system losses can be responsible for substantial energy loss and that duct retrofits are a viable energy conservation strategy for homes with distribution systems located outside of the conditioned space.

Influence of the nature of the gas in the edge-tone phenomenon

The present study deals with the edge-tone phenomenon. Gas injection is performed through a nozzle with a 0.6×20 mm 2 cross-section and two possible lengths of 20 and 50 mm. The effect of the nature of the injected gas on both the flow arrangement and sound frequency is investigated by a coupled experimental and numerical approach. In the experiments, special attention is paid to the definition and experimental measurement of the velocity at the nozzle outlet for the three injected gases. If the head losses in the injection duct are correctly taken into account, no influence of its length is obtained, which contradicts the results published recently by Ségoufin et al. [2004. Experimental investigation of the flue channel geometry influence on edge-tone oscillations. Acta Acustica 90, 966–975]. Injections of air, Neon, and CO 2 into air are then successively considered. The numerical simulations are based on the two-dimensional resolution of the unsteady Navier–Stokes equations, in association with a two-fluid physical model. A homogeneous approach is used to treat the behaviour of the mixture composed of the two gases. The density of the injected gas is found to have a significant influence on the flow pattern and the sound frequency, which suggests that the fluid density should be included in the relations that give the frequency of the edge tone instability. Moreover, it is shown that the jet oscillation frequencies obtained both numerically and experimentally can be derived from a theoretical analysis of the Kelvin–Helmholtz instability, on condition that the parabolic shape of the gas velocity at the nozzle outlet is taken into account.

Ozonolysis of monoterpenes in mechanical ventilation systems

In this investigation the ozonolysis of of three monoterpenes ( α-pinene, Δ 3-carene and limonene) was studied was studied in authentic mechanical ventilation systems, that included either a cross flow or a rotary heat exchanger. The effects of varying three experimental parameters were investigated: the level of ozone (25 and 75 ppb), the reaction time (25 and 75 s), and the surface area in the ventilation duct (14.8 and 29.5 m 2). The initial concentration of each of the monoterpenes was 20 ppb in every experiment, and 1–16% of the α-pinene, <0.5–13% of the Δ 3-carene, and <0.5–16% of the limonene reacted. The effects of humidity (g m −3) and temperature of the outdoor and supply air, and water losses in the ventilation duct, were also evaluated. Experiments were based on a chemometric statistical design. Comparison of the results to theoretically calculated values showed that theoretical calculations underestimated the amounts that reacted in the ventilation systems by factors of 2–13, depending on the monoterpene and experimental settings.

Modeling particle loss in ventilation ducts

Empirical equations were developed and applied to predict losses of 0.01-100 mum airborne particles making a single pass through 120 different ventilation duct runs typical of those found in mid-sized office buildings. For all duct runs, losses were negligible for submicron particles and nearly complete for particles larger than 50 mum. The 50th percentile cut-point diameters were 15 mum in supply runs and 25 mum in return runs. Losses in supply duct runs were higher than in return duct runs, mostly because internal insulation was present in portions of supply duct runs, but absent from return duct runs. Single-pass equations for particle loss in duct runs were combined with models for predicting ventilation system filtration efficiency and particle deposition to indoor surfaces to evaluate the fates of particles of indoor and outdoor origin in an archetypal mechanically ventilated building. Results suggest that duct losses are a minor influence for determining indoor concentrations for most particle sizes. Losses in ducts were of a comparable magnitude to indoor surface losses for most particle sizes. For outdoor air drawn into an unfiltered ventilation system, most particles smaller than 1 mum are exhausted from the building. Large particles deposit within the building, mostly in supply ducts or on indoor surfaces. When filters are present, most particles are either filtered or exhausted. The fates of particles generated indoors follow similar trends as outdoor particles drawn into the building. (C) 2003 Elsevier Ltd. All rights reserved.