Multiple Air Gaps Research Articles

Lightweight concrete façade with multiple air gaps for sustainable and energy-efficient buildings in Singapore

Building façades control the heat exchange rate between indoor and outdoor environment and, therefore, impact the operational energy for maintaining an ideal indoor temperature. In this study, a double skin concrete façade is proposed with multiple air gaps as thermal insulator. An ultra-thin façade skin is pursued by adopting textile reinforced ultra-high performance concrete (UHPC), while high thermal insulation is achieved by minimizing the convection- and radiation-related heat exchange across the air gaps. This new façade system is being compared to two commonly-adopted concrete façade systems: a solid concrete façade and a sandwiched concrete façade. A façade panel attached to a residential bedroom in Singapore is selected as the functional unit for assessing their carbon footprint, resulting operational energy, and costs. Results show that the new façade system has 34%–44% lower carbon footprint than the other two façade systems. The thermal conductivity of the new façade is 92% lower than the solid concrete façade and 64% lower than the sandwiched concrete façade, which helps reduce the related operational energy by 14%–49% for a typical bedroom unit in Singapore. • The new façade reduces the carbon footprint by over 34%. • The new façade reduces the thermal conductivity by over 64%. • The new façade reduces the related cooling energy by over 14%. • The new façade can recover the additional cost investment after 3.5 years due to the energy savings.

Thermal insulation of walls by using multiple air gaps separated by aluminum sheets

Thermal insulation in the building walls is an important factor to reduce heat transfer from the external environment, thus reducing the demand for air conditioning and achieving thermal comfort. In order to improve the thermal performance of building walls, the present work aims to construct hollow (double) walls experimentally; which are made of several air layers separated by thin aluminum sheets, and to find the extent of their impact on improving or reducing heat gain. Tests were conducted on a model room of sandwich panel with dimensions of 2 m length and 2 m width, and 2.4 m height (32.5 latitudes) in kut city, Iraq, in August. A hole was drilled in the southwest wall with the following dimensions: (1 m long, 0.3 m wide). Three models of hollow walls with a 6 cm air gap were built in this hole; one was left with a 6 cm air gap (without dividing), the second was divided into two parts by placing a thin sheet of aluminum 1 mm thick, and the third wall's air gap was divided into three parts by placing two thin sheets of aluminum. The experimental results showed that the quantity of heat gain was lowered when the air layers were increased. The heat gain decrease was 11.5 % and 21 %, respectively, when comparing the wall with a cavity of 6 cm (without splitting) with the two walls in which the air gap was divided into two and three layers.

Air-Gap Interrogation of Surface Plasmon Resonance in Otto Configuration.

In this study, a micromachined chip in Otto configuration with multiple air-gaps (1.86 μm, 2.42 μm, 3.01 μm, 3.43 μm) was fabricated, and the resonance characteristics for each air-gap was measured with a 980 nm laser source. To verify the variability of the reflectance characteristics of the Otto configuration and its applicability to multiple gas detection, the air-gap between the prism and metal film was adjusted by using a commercial piezoactuator. We experimentally verified that the SPR characteristics of the Otto chip configuration have a dependence on the air-gap distance and wavelength of the incident light. When a light source having a wavelength of 977 nm is used, the minimum reflectance becomes 0.22 when the displacement of the piezoactuator is about 9.3 μm.

Modified Preisach Model of Hysteresis in Multi Air Gap Ferrite Core Medium Frequency Transformer

This article presents the modified Preisach model of hysteresis for a 3-phase medium frequency transformer in a 100 kW dual active bridge converter. The transformer magnetic core is assembled out of ferrite I-cores, which results in multiple parasitic air gaps. For this transformer, the hysteresis loops were measured and parameters of the Preisach model were determined. The Preisach distribution function is approximated with a two-dimensional Gauss function series and the feedback function is a 3rd-degree polynomial. The optimized identification of Preisach distribution function parameters was prepared. Two sets of parameters were determined based on the analysis of major and minor hysteresis loop. The developed model is used to analyze the transformer core power loss. A new set of Steinmetz equation parameters for multi air gap ferrite core MFT is proposed.

Design, analysis, and testing of I-type electromagnetic actuator used in single-coil active magnetic bearing

Active magnetic bearing consists of different parts, an actuator being the essential part of that. Depending on construction, electromagnetic power in various actuator structures is unique. This paper offers an experimental description of the study using simulation and evaluation of an I-type single-axis active magnetic bearing. The test will be carried out with multiple air gaps in simulation and then results will be implemented in hardware. An I-type actuator has a more attractive force than any other form and is also easy to design. Here, three configurations are prepared to verify the resistance, inductance profile, and attraction force. A DC and AC test is performed to measure resistance and inductance. A ferromagnetic object is known to be a rotor below the electromagnet or actuator is placed to measure the inductance profile and attraction force by increasing the air gap. Simulation and experimental results are analyzed and compared with the proposed system and presented in this manuscript.

Effective Permeability of Multi Air Gap Ferrite Core 3-Phase Medium Frequency Transformer in Isolated DC-DC Converters

The magnetizing inductance of the medium frequency transformer (MFT) impacts the performance of the isolated dc-dc power converters. The ferrite material is considered for high power transformers but it requires an assembly of type “I” cores resulting in a multi air gap structure of the magnetic core. The authors claim that the multiple air gaps are randomly distributed and that the average air gap length is unpredictable at the industrial design stage. As a consequence, the required effective magnetic permeability and the magnetizing inductance are difficult to achieve within reasonable error margins. This article presents the measurements of the equivalent B(H) and the equivalent magnetic permeability of two three-phase MFT prototypes. The measured equivalent B(H) is used in an FEM simulation and compared against a no load test of a 100 kW isolated dc-dc converter showing a good fit within a 10% error. Further analysis leads to the demonstration that the equivalent magnetic permeability and the average air gap length are nonlinear functions of the number of air gaps. The proposed exponential scaling function enables rapid estimation of the magnetizing inductance based on the ferrite material datasheet only.

Thermal insulation of roofs by using multiple air gaps separated by insulating layers of low infrared emissivity

In recent work we have demonstrated the ability of a new thermal insulation design based on creating air cavities between parallel layers of insulation material with a low infrared emissivity (Expanded Polystyrene, 0.6) and the multimodal heat transfer involved (conduction, convection, and radiation) was modeled for walls. Now, this modeling is developed for roofs, regarding the different heat convection mechanisms involved in both slender air cavities, the vertical (walls) and horizontal (roofs) ones. Another difference is that the air convection is null in a top-heated cavity (roofs in summer) meanwhile this mechanism is active in a bottom-heated cavity (roofs in winter) and so, the optimized design is different in both cases. We studied two designs based on multiple EPS layers of 1 cm thickness, namely: EPSW, which takes advantage of the low emissivity of the white EPS (0.6); and EPSF, which adds an aluminum foil of very-low emissivity (0.04) to each EPS layer. Considering roofs in winter, the EPSW design achieves thermal transmittances ranging from 0.447 W/(m2·K) to 0.096 W/(m2·K) for 4 to 17 layers, respectively, obtaining material savings up to 53% compared to solid EPS insulation. On the other hand, the EPSF design leads to thermal transmittances ranging from 0.238 W/(m2·K) to 0.040 W/(m2·K) for 4 to 17 layers, respectively, obtaining material savings up to 81% regarding solid EPS insulation. For summer conditions, the improvement in insulation is limited by the presence of infrared radiation and very hot roof temperatures in warm climates. An intended thermal transmittance of 0.1 W/(m2·K) can be hardly achieved by using 14 layers of EPSW, whereas it can be obtained with just three EPSF layers, although it implies additional burdens in embodied energy and contaminated emissions to the atmosphere. Therefore, we conclude that the simplest EPSW design is suitable for cold climates meanwhile the EPSF design is preferred for warm climates.

Thermal insulators with multiple air gaps: Performance, cost and embodied impacts

The aim of this work is to demonstrate the potential thermal, environmental and cost advantages of a thermal insulation, which consists on several air chambers between layers of an insulation material with low infrared emissivity. The multimodal heat transfer involved (conduction, convection and radiation) is modeled and numerically solved for different materials and designs. The first design proposed uses multiple EPS layers of 1cm thickness separating air chambers. It achieves global thermal transmittances ranging from 0.439W/(m2K) to 0.126W/(m2K) for 4–13 layers, respectively. In this way, material savings up to 55% were obtained with respect to the solid EPS insulation, leading to lower embodied impacts and cost. A second design, based on thin 0.3cm MDF panels coated with low-emissivity paint, gave thinner walls than the previous one, but higher embodied impacts and cost. A third design, based on EPS separation layers coated with very low emissivity aluminum foil, leads to significant improvements in all aspects considered. For a given total transmittance of 0.1W/(m2K), this design reaches savings of 77% in material, 66% in cost, 72% in embodied impacts, and 38% reduction in wall width with respect to solid EPS insulations.

Analytical Modeling of Permanent Magnet Biased Axial Magnetic Bearing With Multiple Air Gaps

This paper proposes a permanent magnet (PM) biased axial magnetic bearing (MB) with multiple air gaps. However, the inherent complex structure makes finite-element analysis (FEA) very time-consuming. For the sake of simplifying the analysis, an equivalent magnetic circuit model together with the conformal mapping method and Laplace's equation is developed. The conformal mapping method is employed to obtain the flux distributions in rectangular air gaps by accounting fringing effect, while the Laplace's equation is used to predict the leakage flux surrounding PM rings. The developed analytical model is validated by FEA. Consequently, the design parameters in the axial MB are analytically determined.

Thermal insulations of multilayer clothing systems measured by a bench scale test in low level heat exposures

Purpose – The purpose of this paper is to measure the thermal insulation of protective clothing with multilayer gaps in low-level heat exposures. Design/methodology/approach – Nine different combinations of protective clothing systems with multiple air gaps are used to measure the thermal insulation by a self-designed bench-scale test apparatus in different levels of an external thermal radiation of 2-10 kW/m2. The outside and inside surface temperatures of each fabric layer are also measured to calculate the local thermal insulation of each fabric layer and each air gap. Findings – The results show that the total thermal insulation of protective clothing under thermal radiation is less than that in normal environments, and the exposed thermal radiation will worsen the total thermal insulation of the multilayer fabric systems. Air gap plays a positive role in the total thermal insulation, and thus provides the enhanced thermal protection. It is also suggested that the local resistance of the air gap closer to the external thermal radiation is more easily affected by the thermal radiation, due to the different heat transfer ways in the fabric system and the external thermal radiation. Originality/value – Effects of air gap on the thermal insulation of protective clothing, and contribution of the local thermal resistance of each fabric layer and each air gap to the total thermal insulation.

Effects of multiple air gaps on the thermal performance of firefighter protective clothing under low-level heat exposure

The thermal performance of firefighters' protective clothing entrapping multiple air gaps and exposed to low heat fluxes has been studied using a newly designed bench-scale test apparatus. Different air gap sizes (0, 2 and 5 mm), and entrapped positions within the multiple fabric system between the outer shell, the moisture barrier, and the thermal liner, respectively, were investigated at three levels of thermal radiation (2, 5 and 10 kW/m2) over a prolonged period. The effect of air gap size and its position on the heat transfer in a multilayer fabric system are interpreted in terms of a theoretical flat multi-wall structure. The results show that the thermal protective performance of a multilayer fabric system is reduced under low-level heat flux with and without an air gap. It is indicated that the time for skin to burn in direct contact with the inner layer is increased with the size of the air gap, due to an increase in the total thermal resistance of the fabric combination and a decrease in heat radiation between two adjacent fabric layers separated by an air gap. The results also provide an insight into the contribution of the thermal resistance of each fabric layer and each air gap to the overall protective effect of the clothing system. The difference in the received heat flux with different air gap sizes in different positions shows that the effect of air gap size is related to its position.

Numerical Simulation of Heat Transfer in Firefighters' Protective Clothing with Multiple Air Gaps during Flash Fire Exposure

A finite volume model was developed to simulate transient heat transfer in firefighters' protective clothing during flash fire exposure. The model domain consists of three layers of fire-resistant fabrics (outer shell, moisture barrier, and thermal liner) with two air gaps between the clothing layers, the human skin, and the air gap between the clothing and the skin. The model accounts for the combined conduction-radiation heat transfer in the air gaps entrapped between the clothing layers, and between the clothing and the skin. The variation in the air gap properties and energy content during both the exposure and the cool down periods was accounted for. Predictions were obtained for the temperature and heat flux distributions in the fabric layers, skin, and air gaps as a function of time. The influence of each air gap on the clothing performance was investigated as well. This article demonstrates the importance of accurately modeling the contributions of the air gaps in order to predict the protective clothing performance.

Influence of Multiple Air Gaps on the Performance of Electrical Machines With (Semi) Halbach Magnetization

The ever increasing necessity to improve torque density while simultaneously maintaining high efficiency is a constant point of concern for electrical machine designers. This is mainly driven by the need for direct-drive solutions in evermore applications. This paper presents a general mesh-free description of the magnetic field distribution in multiple air-gap electromagnetic machines, although the tool is also useful for single air-gap machines, actuators, and other magnetic devices. The used method is based on transfer relations and Fourier theory, which can provide the magnetic field solution for a wide class of 2-D boundary value problems. This technique is in this paper applied to the rotary multiple air-gap machine with slotless (without slots but with and without rotor back-iron) armature. The presented analysis is compared to finite-element analysis for the multiple-layer winding, which shows the applicability of this method for future optimization. It is shown that multiple air-gap machines make better use of the volume and for short axial lengths where a single-side bearing configuration can be utilized provides a means to improve the achievable torque density.

InGaN Light-Emitting Diode Structure on a Photoelectrochemical Treated GaN:Si Layer

InGaN/GaN multiple-quantum-wells light-emitting diode (MQW-LED) structure was grown on a photoelectrochemical (PEC) treated n-type GaN:Si layer in deionized water. The PEC treated GaN:Si layer consisted of a nanoporous GaN:Si layer with a multiple-air-gaps (MAG) structure and the native GaOx layers that acted as submicro-masks for the epitaxial lateral overgrowth (ELOG) process. The photoluminescence spectrum has a 4.5nm wavelength blueshift phenomenon and a 2.0 times peak intensity enhancement in the MAG-LED structure (compared to a standard-LED) that is caused by a partially reduced piezoelectric field and an increasing light extraction process. The higher internal quantum efficiency and the higher light extraction process were observed in the MAG-LED structures by adding large volume of native GaOx layers and PEC treated multiple-air-gaps layers.

New shape of superconducting coil with improved critical current – design and FEM analysis results

The novel superconducting HTS coil designed for Superconducting Magnetic Energy Storage (SMES) is the aim of the paper. Novelity lies in the shape of the coil that minimises perpendicular component of the flux density of HTS wire. In this paper authors try to find the shape of the coil where perpendicular component of magnetic field is as close as possible to zero. Proposed solution has the helical shape of coil turns and the special shape of the magnetic core (magnetic core with air gap is needed for increasing stored energy). Helical turns are put on toroidal former and then magnetic core on it. Each turn has the same shape, length and is put in the same magnetic flux. Near-uniform distribution of magnetic flux is the result of the shape of winding and also non-uniform shape (or non-concentric) of magnetic core that has multiple radial air gaps. It produces magnetic field distribution in magnetic core shaped coaxially to winding and distribution of stored magnetic energy uniformly on magnetic core circumference. Magnetic energy is stored in air gaps and proposed shape of core is the best solution of core but its fabrication produces technological difficulties in core manufacturing.

Concentric magnetic configuration for loudspeakers

Disclosed is a concentric magnetic configuration for a speaker system which can produce a full range of frequency sounds from a single source magnet. The magnetic configuration of the present invention includes a high frequency pole plate and one or more middle yoke iron plate placed directly on a cylindrical permanent magnet wherein at least one magnetic flux controlling slot is formed beneath the high frequency pole plate and the middle yoke plate. The multiple air gaps defined by the pole plate and middle yoke iron produce a full range of frequency magnetic fields which can drive the high, medium, and low frequency voice coils.

Wide and continuous wavelength tuning of microcavity devices for optoelectronic applications

Ultra-widely tunable microcavity devices implemented by surface micromachining are studied. We model, fabricate, and characterize 1.55-μm vertical-resonator-based optical filters and vertical cavity surface emitting lasers (VCSELs) capable of wide, monotonic, and kink-free tuning by a single control parameter. Our devices are comprised of single or multiple horizontal air gaps in the dielectric and InP-based material system. Distributed Bragg mirrors with multiple air gaps are implemented. Due to the high refractive index contrast between air (n = 1) and InP (n = 3.17), only three periods are sufficient to guarantee a reflectivity exceeding 99.8% and offer an enormous stop-band width exceeding 500 nm. Unlike InGaAsP/InP or dielectric mirrors, they ensure short penetration depth of the optical intensity field in the mirrors and low absorption values. Stress control of the suspended membrane layers is of utmost importance for the fabrication of these devices. By controlling the stress, we are able to fabricate InP membranes that are extremely thin (357 nm thick) and at the same time flat (radius of curvature above 5 mm). Micromechanical single parametric actuation is achieved by both thermal and electrostatic actuation. Filter devices with a record tuning more than 142 nm with 3.2 V are presented.

Magnetic Shunt for Three Phase Reactors

For three phase shunt reactors to function effectively in EHV power systems the behavior of the circuit reluctance must be known under all operating conditions. Difficulties have occurred in effectively designing electromagnetic circuits with multiple air gaps in shunt reactors. This paper describes design techniques for magnetic shunts which can be applied to three phase shunt reactors resulting in size and weight reduction. Performance characteristics of shunt reactors under imbalanced system conditions are presented and magnetic shunt performance for a 345 kV, 100 MVAR three phase shunt reactor is given.