Performance Potential of Mechanical Ventilation Systems with Minimized Pressure Loss

In this work, we propose a rapid optimization approach to examine its application potential for the design and performance prediction and optimization of a solid fuel ramjet (SFRJ) with a bluff body. For this, the shape of the bluff body is parameterized first using the non-uniform rational B-spline method. We then develop a model for predicting SFRJ performances by incorporating both levy motion-gradient descent and support vector regression methods. It is found that a faster prediction is achievable, while the average error is maintained to be less than 5%. We then develop a multi-objective optimization model by considering the full thrust and minimum total pressure loss (TPL). The optimization model is examined using the non-dominated sorting genetic algorithm. A cost parameter is also created to facilitate the tradeoffs between the thrust and TPL in the Pareto front, when different bluff-body design configurations are considered. The present results reveal that an increase in the cost parameter will elevate the turbulence intensity within the SFRJs while drawing the incoming air closer to the fuel surface, resulting in an increase in thrust and regression rate, but the TPL will also increase. When prioritizing the TPL reduction in the design stage, the optimized solution reduces TPL by 50%. Meanwhile, the net thrust is shown to be decreased by less than 3.5%. Furthermore, flow-field investigation reveals that the improved performance of the optimized SFRJ is due to more uniform flow velocity gradients around the bluff body and a reduced rear vortex, resulting in reduced momentum loss. Our proposed optimization approach's robustness has been further confirmed with consistent performances, as the ramjet inlet speed varies over a broad range. It shows that our approach has great potential to be applied for the SFRJ performance prediction and optimization, being operated under various conditions.

Rapid design approach for U-bend of a turbine serpentine cooling passage

Impacts of several urban-sprawl countermeasures on building (space heating) energy demands and urban heat island intensities. A case study

An improved streamline curvature (SLC) throughflow analysis method is presented based on the predecessor's works to simulate the flow fields of a certain transonic axial compressor. The improvements of this method are embodied centrally in minimum loss incidence angle (MIA) model and total pressure loss (TPL) model that ensure accurate and reliable performance prediction at both design and off-design conditions. The improved MIA is set up as a function of inlet Mach number, solidity, thickness, camber angle, etc. according to low-speed minimum incidence angle. Therefore, TPL is divided into two parts, the first one is the minimum loss which considers the revise of Mach number and Reynolds number, and the second one is the additional loss when real incidence angle deviates from MIA. Finally, the internal flow field of a single-stage compressor is simulated. The characteristic curves and spanwise aerodynamic parameters distribution at design and off-design points are illustrated in this article. Compared to the experiment and computational fluid dynamics (CFD) data, this improved SLC method gives reasonable performance trends and generally accurate results, also the MIA and TPL models are demonstrated in this article.

Carbon dioxide is an important parameter for indoor air quality (IAQ) monitoring and demand controlled ventilation (DCV). Usually, CO2 sensors are wall‐mounted at 0.9–1.8 m (3–6 ft) height as prescribed by LEED, although ASHRAE standards seemed to relax this requirement. In this work, we investigate whether positioning these sensors in the ceiling is effective and advantageous. We studied CO2‐level measurements for HVAC control in configurations with mixing ventilation and found that CO2 from human exhalations experiences buoyancy from several factors. We calculated buoyancy from air properties, and we introduced the notion of “stratification temperature” for exhaled air. By simulation, we test the sensitivity to temperature, and we conducted in situ in vivo measurements to acquire more detailed insights in the feasibility of ceiling sensor positions. Buoyancy calculations show that in exhaled air, the positive buoyancy of H2O approximately compensates for the negative buoyancy of CO2, so that thermal buoyancy is the most dominant factor. Exhaled air, containing CO2 to be measured, will rise towards a ceiling that has a temperature below the stratification temperature. Computational fluid dynamics (CFD) simulations of a small office space indicate that this can also be the case in the presence of air flows induced by a mechanical ventilation system. The measurement results support that using “properly mounted” CO2 sensors in the ceiling gives lower variability in CO2 measurements and faster response than wall‐mounted sensors and yields slightly higher values than wall sensors. Our results highlight the need to update the standards and regulations for sensing CO2 to include ceiling‐mounted sensors.

A new continuous adjoint formulation for the optimization of cascade aerofoils with minimum total pressure losses, i.e. an objective function which has never been used before along with the continuous adjoint, is presented. To support a steepest descent algorithm, the adjoint method is used to compute the gradient of the objective function with respect to the design variables. The function is defined as the difference in total pressure between the inlet to and the outlet from the cascade. In contrast to other known continuous adjoint approaches in aerodynamics (such as inverse designs based on target pressure distributions or drag-lift optimization for isolated aerofoils), where the functional is defined over the parameterized solid walls, the present functional consists of integrals over the inlet/outlet boundaries only. To cope with this particular situation, the method of characteristics is used to impose inlet/outlet adjoint boundary conditions. It is worth noting that the objective function gradient is expressed as an integral over the solid walls. The minimization of losses in linear and peripheral compressor cascades, constrained by the desirable flow turning and the minimum allowed blade thickness, are demonstrated.

ACoolHeaD: Framework for Automated Cooling and Heating Demand calculations using spatially and temporally resolved building performance simulations applied to the estimation of heating demand in Germany

Modeling and optimization for energy efficient smart buildings are interesting and promising research areas. According to Paris Protocol signed in 2015, energy efficient, smart and green buildings are imperative concerns. Heating, ventilation and air-conditioning (HVAC) or air-conditioning and mechanical ventilation (ACMV) systems, consume around 40% of the total energy, and the systems also directly impact on the environmental conditions, especially the indoor environmental conditions, such as air temperature, air humidity, air velocity, air quality, etc. In this thesis, the main objective is to systematically optimize the ACMV systems to operate efficiently and maintain indoor environmental conditions as comfortable and healthy as possible for occupants. The thesis is organized into the following systematic three-phase methodology to enhance ACMV systems' energy efficiency and indoor occupants' thermal comfort in smart buildings:

As a Viking colony of Norway, Iceland was settled by an agrarian society whose ongoing development was reliant on timber. While a tacit knowledge and tradition of timber construction was brought to Iceland, a sustainable quantity and quality of timber was not native to the island. As a result, two similar yet materially-differentiated forms of vernacular architecture developed, both adapted to their local contexts and climates. This article utilises drawn and photographic surveys to analyse the influence of material availability on the architecture of two farmhouses in Norway and Iceland. While existing literature focuses on physical descriptions, this article explores how differences in material use and construction techniques impacted on indoor environmental conditions in these dwellings. By using building simulation and isotherm modelling, the article presents an explicit visual reading of the ephemerality of living conditions in the past. In particular, it emphasises the significance of the hearth and its location within the dwelling to the inhabitants’ capacity to adapt to the cold climate.

Energy saving potential and repercussions on indoor air quality of demand controlled residential ventilation strategies

An energy-saving control strategy for multi-zone demand controlled ventilation system with data-driven model and air balancing control

Modeling of waste heat powered energy system for container ships

Modern turbine cascades are usually being optimized for minimum total pressure losses. Gas turbines, however, operating in dirty environments or using coal–derived fuels need cascades that minimize the deposition, erosion and corrosion (DEC) implications of the particle–laden gas. This can be achieved by altering certain geometrical key–parameters of cascades and blades which influence the particle deposition rate, while keeping the inlet and outlet velocities and angles fixed. Since reference cascades have already been optimized for minimum aerodynamic losses, the associated loss increase penalty is accounted for. Two stator and two rotor cascades were optimized by a penalty function method. The results suggest that solid particle deposition rates can be minimized by as much as 40 per cent while keeping profile losses to acceptable limits in both stator and rotor cascades for the particle size range 0.1 to 1 μm.

Under hypersonic flight conditions, the sharp cowl-lip leading edges have to be blunted because of the severe aerodynamic heating. This paper proposes four cowl-lip blunting methods and studies the corresponding flow characteristics and performances of the generic hypersonic inlets by numerical simulation under the design conditions of a flight Mach number of 6 and an altitude of 26 km. The results show that the local shock interference patterns in the vicinity of the blunted cowl-lips have a substantial influence on the flow characteristics of the hypersonic inlets even though the blunting radius is very small, which contribute to a pronounced degradation of the inlet performance. The Equal Length blunting Manner (ELM) is the most optimal in that a nearly even reflection of the ramp shock produces an approximately straight and weak cowl reflection shock. The minimal total pressure loss, the lowest cowl drag, maximum mass-capture and the minimal aeroheating are achieved for the hypersonic inlet. For the other blunting manners, the ramp shock cannot reflect evenly and produces more curved cowl reflection shock. The Type V shock interference pattern occurs for the Cross Section Cutting blunting Manner (CSCM) and the strongest cowl reflection shock gives rise to the largest flow loss and drag. The cowl-lip blunted by the other two blunting manners is subjected to the shock interference pattern that transits with an increase in the blunting radius. Accordingly, the peak heat flux does not fall monotonously with the blunting radius increasing. Moreover, the cowl-lip surface suffers from severe aerothermal load when the shear layer or the supersonic jet impinges on the wall.

Introduction The burner and afterburner are the only components through which energy is added to the engine. That is, in these two components the total temperature of the gas increases. For the primary burner, a part of this energy is used by the turbine to drive the compressor, and the other part is left to generate a high-velocity gas from the nozzle, generating thrust. For the afterburner, all of this energy increase is used to generate an increase of the fluid enthalpy and consequently a higher velocity gas from the nozzle, generating more thrust. As a result of these direct impacts, efficient operation of these components is necessary for the overall efficiency of the engine. However, several complex considerations must be realized in the design of either of these components, and some of the more advanced topics are summarized by Lefebvre (1983) and Peters (1988). Furthermore, Malecki et al. (2001) demonstrate the application of CFD predictions to modern combustor design. The following are essential considerations in the design of a burner: A major objective is complete combustion or fuel will be wasted. Minimal total pressure loss is another important design goal. As discussed in Section 9.2, these first two objectives are in direct conflict. All of the combustion must take place in the combustor and not the turbine, or the turbine life will be reduced. […]