An empirical estimation of underground thermal performance for Malaysian climate

In this study, the soil temperature profile was computed based on the harmonic heat transfer equations at various depths. The meteorological data ranging from January, 1st 2016 to December, 31st 2016 measured by local weather stations were employed. The findings indicted that as the soil depth increases, the temperature changes are negligible and the soil temperature is nearly equal to the mean annual air temperature. Likewise, the results have been compared with those reported by other researchers. Overall, the predicted soil temperature can be readily adopted in various engineering applications in Malaysia

Passive thermal performance prediction and multi-objective optimization of naturally-ventilated underground shelter in Malaysia

The impact of global warming has urged a prudent spending of energy in the building sector nowadays. In general, a typical HVAC system consumes about 60%e70% of the total energy consumption of a building. Therefore, designing an energy-efficient HVAC system is essential to alleviate the worsening greenhouse effect. Recent research works have reported that geothermal energy coupled with optimal insulation is the best approach in minimising the energy consumption. Thus, we attempted to analyse the thermal performance of a naturally-ventilated underground shelter in a hot and humid country such as Malaysia. We proposed an optimal design to enhance the sustainability of the low-energy building. The model was numerically simulated using CFD, and a statistical surrogate model was implemented for obtaining the optimal design. The findings indicated that the room temperature of the shelter was significantly lower than the outdoor temperature during the hottest month and vice-versa during the coldest month. Moreover, the proposed optimal design showed about 3.4% increase in ventilation rate and about 2.8% decrease in room temperature as compared to the previous design. In general, the current work could be used as a guideline for designing low-energy building in Malaysia

The potential influence of building optimization and passive design strategies on natural ventilation systems in underground buildings: The state of the art

Most of the underground buildings rely on mechanical ventilation system for achieving an acceptable indoor thermal comfort level. In order to alleviate the greenhouse effect, it is essential to incorporate a passive system in an underground building to reduce the overall building energy consumption. From the perspective of the indoor occupant, the Indoor Environmental Quality (IEQ) should be maintained at a reasonable level as well if the passive system is used in a building ventilation system. The above problem could be addressed by devising an integrated design procedure that combines both underground building simulation and design optimization methods. The review of this topic, however, is rather scarce in the open literature. Thus, this review paper assesses existing scientific literatures that address the potential influence of building optimization and passive design strategy on the control of IEQ level. The topics covered in this review paper are histories and design considerations of underground buildings, consideration factors required, concept of building ventilation system, IEQ level assessments reported by buildings’ occupants, critical element in building optimization and passive design strategy in the underground building. From the current review, we have found that integrating both optimization approach and passive design strategy into building performance simulation is a promising technique in improving the IEQ level of the underground building. Moreover, the adoptions of soil and natural ventilation can effectively reduce the energy consumption in underground conditioning system. Indeed, there are several important factors that should be taken into account while designing an underground building. Also, there are a few passive designs that can improve thermal comfort and reduce energy consumption in underground buildings. All in all, the primary target of this paper is to assist building engineers and designers in designing an energy-efficient underground building. Meanwhile, the acceptable IEQ level could be maintained

Design analysis of open and ducted propellers in UAV application

The aim of the study was to determine the feasibility of implementing a ducted propeller system for small scale drones. 5” propeller drones are common in first person view (FPV) drone racing and cinematography, increasing the likelihood of injury due to untrained pilots, of which the majority are laceration injuries due to the propeller blades. Furthermore, the addition of a duct improves the thrust output of the entire system. A few key parameters are identified, of which were manipulated to determine the optimum values through a series of ANSYS Fluent CFD simulations. Introducing a duct is shown to reduce the lift a propeller produces; however, the reduction is offset by the lift generated by the duct. Blade tip clearance was investigated, with the optimum value found to be 0.25 mm, producing the most lift from the duct and least reduction of propeller lift, and with thrust outputs up to 35.568% more in some cases compared to open propeller. It was observed that increasing the BTC significantly reduced duct lift. Diffuser length simulations provided unconclusive results, with the duct lift varying depending on the diffuser length. However, the optimum diffuser length was determined to be 65 mm with respect to thrust outputs. In comparison, inlet lip radius shows a clear pattern, deviating from the optimum value of 16.5 mm reduces the duct lift produced, with smaller values severely decreasing performance

CFD: assessment on different bed height effect over drag model of fluidized bed

Fluidized beds are widely used by various industries because of low pressure drop, uniform temperature distribution, high heat transfer rate and large contact area which enhances chemical reaction. It seems that the efficiency of the fluidized bed depends on the knowledge of the flow behaviour which are important for scaling, design and optimization. In modelling of gas-solid phase, drag force is one of the main mechanisms for inter-phase momentum transfer. Therefore in this study, 2D model of fluidized bed was developed to study the effect of using various drag models over different bed height of H/D ratio such as 0.5, 1 and 2. The drag correlations of Gidaspow, Wen Yu, Syamlal-O'Brien, Hill Koch Ladd (HKL) and Representative Unit Cell (RUC) are to be implemented using a multiphase Eulerian Granular Model (EGM) to simulate the interaction between phases. Simulation of the model is be conducted via commercial CFD software ANSYS FLUENT 14. The main contribution of this study is to identify the important of bed height during gasification process in order to contribute in the development of TNB Research of IGCC. From the results obtained show that EGM greatly suitable for dense particle flow. As overall, the result shows Wen Yu and Gidaspow drag model are suitable for dense fluidized bed application. While for Syamlal-O'Brien drag model is more suitable for all range of application. Finally for RUC and HKL can predict highest drag at volume fraction which is more likely occur in dense phase

Design optimization for ventilation shafts of naturally-ventilated underground shelters for improvement of ventilation rate and thermal comfort

A good ventilation system is essential for an underground shelter to provide a comfortable environment with better indoor air quality. Ventilation shafts are widely used for ventilation purpose in an under- ground shelter. In the current work, the position of the ventilation shaft is optimized by employing the Response Surface Methodology (RSM). Two RSMs are constructed. The first RSM is constructed by 32 CFD models via Fractional Factorial Design (FFD) and the second model is constructed by 53 CFD models via Central Composite Rotatable Design (CCRD). The first and the second models are subsequently analysed by using the linear and quadratic models, respectively. The result indicates that both models lead to similar predictions on the inputs (factors) that strongly affect the response. Moreover, the response surface values agree well with the CFD values. Based on desirability functions, the optimized design improves the ventilation system by 24.5% as compared to the actual design. Also, the optimized design meets the comfort temperature and design criteria recommended for a naturally-ventilated underground shelter. Overall, this study finds that statistical analysis is a useful tool for the improvements of venti- lation rate and thermal comfor

A machine learning-based comparative analysis of surrogate models for design optimisation in computational fluid dynamics

Complex computer codes are frequently used in engineering to generate outputs based on inputs, which can make it difficult for designers to understand the relationship between inputs and outputs and to determine the best input values. One solution to this issue is to use design of experiments (DOE) in combination with surrogate models. However, there is a lack of guidance on how to select the appropriate model for a given data set. This study compares two surrogate modelling techniques, polynomial regression (PR) and kriging-based models, and analyses critical issues in design optimisation, such as DOE selection, design sensitivity, and model adequacy. The study concludes that PR is more efficient for model generation, while kriging-based models are better for assessing max-min search results due to their ability to predict a broader range of objective values. The number and location of design points can affect the performance of the model, and the error of kriging-based models is lower than that of PR. Furthermore, design sensitivity information is important for improving surrogate model efficiency, and PR is better suited to determining the design variable with the greatest impact on response. The findings of this study will be valuable to engineering simulation practitioners and researchers by providing insight into the selection of appropriate surrogate models. All in all, the study demonstrates surrogate modelling techniques can be used to solve complex engineering problems effectively

Fluid-solid conjugate heat transfer modelling using weakly compressible smoothed particle hydrodynamics

To date, the Smoothed Particle Hydrodynamics (SPH) method which is mesh-less and fully Lagrangian in nature has been mainly applied in solving solid heat conduction problem and flow convection problem separately. In the current work, we have implemented the Weakly Compressible Smoothed Particle Hydrodynamics (WCSPH) method to solve internal flow problem involving fluid-solid Conjugate Heat Transfer (CHT). In order to ensure heat flux continuity across the interface separating two different materials, the harmonic mean value of thermal conductivities was adopted when modelling the heat transfer between fluid and solid bodies. On the modelling of non-isothermal hydrodynamically fully-developed channel flow, the Dirichlet inlet temperature boundary condition was implemented without having to build a separate temperature reset zone as proposed in the open literature. From the current study, we have found that the particle shifting algorithm is efficient to address the tensile instability problem encountered when simulating flow at high Reynolds number. The WCSPH results were compared against the established analytical and numerical solutions and good agreement was found. The idea of extending the WCSPH method to simulate the flow and heat transfer in parallel-flow and counter-flow heat exchangers was pursued in the current study as well

Application of Bbox-Behnken design with response surface to optimize ventilation system in underground shelter

Ventilation shaft is one of the effective elements in natural venti- lation for ensuring acceptable Indoor Air Quality (IAQ) and thermal comfort. It has been found that the opening of ventilation shaft plays a significant role in the ventilation efficiency of an underground shelter. In this study, we aim to develop a predictive ventilation rate model for a naturally-ventilated un- derground shelter. Computational Fluid Dynamics (CFD) was employed as a simulation tool, where the result was validated with experimental data ob- tained from the previous literature. Goal Driven Optimization (GDO) was used for the optimization process by considering three geometrical factors and their effects on the objective function. From this study, it is found that the predicted response surface values agree well with the CFD values and hence the predictive model is reliable

Performance assessment of passive heating and cooling techniques for underground shelter in equatorial climate

Underground shelter serves as a specialized building structure that can provide either heating or cooling to occupants during different climates depending on the requirements. In this study, the CFD model of the 3D underground shelter was simulated at different seasons of the year in Malaysia. Initially, the soil temperature distributions at various depths were numerically investigated using the Kasuda Model; this model showed that at a depth of more than 10 m, the soil temperature remains constant. The soil thermal properties were considered in our numerical model simulated using ANSYS Fluent. The CFD model was firstly validated with the published experimental data, before it was used to simulate the passive heating and cooling operations within the underground shelter. The results indicated that the temperature of the underground shelter ranged between 27.80℃ and 32.10℃ from day to night. This assessment was evaluated in the coldest and warmest months of the year. Finally, the simulated room temperatures were compared against the standard Malaysian comfort temperature. It was found that natural ventilation alone could not assure a good thermal comfort level within the underground shelter