The Importance of High-Frequency, Small-Eddy Turbulence in Spark Ignited, Premixed Engine Combustion

The different roles played by small and large eddies in engine combustion were studied. Experiments compared natural gas combustion in a converted, single cylinder Volvo TD 102 engine and in a 125 mm cubical cell. Turbulence is used to enhance flame growth, ideally giving better efficiency and reduced cyclic variation. Both engine and test cell results showed that flame growth rate correlated best with the level of high frequency, small eddy turbulence. The more effective, small eddy turbulence also tended to lower cyclic variations. Large scales and bulk flows convected the flame relative to cool surfaces and were most important to the initial flame kernel

Dynamic Modelling of Building Envelope on Energy Usage

This study investigates the influence of the building envelope on the energy usage of a chosen building using the simulation program TRNSYS. The building located at Carleton University, Ottawa, Canada is a small building retroffited as part of the Natural Resources Canada’s Prefabricated Exterior Energy Retrofit (PEER) project. The project\u27s aim is to develop prefabricated technologies to be used for retroffiting existing building envelopes of homes in Canada. The thermal resistance (RSI) of the existing walls were improved from 1.80 m2K/W to about 6.40 m2K/W after installation of the prefarbricated retrofit wall system. Analytical verification of the whole building performance simulation software is performed using a solitary heat transfer mechanism under simplified boundary conditions with known analytical solution. The warm-up period necessary to ensure heat is distributed in the building thermal mass at the start of the simulation is quantified. The thermal performance of the whole building envelope is quantified using the time-lag effect and decrement factor and energy requirement for heating and cooling

Residential solar air conditioning: Energy and Exergy analyses of an ammonia-water absorption cooling system

Large scale heat-driven absorption cooling systems are available in the marketplace for industrial applications but the concept of a solar driven absorption chiller for air-conditioning applications is relatively new. Absorption chillers have a lower efficiency than compression refrigeration systems, when used for small scale applications and this restrains the absorption cooling system from air conditioning applications in residential buildings. The potential of a solar driven ammonia-water absorption chiller for residential air conditioning application is discussed and analyzed in this paper. A thermodynamic model has been developed based on a 10 kW air cooled ammonia-water absorption chiller driven by solar thermal energy. Both energy and exergy analyses have been conducted to evaluate the performance of this residential scale cooling system. The analyses uncovered that the absorber is where the most exergy loss occurs (63%) followed by the generator (13%) and the condenser (11%). Furthermore, the exergy loss of the condenser and absorber greatly increase with temperature, the generator less so, and the exergy loss in the evaporator is the least sensitive to increasing temperature

Energy efficiency and economic feasibility of an absorption air-conditioning system using wet, dry and hybrid heat rejection methods

In tropical and sub-tropical regions, air-conditioning systems account for the greatest electricity consumption and high water use. Solar-driven absorption cooling systems can conveniently reduce electricity consumption at need. The performance of this cooling system depends on the system’s heat rejection. A simulation was performed for a 15 kW single effect ammonia-water absorption cooling system driven by low temperature thermal energy and with three different heat rejection methods (wet cooling, dry cooling, and hybrid cooling). This hybrid cooling system uses wet cooling on the absorber and dry cooling on the condenser. The system performance and economics of the chiller with these cooling methods were evaluated. The analysis showed that a wet cooling system has a higher system performance and water consumption compared to a dry cooling system, which has a high primary energy consumption with no water usage. In hot weather conditions and where there is scarcity of water, hybrid cooling can consume on average 41% less electrical energy than dry cooling and 49% less water than wet cooling and the payback period compared to a wet cooling system can be less than three years

Bubble-pump-driven LiBr-H2O and LiCl-H2O Absorption Air-Conditioning Systems

A thermally-driven bubble pump, powered by solar or waste heat energy, is a simple and efficient technique for lifting a liquid from lower to higher levels, after which it can flow by gravity. In this study, solar thermal driven pumps were incorporated in the solar collector as well as in the refrigerant cycle to provide a design of an air-conditioning system for a residential home that is independent of grid electricity. The crystallization challenge, low pressure, and low efficiency are the main downsides of bubble-pump-driven LiBr-H2O refrigeration systems, in comparison with other bubble-pump-driven diffusion absorption refrigeration systems. Therefore, a complete thermodynamic analysis of each component is necessary to improve the system performance. In this research, a thermodynamic model was developed, introducing a new absorbent-refrigerant pair (LiCl-H2O) and comparing it with LiBr-H2O, in a bubble pump operated absorption chiller driven by solar thermal energy. Under the same operating condition, the highest cooling effect and the performance of the LiCl-H2O system are 49 W and COP=0.56 compared to 34 W and COP=0.46 for a LiBr-H2O system

Greenhouse electrification via transactive energy management strategy

Distributed energy resources have grown significantly in Canada and the world over the past decade, particularly in the agricultural sector. As P2P (peer-to-peer) energy trading plays a fundamental role in renewable energy uptake and system flexibility for the low-carbon energy transition, this paper provides an overview of this approach from a techno-economic standpoint for two greenhouses located in Leamington, Ontario. The real-time site solar irradiation, ambient temperature, and load demand over 8760 h have been utilized to drive the designs. In this investigation, two cases are assessed for pepper greenhouse: Case I: energy purchase from the grid and Case II: energy purchase from excess energy of neighbor which is cucumber-tomato greenhouse. The integration of 50 kW PV/1 kWh battery/35 kW converter achieves the feasibility criteria by recording net present cost (NPC) and cost of energy (COE), which are $29.6k and$0.044/kWh, respectively

Advanced Exergy Analysis Of Licl-H2O Absorption Air Conditioning System

Increasing energy demand for air conditioning due to climate change is posing a continuous threat to the environment. Absorption air-conditioning systems driven by solar thermal or waste heat energy are an alternative for providing cooling comfort in a sustainable manner. The crystallization problem of high performance LiBr-H2O absorption cooling system hinders its small-scale applications. In this study, the potential of a 10 kW LiCl-H2O absorption refrigeration system is discussed and analyzed. The new concept of advanced exergy analysis is coupled with conventional thermodynamic analyses, which provides the available potential of each component for overall system performance improvement. The analyses uncovered that only 45% of the total exergy loss is due to each component’s own internal irreversibilities, whereas the remaining is through the interaction of the irreversibilities of other components in the system. The analyses also reveal that 43% of the total exergy loss is unavoidable and 57% can be reduced by improving the overall system efficiency

Bio-inspired study of thermal effects on NACA0012 airfoil at Reynolds Number of 33,000

The amount of solar and background radiation absorbed by birds vary according to their wing shape, pigmentation, porosity, etc. Birds are equipped with unique features to thrive, including attracting opposite sex, regulating body temperatures, and soaring in the sky. The research focuses on solar/sky radiation by examining how NACA0012 airfoil, representing the wing of a bird, performs when its upper surface temperature is higher or lower than the surrounding air. This is realised by performing 2-dimensional simulations in OpenFOAM at a Reynolds Number of 33,000, where Spalart-Allmaras model is used to simulate the flow turbulence. The upper surface of the airfoil is warmed to 330 K and cooled to 270 K at a pressure of 1 atm, an ambient temperature of 300 K, and a Mach number of 0.0725. The results illustrate the airfoil with the cooler top surface exhibits a lower drag and higher lift than its warmer top surface counterpart. A maximum reduction of drag coefficient from 0.065 to 0.061 and increase in lift coefficient from 0.89 to 0.93 at an angle of attack 11° are achieved. In short, tuning the upper surface of NACA0012 airfoil to temperatures lower than the ambient provides better aerodynamic performance

Studying the Influential Parameters in an Office Building’s Energy Consumption

Research on the energy consumption of buildings has become increasingly important due to the growing global population and depleting energy resources. This study focuses on modeling the energy usage of an office building by examining the various parameters that influence its electricity consumption. An existing office building located in Philadelphia is selected as a reference for simulation, and the simulated results and measured values are compared. The parameters that affect the building, such as ambient temperature, solar radiation, building envelope, wind speed, and other internal gains, are discussed and defined. To verify the model, a transient simulation is run for sinusoidal ambient weather data for 180 hours, with a timestep of 15 minutes. The thermal mass and thermal resistance of the building envelope cause the expected delay and attenuation in the indoor temperature and indoor power demand. The building is then subjected to real case inputs from the actual office building for predictive modeling. The simulation output is compared with the measured power consumption data from the literature, which is provided for each month over the course of a full year (2004). To account for the variability of a building\u27s infiltration rate over a year, the results are plotted for two different infiltration values: 0.25 ACH and 0.85 ACH. It is found that the simulated results for the two infiltration values provided are within the range of the measured values. This study provides valuable information on the factors that affect the energy usage of office buildings. The simulation results demonstrate the predictability of modeling an office building energy usage. As part of future work, this model will be employed to perform a sensitivity analysis on energy consumption for each parameter, with the aim of pinpointing the parameter that exerts the most substantial influence