CI engine performance during cold weather condition using preheated air and engine by waste energy

ABSTRACT

The aim of the current research is to experimentally investigate the performance, combustion and emission parameters of a compression ignition engine in the discharging and air preheating mode during the cold weather condition. For preheating the engine, a thermal energy storage device using phase-change material (PCM) and for preheating the inlet air an air preheater is used. From the results, it is observed that the engine temperature increases with time from 15°C to 27°C in 840?s. PCM temperature rises from 15°C to 60°C in 3000?s. during charging and while in discharging it decreases from 45°C to 30°C within the same time period. Brake thermal efficiency increases and brake-specific fuel consumption decreases with increase in load. Air-preheated diesel gives maximum cylinder pressure as compared to normal diesel. Carbon monoxide and hydrocarbon emissions are reduced during discharging and air preheating as compared to cold weather emission.     

Experimental study on cool release process of gas-hydrate with additives

Cool release process of phase change material (PCM) includes the dissolution process of the PCM. Experimental research on the cool release process in a new gas-hydrate cool storage system is performed in this paper. In the system, the inner-heat exchange/outer-crystallization technology and the integrated condenser/evaporator structure design were adopted. The influences of different proportions of calcium hypochlorite or benzenesulfonic acid sodium salt on the dissolution process are studied. The results show that the instantaneous dissolution rate is close to twice as the corresponding instantaneous formation rate of gas-hydrate, and the cold energy release rate, i.e. energy release per unit time, is obviously higher than the corresponding cold energy storage rate at different conditions, which is mainly due to the heat transfer temperature difference of the discharging (release) and charging (store) processes. Both the charging and the discharging processes are simultaneously dominated by the heat transfer and the mass transfer processes. However, as to the dissolution (discharging) process of the gas-hydrate by heating, the effect of the heat transfer process is the main influence factor. The temperature difference between the heating medium and the gas-hydrate in the discharging process, which is larger than that between the cooling medium and the gas-hydrate in the charging process, makes a higher cold energy release rate compared with the cold energy storage rate. The results also indicate that the dissolution rate of gas-hydrate is accelerated, and the cold energy release rate of the cool storage system is increased by adding reasonable proportions of the additives.     

Experimental analysis of thermal performance of evacuated tube solar air collector with phase change material for sunshine and off-sunshine hours

An experimental investigation of an evacuated tube solar air collector coupled to a latent thermal energy store for generating hot air when no solar radiation is incident was undertaken. Acetamide was used as a phase change material (PCM). The latent thermal energy store was integrated with the manifold of the solar collector and water was used as the working fluid transferring solar gain to the air being heated. The maximum measured temperature differential between the heated air and the ambient air was 37°C and 20.2°C during conditions of incident and non-incident solar radiation, respectively. This occurred using a circular fin configuration at a flow rate of 0.018?kg?s^?1. The efficiency at low (0.018?kg?s^?1) air flow rates was 0.05–0.50 times less as compared to high (0.035?kg?s^?1) air flow rates. This system has advantages over systems using sensible storage as it can be used after sunset due to better heat storing capacity of the PCM.     

Energetic and exergetic analysis and assessment of a thermal energy storage (TES) unit for building applications

The main objective of this study is to investigate the energetic and exergetic performances of a latent energy storage system in both charging (solidification) and discharging (melting) processes. A shell-and-tube TES unit was designed, constructed and tested in Dokuz Eylul University, Izmir, Turkey. This experimental unit basically consisted of a heat exchanger section, a measurement system and flow control systems. For the charging mode, the inlet temperatures varied to be −5 °C, −10 °C and −15 °C, while the volumetric flow rates changed to be 2 l/min, 4 l/min and 8 l/min. The experiments were performed for three different tube materials, copper, steel and PE32 and two various shell diameters of 114 mm and 190 mm to investigate the tube material and shell diameter effects on energetic and exergetic efficiencies. It may be concluded that for the charging period, the exergetic efficiency increased with the increase in the inlet temperature and flow rate. For discharging period, irreversibility increased as the temperature difference between the melting temperature of the PCM and the inlet temperature of the heat transfer fluid (HTF) increased and hence the exergy efficiency increased.     

Experimental investigation of PCM cold storage

This article presents an experimental analysis of cooling buildings using nighttime cold accumulation in a phase change material (PCM), otherwise known as the “free-cooling principle”. Studies of the ceiling and floor free-cooling principle, as well as passive cooling, are presented. The free-cooling principle is explained and some of the types of PCMs suitable for summer cooling are listed. An experiment was conducted using paraffin with a melting point of 22 °C as the PCM to store cold during the nighttime and to cool hot air during the daytime in summer. Air temperatures and heat fluxes as a function of time are presented for different air velocities and inlet temperatures.     

Correlation between the local climate and the free-cooling potential of latent heat storage

The natural cooling of energy-efficient buildings using latent heat thermal energy storage (LHTES) that is integrated into the building services makes possible energy savings and improved thermal comfort. In this article, studies of the free-cooling potential for different climatic locations are presented. Six cities from around Europe with a wide range of climatic conditions were selected. The size of the LHTES was optimized on the basis of the calculated cooling degree-hours. First, we analysed the influence of the width of the phase change temperature range and determined the optimal melting temperature of the phase change material (PCM). Then, the optimal LHTES was selected, based on the ratio of the mass of the PCM and the volume flow rate of air ventilating the building. We found that the optimum PCM has a melting temperature that is approximately equal to the average ambient air temperature in the hottest month, and that the free-cooling potential is proportional to the average daily amplitude of the ambient air's temperature swings. For all the analysed climatic conditions the PCM with a wider phase change temperature range (12 K) was found to be the most efficient. The optimal size of the LHTES for the free cooling of buildings is between 1 and 1.5 kg of PCM per m³/h of fresh ventilation air.     

Performance of phase change material boards under natural convection

The high thermal storage capacity of phase change material (PCM) can reduce energy consumption in buildings through energy storage and release when combined with renewable energy sources, night cooling, etc. PCM boards can be used to absorb heat gains during daytime and release heat at night. In this paper, the thermal performance of an environmental chamber fitted with phase change material boards has been investigated. During a full-cycle experiment, i.e. charging–releasing cycle, the PCM boards on a wall can reduce the interior wall surface temperature during the charging process, whereas the PCM wall surface temperature is higher than that of the other walls during the heat releasing process. It is found that the heat flux density of the PCM wall in the melting zone is almost twice as large as that of ordinary wall. Also, the heat-insulation performance of a PCM wall is better than that of an ordinary wall during the charging process, while during the heat discharging process, the PCM wall releases more heat energy. The convective heat transfer coefficient of PCM wall surface calculated using equations for a normal wall material produces an underestimation of this coefficient. The high convective heat transfer coefficient for a PCM wall is due to the increased energy exchange between the wall and indoor air.     

Limits and potentials of office building climatisation with ambient air

One of the first passive energy standard office buildings in Europe was extensively monitored over 3 years to analyse the summer performance of highly insulated, well sun-shaded and mechanically ventilated buildings. During typical German summer conditions with less than 160 hours ambient air temperatures above 25 $°$C, these buildings perform excellently during summer, even if the internal loads are rather high with 200–400 Wh m⁻² day⁻¹. If ambient air temperatures are significantly higher like in summer 2003 with more than 3 K higher average temperatures than usual, nearly 10% of all office hours are above 26 $°$C. Detailed measurements showed that the night discharging of heavy thermal masses such as the concrete ceiling was not always effective under free convection conditions. Room air temperature decreased by 2–3 K only although measured night air changes were always above 5 h⁻¹. The measured air change rates contained not only cool ambient air but also backflow of warmer air from the corridors, which could be shown by flow visualisation in the rooms and by simulation studies. Improvements to the night ventilation performance can be achieved, if early evening ventilation with high heat gains can be reduced and if fans support the air exchange in the cooler morning hours.Three year measurements and simulation of the earth heat exchanger showed that excellent performance is achieved with COP’s between 35 and 50. Due to the limited fresh air volume flow in such buildings, the earth heat exchanger only removes a fraction of the loads, here about 18% of the total internal loads.     

Thermal storage and nonlinear heat-transfer characteristics of PCM wallboard

For the materials with constant thermophysical properties, the thermal performance of wallboards (or floor, ceiling) can be described by decrement factor f and time lag φ. However, the phase change material (PCM) may charge large heat during the melting process and discharge large heat during the freezing process, which takes place at some certain temperature or a narrow temperature range. The behavior deviates a lot from the material with constant thermal physical properties. Therefore, it is not reasonable to analyze the thermal performance of PCM wallboard by using the decrement factor f and time lag φ. How to simply and effectively analyze the thermal performance of a PCM wallboard is an important problem. In order to analyze and evaluate the energy-efficient effects of the PCM wallboard and floor, two new parameters, i.e., modifying factor of the inner surface heat flux ‘α’ and ratio of the thermal storage ‘b’, are put forward. They can describe the thermal performance of PCM external and internal walls, respectively. The analysis and simulation methods are both applied to investigate the effects of different PCM thermophysical properties (heat of fusion H_m, melting temperature T_m and thermal conductivity k) on the thermal performance of PCM wallboard for the residential buildings. The results show that the PCM external wall can save more energy by increasing H_m, decreasing k and selecting proper T_m (α < 1); that the PCM internal wall can save more energy by increasing H_m and selecting appropriate T_m, k. The most energy-efficient approach of applying PCM in a solar house is to apply it in its internal wall.     

冰蓄冷空调蓄冰罐特性的研究

通过对某大厦冰蓄冷空调系统运行情况的测试,详细研究和分析了蓄冰罐在不同流量下的蓄冰和放冷特性以及在放冷工况时,蓄冰罐进口温度对出口温度和放冷量的影响。     

Sensory And Physiological Effects On Humans Of Combined Exposures To Air Temperatures And Volatile Organic Compounds

Ten healthy humans were exposed to combinations of volatile organic compounds (VOCs) and air temperature (0 mg/m³ and 10 mg/m³ of a mixture of 22 volatile organic compounds and 18, 22 and 26° C). Previously demonstrated effects of VOCs and thermal exposures were replicated. For the first time nasal cross-sectional areas and nasal volumes, as measured by acoustic rhinometry, were shown to decrease with decreasing temperature and increasing VOC exposure. Temperature and pollutant exposures affected air quality, the need for more ventilation, skin humidity on the forehead, sweating, acute sensory irritation and possibly watering eyes in an additive way. Interactions were found for odor intensity (p = 0.1), perceived facial skin temperature and dryness, general well-being, tear film stability, and nasal cavity dimension. The presence of interactions implies that in the future guidelines for acceptable indoor air concentrations of VOCs should depend on room air temperature.     

地板采暖系统用复合相变砂浆填充材料研究

阐述了相变砂浆作为填充层材料在地板采暖中应用的意义,采用溶胶-凝胶法制备了以二氧化硅为载体的复合有机相变颗粒材料,配制了相变石膏砂浆.利用地板采暖试验间进行了相变砂浆和普通砂浆的地板采暖试验,以验证相变砂浆地板采暖系统的蓄放热性能,并对地板表面和室内的温度影响进行了试验分析.通过试验验证了新型相变砂浆作为填充层材料应用到地板采暖是切实可行的,在较好改善室内温度环境的同时降低了地板采暖系统的荷载和厚度.     

Night ventilation and active cooling coupled operation for large supermarkets in cold climates

Night ventilation and active cooling coupled operation strategy is studied for the large supermarkets in cold climates in China. The model on the thermal storage of the indoor goods is set up. Furthermore, based on the thermal balance of the whole room, the temperature change model is founded. The coupled operation process is simulated for the typical supermarket buildings. The overall energy consumption of the system is analyzed. The result shows that the opening time, duration and air flow rate of night ventilation all affect the performance of active cooling. Active cooling will influence night ventilation too. It also turns out that the coupled operation leads to shorter operation time of active cooling. The various operation modes are given at different climatic conditions. Compared with the normal active cooling system, the coupled operation system can save energy at 2.99 kWh/(m² a) in cold climates in China while 3.24 kWh/(m² a) in Harbin.     

相变材料应用于建筑外墙的温度与能耗模拟

使用EnergyPlus能耗模拟软件对相变材料作为外墙表面隔热材料的应用效果进行模拟,在小空间和小型办公室的模型上,改变相变材料的相变温度、材料结构和用量等使用条件,并进一步考虑室内热源和不同气候区的影响,对比分析在空调季节里空间内部温度的变化情况和空调节能效果。模拟结果表明:相变温度稍高的相变材料更有利于夜间散热蓄冷,同时,结合双层复合结构可获得更好的温度抑制和节能效果;内热源的存在会提高房间空调能耗的基数,从而使相变材料空调节能率计算值降低,并且在一定程度上掩盖了相变材料对室内平均温度的抑制作用,尽管如此,相变材料在有内热源环境下使用时空调节能量仍与无内热源时相当。     

Positioning of an isothermal heat storage layer in a building wall exposed to the external environment

The paper presents an idea for the enhancement of a building's thermal insulation component by adding into the structure a thin layer of a phase-change material (PCM). The proposed solution can be dedicated, for example, to an external partition of lightweight construction. The capacity for latent heat storage allowed it to stabilize the temperature inside the insulation layer in a daily cycle and to minimize the temperature difference between the internal and external surfaces. In this paper, different positions of a PCM layer in the thermal insulation of an external wall were analysed. The main goal of this work was to find the best position of the PCM layer, taking into account the indoor temperature and the meteorological conditions. The authors propose two parameters: the amount of stored energy and the dynamism of the charging/discharging processes. Taking into account large temperature fluctuations on the external surface during summer and winter, it was concluded that, for this specific case, the most appropriate solution would be an external position of the PCM with a melting temperature of 20°C.     

Thermal performance analysis of evacuated tubes solar air collector in Indian climate conditions

The thermal performance of one-ended evacuated tubes solar air collector is experimentally investigated during the winter season at NIT Kurukshetra, India [29 ° 58^′(latitude) North and 76 ° 53 ^′ (longitude) East]. The collector consists of 15 one-ended evacuated tubes with different lengths of directional inner aluminium tubes (inserted tubes) and a manifold channel, with air used as a working fluid. The inlet air flows through the directional inner aluminium tubes as a result of forced convection. In this experiment, evacuated tubes are used for producing hot air corresponding to different lengths of directional aluminium tubes without using any intermediate fluid. The temperature of the outlet air depends on the air flow rate, length of the directional aluminium tube and solar intensity. The maximum temperature difference between outlet air and inlet air at solar intensity 904 W/m² was found to be 72.7 °C with a flow rate of 5.06 kg/h and length of 0.83 m.     

冰蓄冷空调技术研究实验室的开发建设

该实验室具有实际工程规模，包括五个系统：冰蓄冷、电蓄热机房系统，低温送风VAV空调末端性能测试系统，风机盘管及VAV空调机组热工测试系统，低温送风空调系统和常规空调系统。重点介绍了实验室机房系统的功能、组成和流程原理，以及储冰测试设备的蓄冰、融冰测试方案、测试流程和使用的数学模型。     

Effect of double layer phase change material in building roof for year round thermal management

Efficient and economical technology that can be used to store large amounts of heat or cold in a definite volume is the subject of research for a long time. Latent heat storage in a phase change material (PCM) is very attractive because of its high-energy storage density and its isothermal behavior during the phase change process. Thermal storage plays a major role in building energy conservation, which is greatly assisted by the incorporation of latent heat storage in building products. Increasing the thermal storage capacity of a building can enhance human comfort by decreasing the frequency of internal air temperature swings so that the indoor air temperature is closer to the desired temperature for a longer period of time. However, it is impossible to select a phase change material to suit all the weather condition in a given location. The PCM that reduces the internal air temperature swing during the winter season is not suitable for the summer season as the PCM remains in the liquid state at all the times during these months and hence the system cannot exploit the latent heat effect. This paper attempts to study the thermal performance of an inorganic eutectic PCM based thermal storage system for thermal management in a residential building. The system has been analyzed by theoretical and experimental investigation. A double layer PCM concept is studied in detail to achieve year round thermal management in a passive manner.     

Study on phase change material and its appropriate thickness for controlling solar cell module temperature

ABSTRACT

Appropriate thickness of phase change material (PCM) to control the solar cell module temperature for increasing power generation was carried out. A PCM, RUBITHERM RT42, with the melting point at 42°C and a thickness of 50?mm was used to absorb heat at the back of a 250?W_p polycrystalline solar cell. A numerical enthalpy method to predict the melting phenomenon of the PCM, RT35, 42, 47, and 55, and the solar cell module temperature was developed. The results agreed well with those of the experimental data. It was found that the maximum generated power was around 167?W in comparison with 147?W of the normal unit at a solar radiation of 867?W/m². The daily power outputs were 0.707 and 0.642?kWh, respectively. From the simulation under Chiang Mai climate, for RT42 PCM, it was found that the appropriate thickness was around 40?mm.     

Refining the use of evaporation in an experimental down-draft cool tower

Direct evaporative cooling has long been recognized as an energy-efficient and cost-effective means for space conditioning in hot dry areas. In order to extend the use of evaporative cooling to include exterior or semi-enclosed spaces, a down-draft evaporative ‘cool tower’ was integrated in the project of a 500 m² glazed courtyard located at the heart of a building complex in the arid Negev Highlands of southern Israel, designed by the authors. The present article describes the development of the cooling tower system, undertaken in three phases: (i) Prototype analysis. Performance of a small-scale tower was monitored, and comparisons were drawn between varying rates and mechanisms of water and air supply. The results indicated a potential for substantial temperature reduction in the order of 10 °C under summer daytime conditions, but a meager cooling output when using a natural draft system. Mechanical-forced air flow was thus utilized in the actual tower. (ii) Field monitoring. The cool tower, approximately 10 m in height and 10 m² in cross-sectional area, was operated and monitored during a summer season; its performance was analyzed using a series of water supply mechanisms and operating modes. The system produced a peak cooling output of just over 100 kW, with a wet bulb temperature depression of close to 85–95% during all hours of operation, and a water consumption rate of approximately 1–2 m³/day. (iii) Refinement. Potential improvement in the system's operation was investigated through the development of a wind capture mechanism for increasing inlet pressure and air flow to the space. Both fixed and dynamic capture units were investigated, with wind speed and direction as well as internal air speeds measured in the small-scale prototype tower. The wind capture unit with the simplest configuration and best performance is recommended for future integration in the full-scale tower.