Maximum Temperature Reduction Research Articles

Experimental investigation on paraffin wax integrated with copper foam based heat sinks for electronic components thermal cooling

Owing to enormously high surface area and high thermal conductivity, copper foam based heat sinks for electronic cooling are investigated in this paper. Copper foam1 with porosity 0.95 and pore density 15 pores per inch and copper foam2 with 0.97 porosity and pore density 35 pores per inch are used to investigate the performance of heat sinks filled with phase change material (PCM). Various configurations of heat sink with PCM volume fractions 0.0, 0.6, 0.7 and 0.8 are investigated under heat load of 8–24 W to figure out the optimum performance of the heat sink. Experimental results revealed that base temperature of the heat sink is reduced as the volume fraction of PCM is increased. Anyhow, discharging process is not affected significantly. Furthermore, copper foam1 (0.95 porosity) exhibited better heat transfer both in charging and discharging as compared to that of copper foam2 (0.97 porosity). Maximum temperature reduction of 9.81% was found for copper foam1/PCM at 8 W and PCM volume fraction of 0.8 when it is compared with copper foam2/PCM composite. For the same porosity, maximum reduction in base temperature was observed for 0.8 volume fraction of PCM at 16 W heat input. Finally, it is concluded that copper foam1/PCM composite impregnated with 0.8 volume fraction is an optimized configuration of heat sink.

Theoretical and Experimental Contributions on the Use of Smart Composite Materials in the Construction of Civil Buildings with Low Energy Consumption

The paper presents the theoretical and experimental studies undertaken for the realization of an intelligent composite material with phase shift that has optimal characteristics in the thermal energy storage process and an experimental method for integrating the material with phase change in a possible efficient system to be used in the construction of a dwelling. It analyzes the main factors in designing such systems (the temperature limits between which the system must operate, the melting/solidification temperature of the Phase Change Material (PCM), the latent heat of the PCM, the degree of thermal loading, the bed configuration of PCM capsules and a PCM-RB01 material is set. A micro-encapsulation method was chosen and a “solar wall” is made where the incident solar radiation is absorbed by the PCM embedded in the wall, so the stored heat is used for heating and ventilation of a home. Experimental research has shown that developed PCM allows a maximum room temperature reduction of about 4 °C during the day and can reduce the night-time heating load. Also, despite the lower thermal energy absorption capacity, the developed PCM-RB01 material provides a superior physical stability compared to the classical types of integration.

GaN transistors efficient cooling by graphene foam

Graphene conductive foams have shown very high potential as cooling material in electronic systems. Its exploitation with discrete GaN transistors is demonstrated in this paper. A proper experimental setup is developed to extract the high temperature thermal performance of this material at different test conditions. The results are very promising, showing a noticeable reduction of the device maximum temperature, especially at high dissipated power densities.Moreover, experimental results allowed the validation of a 3D finite element model of the assembled device, which can be used for thermal layout optimization.Finally, preliminary stress tests are in progress, to evaluate the stability of electrical and thermal performance of the proposed graphene based assembly. Good stability was obtained, both at low and high ambient temperatures.

Copper foam/PCMs based heat sinks: An experimental study for electronic cooling systems

Copper foam (with porosity 97% and pore density 35 pores per inch) based heat sink without phase change material (PCM) and copper foam/PCM composites heat sinks are investigated to observe the behavior of operational time of heat sinks with respect to specific temperature both for charging and discharging. Paraffin wax, RT-35HC, RT-44HC and RT-54HC are used as PCM. Investigations are performed at heat flux of 0.8–2.4 KW/m2 with a gap of 0.4 KW/m2 uniformly distributed. PCM volume fractions of 0.68 and 0.83 are used in composites. Results indicated that at the end of 90 min charging, maximum temperature reduction of 25% is noted for RT-35HC/Copper foam at 0.8 KW/m2 for PCM volume fraction 0.83. Afterwards, RT-44HC/Copper foam reveals maximum temperature reduction of 24% for 1.6 KW/m2. RT-35HC/Copper foam is least efficient at 2.4 KW/m2 which reduces the base temperature only by 5–7%. Maximum enhancement ratio in operation time is noticed as 8 and 7.7 for RT-35HC/Copper foam and RT-44HC/Copper foam respectively at set point temperature (SPT) of 40 °C and 60 °C for respective composites.

Thermal management of concentrator photovoltaic systems using microchannel heat sink with nanofluids

A new cooling method for concentrator photovoltaic system is proposed using wide microchannel heat sink with nanofluids. A comprehensive three-dimensional model is developed. The model couples the two-phase (Eulerian-Eulerian) multiphase model for the conjugate heat transfer of nanofluid flow in a wide microchannel heat sink with the thermal model of the concentrator photovoltaic systems. The model is numerically simulated and validated with the available experimental and numerical data. The influences of nanoparticle types, volume fractions, and coolant flow Reynolds number on the solar cell performance parameters are investigated. Results indicate that using SiC-water nanofluids attains lower cell temperature compared with Al2O3-water nanofluids. The increase of nanoparticles volume fraction ratio remarkably reduces the solar cell temperature and enhances the cell temperature uniformity and electrical efficiency. Furthermore, increasing the flow Reynolds number to a specific value significantly enhances the net electrical power. Further increase of the Reynolds number results in a significant reduction in the cell net gained power. By using 4% SiC-water nanofluid, the reduction in maximum local solar cell temperature is ranged between 8 °C and 3 °C compared with pure water with changing the flow Reynolds number from 12.5 to 250 at solar concentration ratio of 20.

The impact of urban green infrastructure as a sustainable approach towards tropical micro-climatic changes and human thermal comfort

Green infrastructures such as living walls are technological solutions to replace the declined greenery at urbanized environment and also reliable applications for thermal regulation in buildings through insulation effect and escalates the energy use efficiency. Thermal comfort and local climate are spatiotemporally variable. The existing research gap should be addressed by evaluating the performance of vertical green walls in tropical condition. In this study, thermal performance, relative humidity (RH) and CO2 concentration were quantified for basic three types of green infrastructures; such as (T1) living walls, (T2) indirect green façades and (T3) direct green façades located in Colombo metropolitan in Sri Lanka. An in-situ experimental study was conducted considering temperatures at 1 m and 0.1 m distance in front of the green walls, inside the foliage, air gap and external wall surface comparatively to adjacent bare wall control. Three case studies per green infrastructure within Colombo metropolitan area were purposively selected. Simultaneously, RH and CO2 concentration at 0.1 m in front of the green and bare walls were measured for the performance quantification. The internal thermal comfort simulation and occupants’ satisfaction questionnaire survey was executed to assess the green infrastructure performances. The study revealed that vertical greenery systems were highly effective on external wall surface temperature reductions at 1100 h–1500 h time zones. T1 and T2 accounted for superior temperature reduction in the range of 1.61 °C–1.72 °C through the façade relative to the distance than T3. Maximum temperature reduction compared to the bare wall control was obtained for the T1 (0.28 °C–8.0 °C) followed by T2 (1.34 °C–7.86 °C) and T3 (1.34 °C–6.64 °C). Averaged RH increment (1.6%–1.81%) and CO2 reduction (0.63%) occurred near green walls at day time compared to control. An average 28 °C simulated indoor temperature circumstantiate the indoor thermal comfort. 58% and 89.5% occupants’ were satisfied with thermal and visual comfort respectively, thus emphasizing façade greening as a sustainable approach on micro climatic changes and human thermal comfort.

Implementation of Peltier Cooling in Hermetically Sealed Electronic Packaging Unit for Sub-sea Vessel

This paper presents the methodology adopted for implementation of Peltier cooling in hermetically sealed electronic packaging units used in sub-sea vessels. In sub-sea vessels, sonar front-end electronics is packaged in hermetically sealed electronic packaging units. The thermal design of the unit is a highly challenging task considering the heat dissipation of 300W from the electronics, non-availability of chilled air for cooling and IP68 sealing requirements. Cooling fans cannot be integrated, since these units are to be placed in acoustically sensitive pressure capsule area of the subsea vessel. The electronic cooling in this unit is achieved using conduction cooling with external fins. To enhance the cooling, suitable Peltier cooling (Thermo-electric cooling or TEC) module is selected and implemented with the system. Computational fluid dynamic analysis of the unit is carried-out to study the air-flow and thermal performances with Peltier cooler. The unit is realised and the estimated temperatures validated by experimental temperature measurements on the realised unit. The measured temperatures are within the safe operating limits of the electronic components and hence the cooling design of the unit is satisfactory. It is also observed that maximum temperature reduction has occurred at 1.5A current and card edge temperature of Printed circuit board lowered by 9.28 °C by implementing Peltier cooling.

Performance of Hong Kong's common trees species for outdoor temperature regulation, thermal comfort and energy saving

Using a validated ENVI-met model, a parametric study was conducted to investigate the thermal and energy saving benefits in a selected neighbourhood with its current greenery coverage ratio (GCR) of 7.2%, compared to the recommended 30%. To provide information for efficient tree species selection, nine scenarios were tested for the case of 30% GCR. In eight of them, only one tree species was used in each case. The trees represent the eight most common species in Hong Kong. The remaining one featured a mix of tree species.In comparison with the reference case (no trees), results revealed a reduction in maximum temperature of 0.4 °C and 0.5–1.0 °C under the current and 30% GCR situations respectively; and a decrease in average Physiological Equivalent Temperature of 1.6 °C and 3.3–5.0 °C. The area coverage of “Very Hot” thermal sensation reduced from ∼60% in the reference case to ∼50% with the current GCR and 17–21% with 30% GCR. Lastly, a decrease in cooling energy of 1500 kWh per typical summer day was observed with the current GCR, which increased to ∼1900–3000 kWh with 30% GCR, equivalent to 200–450 US$ savings within the 500 × 500 m2 domain. The variations in the estimated benefits between the 30% GCR scenarios reflect the importance of species-specific analysis. Statistical analysis revealed leaf area index was the main driver of the observed benefits, followed by trunk height, tree height and crown diameter. Our findings will encourage city planners and citizens to take actions for urban greening.

Analysis of thermophoresis and Brownian motion effect in heat transfer for nanofluid immersed distribution transformer

This paper presents an analysis of the heat transfer behavior of a three-phase distribution transformer filled with nanofluid. The effect of thermophoresis and Brownian motion is incorporated into the governing equations, thus giving the non-homogenous mathematical model for the nanofluid flow. The results show that in presence of the temperature gradient in a distribution transformer, the nanoparticle volume fraction greatly reduces near the heated wall and consequently modifies the net oil flow in the transformer, owing to reduction in oil viscosity near the heated wall. The results of the complete analysis of the temperature and the velocity field distribution of nanofluid flow show an increased heat transfer in both the natural and forced convection; the increase is relatively higher in former, in the light of thermophoresis effect and Brownian motion. Further, the results of the parametric study show that nanofluid dispersed with the magnetite nanoparticles has higher reduction in maximum temperature ( $$\sim $$ 11 K) followed by silica nanoparticles ( $$\sim $$ 7.3 K) and quartz nanoparticles ( $$\sim 6$$ K). The maximum reduction in temperature increases to 13 K in magnetite nanofluid under the influence of electric and magnetic field while it remains unchanged in silica nanofluid.

Development and analysis of a technique to improve air-cooling and temperature uniformity in a battery pack for cylindrical batteries

In this paper, a passive approach to improve temperature uniformity in a simple battery pack, in which an inlet plenum is added as a secondary inlet to a battery pack with an axial air flow, is examined. This inlet plenum changes the direction of the flow and eliminates the problem of recirculation and non-availability of air between the adjacent cells. Three different configurations are considered to examine the effects of the orientation of inlet plenum and the cells. CFD (computational fluid dynamics) is used to perform detailed simulations of the battery packs and the results are validated with data obtained experimentally from one of the battery pack configuration. The thermal performance of the battery packs is compared to the baseline case, and the results indicate an average maximum temperature reduction of the cells by ∼4% and an improvement in temperature uniformity of the cells by ∼39%. This is a simple battery pack that uses forced air passive cooling (no moving parts required in the battery pack) and introduces mixing and turbulence in the air flow to increase the temperature uniformity in the battery pack.

Investigations on the use of Lanthanum Strontium Zirconate coating in maintaining temperature distributions of gas turbine blades

Increase in the efficiency of a gas turbine system is possible by operating it at increased temperature of hot working gases. However, it puts a direct thermal load on the material of the blade, which in turn demands for increased cooling capacities for the blade. Present paper deals with simulation based investigations on the effects of a ceramic coating of lanthanum strontium zirconate layer onto the surface temperature profile of a TMW4 gas turbine blade through an in-between bond coat layer of NiCoCrAlY. The blade model was simulated in ANSYS Workbench v14.5 for an ultra-high temperature of 1700 °C as operating temperature and calculated convection conditions from the gases and coolant air side. Steady state thermal results show a significant effect of coating in lowering substrate temperatures of blade. The results were evaluated for models with variable thickness of coating, maintaining overall dimensions of the blade constant. A blade model of 150/200 (150 microns thick bond coat and 200 microns thick top coat) experienced 8.4% reduction in maximum temperature of the substrate, while this value increased to 26.5% for a 350/1000 model.

街区尺度屋顶绿化热效应及其与城市形态结构之间的关系

PDF HTML阅读 XML下载 导出引用 引用提醒 街区尺度屋顶绿化热效应及其与城市形态结构之间的关系 DOI: 10.5846/stxb201708111449 作者: 作者单位: 南京工业大学绿色建筑与生态城市实验室,南京工业大学绿色建筑与生态城市实验室,南京工业大学绿色建筑与生态城市实验室,南京工业大学绿色建筑与生态城市实验室,南京工业大学绿色建筑与生态城市实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学青年基金项目（41401179，51408303）；江苏省自然科学基金项目（BK20140941，BK20161547） Thermal effects of block-scale roof greening and their relationships with urban geometry Author: Affiliation: Laboratory of Green Building and Eco-city, NANJING Tech University,Laboratory of Green Building and Eco-city, NANJING Tech University,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:研究探讨大面积屋顶绿化如何改善城市冠层内部三维空间的热环境，改善效果与城市形态结构之间存在的关系。基于三维小气候模型ENVI-met 4.2，开展街区尺度屋顶绿化热效应研究。在南京市选择具有不同形态结构特征的8个典型样区，每个样区设置2种朝向（街道与主导风向平行或相交）、3种屋顶绿化情景（传统光屋顶、简易型绿化、复合型绿化），共对48种情景进行了微气候模拟与分析。结果表明，街区尺度屋顶绿化产生的"冷岛"可从屋面扩散到地面空间，缓解城市冠层热岛效应。白天14：00时，8个样区屋顶1.5 m高处的降温强度最高可达0.64℃，样区平均降温强度最大值为0.44℃；地面1.5 m高处的降温最大值为0.55℃，样区平均降温强度最大值为0.25℃。建筑高度、高宽比、容积率与屋面、地面降温强度之间均存在显著负相关关系；建筑密度与屋面降温强度显著正相关，但与地面降温强度之间无显著相关性。总的来说，紧凑低层建筑区和开敞低层建筑区实施屋顶绿化后产生的降温效应明显高于紧凑和开敞高层建筑区；建筑高度和密度相同时，街道走向与主导风向呈45°夹角比与主导风向平行具有更高的降温强度。研究结果能够促进对亚热带城市地区建筑-植被-大气相互关系的深入认识，并为屋顶绿化实践提供指导。 Abstract:Many studies reported that green roofs can notably alleviate roof-level surface and air temperatures, cutting building cooling loads and energy consumption. However, few studies have explored how large-scale roof greening affects the three-dimensional thermal environment of the urban canopy layer and how green-roof thermal performance correlates with urban geometry. This research investigated the block-scale green-roof thermal performance and its relationships with urban geometry factors by applying the three-dimensional microclimate model ENVI-met 4.2 in Nanjing City. Eight study plots with distinguished urban forms in conjunction with two orientations and three roof greening options generated a total of 48 scenarios for ENVI-met modeling and analysis. Results suggested that block-scale roof greening not only cooled the roof-level ambient atmosphere, but could ameliorate the ground-level microclimate. At 14:00 during the day, the air temperature reduction at 1.5 m height above the roof surface could reach 0.64℃ with an average reduction of 0.44℃. The maximum and average air temperature reductions at 1.5 m height above the ground were 0.55℃ and 0.25℃, respectively. Building height, height-to-width ratio, and floor area ratio had significant negative correlations with both the roof and ground level thermal effects. Building density was positively related with roof-level thermal effects, but had no significant correlation with ground-level thermal effects. Overall, compact low-rise and open low-rise building areas exhibited much higher cooling effects than compact and open high-rise building areas. Study sites with S-N orientation had better thermal performance than SW-NE orientated sites. These findings can deepen our understanding of building-vegetation-climate interactions in urban areas and provide a reference for roof greening practice in humid subtropical cities. 参考文献 相似文献 引证文献

Experimental and numerical investigations of the thermal behavior of small solar ponds with wall shading effect

In this study, a combined numerical and experimental investigation of the thermal behaviour of small solar ponds with various shapes, is presented. For this purpose, two prototypes of solar ponds with square and circular cross sectionsand similar volumes were examined. In the small solar ponds, the side walls shading affects accumulation and storing the solar thermal energy. Therefore, for evaluating the effect of shadow shape and size on the pond performance, a model for temperature distribution in a solar pond was presented, and the thermal behaviour of the pond was investigated considering the shadow effects. Temperature changes in the storage zone were calculated numerically and compared with the experimental results. According to the results, by considering the shadow effect, the maximum temperatures of circular and square ponds were 66.8 °C and 65.8 °C, respectively. Also, the effect of the angular placement of ponds on various geographical directions has been investigated. The maximum temperature was obtained at the placement angle γ=0° for square ponds, whereas the rectangular ponds should have been constructed at γ=90° to achieve the maximum temperature and shadow effect reduction. The results provided a strong perspective for determining the dimensions and angular placement of the solar ponds before construction of a solar pond.

Thermal decomposition study of polyvinyl chloride in the presence of commercially available oxides catalysts

AbstractThe pyrolysis behavior of polyvinyl chloride (PVC) in the presence of commercially available oxides catalysts was investigated using thermogravimetry. The pyrolysis proceeded under a heating rate of 5°C/min in the temperature range of 200–650°C. The thermogravimetric properties in terms of reduction in maximum degradation temperature and percent conversion were studied. The silica gel mesoporous catalyst, with a greater pore size and surface area, was found to be the most active materials in terms of reduction in maximum degradation temperature and increase in percent conversion. The alumina acidic, silica ppt, and alumina neutral catalysts also showed good results; however, their effects were less pronounced as compared to silica gel. The effects of these different catalysts show that surface area, pore size, and number of acidic sites are found to be the major factors for the energy efficient degradation of polymers.

Air Temperature Modification of an Urban Neighborhood Park in Summer

In order to investigate the effect of air temperature reduction on an urban neighborhood park, air temperature data from five inside locations (forest, pine tree, lawn, brick and pergola) depending on surface types and three outside locations (Suwon, Maetan and Kwonsun) depending on urban forms were collected during the summer 2016 and compared. The forest location had the lowest mean air temperature amongst all locations sampled, though the mean difference between this and the other four locations in the park was relatively small (0.2-0.5℃). In the daytime, the greatest mean difference between the forest location and the two locations exposed to direct beam solar radiation (brick and lawn) was 0.5-0.8℃ (Max. 1.6-2.1℃). In the nighttime, the mean difference between the forest location and the other four locations in the park was small, though differences between the forest location and locations with grass cover (pine tree and lawn) reached a maximum of 0.9-1.7℃. Comparing air temperature between sunny and shaded locations, the shaded locations showed a maximum of 1.5℃ lower temperature in the daytime and 0.7℃ higher in the nighttime. Comparing the air temperature of the forest location with those of the residential (Kwonsun) and apartment (Maetan) locations, the mean air temperature difference was 0.8-1.0℃, higher than those measured between the forest location and the other park locations. The temperatures measured in the forest location were mean 0.9-1.3℃ (Max. 2.0-3.9℃) lower in the daytime than for the residential and apartment locations and mean 0.4-1.0℃ (Max. 1.3-3.1℃) lower in the nighttime. During the hottest period of each month, the difference was greater than the mean monthly differences, with temperatures in the residential and apartment locations mean 1.0-1.6℃ higher than those measured in the forest location. The effect of air temperature reduction on sampling locations within the park and a relatively high thermal environment on the urban sampling locations was clearly evident in the daytime, and the shading effect of trees in the forest location must be most effective. In the nighttime, areas with a high sky view factor and surface types with high evapotranspiration potential (e.g. grass) showed the maximum air temperature reduction. In the urban areas outside the park, the low-rise building area, with a high sky view factor, showed high air temperature due to the effect of solar (shortwave) radiation during the daytime, while in the nighttime the area with high-rise buildings, and hence a low sky view factor, showed high air temperature due to the effect of terrestrial (longwave) radiation emitted by surrounding high-rise building surfaces. The effect of air temperature reduction on the park with a high thermal environment in the city was clearly evident in the daytime, and the shading effect of trees in the forest location must be most effective. In the nighttime, areas with high sky view factor and surface types (e.g., grass) with evapotranspiration effect showed maximum air temperature reduction. In the urban areas outside the park, the high sky view factor area (low-rise building area) showed high air temperature due to the effect of solar (shortwave) radiation during the daytime, but in the nighttime the low sky view factor area (high-rise building area) showed high air temperature due to the effect of terrestrial (longwave) radiation emitted surrounding high-rise building surfaces.

Ground experimental investigation of thermodynamic vent system with HCFC123

Thermodynamic vent system (TVS) is of significance to long term on-orbit storage of cryogenic fuel. In the present study, one ground experiment is established to investigate the pressure control performance of TVS with the working fluid of HCFC123. The tank pressure variation and fluid temperature change are respectively studied in self-pressurization, injection mixing and active refrigeration phases. The refrigeration capacity supplied by TVS and fluid thermal stratification during different phases, are specially illustrated. The effectiveness of the pressure control performance by means of TVS has been proven in the present experiment. The total venting gas loss is about 17.3 kg for 16 throttling cycles. The corresponding refrigeration capacity of TVS is 1216–1415 W, with circulation volume flow of 95 L/h and throttling ratio of 16.8–18.9%. Moreover, it costs approximately 6 h for the liquid thermal stratification developing fully. While in active refrigeration phase, the vapor has the maximum temperature reduction of 9.2 °C, and the variation of the liquid temperature is limited in 2.0 °C. When compared to direct venting method, TVS has recovered more than 23.22% venting loss for 4.75 h' operation. On the whole, the effective pressure control and heat load elimination of TVS are greatly confirmed.

Thermal behavior of a PV panel integrated with PCM-filled metallic tubes: An experimental study

The current research work aims to maintain high photovoltaic (PV) efficiency by keeping them at low operating temperature. For this purpose, commercially available phase change material (PCM) RT24 encapsulated in copper tubes was attached at the back side of a PV panel as a heat sink. The main concept of using the copper tube as PCM encapsulation is to produce a fin effect on the back of the PV panel to enhance the rate of heat transfer from the PV panel to ambient air. The experimental results showed that a maximum temperature reduction of 8.5 °C can be achieved at the front surface of the PV panel with 2.5 kg of PCM per square meter of the PV panel area. The PV back surface was also cooled down from 62 °C to 56 °C by the PCM. Enhancement in efficiency up to 3% was observed. The fin effect for the PV panel cooling was observed as the PV panel was maintained at a lower temperature, even after the PCM was completely utilized. The total cost incurred for the current PCM-based thermal regulation of the PV panel was $93/m2 of the PV area or $0.60/W of the PV power.

How to improve efficiency of using water when extinguishing fires through the explosive breakup of drops in a flame: Laboratory and field tests

The study reports results of the experimental research on the explosive breakup of heterogeneous water drops in high-temperature (800–1200 K) conditions typical for fires. The temperature of heating conforms to mean values for large forest fires. We use water drops containing special-purpose inclusions, such as 1–3 mm solid opaque particles (natural graphite). Laboratory experiments enable us to define conditions for the intensive fragmentation of such the drops. This process is characterized by formation of droplets of smaller size. The number of fragments can be from several ones to several hundreds. As a result, the evaporation surface area of liquid increases 3–15-fold during such the fragmentation. This effect is important for the most complete water evaporation in a flame during the fire extinguishing process. In such a case, the maximum temperature reduction in a flame zone becomes possible by absorption of heat of phase change. Field tests show that the usage of suspensions based on water facilitates a dramatic drop in temperature in a flame zone by 40–70 K as compared to water without additives. Consequently, fire extinguishing occurs during shorter time and by using smaller volume of water. Both the characteristics can decrease by 30–40% as compared to water without additives.

THE THERMAL POTENTIAL OF AN EARTH TUBE HEAT EXCHANGER SYSTEM IN AIR TEMPERATURE MODERATING

The potential of earth tube heat exchangers in tempering ventilation air in delta region was studied experimentally by using two diffident systems. The two systems were installed at the research farm, faculty of agriculture, Kafrelsheikh University (31.07° N and 30.57° E), Kafrelsheikh governorate, Egypt. The first system (S1) consisted of one pipe with inner diameter of 10.85 cm. The second system (S2) consisted of two coaxial pipes the first pipe with inner diameter of 10.85 cm surrounded by the other one with inner diameter of 16.2 cm and the annular space between them filled by water and sealed. The length of both systems was 12 m and buried at a depth of 75 cm within two ditches 5 m apart and refilled with earth. The ambient air was blown by a 0.75 kW blower to pass through the two buried systems. The systems were operated during cooling and heating modes at four operating durations and five air velocities. It was found that, the maximum temperature reduction and rise were 12.65 °C at air velocity 1.8 m/s, 12 hours operating duration and 6.27 °C at velocity 3.7 m/s, 12 hours operating duration under cooling and heating modes for S1 respectively. Maximum thermal energy rate removed during cooling mode was 679.9 W for S2 at air velocity 9.7 m/s and 22 hours operating duration and the corresponding COP was 3.96. The maximum thermal energy rate added during heating mode was 629.7 W for S1 at air velocity 9.7 m/s, 12 hours operating duration and the corresponding COP was 3.67. Both systems contribute in air temperature control which declares in diminishing its amplitude. It was found that when the air velocity (mass flow rate) increase the thermal energy rate removed / added increases although the temperature reduction / rise decreases. This was because of the effect of increasing mass flow rate was predominant than the effect of temperature reduction/ rise in thermal energy rate exchanged evaluation. Key words: Earth tube, thermal potential, earth to air heat exchanger

A STUDY ON THE COOLING EFFECTS OF GREENING FOR IMPROVING THE OUTDOOR THERMAL ENVIRONMENT IN PENANG, MALAYSIA

Shade tree coverage and reflective pavements are useful mitigation strategies to help cool theair and provide shade. It also helps to lower building energy consumption by providing better outdoor boundary conditions. This study presents a simulation approach to evaluate and determine the cooling effect of greening modification developments of a study area on the surrounding environment. This study presents two approaches, including an on-site measurement and a numerical simulation model that uses ENVI-met V 4.0 BETA. Five scenarios with different types of tree coverage and density canopy by adding reflective pavements at ground surface are used. This study was conducted at the RST Complex of Universiti Sains Malaysia. The simulation results showed significantly lower air temperatures in three greening scenarios compared to the current condition scenario with 10% tree coverage. Increasing 20% of tree coverage with less dense and high dense of canopy in the study area led to a maximum air temperature reduction of up to 0.97 °C and 1.15 °C, respectively. Meanwhile, increasing 20% tree coverage with a highly dense canopy and applying reflective pavements on the ground surface contributed to a maximum air temperature reduction of up to 1.16 °C. The outcome of this study could be used to help urban planners and designers to select strategies for designing outdoor spaces to relieve heat stress with the main aim of improving the outdoor living environment.