Asphalt Solar Collector Research Articles

Effect of Material Composition and Environmental Condition on Thermal Characteristics of Conductive Asphalt Concrete.

Conductive asphalt concrete with high thermal conductivity has been proposed to improve the solar energy collection and snow melting efficiencies of asphalt solar collector (ASC). This paper aims to provide some insight into choosing the basic materials for preparation of conductive asphalt concrete, as well as determining the evolution of thermal characteristics affected by environmental factors. The thermal properties of conductive asphalt concrete were studied by the Thermal Constants Analyzer. Experimental results showed that aggregate and conductive filler have a significant effect on the thermal properties of asphalt concrete, while the effect of asphalt binder was not evident due to its low proportion. Utilization of mineral aggregate and conductive filler with higher thermal conductivity is an efficient method to prepare conductive asphalt concrete. Moreover, change in thermal properties of asphalt concrete under different temperature and moisture conditions should be taken into account to determine the actual thermal properties of asphalt concrete. There was no noticeable difference in thermal properties of asphalt concrete before and after aging. Furthermore, freezing–thawing cycles strongly affect the thermal properties of conductive asphalt concrete, due to volume expansion and bonding degradation.

STUDY THE EFFECT OF THE ENVIRONMENTAL PARAMETERS ON THE PERFORMANCE OF A PROTOTYPE FOR ASPHALT SOLAR COLLECTOR USING AIR AS A WORKING FLUID

Diminution of fossil fuel inspires researches to look for renewable energy sources. Heat island and road accidents resulted from tires explosion due to excessive asphalt heat (reach to 70 oC) were another problems. These problems oriented researchers to use asphalt as a heat collector. They found by using asphalt as a heat collector it will gain energy, reduce heat island and reduce road accidents as well. Recently researchers started to use some applications of asphalt solar collector (ASC). Majority of these applications used to heat and cool water. In this research, the first ASC prototype was built outside the laboratory and using atmospheric air as a working fluid. The environmental parameters such as ambient temperature, variation of solar day time, asphalt surface temperature is considered. This prototype consisted of buried pipes under asphalt layers with two opening ends. One end is connected to atmospheric air duct and the other ends connected to Unplasticized Poly Vinyl Chloride (UPVC) chimney. It has been found compatibility with the laboratory study in the strong effect of the chimney height on the air flow velocity through the ASC. Also it can be concluded that the ASC prototype performance for producing energy depends on prototype components in terms of chimney height, asphalt temperature and the environmental / atmospheric conditions in terms of ambient air temperature, and ambient wind speed. Key words: Asphalt collector, solar energy, energy harvesting, and air velocity.

Construction and configuration of convection-powered asphalt solar collectors for the reduction of urban temperatures

In this paper, an analysis of a convection-powered asphalt solar collector prototype is approached by the means of experimental trials and computational fluid dynamics (CFD) simulations in order to evaluate how to optimise its design for the reduction of high urban pavement temperatures. Since the energy harvesting setup consists of a series of pipes buried in the pavement, their arrangement is here studied and experimentally compared to a possible construction technique consisting of concrete corrugations that aim at replacing the pipes. CFD simulations are employed to optimise the air collection chamber which is placed immediately before the heated air leaves the asphalt solar collector prototype. The data gathered is analysed in terms of energy harvested and exergy.The results obtained show that for an overall optimal performance, pipes should be installed in a single row under the pavement wearing course. This allowed a surface temperature reduction of up to 5.5 °C in the pavement prototype studied and the highest absorbed energy and exergy measured. In addition, the CFD simulations showed that care has to be put in finding the optimal shape and size for the air collection chamber, as they significantly influence the behaviour of the system.

The Potential of Heat Collection from Solar Radiation in Asphalt Solar Collectors in Malaysia

The implementation of asphalt solar collectors as a means of an energy source is being widely studied in recent years. Asphalt pavements are exposed to daily solar radiation, and are capable of reaching up to 70°C in temperature. The potential of harvesting energy from solar pavements as an alternative energy source in replace of non-renewable energy sources prone to depletion such as fuel is promising. In Malaysia, the sun intensity is quite high and for this reason, absorbing the heat from sun radiation, and then utilizing it in many other applications such as generating electricity could definitely be impressive. Previous researches on the different methods of studying the effect of heat absorption caused by solar radiation prove to be quite old and inaffective. More recent findings, on the otherhand, prove to be more informative. This paper focuses on determining the potential of heat collection from solar radiation in asphalt solar collectors using steel piping. The asphalt solar collector model constructed for this research was prepared in the civil engineering laboratory. The hot mixed asphalt (HMA) contains 10% bitumen mixed with 90% aggregates of the total size of asphalt. Three stainless steel pipes were embedded into the interior region of the model according to the design criteria, and then put to test. Results show that harvesting energy from asphalt solar collectors proves highly potential in Malaysia due its the hot climate.

Finite Element Approach to Assess the Benefits of Asphalt Solar Collectors

Asphalt solar collectors (ASCs) consist of a pipe network embedded in the surface asphalt layer of an asphalt pavement. As fluid circulates in the pipes, it absorbs heat from the pavement and cools it down. While previous research has concentrated on studying ASC parameters independently, this study combined them in a comprehensive model to evaluate the potential of ASCs to harvest energy from pavements and mitigate the negative impact of their high surface temperatures. For that purpose, a finite element model of an ASC was developed to predict the temperature profile of the pavement, pipes, and circulating fluid. The model was validated under field conditions with two flow configurations: a closed loop system with reservoir and a single-pass system. The single-pass system was shown to yield a higher efficiency than a closed loop system would (21.9% versus 10.9%). Once validated, the model was used to simulate ASC water and pavement temperatures during representative days of four seasons for a specific climate. The finite element model predicted that a single-pass ASC would increase water temperatures by an average of 4.0°C, 7.5°C, 10.2°C, and 13.6°C and reduce pavement surface temperatures by an average of 0.5°C, 0.7°C, 2.5°C, and 3.2°C throughout the days in winter, autumn, spring, and summer, respectively. These reductions resulted in a 3-year extension of the pavement lifetime for a prescribed set of traffic, structural, climatic, and materials conditions. The potential energy gain and service life extension were used to conduct an economic analysis, which estimated a 5-year payback period of the ASC.

Investigation of heat-collecting properties of asphalt pavement as solar collector by a three-dimensional unsteady model

Using asphalt pavement as a solar collector is a technology of increasing interest in China. Researchers have pointed out that the heat quality of the coolant medium needed further investigation for inter-seasonal storage, though the energy potential of an asphalt solar collector was considerable. In this paper, a three-dimensional unsteady model is developed to investigate the heat-collecting properties of asphalt solar collector at typical Chinese summer time. The temperature rise of outlet water (ΔT) is used as the indicator of heat quality. The results from a big-scale slab of 4 m × 4 m show that ΔT reaches over than 10°C, while the asphalt pavement is cooled down effectively. In addition, the higher the ambient temperature is, the better the heat-collecting properties of asphalt solar collector achieves. It can be concluded that the heat-collecting properties of asphalt solar collector are good enough to provide high-quality heat under certain conditions.

Influence of early colour degradation of asphalt pavements on their thermal behaviour

Environmental goals such as the reduction of fossil fuel consumption or greenhouse gas (GHG) emissions through the development of new renewable energy sources have led to the emergence of the so called asphalt solar collectors. Moreover, in recent years, engineers are devoting increased interest to the effect of the thermal loads on the mechanical behaviour of pavements. Several approaches to these topics can be found in the literature. However, a study of the influence of the colour degradation suffered by pavements on their thermal behaviour is still necessary since both the efficient application of the asphalt collectors and the proper study of the effect of the solar radiation on the asphalt pavement behaviour are directly affected by the loss of colour occurring as time goes by.Therefore, the thermal behaviour of two different asphalt mixes was studied before and after being subjected to a colour degradation process. The degradation of five different asphalt mixes was studied and the results were compared to those obtained in the access roads to seven low volume car parks.The final results show that there are large differences between the two asphalt mixes with different gradations and densities. The importance attributed by other authors to conductivity was also confirmed. Furthermore, the results showed that it was possible to simulate the early colour degradation suffered by a low volume road. Finally, a slight reduction in temperature and energy collection capacity was measured after the colour degradation process.

Effect mechanism of mixing on improving conductivity of asphalt solar collector

This paper investigates the influence of different mixing parameters of 1 forced mixing on the conductivity of asphalt solar collector (ASC). Graphite powder and carbon fibers were used to improve the conductivity of asphalt concrete. The conductivity of ASC was measured with the same mix gradation, mixing procedure but different mixing parameters. The rational vibrating mixing parameters are obtained according to orthogonal experiments of the conductivity. A laboratory test of volume index and conductivity was performed after determining the rational mixing parameters. The effects of common forced mixing the on microstructure of ASC were investigated using scanning electron microscopy (SEM) and computed tomography (CT). The results obtained show that the mixing parameters have a major impact on the conductivity of asphalt concrete, among which the temperature have the strongest influence, while the revolutionary speed has less influence. The rational mixing parameters include: Bitumen temperature T1 160°C, aggregate temperature T2 180°C, mixing time t 90s and mixing revolution speed v 45r/min. ASC can obtain good conductivity and volume index with rational mixing parameters. The resistivity drops from insulation to 39.8ohmm and the thermal conductivity increases from 1.531W/mK to 2.120W/mK. The microstructure of ASC showed that the conductive fillers have uniform distributions in the sample. Conductive particles and carbon fibers promote the formation of conductive networks, because fibers may bridge up several isolated conductive particles.

Simulation study of heat energy potential of asphalt solar collectors

Using black asphalt pavements as solar collectors is an emerging technology for snow-melting of pavements in winter or cooling and heating of adjacent buildings. The primarily concerned issues of this technology are the heat energy potential and its critical parameters. In this paper, a transient, two-dimensional finite element model is developed to investigate the heat transfer process in both neat and conductive asphalt pavements. The results from thermal properties tests show that thermal conductivity of asphalt mixtures may increase by more than 30% due to the addition of conductive fillers. Besides, the modelling results indicate that the higher thermal conductivity may result in acceleration of the heat conduction and increase in temperature at deeper depths in asphalt pavements. According to the calculated results of heat energy potential based upon the model, the energy derived from a neat asphalt collector or a conductive one is considerable. Thermal properties of asphalt materials have no significant impact on energy absorption in asphalt pavements.

Structural and Thermal Analysis of Asphalt Solar Collector Using Finite Element Method

The collection of solar energy using asphalt pavements has got a wide importance in the present energy scenario. Asphalt pavements subjected to solar radiation can reach temperature up to 70°C because of their excellent heat absorbing property. Many working parameters, such as pipe diameter, pipe spacing, pipe depth, pipe arrangement, and flow rate, influence the performance of asphalt solar collector. Existing literature on thermal energy extraction from asphalt pavements is based on the small scale laboratory samples and numerical simulations. In order to design an efficient asphalt solar collector there should be a payoff between the thermal and structural stability of the pavement, so that maximum heat can be absorbed without structural damage due to external load condition. This paper presents a combined thermal and structural analysis of asphalt solar collector using finite element method. Analysis is carried out in different models so as to obtain optimum pipe spacing, pipe diameter, depth, and pipe arrangement under the specified condition.

Study on Volume Performance of Conductive Asphalt Concrete Based on Freeze-Thaw Cycle

Conductive asphalt concrete, a kind of intelligent materials, can serve as asphalt solar collector, asphalt heater and self monitor. And moisture damage is one of the most common performance degradation of asphalt concrete. This paper investigates the volume properties of conductive asphalt concrete based on Freeze-thaw cycles. Marshall specimen was frozen and thawed repeatedly and a cycle consists 16h at -18oC and 8h at 60oC. The change of air void and weight loss ratio were chosen to evaluate the moisture resistance of conductive asphalt concrete. Three types of asphalt mixture (control, CAC 1 and CAC 2) were used to study the effect of initial void and material composition on moisture resistance. The results show that both the framework structures and the material composition have a great effect on antifreeze-thaw property of asphalt concrete, which provides an efficient guidance for application of this technology in pavement.

Study of ice and snow melting process on conductive asphalt solar collector

This paper investigates the snow melting process on asphalt pavements as solar collector by experiments and numerical simulation. A numerical simulation method was used to predict the general design requirements for snow melting system of asphalt pavements, and a type of experimental asphalt snow melting system has been built using the design parameters obtained from the preceding simulation. Graphite powders were used to improve the thermal conductivity of asphalt concrete and thus resulting in an improved efficiency of asphalt collector. A laboratory snow melting test was performed after real snowstorm events. The effects of thermal conductive asphalt concrete (CAC) on snow melting performance and asphalt pavement temperature distribution were evaluated. The heat transfer in the asphalt slabs and the heat requirement for the snow melting were analyzed. The results that are obtained show that asphalt solar collector (ASC) provides us a better alternative method for snow melting. The higher fluid temperature is a positive way to improve the performance of snow melting system. However, it is unnecessary to keep a too high fluid temperature so as to reduce the waste of energy. The non-uniform temperatures in the asphalt slabs are noticeable. Furthermore, the heat-transmission and the snow melting performance can be enhanced using CAC.

Laboratory investigation into thermal response of asphalt pavements as solar collector by application of small-scale slabs

This paper investigates the thermal response of asphalt pavements as solar collector by application of small-scale asphalt slabs. The copper tubes were embedded in the asphalt slabs for the purpose of water circulation and the thermal sensors were also embedded in different depths for temperature measurement during slab preparation. A laboratory irritation simulation test was performed to heat up the asphalt slabs. The thermal energy stored in the slabs was collected by circulating water. The effects of flow rate, the time for starting collection and the initial temperature distribution of the slabs on the process of heat collection were evaluated. The results show that the asphalt pavement can be cooled down by the solar collection and thus is good for reducing the effect of heat-island in a city, but the temperature gradients between the slabs’ surface and the pipe are noticeable. Furthermore, the efficiency of an asphalt collector can be above 33.3% and the increase of flow rate result in a limited decrease of the surface temperature of asphalt pavement. The steady state temperature distribution in specimens could be used to set the starting collection time. ► Researches into asphalt pavements used as solar collector have been conducted. ► A laboratory irritation simulation test for heat energy collation was performed. ► The characteristics of heat collection in Asphalt Solar Collector were analyzed. ► Various factors may affect the heat collection are taken into account in tests.

Design and Performance of an Asphalt Pavement Snow Melting System

Asphalt pavement can be used in solar energy harnessing, by means of solar collector developed in heating and cooling the adjacent buildings, as well as keeping the pavement ice-free directly. In the light of the actual situation of preparation and formation of a larger asphalt concrete slab, an experimental method and evaluation system for asphalt pavement snow melting was designed and constructed. The feasibility of snow melting using asphalt solar collector was verified, and the effect of the heat exchanger on the temperature distribution was quantitatively tested The results indicated that although the entire snowmelt time is longer than expected, it is acceptable for us to use asphalt solar collector for snow melting, especially, low temperature water about 25°C is used for snow melting. Besides, the melting process of ice and snow generally includes three phases: the starting period, the linear period and the accelerated period. The snow melting system is controlled to maintain the asphalt pavement surface temperature of 3 to 5°C which is sufficient to prevent freezing of the road.

Effects of conductive fillers on temperature distribution of asphalt pavements

The sun provides a cheap and abundant source of clean and renewable energy. Solar cells have been used to capture this energy and generate electricity. A more useful form of the solar cell would be asphalt pavements, which get heated up by solar radiation. Graphite powders are utilized as thermal conductive fillers to make an asphalt collector conductive so as to improve the efficiency of the asphalt collector. Accounting for the important application conditions and evaluating the effects of the heat conductive materials and the solar energy absorbability of the conductive asphalt collector, a finite element model has been developed to predict temperature distributions in the conductive asphalt solar collector. In this study, an experimental validation exercise was conducted using the measured data taken from full-depth asphalt slabs. Validation results showed that the model can satisfactorily predict the temperature distributions in asphalt concrete slabs. The optimal depth is 25–50 mm for placing pipes that serve as the heat exchanger. Meanwhile, the effect of the surroundings on the solar energy potential of the asphalt collector was noticeable.

Numerical simulation on the thermal response of heat-conducting asphalt pavements

Using asphalt pavements as a solar collector is a subject of current interest all over the world because the sun provides a cheap and abundant source of clean and renewable energy, which can be captured by black asphalt pavements. A heat-conducting device is designed to absorb energy from the sun. In order to validate what parameters are critical in the asphalt collector, a finite element model is developed to predict the thermal response of the heat-conducting device compared to the conventional asphalt mixture. Some factors that may affect the asphalt pavement collector are considered, including the coefficient of heat conductivity of the asphalt pavement, the distance between pipes with the medium, water, and the pipe's diameter. Ultimately, the finite element model can provide pavement engineers with an efficient computational tool that can be a guide to the conductive asphalt solar collector's experiment in the laboratory.

Numerical Simulation of Temperature Distribution in Conductive Asphalt Solar Collector due to Pavement Material Parameters

Asphalt pavement serving as solar collector has been developed for the heating and cooling of adjacent buildings as well as to keep the pavement ice-free directly. Material parameters such as thermal conductivity and heat capacity are some of the critical parameters related to the efficiency of the asphalt collector. Graphite powders were utilized as thermal conductive fillers to make asphalt collector conductive so as to improve the efficiency of the asphalt collector. The material parameters change with the addition of graphite consequently. In order to access the solar energy absorbability of conductive asphalt collector, it is necessary to predict the temperature distribution within the asphalt layers. A transient, two-dimensional finite element model is developed to predict temperature distributions in conductive asphalt solar collector due to material parameters. The ability of accurately predict asphalt pavement temperature at different depths will greatly help pavement engineers in determining the solar energy potential of conductive asphalt collector. The results from the prediction model show that the surface temperature of pavement decreases slightly with addition of graphite. The differential maximum asphalt temperature variation at a depth of 10cm is significantly more than that at the surface. Higher temperature and lower temperature gradient can also be observed at the depth of 10cm because the heat conduction is accelerated by the addition of graphite.