Analysis of the performance of an air-powered energy-harvesting pavement

Current energy-harvesting pavements do not have the features needed for large-scale applications. For example, the use of water as an operating fluid may create problems with the pavement structure if leakage occurs. Moreover, the design of such systems is not trivial, as the systems need auxiliary machinery to work (e.g., pumps or additional heaters to control the temperature of the working fluid). These problems can be solved if air is used as the operating fluid. This paper presents the prototype of an energy-harvesting pavement that uses air as the operating fluid and has been built, tested, and analyzed. The prototype consists of a set of pipes buried in an aggregate layer that is covered by a layer of a dense asphalt mixture. The pipes are connected to an updraft chimney. The pavement surface is irradiated with infrared light; thus, heat travels through the layers until it reaches the air in the pipes. Through natural convection, air flows through the chimney. The prototype provides satisfactory thermal properties that show a noticeable withdrawal of energy. The performance of the prototype is heavily influenced by the height of the chimney. Moreover, an air mass flow ranging from 0 (obstructed pipes) to 0.5 m/s (chimney 1 m high) is measured. Analysis of the results shows that the prototype proved useful in reducing the urban heat island effect by lowering the pavement surface temperature by more than 6°C

A Thermal Analysis of a Hot-Wire Probe for Icing Applications

This paper presents a steady-state thermal model of a hot-wire instrument applicable to atmospheric measurement of water content in clouds. In this application, the power required to maintain the wire at a given temperature is used to deduce the water content of the cloud. The model considers electrical resistive heating, axial conduction, convection to the flow, radiation to the surroundings, as well as energy loss due to the heating, melting, and evaporation of impinging liquid and or ice. All of these parameters can be varied axially along the wire. The model further introduces a parameter called the evaporation potential which locally gauges the maximum fraction of incoming water that evaporates. The primary outputs of the model are the steady-state power required to maintain a spatially-average constant temperature as well as the variation of that temperature and other parameters along the wire. The model is used to understand the sensitivity of the hot-wire performance to various flow and boundary conditions including a detailed comparison of dry air and wet (i.e. cloud-on) conditions. The steady-state power values are compared to experimental results from a Science Engineering Associates (SEA) Multi-Element probe, a commonly used water-content measurement instrument. The model results show good agreement with experiment for both dry and cloud-on conditions with liquid water content. For ice, the experimental measurements under read the actual water content due to incomplete evaporation and splashing. Model results, which account for incomplete evaporation, are still higher than experimental results where the discrepancy is attributed to splashing mass-loss which is not accounted in the model