Non-combustion non-solar deployment characterization of a free-piston Stirling engine to integrate with an exothermic reactor

Background: A small 1 kW free-piston β type Stirling engine was tested for its feasibility of integration with an exothermic reactor under the EU funded research project SOCRATCES (GA 727348). The engine’s heat receptor was minimally modified to adapt it to the reactor’s integration needs, introducing, instead of a combustion chamber, a CFD-optimized hooded enclosure. The open-loop configuration also included a small plate heat exchanger acting as a recuperator. The study attempted to investigate the performance of the Stirling engine under these non-combustion non-solar deployment conditions, focusing on conversion efficiency and thermal loss. Methods: A number of tests were run under different temperatures and flowrates to assess the engine’s response. Temperature, power, pressure and flowrate were measured at points of interest. Results: It was found that the engine is able to operate at efficiencies comparable to that of gasoline engines at much lower working fluid temperatures. It was possible to demonstrate, with the aid of a downstream recuperator, that the system in an open-loop configuration can minimize thermal loss significantly, virtually eliminating it in some cases. Conclusions: The Stirling engine appears to be a sound choice, in terms of conversion efficiency, at comparatively low temperatures, to be integrated with an exothermic reactor, at least at small-scale applications.

Evaluation of the Thermofluidic Performance of Climatic Chambers: Numerical and Experimental Studies

Climatic chambers are highly important in research and industrial applications and are used to examine manufactured samples, specimens, or components in controlled environment conditions. Despite the growing industrial demand for climatic chambers, only a few published studies have specifically concentrated on performance analysis and functional improvements through numerical and experimental studies. In this study, a 3D computational fluid dynamics (CFD) model of a climatic chamber was developed using Ansys Fluent to simulate the fluid flow, heat, and mass transfer to obtain the velocity, temperature, and relative humidity fields in the interior box of a 1200 L climatic chamber. The results were then validated with experimental data from a prototype. Finally, the heat losses of the surrounding components of the chamber were calculated, and the relationship between the inside temperature and the overall thermal loss was modelled. This validated numerical model provides the possibility of optimising the performance of climate chambers by reducing the thermal loss from the walls and modifying the air flow pattern inside the chamber.

Enhancing the cooling potential of photoluminescent materials through evaluation of thermal and transmission loss mechanisms

Photoluminescent materials are advanced cutting-edge heat-rejecting materials capable of reemitting a part of the absorbed light through radiative/non-thermal recombination of excited electrons to their ground energy state. Photoluminescent materials have recently been developed and tested as advanced non-white heat-rejecting materials for urban heat mitigation application. Photoluminescent materials has shown promising cooling potential for urban heat mitigation application, but further developments should be made to achieve optimal photoluminescence cooling potential. In this paper, an advanced mathematical model is developed to explore the most efficient methods to enhance the photoluminescence cooling potential through estimation of contribution of non-radiative mechanisms. The non-radiative recombination mechanisms include: (1) Transmission loss and (2) Thermal losses including thermalization, quenching, and Stokes shift. The results on transmission and thermal loss mechanisms could be used for systems solely relying on photoluminescence cooling, while the thermal loss estimations can be helpful to minimize the non-radiative losses of both integrated photoluminescent-near infrared (NIR) reflective and stand-alone photoluminescent systems. As per our results, the transmission loss is higher than thermal loss in photoluminescent materials with an absorption edge wavelength (λAE) shorter than 794 nm and quantum yield (QY) of 50%. Our predictions show that thermalization loss overtakes quenching in photoluminescent materials with λAE longer than 834 nm and QY of 50%. The results also show that thermalization, quenching, and Stokes shift constitute around 56.8%, 35%, and 8.2% of the overall thermal loss. Results of this research can be used as a guide for the future research to enhance the photoluminescence cooling potential for urban heat mitigation application.

Thermal Effects on Photovoltaic Array Performance: Experimentation, Modeling, and Simulation

The performance of photovoltaic (PV) arrays are affected by the operating temperature, which is influenced by thermal losses to the ambient environment. The factors affecting thermal losses include wind speed, wind direction, and ambient temperature. The purpose of this work is to analyze how the aforementioned factors affect array efficiency, temperature, and heat transfer coefficient/thermal loss factor. Data on ambient and array temperatures, wind speed and direction, solar irradiance, and electrical output were collected from a PV array mounted on a CanmetENERGY facility in Varennes, Canada, and analyzed. The results were compared with computational fluid dynamics (CFD) simulations and existing results from PVsyst. The findings can be summarized into three points. First, ambient temperature and wind speed are important factors in determining PV performance, while wind direction seems to play a minor role. Second, CFD simulations found that temperature variation on the PV array surface is greater at lower wind speeds, and decreases at higher wind speeds. Lastly, an empirical correlation of heat transfer coefficient/thermal loss factor has been developed.

Improved synthesis and properties of BTDA-TDI/MDI ternary copolyimides via microwave-assisted polycondensation

Polyimides are usually synthesized over a long period of time, and the process is complex. In order to shorten the synthesis time and simplify the process, we developed an improved synthesis method, namely, microwave-assisted polycondensation. The 3,3′-4,4′-benzophenone tetracarboxylic dianhydride (BTDA)–2,4-tolylene diisocyanate (TDI)/1,1′-methylenebis(4-isocyanatobenzene) (MDI) ternary copolyimides prepared in this work have been synthesized using microwave heating at rather short reaction times (15 min), without the need for either the once-off addition of TDI/MDI or the drop-wise addition of that mixture. The structure of the desired ternary copolyimide was confirmed by proton nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy. Its glass-transition temperature is above 400°C, and the temperature for 5% thermal loss under nitrogen atmosphere is 508.8°C. The tensile strength is 141 MPa, which shows that the microwave-assisted copolyimide has excellent heat resistance and mechanical properties.