Journal of Cold Regions Engineering

Researchers at the National Research Council (NRC) Canada–Construction Portfolio in association with the Canadian Polyisocyanurate Council conducted collaborative research activities on the long-term thermal resistance (LTTR) of polyisocyanurate (polyiso) foam insulation with impermeable facers. Polyiso boards are commonly used in building envelope constructions (roofs and walls) in cold regions. The primary objective of the research project was to contribute towards the development of a comprehensive test procedure that could be used to measure the LTTR of polyiso foam insulation products with impermeable facers. As a part of that initiative, a project was initiated in 2001 that consisted of accelerated aging tests using thin slices in parallel with a field investigation in which polyiso boards were installed in a purpose-built test hut at the NRC’s Ottawa campus. The polyiso boards installed in the field were monitored for a period of 6 years and subsequently removed from the test hut and tested in the laboratory. This paper presents the field thermal performance of the rigid polyiso foam boards with impermeable facers and critically examines its relationship with the laboratory-measured thin slice aging data. It is hoped that these observations will help construction professionals and researchers to develop a better understanding on the LTTR of impermeably faced polyiso foam insulation boards.

This study assesses the performance of a Coanda-effect intake screen for a small hydropower plant during winter operations. The unique self-cleaning screen utilizes the Coanda-effect for withdrawing water. This screen consists of panels with 2-mm-wide horizontal wedge wires with 1 mm spacing. Beneath the screen is a canal conveying water to the power plant intake. A broad understanding of the Coanda-effect screen’s winter performance in a cold climate was obtained from experiments in a frost laboratory and a monitoring program consisting of hydrological measurements, an online web camera, and field observations of an intake structure in Norway. Various freezing processes were observed, and critical hydrological conditions for ice blockage of the Coanda-effect screen were evaluated. The Coanda-effect screen performed well under all normal conditions without snow or ice and was entirely self-cleaning. Two main types of ice formation were observed on the screen: type I where frazil ice particles stick to the screen wires but with openings remaining underneath the ice, and type II where solid ice forms between the wires at very low temperatures. During the winter of 2011–2012, there were a few periods with reduced intake capacity or complete blockage from ice. The complete ice blockage events were all related to supercooled water just upstream from the screen, thus indicating frazil ice and intake screen and air temperatures below 0°C. The screen reopened without any operational interventions after all ice blockage events, and the intake performed well even during periods with solid ice cover over the screen, whereby water entered the intake through the screen wires underneath the ice cover. In spite of some periods with reduced intake capacity, the intake screen performed reasonably well in a cold climate.

In this study, a series of laboratory investigations were performed to examine the heat transfer performance of a two-phase closed thermosyphon (TPCT) with different inclination angles under low-temperature conditions. A stainless steel TPCT with ammonia as the working fluid was tested with inclination angles ranging from 0 to 90° from the horizontal. In order to simulate low-temperature conditions, the temperature in the jacket of evaporator section was controlled at $-0.5°\mathrm{C}$, and the temperature in the jacket of the condenser section was changed from $-0.7$ to $-15.0°\mathrm{C}$. The experimental results show that inclination angle has a significant impact on the heat transfer performance of a TPCT under the experimental conditions, but the inclination angle does not control the startup temperature difference for the TPCT when the inclination angle is more than 0°. A horizontal TPCT has a good heat transfer performance and a small startup temperature difference; however, the thermal semiconduction effect disappears, because gravity has a limited effect on the circulation of the working fluid in a horizontal TCPT. These research results can help to guide decisions about the placement angle of TPCTs in cold regions engineering.