Effect Of Vertical Temperature Gradients Research Articles

Thermal comfort in environments with different vertical air temperature gradients.

The use of displacement ventilation for cooling environments is limited by the vertical temperature gradient. Current standards recommend a temperature difference of up to 3K/m between the head and the feet. This paper reviews the scientific literature on the effect of vertical temperature gradients on thermal comfort and compares this to the results of our own experiments. Early experiments have demonstrated a high sensitivity of dissatisfied test subjects to changes in the temperature gradient between head and foot level. Recent studies have indicated that temperature gradients of 4-5K/m are likely to be acceptable, and the mean room temperature may have a greater sensitivity on the percentage of dissatisfied (PD). In new experiments, test subjects have evaluated the thermal comfort of different vertical air temperature gradients in a modular test chamber, the Aachen comfort cube (ACCu), where they have assessed vertical temperature gradients of ΔT/Δy=1, 4.5, 6, 8, and 12K/m at a constant mean room temperature of 23°C. The results of the different temperature gradients are in contrast to ANSI/ASHRAE Standard 55 (Thermal Environmental Conditions for Human Occupancy, Atlanta GA, American Society of Heating, Refrigerating and Air Conditioning Engineers, 2013) as the PD increases almost constantly with higher vertical air temperature gradients. The PD for the overall sensation increases by approximately 7% between gradients of 1 and 8K/m. The evaluation of our own tests has revealed that vertical temperature gradients of up to 8K/m or higher are likely to be acceptable for test subjects.

Projecting the impacts of atmospheric conditions under climate change on air quality over the Pearl River Delta region

Anthropogenic climate change has been increasingly confirmed by weather observation and scientific literature in recent decades. Atmospheric stability, which has strong effects on vertical mixing of air pollutants and thus air quality, may be affected under climate change. This study aims to statistically assess the impacts of climate change alone on the future air quality in the Pearl River Delta region in the near future (2030–2039) and the far future (2090–2099) under two Representative Concentration Pathways (RCP) scenarios, i.e., RCP 4.5 and RCP 8.5, based on the future surface and upper level meteorological data projected by one regional climate model (RCM): WRF, and by four general circulation models (GCMs): CanESM2, MIROC, MRI-CGCM3 and MPI-ESM-LR. The arithmetic means of projections reveal an increase in the levels of air pollutants [ozone (O3), respirable suspended particulates (RSP) and sulphur dioxide (SO2)] in various seasons, even though a decrease is projected to occur in June-July-August. These changes in projected mean concentration are more significant in the far future, and under the RCP8.5 scenario. Among difference meteorological variables, surface temperature is most associated with the projected change in the three pollutants, with a range from 56.9% to 65.2% in all seasons and for all pollutants, relative to all contributions in RCP8.5 for example. Other notable associations include positive effects of vertical temperature gradient and the temperature–dew point difference on pollutant concentration. We found an increase in frequency of high pollution levels in December–January–February and March–April–May, as the occurrence proportion of pollutant concentration greater than the recent 95th percentile is 9.5%–9.6% and 6.4%–9.2%, respectively. We conclude that climate change alone is projected to have significant effect on air quality in the Pearl River Delta region in future, implying the necessity of more stringent air pollutant emission control policies to mitigate air pollution in the future.

Influence of vertical temperature gradients on wafer quality and cell efficiency of Seed-assisted high-performance multi-crystalline silicon

The effect of vertical temperature gradients on the performance of Seed-assisted high-performance (HP) multi-crystalline silicon (mc-Si) is investigated by numerical simulations and contrast experiments. The vertical temperature gradients are designed by keeping the temperatures at the top and lowering the temperatures at the bottom. Two Seed-assisted HP mc-Si ingots were grown by means of a larger and a conventional vertical temperature gradient. It is found that the larger vertical temperature gradients result in the more parallel growth direction of grains and the longer crystal growth length, increases the percentages of <112> grain orientation and random grain boundaries, which are benefit for crystal quality. The experimental results also confirm that the wafer of ingot grown with a larger vertical gradient has the better quality, and their cell efficiency can increase.

Effects of Vertical Temperature Gradient on the Growth Morphology and Properties of Single Domain YBCO Bulks Fabricated by a New Modified TSIG Technique

Single domain YBCO bulk superconductors have been fabricated with different vertical temperature gradients (VTG) by a modified top-seeded infiltration and growth (TSIG) process with a new solid phase (Y2O3+BaCuO2) and a new liquid phase (Y2O3+6CuO+10BaCuO2). It is found that the angle α (between the upper surface and interface of a- and c-growth sectors) is very sensitive to the VTG, which means that the growth rate in c-axis direction (Rc) can be changed by the VTG, according to tan α = Rc/Ra; Ra is the growth rate in the a-axis direction. It is also found that the 4-fold growth sectors did not cover the whole surface of the sample grown with a positive VTG, and the volume fraction of the single c-axis growth sector (Vfc) is 37.5% of the sample grown with a zero VTG, but it is reduced to 25% by a positive VTG, and enlarged to 53.6% by a negative VTG. The results of levitation force and trapped field of the samples show that a negative (or positive) VTG can improve (or reduce) levitation force and trapped...

VERTICAL TEMPERATURE GRADIENTS IN THE SEMI-CLOSED GREENHOUSES: OCCURRENCE AND EFFECTS

Semi-closed greenhouses have been developed in which window ventilation is minimized due to active cooling, enabling enhanced CO2 concentrations at high irradiance. Cooled and dehumidified air is blown into the greenhouse from below or above the canopy. Cooling below the canopy may induce vertical temperature gradients along the length of the plants. Our first aim was to analyze the effect of the positioning of the inlet of cooled and dehumidified air on the magnitudes of vertical temperature and VPD gradients in the semi-closed greenhouses. The second aim was to investigate the effects of vertical temperature gradients on assimilate production, partitioning, and fruit growth. Tomato crops were grown year-round in four semi-closed greenhouses with cooled and dehumidified air blown into the greenhouses from below or above the crop. Cooling below the canopy induced vertical temperature and VPD gradients. The temperature at the top of the canopy was over 5°C higher than at the bottom, when outside solar radiation was high (solar radiation >250 J cm-2 h-1). Total dry matter production was not affected by the location of the cooling (4.64 and 4.80 kg m-2 with cooling from above and from below, respectively). Percentage dry matter partitioning to the fruits was 74% in both treatments. Average over the whole growing season the fresh fruit weight of the harvested fruits was not affected by the location of cooling (118 vs 112 g fruit-1). However, during summer period the average fresh fruit weight of the harvested fruits in the greenhouse with cooling from below was higher than in the greenhouse with cooling from above (124 vs 115 g fruit-1)

Travelling neutral disturbances and minor constituent particle mass

The mass cut-offs for critical or resonant coupling of minor species acoustic waves (so-called travelling neutral disturbances) and acoustic-gravity waves in the main atmosphere are shown and explained. The effects of vertical temperature gradients and the diffusion of the minor species on the mass cut-offs are also demonstrated. The wave characteristics of these minor species waves are examined. The wave number surface is shown to be such that energy and group velocity directions are more nearly vertical than those of gravity waves for the same phase velocity direction. It is expected that these coupled waves, when properly excited, will act to damp gravity waves and redistribute energy vertically. Implications for the thermosphere and mesosphere are discussed. Under ordinary conditions such resonant coupling is judged more likely for lighter mass species, such as helium and hydrogen.