Latest news with #evaporation
ABC News
2 days ago
- Climate
- ABC News
Why your clothes are drying faster in the cold weather
It has been a frosty start to winter, but for many areas of Australia, the lower temperatures are coinciding with faster drying clothes. This sounds like a fallacy since drying relies on evaporation, and the warmer it is the faster moisture in your clothes converts to a gas and escapes. For southern and central Australia, drying is generally — but not always — faster in summer. However, the difference is often minimal across eastern states and conditions this week in coastal regions like Sydney and Brisbane, despite cold temperatures, have been optimal for washing productivity. So how can laundry times be shorter when the weather is cooler？ The answer can be found in the details of the drying process. Firstly, while higher temperatures lead to faster evaporation, even in air below freezing, some molecules of water can still break free and convert into a gas. However, what is critical for efficient drying is not just evaporation, but more specifically the rate of evaporation (moisture leaving your clothes) relative to the rate of condensation (moisture arriving on your clothes). Despite the intuition that your laundry will dry faster in hot weather, surprisingly, science tells us the air temperature is the least important variable in determining drying times. The two most important factors are fairly obvious — that it is not raining and the sun is shining. Direct sunlight supplies far more energy compared to what is emitted from the ground or the air, which is why bitumen and car seatbelt buckles get so hot. The next three factors, in order of importance, account for remaining day-to-day drying variability： From this hierarchy, humidity is more important than wind and temperature, and that is because the moisture in your clothes has to evaporate into the air — and the process is far more efficient when humidity is low. If the surrounding air is saturated with moisture (high humidity), condensation back onto your clothes will negate evaporation. This is the same reason why it feels hotter when it is humid, as evaporation of your sweat is restricted and therefore less cooling occurs through the absorption of latent heat. Next comes wind. On a still day, a slim layer of air around your clothes will become humid due to the evaporation, which reverts us to the saturated air-drying issue. On a windy day, though, the water vapour from your laundry is blown away and continuously replaced by unsaturated air. This is why hair dryers have a fan. And finally, the last and the least variable is temperature, which also affects drying times but to a lesser degree than wind and humidity. Based on the above, let's compare drying times between a typical humid, summer day and the wintry, dry weather seen this week along parts of the east coast. The results, calculated from an online calculator based off a thick garment with 4-millimetre fabric thickness, revealed a considerable improvement in drying under the cool scenario — even with only a 5 -kilometre-per-hour increase in the wind speed. So what comes out in the wash is do not let the winter cold stop you from hanging out your washing — just time your laundry to coincide with days of lower humidity and sufficient wind.
The National
10-05-2025
- Science
- The National
More than one billion litres of water evaporate from UAE swimming pools each year, research suggests
With its endless sunshine and sizzling temperatures, the UAE is the perfect place at which to kickback and enjoy an afternoon by the pool. But a new study suggests that the desire to take a dip consumes significant amounts of water, with more than a billion litres probably evaporating each year from the country's pools. While the losses are significant, they are potentially avoidable, because, for any given pool, the researchers said that pool covers could cut evaporation by as much as 95 per cent. Given the heavy environmental cost of producing desalinated water, they suggested that incentives could be introduced to encourage the use of covers, as is done in some other countries. The new study involved two scientists from the UK's Loughborough University, calculating water losses from swimming pools in the Palm Jumeirah development. Specialist mapping software was used to identify swimming pools on the development and to calculate their total area. This calculated that there are 1,859 'water bodies' – typically swimming pools – on the Palm Jumeirah with a total area of 173,500 square metres. From this, the researchers used established formulas to determine how much water is lost each year. In Palm Jumeirah alone, this works out at an average of 603.1 million litres lost each year between 2010 and 2020. This, the new study reported, is equivalent to the annual water use of around 3,000 people, which is about one third of the development's population. 'If the present study was upscaled from the Palm Jumeirah to all of the UAE, the water saving could amount to billions of litres per year (even with a moderate assumption of twice as many pools),' the researchers wrote. If the whole of the UAE had twice as many pools as the Palm Jumeirah does – a very conservative estimate – then water losses from evaporation would be well in excess of one billion litres per year. The new study, 'Evaporation losses from residential swimming pools and water features under climate variability and change,' is published in The Geographical Journal. While they are in use, solid pool covers – common types include foam covers, bubble covers and solid track covers) – cut losses from evaporation by about 95 per cent. If such covers had been deployed on all pools for 22 hours a day – leaving two hours for swimming, then the 603.1 million litre annual loss would have been cut by 524.6 million litres a year. This is an 87 per cent reduction. The first author of the study, Alicia Cumberland, a postgraduate student in the university's Department of Geography and Environment, said that in some other parts of the world, such as Victoria in Australia and Southern Nevada, the authorities have provided financial incentives to encourage residents to install pool covers to reduce water loss. She said that similar measures could be considered in the UAE. 'I think it would be very beneficial if they included policies where if you're not using your swimming pool, pool covers are mandated and they'll provide subsidies. It would go a long way to helping people save water and energy bills,' she said. Another measure, she said, could be for new developments to install communal pools that could be used by residents from a number of properties, instead of providing every home with its own pool. The amount of water used in the UAE, at around 550 litres per person per day, according to figures from the Ministry of Climate Change and Environment, is one of the highest in the world. According to previous research, 63 per cent of Dubai's water consumption is accounted for by residential use, which in 2023 accounted for 380 billion litres. Much of the water provided to households has been produced through desalination, an energy-intensive process that generates carbon emissions, so reducing water use offers environmental benefits. The other author of the study, Prof Rob Wilby, professor of hydroclimatic modelling in the Department of Geography and Environment, said that while people were becoming more accustomed to thinking about their personal and household carbon footprints, 'just as much attention is needed to our water footprints'. 'In the case of pools, we can reduce both carbon emissions and evaporated water by using covers,' he said. 'This way, less energy is needed to treat and pump the smaller amounts of water for topping up the pool. This win-win is especially important for hot and arid parts of the world like the UAE.' Various types of pool cover are available, Ms Cumberland said, among them foam covers, bubble covers and solid track covers, the last of which are controlled automatically. Variation between them in terms of the amount of water saved is modest, ranging between 94 and 96 per cent. Chemical suppressants can be added to pools to reduce water loss, but these are likely to reduce evaporation by only about 14 or 15 per cent, Ms Cumberland said. One uncertainty in the latest research, the authors said, was the extent to which pool covers are currently being used, with the figures calculated on the basis that all pools are kept uncovered. A key focus of the study was understanding how evaporative losses from pools may change as a result of climate change. The researchers calculated that current losses from pools on Palm Jumeirah, of about 600 million litres a year, could rise to as much as 675 million litres annually by 2050.
