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Multistage Sound Wave Engine Used To Develop Innovative Refrigerator



Fridge by francois schnell via flickr

A refrigerator powered solely by waste heat that forms sound waves in a multistage travelling wave thermoacoustic engine, has been developed by Shinya Hasegawa and colleagues at Tokai university.

The refrigerator produced the gas oscillations and refrigeration at a temperature lower than the boiling point of water and achieved a minimum cold temperature of -107.4 °C when the hot temperature was 270 °C. The findings are published in the journal of Applied Thermal Engineering, November 2016.

The operation of thermoacoustic (TA) engines is based on the heating, cooling and oscillation of acoustic (sound) waves created by the thermal expansion and contraction of gases such as helium enclosed dedicated cavities. The potential of TA engines for generating clean and renewable energy was demonstrated in seminal reports published in the late 1990s and early 2000s by researchers in the USA. Notably, these reports into the modern implementations of TA engines have led to increased worldwide research on the development of high efficiency TA engines to convert heat into useful power.

Two of the main hurdles to the proliferation of this technology are (1) high efficiency systems operable at less than 300 °C as compared to the 400 to 600 °C range at the moment; and (2) robust design so that the systems could be used in a wide range of environments such as fishing boats and heavy industries.

Hasegawa and colleagues have designed a high efficiency multistage-type thermoacoustic (MS-TA) engine, without moving parts, that operates at less than 300 oC; the temperature of more than 80% of industrial waste heat. The design of the MS-TA engine was based on finite element numerical analysis conducted by Hasegawa and his group.

Background and aims

“TA engines do not have moving parts, are easy to maintain, potentially high efficiency, and low cost,” says Shinya Hasegawa, an associate professor at the Department of Prime Mover Engineering, Tokai University, Hiratsuka, Japan. “My goals in this research are to develop TA engines that operates at less than 300 oC with more that 30% efficiency, and also to demonstrate a refrigerator operating at -200 oC at these low temperatures.”

Double loop travelling wave thermoacoustic refrigerator (TWTR)

The TWTR consists of three etched stainless steel mesh regenerators installed at optimal positions (“close to the sweet spot”) within the prime mover loop and one fixed in the refrigerator loop. This configuration was designed to trigger thermoacoustic oscillations at lower temperatures and yield a refrigerator temperature of less than -100 oC.

The diameters of the regenerators ranged between 0.2 to 0.3 mm and their lengths were 30 to 120 mm, depending on location. Furthermore, the TWTR had heat exchangers in the form of parallel plates of copper (1.0 mm thick and 27.0 in length) with a 2.0 mm gap.

The thermoacoustic energy conversion of this design is determined by two factors: the ratio of the diameter of the flow channel and thermal penetration depth, and the phase difference between the pressure and cross-sectional mean velocity.

The overall performance of the TWTR system is expressed in terms of the coefficient of performance (COP) and given by the ratio of the cooling power to the total input heating power, that is, the sum of the heating power of each engine.


The COP increased as the temperature of the heat exchangers in the primer loop was increased and the maximum value of COP was 0.029 at 260 °C, and  the corresponding cooling power was 35.6 W.

Furthermore, the researchers obtained gas oscillations at 85 °C —that is lower than the boiling point of water—thereby opening up possibilities for applications of this technology for refrigeration and power generation using low temperature waste heat in factories and automobile engines. Also, refrigeration (−42.3 °C) was achieved at reached 90 °C.

Importantly, the efficiency of the Tokai University TA engine was 18% at minus 107 °C.


“The installment of multiple regenerators in vicinity of the ‘sweet spot’ of the prime mover loop is a major advance in traveling-wave TA engines,” says Hasegawa. “This configuration reduces the temperature for TA oscillations and improves cooling performance.”

Following the successful development of the prototype system reported ion this paper, the next step in this research at Tokai University is the development of practical TA engines with emphasis on contributing to environmental problems.



Is Wood Burning Sustainable For Your Home?



sustainable wood burning ideas

Wood is a classic heat source, whether we think about people gathered around a campfire or wood stoves in old cabins, but is it a sustainable source of heat in modern society? The answer is an ambivalent one. In certain settings, wood heat is an ideal solution, but for the majority of homes, it isn’t especially suitable. So what’s the tipping point?

Wood heat is ideal for small homes on large properties, for individuals who can gather their own wood, and who have modern wood burning ovens. A green approach to wood heat is one of biofuel on the smallest of scales.

Is Biofuel Green?

One of the reasons that wood heat is a source of so much divide in the eco-friendly community is that it’s a renewable resource and renewable has become synonymous with green. What wood heat isn’t, though, is clean or healthy. It lets off a significant amount of carbon and particulates, and trees certainly don’t grow as quickly as it’s consumed for heat.

Of course, wood is a much less harmful source of heat than coal, but for scientists interested in developing green energy sources, it makes more sense to focus on solar and wind power. Why, then, would they invest in improved wood burning technology?

Homegrown Technology

Solar and wind technology are good large-scale energy solutions, but when it comes to small-space heating, wood has its own advantages. First, wood heat is in keeping with the DIY spirit of homesteaders and tiny house enthusiasts. These individuals are more likely to be driven to gather their own wood and live in small spaces that can be effectively heated as such.

Wood heat is also very effective on an individual scale because it requires very little infrastructure. Modern wood stoves made of steel rather than cast iron are built to EPA specifications, and the only additional necessary tools include a quality axe, somewhere to store the wood, and an appropriate covering to keep it dry. And all the wood can come from your own land.

Wood heat is also ideal for people living off the grid or in cold areas prone to frequent power outages, as it’s constantly reliable. Even if the power goes out, you know that you’ll be able to turn up the heat. That’s important if you live somewhere like Maine where the winters can get exceedingly cold. People have even successfully heated a 40’x34’ home with a single stove.

Benefits Of Biomass

The ultimate question regarding wood heat is whether any energy source that’s dangerous on the large scale is acceptable on a smaller one. For now, the best answer is that with a growing population and limited progress towards “pure” green energy, wood should remain a viable option, specifically because it’s used on a limited scale. Biomass heat is even included in the UK’s Renewable Heat Initiative and minor modifications can make it even more sustainable.

Wood stoves, when embraced in conjunction with pellet stoves, geothermal heating, and masonry heaters, all more efficient forms of sustainable heat, should be part of a modern energy strategy. Ultimately, we’re headed in the direction of diversified energy – all of it cleaner – and wood has a place in the big picture, serving small homes and off-the-grid structures, while solar, wind, and other large-scale initiatives fuel our cities.

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7 Benefits You Should Consider Giving Your Energy Employees



As an energy startup, you’re always looking to offer the most competitive packages to entice top-tier talent. This can be tough, especially when trying to put something together that’s both affordable but also has perks that employees are after.

After all, this is an incredibly competitive field and one that’s constantly doing what it can to stay ahead. However, that’s why I’m bringing you a few helpful benefits that could be what bolsters you ahead of your competition. Check them out below:

Financial Advising

One benefit commonly overlooked by companies is offering your employees financial advising services, which could help them tremendously in planning for their long-term goals with your firm. This includes anything from budgeting and savings plans to recommendations for credit repair services and investments. Try to take a look at if your energy company could bring on an extra person or two specifically for this role, as it will pay off tremendously regarding retention and employee happiness.

Life Insurance

While often included in a lot of health benefits packages, offering your employees life insurance could be an excellent addition to your current perks. Although seldom used, life insurance is a small sign that shows you care about the life of their family beyond just office hours. Additionally, at such a low cost, this is a pretty simple aspect to add to your packages. Try contacting some brokers or insurance agents to see if you can find a policy that’s right for your firm.

Dedicated Time To Enjoy Their Hobbies

Although something seen more often in startups in Silicon Valley, having dedicated office time for employees to enjoy their passions is something that has shown great results. Whether it be learning the piano or taking on building a video game, having your team spend some time on the things they truly enjoy can translate to increased productivity. Why? Because giving them the ability to better themselves, they’ll in turn bring that to their work as well.

The Ability To Work Remotely

It’s no secret that a lot of employers despise the idea of letting their employees work remotely. However, it’s actually proven to hold some amazing benefits. According to Global Workplace Analytics, 95% of employers that allow their employees to telework reported an increased rate of retention, saving on both turnover and sick days. Depending on the needs of each individual role, this can be a strategy to implement either whenever your team wants or on assigned days. Either way, this is one perk almost everyone will love.

Health Insurance

Even though it’s mandated for companies with over 50 employees, offering health insurance regardless is arguably a benefit well received across the board. In fact, as noted in research compiled by KFF, 28.6% of employers with less than 50 people still offered health care. Why is that the case? Because it shows you care about their well-being, and know that a healthy employee is one that doesn’t have to worry about astronomical medical bills.

Unlimited Time Off

This is a perk that almost no employer offers but should be regarded as something to consider. According to The Washington Post, only 1-2% of companies offer unlimited vacation, which it’s easy to see why. A true “unlimited vacation” program could be a firm’s worse nightmare, with employees skipping out every other week to enjoy themselves. However, with the right model in place that rewards hard work with days off, your employees will absolutely adore this policy.

A Full Pantry

Finally, having a pantry full of food can be one perk that’s not only relatively inexpensive but also adds to the value of the workplace. As noted by USA Today, when surveying employees who had snacks versus those who didn’t, 67% of those who did reported they were “very happy” with their work life. You’d be surprised at how much of a difference this could make, especially when considering the price point. Consider adding a kitchen to your office if you haven’t already, and always keep the snacks and drinks everyone wants fully stocked. Doing so will increase morale tremendously.

Final Thoughts

Compiling a great package for your energy company is going to take some time in looking at what you can afford versus what’s the most you can offer. While it might mean cutting back in other areas, having a workforce that feels like you genuinely want to take care of them can take you far. And with so many different benefits to include in your energy company’s package, which one is your favorite? Comment with your answers below!

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