Heat-powered fan for cookstoves could improve health and help mitigate global warming

Better, more efficient cookstoves in developing countries means improved health locally and the potential for a decrease in global warming. Even Hillary Clinton thinks so.

An engineering grad student at Penn State University is working to design a simple, heat-powered fan that would help mitigate the health and environmental effects that millions of inefficient cookstoves have on the planet. I spoke recently with Paul Montgomery and his research adviser, Steven Garrett.

Before we talk about your solution, explain the problem you're trying to solve.

Montgomery: In the areas of the world that primarily burn biomass as a fuel source for these cookstoves, they release an immense amount of pollutants, mostly black carbon soot. In areas of Southeast Asia, it accounts for 75 percent of the soot production. The problem with 2.5 billion people using this is there is a lot of global warming potential in the output of the soot, as well as health effects. More than 1.5 million women and children die each year because they're inhaling these fumes and getting respiratory problems.

There have been studies done that have shown that [having] a continuous stream of air blowing over the combustion process cuts down on a lot of the soot being produced. The main problem is getting the electricity to power the fans. The majority of the people using these cookstoves don't have an electrical grid, so we have to find a way for them to produce the energy to power these fans. This project proposes using a heat engine, a thermo-acoustic engine to do that.

How could you use heat to power fans?

Montgomery: Cookstoves produce about six kilowatts of power, which is a considerable amount. It's a high-quality heat too, around 800 degrees Celsius. This device is taking some of that heat and turning it into an acoustical wave. It's offloading air back and forth within this closed volume. We're essentially using a loudspeaker in reverse, meaning that acoustical signal is going to move our loudspeaker back and forth and produce an electrical signal. [This is in contrast to] when you flip on your speakers and there's an electrical signal causing the speakers to move back and forth and causing the acoustic signal. The temperature difference causes the air on the molecular level to expand and contract. Once that temperature gets high enough, the air will move back and forth and drive the loudspeaker.

How does this work advance previous efforts?

Garrett: There have been some very sophisticated thermo-acoustic electrical generators. Once of our colleagues at Los Alamos National Laboratory, Scott Backhaus, developed a space-based electrical generator that used a high-quality heat source. The acoustic oscillations drove a very fancy linear alternator. The linear alternator was about a half-million dollars. So at that level it has been done and it has worked very successfully

Everybody appreciates that this problem is important. Secretary of State Hillary Clinton just initiated the UN Foundation's Global Alliance for Clean Cookstoves. The question is: How do you produce a cookstove that reduces the pollution that causes the health problems locally and reduces the pollution that causes global warming? Black carbon is a very potent global warming gas. In industrial countries, most of our black carbon comes from diesels and we have regulations that limit the amount of black carbon. In developing countries, most of that black carbon is coming from people just cooking their meals on a daily basis. If you add a fan, you can improve the efficiency of combustion, reduce the cooking time and reduce the level of pollutants to something that's acceptable both for health quality and for mitigating global warming.

How far along is this project?

Montgomery: We just finished the testing on the first prototype, the one Dr. Garrett and I built and designed. Through that testing, we were able to find out a lot of different characteristics of it, [such as] how we can extract the most power out of it and how we can get rid of some of the losses. What I'm doing now is pointing it in the right direction as far as future prototypes go.

Garrett: It was a proof of concept [study] funded by a private foundation.

Where will you be doing trials?

Montgomery: Our main focus is Southeast Asia because they have a bigger technical background.

Garrett: Southeast Asia is particularly attractive because it has both a high concentration of biomass users and a high concentration of indigenous engineering talent and infrastructure. That would be a place where it would be good to introduce this kind of technology and have people who would be knowledgeable and able to make changes on the fly.

How much will the device cost?

Garrett: It's too early to say what it's going to cost. Whether it's going to cost $10 or $25, Paul's efforts were a proof of concept. We wanted to show that you could make these simplifications and still be able to generate electricity. We've got a way to go. But as part of this Global Alliance for Clean Cookstoves, there's an understanding that there has to be research and development that takes those that are better than the ones used now and brings them to a level where they're competitive with the emissions that we require for wood-burning products in the United States or the European Union.

Image, top: Paul Montgomery

Image, bottom: Steven Garrett / Photo by Rolex/Kirsten Holst

This post was originally published on Smartplanet.com