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15.05.2007 » Pressrelease » Solar Energy
Pumping Solar Energy
Thermofluidics Ltd, a Cambridge UK based company, is currently working on a class of thermofluidic oscillators known as 'Non-Inertive-Feedback Thermofluidic Engines' (NIFTEs), which are not dependent on inertia to generate or sustain oscillations.
This means that they can sustain much greater pressure amplitudes than their predecessors and can be much more powerful for a given size. They can be applied to thermally powered pumping and mixing, and heat pumping applications on a far wider range of scales than before, using a variety of different heat sources.
NIFTE devices may also provide a cost effective solution to many heat and fluid transfer problems, particularly improving energy efficiency, and providing pumping power when heat is available but electricity is not. The absence of dynamic seals and bearings gives NIFTE devices advantages over mechanical heat engines. Apart from increased reliability and low maintenance, NIFTEs can be manufactured from very low cost materials using cheap and well established production techniques. This makes them economically feasible in application areas where pumps are not currently viable.
NIFTEs are capable of pumping many different fluids, from shear sensitive biological cultures to viscous and chemically, or mechanically abrasive media. They have a gentle pumping action, and operate in almost total silence. NIFTEs can be tuned during operation to suit a range of different pumping head and flow requirements, and available power sources.
Vapour cycle NIFTEs are particularly well suited to using heat at low temperatures, such as waste heat from process loads or heat obtained from solar collectors, thereby making them well suited to applications in remote areas or hostile conditions, or helping users to meet increasingly stringent emission standards.
Thermofluidics sees applications for their product in solar energy and pumping systems. Solar powered pumps for water supply, sanitation, and irrigation tend to be expensive, fault prone and unreliable, particularly on smaller scales. The majority of existing solar pumping systems are based on photovoltaic solar cells, which convert sunlight to electricity before it is converted to hydraulic work by an electric pump. Photovoltaic cells remain expensive. In addition, they only operate efficiently over a small range of voltages. As the level of sunlight which falls on cells increases or decreases, the current which they can deliver also increases or decreases. In order to operate efficiently, electricity must always be taken from them with a maximum product of voltage times current. This means that they can only drive the majority of electric pumps efficiently under one pre-determined level of sunlight. Some photovoltaic pumping systems use power modulating circuitry known as 'maximum power point trackers', to match the photovoltaic cells to the pump under a range of conditions. However, these add extra losses to the system, they are fault prone, and they are expensive.
Solar powered pumps based on NIFTE devices can use off-the-shelf solar thermal (hot water) collectors to convert solar radiation into usable heat. Solar thermal collectors are much cheaper than photovoltaic solar cells. Furthermore, pumps based on NIFTEs can use the water which they pump as a source of cooling water. In this application, they could undercut the cost of photovoltaic systems by up to 5 times.
Unlike photovoltaic pumping systems, solar pumps based on NIFTEs do not require power point tracking to operate at peak performance under different sunlight levels. This is because solar thermal collectors can operate efficiently over a large range of temperatures (c.f. photovoltaic cells which only operate efficiently over a small range of voltages). NIFTEs can be pre-tuned to match a given collector to a given pumping load, so that as the level of sunlight changes, the collector automatically changes to a new optimum collecting temperature, which is also the new optimum heat input temperature to the NIFTE, pumping at the new peak flow rate.
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