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Germany: New sensor for measuring air flow in cold storage fruit and vegetables

Scientists at the Leibniz Institute for Agricultural Engineering and Bioeconomy in Potsdam have developed a new sensor system for measuring air flow in cold storage rooms for fruit and vegetables. The sensors measure the product environment. This makes it possible to design storage rooms with the best possible air flow, for heat dissipation. The sensor system was recently presented in the renowned journal 'Sensors'.

Air Speed Logger between some apples (Photo: ATB)

The ASL (Air Speed Logger) sensor system consists of four interconnected plastic spheres, each 80 mm in diameter, positioned like the apples in large crates. In the space between the balls, silicon diodes are attached. They calorimetrically record the air velocity between the balls. A special feature of the system is the direction-independent measurement of low flow velocity in the range between 0 and 1.5 m/s.

So far it has not been possible to carry out continuous flow measurements in fruit or vegetable crates without disturbing the storage process. The new, autonomous Air Speed Logger has therefore been specially designed to determine the air velocity and air temperature in bulk environments and in containers of stored agricultural products.

Taking the measurements is simple: The ball system is placed between the fruits. Battery and data loggers are integrated into the balls and allow the recording of data over a period of up to 28 hours. Compared to traditional anemometers, the system is relatively insensitive to mechanical damage as the four balls are protecting the sensor units.

The system is suitable for the validation of air flow models, which are created, for example, by means of computational fluid dynamics (CFD). They are the basis for the development of optimized cold storage and ventilation concepts that best meet the requirements of the stored fruit and vegetable products, in order to reduce storage losses.

Laboratory scale and practice fruit camp tests revealed stable air velocity values in the interstitial spaces at different air flow levels. The sensitivity of the sensor increases noticeably with decreasing air velocity values. However, the influence of rapid temperature changes on the air velocity measurement must be considered. Measurements in storage rooms should be made at stable temperatures.

The new device is adapted to the size of apples and is particularly suitable for products of a similar size and shape, such as onions, potatoes, kiwi and oranges. It can also be used - after adjustments - to determine the air velocity distribution within other porous bulk materials.

The Air Speed Logger was developed as part of the project "Flow Sensor Based Air Management in Fruit and Vegetable Storage - COOL". The project, on which three research institutions and five industrial partners from the fields of sensor technology, storage, cold storage, refrigeration and large box production have been working together, is funded by the Federal Ministry for Economic Affairs and Energy (BMWi) and coordinated by the Leibniz Institute for Agricultural Engineering and Bioeconomy (ATB). The aim of the project is to optimize the ventilation through uniform airflow in the storage room, while reducing energy consumption and avoiding product losses.

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