A Fast Optical Method for the Determination of Liquid Levels in Microplates
Parallel liquid handling systems are widely used in different applications of life sciences. In order to avoid false positive or negative results which lead to higher costs due to the replication of the experiments it is necessary to monitor the process and success of liquid delivery. An easy method for the determination of the liquid levels in microplates has been developed and evaluated. The optical method bases on the measurement of the liquid level using CCD cameras followed by special algorithms for the evaluation and visualization of the measured data. The proposed method was tested in changing environmental lighting for two different liquids. These tests confirm our approach towards optical liquid level determination for smallest volumes in microplates and also show the challenges regarding environmental lighting and different physical properties of fluids.
LLS-Liquid Level Sensing methods in qPCR set-up
One of the main goals of all liquid level sensing techniques in automated pipetting systems is to obtain most precise control over actual pipetting performance, which largely depends on ensuring optimum liquid level (meniscus) in the well and precise immersion of the pipette tip in the liquid. Various techniques for liquid level sensing are reported in literature. All of them have some advantages and limitations. Some of the techniques are used for checking the proper setup of a workstation deck prior to starting a run. Other so-called ‘real time’ level sensing devices are able to track the meniscus in each well at every pipetting step. Real time level sensing systems give the additional benefit of being able to monitor the whole pipetting procedure and provide for a consistently pipetting protocol after each run. Tracking the meniscus in each well at every pipetting step enables the pipette tip to be positioned near the liquid surface. To avoid wetting on the outside of the tip the robot calculates the minimal submersion depth necessary for pipetting the set volume. By these actions both hydrostatic pressure of the liquid and wetting of the pipette tip are minimized. Therefore accuracy in pipetting smaller volumes is enhanced as well as aerosol formation due to droplet transfer at the outside of the tip is minimized. This kind of real time level sensing gives maximum safety control for the precision and safety of all performed pipetting steps. Depending on the field of application only a few of these methods provide adequate performance for setting up polymerase chain reaction (PCR) and quantitative real-time PCR (qPCR) applications.
Techno-economic analysis of solar thermal power plants using liquid sodium as heat transfer fluid
Abstract Solar thermal power plants with central receiver and thermal storage are expected to be one key technology in future electricity generation, because they are renewable and due to the thermal storage independent of the current solar radiation. State-of-the-art solar power plants often use molten nitrate salts as heat transfer fluid. The use of liquid sodium instead leads to lower electricity generation costs. Sodium has a high thermal conductivity and thus large heat transfer rates are possible. Hence, a smaller absorber surface is sufficient for the same thermal power. As a result, the sodium receiver achieves a higher efficiency at lower investment cost. Additionally, the aiming strategy, which reduces the peak heat flux on molten salt receivers isn’t necessary for sodium. Even at high heat flux densities, the absorber tubes will be cooled sufficiently due to the high heat transfer coefficients. Therefore, the sodium receiver in this analysis is designed for one single aim point, resulting in a heat flux density of q mean = 1.06 MW / m 2 and q peak = 2.99 MW / m 2 . The state-of-the-art system with molten salt considers q mean = 0.51 MW / m 2 and q peak = 1.0 MW / m 2 . The presented techno-economic analysis of two sodium based concepts compared to a reference system with molten salt results in up to 16% lower electricity generation costs.