Pedal Cooling Cell
This page presents an example of a model created using dada-engine-solver, you can find it in the folder examples/pedal_cooling_cell/. This research has not been carried out in sufficient depth to claim that it provides an optimal result.
The aim is to size the motor for a low-tech cooling cell driven by a pedal mechanism. The working gas is air, the initial load corresponds to a pressure of 1 bar when the machine is in its maximum volume position. The target power for the input work is 150W, the work required to circulate the external heat-transfer fluids, as well as mechanical losses, have not been estimated.
A few tests have shown me that the maximum speed is reached quickly, and efficiency is at its highest when the frequency approaches 0, at the expense of power. A frequency of 1.4 Hz is recognised as comfortable for pedalling, ideally a machine operating at 2.8 Hz would have benefit from one pedal stroke per compression, but I haven’t found a solution at those frequencies. I did, however, find a solution at 0.933 Hz, which equates to one compression every three pedal strokes, that might be acceptable with a suitable flywheel.
Sources temperatures were set at 25°C for the hot source and -15°C for the cold source, with the aim of producing ice. The wiped volumes of the cylinders are approximately 14.2 and 10.8 l. Each microtube heat exchangers consist of approximately 220 tubes with an internal diameter of 3 mm, measuring approximately 48 cm in length for the hot exchanger and 31 cm for the cold exchanger. Simulations show that efficiency improves by increasing the number of tubes, combined with a reduction in their length and internal diameter, which takes us away from the low-tech objective.
I achieved a COP of 1.64, equivalent to 25% of the Carnot COP, by operating this configuration using a synthetic law of motion. This is a purely thermodynamic COP, the only losses taken into account are the pressure drops in the heat exchangers.
I then adapted mechanical assemblies to approximate this law of motion, before optimising these mechanisms by seeking the maximum COP they could produce in this configuration, I subsequently sought further optimisation by jointly modifying both the mechanism and the thermodynamic component, which explains the final differences in dimensions. The maximum coefficients obtained with the slider-crank, 4-bar and 6-bar linkage mechanisms are 1.53, 1.57 and 1.6 respectively.
Below are animations of the three mechanisms tested, along with a link to the detailed HTML report generated by the software, you’ll have to download the file and open it from your drive. The mechanisms were deliberately chosen asymmetrical in order to give an idea of the variety of possible solutions.
