Question

Engine Cycles

a. Write a description of an 'engine cycle'. Use figures, grabs and/or image to help support your description. Cite and material that used to prepare this description.

b. Provide a real world example of an engine cycle(that is NOT a car, truck, lawn mower or other engine). Describe the transfer of energy through the cycle.

Answer 1

Any series of thermodynamic phases constituting a cycle for the conversion of heat into work is termed as Engine cycle. An engine cycle may be plotted as a closed curve in coordinates of the volume and pressure (V, p) or the entropy temperature (S, T) of the working fluid. The area bounded by the contour is proportional to the work done. The following Figure gives an example of a carburetor engine. It consists of compression of the working fluid (adiabatic curve ac), addition of the heat Q₁ (isochoric curve cz), incomplete expansion (adiabatic curve zb), and rejection of the heat Q₂ (isochoric ba).

2)Drinking birds( also known as dippy birds and dipping birds) are toy heat engines that mimic the motions of a bird drinking from a water source. First, The water evaporates from the felt on the head. Evaporation lowers the temperature of the glass head due to the heat of vaporization. The temperature decrease causes some of the dichloromethane vapor in the head to condense. By ideal gas law, The lower temperature and condensation together cause the pressure to drop in the head. The pressure differential between the head and base causes the liquid to be pushed up from the base. As liquid flows into the head, the bird becomes top heavy and tips over during its oscillations. When the bird tips over, the bottom end of the neck tube rises above the surface of the liquid. A bubble of vapor rises up the tube through this gap, displacing liquid as it goes. Liquid flows back to the bottom bulb (the toy is so designed that when it has tipped over the neck's tilt allows this), and vapor pressure equalizes between the top and bottom bulbs. The weight of the liquid in the bottom bulb restores the bird to its vertical position.The liquid in the bottom bulb is heated by ambient air, which is at a temperature slightly higher than the temperature of the bird's head.  The drinking bird like a heat engine exploits a temperature difference to convert heat energy to a pressure differential within the device and perform mechanical work. Like all heat engines, the drinking bird works through a thermodynamic cycle.