THERMODYNAMICS LAB 1IntroductionAll engines work on a thermody namic cycle. In this lab exerciseyou will have the opportunity to study an example of a gas pistonengine working between a high temperature and a low temperaturereservoir. In this case the high temperature will be water close toboiling and the low temperature that of an ice b ath. A picture of yourapparatus is at right. The Heat Engine Apparatus is designed withtwo pressure ports with quick-connect fittings for connecting to theair chamber tubing. One of these p ressure ports should be connectedto a Pasco pressure sensor and the other should be connected to aaluminum can with a r ubber stopper. The system can be vented(opened to the air) by removing the rubber cap. The Pasco pressuresensor should be plugged into channel A of the PASCO interface.In addition to the Heat E ngine Apparatus you will us e a Pasco rotarysensor. Th e rotary s ensor should be plugged into channels 1 (yellow)and 2 (black) of the PASCO interface.ThumbScrewLockSmall HolePressurePortsTo monitor position you should tie one end of a 1.0 to 1.5 m length of string through thesmall hole in the black plastic cap of the piston’s plunger. The plunger has a d iameter of 3.25cm and makes a fairly tight s eal with the glass wall. The other end of the string should betied to a 20 or 30 gram mass and the string loop over the middle pulley of the rotary sensor.When moving the piston up or down the string should rotate th e rotary sensor withou tslipping. If th e proper PASCO calibration is used , then the rotary sensory output will reflectposition of the plunger.There will be just three main tasks to execute:• Check the calibration of the rotary sensor read ou t.• Check the reproducibility of a pressu re sweep.• Run a thermodynamic cycle and estimate the efficiency.Calibration of the rotary sensorWith the rubber stopper detached, move the plunger down or up stepwise a total distanceof five centimeters. At each centimeter on th e glass scale record the value on the PASCOdisplay.Scale Pasco12345Comment on the calibration:THERMODYNAMICS LAB 2Reproducibility of a pressure cycle.Now tightly p lug the rubber stopper into the aluminum can. The p lunger should be lockedin position about 1/3 of the way down from the top m ost point. With the Pasco recording,unlock the thumbscrew and slowly increase the pressure from approx im ately 100 to about 115kPa and then slowly release the pressure. The w hole experiment should require no more thanthirty seconds. When done stop recording and print out a copy to the pV display for this runand paste it into the space provided below or attach the plot at the end.Is this process perfectly reversible? Discuss the outcome with your lab partners and identifytwo likely reasons why the process may not be reversible.Getting ready for the thermodynamic cyclePrepare your hot water bath by pouring deionized water into the Steam Generator until thewater is about 1 inch from the top. The aluminum can should be fully submersible. Turn onthe generator.Prepare your cold water bath by filling the plastic beaker with a mixture of about 50%water and 50% ice. Use the digital thermometer as a stir bar.Record the temperatures of the water baths.Temperature of hot water bath (in Kelvin):Temperature of cold water bath (in Kelvin):THERMODYNAMICS LAB 3Estimate the volume of air inside the aluminum canInner diameter of Al can:Height of air space ins ide the canVolume of air space inside the canRunning a test thermodynamic cycleFirst place the aluminum can inside the ice bath and wait for the air pressure to reach steadystate. Does the height of the plunger change? Why does this hap pen .Does the pressure inside the piston change? Why does this happen.Then start the Pasco data r ecording and insert th e aluminum can into the s team generatoruntil the height of the plunger stops changing then put the can back into the ice water bath.Repeat this procedure at second time to check for reversibility.Displacement of the plunger:Volume change of air in piston:Number of moles of air in Al cylinder when cold:Number of moles of air in Al cylinder when hot:From the difference in the number of moles estimate the expected volume change of air in thepiston:Qualitatively, discuss how well do the two methods of calculating the volume change agree.How much work was done on the system by the world when the piston volume wasincreased:How much work was done on the system by the world when the piston volume wasdecreased:What was the net work done?You can crudely estimate the thermal energy transferred from the high temperature reservoirby assu ming all of the cold gas in the aluminum can reaches the temperature of the hot water.This is an upper limit in Q.Maximum Qhot:In the same way you can crudely estimate the thermal energy transferred to the coldtemperature reservoir by assuming all of the hot gas in the aluminum can r eaches thetemperature of the ice water. This is close to the lower limit in Q.Minimum Qcold:The first Law of Thermodynamics states that ∆Ethermal= W + Q but you cannotquantitatively assess this here. The second Law of Thermodynamics states that, in any realprocess, W < ∆Ethermal. What is the net work done in this cycle?Wnet:The efficiency, ǫ, of any thermodynamic cycle is defined to be W/Qhot. What is the efficiencyhere?ǫ:THERMODYNAMICS LAB 4A real engine cycleIn this cycle you will employ a four step sequence that will convert thermal energy to gravi-tational potential energy.1. Place the aluminum can in the ice water bath.2. Put a 500 gm mass on top of the plunger cap.3. Transfer the aluminum can to the hot water bath.4. Remove the mass from the plunger cap.5. Transfer the aluminum can back to the ice water bath.Now set the Pasco interface to record your data and perform the above cycle twice to test f orreproducibility. Make sure you wait long enough at each step to m ake certain the volume ofgas in the piston reaches steady state.The whole experiment should require less than five minutes. When done s top record-ing and print out a copy to the pV display for this run and either attach the plot at the endor paste it into the space provided below. Is this cyclic pr ocess repeatable?THERMODYNAMICS LAB 5Calculate the net work done on the world in one full cycle. If all went well your curve shou ldlook like a parallelogram and, if so, you can calculate the work done (on the world) bymultiplying the base (change in volume) times the height (change
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