Lab 6: Heat Engines and Cycles

  Today, we started a thermoelectric cooler demo first. We put the cooler metals into a cup of cold water and a cup of hot water, then the fan started rotating. If we reverse the metals, the fan started rotating opposite way.

  The lead will hot on one side and cold on the other if we attach a power supply.

  Then we found out c_v=(3/2)R and c_p=(5/2)R.

  This is a in class activity we did. First, we found out two equations that equal to n△T. Then we made them equal to each other and we found the relationship of △p and p.

  Then we found out p_f/p_i= -(v_f/v_i)^(5/3) by integrate 1/p and -c_p/(c_v *v). Last, we prove that Tivi^(y-1)=Tfvf^(y-1).

  There is another activity we did in class is about work in an adiabatic expansion. The answer we got is W=1246J.

  Then we started talking about Carnot engine cycle. Isothermal expansion is A to B; Adiabatic expansion is B to C; Isothermal compression is C to D; Adiabatic compression is D to A.

  We used nRT ln(vf/vi) to found work; (3/2)nRT to found internal energy; W+△E to found heat energy.

  All these pictures are Otto Cycle.

  There are three ways to increase the power of a engine.

  In conclusion, thermoelectric cooler and Otto cycle are the most important experiments we did today. For thermoelectric cooler lab, if we reverse the hot and cold water, the rotation of the fan will also reverse. For the Otto cycle lab, if we want to increase the engine power, we need increase revolutions, volume and maximum pressure. Also, for the Carnot cycle engine problem, we identity each expansion and compression first, then use equations to found out work , internal energy and heat energy. For the last, we could found efficiency by using w/Q_h.

Lab 5: Heat

  There are four state variables can influence thermodynamic state:

  These are the answers for the lab manual questions. First graph is Isobaric process, second graph is Isochoric process, and third graph is Isothermal process.

  These are example problems for us to solve by using the processes that list above.

  Professor gave us four graphs and wanted us to match the graphs and the processes. Isothermal process graph and Adiabatic process graph are very similar but Isothermal process graph  is gradual change of volume and Adiabatic process graph is sudden change of volume.

  Now we know a rubber band will shrink because heating after we watch a rubber band heating video on  youtube.

  These are the steps for can lifter cycle.

  The engine will not work if environmental temperature and heat gun temperature are the same. Also, not all heat will transfer to work. Some will escape to environment.

  This is the equation we found for thermal efficiency.

  This is an example problem for us to do about the cycle. First, we found out internal energy by using the equation E_int=(3/2)P*V. Second, we found out △E by using p2-p1, p3-p2, p4-p3 and p1-p4. Last, we need to found out net work and net heat. It was easy for us to calculate work because we can use the equation W=P△V. Now, we knew work and △E, so we could calculate heat by using  Q=△E+W. Then we just add them up to found the net work and net heat.

  Last, we did the mass lifter heat engine experiment. 

  First, we collected four different volume and pressure by using the pressure sensor. Then we used E=(3/2)PV to find the internal energy. Last, we found the mass and heat for each process.

  In conclusion, there are three important processes need us to remember; Isobaric process - pressure is constant; Isochoric process - volume is constant; Isothermal process - temperature is constant. The can lifter cycle experiment is very interesting. We could find internal energy by using E_int=(3/2)P*V and find △E by subtract each process.

Lab 4: Kinetic Theory and PV Diagrams

  We started a quiz today. We were using q=ml and q=mc(Tf-Ti) to find the heat of evaporation and boiling.

  After the quiz, we started the first law of thermodynamic experiment. We figured out the definition of work and two graphs show work equals the area under the curve.

  When we put a flask into the hot water, the volume of the air in the syringe will bigger. But we put the flask into the ice water, the volume of the air in the syringe will smaller.

   After the experiment, we found out the relationship of work, heat and energy.

  There is an example problem for us to solve.

  Then we did an experiment on the computer. These images tell us that atoms will move faster if temperature and pressure are increasing.

2D Molecular Motion activity:

  We found out the speed v of a molecule by using pythagorean theorem. So we found out the equation  v^2=3v_x^2. 

  We found out the equation P=Nmv^2/3V by using p=Nmv_x^2/V and v^2=3v_x^2.

  There is the equation for T.

  Also, we found out a equation for the relationship of V and T.

  

  Isothermal compression of a gas.

  Adiabatic compression of a gas.

  

  This is our final experiment.

  We were trying to found out the final temperature by using the equation Ti^(3/2)Vi=Tf^(3/2)Vf.

  In conclusion, we did a quiz at beginning of the class which is very surprised me. But it is a good problem for us to practice. After the quiz, we did some interesting but hard experiments. All these experiments are hard and a little confused. However, we understood all of them through group discussion.