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.