Students should submit the exam at the beginning of the class.The exam will be conducted according to the policies outlined in the Northeastern University honor code. It is expected that you will work independently and if questions arise, you should contact the instructor.
1. Determine the amount of electricity used in a manufacturing process for the following conditions. The machine has a mass of 650 Kg, a specific heat of 1130 J/(Kg K) and is at an initial temperature of 24 C. To begin the process the machine's temperature is increased to 180 C and is held at that temperature until the end of the manufacturing process. The material to be processed also has an initial temperature of 24 C, a mass of 7 Kg and a specific heat of 765 J/(Kg K). During the manufacturing processthis material is heated to 140 C and is made into the desired part. During the process a power input to motors that drive the manufacturing tool require 0.75 kW and there is a heated nozzle that requires an electrical power input of 200 W over a period of 5 hours. The input electricity must power the motors, heater nozzle and provide the required heat input to the system. At the end of the manufacturing time both the machine and the finished material parts are 180 C. The end point time in this problem is not given and it is not necessary to answer the question.
2. An owner of a manufacturing shop is considering installing a hybrid co-generation system to provide the required electrical power and thermal load needs. The following conditions are representative of his energy needs: power load of 1500 kW and a thermal load, a heating load of 500 kW and a cooling load 4500 kW. The hybrid co-generation unit he wants to install has a maximum power output of 5000 kW. Determine the HLRP value, the first law energy utilization factor, EUF, and the rate of carbon dioxideproduced for these stated conditions. Determine the fuel cost to operate this system for 7 hourswhen the fuel cost is $0.0734/kWh
3. Determine how long an energy storage device can be used when the required power load is a polynomial function of time, (Power) = a0- bt2, where a0 = 3.4(105)W and b = 6.1(10-2) W/s2 are known constants and t is the time in seconds.The energy stored in the device at the start of this process is 1.1(1010) J and the device is discharged to 80% of the initial energy stored so that it can be recharged. Can the device provide 4 MW of power at any time during the discharge phase? How many kWh of power will the device provide?
4. A large auditorium is temperature controlled to a temperature of 19 C and the heating/air conditioning system provides 25 kW of heat transfer (rate) from this room to the environment. The rate of heat transfer provided to the room remains constant over the time period of a performance, 3 hours. The rate of transfer from the room to the environment also remains constant over this period. The auditorium holds 2000 people who each dissipate 0.3 kJ of energy over the period of the performance. The mass of air in the room is 0.213 kg and has a specific heat of 0.760 kJ/(kg K). What is the temperature of the room at the end of the performance?
5. A bicycle rider is at the top of a hill and begins their descent. The mass of the rider and bicycle is 110Kg. The hill has an elevation of 80 m and the distance of the road down it is 1.3 km. The drag force on the rider is 57 N during this descent. The rider will constantly pedal downhill and adds 0.5 kJ of work to the process. Determine the final velocity of the rider if they start the descent at a velocity of 2.8 m/s.