There is a typo in the problem related to combustion of hydrazine. The sentence alluded to products should read: "Because of the fuel choice, expected products of combustion are H2, N2 and H2O"In the version you received, the term O2 should have been N2.

• For each question include the statement of the question before your solution.

• For each question include a schematic, suitable thermodynamic diagrams, and engineering model.

Problem #1

One of the students happens to be a small scale rocket-motor aficionado who is attempting to decide which fuel to use in the combustion chamber of a rocket. For her initial testing, one of her choices, because of her deep concern about environmental pollution, is to burn liquid hydrazine (N2H4) at 25 °C and 1 atm in presence of liquid O2 at 90 K and 1 atm. From the literature review she has determined that the mass ratio of oxidant to fuel should be 0.6 kg O2/kg N2H4. Also from the rocket design specification your fellow student has determined that the acceptable thermal energy loss to the surroundings is 80 kJ/kg N2H4. Because of the fuel choice, expected products of combustion are H2, O2 and H2O. You are asked to determine the temperature of the products in Kelvin temperature units.

Note: to receive credit you MUST show your procedure step-by-step with all hand-calculated details for the first iteration and then tabulate your results for the next iterations. Your final answer should be within a +/- 0.5 K error.
Use the following data for liquid hydrazine:

Molar mass

32.0452 g mol-1

Std enthalpy of formation (Δfho,298)

50.63 kJ mol-1

On next page you will find a p-h diagram for O2 in case you have any concerns about oxidant conditions.

Problem #2

Gaseous ethanol (CH3CH2OH, also expressed as C2H5OH) is burned with 200 % of theoretical air at standard conditions. During the combustion process 90% of the Carbon in the fuel is converted to CO2 and 10% is converted to CO. Determine the rate of heat transfer from the combustion in kJ/s for the combustion of 3 kg/h of fuel when the reactants and products are at 25 °C and 1 atm.

Problem #3

For the combustion process in Question #2 determine the adiabatic flame temperature in K (15 points) and the dew point temperature of water in the products (5 points).

To receive full credit, you need to show all hand-calculated details for the first iteration and present the result of the other iterations in tabulated form. Your final answer should be within a +/- 0.5 K error.

Problem #4

Ambient air at 1 atm, 32° C and 75 % relative humidity enters a 400 mm internal diameter air-cooling duct with a velocity of 120 m/min. Inside the duct there is a cooling coil. The air leaves the duct saturated at 20 °C and 1 atm.

You also know that the cooling coil is receiving cold water from the local chilled water plant and the temperature of the chilled water when it leaves the cooling coil increases by 6 °C with respect to its inlet temperature.

a.Without using a psychrometric chart determine the amount of water that needs to be supplied to the cooling coil to produce the given exit conditions for the air. Your solution must include hand-calculations and show all the steps required to get the answer. If you need a value for the specific heat of water for the water going inside the cooling coil use 4.16 kJ/kg-K. Hint: verify your partial answers using a psychrometric chart and represent the inlet and exit states for the air on it so that you gain visual understanding of the process, submit the psychrometric chart with your solution.

b.You are interested in analyzing how changes in the inlet relative humidity of air affect both the required mass flow rate of chilled water needed for the cooling coil and the heat removed from the air. All of the other operating conditions remain unchanged.
For your analysis consider the relative humidity of air at the inlet varying from 50% to 90%. Use EES or any other suitable software to study the effect of varying the relative humidity of ambient air that enters the duct. The result of your analysis should be a table that shows the heat removed in kJ/s and chilled water mass flow rate in kg/s ranging from relative humidity 50% to 90% in 5% increments and a plots for heat removed and mass flow rate as a function of relative humidity.