SUES FALL 2008 FINAL TEST MASTER ANSWER.doc

（勤奋、求是、创新、奉献）2008 2009学年第1学期考试试卷主考教师：_ Thomas A. Hamade_学院 _ 汽车工程学院_ 班级 姓名 _ 学号 _先进制造工艺（美）课程试卷A答案（本卷考试时间120分钟）题号一二三四五六七八九十总分题分81291654100得分. Fill in the blank（4 blanks, 4 points each, 16 points total）1. Heat Transfer deals with the determination of the rates of energy transfers as well as variation of temperature. 2. A water vapor at temperature and pressure higher than the saturation point is known as _superheated_ steam.3. Fluid flow is the science that deals with the behavior of moving fluids.4. The enthalpy is H = U + PV and the internal energy for a closed system is given as dU = Q W.5. Thermal Science is the science of energy transformation in thermodynamics, fluid flow and heat transfer.6. The ideal gas law is used to approximate P, T, V relationship for many gases.7. The expansivity of fluids is an energy form and represented by pressure and volume of fluids according to the following relationship between pressure and volume of the fluid: _PV_.8. The Bernoulli equation is used to predict flow conditions of a fluid along the streamlines.9. One British thermal unit (BTU) is equal _252_ calories and each calorie is equal _4.187_ Joules.10. 273 K is equal _ 0F and 0 K is equal to _ R.11. The lowest possible pressure is 0Pa and the lowest possible _temperature_ is 0 K.12. The weight of matter on the moon is much than that on earth because of the _ constant is much lower. Choose the right answers:（4 questions, 4 points each, 16 points total)1. Which one of the following devices is used to generate electric power: (a)Pump (b)Electric motor (c)Gas heaters _X_(d)Turbine2. Which one of the following devices is used to compress fluids: (a)Nozzle _X_(b)Compressor (c)Turbine (d) None mentioned3. Which one of the following is a open system: (c)a. Gas inside cylinder exchanges heat with surrounding but no mass enters the system.b. Gas isolated so matters from surrounding do not enter the system.c. Fluid flows in and out of the system from surrounding.d. Gas doing work on surrounding, however no matter enters the system.e. None of the above.4. At what temperature water evaporates when the pressure is 0 kPa:a. 0 oC c. 0 K d. 0 R _X_e. All mentioned 5. In steady heat transfer through a wall is always: a. Variable _X_b. Constant c. Not Importantd. Depends on pressure.6. Metals thermal conductivity is:a. same as gases_X_b. Greater than non-metalsc. Same as insulators d. None mentioned.7. Heat can be transferred in many modes such as:a. Conductionb. Convectionc. Radiation_X_d. All mentioned.8. The Bernouli Equation is valid for:a. Steady state, incompressible flow where net frictional forces are negligible.b. Unsteady state heat transfer.c. Steady state compressible flow.d. None above. 9. The mechanisms for heat transfer are: 9A0a. conduction, convection & radiationb. Work and heat additionc. Internal energy changesd. Vibration and rotation of atoms.10. Which one of the equations used in fluid flow: a. Einstein Equationb. E = mghc. Bernoulli Equation.d. PV = nRT 11. Saturated liquid vapor data are used to:a. Determine the potential and kinetic energy of a control volume.b. Determine the superheated temperature.c. Determine the boiling point temperature at various pressuresd. Determine the work added and heat removed from solids.12. The units for energy density are the same units as:a. Temperatureb. Pressured. Energye. Force. Answer the following questions with “True” or “False”（12 questions, 2 point each question, 24 points total）1. The barometer is used to measure the atmospheric pressure: _X_TRUE _FALSE. 2. Volume and density and specific heat are extensive properties while volume, and dimensions are intensive properties. _TRUE _X_FALSE3. Convection is the transfer of energy between energetic hot object and less energetic cold object._X_TRUE _FALSE4. The potential energy of moving objects is equal to (mgh) which is different than the kinetic energy. _X_TRUE _FALSE5. Heat is added or removed from system and work is obtained by or done on a system. Both can not cause any changes in the internal energy and enthalpy of the system. _TRUE _X_FALSE6. Saturated liquid-vapor mixtures co-exist when liquid and vapor phases are at equilibrium. _X_TRUE _FALSE7. Air can be compressed adiabatically without changing its temperature. _TRUE _X_FALSE8. Latent heat of fusion is the amount of energy lost during solidification of ice. _X_TRUE _FALSE9. Convection is the energy emitted by matter in the form of electromagnetic waves._TRUE _X_FALSE10. For fluids the volumetric flow rate is the same as the mass flow rate._TRUE _X_FALSE11. Superheated vapor is a single phase region at saturation liquid with the liquid phase. _TRUE _X_FALSE12. Van der Waals Equation of State was proposed to improve prediction of pressure, temperature and specific volumes relationship for ideal gases instead of using the real gases. _TRUE _X_FALSE13. Virial equation is not the same equation as the ideal gas law and it describes gas behavior more accurately than the gas law. _X_TRUE _FALSE14. An open system when matter flows in and out of system from surrounding. _X_TRUE _FALSE15. A nozzle is a device that increases the velocity of a liquid at the expense of pressure. _X_TRUE _FALSE16. Specific heat is the energy required to raise the temperature of a unit mass of substance one degree, either at constant pressure (Cp) or at a constant volume (Cv). _X_TRUE _FALSE17. Heat transfer is a non-equilibrium phenomena since in a system that is in equilibrium there can be no temperature differences and thus no heat flow. _X_TRUE _FALSE18. There can be heat transfer between two bodies that are at the same temperature (regardless of pressure) since the driving force for heat transfer is temperature independent. _TRUE _X_FALSE19. The number of moles of a substance is an extensive property._X_TRUE _FALSE20. Isothermal system is the same as adiabatic system. _TRUE _X_FALSE21. Isobaric system operates at constant pressure._X_TRUE _FALSE22. A tank that has a mixture of propane gas and propane liquid is considered a pure substance._X_TRUE _FALSE23. It is impossible for water to vaporize at -10OC. _TRUE _X_FALSE24. Heat flows from hot bodies to cold bodies._X_TRUE _FALSEIV. Answer the following questions (6 questions, 6 points each, 36 points total）1. Write down the Mechanical Energy Balance using heights to visualize various terms of the Bernoulli Equation: H = Constant = 2. When piping losses are negligible, there is negligible dissipation of mechanical energy into thermal energy. Then when there are no mechanical devices such as fans, turbines, pumps, the Bernoulli Equation reduces to degenerate form of the energy equation. The Bernoulli equation then between any two points along the streamline of a flow is written as: 3. Write down Fouriers law for steady flow constant k conduction:4. Write down Newtons Law for cooling at constant heat transfer coefficient (h):5. Write down the radiation heat transfer between two-surface enclosures in terms () time the difference between their body temperatures to a known power.6. Define internal energy and express its SI and English units. Internal energy is the sum of all the microscopic forms of energy of a substance. Units: SI Joules or calories, & BTU(English)7. Define kinetic energy and give its equation: Kinetic energy is the energy a system posses as a result of its motion relative to some reference frame. KE = (1/2) m28. Define potential energy and give its equation: potential energy is the energy of a system as a result of its elevation in a gravitational field. PE = mgh9. Define viscosity and give its units. A property that represents the internal resistance of fluid to motion or fluidity and has the units of 1poise = gm/cm.s = 0.1Pa.s10. What is a pitot tube? Pitot tube is a small tube with its open end aligned into flow so as to sense the full impact pressure of the flowing fluid. It measures the stagnation pressure.11. Define the thermal conductivity and give its units. The thermal conductivity of a material is a measure of the material ability to conduct heat. W/m , J/m.s12. Give three examples of steady state system. (a) water flowing at a constant velocity. (b) Car moving at a constant speed. (c) Temperature of water is constant during boiling at one atmosphere. The pressure of a closed tank is constant at a constant temperature. Any process function independent of time.13. Give three examples of unsteady state system. (a) hot water is cooling to room temperature. (b)The pressure rise in a piston during compression. (c)The volume of a conical container changes with time during filling. (d) a pump is started to pump water. Any process that is time dependent.14. Can you calculate the volume of liquid water using PV=nRT? Why not. V. Solve the following problems（13 problems，108 points total）1. (8POINTS) Calculate the pressure in Atmosphere of a monometer if the height inside the monometer is 800mm-Hg. The density of mercury liquid mercury (Hg) is about 13.55 g/cc at room temperature. Use P = gh , where g = 9.807m/s2.2. (8POINTS) A car weighs 1000kg is accelerated from rest to 100km/hour speed. Calculate the work obtained by the car in BTU. Use KE = (1/2) m2.3. (8POINTS) A 3000 pounds rock is falling vertically at an acceleration of 32.174 ft/s2. Find the amount of potential energy loss (in BTU) when it hits the ground 100 feet below.4. (10POINTS) Find the saturated vapor pressure of water at 50oC. Calculate hg at 50oC and then compare to hf values (at same temperature) tabulated on page 994 textbook for the saturated water. (use h = U + PV)5. (10POINTS) (5-65) A rigid tank contains 10 kgm of air at 1 ATM and 100oC . The air is heated until its pressure doubles. Determine 9a) the volume of the tank and (b) the amount of heat transfer.6. (10POINTS) (6-8E) Superheated steam is flowing through a 2 cm inside diameter straight pipe at 1500psi and 1500oF. Determine the speed of steam inside the pipe in m/s (Hint: use steam table at the end of the textbook).7. (12POINTS) (6-52) Steam flows at steady state through an adiabatic turbine at 10kg/s. It enters the turbine at P1= 10Mpa, T1= 400oC and 1 = 200m/s. The exit conditions are P2= 1MPa, T2 = 400oC, 2 = 100m/s. After one hour of operation determine: (a) the change in enthalpy, (b) the change in kinetic energy and (c) the work output by the turbine. (hint use superheated steam tables).(10POINTS) (6-87) A thin walled double-pipe counter-current flow heat exchanger is used to cool transmission oil fluid (Cp =2.5 kJ/kg. 0C) from 2000C to 60oC at the rate of 4kg/s. The cooling water enters at 4kg/s and room temperature. Determine the exit temperature of water in oC. (See Figure P6-87 on page 241 textbook for similar heat exchanger)1. Find the specific volume, internal energy and the enthalpy for superheated steam (water) at 10mPa and 1200 oC. Use p1000 textbook for superheated steam.V = 0.067938 m3/kg , u = 4452.4kJ/kg , h = 5131.72. A 1000 watts electric heater is used to evaporate completely 100g of saturated water at 1 atmosphere. Calculate the time required to completely boil the water. Note: E(heater) = heat gain by water. Use the steam tables on p994 for Hfg .Hfg = (2256.4 kJ/kg) x 100g x (1kg/1000g) x (1000J/kJ) x (1W.s/J) = 1000W x t (time)t = 225.64s3. A vertical piston-cylinder device with cross sectional area of 80cm2 is filled with water and covered with a 10kg piston that serves as a lid exposed on the outside to the atmospheric pressure (=1atm). Determine the boiling temperature of the covered water. Assume local a = 9.807 m/s2. Use PT = PATM + ma.PT = PATM + ma = P* =1ATM x(101.3kPa/1ATM) + (10kg/80cm2 ) (100cm2/1m2) x 9.807 m/s2 x 1N/ (1kgm.m/s2)x(1kN/1000N) x kPa/kN = 101.3kPa + 12.3 kPa = 113.6 kPa , Now from Table for water saturated pressure data at 113.6kPa, the boiling point of water is extrapolated between 120.90kPa and 101.3kP soT * = (105-100)/(120.90-101.3) ) x (113.6-101.3) oC + 100oC = 104.00oC4. Calculate the ideal gas constant R for a gas having a volume of 22.4 liters at 0oC and 1 atmosphere. PV = nRT, R = PV/nT = 1ATMx22.4 liter / (1gmol x 273K) = 0.0821 lATM / gmol K approx. same as universal R constant in book = 0.0831 ATM.l/ gmol K5. If an exhaust emission from an internal combustion engine is discharged to atmosphere at the rate of 100 liters/s at 250oC. Calculate the mass rate of exhaust emission discharged to atmosphere. Assume the molecular weight of the discharged gas is about the same as air (28.96g/ g-mole) and the air density can be found in book appendix page 1018. Also, assume ideal gas behavior. From Table A-21for ideal-gas properties of air at 520K (or 247oC) v =154.1m3/kg . Because assuming ideal gas behavior then at 250oC (523K) v approximately = 154.1m3/kg .Then: m = (100 l/s) / (154.1 m3/kg) x 1000 l/ 1m3) = 0.0065kg/s = 0.6g/s6. (5-11) A mass of 10 kg of saturated water vapor at 543.49 kPa is heated at constant pressure until the temperature reaches 300oC. Calculate the work done ( kJ ) by the steam during this process. (note use Table A-4 through A-6 of the textbook to find the corresponding specific volumes). Use: W = m P (2- 1).From p994: At P*= 543.49kPa, T = 155oC, vg = 0.34648 m3 /kg = v1 . Now from p998, find v2 at 543.49kP and 300oC by extrapolating between the table points as following: At 0.500MPa, v = 0.52261 m3 /kg , and at 0.600MPa, v = 0.43442 m3 /kg . Then v2 = 0.43442 + (0.52261-0.43442)/(0.6MPa -0.5MPa) x (0.54349-0.5) = 0.47228 m3 /kg Then 7. (5-33)1000 liters of water is contained in a rigid container that is equipped with a stirring device. Determine the rise in water temperature due to stirring water continuously for thirty minutes using 200watts of stirring power. Assume the container is adiabatic (no heat loss to surrounding) and no power loss through the motor.Analysis This is a closed system since no mass enters or leaves. The energy balance for closed system can be expressed as Then,Dividing this by the mass in the system givesNegligible temperature rise for water because of low power input and large mass of water.8. (5-86)One cubic meter of mild steel is heated from 25oC to 500oC. Using the properties in Table A-3b and assuming constant heat capacity, calculate heat transferred to the steel. Density = 7.83 g/cm3, and heat capacity Cp = 0.500 kJ/kg.KAnalysis The internal energy and enthalpy changes are equal for a solid. Then,9. (6-6E) Determine the volumetric flow rate of water flowing in a nozzle wit an average diameter of 1cm at an exit speed of 5m/s. How much is the maximum kinetic energy (calories) that can be obtained from the water jet exiting the nozzle in 1s. Assumptions 1 Water is an incompressible substance. 2 Flow through the hose is steady. 3 There is no waste of water by splashing.Properties We take the density of water to be 1.000g/cm3 (Table A-3E).Analysis (a) The volume and mass flow rates of water arem = 1s x 392.7g/s = 392.7g = 0.3927kgmKE = m 2 = (1/2) 0.3927 kgm x (5m/s)2 x 1N/(kgmm /s2) x 1J/N.m x 1calorie/4.187JKE = 1.17calorie10. (6-24) Saturated water enters a pump at room temperature is compressed using a pump to an exit pressure of 543.49kPa. The specific volume remains relatively constant. Determine the flow work in kJ/kg required by the pump.Assumptions 1 Flow through the pump is steady. 2 The state of water at the pump inlet is saturated liquid. 3 The specific volume remains constant.Properties The specific volume of saturated liquid water at 250C (room temperature) is 0.001003m3/kg and the saturated vapor pressure = 3.1698kPa, then at the compressed exit conditions of 543.49 kPa:Water3.1698 kPa K543.49kPa (Table A-5E)Negligible differences in specific volume.Then the flow work relation gives12-5 A river is flowing at a specified velocity, flow rate, and elevation. The total mechanical energy of the river water per unit mass, and the power generation potential of the entire river are to be determined. Assumptions 1 The elevation given is the elevation of the free surface of the river. 2 The velocity given is the average velocity. 3 The mechanical energy of water at the turbine exit is negligible. Properties We take the density of water to be r = 1000 kg/m3.Analysis Noting that the sum of the flow energy and the potential energy is constant for a given fluid body, we can take the elevation of the entire river water to be the elevation of the free surface, and ignore the flow energy. Then the total mechanical energy of the river water per unit mass becomes 3 m/sRiver90 m The power generation potential of the river water is obtained by multiplying the total mechanical energy by the mass flow rate, Therefore, 444 MW of power can be generated from this river as it discharges into the lake if its power potential can be recovered completely. Discussion Note that the kinetic energy of water is negligible compared to the potential energy, and it can be ignored in the