In: Mechanical Engineering
An 8-m-long, uninsulated square duct of cross section 0.2 m X 0.2 m and relative roughness 10-3 passes through the attic space of a house. Hot air enters the duct at 1 atm and 91oC at a volume flow rate of 0.15 m3/s. The duct surface is nearly isothermal at 60oC. Determine the rate of heat loss from the duct to the attic space and the pressure difference between the inlet and outlet sections of the duct. Evaluate air properties at a bulk mean temperature of 80oC. Is this a good assumption? Taking a bulk mean fluid temperature of 80oC based on the problem statement (this assumes that the air does not loose much heat to the attic), the properties of air are: cp = 1008 J/kg∙oC k = 0.02953 W/m∙oC ν = 2.097 × 10-5 m2/s ρ = 0.9994 kg/m3 Pr = 0.7154
In: Mechanical Engineering
A single stage simple vapr compression refrigeration cycle using R12 refrigerant is operating at a condenser temperature of 40 degrees C and an evaporator temperature of -5 degrees C. If the compressor is a reciprocating type compressor with 4 cylinder, rotating at 1800 RPM, has a cylinder diameter of 5cm, stroke length to diameter ratio of 1.4, and clearance ratio of 5%. Assume a polytropic index to be 1.13. 1- Sketch the cycle flow diagram, and identify the states on the P-H diagram. Calculate the refrigeration effect, refrigeration capacity in TR, the compressor power in HP, the cycle COP, the temperature of the refrigerant after exiting the compressor, and the cycle refrigeration efficiency.
In: Mechanical Engineering
A closed piston-cylinder system undergoes a cycle:
Process 1 to 2 is an expansion process where heat is added. The
temperature remains constant.
Process 2 to 3 is a constant volume heat addition process.
Process 3 to 4 is a compression process where heat is lost. The
pressure remains constant.
Process 4 to 1 is polytropic expansion, Pvn=constant
with n=1.4 and it is adiabatic (Q=0).
Assume air, ideal gas, with constant specific heats, k=1.4.
R=.287kJ/kgK
State 1: T=300K, P=150kPa
State 2: T=300K, P=100kPa
State 3: P=600kPa
State 4: P=600kPa
a.) Find the temperature for State 3 and State 4.
b.) For all 4 States, find volume(m3/kg)
c.) For each process, (1-2, 2-3, 3-4, 4-1), find Q/m(kJ/kg),
W/m(kJ/kg), and Δu(kJ/kg)
d.) Plot all 4 States on a P-v diagram
e.) Is this a power or refrigeration cycle?
f.) Calculate the efficiency or coefficient of performance based
on your answer to part e.
In: Mechanical Engineering
Engineering Mechanics (8th Edition) Chapter 3, Problem 212P
In: Mechanical Engineering
Saturated liquid water at 1 MPa enters a D = 5 cm pipe at a rate of m(dot) = 2 kg/s. Heat is transferred to the water at a rate of Q(dot) = 5000 kW. The exit is at 1 MPa pressure.
(a) Neglecting kinetic energy, calculate the temperature at the pipe exit. (ans = 400◦C)
(b) Using your answer in a), calculate the exit velocity of the water. (ans = 312 m/s)
(c) Based upon your answer, should kinetic energy be included in your analysis? (ans = probably)
(d) Including the exit kinetic energy, recalculate the exit temperature. Iterate this procedure a couple of times. (ans = 378◦C)
In: Mechanical Engineering
One kg of water in a piston-cylinder assembly,
initially at 1.5 bar and 200 C, cools at constant pressure with no
internal irreversibilities to a final state where the water is a
saturated liquid. For the water as the system, determine the work,
the heat transfer, and the amounts of exergy transfer accompanying
work and heat transfer, each in kJ. Let T0 = 20 °C, p0=1 bar and
ignore the effects of motion and gravity.
THERE ARE SOME DIFFERENT ANSWERS TO THIS QUESTION. I FOUND AN
ANOTHER ANSWER, I HAVE MANY QUESTION MARKS IN MY MIND. ADDITION OF
EXERGY TRANSFER ACCOMPANYING WORK AND HEAT SHOULD BE EQUAL TO
E2-E1. SINCE ITS INTERNALLY REVERSIBLE. ON THE OTHER HAND WHEN I
USE 'E2-E1=(U2-U1)+P0×(V2-V1)-T0(S2-S1)' I FIND AN ANOTHER NUMBER.
PLEASE HELP.
In: Mechanical Engineering
Determine the specific volume (m3/kg) of air at T = 159.6 K and P = 37.5 bar using the generalized compressibility chart.
In: Mechanical Engineering
A cylindrical specimen of some metal alloy 8.6 mm in diameter is stressed in tension. A force of 9070 N produces an elastic reduction in specimen diameter of 0.0048 mm. Calculate the elastic modulus (in GPa) of this material if its Poisson's ratio is 0.33.
In: Mechanical Engineering
Compare the following: belt drive, chain drive, and gear system.
What are the fundamental characteristics of each? What are the advantages and disadvantages of each?
In: Mechanical Engineering
Water flows upward and then is discharged to the right through a 3 inch diameter pipe elbow, at a steady flow rate of 1 cubic foot per second, the gage pressure at the entrance to the elbow is 30 psi. What vertical and horizontal force is necessary to hold the elbow stationary, neglecting any required torque.
In: Mechanical Engineering
3. Sketch a T-v diagram and find the specified state for the following states
a. Propane at critical temp & press find T(°C), p(bar) and v(m3 /kg)
b. Water v=.05 m3 /kg, T=140°C find p(bar)
c. Water at p=30 MPa, T=100°C find v(m3 /kg)
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Explain what the viscoelastic behavior of plastic materials is.
In: Mechanical Engineering
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In your own words describe the mechanisms for the elastic deformation of thermoplastics and for the plastic deformation of thermoplastics. please write clearly |
In: Mechanical Engineering
how we can regenerated fix bed reactor inside catalysts we want use again catalysts
In: Mechanical Engineering