w07-hw2
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Department of Chemical Engineering Winter, 2007 University of California, Santa Barbara CHE 110A Problem Set No. 2 Due Wednesday, January 24, 2007 Problem 1. Smith, van Ness, Abbott, 2.3, page 56 An egg, initially at rest, is dropped onto a concrete surface and breaks. With the egg treated as the system, (a) What is the sign of W? (b) What is the sign of P E ∆ ? (c) What is K E ∆ ? (d) What is t U ∆ ? (e) What is the sign of Q ? In modeling this process, assume the passage of sufficient time for the broken egg to return to its initial temperature. What is the origin of the heat transfer of part (e)? Problem 2. Smith, van Ness, Abbott, 2.6, page 57 Comment on the feasibility of cooling your kitchen in the summer by opening the door to the electrically powered refrigerator. Problem 3. Smith, van Ness, Abbott, 2.11, page 57 A tank containing 20 kg of water at 20 °C is fitted with a stirrer that delivers work to the water at the rate of 0.25 kW. How long does it take for the temperature of the water to rise to 30 °C, if no heat is lost from the water? For water, 1 1 4.18 kJ kg C. P C − − = ⋅ ⋅° Problem 4. Smith, van Ness, Abbott, 2.17, page 58 A hydroturbine operates with a head of 50 m of water. Inlet and outlet conduits are 2 m in diameter. Estimate the mechanical power developed by the turbine for an outlet velocity of 1 5m s − ⋅ .
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Transcript of w07-hw2
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Department of Chemical Engineering Winter, 2007 University of California, Santa Barbara CHE 110A Problem Set No. 2
Due Wednesday, January 24, 2007 Problem 1. Smith, van Ness, Abbott, 2.3, page 56
An egg, initially at rest, is dropped onto a concrete surface and breaks. With the egg treated as the system, (a) What is the sign of W? (b) What is the sign of PE ? (c) What is KE ? (d) What is tU ? (e) What is the sign of Q ? In modeling this process, assume the passage of sufficient time for the broken egg to return to its initial temperature. What is the origin of the heat transfer of part (e)?
Problem 2. Smith, van Ness, Abbott, 2.6, page 57
Comment on the feasibility of cooling your kitchen in the summer by opening the door to the electrically powered refrigerator.
Problem 3. Smith, van Ness, Abbott, 2.11, page 57
A tank containing 20 kg of water at 20 C is fitted with a stirrer that delivers work to the water at the rate of 0.25 kW. How long does it take for the temperature of the water to rise to 30 C, if no heat is lost from the water? For water,
1 14.18 kJ kg C .PC =
Problem 4. Smith, van Ness, Abbott, 2.17, page 58
A hydroturbine operates with a head of 50 m of water. Inlet and outlet conduits are 2 m in diameter. Estimate the mechanical power developed by the turbine for an outlet velocity of 15 m s .
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Problem 5. Smith, van Ness, Abbott, 2.23, page 59
A stream of warm water is produced in a steady-flow mixing process by combining 11.0 kg s of cool water at 25 C with 10.8 kg s of hot water at 75 C. During
mixing, heat is lost to the surroundings at the rate of 130 kJ s . What is the temperature of the warm-water stream? Assume that the specific heat of water is constant at -1 14.18 kJ kg K .
Problem 6. Smith, van Ness, Abbott, 2.24, page 59
Gas is bled from a tank. Neglecting heat transfer between the gas and the tank, show that mass and energy balances produce the differential equation:
dU dmH U m
=
Here, U and m refer to the gas remaining in the tank; H is the specific enthalpy of the gas leaving the tank. Under what conditions can one assume H H = ?
Problem 7.
A container of gas is compressed from state 1 to state 2 via the two paths shown in the figure below. Path A goes through state A and a path B goes through state B. Calculate and compare the work done in compressing the gas by the two paths.
