MECH4422- THERMAL ENGINEERING
Lab#07 (Solution)
Practice Problems: (Chapter 5 & 6)
1. Refrigerant 134a flows at steady state through a horizontal tube having an inside diameter of 0.05
m. The refrigerant enters the tube with a quality of 0.1, temperature of 36°C, and velocity of 10 m/s.
The refrigerant exits the tube at 950 kPa as a saturated liquid. Determine,
a) the mass flow rate of the refrigerant, in kg/s.
b) the velocity of the refrigerant at the exit, in m/s.
c) the rate of heat transfer, in kW, and its associated direction with respect to the refrigerant.
School of Energy / Mechanical Engineering
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MECH4422- THERMAL ENGINEERING
Lab#07 (Solution)
2. Electronic components mounted on a flat plate are cooled by convection to the surroundings and by
liquid water circulating through a U-tube bonded to the plate. At steady state, water enters the tube
at 20°C and a velocity of 0.4 m/s and exits at 25°C with a negligible change in pressure. The electrical
components receive 0.5 kW of electrical power. The rate of energy transfer by convection from the
plate-mounted electronics is estimated to be 0.08 kW. Kinetic and potential energy effects can be
ignored. Determine the tube diameter, in cm.
School of Energy / Mechanical Engineering
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MECH4422- THERMAL ENGINEERING
Lab#07 (Solution)
3. Steam flows steadily through an adiabatic turbine. The inlet conditions of the steam are 10 MPa,
450°C, and 80 m/s, and the exit conditions are 10 kPa, 92 percent quality, and 50 m/s. The mass flow
rate of the steam is 12 kg/s. Determine (a) the change in kinetic energy, (b) the power output, and
(c) the turbine inlet area.
School of Energy / Mechanical Engineering
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MECH4422- THERMAL ENGINEERING
Lab#07 (Solution)
4. A computer cooled by a fan contains eight PCBs, each dissipating 10 W power. The height of the
PCBs is 12 cm and the length is 18 cm. The cooling air is supplied by a 25-W fan mounted at the
inlet. If the temperature rise of air as it flows through the case of the computer is not to exceed
10°C, determine (a) the flow rate of the air that the fan needs to deliver and (b) the fraction of the
temperature rise of air that is due to the heat generated by the fan and its motor.
School of Energy / Mechanical Engineering
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