# Overview

The is the Mechanical Engineering PM Thermal / Fluids Session. Questions are ordered from Q 121 through Q 160. Problems are in either S.I. or U.S. Customary Units.

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#### Question to Topic Map

 Q 121–Q 122 Material Properties Q 123–Q 126 Fluid Mechanics Q 127–Q 130 Heat Transfer Principles Q 131–Q 133 Mass Balance Principles Q 134–Q 137 Thermodynamics Q 138–Q 145 Equipment Q 146–Q 158 Systems Q 159–Q 160 Codes and Standards

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## Q 121

At a particular temperature and pressure, the surface tension of water is 0.065 N/m. Under ideal conditions, the contact angle between glass and water is zero. A technician in a commercial laboratory observes water in a glass capillary tube with a diameter of 0.11 mm. The height of the capillary rise in (m) is most nearly.

## Q 122

A sliding plate viscometer is used to measure the viscosity of a Newtonian fluid. It has the following characteristics:

• gap between stationary and moving plate: 6 mm
• dimensions: 70 cm x 50 cm

A force of 100 N is required to keep the top plate moving at a constant velocity of 10 m/s. The viscosity of the fluid in N∙s / m^2 is most nearly.

## Q 123

A 300 lbm car top carrier measures 48 inch long by 36 inch wide by 12 inch high.

If a 3500 lbm sedan is driven at 80 mph into a 12 mph headwind, the added net motor power required when the carrier is used in horsepower is most nearly.

## Q 124

Hot water at 80 °C flows through the pipe system, with a minimum ID of 15 mm. The flow rate is 185 L / min. There are two 90 degree bends and one 45 degree bend in the system.

If the loss coefficients for the 90 degree elbows and 45 degree elbow are 1.2 and 0.6 respectively, the sum of the minor (head) losses for the system in meters is most nearly.

## Q 125

A 3 inch diameter magnesium alloy sphere achieves a terminal velocity of 75 inches/sec when dropping through a tall column of liquid. The density of the liquid is 87 lbm/ft^3. The final drag coefficient of the sphere is most nearly.

## Q 126

The Darcy friction factor for both of the pipes shown is 0.035. The total flow rate is 500 m^3 per hour. The flow rate in m^3 / second in the 150 mm pipe is most nearly. ## Q 127

The rectangular wall of a pizza oven is made from 7 in. thick fire-clay brick surrounded by 0.25 in. of steel on the outside. 0.20 inch diameter mild steel bolts connect the steel to the brick. The furnace is surrounded by 70 °F air with convection coefficient of 1.65 Btu / hr-ft^2 x °F, while the inner surface of the brick is held constant at 500 °F. The outside surface temperature of the steel in degree F is most nearly.

## Q 128

A solid ceramic sphere 250 mm in diameter is at a temperature of 500 °C. It is dropped into a large tank of 60 °C oil. The average convective heat transfer coefficient is 600 W / (m^2 x K) and the oil is stirred uniformly. The time in seconds it takes after submersion for the sphere to reach 150 °C is most nearly.

## Q 129

A small distiller evaporates 10 L of water per half hour. Alloy tubing exposed to the air serves a condenser to recover steam. The outside surface of the tubing is at 99 °C. The ambient temperature is 20 °C. The inside diameter of the tube is 0.85 cm, and the outside diameter is 1.2 cm.

In order to condense all the steam, the tube length in meters is most nearly.

## Q 130

In one hour, the black body radiation that escapes a 5 cm by a 10 cm rectangular opening in a furnace whose internal temperature is 700 °C in kJ is most nearly.

## Q 131

A high performance 12 inch bore, 18 inch stroke single cylinder four-stroke engine runs at 6000 rpm. The gross weight of a prony brake is 200 pounds, the tare weight is 20 pounds, and the arm length is 66 inches. The indicator card shows an area of 1.30 inch^2 with an overall length of 3 inches. The spring scale was 200 psi/inch.

The mechanical efficiency (%) of the engine is most nearly.

## Q 132

A special species of coal in Alberta, Canada has the following composition by weight:

``````80%        carbon
4%        hydrogen
2%        oxygen``````

The stack gases have a composition by volume of:

``````5%        carbon dioxide
5%        carbon monoxide
10%        oxygen
80%        nitrogen``````

The amount of pounds of air required to burn one pound of coal is most nearly.

## Q 133

A furnace is used to heat water with an efficiency of 50%. It goes from 15 °C to 150 °C by burning 300 standard liters of methane. Assuming a 20,000 Btu / lbm heating value, the amount of water (in kg) that can be heated is most nearly.

## Q 134

An ideal compressible fluid is flowing from point A to point B. The properties of the fluid at point A and point B are as follows:

 Point Density (lbm per cubic foot) Internal Energy (Btu per lbm) Pressure (psia) A .456 127.3 73.2 B .0201 53.1 3.62

The change in enthalpy from points A and B, in Btu / lbm is most nearly.

## Q 135

A boiler burns 1.0 lbm of natural gas to generate 30 psig saturated steam from 14 lbm of 80 °F feedwater. The natural gas has a higher heating value (HHV) of 25,000 Btu / lbm. The combustion efficiency (%) of the boiler is most nearly.

## Q 136

A two pound block of steel (c = .10 Btu / lbm∙°F) is removed from an oven and quenched in a four pound aluminum (c = .20 Btu / lbm∙°F) tank filled with ten pounds of castor oil (c = .43 Btu / lbm∙°F). The oil and the tank are initially in equilibrium at 75 °F. Their temperature rises to 100 °F after quenching.

The initial steel temperature in °F is most nearly.

## Q 137

A 1500 m^3 room contains air at 60 C and 50 kPa at a relative humidity of 30%. The partial pressure of the water vapor in the room in kPa is most nearly.

## Q 138

A joint is made between two metal pieces by closely fitting their surfaces and distributing a molten nonferrous filler metal to the interface by capillary attraction. The pieces to be joined have a melting point of 1400 °F, and the filler melts at 900 °F. This process is most accurately termed:

##Q 139

A 360 V electric pump adds 700 ft of pressure head to a 80 °F, 3.0 lbm per second water flow. At operating speed, the motor is 90% efficient and the pump is 60% efficient. The motor current draw in amps is most nearly.

## Q 140

In the system shown, the flow rate of 68 °F water is 3000 gpm, and the head loss (in feet) in the pipes is given by .02 (L/D)(v^2 / 2g) where L is the length of pipe in feet, D is the pipe diameter in feet, v is the velocity in ft/sec, and g is the acceleration of gravity in ft/sec^2. If the motor driving the pump is 75% efficient and the pump is 80% efficient, the power that must be supplied to the motor in kw is most nearly.

## Q 141

A steam turbine operates as a component of a Rankine cycle. Steam is supplied to the turbine at 1400 psia and 1000 °F. The turbine exhausts at 74 psia. The expansion is not reversible, and the exhaust is vapor at 100% quality. The thermal efficiency of the turbine is most nearly.

## Q 142

The power output from a generator that is driven by an impulse turbine is 250,000 kW. The turbine wheel is mounted on a 2 ft diameter steel shaft. It has a 15 ft diameter and is spun by a 2 ft diameter water jet.

Assume ideal conditions such as v.jet = 2 ∙ v.vane and the jet is deflected by 180 degrees. The angular speed in rpm of the turbine wheel is most nearly

## Q 143

A two stage air compressor with an ideal intercooler takes air at 14.7 psia and 70 °F and compresses it to 400 psia. The pressure staging area is ideal. The mass flow rate of air is 20 lbm per minute.

The heat removed by the intercooler in BTU/min is most nearly.

## Q 144

A parallel flow tube and shell heat exchanger is designed using 3 in. OD tubing. 30,000 lbm / hr of water at 35 °F is used to cool 30,000 lbm/hr of a 95% ethyl alcohol solution (cp = 0.9 Btu / lbm x °F) from 170 °F to 100 °F.

If the overall coefficient of heat transfer based on the outer tube area is 200 Btu / (hr × ft^2 ×°F), then the heat-transfer surface area in square feet of the heat exchanger is most nearly.

## Q 145

You are considering the attachment of a diffuser to a tank exit. With the diffuser attached, the flow rate is 14.7 fps. With the diffuser attached, the flow rate will increase percentage wise by most nearly.

## Q 146

The input shaft of a steel gearbox for the 2014 Chevy Spark transmits 83.0 ft∙lbf torque while rotating at 4800 rpm. The gearbox housing is approximately 6 inches wide, 8 inches hight, and 8 inches deep and is exposed to air on all sides.

The air outside the gearbox has a temperature of 68 °F and has a film coefficient of 1.65 Btu / hr∙ft^2∙°F. If the output shaft delivers 76 hp, the maximum possible temperature of the gearbox in °F is most nearly.

## Q 147

Water at 280 °F and 80 psia empties through 100 feet of 1.5 inch Schedule 40 pipe by a pump whose inlet and outlet are 25 feet below the surface of the water level when the tank is full. Assume a roughness of .0002 ft and a Reynolds Number of 8.85 x 10^5. The density of water is 57.9 lbm / ft^3.

The pumping rate is 100 gpm, and the NPSHR is 10 feet for that rate. If the inlet line contains three gate valves and three long-radius elbows, and the discharge is into a 2 psig tank, the Net Positive Suction Head Available (NPSHA) in feet is most nearly.

## Q 148

Water at 500 psig will be used to drive a 250 hp turbine at 1750 rpm against a backpressure of 30 psig.

If the 6 inch diameter jet discharging 45 fps is deflected 85 degrees by a single moving vane with velocity of 10 fps, the total force in lbf acting on the blade is most nearly.

## Q 149

4 cubic feet per second of water is pumped from a feed tank mounted on a platform to an open reservoir through a 6 inch schedule 40 (ε / D = .002) steel pipe. The NPSHA (Net Positive Suction Head Available) in feet is most nearly. ## Q 150

You are analyzing the initial design of a turbine. Steam at 300 psia enters an isentropic turbine operating in a Rankine cycle. The steam exits the turbine at 150 °F. Requirements state moisture content of the steam in the turbine is not to exceed 25% in order to minimize long-term corrosion.

The minimum temperature to which the high-pressure steam must be heated is most nearly.

## Q 151

At the start of the compression stroke of an air-standard Otto cycle, the pressure is 14.7 psia and the temperature is 50°F . The maximum pressure in the cycle is 800 psia, and the compression ratio is 11.5:1.

The difference in efficiency percentage between this cycle and a Carnot cycle operating between the same temperature is most nearly.

## Q 152

The net power output from a steam-based power plant operating on Rankine cycle is 400 MW. The cycle has steam entering an isentropic turbine at 1200 °F and 1800 psia., and the cooling water entering the condenser at 56 °F and leaving as saturated liquid at 93 °F. Neglect the pump work.

The condenser pressure is 10 psia. The mass flow rate in lbm/hr of the steam is most nearly.

• [A] 8.9 x 10^4
• [B] 5.6 x 10^5
• [C] 7.7 x 10^5
• [D] 2.5 x 10^6

## Q 153

A refrigeration cycle uses Freon-12 to removed 10,000 Btu's per hour. The refrigerant leaves the evaporator saturated at 0 °F. The pressure of the refrigerant entering the condenser is 70 psia. The refrigerant leaves the condenser as a saturated liquid. The isentropic efficiency of the compressor is 70 percent.

The coefficient of performance of the refrigeration cycle is most nearly.

## Q 154

The relative velocity of a certain point on a marine propeller 12 feet below the surface of sea water is approximately 6.1 times the boat velocity. The mole fraction of water in the seawater is .99. Assume a 70 °F temperature.

The practical limit of the boat velocity in ft/sec is most nearly.

## Q 155

A 6 inch pump operating at 1900 rpm discharges 1250 gpm of cold water (s.g. = 1.00) against an 100 foot head at 70 percent efficiency. A homologous 9 inch pump operating at 1000 rpm is being considered as a replacement. The new power requirement (in hp) would be nearly.

## Q 156

You are tasked with selecting from 4 different motors.

 Motor Power Cost 1 5 hp \$1000 2 10 hp \$1500 3 13 hp \$1700 4 17 hp \$1700

Each pump has a variable rate of efficiency based on the following table.

 specific speed = 1000 rpm / 60% specific speed = 2000 rpm / 65% specific speed = 3000 rpm / 70% specific speed = 4000 rpm / 75%

The pump needs to provide 50 feet of added head @ 2 cfs. Assume a motor speed of 2400 rpm. What selection is the most cost efficient?

## Q 157

A 200 hp internal combustion engine burns propane at a rate of 0.02 lbm/sec when mixed with theoretical air. The engine takes in air and fuel at 77 °F and 1 atm. The air-fuel mixture burns completely and leaves the engine at 1240 °F. Assume The enthalpy of the products is -685,000 Btu / lbmol. The rate of heat transfer from the engine (Btu/sec) is most nearly.

## Q 158

A six-cylinder 4-stroke engine has a 100.4 mm bore and a 84.4 mm stroke. The brake mean effective pressure while running at 4200 rpm is 120 psig. The brake horsepower is most nearly.

## Q 159

A trapezoidal channel has a 5 foot depth, a 7 ft width at its basin, and a 9 ft width at its open top. The hydraulic radius in ft is most nearly.

## Q 160

Based on a psychrometric chart (ASHRAE Psychometric Chart #1), sea level air at a dry-bulb temperature of 100 °F and 50% relative humidity has a dew point of most nearly.