Exam 2 MC questions from HW

250kJ

A 5kg piece of metal (c=0.5 kJ/kg*K) is heated from 50 to 100 degrees Celsius. Determine the change in internal energy 125kJ 932kJ 250kJ 0kJ

0.25 or 25%

A heat engine accepts heat at a rate of 200kW, and it produces a net power output of 50kW. Determine the thermal efficiency of this engine. .75 or 75% 50kW 200kW .25 or 25%

a

A heat engine that accepts heat from and rejects heat to the same thermal energy reservoir is an example of a device that violates which of the following? a) kelvin-Planck statement of the second law b) Clausius statement of the second law c) first law

reversible process

A process in which both the system and the surroundings can be returned to their initial state at the end of the process is called a ______________.

13.33kW

A refrigerator with a COP of 3.0 accepts heat a rate of 10kW. Determine the rate of heat rection

3.33kW

A refrigerator with a COP of 3.0 removes heat from the refrigerated space at a rate of 10kW. Determine tha rate of power input.

source

A reservoir that supplies heat to a system is called a __________.

incompressible

A substance that has a constant specific volume or density is called an _________ substance.

1.5

An ideal gas (cv= 2kJ/kg*K cp=3kJ/kg*K) is heated from 100 to 200 degrees Celsius. Determine k, the ratio of specific heats. 1.5 1 2 0.67

300kJ/kg

An ideal gas (cv= 2kJ/kg*K cp=3kJ/kg*K) is heated from 100 to 200 degrees Celsius. Determine the change in enthaply. 200kJ/kg 100kJ/kg 300kJ/kg

75%

Determine the theoretical maximum efficiency for a heat engine operating between the temperatures of 1200K and 300K 75% 25% 100% Not enough info

remains constant

During a steady flow process, the fluid properties at an inlet or exit must _________. remain constant increase decrease

decrease

During a throttling process, if the flow energy increase due to the significant increase of the specific volume, the temperature of a fluid will ____. decrease increase stay the same

c,d,

For a compressor with an intercooler, which of the following energy changes are usually neglected in the energy balance equation? a) work b) heat transfer c) kinetic energy d) potential energy

b,c

From the following list, select all of the devices to which the Clausisus statement of the second law directly applies. a) automobile engine b) heat pump c) air conditioner d) coal fired power plant

a,d

From the following list, select the characteristics of a refrigerator (select all that apply) a) receive heat from a low-temperature reservoir b) received heat from a high-temperature reservoir c) reject heat to a low-temperature reservoir d) reject heat to a high-temperature reservoir

a,d

From the list below, select all that are examples of irreversibilities a) friction b) phase change c) restrained expansion d) heat transfer through a finite temperature difference

density, average flow velocity, cross sectional area

IN a single-stream, steady flow system, the mass flow rate can be defined as the product of ______, _______, and ________

unsteady

If properties are allowed to change within the control volume, the processes are called _______flow

remain zero

In a steady flow process, the change of total energy of the control volume must ______. remain zero increase decrease

flow

In an open system, when mass flows across control volume boundaries, some work is required to push the mass into or out of the control volume, and this is known as _____ Work.

5kJ/kg*K

It is observed that it takes 10kJ to raise the temperature of 1kg of a substance by 2 degrees Celsius. Determine the specific heat of the substance. 0.0364 kJ/kg*K 0. 2kJ/kg*K 10 kJ/kg*K 5 kJ/kg*K

1a,2b

Match the device with its appropriate function: 1) nozzle 2) diffuser a) a device that increases the velocity of a fluid at the expense of pressure b) a device that increases the pressure of a fluid by slowing it down

1b, 2a

Match the device with its associated task. 1) heat exchanger 2) mixing chamber a) a device where two fluids exchange heat when mixed b) a device where two fluids exchange heat without mixing

1A 2C 3D 4B

Match the device with its task 1) turbine 2) fan 3) compressor 4) pump a) produces shaft work b) increases pressure for liquids c) increases the pressure of a gas slightly and is mainly used to move a gas d) increase pressure of gases and vapors

ocean, large lake, pool

Rank the following bodies of water from the BEST (at the top) to the WORST examples of a thermal energy reservoir large lake pool ocean

decrease

Refrigerant flow across a throttle valve usually experience a large pressure drop. This large pressure drop in the refrigerant across a throttle valve causes its temperature to _______. stay the same decrease increase

a,b,d

Select all of the following that are characteristic of all heat engines. a) they reject heat to a low temperature sink b) they receive heat from a high temperature source c) they operate with a piston and cylinder device. d) they convert some heat to work

a,b,d

Select all that apply: A device that transfers heat from a low-temperature medium to a high-temperature medium is called a ___________. a) refrigerator b) chiller c) heat exchanger d) heat pump

Reversible isothermal expansion, Reversible adiabetic expansion, Reversible isothermal compression, Reversible adiabetic compression

Starting with receiving heat from a energy source, put the following process that make up the Carnot cycle in order from top to bottom. Reversible adiabetic expansion Reversible adiabetic compression Reversible isothermal expansion, Reversible isothermal compression,

+500kJ

Steam expands in a piston-cylinder device from 2m^3 to 3m^3 at a constant pressure of 500 kPA. Determine the boundary work for this process -1000 kJ +500 kJ 0 kJ +1000 kJ -500 kJ

False

True/False: After John is told that a heat pump supplies 10kJ of heat to a house while consuming 3kJ of net work, he immediately believes that the heat pump violates the first law of thermodynamics

True

True/False: In a single-stream, steady flow system, the mass flow rates for the inlet and outlet must be the same

2 m/s

Water flows through a pipe with a cross sectional area of 0.002 m^2 at a mass flow rate of 4kg/s. The density of water is 1000kg/m^3. Determine its average velocity. .002 m/s 20 m/s 2 m/s .2 m/s 200 m/s

a

Which of the following best defines the term boundary work? a) work associated with expansion or compression of a moving boundary b) heat crossing the boundary of a system c) work crossing the boundary by a rotating shaft work

a,b,d

Which of the following devices are considered as mixing chambers? a) a T-elbow b) A hot and cold water tub c) an L-shape pipe d) a Y-elbow e) a 45 degree elbow

a,c,d

Which of the following energies are part of the total energy of a flowing fluid? a) kinetic energy b) heat c) potential energy d) enthalpy e) shaft work

PV^n=C

Which of the following relationships represents a polytropic process? PV=C (PV)^n=C PV^n=C

Q(dot)-W(dot)= dE/dt

Which of the following represents the rate form of the first law? Q-W= delta E Q(dot)-W(dot)= dE/dt q-w = delta e

b,d,e

Which of the following statements are true (Select all that apply) a) during a steady flow process, the boundary of the control volume is allowed to move b) the steady flow implies that the fluid properties can change from point to point, but at any point, they remain constant during the entire process c) during a steady flow process, only mass in the control volume remains constant. d) the steady flow process is a process during which a fluid flows through a control volume and does not change with time e) during a steady flow process, boundary work is zero

b,d

Which of the following statements are true (Select all that apply) a) the conservation of mass principle holds only for incompressible fluids b) in a steady flow process, the total rate of mass entering a control volume is equal to the total rate of mass leaving it. c) the conservation of mass principle is only applicable to closed systems d) the time rate of change of mass within a control volume plus the net flow rate in/out of the control surface must equal to zero e) the conservation of mass principle is true only if the control volume has a fixed volume.

a,d,e

Which of the following statements are true regarding throttling valves? a) for a single stream, steady flow throttle valve, the inlet and outlet enthalpies can be approximated to be the same b) the pressure drops across a throttle valve is often accompanied by a large increase in temperature c) since pressure drops across a throttle valve, work cannot be neglected d) throttle valves are flow-restricting devices that cause a pressure drop in a fluid e) the flow through a throttle may be assumed to be adiabetic

Heat transfer

Which one of the following reversibility describes the transfer of energy from a high-temperature body to a low-temperature body? heat tranfer friction chemical reactions

a

Which one of the following statements accurately defines the thermal efficiency of a heat engine? a) the net work output divided by the heat input b) the net heat output divided by the heat input c) the net work output divided by the work input d) the net heat output divided by the work input

d

Which statement accurately defines the coefficient of performance of a heat pump? a)the net heat output divided by the heat input b) the heat removed from cold environment divided by the work input c) the work input divided by the heat discharged to the heated space d)The heat discharged to the heated space divided by the work input

d

Which statement accurately defines the coefficient of performance of a refrigerator? a) the net heat output divided by the heat input b) the heat rejected to the surrounding divided by the work input c) the work output divided by the heat removed from the refrigerated space d) the heat removed from the refrigerated space divided by the work output

working

the ________ fluid is the substance to and from which heat is transferred in a heat engine or other cyclic device.