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Thermo E2
| Question | Answer |
|---|---|
| adiabatic: | heat transfer equals zero |
| rigid system: | zero change in volume |
| isothermic: | temperature remains constant |
| if gas is compressible what will change? | density or specific volume |
| flow ___________ is energy needed to push fluid into or out of a control volume. | work |
| a _____________ is a device that increases velocity of a fluid at expense of pressure. | nozzle |
| a ______________ is a device that increases the pressure of a fluid by slowing it down. | diffuser |
| nozzle: ___________ -----> ____________ | enthalpy, KE |
| diffuser: __________ -----> ____________ | KE, enthalpy |
| ______________ or ______________ are devices used to increase pressure of a fluid, work supplies to these devices from an external source through rotating shaft. | compressors, pumps |
| ______________ drives electric generator in steam, gad, or hydroelectric power plants as fluid passes through turbine, work is done against blades attached to shaft and shaft rotates and ______________ produces work. | turbine, turbine |
| ______________ valves are any find of flow restricting devices that cause significant pressure drop in fluid. | throttling |
| temperature of an ideal gas __________ change during throttling and h is constant. | doesn't |
| during throttling process, enthalpy of fluid __________ ______________ internally. | remains constant |
| heat exchanges - | two moving fluid steams exchange heat without mixing |
| nozzle requires what energy inputs? | none |
| turbine requires what energy output? | work |
| compressor or pump requires what energy input? | work |
| heat exchanger requires what energy input? | heat transfer |
| operation of a throttling valve with negligible heat transfer, and change in KE and PE. | throttling valves produce pressure drop without involving any work |
| working fluid is air continuously circulating in a closed loop and always behaves as an __________ gas. | ideal |
| all processes that make up a cycle are internally ____________. | reversible |
| ______________ process replaced by a heat-addition process from an external source. | combustion |
| ______________ process replaced by heat-rejection process that restores working fluid to initial state | exhaust |
| diesel cycle: | the ideal cycle for compression -ignition engines |
| which device has work output, usually with negligible heat transfer and change in KE and PE | turbine |
| compressor or pump needs ________ input | work |
| flow energy: | the energy needed to push fluid into or out of a control volume |
| heat addition: constant volume: | combustion |
| heat addition: constant pressure: | combustion |
| Kevin-Planck statement: | no cyclic device can receive heat from a single reservoir and produce a net amount of work |
| clausis statement: | no cyclic device produces no effects other than transfer heat, cold to hot |
| Mark I universe rules: | E is conserved atoms can only have 0 or 1 unit of E E can move by conduction only |
| energy is conserved by _____________ is not | entropy |
| in the absence of friction, pendulum of grandfather clock ____________ create any entropy | doesn't |
| internally reversible process: | if no reversibility's occur within boundaries of a system during process |
| externally reversible: | if no irreversibility's occur outside system boundaries |
| totally reversible process: | involves no irreversibility's within system or its surroundings |
| totally reversible process involves no __________ ___________ through finite temperature difference, no non quasi equilibrium changes and o friction | heat transfer |
| factors that cause processes to be irreversible are called: | irreversiblity |
| true or false expansion of a fluid in throttling valve is an ___________ process. | irreversible |
| the larger the irreversibility's in a power plant the _____________ the thermal efficiency | smaller |
| the smaller the electrical resistance during current flow in a wire the ___________ the irreversibility | smaller |
| heat transfer is always accompanied by entropy transfer in amount of: | Q/T |
| for an adiabatic closed system entropy generated expression simplifies to: | entropy generated= change in entropy of the system |
| a reservoir that supplies energy in the form of heat is called a: | source |
| a reservoir that absorbs E in the form of heat is called a: | sink |
| thermal E reservoirs are often referred to as _________ reservoirs since they supply or absorb E in form of __________. | heat, heat |
| correct statements about refrigerators and heat pumps: | 1. COP of fridge decreases refrigerated space temp 2. clausis statement asserts that a fridge cannot operate without E input from external source. |
| true of false: The specific heat at constant pressure can be less than the specific heat at constant volume. | false cp=cv+R --> cp > cv |
| true or false: For incompressible substance, the entropy will not change for any isothermal process. (isothermal means T = Const). | true |
| true or false: Enthalpy (h), internal energy (u), and entropy (s) are dependent on temperature alone for an ideal gas | false |
| true or false: The COP of a refrigerator cannot be less than one. | false |
| Heat is transferred to a closed system from a thermal energy reservoir. If the entropy change of the reservoir is 0.8 kJ / K− and that of the system is0.5 kJ / K , this process is | impossible Sgen must be greater than 0 |
| true or false: Throttling valves produce a pressure drop without involving any work | true |
| true or false: For an ideal gas, the temperature decreases during a throttling process | false |
| true or false: Internal energy values at the inlet and exit of a throttling valve are the same | false |
| Heat addition process in the ideal Otto Cycle is ____ process | Constant Volume Process |
| Heat addition process in the ideal Diesel Cycle is ____ process | Constant Pressure Process |
| Heat addition process in the ideal Brayton Cycle is ____ process | Constant Pressure Process |
| Heat rejection process in the ideal Otto Cycle is ____ process | Constant Volume Process |
| Heat rejection process in the ideal Diesel Cycle is ____ process | Constant Volume Process |
| Heat rejection process in the ideal Brayton Cycle is ____ process | Constant Pressure Process |
| true or false: The state of the refrigerant at the inlet/exit of components of refrigerator operating on ideal vapor-compression refrigeration cycle: Saturated vapor at the compressor inlet and superheated vapor at the compressor exit | true |
| true or false: The state of the refrigerant at the inlet or exit of the components of a refrigerator operating on the ideal vapor compression refrigeration cycle: Saturated vapor at the evaporator exit and superheated vapor at the condenser inlet | true |
| efficiency of an irreversible heat engine always less than efficiency of a ___________ one operating between same 2 reservoirs. | reversible |
| efficiencies of all reversible heat engines operating between same 2 reservoirs are ______________. | the same |
| Carnot heat engine cycle is a totally ______________ system. | reversible |
| cyclic heat engine: | working fluid of heat engine can return to thermo initial state at the end of the cycle vs. reversible heat engine |
| second carnot principle: | efficiency of reversible engine is independent of working fluid or its property |
| reversible cycles: | heat transfer ration Q high over Q low can be replaced by absolute temp T high over T low |
| thermo temp scale: | temp scale that's independent of properties of substances used to measure temp |
| true or false: no heat engine can have a higher efficiency than a reversible heat engine operating between same high and low temps. | true |
| property: | quality whose cyclic integral is zero |
| entropy: | extensive property of a system |
| true or false: During a heat transfer process between a hot body at 50ºC and a cold body at 10ºC, the increase in the entropy of t cold body is equal to the decrease in the entropy of the hot body | false the net entropy will increase in an irreversible world |
| true or false: For incompressible substance, the entropy will not change for any isothermal process. (isothermal means T = Const) | true |
| In an isothermal process (T = Const), the entropy of an ideal gas will increase if the pressure ________ or the volume ___________. | decreases, increases |
| true or false: The entropy of an ideal gas varies with specific volume or pressure as well as the temperature. | true |
| By which mechanism(s) can entropy be transferred to or from a system? | heat transfer and mass flow (work will not change systems entropy) |
| The magnitude and direction of entropy transfer that accompanies heat transfer Q through a section at temperature T are: | Q/T; same direction as Q |
| true or false: No entropy is generated during reversible processes. | true |
| true or false: Entropy is a conserved during any process, just like energy. | false (entropy is increasing in irreversible world) |
| true or false: The more irreversible a process is, the larger the entropy generated during that process | true |
| true or false: The entropy changes of a system can be negative during a process | true (transfer of entropy can be negative) |
| true or false: The entropy generation cannot be negative during any process | true |
| true or false: Actual heat engines cannot have a thermal efficiency of 100 percent but ideal heat engines can. | false (the upper limit of any HE is determined by carnot efficiency) |
| true or false: No heat engine can convert all the heat it receives to useful work. | true |
| true or false: The requirement that a heat engine must operate on a cycle is the expression of the Kelvin-Planck statement the second law. | false (impossible to produce work from single thermal reservoir) |
| true or false: The COP of a refrigerator is equal to the COP of a heat pump for fixed values of QL and QH. | false |
| The minimum COP value of a heat pump is zero. | false it is 1 |
| The COP of a refrigerator cannot be less than 1. | false it can be smaller than 1 |
| true or false: On the Kelvin scale, the temperature ratios are related to the heat transfer ratios of reversible heat engines. | true |
| true or false: On the Kelvin scale, temperatures vary between zero and infinity. | true |
| true or false: The magnitudes of temperature change units on the Kelvin and Celsius scales are identical. | true |
| A refrigerator is claimed to absorb 5 kJ of heat from the refrigerated space at 200 K and rejects 10 kJ of heat to a medium at 300 K. This refrigerator is: | irreversible COP(R) < COP(Carnot) |
| steady flow process: | no change with time |
| well insulated: | no heat transfer |
| adiabatic: | no heat transfer |
| unsteady flow process: | conditions within device are changing |
| uniform flow process: | at inlet is constant |
| internally reversible: | Sgen=0 |
| single inlet and exit | mass flow rates are equal |
| max work when ___________ = 0 | Sgen |
Created by:
mccurdyo