Mechanical Engineering and Thermodynamics Practice Flashcards

250 flashcards covering thermodynamics, fluid mechanics, refrigeration, and boiler operations based on lecture notes.

What is the heat exchanger in which low-pressure refrigerant boils or vaporizes to absorb heat from the refrigerated area?

Chiller

In an air standard Brayton cycle, given air at $300\,K$ and $1300\,K$ with $T_2 = T_4 = 624.5\,K$ and $m = 1.5\,kg/s$, what is the net power produced?

$$529.76\,kW$$

In an air standard Otto cycle, if the clearance volume is $12\%$ of the displacement volume, what is the thermal efficiency?

$$59.08\%$$

What refrigeration system evaporates only part of the circulated refrigerant while the remainder is separated from the vapor and recirculated?

Flooded refrigeration system

In an air standard Brayton cycle where air enters at $1\,bar$ and $15\,^{\circ}C$, and leaves at $10\,bar$ with a maximum temperature of $1000\,^{\circ}C$, what is the maximum net work?

$$352.19\,kJ/kg$$

What is the term for ice formation on a refrigeration system expansion device that renders it inoperative?

Freeze up

What is the clearance volumetric efficiency of an ammonia compressor designed with $4\%$ clearance operating between $35\,^{\circ}C$ and $-15\,^{\circ}C$ ($P_d = 1167.2\,kPa$, $P_s = 497.48\,kPa$, $k=1.304$)?

$$96.31\%$$

In a lithium bromide solution absorption refrigeration system, what substance serves as the refrigerant?

Water

In an ammonia solution absorption refrigeration system, what substance serves as the absorbent?

Water

In an ammonia solution absorption refrigeration system, what substance serves as the refrigerant?

Ammonia

A water tube boiler has a percentage rating of $200\%$, a factor of evaporation (F.E.) of $1.1$, and heating surface of $400\,ft^2$. What is its rate of evaporation?

$$1138\,kg/hr$$

What name is given to the pressure vessel mounted above the generator in an absorption system through which the vapor leaving the generator passes?

Analyzer or Bubble Column

If a Carnot cycle is represented by a rectangle on a T-S diagram with localized ellipse inscribed, what is the thermal efficiency of the cycle represented by an ellipse with a major axis twice its minor axis?

$$44.88\%$$

What is the critical radius for an asbestos cement ($k = 0.208\,Btu/hr \cdot ft \cdot ^{\circ}F$) covered pipe with an external heat transfer coefficient of $1.5\,Btu/hr \cdot ft^2 \cdot ^{\circ}F$?

$$2.44\,cm$$

Given air density of $0.075\,lb/ft^3$, a barometer reading $30.150\,in\,Hg$ at the foot of a mountain and $28.607\,in\,Hg$ at the camp, what is the mountain height?

$$1455.54\,ft$$

What component in an absorption system Return liquid to the top of the bubble column to ensure the vapor going to the condenser is lowered in temperature and enriched in ammonia?

Rectifier

In a geothermal power plant with ground water flow of $4000\,kg/s$ and quality after throttling at $20\%$, if turbine power is $80\,MW$, what is the steam enthalpy change?

$$100\,kJ/kg$$

What is the partial pressure of $CO_2$ in a gas mixture containing $35\%$ $CO_2$ and $65\%$ $N_2$ by weight at $101\,kPaa$?

$$25.75\,kPaa$$

What temperature scale sets the melting point of ice at $0^{\circ}$ and the boiling point of water at $80^{\circ}$?

Reaumur Scale

What is the amount of heat energy required to raise the temperature of one pound of water one degree Fahrenheit?

British thermal unit or BTU

What is the heating value of a fuel with a specific gravity ($SG$) of $0.997$ using the formula $HHW = 51716 - 8793.8(SG)$?

$$42975\,kJ/kg$$

What is the term for mixtures or substances used in laboratories to produce a drop in temperature, such as ice and salt?

Frigorific mixture

The addition of $10\%$ salt (NaCl) by weight to water lowers its freezing point from $32\,^{\circ}F$ to what value?

$$20\,^{\circ}F$$

For every $1000\,ft$ rise in elevation, barometric pressure reduces by approximately how many inches of mercury?

$$1\,inch\,Hg$$

For every $1000\,ft$ rise in elevation, barometric temperature reduces by how many degrees Fahrenheit?

$$1.9\,^{\circ}F$$

What is the maximum temperature of any gas or vapor at which it may be condensed into a liquid regardless of applied pressure?

Critical temperature

Calculate the energy transfer rate across a $6\,inch$ wall of firebrick ($k = 0.65\,Btu/hr \cdot ft \cdot ^{\circ}F$) with a temperature difference of $50\,^{\circ}F$.

$$368.88\,W/m^2$$

What is the name for a refrigerant that exists as a liquid under normal atmospheric conditions and must be evaporated under a pressure below atmospheric?

Vacuum refrigerant

What is the specific gravity ($SG$) at $15.6\,^{\circ}C$ of a fuel with a Baume rating of $28^{\circ}$?

$$0.886$$

Air at $1000\,kPaa$ and $310\,K$ is expanded to $250\,kPaa$ in accordance with $PV^{1.25} = C$. What is the work done?

$$-162.11\,kJ/kg$$

What is the group of refrigerants developed since 1930 to overcome toxic effects of ammonia and sulfur dioxide?

Halogenated refrigerants

In a Rankine cycle with thermal efficiency of $25\%$ and a boiler factor of evaporation of $1.15$, what is the steam mass flow rate for a cycle output of $13750\,kW$?

$$5.3\,kg/s$$

Which refrigeration component combines the functions of a cooling tower and a condenser?

Evaporative condenser

A boiler generates steam at $81700\,kg/hr$ with steam enthalpy at $3187\,kJ/kg$ and feed at $604.83\,kJ/kg$. If efficiency is $82\%$ and fuel heating value is $32567.85\,kJ/kg$, find the fuel mass per day in metric tons.

$$189.6\,metric\,tons/day$$

What factor includes the sum of heat transfer rates of dirt and foreign material building up on the water side of condenser tubes?

Fouling factor

What is the latent heat load of a heater if the air flow is $10\,kg/s$ entering at $16\,^{\circ}C$, maintained at $27\,^{\circ}C$, and the Sensible Heat Ratio is $0.71$?

$$45.21\,kW$$

What evaporator type is arranged with an accumulator located above the coil ensuring the inside of the evaporator is full of refrigerant?

Flooded evaporator

If a plant has an average load of $34500\,kW$ and a load factor of $0.75$, what is the reserve power if capacity is $80000\,kW$?

$$34000\,kW$$

What is the standardized industry term for a device that meters or regulates the flow of liquid refrigerant to an evaporator?

Expansion Valve

For the hydrocarbon fuel $C_{12}H_{30}$ burning with $25\%$ excess air, what is the actual air-fuel ratio?

$$23.29\,kg\,air/kg\,fuel$$

What is the 'value of the controlled condition actually maintained under steady state conditions' called?

The value of the controlled condition actually maintained under steady state conditions

If a container of Helium is dropped $3000\,m$ above the ground, what is the change of temperature (using $R=2.078575\,kJ/kg \cdot K$ and $k=1.666$)?

$$9.43\,^{\circ}C$$

In a pneumatic temperature control system for a steam water heater, what is the 'manipulated variable'?

The steam supply

Which valve is designed to allow a fluid to pass through in only one direction?

Check valve

Determine the work done in Btu for a car weighing $3153\,lb$ accelerated from $55\,fps$ to $100\,fps$ in $10\,seconds$.

$$125.92\,Btu$$

How is a solenoid valve classified?

Magnetic stop valve

What is a thermostat?

A temperature operated switch

Find the runner diameter of a turbine operating at $450\,rpm$ with a head of $60\,m$ and a peripheral coefficient of $0.60$.

$$0.874\,m$$

What is one of the main purposes of refractory in a boiler furnace?

Prevent excessive furnace heat losses

In a double pipe counter flow heat exchanger, water ($120\,^{\circ}C$ to $55\,^{\circ}C$) heats oil ($26\,^{\circ}C$ to $65\,^{\circ}C$). What is the log mean temperature difference (LMTD)?

$$40.62\,^{\circ}C$$

Balance pressure traps belong to which specific type of steam trap family?

Thermostatic

In a Rankine cycle, if entropy $s = 6.2575$ and at $2\,MPa$ we have $s_f = 1.0910$ and $s_{fg} = 6.5029$, what is the steam quality?

$$79.45\%$$

Calculate the turbine work in $kJ/kg$ if steam enters at $h_1 = 3531\,kJ/kg$, exits at $h_2 = 2290\,kJ/kg$, with in/out velocities of $15\,m/s$ and $300\,m/s$ and a $3\,m$ height difference.

$$1196.24\,kJ/kg$$

What is the indicated power of a 4-cylinder, 4-stroke Diesel engine with $20\,cm$ bore, $30\,cm$ stroke, $600\,rpm$, and $450\,kPa$ mean effective pressure?

$$189.53\,Hp$$

What is a characteristic feature of thermodynamic steam traps?

They operate by holding back condensate until it has cooled

Determine the temperature of water entering a cooling tower if the approach is $10\,^{\circ}C$, efficiency is $65\%$, and leaving water is $27\,^{\circ}C$.

$$45.57\,^{\circ}C$$

What are the main considerations for steam trap selection?

Air venting, plant performance, flow capacity and reliability

Using the ASHRAE formula $h = 1.007(t) - 0.026 + W[2501 + 1.84(t)]$, what is the enthalpy of moist air at $30\,^{\circ}C$ with a humidity ratio of $0.015\,kg/kg$?

$$68.527\,kJ/kg\,da$$

What is the equivalence ratio of a mixture containing $75\,g$ of butane ($C_4H_{10}$) and $4050\,g$ of air (stoichiometric $AFR = 15.385$)?

$$0.82$$

When can temperature controlled applications be effectively trapped?

If the pressure on the trap is always higher than backpressure

Find the air HP of an industrial fan delivering $25\,m^3/s$ with static pressure of $127\,mm$ water and air density of $1.18\,kg/m^3$.

$$52.3\,Hp$$

What is the Indicated Mean Effective Pressure ($IMEP$) if Brake Mean Effective Pressure is $750\,kPa$ and mechanical efficiency is $80\%$?

$$136.01\,psi$$

Unless designed to flood, what is the rule for removing condensate from heat exchangers?

Condensate is removed at steam temperature

What is the mechanical efficiency of a 12-cylinder engine ($300\,mm$ bore, $450\,mm$ stroke) running at $600\,rpm$ with $8\,kNm$ torque and $500\,kPa$ indicated pressure?

$$79.01\%$$

How is flash steam produced?

From condensate passing from high to low pressure systems

Calculate the heat rejected (in Btu) for $2\,kg$ of steam at $1.4\,MPa, 250\,^{\circ}C$ ($h_1=2907.4\,kJ/kg$) until quality becomes $0.70$ at the same pressure ($h_2=2250.803\,kJ/kg$).

$$1244.73\,Btu$$

Are steam traps required to pass air?

Air should be removed as soon as it reaches the trap

A turbo-generator requires $145000\,kg/hr$ steam at $145\,MW$ and $23000\,kg/hr$ at zero load. What is the steam rate at $75\%$ rated load?

$$4.811\,kg/kW \cdot hr$$

What is a system employing open sprinklers attached to a piping system where water is released by a fire detection system?

Deluge system

What is probably the first consideration when selecting a control system?

In the event of power failure, must the valve fail open or fail closed

Find the total heat transmitted from a brick wall ($0.15\,m$, $k=0.81$, area $30\,m^2$) with surface temperature $130\,^{\circ}C$ and air at $29\,^{\circ}C$.

$$45.21\,kW$$

What range of humidity ratio is typically used for comfort air conditioning?

$0.003$ to $0.030$

In a refrigeration system, where shall the refrigerant be ideally charged?

Low pressure side

What is the volume flow rate of cooling water in lps (liters per second) for a $1500\,kW$ diesel engine with generator efficiency of $85\%$ and a $18\,^{\circ}C$ temperature rise?

$$20.66\,lps$$

Why is a boiler feed tank heated to approximately $90\,^{\circ}C$?

To reduce the gas content of the water

What device is used to dry air in a steam system?

Separator

What specifically causes water hammer in a boiler?

Slugs of water in the steam

Calculate the minimum power required for a Carnot refrigerator removing $18000\,kJ/hr$ at $-8\,^{\circ}C$ with surroundings at $25\,^{\circ}C$.

$$0.623\,kW$$

How does air enter a steam system?

Through joints on shut down of the steam system

Find the number of jets for a Pelton wheel ($25000\,kW$, $290\,m$ head) if the nozzle jet diameter is $200\,mm$.

$4$ jets

Why should strainers installed on steam lines be fitted on their sides?

To prevent the build up of water in the strainer body

What is the approximate diameter of the jet for a Pelton wheel hydro plant with power of $5000\,kW$, specific speed of $20\,rpm$, and discharge of $2020\,lps$?

$$191\,mm$$

What is a result of using a heat exchanger rating to calculate its steam consumption?

The true connected heat load may be different from the rated figure

What is the effect of supplying a heat exchanger with $3\,bar\,g$ steam when its design rating is for $2\,bar\,g$?

The output should be reduced because the difference in temperature between the steam and product is reduced

Determine the velocity of flow of oil inside a $25\,mm$ OD steel tube (wall thickness $1.65\,mm$) carrying $0.34\,lps$.

$$181\,fpm$$

How does the heat loss from the lid of a closed tank compare with that of the bottom?

Losses from the top are approximately double those from the bottom

Determine the thermal efficiency of a Carnot engine using Helium ($k=1.35$) if the volume expansion ratio during heat addition is $1.5$ and total expansion ratio is $10$?

$$24.37\%$$

What is the disadvantage of heating a tank by direct steam injection?

It dilutes the tank content

For large-scale cooling applications like a hospital, which chiller type is generally selected for high efficiency and capacity?

Centrifugal chiller

Inside a furnace it is $320\,^{\circ}C$ and outside is $10\,^{\circ}C$. What is the temperature difference in $^{\circ}R$?

$$594\,R$$

Refrigeration condensers are rated based on their ability to reject the total heat coming from which two sources?

Compressor work and net refrigeration effect

What is the heat transfer rate per unit surface from a fluid ($120\,^{\circ}C$) to a surface ($10\,^{\circ}C$) with $h_c = 225\,W/m^2 \cdot K$?

$$24750\,W/m^2$$

When should the lower end of the published U-value range for a steam coil be used?

When scaling or fouling of the coil takes place

When should steam coils enter and leave the top of a tank?

When the tank contains a corrosive solution

What range of U-values ($W/m^2 \cdot ^{\circ}C$) applies to a mild steel jacket around a stainless steel tank containing water and detergent?

$450$ to $1100$

A room ($5 \times 4 \times 3\,m$) has air at $25\,^{\circ}C$ and $101.3\,kPaa$. If water vapor mass is $0.45\,kg$ ($R_v = 0.4615\,kJ/kg \cdot K$) and sat pressure is $4.559\,kPaa$, what is the relative humidity?

$$94.08\%$$

How does the quantity of heat required for direct steam injection compare to steam coil heating for the same tank?

The same amount of heat will be required

What is the maximum range of discharge for a fire hose with a velocity of $15\,m/s$ oriented at $45\,^{\circ}$?

$$23\,m$$

Which parameter has the greatest limiting effect on the thermal performance of an open evaporative cooling tower?

Wet bulb temperature

How long will it take for the water level in a $12\,m$ high cylinder ($3\,m$ diameter) to drop to $6\,m$ through a $100\,mm$ bottom hole ($C_d = 0.98$)?

$$24\,minutes$$