ENGINEERING COLLEGE

An automobile engine consumes fuel at a rate of 27.4 L/h and delivers 55 kW of power to the wheels. If the fuel has a heating value of 44,000 kJ/kg and a density of 0.73 g/cm3, deter- mine the efficiency of this engine in percentage(

Answers

Answer 1

Answer:

The efficiency of the engine is 22.5%.

Explanation:

Efficiency = power output ÷ power input

power output = 55 kW

power input = specific energy×volumetric flow rate×density

specific energy = 44,000 kJ/kg

volumetric flow rate = 27.4 L/h = 27.4 L/h × 1000 cm^3/1 L × 1 h/3600 s = 7.61 cm^3/s

density = 0.73 g/cm^3 = 0.73 g/cm^3 × 1 kg/1000g = 7.3×10^-4 kg/cm^3

power input = 44,000 kJ/kg × 7.61 cm^3/s × 7.3×10^-4 kg/cm^3 = 244.4332 kJ/s = 244.4332 kW

Efficiency = 55 ÷ 244.4332 = 0.225 × 100 = 22.5%

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For some transformation having kinetics that obey the Avrami equation (Equation 10.17), the parameter n is known to have a value of 2.1. If, after 146 s, the reaction is 50% complete, how long (total time) will it take the transformation to go to 86% completion?

Answers

Answer:

t = 25.10 sec

Explanation:

we know that Avrami equation

$Y = 1 - e^(-kt^n)$

here Y is percentage of completion of reaction = 50%

t is duration of reaction = 146 sec

so,

$0.50 = 1 - e^(-k^146^2.1)$

$0.50 = e^(-k306.6)$

taking natural log on both side

ln(0.5) = -k(306.6)

$k = 2.26* 10^(-3)$

for 86 % completion

$0.86 = 1 - e^{-2.26* 10^(-3) * t^(2.1)}$

$e^{-2.26* 10^(-3) * t^(2.1)} = 0.14$

$-2.26* 10^(-3) * t^(2.1) = ln(0.14)$

$t^(2.1) = 869.96$

t = 25.10 sec

The average flow speed in a constant-diameter section of the Alaskan pipeline is 2.5 m/s. At the inlet, the pressure is 8.25 MPa (gage) and the elevation is 45 m; at the outlet, the pressure is 350 kPa (gage) and the elevation is 115 m. Calculate the head loss in this section of pipeline.

Answers

Answer:

head loss = 805.327 m

Explanation:

given data

average flow speed v = 2.5 m/s

inlet pressure Pi = 8.25 MPa

elevation Zi = 45 m

outlet pressure Po = 350 kPa

elevation Zo = 115 m

we consider oil Specific Gravity = 0.92

to find out

head loss in this section of pipeline

solution

we find here head loss that is inlet and outlet

Hi = $(Pi)/(\rho g) +(Vi^2)/(2g) +Zi$ ..............1

put here value

Hi = $(8.25*10^6)/(920*9.81) +(2.5^2)/(2*9.81) +45$

Hi = 959.425 m

and

Hout = $(Pout)/(\rho g) +(Vout^2)/(2g) +Zout$ ..............2

put here value

H out = $(350*10^3)/(920*9.81) +(2.5^2)/(2*9.81) +115$

H out = 154.098 m

head loss is = Hi - H out

head loss is = 959.425 - 154.098

head loss = 805.327 m

Clothing made of several thin layers of fabric with trapped air in between, often called ski clothing, is commonly used in cold climates because it is light, fashionable, and a very effective thermal insulator. So, it is no surprise that such clothing has largely replaced thick and heavy old-fashioned coats. Consider a jacket made up of six layers of 0.1 mm thick synthetic fabric (k = 0.026W/m.K) with 1.2 mm thick air space (k = 0.026 W/m.K) between the fabric layers. Assuming the inner surface temperature of the jacket to be 25˚C and the surface area to be 1.25 m2 , determine the heat loss through the jacket when the temperature of the outdoors is -5˚C and the heat transfer co-efficient of outer surface is 25 W/m2 .K. What would be the thickness of a wool fabric (k = 0.035W/m.K) if the person has to achieve the same level of thermal comfort wearing a thick wool coat instead of a jacket. (30 points)

Answers

Answer:

Q=127.66W

L=9.2mm

Explanation:

Heat transfer consists of the propagation of energy in the form of heat in different ways, these can be convection if it is through a fluid, radiation through electromagnetic waves and conduction through solid solids.

To solve any problem related to heat transfer, the general equation is used

Q = delta / R

Where

Q = heat

Delta = the temperature difference

R = is the thermal resistance by conduction, convection and radiation

to solve this problem we propose the previous equation

Q = delta / R

later we find R

$R=[tex]r=(6L1)/(AK1) +(5L2)/(AK2)+(1)/(Ah)$

$R=(6(0.0001))/((1.25)(0.026)) +(5(0.012))/((1.25)(0.026))+(1)/((25)(1.25)) =0.235 K/w$

Q=(25-(-5))/0.235=127.66W

part b

we use the same ecuation with Q=127.66

Q = delta / R

Δ $R=(L)/(KA) +(1)/(hA) \nR=(L)/((0.035)(1.25)) +(1)/((25)(1.25))\n R=22.85L+0.032\nQ=(T1-T2)/R\n\n127.66=(25-(-5))/(22.85L+0.032)\nsolving for L\nL=9.2mm$

2) The switch in the circuit below has been closed a long time. At t=0, it is opened.Find the inductor current for il(t) for t> 0.

Answers

Answer:

il(t) = e^(-100t)

Explanation:

The current from the source when the switch is closed is the current through an equivalent load of 15 + 50║50 = 15+25 = 40 ohms. That is, it is 80/40 = 2 amperes. That current is split evenly between the two parallel 50-ohm resistors, so the initial inductor current is 2/2 = 1 ampere.

The time constant is L/R = 0.20/20 = 0.01 seconds. Then the decaying current is described by ...

il(t) = e^(-t/.01)

il(t) = e^(-100t) . . . amperes

Annealing is a process by which steel is reheated and then cooled to make it less brittle. Consider the reheat stage for a 100-mm-thick steel plate ( 7830 kg/m3 , c 550 J/kg K, k 48 W/m K), which is initially at a uniform temperature of Ti 200 C and is to be heated to a minimum temperature of 550 C. Heating is effected in a gas-fired furnace, where products of combustion at T 800 C maintain a convection coefficient of h 250 W/m2 K on both surfaces of the plate. How long should the plate be left in the furnace

Answers

Answer:

T = 858.25 s

Explanation:

Given data:

Reheat stage for a 100-mm-thick steel plate ( 7830 kg/m3, c 550 J/kg K, k 48 W/m K),

initial uniform temperature ( Ti ) = 200 c

Final temperature = 550 c

convection coefficient = 250 w/m^2 k

products combustion temp = 800 c

calculate how long the plate should be left in the furnace ( to attain 550 c )

first calculate/determine the Fourier series Number ( Fo )

$(T_(0)-T_(x) )/(T_(1)-T_(x) ) = C_(1) e^{(-0.4888^(2)*Fo )}$

= 0.4167 = $1.0396e^(-0.4888*Fo)$

therefore Fo = 3.8264

Now determine how long the plate should be left in the furnace

Fo = $((k)/(pc_(p) ) ) ( (t)/((L/2)^2) )$

k = 48

p = 7830

L = 0.1

Input the values into the relation and make t subject of the formula

hence t = 858.25 s

Young students show a preference for which modality?

Answers

Answer. In the present study, it was found that 61% students had multimodal learning style preferences and that only 39% students had unimodal preferences. Amongst the multimodal learning styles, the most preferred mode was bimodal, followed by trimodal and quadrimodal respectively

Explanation:

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