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Pie
3 years ago
12

An air conditioner using refrigerant R-134a as the working fluid and operating on the ideal vapor-compression refrigeration cycl

e is to maintain a space at 22°C while operating its condenser at 1000 kPa.
a. Determine the COP of the system when a temperature difference of 2°C is allowed for the transfer of heat in the evaporator.
Engineering
1 answer:
Oduvanchick [21]3 years ago
6 0

Answer:

COP=13.37

Explanation:

Considering the allowed temperature difference the temperature in the evaporator will be 20°. The enthalpy and entropy at this temperature are obtained from table for the saturated vapor phase:

h_1=261.64 kJ/kg

s_1=0.92254 kJ/kgK

The enthalpy at state 2 is determined from the given condenser pressure and the condition s_2 = s_1 with data from table using interpolation:  

h_2=273.18 kJ/kg

The enthalpy at states 3 and 4 is determined from the saturated liquid value for the condenser pressure from table:  

h_3=h_4=107.34 kJ/kg

the COP is then:

COP=qL/w

       = h_1- h_4/ h_2- h_1

       =13.37

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Problem 4.041 SI Refrigerant 134a enters an insulated compressor operating at steady state as saturated vapor at -26oC with a vo
Rom4ik [11]

Answer:

0.0297M^3/s

W=68.48kW

Explanation:

Hello! To solve this problem, we must first find all the thermodynamic properties at the input (state 1) and the compressor output (state 2), using the thermodynamic tables

Through laboratory tests, thermodynamic tables were developed, these allow to know all the thermodynamic properties of a substance (entropy, enthalpy, pressure, specific volume, internal energy etc ..)  

through prior knowledge of two other properties such as pressure and temperature.  

state 1

X=quality=1

T=-26C

density 1=α1=5.27kg/m^3  

entalpy1=h1=234.7KJ/kg

state 2

T2=70

P2=8bar=800kPa

density 2=α2=31.91kg/m^3  

entalpy2=h2=306.9KJ/kg

Now to find the flow at the outlet of the compressor, we remember the continuity equation that states that the mass flow is equal to the input and output.

m1=m2

(Q1)(α1)=(Q2)(α2)

\frac{(Q1)(\alpha 1) }{\alpha 2} =Q2\\Q2=\frac{(0.18)(5.27) }{31.91} =0.0297M^3/s

the volumetric flow rate at the exit is 0.0297M^3/s

To find the power of the compressor we use the first law of thermodynamics that says that the energy that enters must be equal to the energy that comes out, in this order of ideas we have the following equation

W=m(h2-h1)

m=Qα

W=(0.18)(5.27)(306.9-234.7)

W=68.48kW

the compressor power is 68.48kW

4 0
3 years ago
Choose the best data type for each of the following so that any reasonable value is accommodated but no memory storage is wasted
stiks02 [169]

Answer:

Explanation:

Part (a):

Statement : The number of siblings you have

Suitable Data type : Byte

Typical Value : From -128 and up to 127

Explanation: Byte data type is the most suitable since it can covers minimum and maximum number of siblings one can have.

Part (b):

Statement : Your final grade in this class

Suitable Data type : Char

Typical Value : 1 byte

Explanation: Grades is in the form of alphabetical letter which is either A, B, C, D, F or E which can be stored in character data type.

Part (c):

Statement : Population of Earth

Suitable Data type : Long

Maximum Value : 9223372036854775807

Explanation: Long Data takes up to 8 bytes and can store up to 9223372036854775807 which can cater for more than 36 billion. The population of earth is only around 7 billion currently making Long data type the most suitable data type to store earth population.

Part (d):

Statement : Population of US Country

Suitable Data type : Integer

Typical Value :2147483647

Explanation: Integer data type takes up to 4 bytes and can store up to  2147483647 making it suitable to store U.S population.

Part (e):

Statement : The number of passengers on bus

Suitable Data type : Byte

Typical Value :From -128 up to 127

Explanation: The typical maximum number of passengers of a bus are only around 72. Byte data type is the most suitable since it can cater the number up to 127.

Part (f):

Statement : Player's score in a Scrabble game

Suitable Data type : Short

Typical Value : 32767

Explanation: The maximum point can be scored in the Scrabble game is only 830 therefore the most suitable data type for this case is the short data type.

Part (g):

Statement : One team's score in a Major League Baseball game

Suitable Data type : Byte

Typical Value : From -128 up to 127

Explanation: The maximum point can be scored in the Base ball game is only 49 therefore the most suitable data type for this case is the Byte data type since it can cater up to 127.

Part (h):

Statement : The year an historical event occurred

Suitable Data type : Short

Maximum Value: 32767

Explanation: The historic event year can be any number from 1 to 2020 therefore the most suitable data type is the short data type.

Part (i):

Statement : The number of legs on an animal

Suitable Data type : Short

Maximum Value: 32767

Explanation: The most number of legs found are 750 legs therefore the most suitable data type is the short data type which can cater up to 32767.

Part (j):

Statement : The Price of an automobile

Suitable Data type : Float

Maximum Value: 340282350

Explanation: The most expensive car is around 15 million therefore the most suitable data type is the float data type which can cater up to 340 million.  

3 0
3 years ago
Torque is a twisting force. If the required torque applied on a 3 ft wrench is 45 ft·lb, what is the force that must be applied?
natka813 [3]

Answer:

15 lbs

Explanation:

assuming you push from the end of the wrench (3ft)

torque = force(distance)

force = torque/distance

(45 ft·lb)/(3 ft)= 15 lbs

8 0
3 years ago
A power company desires to use groundwater from a hot spring to power a heat engine. If the groundwater is at 95 deg C and the a
prisoha [69]

Answer:

W  = 12.8 KW

Explanation:

given data:

mass flow rate = 0.2 kg/s

Engine recieve heat from ground water at 95 degree ( 368 K)  and reject that heat to atmosphere  at 20 degree (293K)

we know that maximum possible efficiency is given as

\eta = 1- \frac{T_L}{T_H}

\eta = 1 - \frac{ 293}{368}

\eta = 0.2038

rate of heat transfer is given as

Q_H = \dot m C_p \Delta T

Q_H = 0.2 * 4.18 8(95 - 20)

Q_H = 62.7 kW

Maximuim power is given as

W = \eta Q_H

W = 0.2038 * 62.7

W  = 12.8 KW

3 0
2 years ago
Analyze the example of this band saw wheel and axle. The diameter of the wheel is 14 inches. The diameter of the axle that drive
Kazeer [188]

The answer for the ideal mechanical advantage and actual mechanical advantage for the different scenarios are;

A) Ideal Mechanical Advantage = 18.67

B) Actual Mechanical Advantage = 4.1067

We are given;

Input distance; The diameter of the wheel; d_w = 14 inches

Output distance; The diameter of the axle that drives the wheel; d_a = 3/4 inches

The force needed to cut a one-inch-thick softwood board; F = 1.75 pounds

The efficiency of the band saw; η = 22% = 0.22

A) Formula for Mechanical advantage is;

M.A = Force output/Force input = (Input distance)/(Output distance)

Thus;

Ideal mechanical advantage = 14/(3/4)

Ideal mechanical advantage = 18.67

B) Now, we are given that efficiency of the band saw is η = 22% = 0.22.

Thus using the mechanical advantage formula above;

Actual mechanical advantage = 0.22 × Expected output

Actual mechanical advantage = 0.22 × 18.67

Actual mechanical advantage ≈ 4.1067

Read more about Mechanical Advantage at; brainly.com/question/18345299

5 0
2 years ago
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