![alyssakretzmeier](/avatars/12139.jpg)
alyssakretzmeier
17.06.2020 •
Engineering
A power cycle operating between two reservoirs receives energy QH by heat transfer from a hot reservoir at temperature TH = 2000 K and rejects energy QL by heat transfer to a cold reservoir at TL= 400 K. For each of the following cases determine whether the cycle operates reversibly, irreversibly, or is impossible:(a) QH = 1100 kJ, Wcycle = 900 kJ.(b) QH = 1000 kJ, QL = 200 kJ.(c) Wcycle = 1400 kJ, QL = 600 kJ.(d) ? = 50%
Solved
Show answers
More tips
- F Family and Home Daughter says: If you don t want to do it, don t do it. Should we persuade her?...
- H Health and Medicine How Did Inna Lose Weight on Dom 2?...
- H Health and Medicine Coughing: Causes, Types, and Treatment Methods...
- H Health and Medicine How to Treat the Flu: A Comprehensive Guide...
- O Other What is a Disk Emulsifier and How Does it Work?...
- F Family and Home What does a newborn need?...
- F Family and Home Choosing the Right Car Seat for Your Child: Tips and Recommendations...
- F Food and Cooking How to Get Reconfirmation of Registration?...
- C Computers and Internet How to Get Rid of Spam in ICQ?...
- A Art and Culture Who Said The Less We Love a Woman, the More She Likes Us ?...
Answers on questions: Engineering
- E Engineering Although humans have long wondered about the origin of knowledge, the actual field of psychology did not come into existence until the late 1800’s because:...
- M Mathematics WHAT IS THE EQUATION OF THE LINE IN SLOPE - INTERCEPT FORM...
- M Mathematics If you solve this i love you...
- G Geography The physical qualities of the original location for a city is referred to as the? O site O situation O relative location O absolute location...
- M Mathematics Pls help me with this question...
- H History Which of the following is NOT one of the Paine s arguments? A. Ties to Britain drag the colonies into war they have no interest in. B. The North American colonies would...
- H History Plz help will give brainliest. Match each section with its primary interests. Answers for all of the are eather North, South, East, or West 1. wanted high tariffs 2....
- A Arts Stream Christmas in Korea by Oli London https://youtu.be/u7lZ0w3dnE4...
- M Mathematics Which expressions are polynomials? Select the two correct answers....
- E English In what ways is poetry important to our lives?...
Ответ:
a) q' = 351.22 W/m
b) q'_total = 1845.56 W / m
c) q'_loss = 254.12 W/m
Explanation:
Given:-
- The diameter of the steam line, d = 100 mm
- The surface emissivity of steam line, ε = 0.8
- The temperature of the steam, Th = 150°C
- The ambient air temperature, T∞ = 20°C
Find:-
(a) Calculate the rate of heat loss per unit length for a calm day.
Solution:-
- Assuming a calm day the heat loss per unit length from the steam line ( q ' ) is only due to the net radiation of the heat from the steam line to the surroundings.
- We will assume that the thickness "t" of the pipe is significantly small and temperature gradients in the wall thickness are negligible. Hence, the temperature of the outside surface Ts = Th = 150°C.
- The net heat loss per unit length due to radiation is given by:
q' = ε*σ*( π*d )* [ Ts^4 - T∞^4 ]
Where,
σ: the stefan boltzmann constant = 5.6703 10-8 (W/m2K4)
Ts: The absolute pipe surface temperature = 150 + 273 = 423 K
T∞:The absolute ambient air temperature = 20 + 273 = 293 K
Therefore,
q' = 0.8*(5.6703 10-8)*( π*0.1 )* [ 423^4 - 293^4 ]
q' = (1.4251*10^-8)* [ 24645536240 ]
q' = 351.22 W / m ... Answer
Find:-
(b) Calculate the rate of heat loss on a breezy day when the wind speed is 8 m/s.
Solution:-
- We have an added heat loss due to the convection current of air with free stream velocity of U∞ = 8 m/s.
- We will first evaluate the following properties of air at T∞ = 20°C = 293 K
Kinematic viscosity ( v ) = 1.5111*10^-5 m^2/s
Thermal conductivity ( k ) = 0.025596
Prandtl number ( Pr ) = 0.71559
- Determine the flow conditions by evaluating the Reynold's number:
Re = U∞*d / v
= ( 8 ) * ( 0.1 ) / ( 1.5111*10^-5 )
= 52941.56574 ... ( Turbulent conditions )
- We will use Churchill - Bernstein equation to determine the surface averaged Nusselt number ( Nu_D ):
- The averaged heat transfer coefficient ( h ) for the flow of air would be:
- The heat loss per unit length due to convection heat transfer is given by:
q'_convec = h*( π*d )* [ Ts - T∞ ]
q'_convec = 36.58951*( π*0.1 )* [ 150 - 20 ]
q'_convec = 11.49493* 130
q'_convec = 1494.3409 W / m
- The total heat loss per unit length ( q'_total ) owes to both radiation heat loss calculated in part a and convection heat loss ( q_convec ):
q'_total = q_a + q_convec
q'_total = 351.22 + 1494.34009
q'_total = 1845.56 W / m ... Answer
Find:-
For the conditions of part (a), calculate the rate of heat loss with a 20-mm-thick layer of insulation (k = 0.08 W/m ⋅ K)
Solution:-
- To reduce the heat loss from steam line an insulation is wrapped around the line which contains a proportion of lost heat within.
- A material with thermal conductivity ( km = 0.08 W/m.K of thickness t = 20 mm ) was wrapped along the steam line.
- The heat loss through the lamination would be due to conduction " q'_t " and radiation " q_rad":
q' = ε*σ*( π*( d + 2t) )* [ Ts^4 - T∞^4 ]
Where,
T_o = T∞ = 20°C
T_s = Film temperature = ( Th + T∞ ) / 2 = ( 150 + 20 ) / 2 = 85°C
r_2 = d/2 + t = 0.1 / 2 + 0.02 = 0.07 m
r_1 = d/2 = 0.1 / 2 = 0.05 m
- The heat loss per unit length would be:
q'_loss = q'_rad - q'_cond
- Compute the individual heat losses:
Therefore,
q'_loss = 351.22 - 97.10
q'_loss = 254.12 W / m .... Answer
- If the wind speed is appreciable the heat loss ( q'_loss ) would increase and the insulation would become ineffective.