A 1,135 ft², 8 in. thick concrete wall has inside and outside surface temperatures of 19°C and 8°C. A 2 in. insulation batt with a thermal conductivity of k= 0.03 Btu/(h· ft °F) is added to the wall. Determine the reduction in heat transfer rate. What is the thickness of the insulation in meters? 0.0508 ✔m What is the thermal conductivity value of the insulation batt in W/(mK)? 0.05189 ✓ W/(m .K) What is the R-value of the concrete wall (in m². K/W)? 0.133 x Your response is within 10% of the correct value. This may be due to roundoff error, or you could have mistake in your calculation. Carry out all intermediate results to at least four-digit accuracy to minimize roundoff error. m². K/W What is the R-value of the insulation batt (in m². K/W)? 0.977 ✔m². K/W What is the heat transfer rate (in W) when the insulation is added? 1046.04 ✔ W What is the percent reduction in the heat transfer rate? 89.82 X Your response is within 10% of the correct value. This may be due to roundoff error, or you could have a mistake in your calculation. Carry out all intermediate results to at least four-digit accuracy to minimize roundoff error.%

A 1,135 ft², 8 in. thick concrete wall has inside and outside surface temperatures of 19°C and 8°C. A 2 in. insulation batt with a thermal conductivity of k= 0.03 Btu/(h· ft °F) is added to the wall. Determine the reduction in heat transfer rate. What is the thickness of the insulation in meters? 0.0508 ✔m What is the thermal conductivity value of the insulation batt in W/(mK)? 0.05189 ✓ W/(m .K) What is the R-value of the concrete wall (in m². K/W)? 0.133 x Your response is within 10% of the correct value. This may be due to roundoff error, or you could have mistake in your calculation. Carry out all intermediate results to at least four-digit accuracy to minimize roundoff error. m². K/W What is the R-value of the insulation batt (in m². K/W)? 0.977 ✔m². K/W What is the heat transfer rate (in W) when the insulation is added? 1046.04 ✔ W What is the percent reduction in the heat transfer rate? 89.82 X Your response is within 10% of the correct value. This may be due to roundoff error, or you could have a mistake in your calculation. Carry out all intermediate results to at least four-digit accuracy to minimize roundoff error.%

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter2: Steady Heat Conduction

Section: Chapter Questions

Problem 2.38P: 2.38 The addition of aluminum fins has been suggested to increase the rate of heat dissipation from...

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In a multilayered rectangular wall, the thermal resistance of the first layer is 0.005 °C/W, the resistance of the second layer is 0.2° C/W, and for the third layer it is 0.1 ° C/W. The overall temperature gradient in the multilayered wall from one side to another is 70° C. a. Determine the heat flux through the wall. b. If the thermal resistance of the second layer is doubled to 0.4° C/W, what will be its influence in % on the heat flux, assuming the temperature gradient remains the same?
The passenger compartment of a minivan traveling at 60 mph can be modeled as a 3.2-ft-high, 6-ft-wide, and 11-ftlong rectangular box whose walls have an insulating value of R-3 (i.e., a wall thickness-to-thermal conductivity ratio of 3 h?ft2?°F/Btu). The interior of a minivan is maintained at an average temperature of 70°F during a trip at night while the outside air temperature is 90°F. The average heat transfer coefficient on the interior surfaces of the van is 1.2 Btu/h?ft2?°F. The air flow over the exterior surfaces can be assumed to be turbulent because of the intense vibrations involved, and the heat transfer coefficient on the front and back surfaces can be taken to be equal to that on the top surface. Disregarding any heat gain or loss by radiation, determine the rate of heat transfer from the ambient air to the van. Assume the air flow to be entirely turbulent because of the intense vibrations involved. Use a film temperature of 80°F for evaluations of air properties at 1 atm.
On a multi-layered rectangular wall, the thermal resistance of the first layer is 0.005 ° C / W, the resistance of the second layer is 0.2 ° C / W, and the third layer is 0.1 ° C / W.The overall temperature gradient in the wall is multilayered from one side. to the other side is 50 ° C. a. Determine the heat flux through the walls. = Answer watts / m2. b. If the thermal resistance of the second layer is changed to 0.3 ° C / W, what is the effect in% on heat flux, assuming the temperature gradient remains the same? = AnswerAnswer %.
1 mm thick copper plate (k=386 W/m-c) that are 15 cm x 20 cm in size if the thermal contact conductance on both sides of the copper plate is estimated to be 6,000 W/m-c, determine the % error involved in the total thermal resistance of the plate if the thermal contact conductance are ignored.
Steam at 235°C is flowing inside a steel pipe(k = 61 W/m·K) whose inner and outer diameters are10 cm and 12 cm, respectively, in an environment at 20°C.The heat transfer coefficients inside and outside the pipeare 105 W/m2·K and 14 W/m2·K, respectively. Determine(a) the thickness of the insulation (k = 0.038 W/m·K) neededto reduce the heat loss by 95 percent and (b) the thickness ofthe insulation needed to reduce the exposed surface temperatureof insulated pipe to 40°C for safety reasons.
Consider a steam pipe of length 15 ft, inner radius 2 in., outer radius 2.4 in., and thermal conductivity 7.2 Btu/hr-ft-°F. Steam is flowing through the pipe at an average temperature of 250°F, and the average convection heat transfer coefficient on the inner surface is given to be 1.25 Btu/hr-ft2-°F. If the average temperature on the outer surfaces of the pipe is 160°F, determine the rate of heat loss from the steam through the pipe. ANSWER:______Btu/hr
Steam at 320°C flows in a stainless steel pipe (k = 15 W/m-°C) whose inner and outer diameters are 5 cm and 5.5 cm, respectively. The pipe is covered with 3-cm-thick glass wool insulation (k = 0.038 W/m-°C). Heat is lost to the surroundings at 5°C by natural convection and radiation, with a combined natural convection and radiation heat transfer coefficient of 15Wm2-°C. Taking the heat transfer coefficient inside the pipe to be 80 W/m2-°C, determine the rate of heat loss from the steam per unit length of the pipe. Also determine the temperature drops across the pipe shell and the insulation.
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Steam at 235°C is flowing inside a steel pipe (k = 61 W/m ∙ °C) whose inner and outer diameters are 10 cm and 12 cm, respectively, in an environment at 20°C. The heat transfer coefficients inside and outside the pipe are 105 W/m2 ∙ °C and 14 W/m2 ∙ °C, respectively. Determine (a) the thickness of the insulation (k = 0.038 W/m ∙ °C) needed to reduce the heat loss by 95 percent and (b) the thickness of the insulation needed to reduce the exposed surface temperature of insulated pipe to 40°C for safety reasons.
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Consider a steam pipe of length L = 26 m, inner radius ? = 5 cm, outer radius ? = 7 cm, and thermal conductivity k = 25 W/m·K, as shown in Fig. The inner and outer surfaces of the pipearemaintainedataveragetemperaturesof? =120°Cand? =50°C,respectively.Obtain a general relation for the temperature distribution inside the pipe under steady conditions and determine the rate of heat loss from the steam through the pipe.
Liquid flows in a metal pipe with an inner diameter of D1 = 20 mm and an outer diameter of D2 = 30 mm. The thermal conductivity of the pipe wall is 10 W/m⋅K. The inner surface of the pipe is coated with a thin polyvinylidene chloride (PVDC) lining. Along a length of 95 cm, the pipe outer surface is exposed to convection heat transfer with hot gas, at T∞ = 95° C and h = 6 W/m2 ⋅K, and thermal radiation with a surrounding at Tsurr = 95° C. The emissivity at the pipe outer surface is 0.3. The liquid flowing inside the pipe has a convection heat transfer coefficient of 52 W/m2⋅K. If the outer surface of the pipe is at 86° C, determine the temperature at the PVDC lining and the temperature of the liquid.The ASME Code for Process Piping (ASME B31.3-2014, A323) recommends a maximum temperature for PVDC lining to be 81° C. Does the PVDC lining comply with the recommendation of the code?