Concept explainers
Calculate the reduction in heat transfer rate.
Answer to Problem 28P
The reduction in heat transfer rate is
Explanation of Solution
Given data:
Area of the concrete wall,
Thickness of the concrete wall,
Thickness of the insulation batt,
Inside temperature of concrete wall,
Outside temperature of concrete wall,
From Table 11.3 in the textbook, the thermal conductivity of the concrete wall is,
The thermal conductivity of the insulation batt is,
Formula used:
The formula for the heat transfer is,
Here,
Calculation:
Convert the unit of area of cross section into meter.
Convert the unit of thickness into meter for
Convert the unit of thickness into meter for
Substitute
From the truth the temperature difference in
Substitute
Change the unit of thermal conductivity for insulation batt,
For the temperature difference
Rearrange equation (1), we get
Here,
From equation (3), the expression for the heat transfer rate of the concrete wall with insulation batt is,
Substitute
Hence the reduction in heat transfer is,
Substitute
Therefore, the reduction in heat transfer rate is
Conclusion:
Hence, the reduction in heat transfer rate is
Want to see more full solutions like this?
Chapter 11 Solutions
Engineering Fundamentals
- 100°? air flows through a round aluminum tube of ID 60mm and OD 80mm at 4 ?? .The tube is covered in 5mm thick fiberglass insulation. The tube is surrounded by RT air flowing at 5?? over the outside of the insulation. What is the heat rate through the wall of the tube? Assume that the air temperature is constant throughout the tube. Note: RT is 25 celsiusarrow_forwardDo a quick calculation of the thermal conductance (U value) across a cavity wall consisting of:1. Outer skin 220mm brickwork (North facing, exposed aspect) 2. 20mmcavity 3. Inner skin of 10mm plasterboard Compare this with the worked example of an insulated brick veneer wall in the worked example. Show your working.arrow_forwardProblems: Q1/ The inner and outer surfaces of a 5-m 6-m brick wall of thickness 30 cm and thermal conductivity 0.69 W/m °C are maintained at temperatures of 20°C and 5°C, respectively. Determine the rate of heat transfer through the wall, in W. Answer: 1035 W Brick wall 20°C 5°C 30 cmarrow_forward
- 3. 6.0" wide wooden fence posts are embedded in a concrete driveway a distance 12.125" apart. There is a 1/16" gap between the post and the concrete (see diagram). The posts are installed when the temperature is 12°C. Determine if the gap will close when the temperature increases to 32°C and if not how big the gap will be at that temperature. The thermal expansion coefficients of wood and concrete are awood =32 x 105 °C and aconcrete =13 x 106 °C. 1 inch3D2.54 cm. 6.0" 12.0" 0.0625"arrow_forwardA cold-storage warehouse is to be constructed of a number of individual rooms that are maintained at various temperatures. The walls of one room are constructed of 4 inches thick masonry on the outside of 0.5 inches thick plywood on the side. Sandwiched between the masonry and plywood is glass fiber insulation that is 3.5 inches thick. The inside-wall temperature is to be maintained at −10°F and the outside-wall temperature is 70°F. As a first step in sizing the required cooling unit, determine the heat flow the wall on a per-square-foot basis.arrow_forwardCivilarrow_forward
- A commercial building is built on a slab on grade foundation that is a 40 m by 18 m rectangular shape. Assume the outside design temperature is -15°C. Determine the rate of heat loss through the exterior edge of a concrete slab, a. For an uninsulated slab edge perimeter. b. For a slab edge perimeter insulated with 25 mm of perimeter insulation (an RSI-value of about 0.44).arrow_forwardCalculate the thickness of the masonry wall having thermalconductivity of 0.75 W/mK if the heat transfer is to be 80% of theheat transfer through a composite structural wall having athermal conductivity of 0.25 W/mK and a thickness of 100mm.Assume that both walls are subjected to same surfacetemperature.arrow_forwardQ4: Consider the heat flow in one direction (x-axis) through the composite wall shown in Figure Q4. Draw the thermal circuit then determine T1 and T2, and the heat flux (q, W/m2), knowing that the thermal conductivity of the Fir (0.11 W/m.°C), the concrete cinder block (0.76 W/m.°C), the building brick (0.69 W/m.°C) and the yellow pine (0.147 W/m.°C). Consider also the concrete cinder block and building brick sections are of equal thickness.arrow_forward
- Help your customer to calculate the heat losses through a composite wall that includes an 8-mm-thick hardwood siding, 40-mm by 130-mm hardwood studs with glass fiber insulation (paper faced, 28 kg/m3 ), and a 12-mm layer of gypsum (vermiculite) wall board as shown. The wall is 2.5 m high by 6.5 m wide. - 20 °C Wood siding Stud 130 mm Insulation Wall board 21 °C 40 mm Figure 1: The top view of thecomposite wall.arrow_forwardA concrete wall has a thermal resistance of 0.095 K/W. There is a glass window in the concrete wall with a thermal resistance of 0.046 K/W. What is the total thermal resistance for the whole configuration (wall+ window) (K/W)? O A. 0.1410 B. 32.2654 C. 0.6738 OD. 0.0310 OE. None of them.arrow_forwardQ- To complement the construction Q- What is the correct Sentence of a wall or to connect a wall to be scientifically? constructed with a previously Thermal insulation value of brick constructed wall specially If the wall units wall was a measure of the is to be connected vertically when capacity of the wall to retention heat between inside and outside the building and the greater the value of the coefficient the lower O Non of them the amount of heat leaking. The previously built wall each brick is left on the head so that it will Thermal transmittance coefficient of brick units wall was a measure of down away from the face of the wall about quarter brick and this works the ability of the wall to escape heat between inside and outside the done between row and row. building and the greater the value of It is left without completion, and each row is an apostate from the row under of it about a quarter or the coefficient the lower the amount of heat leaking. O All answers corrected half…arrow_forward
- Engineering Fundamentals: An Introduction to Engi...Civil EngineeringISBN:9781305084766Author:Saeed MoaveniPublisher:Cengage Learning