Consider a 20-cm-thick concrete plane wall
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HEAT+MASS TRANSFER:FUND...-CONNECTPLUS
- 2.38 The addition of aluminum fins has been suggested to increase the rate of heat dissipation from one side of an electronic device 1 m wide and 1 m tall. The fins are to be rectangular in cross section, 2.5 cm long and 0.25 cm thick, as shown in the figure. There are to be 100 fins per meter. The convection heat transfer coefficient, both for the wall and the fins, is estimated to be K. With this information determine the percent increase in the rate of heat transfer of the finned wall compared to the bare wall.arrow_forward/ Hot square plate (1 m ×1 m) is to be cooled by attaching aluminum circular pin fins (D=0.25 cm, L= 3 cm) distributed with distance 0.6 cm as illustrated in Figs.(1-a) & (1-b). If the fin base temperature is 100°C, cooling air temperature is 30°C and h= 35 W/m. °C. Determine the total rate of heat transfer from the finned plate and the effectiveness of the fins? Assume k= 237 W/m.°C and nr=tanh mL/ mL.arrow_forwardConsider a wall heated by convection on one side and cooled by convection on the other side. Show that the heat-transfer rate through the wall is q = (T1 - T2) / (1/h1A + x/kA + 1/h2A) where T1 and T2 are the fluid temperatures on each side of the wall and h1 and h2 are the corresponding heat-transfer coefficients.arrow_forward
- 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?arrow_forwardSteam passes into tubes in a heating system whose outer diameter is 3 cm and whose wall is held at a temperature of 120°C. Tubes are connected to circular aluminium alloy fins (k = 180 W/m. ° C) with an outer diameter of 6 cm and a constant thickness of 2 mm. The distance between the two fins is 3 mm and the tube length is 200 fins per meter. With h = 60 W/m2.°C, the heat is transmitted to the ambient air at 25°C. Evaluate the increase in heat transfer from the tube per meter of its length as a result of adding fins.arrow_forwardConsider 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/hrarrow_forward
- At what rate is heat lost through a 1.3m ×2.7m rectangular glass window that is 0.32cm thick when the inside surface temperature of the glass is 22°C and the outside surface temperature of the glass is 16°C? The thermal conductivity of glass is 0.75 W/(m·K)[1m = 100 cm]arrow_forwardA rectangular fin with k=43 W/m.C , thickness t=2 cm , length L=14 cm and width W=1 m. The base of the fin is maintained at a temperature of 200 C while the fin is exposed to a convection environment at T∞= 15 C and h∞ = 20 W/m2 .C .Using the chart , calculate the heat lost from the fin .arrow_forwardA 12-m-long and 5-m-high wall is constructed of two layers of 1-cm-thick sheetrock (k = 0.17 W/m·K) spaced 16 cm by wood studs (k = 0.11 W/m·K) whose cross section is 16 cm * 5 cm. The studs are placed vertically 60 cm apart, and the space between them is filled with fiberglass insulation (k = 0.034 W/m·K). The house is maintained at 20°C and the ambient temperature outside is 29°C. Taking the heat transfer coefficients at the inner and outer surfaces of the house to be 8.3 and 34 W/m2·K, respectively, determine (a) the thermal resistance of the wall considering a representative section of it and (b) the rate of heat transfer through the wall.arrow_forward
- A pipe is used to transport refrigerant R-134a with an inner radius of 0.03m, outer radius of 5 cm, and thermal conductivity of k=2.5 W/m-K. The inner and outer surfaces of the pipe are maintained at an average temperature of 20°C and 40°C, respectively. Obtain a general relation for the temperature distribution inside the pipe under steady conditions. Determine the rate of heat gain per unit length by the refrigerant through the pipe.arrow_forward3. A food product with 80% moisture content in a 7 cm diameter can wants to be frozen. The density of the product is 1000 kg / m³, the thermal conductivity is 1.0 W / (m K), and the initial freezing temperature is -2 ° C. After 11 hours in the freezing medium -30 ° C, the product temperature becomes -10 ° C. Estimate the convection heat transfer coefficient of the freezing medium. Assume the can as an infinite cylinder. h = Answer W / (m² K).arrow_forwardA concrete wall of 16.44 cm thickness (k = 1.37 W / mC,? = 7x10-7 m2 / s) having a uniform temperature of 54 C in the beginning was suddenly exposed to the air flow at 10C. The convection heat transfer coefficient of air is 10 W / m2C and after a certain time, find the time taken for the center temperature of the wall to be 30 C (minutes).arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning