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Fundamentals of Heat and Mass Transfer
- QUESTION 4 Cold air at 5 °C enters a 12-cm-diameter 20-m-long isothermal pipe at a velocity of 2.5 m/s and leaves at 19 °C as shown in Figure Q4. Take the pressure of air 1 atm, i. estimate the rate of heat transfer to the air, and ii. calculate the surface temperature of the pipe. T, Air 5°C 12 cm 19°C 2.5 m/s 20 m Figure Q4arrow_forwardConduction 1. A thermodynamic analysis of a proposed Brayton cycle gas turbine yields P= 5 MW of net power production. The compressor, at an average temperature of T. = 400°C, is driven by the turbine at an average temperature of T₁ = 1000°C by way of an L = 1m-long, d= 70mm - diameter shaft of thermal conductivity k = 40 W/m K. Compressor min T Combustion chamber Shaft L Turbine Th out (a) Compare the steady-state conduction rate through the shaft connecting the hot turbine to the warm compressor to the net power predicted by the thermodynamics- based analysis. (b) A research team proposes to scale down the gas turbine of part (a), keeping all dimensions in the same proportions. The team assumes that the same hot and cold temperatures exist as in part (a) and that the net power output of the gas turbine is proportional to the overall volume of the device. Plot the ratio of the conduction through the shaft to the net power output of the turbine over the range 0.005 m s Ls 1 m. Is a…arrow_forward(heat transfer ) thanks The velocity of the fluid flowing in parallel over a 500mmx500mm flat heater surface is U= 19 m/s and the inlet velocity temperature is T_∞15 C. The surface temperature of this plate is T_s140 C, the friction force is F_D=0.4 N and the surface area of the plate is A=0.32 m2. According to this;(F_D= 0.4N A=32 m2)a) Surface shear stressb) Find the coefficient of frictionc) Heat transfer coefficientd) What is the amount of heat transfer (electric power) that must be given to maintain a constant surface temperature?arrow_forward
- How long should it take to boil an egg? Model the egg as a sphere with radius of 2.3 cm that has properties similar to water with a density of = 1000 kg/m3 and thermal conductivity of k = 0.606 Watts/(mC) and specific heat of c = 4182 J/(kg C). Suppose that an egg is fully cooked when the temperature at the center reaches 70 C. Initially the egg is taken out of the fridge at 4 C and placed in the boiling water at 100 C. Since the egg shell is very thin assume that it quickly reaches a temperature of 100 C. The protein in the egg effectively immobilizes the water so the heat conduction is purely conduction (no convection). Plot the temperature of the egg over time and use the data tooltip in MATLAB to make your conclusion on the time it takes to cook the egg in minutes.arrow_forwardYou and your younger brother are designing an air rifle that will shoot a lead pellet with mass m = 1.20 g and cross-sectional area A = 0.0150 cm². The rifle works by allowing high-pressure air to expand, propelling the pellet down the rifle barrel. Because this process happens very quickly, no appreciable thermal conduction occurs and the expansion is essentially adiabatic. Your design is such that, once the pressure begins pushing on the pellet, it moves a distance of L = 40.0 cm before leaving the open end of the rifle at your desired speed of v = 110 m/s. Your design also includes a chamber of volume V = 13.0 cm³ in which the high-pressure air is stored until it is released. Your brother reminds you that you need to purchase a pump to pressurize the chamber. To determine what kind of pump to buy, you need to find what the pressure of the air must be in the chamber (in Pa) to achieve your desired muzzle speed. Ignore the effects of the air in front of the bullet and friction with…arrow_forward30°C, 10m/s 2m Electronic components inside D= 20cm Figure 5 You are designing components of an electronic systems that needs to be inside a 2 m long horizontal duct. The components are sensitive so the cooling mechanism is only done by air flowing over the duct at 30°C and 10 m/s. Initially you proposed a square cross-section with 20-cm length for the duct but is rejected by your client because they said a circular cross- section is better. If the surface temperature of the duct cannot exceed 60°C, find the maximum power rating in kW of the electronics devices that can be located inside the circular cross-section duct. Is it true that circular cross-section is better than a square one for this application?arrow_forward
- Forced air at T∞ = 25°C and V = 12 m/s is used to cool electronic elements on a circuit board. One such element is a chip, 4 mm × 4 mm, located 153 mm from the leading edge of the board. Experiments have revealed that flow over the board is disturbed by the elements and that convection heat transfer is correlated by an expression of the form Nu_x=0.04Re_x^{0.85}\Pr^{\frac{1}{3}}Nux=0.04Rex0.85Pr31 Estimate the surface temperature of the chip if it is dissipating 32 mW.arrow_forwardAir enters a duct (100 cm *10̟cm*10 cm) at 32°C at a rate of 0.28m /min to cool 138 W electronic component placed on the duct. Assuming 85 percent of the heat generated inside is transferred to air flowing through the duct and the remaining 15 percent is lost through the outer surfaces of the duct. What is the exit temperature of air (°C)? C,= 1007 J/kg.°C, v =1.654×10-S m²/s, p 1.146 kg/m Pr = 0.7268, k = 0.02625 W/m.°C Select one or more:arrow_forwardA solid hemisphere of radius 5 cm to be cooled in air (at 20 o C, h=10 W/m 2 .K) from 200 oC to center of 150 oC, assume following sphere properties ρ=8500kg/m3, k=20W/m.K , C=400 J/kg.Ka. List assumptions and justify selected method of solution b. How long does it take to cool the hemisphere? c. What is the temperature of the surface at end of cooling?arrow_forward
- The liquid food is flowed through an uninsulated pipe at 90 ° C. The product flow rate is 0.3 kg / s and has a density of 1000 kg / m³, specific heat 4 kJ / (kg K), a viscosity of 8 x 10-6 Pa s, and a thermal conductivity of 0.55 W / (m) K). Assume that the change in viscosity is negligible. The internal diameter of the pipe is 30 mm with a thickness of 3 mm made of stainless steel (k = 15 W / [m ° C]). The outside temperature is 15 ° C. If the outer convective heat transfer coefficient is 18 W / (m² K), calculate the heat loss at steady state per meter pipe length. a. Find the convection coefficient in pipe = W / m² ° C. b. Calculate heat loss per meter pipe length = wattsarrow_forwardThe liquid food is flowed through an uninsulated pipe at 90 ° C. The product flow rate is 0.4 kg / s and has a density of 1000 kg / m³, specific heat 4 kJ / (kg K), a viscosity of 8 x 10-6 Pa s, and a thermal conductivity of 0.55 W / (m) K). Assume that the change in viscosity is negligible. The internal diameter of the pipe is 20 mm with a thickness of 3 mm made of stainless steel (k = 15 W / [m ° C]). The outside temperature is 15 ° C. If the outer convective heat transfer coefficient is 18 W / (m² K), calculate the heat loss at steady state per meter of pipe length. a.Find the convection coefficient in the pipe = AnswerW / m² ° C. b. Calculate heat loss per meter pipe length = Answerwatt.arrow_forwardbetween two concentric spherical sheets there is air. The inner spherical sheet has a radius of 10 cm and is filled with ice at 0 ° C, the outer spherical sheet has a radius of 10.05 cm and is at a temperature of 15 ° C. What amount of heat will be transmitted from one sheet to another by conductivity ends in 1/4 hour ?. Considering that the air is pressurized, it is considered to be 15 N / m ^ 2 and at a temperature of 2 ° C. The diameter of the air molecules is taken equal to 3 x 10 ^ -10 m. the molar mass of air is taken equal to 29 g / mol; Boltzman's constant k = 1.38 x 10 ^ -23 J / Karrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning