Water at a temperature of
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Fundamentals of Heat and Mass Transfer
- 3.9 The heat transfer coefficients for the flow of 26.6°C air over a sphere of 1.25 cm in diameter are measured by observing the temperature-time history of a copper ball the same dimension. The temperature of the copper ball was measured by two thermocouples, one located in the center and the other near the surface. The two thermocouples registered, within the accuracy of the recording instruments, the same temperature at any given instant. In one test run, the initial temperature of the ball was 66°C, and the temperature decreased by 7°C in 1.15 min. Calculate the heat transfer coefficient for this case.arrow_forwardFor flow over a slightly curved isothermal surface, the temperature distribution inside the boundary layer t can be approximated by the polynomial T(y)=a+by+cy2+d3(yt), where y is the distance normal to the surface. (a) By applying appropriate boundary conditions, evaluate the constants a, b, c, and d. Fluid (b) Then obtain a dimensionless relation for the temperature distribution in the boundary layer.arrow_forwardFluid flows over a flat plate, 1.2 m long. The direction of flow is along the length of the plate and parallel to the surface of the plate. The plate is held at a constant temperature of 283 K. Velocity and temperature profiles are assumed to be linear inside the boundary layers. The free stream temperature of the fluid is 340 K and it travels at 5 m/s. The fluid properties are as follows: thermal conductivity = 0.029 W/mK, density = 0.92 kg/m3, viscosity = 12.9 x 10-6 Pa.s, and specific heat capacity = 1003 J/kgK. The value of the Nusselt number at the tailing edge of the flat plate is: [ans1] The convective heat transfer from the middle of the flat plate is: [ans2] W/m2 step by step working out piease, hit final answer is 145, -281 respectivelyarrow_forward
- 4.Water at a temperature of T∞ = 25°C flows over one of the surfaces of a steel wall (AISI 1010) whose temperature is Ts,1 = 40°C and thermal conductivity of steel is 671 w/m.k. The wall is 0.35 m thick, and its other surface temperature is Ts,2 = 100°C. For steady state conditions what is the convection coefficient associated with the water flow?arrow_forwardWater at a temperature of T∞= 25°C flows over one of the surfaces of a steel wall (AISI 1010) whose temperatures Ts,1= 40°C and thermal conductivity of steel is 671 w/m.k. The wall is 0.35 m thick, and its other surface temperature is Ts,2= 100°C. For steady state conditions what is the convection coefficient associated with the water flow?arrow_forwardA thick-walled cylindrical tubing of hard rubber (k=0.151 W/m*K) having an inside radius of 5 mm and an outside radius of 20 mm is being used as a temporary cooling coil in a bath. Ice water is flowing rapidly inside, and the inside wall temperature is 275 K. The outside surface temperature is 300 K. A total of 20 W must be removed from the bath by the cooling coil. How many meter of tubing are needed?arrow_forward
- Air at 22˚C and at atmospheric pressure flows over a flat plate at a velocity of 1.65 m/s. If the length of the plate is 2.179 m and its temperature is 98 ˚C, Calculate Heat rate by using exact and approximate methods both. What is the %age difference of the heat transfer rate values by these methods? Take width of the plate as unity. Properties given at 60˚C are as follows: Density: 1.058 kg/m3 , cp = 1.005 kJ/kg˚C, k= 0.02897 w/m˚C, Kinematic viscosity is 18.97 × 10-6 m2 /sarrow_forwardProblem: Convection related Water enters a tube at 27°C with a flow rate of 450 kg/h. The rate of heat transfer from the tube wall to the fluid is given as qs′(W/m)=ax, where the coefficient a is 20 W/m^2 and x(m) is the axial distance from the tube entrance. (a) Beginning with a properly defined differential control volume in the tube, derive an expression for the temperature distribution Tm(x) of the water. (b) What is the outlet temperature of the water for a heated section 30 m long? (c) Sketch the mean fluid temperature, Tm(x), and the tube wall temperature, Ts(x), as a function of distance along the tube for fully developed and developing flow conditions.arrow_forwardWater enters a tube at 29°C with a flow rate of 460 kg/h. The rate of heat transfer from the tube wall to the fluid is given as qs′(W/m)=ax, where the coefficient a is 25 W/m2 and x(m) is the axial distance from the tube entrance. (a) Beginning with a properly defined differential control volume in the tube, derive an expression for the temperature distribution Tm(x) of the water. (b) What is the outlet temperature of the water for a heated section 31 m long? (c) Sketch the mean fluid temperature, Tm(x), and the tube wall temperature, Ts(x), as a function of distance along the tube for fully developed and developing flow conditions. (d) What value of a uniform wall heat flux, qs″ (instead of qs′=ax), would provide the same fluid outlet temperature as that determined in part 8.13b? For this type of heating, sketch the temperature distributions requested in part 8.13c.arrow_forward
- A thermocouple junction is in the form of 8 mm diameter sphere. Properties of materialare: Cp = 420 J/kg-K; ρ = 8000 kg/m3 ; k = 40 W/m-K; h = 40 W/m2 -K. This junction isinitially at 40 oC and inserted in a stream of hot air at 300 oC. Find the following:a. Time constant of the thermocouple.b. The thermocouple is taken out from the hot air after 10 seconds and kept in still airat 30 oC. Assuming the heat transfer coefficient in air is 10 W/m2-oC, find thetemperature attained by the junction 20 seconds after removal from hot air.arrow_forwardA thermocouple junction of spherical form is to be used to measure the temperature of a gas stream. h = 400w/m^2 deg C; k(thermocouple junction) = 20 w/m deg C; cp = 400 J/kg deg C; and density = 8500 kg/m^3;Calculate the following:i. Junction diameter needed for the thermocouple to have the thermal time constant of one second.ii. Time required for the thermocouple junction to reach 198 deg C if junction is initially at 25 deg C and is placed in gas stream which is at 200 deg C.arrow_forwardA graduated cylinder full of water in the lab on a bench that has just been waxed. The cylinder is 1 cm^2 in the inner cross-sectional area, and the water is 10 cm high. The temperature is at room temperature (25 °C) and remains constant. Water-air interface energy (i.e., water surface tension) is approximately 0.072 N/m at 25 °C. All the water spills and forms a puddle that can be approximated as a thin disk. (a) If this disk’s diameter is 14 cm, calculate the work required to create just the air-water interface. (b) Calculate the change in the gravitational potential energy of the water puddle in (b) (g = 9.8 m/s2arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning