A10-m-long section of a 6-cm-diameter horizontal hot water pipe passes through a large room whose temperature is 22°C. If the temperature of the outer surface of the pipe is 65°C, determine the rate of heat loss from the pipe by natural convection. The
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- An electrical transmission line of 1.2-cm diameter carries a current of 200 amps and has a resistance of 310-4 ohm per meter of length. If the air around this line is at v, determine the surface temperature on a windy day, assuming a wind blows across the line at 33 km/h.What is the rate of heat loss through a 4-cm Fiberglass wall of the inside temperature is 22 °C and the outside temperature is 45 °C and windy (17 kph) ? the area of the wall is 100 square meters. Include surface films. Assume the k-value for 4-cm fiberglass is 0.056 W/m. °C and the surface air film coefficient for windy velocity (17 kph) is 0.053 for out film and the inner film Rs value is 0.093 as per the surface film coefficient tables ?The rectangular wall of a furnace consists of 3in. fire clay brick surrounded by 0.25in. of steel on the outside. There are six 0.25in.diameter mild steel bolts per square foot connecting the steel and the brick. The furnace is surrounded by 70°F air (with a film coefficient of 1.65 Btu/hr-ft²-°F), while the inner surface of the brick is maintained at a constant 1000°F. Determine the heat flux per square foot through this wall?
- An average man has abody surface area of 1.8m2 and a skin temperature of 33degrees celcius .The convection heat transfer coefficient for a clothed person walking in still air is expressed as {h,8.6V^0.53}FOR 0.5<v<2m/s,where V is the walking velocityin m/s.Assuming the average surface temperature of the clothed person to be 30degrees celcius, determine the rate of heat loss from an average man walking in still air at 10degrees celcius by convectionat a walking velocity of (a)0.5m/s (b)1.0m/s (c)1.5m/s (d)2.0m/sWater at 10°C is is flowing at 0.8 m/s across a long cylinder that is made of a material that generates heat by 8.5 kW/m³. The cylinder has a diameter of 0.3 m. Thermal conductivity of the cylinder is 28 W/m.°C. Assuming the film temperature is same as the water temperature, find out the surface temperature of the cylinder. Then comment whether the assumption related to film temperature was reasonable. T₂ = 10'33 °CA 10 cm outer diameter pipe carrying saturated steam at a temperature of 195C is lagged to 20 cm diameter with magnesia and further lagged with laminated asbestos to 25 cm diameter. The entire pipe is further protected by a layer of canvas. If the temperature under the canvas is 20°C, find the mass of steam condensed in 8 hrs on a 100m length of pipe and interface temperature. Take thermal conductivity of magnesia as 0.07 W/m – K and that of asbestos as 0.082 W/m – k. Neglect the thermal conductivity of the pipe material. The latent heat of steam for given conditions can be taken as 1951 kJ/kg–K.
- Convection 2. For a boiling process such as shown in Figure below, the ambient temperature Tin Newton's law of cooling is replaced by the saturation temperature of the fluid Tsat. Consider a situation where the heat flux from the hot plate is q=20 x 105 W/m². If the fluid is water at atmospheric pressure and the convection heat transfer coefficient is hw=20 x 103 W/m2 K, determine the upper surface temperature of the plate, Ts, w. In an effort to minimize the surface temperature, a technician proposes replacing the water with a dielectric fluid whose saturation temperature is Teat, d=52 °C. If the heat transfer coefficient associated with the dielectric fluid is h = 3 x 103 W/m2 K, will the technician's plan work?Water at 10°C is is flowing at 0.8 m/s across a long cylinder that is made of a material that generates heat by 8.5 kW/m³. The cylinder has a diameter of 0.3 m. Thermal conductivity of the cylinder is 28 W/m. °C. Assuming the film temperature is same as the water temperature, find out the surface temperature of the cylinder. Then comment whether the assumption related to film temperature was reasonable. Ts = 10'33 °℃Electronic components are attached under a thin square plate and the all the energy dissipated by components is removed by water flow over the top surface. The plate length is 0.18 m and the thermophysical properties of water may be approximated as: k = 0.620 W/mK, Pr = 5.2, ν = 0.96x10-6 m2/s Water flow velocity is 1.5 m/s and the amount of dissipated energy (q’’) from the components can be estimated as uniformly distributed heat flux of 80000 W/m2. One approach to analyze this problem is to assume the plate has an isothermal temperature as a boundary condition. Calculate the average isothermal plate temperature in °C for the given conditions blank If the boundary layer is ‘tripped’ and the flow over the plate is completely turbulent; what will be the average isothermal plate temperature in °C for this case?
- A 5.0-cm-diameter cylinder is heated to a temperature of 200 oC, and air at 30 oC forced across it at a velocity of 50 m/s (h = 180 W/m2K). If the surface emissivity is 0.7, calculate the total heat loss per unit length if the walls of the enclosing room are at 10 oC. Comment on your calculation. COMPLETE SOLUTIONA 0.1 m diameter long rod at 20 °C is to be heated by a hot fluid of 200 °C. How long does it take the rod temperature to reach 70% of the fluid temperature if the followings are given? Convection coefficient h = 10 W/m2K Thermal conductivity k = 20 W/mK Thermal diffusivity a = 10-5 m2/sricant An oil is acting as a lubricant for a pair of cylindrical surfaces such as those shown in 1. The angular velocity of the outer cylinder is 7908 rpmt. The outer cylinder has a radius of 5.06 cm, and the clearance between the cylinders is 0.027 cm. What is the maxi- mum temperature in the oil if both wall temperatures are known to be 158° F? The physical properties of the oil are viscosity density thermal conductivity 92.3 cp 1.22 g cm-3 0.0055 cal sec-1 cm-1 ° C-1