8 A copper hot-water cylinder of length 1-0m and radius 0-20 m is lagged by 20m of material of thermal conductivity 0-40 W m K. Estimate the temperature of the outer surface of the lagging, assuming heat loss is through the sides only, if hea has to be supplied at a rate of 0-25 kW to maintain the water at a steady temperature of 60°C.

8 A copper hot-water cylinder of length 1-0m and radius 0-20 m is lagged by 20m of material of thermal conductivity 0-40 W m K. Estimate the temperature of the outer surface of the lagging, assuming heat loss is through the sides only, if hea has to be supplied at a rate of 0-25 kW to maintain the water at a steady temperature of 60°C.

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter1: Basic Modes Of Heat Transfer

Section: Chapter Questions

Problem 1.21P: 1.21 In an experimental set up in a laboratory, a long cylinder with a 5-cm diameter, and an...

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1.21 In an experimental set up in a laboratory, a long cylinder with a 5-cm diameter, and an electrical resistance heater inside its entire length is cooled with water flowing crosswise over the cylinder at and a velocity of 0.8 m/s. For these flow conditions, 20 kW/m of power is required to maintain a uniform temperature of at the surface of the cylinder. When water is not available, air at is used with a velocity of 10 m/s to maintain the same surface temperature. However, in this case, the cylinder surface heat dissipation rate is reduced to 400 W/m. Calculate the convection heat transfer coefficients for both water and air, and comment on the reason for the differences in the values.
A mild-steel cylindrical billet 25 cm in diameter is to be raised to a minimum temperature of 760C by passing it through a 6-m long strip-type furnace. If the furnace gases are at 1538C and the overall heat transfer coefficient on the outside of the billet is 68W/m2K, determine the maximum speed at which a continuous billet entering at 204C can travel through the furnace.
The handle of a ladle used for pouring molten lead is 30 cm long. Originally the handle was made of 1.9cm1.25cm mild steel bar stock. To reduce the grip temperature, it is proposed to form the handle of tubing 0.15 cm thick to the same rectangular shape. If the average heat transfer coefficient over the handle surface is 14 W/m K, estimate the reduction of the temperature at the grip in air at 21C.
Plate glass 5 mm thick at200°C is to be cooled fromb bothsides using air at 40°C. Ifs surfacecracks are to bea avoided determine them maximumvalue of convective heat transfer coefficient. Material properties are density = 2500 kg/m3, = specific heat 670 J/kgK. Thermal conductivity 0.744 W/mk. Also determine the time required in this to cool the plate to 80°C.
A spherical shaped vessel of 1.4 m diameter is 90 mm thick. Find the rate of heat leakage, if the temperature difference between the inner and outer surfaces is 220oC. Thermal conductivity of the material of the sphere is 0.083 W/m-K.
Fluid is flowing through a 20 mm inside diameter and 25 mm outside diameter brass tube at no leaking with temperature at 149oF and length of 10 m. Surface conduction of hot fluid is 5.2 W/m2-K and thermal conductivity of brass is 12.84 W/m2-K. Brass tube is covered by silica of 6 mm thickness with thermal conductivity of 13.84 W/m-K. Outside of it, is a fluid with 45oC with surface conductance of 3.2 W/m2-K. Find the heat transfer from the hot fluid with temperature of 149oF to fluid with temperature of 45oC.
An ordinary egg can be approximated as a 5.5-cm-diameter sphere whose thermal conductivity of roughly k = 0.6- W mk overall density of p = 1000; and heat capacity of C₂ = 3000- kg m² The egg is initially at a uniform temperature of T₂ = 10°C and is dropped into boiling water at T.. = 90°C W - determine how long it will take for the egg to m²K Taking the convective heat transfer coefficient to be h reach T = 70°C. In solving the problem, please follow the steps below. For the Lump Model In solving this problem, please use the lump model method (ignoring the requirement of small Biot number and discuss the outcomes, 1. 2. Compute the characteristic length Lc Compute the volume and surface area of the sphere (as the egg model) Vol As 3. Compute the diffusivity α = = 10- k p Cp = J kgk Compute non-dimensional excessive temperature 0 = h Lc k 4. Compute the Biot number using the characteristic length found above Bi = T-Too 5. Ti-Too 6. Calculate the Fourier number from the equation =…
Solve this with diagram: An engine cover is made from 1 cm thick stainless steel plate (k = 14 W/m K). Air on the inside of the engine cover is heated to 340°C with a heat transfer coefficient of 7 W/m2K. Outside of the engine coverthe ambient air has a temperature of 70°C. If oil was spilled on the outside of the engine cover (ambient side), it could ignite if the surface temperature were to exceed 200°C. In this configuration, would spilled oil ignite? Use calculations to justify your answer. If a 4 mm thermal coating (k = 1.1 W/m K) was applied tothe outside of the engine, what would the outside temperature of the engine cover be reduced to? Solve it with resistors method
Solve this with diagram: An engine cover is made from 1 cm thick stainless steel plate (k = 14 W/m K). Air on the inside of the engine cover is heated to 340°C with a heat transfer coefficient of 7 W/m2K. Outside of the engine coverthe ambient air has a temperature of 70°C. If oil was spilled on the outside of the engine cover (ambient side), it could ignite if the surface temperature were to exceed 200°C. In this configuration, would spilled oil ignite? Use calculations to justify your answer. If a 4 mm thermal coating (k = 1.1 W/m K) was applied tothe outside of the engine, what would the outside temperature of the engine cover be reduced to?
An electric motor is to be connected by a horizontal steel shaft (k - 42.56 W/m.K), 25 mm in diameter to an impeller of a pump, circulating liquid metal at a temperature of 540°C. If the temperature of electric motor is limited to a maximum value of 52°C with the ambient air at 27°C and heat transfer coefficient of 40.7 W/m?K, what length of shaft should be specified between the motor and pump ?
Shown below is an insulated copper block that receives energy at a rate of 100 W from anembedded resistor. If the block has a volume of 10-3 m3and an initial temperature of 20oC, howlong would it take, in minutes, for the temperature to reach 60oC? Copper has a specific heatcapacity ccu = 0:385 kJ/ kg.K and a density of cu = 8930 kg/m3.
Consider a steam pipe of length 20 m, inner radius 7 cm, ouler radius n 12 cm, and thermal conductivity 20 Wim K. The inner and outer surfaces of the pipe are maintained at average temperatures of T 160'C and Ta 65'C, respectively. Applying a general relation for the temperahure distribution inside the pipe under steady conditions, determine the rate of heat loss from the stoam through the pipe.