1-102 A 1.4-m-long, 0.2-cm-diameter electrical wire extends across a room that is maintained at 20°C. Heat is generated in the wire as a result of resistance heating, and the surface tem- perature of the wire is measured to be 240°C in steady op- eration. Also, the voltage drop and electric current through the wire are measured to be 110 V and 3 A, respectively. Dis- regarding any heat transfer by radiation, determine the con- vection heat transfer coefficient for heat transfer between the outer surface of the wire and the air in the room. Answer: 170.5 W/m². °C Room

The exhaust duct from a heater has an inside diameter of 114.3 mm with ceramic walls 6.4 mm thick. The average k=1.52 W/m· K. Outside this wall, an insulation or rock wool 102 mm thick is installed. The thermal conductivity of the rock wool is k= 0.046+ 1.56 x 104 T°C (W/m · K). The inside surface * = temperature of the ceramic is T1 = 588.7 K, and the outside surface temperature of the insulation is 311 K. Calculate the heat loss for 1.5 m of duct and the interface temperature T2 between the ceramic and the insulation. [Hint: The correct value of km for the insulation is that evaluated at the mean temperature of (T2 + T3)/2. Hence, for the first trial assume a mean temperature of, say, 448 K. Then calculate the heat loss and T2 Using this new T2, calculate a new mean temperature and proceed as before.]

(a) What is the heat loss per unit length of the pipe?(b) The pipe material is switched to PTFE (k = 0.38 W/(m⋅K)). To maintain the same heat loss as theprevious question, if all other parameters are to remain the same as before, what is the required thicknessof the pipe wall in centimeters?

Example • The cylinder is made from aluminum with diameter and thickness of 5 cm and 1 cm respectively. The wall temperature in the inside of cylinder is 50°C, while the temperature of the air is 30°C. the coefficient of convection in the air is 10 W/m2-C. Calculate the heat loss from the cylinder per unit length! • Calculate the thickness of the insulation so heat loss from cylinder will decrease 50% of initial condition. Thermal conductivity of the isolator (k) : 0.5 W/m°C state.pptx 7 MB VIEW Tampilkan semua

À wall of area 30 m² having a density of 1500 kg/m', thermal conductivity 30 W/m.K, and specific heat capacity 4 kJ/kg.K. The temperature distribution across a wall 0.5 m thick at a certain instant of time is given as T(x) = 30-5 x-7x The wall is generating a uniform heat (q.) of 1000 W. (1) Find the rate of heat transfer entering and leaving the wall (in W). (2) Find rate of energy stored in Watt. (3) Find (dFT/dx²) (4) Derive the change in temperature with respect to time equation (time rate of temperature change)- remember to substitute the value of (d T/dx²) from (part 3) and values of all other properties into final equation. %3D

Q3) A fused-quartz sphere has a thermal diffusivity of 9.5 x 107 m²/s, a diameter of 2.5 cm, and a thermal conductivity of 1.52 W/m. °C. The sphere is initially at a uniform temperature of 25 °C and is suddenly subjected to a convection environment at 250 °C. The convection heat-transfer coefficient is 110 W/m². °C. Calculate the temperatures at the center and at a radius of 5 mm after a time of 8 min.

.240mm steam main pipe, 210m long is covered with 50mm of high temperature insulation (k-0.092 W/m °C) and 40mm of low temperature insulation (k-0.062 W/m °C). The inner and the outer surface temperature as measured are 390 °C and 40 °C respectively. Calculate: 1- The total heat loss per hour. 2- The temperature between two layers of insulation.

A copper electric wire of radius R, = 1 mm is isolated by a layer of PVC so that the outer radius of the wire Rg = 2 mm, as shown in Figure below. The wire exchanges heat with the air at 20°C according to a heat transfer coefficient h=20 W/m2°c: Given that : k=copper electrical conductivity=4.0 × 1070hm-'m¯! kpvc= PVC thermal conductivity = 0.3- m°C kco = copper thermal conductivity = 100 m°C %3D (amp/m)² And that the electrical heating source is given by : S, amp²s /kgm³ If the temperature (T,) on the outer surface (r = RG) is 25°C, what is the electrical current C (amp) that passes through this wire? Dont forget to state your hypothesis clearly.     Hi, Could you please tell me what the book's name is? Thank you!

In a movie theater in winter, 500 people are watching a movie. The heat losses through the walls, windows, and the roof are estimated to be 150,000 Btu/h. Determine if the theater needs to be heated or cooled.