A22-mm-diameter and 10-m-long electric wire is tightly wrapped with a 1-mm-thick plastic cover whose thermal conductivity isk=0.15 Wim K Electricalmeasurements indicate that a current of 13 A passes through the wire and there is a voltage drop of 8 V along the wire. Assume that the insulated wire is exposed to a medium at T. - 48°C with a heat transfer coeficient of h = 24 W/m? K 2K. Electrical wire Insulation The heat generated is [x] in Watts The total thermal resistance is ly) in C/W The temperature at the intertace of the wire and the plastic cover is (2] in C A2.2-mm-diameter and 10-m-long electric wre is tightly wrapped with a 1-mm-thick plastic cover whose thermal conductvity is k 0 15 W/m K. Electrical measurements indicate that a current of 13A passes through the wire and there is a voltage drop of 8 V along the wire. Assume that the insulated wire is exposed to a medium at T48°C with a heat transfer coefficient of h= 24 Wim K Selected Answer: Electrical wire Insulation Activate Windows Go to Se ate Window The heat generated is 104 in Watts The total themal resistance is o 0.067 inC/W The temperature at the interface of the wre and the plastic cover is o 59 in Co

A22-mm-diameter and 10-m-long electric wire is tightly wrapped with a 1-mm-thick plastic cover whose thermal conductivity isk=0.15 Wim K Electricalmeasurements indicate that a current of 13 A passes through the wire and there is a voltage drop of 8 V along the wire. Assume that the insulated wire is exposed to a medium at T. - 48°C with a heat transfer coeficient of h = 24 W/m? K 2K. Electrical wire Insulation The heat generated is [x] in Watts The total thermal resistance is ly) in C/W The temperature at the intertace of the wire and the plastic cover is (2] in C A2.2-mm-diameter and 10-m-long electric wre is tightly wrapped with a 1-mm-thick plastic cover whose thermal conductvity is k 0 15 W/m K. Electrical measurements indicate that a current of 13A passes through the wire and there is a voltage drop of 8 V along the wire. Assume that the insulated wire is exposed to a medium at T48°C with a heat transfer coefficient of h= 24 Wim K Selected Answer: Electrical wire Insulation Activate Windows Go to Se ate Window The heat generated is 104 in Watts The total themal resistance is o 0.067 inC/W The temperature at the interface of the wre and the plastic cover is o 59 in Co

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 1.45P: An electronic device that internally generates 600 mW of heat has a maximum permissible operating...

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3.16 A large, 2.54-cm.-thick copper plate is placed between two air streams. The heat transfer coefficient on one side is and on the other side is . If the temperature of both streams is suddenly changed from 38°C to 93°C, determine how long it takes for the copper plate to reach a temperature of 82°C.
2.9 In a large chemical factory, hot gases at 2273 K are cooled by a liquid at 373 K with gas-side and liquid-side convection heat transfer coefficients of 50 and , respectively. The wall that separates the gas and liquid streams is composed of a 2-cm thick oxide layer on the gas side and a 4-cm thick slab of stainless steel on the liquid side. There is a contact resistance between the oxide layer and the steel of . Determine the rate of heat loss from hot gases through the composite wall to the liquid.
Estimate the rate of heat loss per unit length from a 5-cm ID, 6-cm OD steel pipe covered with high-temperature insulation having a thermal conductivity of 0.11 W/(m K) and a thickness of 1.2 cm. Steam flows in the pipe. It has a quality of 99% and is at 150C. The unit thermal resistance at the inner wall is 0.0026(m2K)/W the heat transfer coefficient at the outer surface is 17W/(m2K) and the ambient temperature is 16C.
An electronic device that internally generates 600 mW of heat has a maximum permissible operating temperature of 70C. It is to be cooled in 25C air by attaching aluminum fins with a total surface area of 12cm2. The convection heat transfer coefficient between the fins and the air is 20W/m2K. Estimate the operating temperature when the fins are attached in such a way that (a) there is a contact resistance of approximately 50 K/W between the surface of the device and the fin array and (b) there is no contact resistance (in this case, the construction of the device is more expensive). Comment on the design options.
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.
A plane wall (0.8 m x 0.6 m) at 10 oC is to be heated by attaching 7-cm-long, 3-mm-diameter pin fins (k=200 W/mK, ρ=5000 kg/m3 ) to it. nfin=2000 fins are to be used in total. Temperature of the surrounding fluid is 100 oC, and the heat transfer coefficient on the surfaces is 35 W/m2K. Total (material + manufacturing) cost of the fins is 850 TL/kg. neglecting heat transfer from the fin tips a. nfin=? b.Fin effectiveness= c.Overall fin effectiveness= d.Total cost of fins (TL)=
Q4: A spherical object that is made of a material with specific heat=383 J/kg K , and density = 8954 kg/m’. The diameter of the sphere is 5-cm and it is initially at a uniform temperature of 150¢C. It is suddenly exposed to an environment at 20-C having a heat-transfer coefficient h=28W/m? -
2. A 15-cm X 20-cm hot surface at 85°C is to be cooled by attaching 4 cm-long aluminum (k = 237 W/m-°C) fins of 2-mm X 2-mm square cross section. The temperature of surrounding medium is 25°C and the heat transfer coefficient on the surfaces can be taken to be 20 W/m2-°C. If it is desired to triple the rate of heat transfer from the bare hot surface, determine the number of fins that needs to be attached.
A total of 10 rectangular aluminum fins (k =203 W/m·K) are placed on the outside flat surface of anelectronic device. Each fin is 100 mm wide, 20 mm highand 4 mm thick. The fins are located parallel to each otherat a center-to-center distance of 8 mm. The temperature atthe outside surface of the electronic device is 60°C. The airis at 20°C, and the heat transfer coefficient is 100 W/m2·K. Determine (a) the rate of heat loss from the electronic device to the surrounding air and (b) the fin effectiveness.
/ Hot square plate (1 m ×1 m) is to be cooled by attaching aluminum circular pin fins (D=0.25 cm, L= 3 cm) distributed with distance 0.6 cm as illustrated in Figs.(1-a) & (1-b). If the fin base temperature is 100°C, cooling air temperature is 30°C and h= 35 W/m. °C. Determine the total rate of heat transfer from the finned plate and the effectiveness of the fins? Assume k= 237 W/m.°C and nr=tanh mL/ mL.
A 3-mm-diameter and 5-m-long electric wire is tightly wrapped with a 2-mm thick plastic cover whose thermal conductivity is k = 0.15 W/m · °C and inside convective coefficient of 4 W/m2. Electrical measurements indicate that a current of 10 A passes through the wire and there is a voltage drop of 8 V along the wire. If the insulated wire is exposed to a medium at T = 30°C with a heat transfer coefficient of h = 12 W/m2 · °C. Determine 1. The temperature at the interface of the wire and the plastic cover in steady operation. 2. The interface temperature when the thickness of the plastic cover is doubled. 3. The minimum temperature that the interface can reach.
A 3-mm-diameter and 5-m-long electric wire is tightly wrapped with a 2-mm thick plastic cover whose thermal conductivity is k = 0.15 W/m · °C and inside convective coefficient of 4 W/m2. Electrical measurements indicate that a current of 10 A passes through the wire and there is a voltage drop of 8 V along the wire. If the insulated wire is exposed to a medium at T = 30°C with a heat transfer coefficient of h = 12 W/m2 · °C. Determine: 1. The minimum temperature that the interface can reach.