10A.4. Current-carrying capacity of wire. A copper wire of 0.040 in. diameter is insulated uni- formly with plastic to an outer diameter of 0.12 in. and is exposed to surroundings at 100°F. The heat transfer coefficient from the outer surface of the plastic to the surroundings is 1.5 Btu/hr ft F. What is the maximum steady current, in amperes, that this wire can carry without heating any part of the plastic above its operating limit of 200°F? The thermal and electrical conductivities may be assumed constant at the values given here: k (Btu/hr.ft.F) k (ohm ¹ cm ¹) 220 5.1 X 105 0.20 0.0 Copper Plastic

10A.4. Current-carrying capacity of wire. A copper wire of 0.040 in. diameter is insulated uni- formly with plastic to an outer diameter of 0.12 in. and is exposed to surroundings at 100°F. The heat transfer coefficient from the outer surface of the plastic to the surroundings is 1.5 Btu/hr ft F. What is the maximum steady current, in amperes, that this wire can carry without heating any part of the plastic above its operating limit of 200°F? The thermal and electrical conductivities may be assumed constant at the values given here: k (Btu/hr.ft.F) k (ohm ¹ cm ¹) 220 5.1 X 105 0.20 0.0 Copper Plastic

Elements Of Electromagnetics

7th Edition

ISBN:9780190698614

Author:Sadiku, Matthew N. O.

Publisher:Sadiku, Matthew N. O.

ChapterMA: Math Assessment

Section: Chapter Questions

Problem 1.1MA

See similar textbooks

Similar questions

1. Humans are able to control their rates of heat production and heat loss to maintain a nearly constant core temperature of Te = 37°C under a wide range of environmental conditions. This process is called thermoregulation. From the perspective of calculating heat transfer between a human body and its surroundings, we focus on a layer of skin: fat, with its outer surface exposed to the environment and its inner surface at a temperature slightly less than the core temperature, T = 35°C = 308 K. Consider a person with a skin/fat layer of thickness L = mm and effective thermal conductivity k = 0.3 "- The person has a surface area A = 1.8 m? and is dressed in a bathing suit. The m· K emissivity of the skin is ɛ = 0.95. a). When the person is in still air at T = 282 K, what is the skin surface temperature and rate of heat loss to the environment? Convection heat transfer to the air is characterized by a free convection coefficient of h 2 m2 -K b). When the person is in water at T = 282,…
16
A hot fluid (60° C) flows inside an copper tube with 1.7 cm OD and 1.5 cm ID. The inside of the pipe has a heat transfer coefficient of 130 W/m2-K. The tube is exposed to a room with air and surrounding walls of 23° C. The heat transfer coefficent between the outside of the walls and the room air is 15 W/m2 K. Draw an equivalent circuit diagram of the heat transfer, and quantify the resistance to heat flow by each of the two convective processes, conduction in the tube, and radiation between the outside of the tube and the room walls. Are any of the resistances negligible to the overall heat transfer, and if so, which ones?
2. A steel plate of k=50w/mk and thickness 10cm passes a heat flux by conduction of 25kW/m² . If the temperature of hot surface of plate is 100C, then what is the temperature of the cooler side of plate?
7
b. A slab of stone of area (3600 + R) cm² and thickness 10 cm is exposed on the lower surface to steam of (100 + R )° C. A block of ice at 0° C rests on upper surface of the slab. In one hour 4.8 kg of ice is melted. Calculate the thermal conductivity of the stone. Consider the specific latent heat of ice is (3.36 + R) x10° Joules. R=76
8. Four 20-watt lamps and two ½ - hp motors of the forced-draft evaporators are installed inside a refrigerated space. The lamps are usually switched on 16 hours per day. Calculate the heat load component of the lamps and the motors, in Btu/day.
What is the heat transfer rate of initial temperature of 26 degree Celsius and the final temperature is 85 degree Celsius.
What is the payback time on a solar hot-water system that cost$ 5,000? Assume the system reduces electrical energy consumption by 4,000 kWhr each year and ilectricity costs 16 cents per kWhr. O 8 years O 4 years O 12 years O 15 years.