An electrical resistor is connected to a battery, asshown schematically. After a brief transient, the resistorassumes a nearly uniform, steady-state temperature of95°C, while the battery and lead wires remain at theambient temperature of 25°C. Neglect the electrical resistance of the lead wires.
(a) Consider the resistor as a system abut whicha control surface ¡s placed and Equation 1,12c is applied. Determine the corresponding values of
(b) If electrical energy is dissipated uniformly within theresistor, which ¡s a cylinder of diameter
(e) Neglecting radiation from the resistor, what is theconvection coefficient?
Want to see the full answer?
Check out a sample textbook solutionChapter 1 Solutions
Fundamentals of Heat and Mass Transfer
- 1.63 Liquid oxygen (LOX) for the space shuttle is stored at 90 K prior to launch in a spherical container 4 m in diameter. To reduce the loss of oxygen, the sphere is insulated with superinsulation developed at the U.S. National Institute of Standards and Technology's Cryogenic Division; the superinsulation has an effective thermal conductivity of 0.00012 W/m K. If the outside temperature is on the average and the LOX has a heat of vaporization of 213 J/g, calculate the thickness of insulation required to keep the LOX evaporation rate below 200 g/h.arrow_forwardA 0.6-cm diameter mild steel rod at 38C is suddenly immersed in a liquid at 93C with hc=110W/m2K. Determine the time required for the rod to warm to 88C.arrow_forward1.4 To measure thermal conductivity, two similar 1-cm-thick specimens are placed in the apparatus shown in the accompanying sketch. Electric current is supplied to the guard heater, and a wattmeter shows that the power dissipation is 10 W. Thermocouples attached to the warmer and to the cooler surfaces show temperatures of 322 and 300 K, respectively. Calculate the thermal conductivity of the material at the mean temperature in W/m K. Problem 1.4arrow_forward
- 2. In determining the thermal conductivity of a plateflat insulator, the temperature was measured on both sides of the 25 mm thick plate and gave the results of 318.4 K and 303.2 K. FluxThe measured heat is 35.1 W.m-2. Illustrate the problem in a simple schematic/drawing, then calculate the thermal conductivity inbtu/h.ft.oF and in W/m.K! (0.033 ; 0.058) 3. A coil-shaped cooling pipe is made of SS-304 material. This pipe is 1 ft long, 0.4 inch outside diameter, and inch inside diameter. This coil cooling pipe is used to cool the water in the bath. The temperature of the inner coil pipe is 40oF while the outer coil in contact with water is 80oF. The thermal conductivity of SS-304 is a function of temperature where k(T) = 7.75 + (7.78 x 10-3).T where k is in Btu/h.ft.oF and T is in oF. Calculate the rate of heat dissipation in watts! (1287.7)arrow_forwardA hollow cylindrical copper conductor 1.27cm. i.d. and 5.1cm. o.d. carries a current density 5000 amp/cm². For copper K = .38 kW/m°K and electrical resistivity = 2 x 10-6 ohm cm. Find the position and magnitude of the maximum temperature and the internal and external heat removal when (a) the outside temperature is 37.8°c and no heat removal occurs on the inside and (b) the outside is at 37.6°C and the inside at 27.2°C.arrow_forwardThere is 100 grams of water in a brass calorimeter of mass 200 grams. It is found that 590 calories are required to raise the temperature of water and container from 20°C to 25°C. What is the specific heat of the brass? COMPLETE FBD SOLUTION AND REQUIREMENTS PS. THIS IS A HEAT TRANSFER PROBLEMarrow_forward
- (Q4) A 4m x 6m wall consists of 4 glass windows of 2m x 1.5m dimensions. The wall has thickness of 0.13m and a thermal conductivity of 0.5 W/m.K, while the glass windows are 6 mm thick with a thermal conductivity of 1.228 W/m.K. The values of intemal and external surface conductance for the wall (including glass) are 7.8 W/m? K and 34.4 W/m².K, respectively. The intemal and extemal temperatures are 22° C and 42°C, respectively. Calculate the total heat transfer rate through the wall. What percentage of this heat transfer is through the windows?arrow_forwardIn this question, we are concerned with the evolution of the temperature u(x, t) in a homogeneous thin heat conducting rod of length L = 1. We can consider that the rod is laterally insulated as to have a one-dimensional problem. The evolution of the temperature is governed by the one-dimensional heat equation ди 0 0 = K Ət Əx2' Assume that this equation is subject to the following initial conditions u(x,0) = f(x) and boundary conditions (0, t) = 0 and ди (1,t) + и(1,t) — 0 (i) Discuss briefly the physical meaning of the boundary conditions.arrow_forwardThe physics of the conduction heat transfer of thermosses phenomenon and the mathematical model should be discussed.arrow_forward
- A refrigeration storage is supplied with 10,000 kg of fish at a temperature of 20•C. The fish has to be cooled to -10°C for preserving it for a long period without deterioration. The cooling takes place in 10 hrs. The specific heat of fish is 0.7 above freezing point and 0.3 below freezing point which is -3°C. The latent heat of freezing is 55.5 kCal/kg. Find the refrigerating capacity of the plant in tons. Ans. 24.38 tons of Refrigerationarrow_forwardConsider a solid sphere of radius R with a fixed surface temperature, TR. Heat is generated within the solid at a rate per unit volume given by q = ₁ + ₂r; where ₁ and ₂ are constants. (a) Assuming constant thermal conductivity, use the conduction equation to derive an expression for the steady-state temperature profile, T(r), in the sphere. (b) Calculate the temperature at the center of the sphere for the following parameter values: R=3 m 1₁-20 W/m³ TR-20 °C k-0.5 W/(m K) ₂-10 W/m³arrow_forwardQ1 Passage of an electric current through a long conducting rod of radius r; and thermal conductivity k, results in uniform volumetric heating at a rate of ġ. The conduct- ing rod is wrapped in an electrically nonconducting cladding material of outer radius r, and thermal conduc- tivity k, and convection cooling is provided by an adjoining fluid. Conducting rod, ġ, k, 11 To Čladding, ke For steady-state conditions, write appropriate forms of the heat equations for the rod and cladding. Express ap- propriate boundary conditions for the solution of these equations.arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning