IMPROVEMENT WITH RADIATION SHIELD. A shield having an emissivity of 0.1 Example 8.13 is placed around the thermometer in Example 8.12 such that the area ratio A/A, is 0.3. The temperature indicated by the thermometer under these conditions is 5°C. The convection heat- transfer coefficient is assumed to be the same, and the shield may be assumed essentiallv to surround the thermometer. Calculate the true air temperature under these circumstances. And find estimate its uncertainty? , = 0.1, A h = 10 W/m2-C E= 0.9, 0.3, T, = 273 +5 278 K, T, = 263 K %3D %3D %3D A,

IMPROVEMENT WITH RADIATION SHIELD. A shield having an emissivity of 0.1 Example 8.13 is placed around the thermometer in Example 8.12 such that the area ratio A/A, is 0.3. The temperature indicated by the thermometer under these conditions is 5°C. The convection heat- transfer coefficient is assumed to be the same, and the shield may be assumed essentiallv to surround the thermometer. Calculate the true air temperature under these circumstances. And find estimate its uncertainty? , = 0.1, A h = 10 W/m2-C E= 0.9, 0.3, T, = 273 +5 278 K, T, = 263 K %3D %3D %3D A,

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.

Chapter7: Forced Convection Inside Tubes And Ducts

Section: Chapter Questions

Problem 7.48P

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IMPROVEMENT WITH RADIATION SHIELD. A shield having an emissivity of 0.1 Example 8.13 is placed around the thermometer in Example 8.12 such that the area ratio A/A, is 0.3. The temperature indicated by the thermometer under these conditions is 5°C. The convection heat- transfer coefficient is assumed to be the same, and the shield may be assumed essentially to surround the thermometer. Calculate the true air temperature under these circumstances. And estimate its uncertainty E, = 0.1, A = 0.3, A, € = 0.9, h = 10 W/m2 - °C T, = 273 +5 = 278 K, T, = 263 K
Write the appropriate Nusselt value for the each set of conditions provided below.1. Forced convection over a flat plate at constant qs. Calculated Re at mean temperature is 3500 and Pr= 0.7154. 2. Natural convection in a small holding tank with a heating element at the bottom. The calculated Ra number is 2.37 x10^93. Forced convection through an elliptical duct at constant Ts, where a/b=8. The temperature of the fluid at the inlet is higher than at the exit. Flow is fully developed with Re = 33370 and Pr= 0.693. 4. Natural convection over a sphere with Ra = 5 x 10^9 and Pr = 0.7362 PS. Do not round off intermediate values
A chromel–constantan thermocouple measuring the temperature of a fluid is connected by mistake with copper–constantan extension leads (such that the two constantan wires are connected together and the copper extension lead wire is connected to the chromel thermocouple wire). If the fluid temperature was actually 250 C and the junction between the thermocouple and extension leads was at 90 C, what e.m.f. would be measured at the open ends of the extension leads if the reference junction is maintained at 0 C? What fluid temperature would be deduced from this (assuming that the connection error was not known)?
A composite plane wall consisting of materials, 1.5-in steel (k = 312 BTU-in/HR.ft2.0F) and 2-in aluminum (k = 1400 BTU-in/HR.ft2.0F), separates a hot gas at Ti = 2000F, hi = 2 BTU/HR.ft2.0F, from cold gas at To = 80 deg F, ho = 5. If the hot fluid is on the aluminum side, find: a) Transmittance, U; b) The heat through 100 sq. ft of the surface under steady state condition and c) The interface temperature at the junction of the metals.
Q1/ consider a (0.8m) high and (1.5m) wide double pane widow consisting of two (4mm) thick layers of glass (k=0.78W/m.°C) separated by a (10mm) wide stagnant air space (k=0.026W/m.C). ). Take the (hi) on the inner surface = 10W/m2.°C and (ho) on the outer surface = 40W/ m².°C. Determine The steady rate of heat transfer through this double pane window is equal The temperature of its inner surface for a day during which the room is maintained at (293K) while the temperature of the outdoor is (263K) is equal to *
A camera used for monitoring marine life is placed in water where T.. -5°C and the convection heat transfer coefficient h=1420 W/m²K. The camera is operating, but its battery is experiencing thermal runaway, causing the camera to become very hot, and there is volumetric heat generation, qe inside it. There is no heat generation within the waterproof, protective enclosure surrounding it. 00:08 The camera is already compromised; however, its owner hopes to save the protective case. Each interface (between layers A and B and between layers B and C) must not exceed a temperature of 185°C, or these plastic, protective layers will begin to melt. Approximate the camera and its casing as a composite, rectangular object with flat surfaces. The device's total thickness, L=LA + 2LB +Lc, is much smaller than its area (into the page); therefore, 1-D conduction can be approximated through the layers. On the left surface of layer A, the temperature is measured to be T₁ = 8.0°C, and the temperature on…
What external data can I use to support the claim that the consumers living within regions with hot climate will buy the stainless steel pan with digital thermometer reading that is powered by the heat generated while cooking and that sales will be higher in summer?
04. Airflow through a long. 0.2m square air conditioning duct maintains the outer duct surface temperature at 10 °C. If the horizontal duct is uninsulated and exposed to air at 35 °C as shown in the figure below, what is the heat gain per unit length of the duct? Air, Too-35°C NW-0.2m H=0.2 m -T₂-10°C
1. A composite furnace wall is made up of a 12-in. lining of magnesite refractory brick, a 5-in.thickness of 85% magnesia, and a steel casing 0.10-in. thick. Flue gas temperature is 2200 F andthe boiler room is at 80 F. Gas side film coefficient is 15 Btu/hr-sq.ft-F and air side is 4.0.Determine:a. The thermal current Q/Ab. Interface temperaturesc. Effect on thermal current and inside refractory wall temperature if the magnesia insulation weredoubled.
The interior of a refrigerator whose dimensions are 0.05 x 0.05 dam base area and 1.25 m high, must be kept at 4 °C. The refrigerator walls are constructed of two steel sheets (k= 35 kcal/h.m.°C) 3 mm thick, with 65 mm of material insulation (k=0.213 kcal/h.m.°C) between them. The film coefficient of the inner surface is 10 kcal/h.m².°C, while on the external surface it varies from 8 to 12.5 kcal/h.m².°C. Calculate: a) The power (in HP) of the refrigerator motor so that the heat flux removed from the inside the refrigerator maintain the specified temperature, in a kitchen whose temperature can vary from 21 to 36 °C; b) The temperatures of the inner and outer surfaces of the wall. Given 1 HP = 641.2 Kcal/h
pnts) Chips of width L _ 15 mm on a side are mounted to a substrate that is installed in an enclosure whose walls and air are maintained at a temperature of Tsur=T∞=25oC. The chips have an emissivity of ε=0.60 and a maximum allowable temperature of Ts=85oC. (a) If heat is rejected from the chips by radiation and natural convection, what is the maximum operating power of each chip? The convection coefficient may be approximated as h=11.7 W/m2K. (b) If a fan is used to maintain airflow through the enclosure and heat transfer is by only forced convection, with h=250 W/m2K, what is the maximum operating power?
It is required to air condition a factory building (27m x 18m x 4m). The 27m wall is type B and facessouth. The following date is available: Two glass windows in south wall 3m x 1.5m each with internalshade, Lighting load is 20 Watt fluorescent per m2 floor area ; The inside air conditions are, DBT=24 oCand RH=50%. The outside air conditions are, DBT= 40 oC, WBT=30 oC. Other related data are: dailyRange (DR)=18.0 oC, Uwall =1.4 W/m2 k, Uglass=3.5 W/m2 k, Scglass =0.7, occupancy = 8 persons doing lightbench work and, CLFoccupancy= 0.75. The building is of heavy construction with light color located at 32 N.Calculate the building cooling load from the south wall, windows, lighting and occupancy on August at4.0 p.m.