A technique for measuring convection heat transfer coefficients involves bonding one surface of a thin metallic foil to an insulating material and exposing the other surface to the fluid flow conditions of interest. L Th = Foil (Pelect T) Foam Insulation (k) -Ть By passing an electric current through the foil, heat is dissipated uniformly within the foil and the corresponding flux, Pee may be inferred from related voltage and current measurements. If the insulation thickness Land thermal conductivity k are known and the fluid, foil, and insulation temperatures (T., Ts, T₁) are measured, the convection coefficient may be determined. Consider conditions for which T = T = 25°C, P =2200 W/m², L = 10 mm, and k = 0.040 W/m.K. elec (a) With water flow over the surface, the foil temperature measurement yields T, = 27°C. Determine the convection coefficient, in W/m²K. What error, in percent of this value, would be incurred by assuming all of the dissipated power to be transferred to the water by convection? (b) If, instead, air flows over the surface and the temperature measurement yields T, = 125°C, what is the convection coefficient, in W/m²K? The foil has an emissivity of 0.15 and is exposed to large surroundings at 25°C. What error, in percent of this value, would be incurred by assuming all of the dissipated power to be transferred to the air by convection? Part A With water flow over the surface, the foil temperature measurement yields T, = 27°C. Determine the convection coefficient, in W/m²K. What error, in percent of this value, would be incurred by assuming all of the dissipated power to be transferred to the water by convection? ha = W/m²-K error = i % SUPPORT
A technique for measuring convection heat transfer coefficients involves bonding one surface of a thin metallic foil to an insulating material and exposing the other surface to the fluid flow conditions of interest. L Th = Foil (Pelect T) Foam Insulation (k) -Ть By passing an electric current through the foil, heat is dissipated uniformly within the foil and the corresponding flux, Pee may be inferred from related voltage and current measurements. If the insulation thickness Land thermal conductivity k are known and the fluid, foil, and insulation temperatures (T., Ts, T₁) are measured, the convection coefficient may be determined. Consider conditions for which T = T = 25°C, P =2200 W/m², L = 10 mm, and k = 0.040 W/m.K. elec (a) With water flow over the surface, the foil temperature measurement yields T, = 27°C. Determine the convection coefficient, in W/m²K. What error, in percent of this value, would be incurred by assuming all of the dissipated power to be transferred to the water by convection? (b) If, instead, air flows over the surface and the temperature measurement yields T, = 125°C, what is the convection coefficient, in W/m²K? The foil has an emissivity of 0.15 and is exposed to large surroundings at 25°C. What error, in percent of this value, would be incurred by assuming all of the dissipated power to be transferred to the air by convection? Part A With water flow over the surface, the foil temperature measurement yields T, = 27°C. Determine the convection coefficient, in W/m²K. What error, in percent of this value, would be incurred by assuming all of the dissipated power to be transferred to the water by convection? ha = W/m²-K error = i % SUPPORT
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 1.68P
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Transcribed Image Text:A technique for measuring convection heat transfer coefficients involves bonding one surface of a thin
metallic foil to an insulating material and exposing the other surface to the fluid flow conditions of interest.
L
Th
=
Foil (Pelect T)
Foam Insulation (k)
-Ть
By passing an electric current through the foil, heat is dissipated uniformly within the foil and the
corresponding flux, Pee may be inferred from related voltage and current measurements. If the insulation
thickness Land thermal conductivity k are known and the fluid, foil, and insulation temperatures (T., Ts, T₁)
are measured, the convection coefficient may be determined. Consider conditions for which T = T =
25°C, P =2200 W/m², L = 10 mm, and k = 0.040 W/m.K.
elec
(a) With water flow over the surface, the foil temperature measurement yields T, = 27°C. Determine the
convection coefficient, in W/m²K. What error, in percent of this value, would be incurred by assuming all of
the dissipated power to be transferred to the water by convection?
(b) If, instead, air flows over the surface and the temperature measurement yields T, = 125°C, what is the
convection coefficient, in W/m²K? The foil has an emissivity of 0.15 and is exposed to large surroundings at
25°C. What error, in percent of this value, would be incurred by assuming all of the dissipated power to be
transferred to the air by convection?
Part A
With water flow over the surface, the foil temperature measurement yields T, = 27°C. Determine the
convection coefficient, in W/m²K. What error, in percent of this value, would be incurred by assuming all
of the dissipated power to be transferred to the water by convection?
ha
=
W/m²-K
error =
i
%
SUPPORT
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