The sensible heat-transfer coefficient for a dry surface has been determined to be 50 W/(m2-C) at a certain Reynolds number. Estimate the total heat transfer to the surface per unit area at a location where the wall temperature is 10 C and the state of the moist air flowing over the surface is given by 24 C dry bulb and 18 C wet bulb. Assume that the Reynolds number does not change and the Lewis number is 0.82. Assume that the condensate present on the surface will increase the transfer coefficients by about 15 percent.

The sensible heat-transfer coefficient for a dry surface has been determined to be 50 W/(m2-C) at a certain Reynolds number. Estimate the total heat transfer to the surface per unit area at a location where the wall temperature is 10 C and the state of the moist air flowing over the surface is given by 24 C dry bulb and 18 C wet bulb. Assume that the Reynolds number does not change and the Lewis number is 0.82. Assume that the condensate present on the surface will increase the transfer coefficients by about 15 percent.

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.

Chapter9: Heat Transfer With Phase Change

Section: Chapter Questions

Problem 9.21P

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The sensible heat-transfer coefficient for a dry surface has been determined to be 50 W/(m2-C) at a certain Reynolds number. Estimate the total heat transfer to the surface per unit area at a location where the wall temperature is 10 C and the state of the moist air flowing over the surface is given by 24 C dry bulb and 18 C wet bulb. Assume that the Reynolds number does not change and the Lewis number is 0.82. Assume that the condensate present on the surface will increase the transfer coefficients by about 15 percent
Water at 900 C and a rate of 0.5 kg/s is cooled to 45° C in a copper pipe of 2 cm outer diameter and 2 mm thickness by a vapor that is condensing on its outer surface at 30° C: a. Determine the pipe length. b. Determine the pressure drop.
Saturated steam at 20 psia is condensing at a vertical plate with a width of 1.211 m and a height of 1 m. The surface temperature of the wall is measured as 212 °F. Determine: A. Heat transfer coefficient. B. Heat transfer rate of the vertical plate. C. If the vertical plate will be welded at each side to form a cylinder with the same height, calculate the new values of heat transfer coefficient and heat transfer rate of the vertical cylinder.
The condensation process of vapors on the outside of horizontal tube banks is described by the equation below, NNU = 0.725 (gp² hfg Do³) μ Δt Ν k where N tubes/row At = hfg Density, p Dynamic viscosity, μ Latent heat, hfg Thermal conductivity, k AT = difference between wall surface & R-22 NNu 3 1,109 kg/m 0.00018 Pa s = Refrigerant - 22 condenser operating at 45 C cooled with water from cooling tower entering at 30 C and leaves at 36 C. The condenser is shell-tube type with copper tubes of 14 mm ID & 16 mm OD arranged with 3 tubes per row (N). a) Considering the results of sample problem #2 (fw = 6,909.4 W/m²K film coefficient at water side), compute the overall heat transfer coefficient based on outer surface area in W/m² K of a water-cooled shell-tube R-22 condenser. At 45 C R-22 properties are: 160.9 kJ/ kg 0.0779 W/m K (*50-45) = 5 C (*from sample problem #2 pipe wall temperature) diff. of temp between wall & fluid latent heat of condensation generally a function of (NR₂. Nor) D/ k
The condensation process of vapors on the outside of horizontal tube banks is described by the equation below, NNU = 0.725 (g p² hfg Do³) μ Δt Ν κ At 45 C R-22 properties are: Density, p Dynamic viscosity, μ Latent heat, hfg Thermal conductivity, k where N tubes/row At = hfg AT = difference between wall surface & R-22 NNu Refrigerant - 22 condenser operating at 45 C cooled with water from cooling tower entering at 30 C and leaves at 36 C. The condenser is shell-tube type with copper tubes of 14 mm ID & 16 mm OD arranged with 3 tubes per row (N). a) Compute the convective heat transfer of R-22 in W/m²K. = 1,109 kg/m³ 0.00018 Pa s 160.9 kJ/kg 0.0779 W/m K (*50-45) = 5 C (*from sample problem #2 pipe wall temperature) diff. of temp between wall & fluid latent heat of condensation generally a function of (NR₂. Npr) D/ k
Air at 25°C and atmospheric pressure flows with a velocity of 3 m/s inside a 10mm diameter tube of 1 m length. The inside surface of the tube contains a deposit of naphthalene. Determine the average mass transfer coefficient for the transfer of naphthalene from the pipe surface into the air.
Which of the following is not an assumption that Nusselt made in analytically deriving the average heat transfer coefficient over a vertical surface surrounded by vapor undergoing film condensation? A. Film thickness is zero at the top of surface B. Falling film is undergoing laminar flow C. Heat transfer from the condensing vapor to the surface is happening via natural convection D. All the assumptions above are important to the film condensation problem
Water at atmospheric pressure is boiled in a container using a horizontal 8 mm electric wire (ε=0.9) whose temperature is maintained by an electric current at 250oC. Estimate the boiling heat transfer coefficient between the water and the wire surface. Properties of Water, liquid: ρl = 957.9 kg/m3, hfg = 2257 kJ/kg, vapor: ρv = 4.8 kg/m3, Cp,v = 2560 J/kg.K, μv = 14.85*10-6 N.s/m2, kv=0.0331 W/mK. Select one: a. 247 W/m2K b. 440 W/m2K c. 90.7 W/m2K d. 710 W/m2K
From an open water surface with air temperature 22°C, relative humidity is 40% and wind speed is 3 m/s, all measured at height 2 m above the water surface. Assume a roughness height of 0.03 cm. The net radiation is 200 W/m^2. Cp = 1005 J/kg-K A. Calculate the latent heat of vaporization (J/kg) B. Calculate the evaporation using Energy Balance Method (mm/day) C. Calculate the saturation deficit of the vapor pressure (Pa) D. Calculate the evaporation using Priestley-Taylor Method (mm/day)
Saturated steam at 1 atm condenses on a 3-m-high and 5-m-wide vertical plate that is maintained at 90 0C by circulating cooling water through the other side. Determined (a) the rate of heat transfer by condensation to the plate, and (b) the rate at which the condensate drips off the plate at the bottom (Please use the condensation formulations at the Geankoplis).
Water is to be boiled at atmospheric pressure in a polished copper pan by means of an electric heater. The diameter of the pan is 0.48 m and is kept at 108 deg C. What is the power required to boil the water? Tsat 100°C; Properties of water at 100°C: Density, pl= 961 kg/m3; Kinematic viscosity, v = 0.293x10-6 m2/s: Prandti Number. Pr 1.740; Specific heat, Cpl = 4216 J/kg.K; Dynamic viscosity, u = p x v = 961 x 0.293 x 10-6 = 281.57 x10-6 Ns/m2; hfg 2256.9 kJ/kg; pv = 0.597 kg/m3; a = 0.0588 N/m; Csf=0.013; n=1: %3D Select one: O a. 11633.5098 O b. 13259.1393 O c. 16641.2421 O d. 9493.7946
Saturated, pure steam at a temperature of 170 oC condenses on the outer surface of a vertical tube of outer diameter 2 cm and length 1.5 m. The tube surface is maintained at a uniform temperature of 150 oC. Calculate: the local film condensation heat-transfer coefficient at the bottom of the tube. the average condensation heat-transfer coefficient over the entire length of the tube. the total condensation rate at the tube surface.