Fundamentals of Heat and Mass Transfer
7th Edition
ISBN: 9780470917855
Author: Bergman, Theodore L./
Publisher: John Wiley & Sons Inc
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Chapter 9, Problem 9.110P
To determine
The minimum vertical velocity of air flow.
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Students have asked these similar questions
Natural Convection:
Calculate the heat transfer rate (W) of a 4 m high and 10 m wide large vertical plate
which is maintained at 65°C and exposed to atmospheric air at 21°C, with the given
properties below:
k = 0.0275 W/m-K (thermal conductivity)
Pr= 0.7 (Prandtl Number)
Vair = 17.2x10-6 m²/s (kinematic viscosity)
Vertical plate
It
L
Round off your answer to three (3) decimal places.
Q1
(a) Differentiate between free and forced convection with examples.
(b) Define Nusselt (Nu), Prandtl (Pr), Reynolds (Re) and Grashof (Gr)
dimensionless numbers. State which numbers are used in free and forced
convection to determine the heat transfer coefficient.
(c) A vertical pipe 90 mm diameter and 2.5 m height is maintained at a
constant temperature of 125 °C, The pipe is surrounded by still
atmospheric air at 25 °C. Find heat loss by natural convection.
Properties of water at 75 °C:
Density =
1.0145 kg/m³
Kinematic viscosity = 20.55 x10-6 m²/s
Prandtl number (Pr) = 0.693
Thermal conductivity (k) = 30.06 x 10-3 W/m K
g × ß x L³ × AT
Grashof number, Gr =
V²
Nu =
0.10(GrPr)0.333
What is the rate of heat loss from a heated horizontal pipe as a resuit of natural (free) convection that have a length of 1
m and surface temperature of 100 deg C. the ambient air is at 0 deg C and the diameter of the pipe is 0.152 m. Film
temperature( Tf): averaged boundary layer temperature Tf=50 C. kf=0.03 W/m.K. Pr=0.7, v=2*10-5 m2/s, B=0.0031(1/K)
Select one:
O a. 320.0805
O b. 285.978
O . 435.6743
O d. 315.2324
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Chapter 9 Solutions
Fundamentals of Heat and Mass Transfer
Ch. 9 - The one-dimensional plane wall of Figure 3.1 is of...Ch. 9 - Using the values of density for water in Table...Ch. 9 - Consider an object of Characteristic length 0.01 m...Ch. 9 - To assess the efficacy of different liquids for...Ch. 9 - In many cases, we are concerned with free...Ch. 9 - The heat transfer rate due to free convection from...Ch. 9 - Consider a large vertical plate with a uniform...Ch. 9 - For laminar free convection flow on a vertical...Ch. 9 - Consider an array of vertical rectangular tins,...Ch. 9 - A number of thin plates are to be cooled by...
Ch. 9 - Prob. 9.11PCh. 9 - Prob. 9.13PCh. 9 - The plate described in Problem 9.14 has been used...Ch. 9 - Determine the average convection heat transfer...Ch. 9 - Consider a vertical plate of dimension 0.025m0.50m...Ch. 9 - During a winter day, the window of a patio door...Ch. 9 - Prob. 9.20PCh. 9 - A household oven door of 0.5-m height and 0.7-m...Ch. 9 - Consider a vertical, single-pane window of...Ch. 9 - Consider laminar flow about a vertical isothermal...Ch. 9 - Consider the conveyor system described in Problem...Ch. 9 - Prob. 9.25PCh. 9 - Consider an experiment to investigate the...Ch. 9 - The vertical rear window of an automobile is of...Ch. 9 - Prob. 9.28PCh. 9 - Prob. 9.29PCh. 9 - Prob. 9.30PCh. 9 - A refrigerator door has a height and width of...Ch. 9 - In the central receiver concept of a solar power...Ch. 9 - Prob. 9.34PCh. 9 - Airflow through a long, 0.2-m-square air...Ch. 9 - Prob. 9.36PCh. 9 - An electrical heater in the form of a horizontal...Ch. 9 - Consider a horizontal 6-mm-thick, 100-mm-long...Ch. 9 - Prob. 9.39PCh. 9 - Prob. 9.40PCh. 9 - Prob. 9.41PCh. 9 - Many laptop computers are equipped with thermal...Ch. 9 - Prob. 9.43PCh. 9 - At the end of its manufacturing process, a silicon...Ch. 9 - Integrated circuit (IC) boards are stacked within...Ch. 9 - Prob. 9.48PCh. 9 - Prob. 9.50PCh. 9 - Prob. 9.51PCh. 9 - Prob. 9.52PCh. 9 - Prob. 9.53PCh. 9 - Prob. 9.54PCh. 9 - Prob. 9.55PCh. 9 - Prob. 9.56PCh. 9 - Prob. 9.57PCh. 9 - A horizontal tube of 12.5-mm diameter with an...Ch. 9 - Prob. 9.60PCh. 9 - Prob. 9.61PCh. 9 - Prob. 9.63PCh. 9 - Prob. 9.64PCh. 9 - Common practice in chemical processing plants is...Ch. 9 - Consider the electrical heater of Problem 7.49. If...Ch. 9 - Prob. 9.67PCh. 9 - A billet of stainless steel, AISI 316, with a...Ch. 9 - Lone stainless steel rods of 50-mm diameter are...Ch. 9 - Hot air flows from a furnace through a...Ch. 9 - A biological fluid moves at a flow rate of...Ch. 9 - A sphere of 25-mm diameter contains an embedded...Ch. 9 - Prob. 9.79PCh. 9 - A vertical array of circuit boards is immersed in...Ch. 9 - Prob. 9.81PCh. 9 - The front door of a dishwasher of width 580 mm has...Ch. 9 - A natural convection air healer consists of an...Ch. 9 - A bank of drying ovens is mounted on a rack in a...Ch. 9 - Prob. 9.85PCh. 9 - Prob. 9.86PCh. 9 - Prob. 9.87PCh. 9 - To reduce heat losses, a horizontal rectangular...Ch. 9 - Prob. 9.89PCh. 9 - Prob. 9.90PCh. 9 - Prob. 9.91PCh. 9 - Prob. 9.92PCh. 9 - A 50-mm-thick air gap separates two horizontal...Ch. 9 - Prob. 9.94PCh. 9 - A vertical, double-pane window, which is 1 m on a...Ch. 9 - The top surface (0.5m0.5m) of an oven is 60°C for...Ch. 9 - Prob. 9.97PCh. 9 - Prob. 9.98PCh. 9 - Consider the cylindrical. 0.12-m-diamter radiation...Ch. 9 - Prob. 9.100PCh. 9 - A solar collector design consists of an inner tube...Ch. 9 - Prob. 9.104PCh. 9 - Prob. 9.105PCh. 9 - Liquid nitrogen is stored in a thin-walled...Ch. 9 - Prob. 9.108PCh. 9 - Prob. 9.109PCh. 9 - Prob. 9.110PCh. 9 - Prob. 9.111PCh. 9 - Prob. 9.114PCh. 9 - Prob. 9.115PCh. 9 - Prob. 9.116PCh. 9 - Prob. 9.117PCh. 9 - A water bath is used to maintain canisters...Ch. 9 - On a very Still morning, the surface temperature...Ch. 9 - Fuel cells similar to the PEM cell of Example 1.5...
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- A vertical cylinder 1.5m high and 180 mm in diameter is maintained at 100C in an atmosphere environment of 20C.calculate heat loss by free convection from the surface of the cylinder for air take p=1.06 kg/ m2.v=18.97*10 -6 m2/s.Cp=1.004kJ/kg2C and k=0.1042kJ/ mh2Carrow_forwardWrite the comparison between forced and free convection in a non-isothermal system?arrow_forwardThe free convection heat transfer coefficient on a thin hot vertical plate suspended in still air can be determined from observations of the change in plate temperature with time as it cools. Assuming the plate is isothermal and radiation exchange with its surroundings is negligible, evaluate the convection coefficient at the instant of time when the plate temperature is Tplate = 277 °C and the change in plate temperature with time (dT/dt) is −0.022 K/s. The ambient air temperature is Tinf = 28°C and the plate measures 0.7 × 0.7 m with a mass of 5.56 kg and a specific heat of 2,780 J/kg · K.arrow_forward
- Two vertical plates, each 200 mm high and at 90°C are placed in a tank of water at 30 °C. Calculate the minimum spacing which will prevent interference of the free convection thermal boundary layers. (k-0.674 W/mK, kinematic viscosity 0.556x 10 m/s, Pr-3.54). If the plates orientation is changed to horizontal what will be the minimum spacing which will prevent interference of the free convection thermal boundary layersarrow_forwardExperiment No. (5) Heat Transfer, Power Input and Surface temperature Questions and Discussions 1. What is the difference between natural and forced convection heat transfer? 2. What sources of error are there in this experiment? 3. Mention the parameters you utilized during the calculation and discuss them briefly. 4. In what functions does Nusselt number in natural convection differ from forced convection, Discuss. 5. Give two examples of natural convection heat transfer. 6. In natural convetion, what makes the hot part of fluid to move?arrow_forwardA sphere of 74 mm diameter is moving through the air at a velocity of 0.035 m/s. The surface temperatureof the sphere is uniform at 40◦C and the air temperature is 20◦C. What is the average convection coefficientbetween the sphere and airarrow_forward
- A double window called thermopane is one in which two layers of glass are used separated by a layer o dry stagnant air: In a given window, each of the glass layers is 6.35 mm thick separated by a 6.35 mm space of stagnant air. The thermal conductivity of the glass is 0.869 W/m K and that of air is 0.026 over the temperature range used. For temperature drop of 27.8 K over the system, calculate the heat loss for a window 0.914 m 1.83 m.arrow_forwardPlease solve ASAParrow_forwardThe rear window of an automobile is defogged by passing warm air over its inner surface. If the warm air is at Tzi and the corresponding convection coefficient is h; = 30 W/m2-K, what are the inner and outer surface temperatures, in °C, of 4-mm-thick window glass, if the outside ambient air temperature is T, = -12.5°C and the associated convection coefficient is h, = 65 W/m2-K? Evaluate the properties of the glass at 300 K. = 40°C °C °Carrow_forward
- Before introducing apples to cold storage, they should be cooled to a temperature of 3°C in order to avoid problems when exposing the hot apples to the much lower temperature in the storage. It is assumed that the apples are initially at 25°C, they are spheres of 7 cm diameter and that the cooling is carried out by means of an airstream at −1°C, to a such velocity that the heat convection coefficient is 30 W/(m2 °C). Calculate the necessary time to cool the apples so that its geometric center reaches 3°C. Data (apple properties): density, 930 kg/m3 ; thermal conductivity, 0.50 W/(m °C); specific heat, 3.6 kJ/(kg °C).arrow_forwardDifferentiate between free and forced convection with examples.arrow_forwardA food product with 80% moisture content in a 10 cm diameter can wants to be frozen. The density of the product is 1000 kg / m³, the thermal conductivity is 1.0 W / (m K), and the initial freezing temperature is -2 ° C. After 14 hours in the freezing medium -30 ° C, the product temperature becomes -10 ° C. Estimate the convection heat transfer coefficient of the freezing medium. Assume the can as an infinite cylinder.arrow_forward
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