Fundamentals of Heat and Mass Transfer
7th Edition
ISBN: 9780470501979
Author: Frank P. Incropera, David P. DeWitt, Theodore L. Bergman, Adrienne S. Lavine
Publisher: Wiley, John & Sons, Incorporated
expand_more
expand_more
format_list_bulleted
Videos
Textbook Question
Chapter 9, Problem 9.5P
In many cases, we are concerned with free convection involving gases that are contained within sealed enclosures. Consider air at 27°C and pressures of 1, 10, and 100 bars. Determine the figure of merit described in Problem 9.4 for each of these three pressures. Which air pressure will provide the most effective cooling? Hint: See Problem 6.22.
Expert Solution & Answer
Want to see the full answer?
Check out a sample textbook solution
Students have asked these similar questions
The onset of free convection. Plastic shrink wrap can be used to insulate windows by trapping air between your window and the wrapping. Calculate the critical gap width between the plastic and the window at which free convection will occur on an average winter’s day, when the outside temperature is 41°F and the inside temperature is 68°F. Would you expect there to be more or less heat transfer when the spacing is above this gap? Explain.
A thin plate with a length of 0.5m is cooled by vertical suspension in a very large box filled with quiescent carbon monoxide at a temperature of 44°C. If the plate surface temperature is 80°C, please answer the following:
1. What is the thickness of the free convection boundary layer at the upper edge of the plate?
2. What is the velocity in the x-direction at half the plate length?
3. Calculate the average Nusselt number for the plate. Justify your choice of correlation
Problem: Convection related
A horizontal uninsulated steam pipe passes through a large room whose walls and ambient air are at 300 K. The pipe of 125-mm diameter has an emissivity of 0.85 and an outer surface temperature of 373 K. Calculate the rate of heat loss per unit length from the pipe.
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...
Knowledge Booster
Learn more about
Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, mechanical-engineering and related others by exploring similar questions and additional content below.Similar questions
- 1.13 If the outer air temperature in Problem is –2°C, calculate the convection heat transfer coefficient between the outer surface of the window and the air, assuming radiation is negligible.arrow_forwardA horizontal steam pipe with an outside diameter of 60.0 mm passes through a large room whose walls are at a temperature of 298 K. The outer surface of the pipe wall has a surface temperature of 443 K and an emissivity of 0.8. The air temperature in the room is 303 K. Calculate the rate of heat loss per unit length of the pipe by radiation and natural convection.arrow_forward1-mm-diameter cylindrical resistor, insulated with a sheath of thermal conductivity, k, of 0.12 W/m-K, is located in an evacuated enclosure. The surface emissivity of the sheath is 0.85. The resistor is maintained at 450 K and the enclosure is at 300 K. What is the radius of the sheath that maximises the rate of heat loss from the resistor? Evaluate the corresponding maximum heat rate per unit length of the resistor and the sheath surface temperature. Determine the value of the parameter hirerlk where h, is the linearised radiation heat transfer coefficient at the critical radius, rer. Comment on your results. State all assumptions made. What is the rate of heat loss per unit length from the uninsulated resistor if its surface emissivity is the same as the sheath surface of the insulated resistor?arrow_forward
- A plate (0.5 m * 0.5 m) is inclined at an angle of 30°. The top surface of the plate is well insulated. Estimate the rate of heat loss from the plate when the bottom surface is maintained at 60°C and the surrounding atmospheric quiescent air is at 0°C.arrow_forwardCalculate the free convection heat transfer coefficient for a plate 6 ft high and 8 ft wide at 120 °F that is exposed to nitrogen at 60 °F. (see attached)arrow_forwardQuestion One Explain how heat is transferred from one point to another illustrating with appropriate diagram. Calculate the heat flow per square meter (heat flux) through water medium with thermal conductivity of 0.6, flowing in a 5 cm thickness space, if the temperatures on the two surfaces are 50 and 210°C, respectively. Question 2 Distinguish between force and free convection with the aid of appropriate illustrations. What is the approximate temperature difference between a hot plate and the surrounding air if the heat flux from the plate is 800 W/m2? Assume that the air is flowing past the surface with a velocity of 5 m/s giving a heat transfer coefficient of 20 W/(m2K). Question 3 Explain the differences between laminar and turbulent flow Water (ν = 0.86x10-6m2/s) flows through a tube with the diameter 12 mm at a velocity of 2 m/s. Determine if the flow is laminar or turbulent!arrow_forward
- Question: a) We want to increase heat transfer by placing fans to provide forced convection to reduce the length of the pipe necessary (Note that the outside surface temperature of the pipe remains the same at 100oC). What is the rate of heat transfer from pipe to the air per meter length if the air speed over the pipe surface is 5m/s? What is the total length of the pipe necessary? Problem: Consider a rectangular warehouse with the dimensions of 40m long x 20m widex10m height. The overall heat transfer coefficient for all sidewalls is Uwall=0.3 W/m2K (Approx. R=20 hr.ft2.oF/Btu) and for the flat roof, it is Uroof= 0.20W/m2K. The floor can be assumed to be insulated and we can ignore the heat transfer through the doors, etc. We want to maintain the inside air temperature at 15oC while the outside temperature is 0oC by using a thin-walled, 5.0cm diameter copper pipe that carries steam. Steam enters the pipe as saturated vapor at 100oC. So, as it starts losing heat to the inside air, it…arrow_forwardArrays of parallel equally spaced vertical thin plates are connected to the surface of a natural convection air heater. The plates are maintained at a fixed temperature of 75°C by embedding electrical heaters. The plates are 305-mm high and 305-mm long. The whole set-up is in an area where the air temperature is 20°C. The total width of the array cannot exceed 150-mm. What is the plate spacing in millimeters that maximizes heat transfer from the array?arrow_forwardA loaf of bread having a surface temperature of 373 K is being baked in an oven whose walls and the air are at 477.4 K. The bread moves continuously through the large oven on an open chain belt conveyor. The emissivity of the bread is estimated to be 0.85, and the loaf can be assumed to be a rectangular solid 114.3 mm high × 114.3 mm wide × 330 mm long. Calculate the radiation heat-transfer rate (in SI and AES units) to the bread, assuming that it is small compared to the oven and neglecting natural convection heat transfer.arrow_forward
- The production line of a special biscuit at 30 ̊C and 1 atm has a 0.8 X 0.8 (m) square plate. One side of the plate is maintained at a temperature of 100 ̊C, while the other side is insulated. Determine the rate of heat transfer from the plate by natural convection if the plate (i) Is horizontal with the hot surface facing down; (ii) Is horizontal with the hot surface facing up; Data: The properties of air at the film temperature are: thermal conductivity, k= 0.0279 W/m.k); kinematic viscosity= 1.815 x 10-5 m2/s; Pr = 0.709arrow_forwardA cylinder 6”in diameter and 18”long is suspended horizontally in a largeroom. The air and wall surfaces of the room are at a temperature of 60 °Fwhile the surface temperature of the cylinder is 440 °F. Compute (a) thesurface coefficient due to free convection, (b) the heat transferred by freeconvection (neglecting the end areas), (c) the surface coefficient due toradiation if the surface emissivity is 0.75, and (d) the total heattransferred by free convection and radiation (neglecting end areas)arrow_forwardA school classroom is 16.7m long, 10m wide and 3 .5m high. There is a 4m x 6m window in the east wall. Only the east wall/window is exterior. Assume the thermal conditions in adjacent spaces (west, south, north, above and below) are the same as those of the classroom. Determine the cooling load at2:00 pm, 21 July as maximum Other known conditions include: Latitude = 36o N Ground reflectance = 0.2 Clear sky with a clearness number = 1.0 Overall window heat transmission coefficient = 7.0 W/m2.K Room dry-bulb temperature = 25°C Permissible temperature exceeded = 2.5% Schedule of occupancy: 7people enter at 10:00am and stay for 12 hours Lighting schedule: 300 W on at 10:00AM for 12hours Exterior wall structure: • Outside surface, A0 • Face brick (100 mm), A2 • Insulation (50 mm), B3 • Concrete block (100 mm), C3 • Exterior window: •double glazing window • No exterior shading, SC = 1.0arrow_forward
arrow_back_ios
SEE MORE QUESTIONS
arrow_forward_ios
Recommended textbooks for you
Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning
Principles of Heat Transfer (Activate Learning wi...
Mechanical Engineering
ISBN:9781305387102
Author:Kreith, Frank; Manglik, Raj M.
Publisher:Cengage Learning
Heat Transfer – Conduction, Convection and Radiation; Author: NG Science;https://www.youtube.com/watch?v=Me60Ti0E_rY;License: Standard youtube license