introduces a practical solution

... the maximum amount of radiation at a given temperature and which absorbs all the radiation incident on it Real bodies emit and absorb less radiation than a blackbody at the same temperature ... the surface The Kirchhoff's law of radiation states that the emissivity and the absorptivity of a surface are equal at the same temperature and wavelength 1-46C A blackbody is an idealized body ... is the ratio of the radiation emitted by a surface to the radiation emitted by a blackbody at the same temperature Absorptivity is the fraction of radiation incident on a surface that is absorbed

Ngày tải lên: 07/03/2018, 16:28

... often impractical The analytical approach (analysis or calculations) has the advantage that it is fast and inexpensive, but the results obtained are subject to the accuracy of the assumptions and ... the cracks as the heated air in the house expands at constant pressure The amount of heat transfer to the air and its cost are to be determined Assumptions 1 Air as an ideal gas with a constant ... actually running expensive and time-consuming experiments When preparing a mathematical model, all the variables that affect the phenomena are identified, reasonable assumptions and approximations

Ngày tải lên: 07/03/2018, 16:28

... surface The mathematical formulation, the variation of temperature, and the rate of evaporation of oxygen are to be determined for steady one-dimensional heat transfer Assumptions 1 Heat conduction ... inner and outer surfaces The mathematical formulation, the variation of temperature, and the temperatures at the inner and outer surfaces to be determined for steady one-dimensional heat transfer ... = −+ Trang 42-132 The base plate of an iron is subjected to specified heat flux on the left surface and convection and radiation on the right surface The mathematical formulation, and an expression

Ngày tải lên: 07/03/2018, 16:28

... radiation by water is modeled as heat generation Analysis The total rate of heat generation in a water layer of surface area A and thickness L at the top of the pond is determined by integration ... any location is A=2πrL where r is the value of the radius at that location Note that the heat transfer area A depends on r in this case, and thus it varies with location An energy balance on ... may vary from one location to another During transient heat transfer, the temperature and heat flux may vary with time as well as location Heat transfer is one-dimensional if it occurs primarily

Ngày tải lên: 07/03/2018, 16:28

... q s &s &s & Noting that heat transfer is one-dimensional in the radial r direction and heat flux is in the negative r direction, the mathematical formulation of this problem can be ... uniform heat flux on the outer surface and specified temperature on the inner surface The mathematical formulation, the variation of temperature in the pipe, and the outer surface temperature, and ... chemical reactions in a solid, and nuclear reactions in nuclear fuel rods 2-76C The rate of heat generation inside an iron becomes equal to the rate of heat loss from the iron when steady operating

Ngày tải lên: 07/03/2018, 16:28

... that the fin acts as insulation 3-100C Fins enhance heat transfer from a surface by increasing heat transfer surface area for convection heat transfer However, adding too many fins on a surface ... of heat transfer from a surface by increasing the heat transfer surface area 3-98C The fin efficiency is defined as the ratio of actual heat transfer rate from the fin to the ideal heat transfer ... 2 fin wall fin one fin base fins total π θb c h A n A q n q q q& & & Trang 93-115 A commercially available heat sink is to be selected to keep the case temperature of a transistor

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... resistances at a surface are parallel since both the convection and radiation heat transfers occur simultaneously 3-8C For a surface of A at which the convection and radiation heat transfer coefficients ... Trang 1Chapter 3 STEADY HEAT CONDUCTION Steady Heat Conduction in Plane Walls 3-1C (a) If the lateral surfaces of the rod are insulated, the heat transfer surface area of the cylindrical rod ... a a g g L k L k L h T A Q& (b) Noting that the largest resistance is through the air gap, the temperature difference across the air gap is m005.0 W) 210( 2 A k L Q R Q T a a a a & &

Ngày tải lên: 07/03/2018, 16:28

... resistances indicate simultaneous heat transfer (such as convection and radiation on a surface) Series resistances indicate sequential heat transfer (such as two homogeneous layers of a wall) ... b a b a 2 W/m 125 C)2035(2 total 1 4 R T T q& Trang 63-54 A wall consists of horizontal bricks separated by plaster layers There are also plaster layers on each side of the wall, and a rigid ... voids at an interface is by conduction and radiation Evacuating the interface eliminates heat transfer by conduction, and thus increases the thermal contact resistance 3-45C Thermal contact resistance

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... surrounding medium and surfaces are at the same temperature, the radiation and convection heat transfer coefficients can be added and the result can be taken as the combined heat transfer coefficient ... Trang 13-71 A spherical container filled with iced water is subjected to convection and radiation heat transfer at its outer surface The rate of heat transfer and the amount of ice that melts ... properties of water at room temperature, ρ = 1000 kg/m3 and cp = 4180 J/kg.°C Analysis This is a transient heat conduction, and the rate of heat transfer will decrease as the drink warms up and the

Ngày tải lên: 07/03/2018, 16:28

... radiation effects 5 The temperatures of the pipe surface and the surroundings are representative of annual average during operating hours 6 The plant operates 110 days a year Analysis The rate ... 3-184 A cylindrical tank containing liquefied natural gas (LNG) is placed at the center of a square solid bar The rate of heat transfer to the tank and the LNG temperature at the end of a one-month ... W/m7( 11 glass o, glass glass i, glass total, 2 2 glass 2 glass o, 2 glass glass glass glass 2 2 glass 1 glass i, ° =+ + =+ R A h R A k L R A h R W2.214C)2440( 1 Q& Trang 223-179 Steam is flowing

Ngày tải lên: 07/03/2018, 16:28

... have larger resistances against heat conduction 4-7C The heat transfer is proportional to the surface area Two half pieces of the roast have a much larger surface area than the single piece and ... in ambient air at a specified rate The time of annealing and the total rate of heat transfer from the balls to the ambient air are to be determined Assumptions 1 The balls are spherical in shape ... indicates that the ball bearing can stay in the air about 4 s before being dropped into the water Trang 144-25 A number of carbon steel balls are to be annealed by heating them first and then allowing

Ngày tải lên: 07/03/2018, 16:28

... Trang 14-50 A hot dog is dropped into boiling water, and temperature measurements are taken at certain time intervals The thermal diffusivity and thermal conductivity of the hot dog and the ... 84-56 A hot baked potato is taken out of the oven and wrapped so that no heat is lost from it The time the potato is baked in the oven and the final equilibrium temperature of the potato after ... the data and the answers given in Prob 4-50, the center and the surface temperatures of the hot dog 4 min after the start of the cooking and the amount of heat transferred to the hot dog are to

Ngày tải lên: 07/03/2018, 16:28

... water are constant Properties The density and heat of vaporization of the water are ρ = 1000 kg/m3 and hfg = 2490 kJ/kg (Table A-9) Analysis The initial and final masses of the raindrop are ... Trang 44-114 A long roll of large 1-Mn manganese steel plate is to be quenched in an oil bath at a specified rate The temperature of the sheet metal after quenching and the rate at which heat ... will take for the diameter of a raindrop to reduce to a certain value as it falls through ambient air is to be determined Assumptions 1 The water temperature remains constant 2 The thermal properties

Ngày tải lên: 07/03/2018, 16:28

... exposed surface area there Noting that and assuming that τ > 0.2 in all dimensions so that the one-term approximate solution for transient heat conduction is applicable, the product solution ... two-dimensional, and thus the temperature varies in both axial x- and radial r- directions 3 The thermal properties of the granite are constant 4 The heat transfer coefficient is constant and uniform ... W/m.°C and α = 0.124×10-7 m2/s Analysis This rectangular ice block can be treated as a short rectangular block that can physically be formed by the intersection of two infinite plane wall of

Ngày tải lên: 07/03/2018, 16:28

... A region that cannot be filled with simple volume elements such as strips for a plane wall, and rectangular elements for two-dimensional conduction is said to have irregular boundaries A practical ... G Q Q Q for the steady case Again assuming the temperatures between the adjacent nodes to vary linearly and noting that the heat transfer area is Δy×1 in the x direction and Δx×1 in the y direction, ... by calculating the heat loss from the outer surface by convection and radiation Trang 185-58 Heat transfer through a square chimney is considered The nodal temperatures and the rate of heat

Ngày tải lên: 07/03/2018, 16:28

... α=0.44×10−6m2/s, and κ =0.76 The hourly variation of monthly average ambient temperature and solar heat flux incident on a vertical surface is given to be Time of day Ambient Temperature, °C Solar insolation ... equation for boundary nodes 0 and 6 are obtained by applying an energy balance on the half volume elements and taking the direction of all heat transfers to be towards the node under consideration: ... law of cooling using the average temperature at the inner surface of the wall (node 0) as t T T T A h t T T A h t Q ]2/)[( ) in wall Trumbe wall Trumbe & Therefore, the amount of heat transfer

Ngày tải lên: 07/03/2018, 16:28

... surface, or the radiation heat transfer on the surfaces can make it impossible to obtain an analytical solution Therefore, analytical solutions are limited to problems that are simple or can be ... equation as described in Chap 2, and the analytical (exact) solution can be used to check the accuracy of the numerical solution above •0 •5Insulated h, T∞ Trang 105-25 A long triangular fin attached ... Heat transfer at left surface: left surface 1 0 =0 Δ −+ x T T kA Q& Trang 55-17 A plane wall with variable heat generation and constant thermal conductivity is subjected to uniform heat

Ngày tải lên: 07/03/2018, 16:28

... of partial differential equations into a single ordinary differential equation is called a similarity variable A similarity solution is likely to exist for a set of partial differential equations ... to enhanced mixing that cause the friction factor to Convection Equations and Similarity Solutions 6-26C A curved surface can be treated as a flat surface if there is no flow separation and the ... components u and v, and the temperature T at the plate surface and at the edge of the boundary layer are expressed as follows: 6-32C An independent variable that makes it possible to transforming a set

Ngày tải lên: 07/03/2018, 16:28

... temperature of air, and thus the mean temperature, is not known We evaluate the air properties at the assumed mean temperature of 20°C (will be checked later) and 1 atm (Table A-15): Analysis ... same as that on the side surfaces Properties The properties of water at 80°C are (Table A-9) CJ/kg 4197 kg/m8 Water tank D =50 cm L = 95 cm The properties of air at 1 atm and at the anticipated ... period and the money the facility will save a year as a result of insulating the steam pipes are to be determined Assumptions 1 Steady operating conditions exist 2 Air is an ideal gas with constant

Ngày tải lên: 07/03/2018, 16:28

... frontal area of a body is the area seen by a person when looking from upstream The frontal area is appropriate to use in drag and lift calculations for blunt bodies such as cars, cylinders, and ... W/m26.62() =hA T T∞ Q& s s (c) Assuming a uniform distribution of heat transfer and drag parameters over the plate, the average gradients of the velocity and temperature at the surface are determined ... Trang 97-20 Air flows over the top and bottom surfaces of a thin, square plate The flow regime and the total heat transfer rate are to be determined and the average gradients of the velocity and

Ngày tải lên: 07/03/2018, 16:28