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engineering
heat and mass transfer fundamentals and applications

Questions and Answers of Heat And Mass Transfer Fundamentals And Applications

Friction coefficient of air flowing over a flat plate is given as Cf = 0.664(Vx/v)-0.5, where x is the location along the plate. Using EES (or other) software, determine the effect of the air
Air flowing over a flat plate at 5 m/s has a friction coefficient given as Cf = 0.664(Vx/v)-0.5, where x is the location along the plate. Using EES (or other) software, determine the effect of the
Consider a flat plate positioned inside a wind tunnel, and air at 1 atm and 20°C is flowing with a free stream velocity of 60 m/s. What is the minimum length of the plate necessary for the Reynolds
Air flows over a flat plate at 40 m/s, 25°C and 1 atm pressure.(a) What plate length should be used to achieve a Reynolds number of 1 × 108 at the end of the plate?(b) If the critical Reynolds
Consider fluid flowing with a free stream velocity of 5 m/s over a flat plate, where the critical Reynolds number is 5 × 105. Determine the distance from the leading edge at which the transition
Consider fluid flowing with a free stream velocity of 1 ft/s over a flat plate, where the critical Reynolds number is 5 × 105. Determine the distance from the leading edge at which the transition
Consider steady, laminar, two-dimensional, incompressible flow with constant properties and a Prandtl number of unity. For a given geometry, is it correct to say that both the average friction and
Express continuity equation for steady two-dimensional flow with constant properties, and explain what each term represents.
Is the acceleration of a fluid particle necessarily zero in steady flow? Explain.
For steady two-dimensional flow, what are the boundary layer approximations?
For what types of fluids and flows is the viscous dissipation term in the energy equation likely to be significant?
For steady two-dimensional flow over an isothermal flat plate in the x-direction, express the boundary conditions for the velocity components u and v, and the temperature T at the plate surface and
What is a similarity variable, and what is it used for? For what kinds of functions can we expect a similarity solution for a set of partial differential equations to exist?
Consider steady, laminar, two-dimensional flow over an isothermal plate. Does the thickness of the velocity boundary layer increase or decrease with(a) Distance from the leading edge,(b) Free-stream
Consider steady, laminar, two-dimensional flow over an isothermal plate. Does the wall shear stress increase, decrease, or remain constant with distance from the leading edge?
What are the advantages of nondimensionalizing the convection equations?
Under what conditions can a curved surface be treated as a flat plate in fluid flow and convection analysis?
Oil flow in a journal bearing can be treated as parallel flow between two large isothermal plates with one plate moving at a constant velocity of 12 m/s and the other stationary. Consider such a flow
Consider a 5-cm-diameter shaft rotating at 4000 rpm in a 25-cm-long bearing with a clearance of 0.5 mm. Determine the power required to rotate the shaft if the fluid in the gap is(a) Air,(b)
Repeat Prob. 6–59 for a spacing of 0.4 mm.Data from problem 59Oil flow in a journal bearing can be treated as parallel flow between two large isothermal plates with one plate moving at a constant
Consider the flow of fluid between two large parallel isothermal plates separated by a distance L. The upper plate is moving at a constant velocity of V and maintained at temperature T0 while the
Reconsider Prob. 6–61. Using the results of this problem, obtain a relation for the volumetric heat generation rate ėgen, in W/m3. Then express the convection problem as an equivalent conduction
A 6-cm-diameter shaft rotates at 3000 rpm in a 20-cm-long bearing with a uniform clearance of 0.2 mm. At steady operating conditions, both the bearing and the shaft in the vicinity of the oil gap are
Consider a large plane wall of thickness L = 0.4 m, thermal conductivity k = 2.3 W/m · K, and surface area A = 20 m2. The left side of the wall is maintained at a constant temperature of 95°C,
A large steel plate having a thickness of L = 5 in, thermal conductivity of k = 7.2 Btu/h · ft·°F, and an emissivity of ε = 0.6 is lying on the ground. The exposed surface of the plate exchanges
Repeat Prob. 5–32E by disregarding radiation heat transfer from the upper surface.Data from problem 32A large steel plate having a thickness of L = 5 in, thermal conductivity of k = 7.2 Btu/h ·
Reconsider Prob. 6–63. Using EES (or other) software, investigate the effect of shaft velocity on the mechanical power wasted by viscous dissipation. Let the shaft rotation vary from 0 rpm to 5000
A 5-cm-diameter shaft rotates at 4500 rpm in a 15-cmlong, 8-cm-outer-diameter cast iron bearing (k = 70 W/m · K) with a uniform clearance of 0.6 mm filled with lubricating oil (m = 0.03 N·s/m2 and
Repeat Prob. 6–66 for a clearance of 1 mm.Data from problem 66A 5-cm-diameter shaft rotates at 4500 rpm in a 15-cmlong, 8-cm-outer-diameter cast iron bearing (k = 70 W/m · K) with a uniform
Water at 20°C is flowing with velocity of 0.5 m/s between two parallel flat plates placed 1 cm apart. Determine the distances from the entrance at which the velocity and thermal boundary layers
Glycerin at 50°F is flowing over a flat plate at a free stream velocity of 6 ft/s. Determine the velocity and thermal boundary layer thicknesses at a distance of 0.5 ft from the leading edge. Also
Consider a laminar boundary layer flow over a flat plate. Determine the δ/δt ratios for air (at 1 atm), liquid water, isobutane, and engine oil, and mercury. Evaluate all properties at 50°F.
For laminar boundary layers it is reasonable to expect that δ/δt ≈ Prn, where n is a positive exponent. Consider laminar boundary layer flow over a flat plate with air at 100ºC and 1 atm, the
Air at 15°C and 1 atm is flowing over a 0.3-mlong plate at 65°C at velocity of 3.0 m/s. Using EES, Excel, or other software, plot the following on a combined graph for the range of x = 0.0 m to x =
Liquid water at 15°C is flowing over a 0.3-m-wide plate at 65°C a velocity of 3.0 m/s. Using EES, Excel, or other comparable software, plot(a) The hydrodynamic boundary layer(b) The thermal
Saturated liquid water at 5°C is flowing over a flat plate at a velocity of 1 m/s. Using EES (or other) software, determine the effect of the location along the plate (x) on the velocity and thermal
Mercury at 0°C is flowing over a flat plate at a velocity of 0.1 m/s. Using EES (or other) software, determine the effect of the location along the plate (x) on the velocity and thermal boundary
Water vapor at 0°C and 1 atm is flowing over a flat plate at a velocity of 10 m/s. Using EES (or other) software, determine the effect of the location along the plate (x) on the velocity and thermal
Consider a laminar ideal gas flow over a flat plate, where the local Nusselt number can be expressed as Nux = 0.332Rex1/2 Pr1/3. Using the expression for the local Nusselt number, show that it can
Consider air flowing over a 1-m-long flat plate at a velocity of 3 m/s. Determine the convection heat transfer coefficients and the Nusselt numbers at x = 0.5 m and 0.75 m. Evaluate the air
Air with a temperature of 20°C is flowing over a flat plate (k = 15 W/m · K) at a velocity of 3 m/s. The plate surface temperature is maintained at 60°C. Using EES (or other) software, determine
For laminar flow over a flat plate the local heat transfer coefficient varies as hx = Cx-0.5, where x is measured from the leading edge of the plate and C is a constant. Determine the ratio of the
An airfoil with a characteristic length of 0.2 ft is placed in airflow at 1 atm and 60°F with free stream velocity of 150 ft/s and convection heat transfer coefficient of 21 Btu/h·ft2·8F. If a
How is Reynolds analogy expressed? What is the value of it? What are its limitations?
Air at 15ºC and 1 atm flows over a 0.3-m-wide plate at 65ºC at a velocity of 3.0 m/s. Compute the following quantities at x = 0.3 m:(a) Hydrodynamic boundary layer thickness, m(b) Local friction
Reconsider Prob. 7–19E. Using EES (or other) software, evaluate the local friction and heat transfer coefficients along the plate at intervals of 0.1 ft, and plot them against the distance from the
A 12-ft-long, 1.5-kW electrical resistance wire is made of 0.1-in-diameter stainless steel (k = 8.7 Btu/h. ft. °F). The resistance wire operates in an environment at 85°F. Determine the surface
Repeat Prob. 6–63 by assuming the shaft to have reached peak temperature and thus heat transfer to the shaft to be negligible, and the bearing surface still to be maintained at 50°C.Data from
Reconsider Prob. 8–70. Using the EES (or other) software, evaluate the effect of glycerin mass flow rate on the free-stream velocity of the hydrogen gas needed to keep the outlet mean temperature
Reconsider Prob. 9–33. Using EES (or other) software, investigate the effects of the room temperature and the emissivity of the board on the temperature of the hot surface of the board for
Reconsider Prob. 9–78E. Using EES (or other) software, investigate the effect of the length of the fins in the vertical direction on the optimum fin spacing and the rate of heat transfer by natural
What is boiling? What mechanisms are responsible for the very high heat transfer coefficients in nucleate boiling?
Name the different boiling regimes in the order they occur in a vertical tube during flow boiling.
What is the difference between pool boiling and flow boiling?
Draw the boiling curve and identify the different boiling regimes. Also, explain the characteristics of each regime.
How does film boiling differ from nucleate boiling? Is the boiling heat flux necessarily higher in the stable film boiling regime than it is in the nucleate boiling regime?
Draw the boiling curve and identify the burnout point on the curve. Explain how burnout is caused. Why is the burnout point avoided in the design of boilers?
Discuss some methods of enhancing pool boiling heat transfer permanently.
Water is boiled at 120°C in a mechanically polished stainless-steel pressure cooker placed on top of a heating unit. The inner surface of the bottom of the cooker is maintained at 130°C. Determine
A platinum-plated rod with a diameter of 10 mm is submerged horizontally in water at atmospheric pressure. If the surface of the rod is maintained at 10°C above the saturation temperature, determine
A 65-cm-long, 2-cm-diameter brass heating element is to be used to boil water at 120°C. If the surface temperature of the heating element is not to exceed 125°C, determine the highest rate of steam
Water is to be boiled at atmospheric pressure in a mechanically polished steel pan placed on top of a heating unit. The inner surface of the bottom of the pan is maintained at 110°C. If the diameter
Water is boiled at atmospheric pressure by a horizontal platinum-plated rod with diameter of 10 mm. If the surface temperature of the rod is maintained at 110°C, determine the nucleate pool boiling
A 1-mm diameter-long electrical wire submerged in water at atmospheric pressure is dissipating 4100 W/m of heat, and the surface temperature reaches 128°C. If the experimental constant that depends
Water is boiled at sea level in a coffee maker equipped with a 20-cm-long 0.4-cm-diameter immersion-type electric heating element made of mechanically polished stainless steel. The coffee maker
Repeat Prob. 10–16 for a copper heating element.Data from problem 16Water is boiled at sea level in a coffee maker equipped with a 20-cm-long 0.4-cm-diameter immersion-type electric heating element
Repeat Prob. 10–18 for a polished copper pan.Data from problem 18Water is boiled at 1 atm pressure in a 20-cm-internaldiameter Teflon®-pitted stainless-steel pan on an electric range. If it is
Water is boiled at 1 atm pressure in a 20-cm-internaldiameter Teflon®-pitted stainless-steel pan on an electric range. If it is observed that the water level in the pan drops by 10 cm in 15 min,
Exposure to high concentration of gaseous ammonia can cause lung damage. To prevent gaseous ammonia from leaking out, ammonia is transported in its liquid state through a pipe (k = 25 W/m · K, Di,
Reconsider Prob. 10–21E. Using EES (or other) software, investigate the effect of surface temperature of the heating element on the boiling heat transfer coefficient, the electric power, and the
Mechanically polished, 5-cm-diameter, stainless steel ball bearings are heated to 125°C uniformly. The ball bearings are then submerged in water at 1 atm to be cooled. Determine the rate of heat
A 15-m-long polished copper tube with an outer diameter of 5 cm is submerged in water at 270 kPa. The tube is heated with hot gases flowing through it to generate steam by boiling the water. In the
A long hot mechanically polished stainless steel sheet (cp = 450 J/kg∙K, ρ = 7900 kg/m3) is being conveyed at 2 m/s through a water bath to be cooled. The 0.5-m-wide and 5-mm-thick stainless steel
A 1-mm-diameter nickel wire with electrical resistance of 0.129 V/m is submerged horizontally in water at atmospheric pressure. Determine the electrical current at which the wire would be in danger
Water is boiled at 90°C by a horizontal brass heating element of diameter 7 mm. Determine the maximum heat flux that can be attained in the nucleate boiling regime.
In a boiler, water is boiled at 100°C by hot gases flowing through a 10-m-long tube with an outer diameter of 5 cm that is submerged in the water. Determine the maximum rate of water vaporization
Hot gasses flow inside an array of tubes that are embedded in a 3 m × 3 m horizontal flat heater. The heater is used for boiling water in a tank at 160°C. With the interest of avoiding burnout,
Water is boiled by two heaters of different geometries: a spherical heater and a horizontal flat heater. Both heaters are submerged in water that boils at 1 atm. The spherical heater has a diameter
Hot gasses flow inside an array of tubes that are embedded in a 3 m × 3 m horizontal flat heater. The heater surface is nickel-plated and is used for generating steam by boiling water in the
Water is to be boiled at atmospheric pressure on a 3-cm-diameter mechanically polished steel heater. Determine the maximum heat flux that can be attained in the nucleate boiling regime and the
Reconsider Prob. 10–33. Using EES (or other) software, investigate the effect of local atmospheric pressure on the maximum heat flux and the temperature difference Ts - Tsat. Let the atmospheric
Water is boiled at 120°C in a mechanically polished stainless-steel pressure cooker placed on top of a heating unit. If the inner surface of the bottom of the cooker is maintained at 132°C,
Water is boiled at 250°F by a 2-ft-long and 0.5-in diameter nickel-plated electric heating element maintained at 280°F. Determine(a) The boiling heat transfer coefficient,(b) The electric power
Repeat Prob. 10–21E for a platinum-plated heating element.Data from problem 21Water is boiled at 250°F by a 2-ft-long and 0.5-in diameter nickel-plated electric heating element maintained at
Consider steady two-dimensional heat transfer in a V-grooved solid body whose cross section is given in the figure. The top surfaces of the groove are maintained at 32°F while the bottom surface is
How does the finite difference formulation of a transient heat conduction problem differ from that of a steady heat conduction problem? What does the term ρAΔxcp(Ti+1m - Tim)/Δt represent in the
What are the two basic methods of solution of transient problems based on finite differencing? How do heat transfer terms in the energy balance formulation differ in the two methods?
The explicit finite difference formulation of a general interior node for transient heat conduction in a plane wall is given byObtain the finite difference formulation for the steady case by
Consider transient one-dimensional heat conduction in a plane wall that is to be solved by the explicit method. If both sides of the wall are at specified temperatures, express the stability
Consider transient one-dimensional heat conduction in a plane wall that is to be solved by the explicit method. If both sides of the wall are subjected to specified heat flux, express the stability
The explicit finite difference formulation of a general interior node for transient two-dimensional heat conduction is given byObtain the finite difference formulation for the steady case by
Is there any limitation on the size of the time step Δt in the solution of transient heat conduction problems using(a) The explicit method(b) The implicit method?
Express the general stability criterion for the explicit method of solution of transient heat conduction problems.
Consider transient two-dimensional heat conduction in a rectangular region that is to be solved by the explicit method. If all boundaries of the region are either insulated or at specified
The implicit method is unconditionally stable and thus any value of time step Dt can be used in the solution of transient heat conduction problems. To minimize the computation time, someone suggests
Starting with an energy balance on a volume element, obtain the two-dimensional transient explicit finite difference equation for a general interior node in rectangular coordinates for T(x, y, t) for
Starting with an energy balance on a volume element, obtain the two-dimensional transient implicit finite difference equation for a general interior node in rectangular coordinates for T(x, y, t) for
Starting with an energy balance on a disk volume element, derive the one-dimensional transient explicit finite difference equation for a general interior node for T(z, t) in a cylinder whose side
Consider transient heat conduction in a plane wall whose left surface (node 0) is maintained at 50°C while the right surface (node 6) is subjected to a solar heat flux of 600 W/m2. The wall is
Consider transient heat conduction in a plane wall with variable heat generation and constant thermal conductivity. The nodal network of the medium consists of nodes 0, 1, 2, 3, and 4 with a uniform

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