Register

Homework Help Question and Answers

Submit a new Query

Recent Homework Help Question & Answers


Question 42534

posted 11 months ago

Problem 2: How much faster can you cook a potato in a convection oven versus a standard oven? Assume that the potato can be approximated as a cylinder with a diameter of 3 cm and length of 4 cm, with density p=950 kg/m^3, thermal conductivity k=0.8 W/m*K, and specific heat Cp=4.6 kJ/kg*K. The air temperature in both ovens is 190°C. and the potato starts at 20°C.
(a) Assuming a convection coefficient of h=8 W/m^2*K in a standard oven, is it appropriate to use a lumped capacitance approach? Calculate the time required to heat the potato to a temperature of 140°C.
(b) Assuming h=15 W/m^2*K in a convection oven, is the same approach still appropriate? Calculate the time required to heat to the same temperature.

View answer

Question 42535

posted 11 months ago

Problem 3: A very large glass plate (Pyrex) with a thickness of 25.4 mm needs to be rapidly quenched by air jets (h=500 W/m?-K, To=25°C) on its periphery to "temper" it. The glass starts at an initial temperature of 1000°C, and is quenched for 60 seconds.
(a) What type of transient analysis is appropriate for this problem? You must justify your answer.
(b) What is the surface temperature after 60 seconds? Ans: 235°C What is the glass centerline temperature at that time? Does it support your argument in part (a)? Ans: 780°C
(c) How long must the glass be quenched until the glass center line temperature drops below 50°C?

View answer

Question 42533

posted 11 months ago

Problem 1: An interesting feature of some types of additive manufacturing is the ability to print functionally graded materials, where properties vary with direction. Consider a bar of length L=4 cm and heigh tH=1 cm, with a temperature of 20°C at x=0 and a temperature of 100°C atx=L. It is insulated (adiabatic) on its upper and lower faces.
(a) If the bar is constructed of a material with constant thermal conductivity k=115 W/m-K, calculate the magnitude of the heat transfer rate per unit depth (in W/m). Plot the temperature through the bar in the ex-direction from x=0 to L.
(b) Assume that another bar is constructed of a functionally graded material that starts at 20 W/m-K atx=0, and increases linearly to 400 W/m-K at x=L; that is, k(x)=[20+380*(x/L)] W/m-K, where x is in meters.Using the steady finite difference method with five nodes, determine the temperatures at each node and plot on the same figure as in part (a). Some important notes: i) assume each finite-difference control volume has a constant conductivity within it that corresponds to the x-location of that node; ii) when calculating the heat flux from the west face, use the k value from the west control volume, and when calculating east face heat flux, use the k value from the east control volume (this is not precisely correct but is reasonable). How does your plot differ from part (a)?
(c) Estimate the heat transfer rate per unit length through the bar at x=0 using temperatures at nodes 1and 2 and the information above. How does this compare to part (a)? Ans: -1694 W/m (or 1694 W/m in the negative x-direction)

View answer

Question 42798

posted 11 months ago

Problem #2: The United steel product company operated a 5 stand continuouscasting units for convert steel slabs (20' x 28" x 9") into flat products/sheet steel. Thefinal product specification is: sheet thickness =0.08"and W= 34". Before heated slabenter the 5 consecutive rolling stands, it goes through a Roughing mill which reduces thethickness of the incoming slab by about 0.5". After the product goes through the 5stands, the steel strip passes through coiling unit which converts the long strip into steelcoils (see the following flow chart)
A)- Assuming the loss of material in the form of scale removesand others isnegligible, determine:
1)- We lose about 0.5% of the steel in the whole rolling process
2)- What is the speed of the strip when it exits machines 1,2,..,7
B)- Answer question 1 above if the following loses must be considered.
3)- If the inside diameter (hallow space) is 20", determine the final dimensions And weight of the coil.
1)- what is the final length of the sheet product produced in the process
2)- there is a trimming machine before the coiling process which trims each side of the strip by an average of 0.025"

View answer

Question 42797

posted 11 months ago

Problem #1: Part a in Figure 1** is to be produced using impression forging process.We are using a small billet/slug shown in Figure 2, as the input to the system. Assumingthe specific weight of the metal is =0.283 lb/in³ , answer the following questions
1)- is the input material satisfy the requirement of the impression forging (i.e., size of the input material)
2)-Can we use a flash-less Forging Process? . Explain your answer.
3)-In case one: a)- Is the output of this process readily useful or need further processing.Explain why
b)- what is the yield of the system
4)- for a production rate of 500 units/day, determine material loss per month. Use the following assumption Day =8 hours, week =40 hours and a month = 4.2 weeks

View answer

Question 39091

posted 1 years ago

The dimension of 1 nm =
D. 100 Ångström
E. 1000 Ångström
В. 109 сm
C. 10.9 mm
A. 10° m

View answer

Question 39090

posted 1 years ago

3. What would be the closest size estimation of a Helium atom?
Е. 1 pm
P. 1Å
С. 1 nm
В. 1 um
А. 1 mm

View answer

Question 39088

posted 1 years ago

1. Which of the following products must involve microfabrication manufacturing?
E. None of the above
A. Gyroscopes in smartphones
D. All the above
C. Accelerometer for car airbags
B. Microprocessors in Personal Computers

View answer

Question 39092

posted 1 years ago

5. Which of the following correctly describes a typical clean room technology used for micro fabrication?
A. Employs negative pressure against outside world to prevent dust flows in
B. Normal paper and wipes
C. Operators wear protective clothing to prevent human dust entering the room
D. All of the above
E. None of the above

View answer

Question 39087

posted 1 years ago

a) List at least SIX different property requirements necessary for cutting tool materials in machining processes. Give at least TWO examples of cutting tool materials.(5 marks)
b) What is CNC? What are their pros and cons compared to conventional machine tools?(5 marks)
c) Below is an exemplified G code. Please describe each command and the functionof the whole code.(15 marks)

View answer

Questions not Found

Most popular subject

Thermodynamics

Essay/Summary

Mechanics

Complex Analysis

Engineering Economics

Calculus

Modern Physics

General Chemistry

Strength Of Materials

Fluid Mechanics

x