![Queenquestion9130](/avatars/30667.jpg)
Queenquestion9130
07.04.2020 •
Engineering
An electric resistance heater is embedded in a long cylinder of diameter 30 mm. When water with a temperature of 25 oC and velocity of 1 m/s flows crosswise over the cylinder, the power per unit length required to maintain the surface at a uniform temperature of 90 oC is 28 kW/m. When air, also at 25 oC, but with a velocity of 10 m/s is flowing, the power per unit length required to maintain the same surface temperature is 400 W/m.
Calculate and compare the convection coefficients for the flows of water and air.
Solved
Show answers
More tips
- C Cities and Countries How to Easily and Quickly Obtain a Schengen Visa?...
- F Food and Cooking Red Caviar: How to Choose the Best?...
- C Computers and Internet Clearing Cache: How to Speed Up Your Browser...
- S Style and Beauty How are artificial nails removed?...
- S Style and Beauty Secrets of Tying a Pareo: 5 Ways...
- F Food and Cooking Everything You Need to Know About Pasta...
- C Computers and Internet How to Choose a Monitor?...
- H Horoscopes, Magic, Divination Where Did Tarot Cards Come From?...
Answers on questions: Engineering
- P Physics An object of mass 3.07 kg, moving with an initial velocity of 5.07 m/s, collides with and sticks to an object of mass 2.52 kg with an initial velocity of -3.11 m/s....
- P Physics Askier reaches the bottom of a slope with a velocity of 12 meters per second north. if the skier comes to a complete stop in 3 seconds, what is the acceleration...
- B Business 16 sa _ng isang proyekto nakasaad ang pangalan ng proyekto mga kagamitan bilang at halaga dito rin makikita ang pamamaraan sa paggawa ng proyekto...
Ответ:
Water flow,
= 4572.9 w/m².k
Air flow,
= 65.32 w/m²k
Flow of water is 70 times faster than flow of air, which means that the from of water was forced.
Explanation:
Given:
q' = 28 kw/m = 28 x 10³ w/m
D = 30mm = 30 x 10⁻³ m
T∞ (Air) = 25°C
Ts = 90°C
Step 1: The convection heat rate from the cylinder per unit length of the cylinder has the form
q' = h(πD)(Ts - T∞)
h = heat transfer convection coefficient
h = q' ÷ [πD(Ts - T∞)]
⇒ Substitute for the given values
Also for air
,
= 400 w/m
Note that the air velocity is 10 times the water flow, but
is 70 times
. This indicate that the values for convection coefficient are typical for forced convection heat transfer with liquid and gases.
Ответ:
Explanation:
Flow is cross-wise over cylinder which is very long in the direction normal to flow.
Therefore, from analysis, the convection heat rate from the cylinder per unit length of the cylinder has the form.
Note: the air velocity is 10 times that of the water flow, yet
= 70 k![h_{a}](/tpl/images/0585/9790/cc3c0.png)
These values for the convection coefficient are typical for forced convection heat transfer with liquids and gases
Ответ:
If your accelerator gets stuck down, do the following:
Shift to neutral.
Apply the brakes.
Keep your eyes on the road and look for a way out.
Warn other drivers by blinking and flashing your hazard lights.
Try to drive the car safely off the road.
Turn off the ignition when you no longer need to change direction.