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barxatty [35]
2 years ago
6

You’ve experienced convection cooling if you’ve ever extended your hand out the window of a moving vehicle or into a flowing wat

er stream. With the surface of your hand at a temperature of 30°C, consider the two following conditions.
Condition A: a vehicle speed of 35 km/h in air at -5°C with a convection coefficient of 40 W/m2·K.
Condition B: a velocity of 0.2 m/s in a water stream at 10°C with a convection coefficient of 800 W/m2·K.

What is the convection heat flux for these two condition?
Engineering
1 answer:
Anna35 [415]2 years ago
7 0

Answer:

Condition A

Heat flux is 1400 W/M^2

Condition B

Heat flux is 12800 w/m^2

Explanation:

Given that:

T_s is given as  30 degree celcius

condition A

Air temperature =  - 5 degree c

convection coefficient h = 40 w/m^2. k

heat\ flux = \frac{Q}{a}= h\Delta = 40{30 - (-5)} = 1400 w/m^2

condition A

water temperature  = 10 degree c

convection coefficient = 800 w/m^2.k

heat\ flux = \frac{Q}{A} = H(\Delta} = 800\times (30-14) = 12800w/m^2

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Consider a cylindrical nickel wire 2.1 mm in diameter and 3.2 × 104 mm long. Calculate its elongation when a load of 280 N is ap
pshichka [43]

Answer:

Total elongation will be 0.012 m

Explanation:

We have given diameter of the cylinder = 2.1 mm

Length of wire L=3.2\times 10^4mm

So radius r=\frac{d}{2}=\frac{2.1}{2}=1.05mm=1.05\times 10^{-3}m

Load F = 280 N

Elastic modulus = 207 Gpa

Area of cross section A=\pi r^2=3.14\times (1.05\times 10^{-3})^2=3.461\times 10^{-6}m^2

We know that elongation in wire is given by \delta =\frac{FL}{AE}, here F is load, L is length, A is area and E is elastic modulus

So \delta =\frac{FL}{AE}=\frac{280\times 32}{3.461\times 10^{-6}\times 207\times 10^9}=0.012m

4 0
3 years ago
When charging an R-410A system that uses a water-cooled condenser, you must first charge with vapor to a pressure of at least __
kirza4 [7]

Answer:

35psig

Explanation:

Pressure is a force that acts on a surface area. The psig measure the pressure pounds per square inch gauge. It measure the difference in pressure between supply tank and outside air. This pressure is relative to atmospheric pressure. When charging an R-410A system, the vapor pressure should be at least 35 psig before switching to liquid charging.

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What do larger horsepower engines require
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Answer:

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5 0
3 years ago
An average person generates heat at a rate of 84 W while resting. Assuming one-quarter of this heat is lost from the head and di
eimsori [14]

Answer:

Average surface temperature = 11.4 C

Explanation:

Temperature of the surface = Incoming Temperature + (Heat generated by the Average person's head/ Coefficient of heat transfer x Surface Area of head)

Area = πD² = π(0.2)² = 0.1256 m²

h = (Thermal Conductivity/Diameter of Surface)(Nusselt Number)

Nu = 2 + [0.4Re^0.5 + 0.06Re^2/3] x Pr^0.4 x [μ∞/μs]^1/4

where Re is the Reynold Number, Pr = 0.7336 is the Prandtl Number, μ∞ = 1.778 x 10^-5 is the dynamic viscosity and μs = 1.802 x 10^-5 is the Dynamic Viscosity at 15 C

Re = VD/v where V is the velocity of wind, D is the diameter of the sphere and v is the kinematic viscosity

Re = (8.056 x 0.2)/(1.426 x 10^-5) = 1.13 x 10^6

Substituting value of Re into Nu equation

Nu = 2 + [0.4(1.13 x 10^6)^0.5 + 0.06(1.13 x 10^6)2/3] (0.7336 ^0.4){(1.778 x 10^-5)/(1.802 x 10^-5)^1/4}

Nu = 2 + [1076.1](0.8835)(0.9967) = 949.5

Putting Nu values in h

h = (0.02439/0.2)(949.5) = 115.8 W/m² C

putting h value in Ts equation

Ts = 10 + [(84/4)/(115.8 x 0.1256)] = 11.4 C

6 0
3 years ago
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