The
Nusselt number Nu = αl/λf
or the Stanton number St = is used as a dimensionless number for heat transfer in these equations, where 1 is the characteristic dimension of the surface in the flow, the mass velocity of the fluid flow, λ
f
and C
pf
the fluid thermal conductivity and heat capacity.
What is the formula for overall heat transfer coefficient?
R = Resistance(s) to heat flow
in pipe wall (K/W) Other parameters are as above. The heat transfer coefficient is the heat transferred per unit area per kelvin. Thus area is included in the equation as it represents the area over which the transfer of heat takes place.
What is overall heat transfer coefficient?
The overall heat transfer coefficient, or U-value, refers
to how well heat is conducted through over a series of resistant mediums
. Its units are the W/(m
2
°C) [Btu/(hr-ft
2
°F)].
How do you calculate the heat transfer coefficient of a heat exchanger?
As the mass flow may be calculated with
dm = dv x ρ (volume flow times density)
we will get the “qualitative” Heat transfer coefficient α
m
. Using: T2, T
1
the inlet and outlet temperature of the fluids and the volume flow. The heat loss is also taken as constant.
How do you calculate heat transfer?
| Q Heat transferred | A Area of surface |
|---|
What is Q MC ∆ T used for?
Q=mcΔT Q = mc Δ T , where Q is the symbol for
heat transfer
, m is the mass of the substance, and ΔT is the change in temperature. The symbol c stands for specific heat and depends on the material and phase. The specific heat is the amount of heat necessary to change the temperature of 1.00 kg of mass by 1.00oC.
Is the overall heat transfer coefficient constant?
The overall heat transfer coefficient (U) depends on individual heat transfer coefficients and the heat resistance offered by the tube-wall. We assume the coolant heat transfer coefficient (h
cool
) and the tube wall resistance
remains constant
.
Is higher overall heat transfer coefficient better?
Assuming the heat transfer surface and temperature difference remain unchanged,
the greater the U value
, the greater the heat transfer rate. In other words, this means that for a certain heat exchanger and product, a higher U value could lead to shorter batch times and increased production/revenue.
How do you find the heat transfer coefficient of a Nusselt number?
- Nusselt Number : Nu = hL/k.
- Convection Heat Transfer Coefficient : k = Nuk/L.
- Characteristic Length : L = Nuk/h.
- Thermal Conductivity of the Fluid : k = hL/Nu.
- Where, Nu = Nusselt Number, h = Convection Heat Transfer Coefficient, L = Characteristic Length, k = Thermal Conductivity of the Fluid.
Which one has the highest value of overall heat transfer coefficient?
Which one is having highest value of overall heat transfer coefficient? Explanation: Overall heat transfer coefficient for
feed water heaters
is 8500 W/m
2
K while that of steam, alcohol condensers and ammonia condensers are 5000 W/m
2
K, 630 W/m
2
K and 1400 W/m
2
K.
What is transfer formula?
Thus:
dIν=−[Iνα(ν)+Iνσ(ν)−jν(ν)]dx
. This is one form – the most basic form – of the equation of transfer.
What is Heatflow formula?
The equation of heat flow is given by Fourier’s Law of Heat Conduction.
Rate of heat flow = – (heat transfer coefficient) * (area of the body) * (variation of the temperature) / (length of the material)
What is K in heat transfer?
k: The factor k is called the
thermal conductivity constant
. The thermal conductivity constant k is larger for materials that transfer heat well (like metal and stone), and k is small for materials that transfer heat poorly (like air and wood).
What does C stand for in Q MC?
Q = Heat energy (in Joules, J) m = Mass of a substance (kg) c =
Specific heat (J/kg∙K)
What is the L in Q mL?
The specific latent heat (L) of a material… is a measure of the heat energy (Q) per mass (m) released or absorbed during a phase change. is defined through the formula
Q = mL
. is often just called the “latent heat” of the material.
