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Heat Transfer Coefficients Calculators

# Heat Transfer Through a Flat Wall

When calculating heat exchangers, analyzing the heat balance of operating equipment, assessing heat losses and solving many other heat transfer problems, it is often necessary to calculate the heat flow passing through a solid wall separating liquids or gases with different temperatures, which is calculated by the following formula in the simplest case:

q = K × (Tf1 - Tf2);

K - heat transfer coefficient;

Tf1 , Tf2 - is the temperatures of fluids between which the heat exchange takes place.

As you can see, the greatest difficulty here is to determine the heat transfer coefficient K, which depends on the physical properties of the heat carrier, flow regime and coefficient of thermal conductivity of the solid wall. The heat transfer coefficient of a flat wall can be expressed in terms of the convection film coefficients of the wall surfaces:

K = 1 / (1 / α1 + δ / λ + 1 / α2);

α1 , α2 - convection film coefficients of the wall;

λ - heat transfer coefficient of the wall;

δ - wall thickness;

In this calculation, heat transfer through a flat wall of thickness H, with area S, and with thermal conductivity λ is considered. The wall separates a fluid A with a temperature Tfa and a fluid B with a temperature Tfb. For the calculation, the convection film coefficients αa, αb should also be specified, which can be calculated in this Section.

As a result of calculations, the temperatures of the flat wall surfaces Twa, Twb, power P and heat flow Q, transmitted through the wall, and also heat transfer coefficient of the wall K are determined.

### INITIAL DATA

H - Wall thickness;

S - Wall surface area;

λ - Thermal conductivity coefficient of the wall (see table below);

Tfa - Fluid A temperature;

αa - Convection film coefficient (between fluid A and the wall);

Tfb - Fluid B temperature;

αb - Convection film coefficient (between fluid B and the wall);

### RESULTS DATA

К - Heat transfer coefficient;

Q - Heat flow, transmitted through the wall;

Р- Power, transmitted through the wall;

Тwa - Wall temperature on A surface;

Тwb - Wall temperature on B surface.

Wall thickness (H)

Area (S)

Thermal conductivity (λ)

Temperature (Т)

Film coefficient (αа)

Temperature (Тfb)

Film coefficient (αb)

Heat transfer (К)

Heat flow (Q)

Power (Р)

Temperature (Тwa)

Temperature (Тwb)

### BASIC FORMULAS

Heat transfer coefficient:

K = 1 / (1 / αa + δ / λ + 1 / αb);

Heat flow:

Q = K*(Т - Тfb);

Power:

P = Q*S;

Wall temperature Тwa:

Т = (αa - q) / αa;

Wall temperature Тwb:

Тwb = (αbfb + q) / αb.

### INITIAL DATA

H - Wall thickness;

S - Wall surface area;

λ - Thermal conductivity coefficient of the wall (see table below);

Tfa - Fluid A temperature;

αa - Convection film coefficients (between fluid A and the wall);

Tfb - Fluid B temperature;

αb - Convection film coefficient (between fluid B and the wall);

### RESULTS DATA

К - Heat transfer coefficient;

Q - Heat flow, transmitted through the wall;

Р- Power, transmitted through the wall;

Тwa - Wall temperature on A surface;

Тwb - Wall temperature on B surface.

### THERMAL CONDUCTIVITY COEFFICIENTS

 Material Thermal conductivity W/m*ºC (W/inch*ºF) Copper 399 (5.62) Gold 317 (4.64) Aluminium 237 (3.34) Graphite 168 (2.37) Brass 110 (1.55) Iron 80 (1.12) Carbon steel 43 (0.6) Lead 35 (0.49) Stainless steel 15.1 (0.21) Rock 3.37 (0.047) Concrete 0.84 (0.012) Glass 0.81 (0.011) Plastic 0.25 (0.0035) Wood 0.15 (0.0021) Rock wool 0.045 (0.00063) Cork 0.039 (0.00055)