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 × (T_f1 - T_f2);

K - heat transfer coefficient;

T_f1 , T_f2 - 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 T_fa and a fluid B with a temperature T_fb. For the calculation, the convection film coefficients α_a, α_b should also be specified, which can be calculated in this Section.

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

Heat transfer throw flat wall

Heat transfer throw flat wall calculation

INITIAL DATA

H - Wall thickness;

S - Wall surface area;

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

T_fa - Fluid A temperature;

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

T_fb - Fluid B temperature;

α_b - 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;

Т_wa - Wall temperature on A surface;

Т_wb - Wall temperature on B surface.

Metric Imperial

Wall thickness (H)

Area (S)

Thermal conductivity (λ)

Temperature (Т_fа)

Film coefficient (α_а)

Temperature (Т_fb)

Film coefficient (α_b)

Heat transfer (К)

Heat flow (Q)

Power (Р)

Temperature (Т_wa)

Temperature (Т_wb)

BASIC FORMULAS

Heat transfer coefficient:

K = 1 / (1 / α_a + δ / λ + 1 / α_b);

Heat flow:

Q = K*(Т_fа - Т_fb);

Power:

P = Q*S;

Wall temperature Т_wa:

Т_wа = (α_a*Т_fа - q) / α_a;

Wall temperature Т_wb:

Т_wb = (α_b*Т_fb + q) / α_b.

INITIAL DATA

H - Wall thickness;

S - Wall surface area;

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

T_fa - Fluid A temperature;

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

T_fb - Fluid B temperature;

α_b - 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;

Т_wa - Wall temperature on A surface;

Т_wb - Wall temperature on B surface.

THERMAL CONDUCTIVITY COEFFICIENTS

Material	Thermal conductivity W/mºC (W/inchºF)
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)

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