Calculation of Pipe Diameter

 

In our day, energy and the efficient use of energy are among the most important factors, and the main purpose of use of pre-insulated pipes is to keep heat loss at the lowest possible level and obtain the highest efficiency from energy. The calculation method given below can be used for calculating the heat loss theoretically.

First of all, the average fluid temperature is calculated:

Tm (˚C) : Average temperature of the fluid

Tg (˚C) : Temperature at the direction of flow

Td (˚C) : Temperature at the direction of return

Tt (˚C) : Outdoor air temperature

In order to calculate the total thermal conductivity resistance of the pre-insulated pipe system, firstly the resistances of each layer of the system must be calculated respectively.

Carrier Pipe Thermal Conductivity Resistance:

Rtbi (m.°C / W) : Thermal conductivity resistance of the carrier pipe

Din (m) : Inner diameter of the carrier pipe

Dout (m) : Outer diameter of the carrier pipe

λtb(W / m.°C) : Carrier pipe thermal conductivity coefficient (Table 1)

Type of the Service Pipe

Thermal Conductivity Coefficient (W/m.˚C)

Black Steel

76

Stainless Steel

16

PP-R

0,15

Copper

400

CTP

0,31

Polyethylene

0,43

Table 1: Thermal Conductivity Coefficient by Types of Carrier Pipe

Polyurethane Insulation Thermal Conductivity Resistance:

Rpur= ln(DkbinDout)2× π× λpur

Rpur(m.°C / W) : PUR insulation thermal conductivity resistance

Dkbin(m): Inner diameter of the casing pipe

λpur(W / m.°C): PUR insulation thermal conductivity coefficient (0.026 W / m.°C can be taken)

Thermal Conductivity Resistance of the HDPE Casing Pipe:

Rkb(m.°C / W) : Thermal conductivity resistance of the casing pipe

Dkbout(m): Outer diameter of the casing pipe

Dkbin(m): Outer diameter of the casing pipe

λkb(W / m.°C): Thermal conductivity resistance of the casing pipe

Outdoor Thermal Conductivity Resistance:

  • Underground Installation

Rt(m.°C / W) : Thermal conductivity resistance of earth

Z(m) : Filling height of earth

λt(W / m.°C): Thermal conductivity coefficient of earth (Table 2)

Type

Density (kg/m3)

Volumetric Humidity Rate %

Thermal Conductivity Coefficient (W/m.˚C)

Sand

1500

4

1,04

1800

14

1,7

Clay Soil

1500

23

1,5

2000

28

2,6

Table 2: Thermal Conductivity Coefficient of Earth

  • Ground Installation

Rtdout(m.°C / W): Outer convection resistance of the casing pipe

hair(W / m².°C): Air convection coefficient

Thermal Conductivity Resistance between Flow - Return Pipes

Rtbin(m.°C / W): Thermal conductivity resistance between flow - return pipes

C (m) : Distance between the axes of flow - return pipes

After calculating all resistance factors, the total thermal conductivity resistance value of the pre-insulated pipe system can be calculated through the formulas below:

  • If under the ground:

  • If above the ground:

U (W/m.˚C) : Total thermal conductivity coefficient

Total heat loss per metre in pre-insulated pipes:

Q=U× To

Q (W / m) : Total heat loss per metre

The formula below can be used to calculate the fluid temperature at the end of the line according to all calculations:

L (m) : Length of line

m (kg/sec) : Water flowrate

Cp(J / kg.°C) : Fluid specific heat [Table 3]

Tson(°C) : Fluid final temperature

Temperature (˚C)

Density (kg/m3)

Specific Heat (Kj/kg ˚C)

0

1000

4210

5

1000

4204

10

1000

4193

20

998

4183

30

996,02

4179

40

992,06

4179

50

988,14

4182

60

983,28

4185

70

977,52

4191

80

971,82

4198

90

965,25

4208

100

957,85

4219

Table 3: Physical Specifications of Water

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