General information

Useful calculation data

Terms Units Definitions

A m

2

Area of heating surface

Cp kJ/kg°C Specific heat capacity of substance

T1 °C Initial (or inlet) temperature of substance

T2 °C Final (or outlet) temperature of substance

Ta °C Ambient temperature

Tm °C Mean temperature of heated substance

Ts °C Steam temperature

DT °C Temperature rise of heated substance T

2

- T

1

DT

s

°C Temperature difference between steam and substance at start-up T

s

- T

1

DT

m

°C

Mean temperature difference between steam and substance at any heat load

AMTD = Arithmetic Mean Temperature Difference

LMTD = Logrithmic Mean Temperature Difference

f dimensionless Insulation factor

H hours Time in hours

hfg kJ/kg Enthalpy of evaporation

Kvr m

3

/h bar The required capacity index

Kvs m

3

/h bar The valve capacity index (full open valve)

kW kJ/s Rate of heat transfer

L m Length of pipe run

m kg Mass

kg/h Mass flowrate

P1 bar a Upstream pressure

P2 bar a Downstream pressure

Q kJ Amount of heat added to raise temperature

kW Rate of heat transfer

m

kW Mean rate of heat transfer

r

W/m

(watts per metre of pipe)

Radiation loss from pipework

U W/m

2

°C Overall heat transfer coefficient

a m

3

/s Volumetric flowrate of air

w m

3

/h Volumetric flowrate of water

W kg Weight of pipe being heated

TI-GCM-13 CM Issue 3

Heating formulas

11.5.14