How to calculate heat losses using formulae
In order to select an electric heating system (heating cable) for heating a pipeline or tank (vessel), it is necessary to find out what heat losses need to be compensated by the heating cable and how to calculate these losses.
So, in many cases, it is more economical to maintain the temperature in the pipeline for short product shutdown times. At this time, the product in the pipeline may freeze.
The required losses for temperature rise can be calculated using the following formula:
W (W/m) = (P x S) + (C x Q ) x ∆T / E x H x 3600, where
W is the amount of heat required to heat the product (W/m);
P – mass of the pipeline (kg/m);
S – specific heat capacity of the pipe (J/kg °C);
C is the weight of the contents in the pipe (kg/m);
Q is the specific heat capacity of the contents (J/kg °C);
∆T – difference of temperature rise (°C);
H – heating time in hours
E – efficiency coefficient, usually a coefficient of 0.73 is used.
Heat loss compensation for tanks, vessels and hoppers can be calculated using the following formulae
- for flat surfaces:
Heat loss = A x K x (T1 – T2) / E x t;
2. for cylindrical surfaces:
Heat loss = 2.72 x K x L x (T1 – T2) / E x log10 (D/d), where
A – total surface area of the tank, vessel, etc. (square metres);
K – thermal conductivity of the insulation (W/m °C);
T1 is the temperature to be maintained (°C),
T2 – minimum ambient temperature (°C),
t – thickness of thermal insulation (mm),
L – length of the heating surface (mm),
D – outer diameter of the insulation (m),
d – outside diameter of the pipe (m),
E – efficiency coefficient, usually a coefficient of 0.73 is used.
The temperature rise for tanks, vessels and hoppers can be calculated using the following formula:
Power (kW) = mass (kg) x specific heat capacity (J/kgºC) x temperature difference °C / E (0.73) x 1000 x hours x 3600, where
all data in the formula are the same as in the previous formula.
In this case, for the exact amount of heat required to raise the temperature and further to maintain the set temperature, it is necessary to add the result obtained in the last form with the results obtained in the previous formulas, i.e.
Minimum required capacity = capacity for temperature rise losses + capacity to maintain temperature.
In order to select an electric heating system (heating cable) for heating a pipeline or tank (vessel), it is necessary to find out what heat losses need to be compensated by the heating cable and how to calculate these losses.
So, in many cases, it is more economical to maintain the temperature in the pipeline for short product shutdown times. At this time, the product in the pipeline may freeze.
The required losses for temperature rise can be calculated using the following formula:
W (W/m) = (P x S) + (C x Q ) x ∆T / E x H x 3600, where
W is the amount of heat required to heat the product (W/m);
P – mass of the pipeline (kg/m);
S – specific heat capacity of the pipe (J/kg °C);
C is the weight of the contents in the pipe (kg/m);
Q is the specific heat capacity of the contents (J/kg °C);
∆T – difference of temperature rise (°C);
H – heating time in hours
E – efficiency coefficient, usually a coefficient of 0.73 is used.
Heat loss compensation for tanks, vessels and hoppers can be calculated using the following formulae
- for flat surfaces:
Heat loss = A x K x (T1 – T2) / E x t;
2. for cylindrical surfaces:
Heat loss = 2.72 x K x L x (T1 – T2) / E x log10 (D/d), where
A – total surface area of the tank, vessel, etc. (square metres);
K – thermal conductivity of the insulation (W/m °C);
T1 is the temperature to be maintained (°C),
T2 – minimum ambient temperature (°C),
t – thickness of thermal insulation (mm),
L – length of the heating surface (mm),
D – outer diameter of the insulation (m),
d – outside diameter of the pipe (m),
E – efficiency coefficient, usually a coefficient of 0.73 is used.
The temperature rise for tanks, vessels and hoppers can be calculated using the following formula:
Power (kW) = mass (kg) x specific heat capacity (J/kgºC) x temperature difference °C / E (0.73) x 1000 x hours x 3600, where
all data in the formula are the same as in the previous formula.
In this case, for the exact amount of heat required to raise the temperature and further to maintain the set temperature, it is necessary to add the result obtained in the last form with the results obtained in the previous formulas, i.e.
Minimum required capacity = capacity for temperature rise losses + capacity to maintain temperature.
