Heat calculation of far infrared drying furnace
Yang Wenliang
When designing the drum far-infrared drying furnace, the first thing to be determined is the electric power of the drying oven. To calculate the electric power, the heat consumption of the drying oven is the most important parameter. In the “Knowledge Window†column of “Drum†magazine, the author specifically introduced the design of the steel drum drying furnace, but did not explain the problem of heat calculation. Therefore, in response to the letter from several readers, the author hereby introduces the calculation of the heat of the drying furnace:
First, heat consumption per unit time
1, through the furnace and the door cooling Q1:
Q1=KF1·Δt (kcal/hour)
In the formula:
K - Heat Dissipation Factor (Kcal/m 2 ·degree·hour)
F1 - surface area of ​​the furnace (m2)
â–³ t - the difference between operating temperature and room temperature (degrees) (generally 20 degrees)
K value of slag wool insulation layer with different thickness
Slag wool insulation thickness 100mm 120mm 150mm K 1.1 1 0.82, bottom heat dissipation Q2:
When the bottom of the oven is without insulation, the radiation is conducted through the floor
Q2=KF2・△t (Kcal/hour)
In the formula:
K - heat dissipation coefficient, generally take K = 2.5 (Kcal/m 2 · degree · hour)
F2 - furnace bottom area (m2)
â–³t - Same as above
3, the heat consumption of steel drums and holders Q3:
Q3=GC・△t (Kcal/hour)
In the formula:
G - Weight of heated drums and hangers (kg/h)
C - Heat Capacity of Heated Steel Drums and Rack (Kcal/kg・degree)
â–³t - Same as above
For small batch batch ovens, if the holding time is longer in the total heating time, the weight G should be discounted because the heat loss in the holding section is small. If the holding time is 2 times of the heating time, then G" = G/2.
4, ventilation heat loss Q4:
Q4=V・γ・Cp ・△t (Kcal/hour)
In the formula:
V - The amount of fresh air required to maintain the concentration of volatiles in the furnace (m3/h)
γ - Specific gravity of air at operating temperature (kg/m3)
Cp - Specific heat of air at operating temperature (Kcal/Kg/degree)
â–³t - Same as above
The value of V in the above equation can be calculated by the following formula:
V=G1/C (m3/hour)
In the formula:
G1 - Amount of solvent per hour Large amount of evaporation (g/m3)
C - Permissible concentration of solvent in air at operating temperature. Can be selected from the table below:
Working temperature (degrees) 100-150 150-200 200-250 C (g/m3) 4-2 2-1 1-0.55. Heat dissipation Q5 of the circulating air duct outside the furnace:
The circulating air duct is installed outside the drying furnace. The air duct is coated with a 50mm asbestos diatomaceous earth insulation layer.
Q5=KF・△t ​​(Kcal/hour)
In the formula:
K - heat dissipation coefficient, generally take K = 2.5 (Kcal/m 2 · degree · hour)
F - area of ​​the cardiopulmonary bypass duct (meter 2)
â–³t - Same as above
6, heat loss through the door frame and door seam Q6:
Q6=q・L (Kcal/hour)
In the formula:
q - heat loss per unit length of the steel frame through the door frame and door seams (see table below)
L - total length of door frame (m)
q value at various temperatures:
Operating temperature (degrees) 110 120 140 160 180 220 q (Kcal/Hour meters) 166 220 276 338 404 5447, the total heat consumed by the drying furnace Q:
Q=(Q1+Q2+Q3+Q4+Q5+Q6)×1.1
In the formula:
1.1—Conversion factor, taking into account unestimated heat consumption
Second, according to the requirements of the heating time accounting for total heat
1. Heat quantity required to heat steel drum from room temperature to working temperature Q1:
Q1=GCΔt/τ (Kcal/hour)
In the formula:
G - Weight of heated drums (kg)
C——Specific heat of the heated steel drum (Kcal/kg・degree)
Ï„ - time from room temperature to operating temperature (hours)
â–³ t - the difference between operating temperature and room temperature.
2. Absorption of heat in furnace insulation layer Q2:
Q2=GC â–³t/Ï„ (Kcal/hour)
G - weight of insulation material (kg)
C - Specific Heat of Insulation Material (Kcal/kg・degree)
â–³ t - the difference between the operating temperature, the average temperature of the outer wall temperature and the room temperature temperature. which is
Δt=(t1+t2)/2-t
3, bottom heat analysis Q3:
Q3=F・q (Kcal/hour)
In the formula:
F——floor area occupied by drying oven (meter 2)
q - hourly calorie per floor area (Kcal/hour/meter 2)
Working temperature (degrees)
Heat consumption (Kcal/meter 2 hours)
Heating time (hours)
If the floor is red brick and cement, the q value can be checked from the above table. If the floor is concrete or terrazzo, the q value is the value in the table above multiplied by a factor of 1.5.
The prerequisite for this table is that the bottom thickness is not less than 200mm; γ = 1,500 kg/m3 for red bricks, and C = 0.22 kcal/kg.
4, the total heat required for heating Q:
Q=(Q1+Q2+Q3)×1.1
In the formula
1.1 - unpredictable heat consumption
The heat calculated according to the heating time requirement is compared with the heat required for heat preservation, and a larger amount of heat is used to calculate the power.