When the heating roller works, in addition to the heat required by the material, there is also heat dissipation of the roller itself. Therefore, these two aspects must be considered in the design of heating roller. How to calculate is a headache for many people.
It is necessary to know the power required when the heating roller works in order to select the heating roller reasonably. This paper discusses how to calculate the power required by materials. Generally speaking, there are two main types of power calculation.
The material involved is simple and does not contain moisture, and there will be no evaporation during the heating process.
The calculation conditions are as follows:
Yield (P), rising temperature (Δ T), specific heat of material (Cp)
Calculation method:
Q = P × Δ t × Cp converted into kW: Q / 3600
Key point: pay attention to the unit
Q: KJ (kJ) P: kg / HR (kg / h)
Δ T: ℃ CP: kJ / kg. ℃ power: kW
*Example 1 a non-woven fabric has a width of 1.5m, a surface density of 100g / m2, a linear velocity of 20m / min, and an original temperature of 25 ℃. It is necessary to use a heating roller to raise the temperature of the non-woven fabric to 125 ℃. It is known that the specific heat of the nonwoven fabric is 2.5kj/kg. ℃, and the net power required in this process is calculated.
Assuming that the heat utilization rate is 40%, how much power is required for the heating roller?
Answer: output per hour: P = 1.5m × 20m / min × 60 × 0.1kg = 180kg / hr
Net power: q = P × Δ t × Cp
=180kg/hr×（125-25）℃×2.5kJ/kg.℃
=45000kJ/hr
=45000/3600kJ/s
=12.5kW
Actual configuration power ≥ 12.5kw/40% = 31.25kW
The material contains a certain amount of moisture, which needs to be evaporated partially or completely.
The calculation conditions are as follows:
Yield (P), water content (Mw), elevated temperature (Δ T), specific heat of material (Cp).
Calculation method: the heat demand is divided into three parts, which are added after calculation respectively.
1) Material heating demand Q1;
2) Heat required to heat water from current temperature to 100 ℃ Q2;
3) Heat required for evaporation of water from 100 ℃ to 100 ℃ steam Q3;
Among them, the calculation of material heating demand (Q1) is the same as before.
Calculation of heat required for water heating from current temperature (T1) to 100 ℃ (T2):
The specific heat (CW) of water is known to be 4.18 kJ / kg. ℃.
Q2=Mw×（T2-T1）×Cw;
The heat required for water evaporation from 100 ℃ to 100 ℃ steam is known as 2260kj / kg.
Q3=Mw×ΔQ;
The total heat demand is: q = Q1 + Q2 + Q3
*Example 2. the width of a special polymer material is 2m, the thickness is 0.5mm, the density after drying is 300kg / m^{3}, and the moisture content before processing is 12%. It is known that the speed of the production line is 10m / min, the specific heat of the material is 2kJ / kg. ℃, and the material temperature before processing is 20 ℃. It is necessary to heat the material to 160 ℃ with a heating roller. Find the net power required for this process.
Assuming that the heat utilization rate is 50% and the power configuration of each roller is about 35kw, how many heating rolls should be configured reasonably?
Answer:
the output of processed materials per hour：
P=10m/min×2m×0.5×10-3m×300kg/m³×60=180kg/hr；
Water content to be evaporated per hour：
Mw=180kg/hr÷（1-12%）×12%=24.5kg/hr；
Material heating demand：
Q1=P×ΔT×Cp
=180kg/hr×140℃×2kJ/kg.℃
=50400kJ/hr
Heat required to heat water from current temperature to 100 ℃：
Q2=Mw×（T2-T1）×Cw
=24.5kg/hr×80℃×4.18kJ/kg.℃
=8193kJ/hr
Heat required for water evaporation from 100 ℃ to 100 ℃ steam：
Q3=Mw×ΔQ
=24.5kg/hr×2260kJ/kg=55370kJ/hr
The total heat demand is:
q = Q1 + Q2 + Q3：
=50400kJ/hr+8193kJ/hr+55370kJ/hr
=113963kJ/hr
=113963/3600kJ/s
≈32kW
So the net power of the product is about 32kw.
Assuming that the heat utilization rate is 50%, then the actual configuration power is 64KW, and the power configuration of each roller is about 35kw, it is suggested that:
It is reasonable to configure two heating rollers;
If the reasonable power is determined, the selection of roller is half successful.
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