# Heat Calculation Considerations and Equations

"Calculations determine the amount of heater wattage required for process startup and process operation"

CONSIDERATIONS FOR PROCESS STARTUP:

1. Wattage to heat material
2. Wattage to heat container or tank (if applicable)
3. Wattage to heat racks and hardware in container(if applicable)
4. Wattage to change material state (if applicable)
5. Wattage to counteract material or container heat loss (if applicable)
CONSIDERATIONS FOR PROCESS OPERATION:
1. Wattage to heat material transferred in and out (if applicable)
2. Wattage to heat racks and hardware transfer in and out (if applicable)
3. Wattage to change material state (if applicable)
4. Wattage to counteract material or container heat loss (if applicable)
I. THE WATTAGE REQUIRED TO RAISE THE TEMPERATURE OF ANY MATERIAL DEPENDS UPON THESE PRIMARY FACTORS:
1. The weight of the material
2. The temperature change required (final temperature - initial temperature) commonly expressed as "ÆT"
3. The specific heat of the material (see definition terminology. Specific heat charts list specific heat values for many materials.
4. Heatup time required
II. BASIC EQUATION (INITIAL MATERIAL HEATUP):

 Wattage = WEIGHT (lbs) X SPEC. HEAT (btu/lb °F) X TEMP. CHANGE (°F) 3.412 (BTU TO WATT/HR CONVERSION) X HEATUP TIME IN HOURS

III. EQUATIONS FOR ADDITIONAL WATTAGE REQUIREMENTS

2. Wattage req'd to heat container or tank (if applicable):

 Wattage = Wt. of container (LB) x Sp. Ht. (Btu/lb. °F) x temp. changes (°F) - watts 3.412 Btu/watt hr. x heatup time (hr)

3. Wattage required to heat hardware in container (if applicable):

calculation similar to #1 and #2 = watts

4. Wattage required to melt a solid to a liquid (if applicable) at constant temperature:

 Wattage = Heat of fusion (Btu/lb) x weight of material melted/hr. (lb/hr) 3.412 Btu/watt hr.

5. Wattage required to change a liquid to a vapor state at constant temperature (if applicable):

 Wattage = Heat of vaporization (Btu/lb) x weight of mat'l vaporized/hr 3.412 Btu/watt. hr

Heats of fusion (solid to liquid) and vaporization (liquid to gas) are the heat energy required to change a lb. of the material from state to state at constant temperature.

6. Wattage to counteract liquid surface losses (if applicable) See Graph for loss rate of materials:

 average wattage loss = Total liquid surface area (sq. ft.) x loss rate at final temp. (watts/sq. ft.) 2

7. Wattage to counteract losses from container walls, platen surfaces, etc. See Graph for losses from surfaces:

 average wattage loss in heatup = Total area of surface (sq. ft.) x Loss rate @ final temperature (watts/sq. ft.) 2

IV. OPERATING WATTAGE REQUIREMENTS

Operating requirements should include some or all of the following plus some miscellaneous losses which should be estimated and included:

1. Wattage to counteract losses from open liquid surfaces: (See graph for loss rates of water and oils) Total liquid surface area (sq. ft.) x loss rate at operating temperature (watts/sq. ft.) = operating wattage losses

2. Wattage to counteract container or platen surface losses, (See graphs for loss rates) Total liquid surface area (sq. ft.) x loss rate at operating temperature (watts/sq. ft.) = operating wattage losses

3. Wattage required to heat material transferred in and out of the system (Metal dipped in heated tanks, air flows, make-up liquids, etc.)

 wattage to heat material = [Weight of material heated per hour (Lb/hr)] x [Sp. ht. (Btu/LB °F)] x [Temperature changes of material (°F.)] 3.412 Btu/watt. hr

4. Heatup of racks or containers, etc. transferred in and out of the system:

 wattage to heat equipment = Weight of items (Lb/hr) heated/hr. x Sp. ht. of material (Btu/LB °F) x temperature change (F) 3.412 Btu/watt. hr

5. Melting or vaporization of material requirements should also be included if applicable. Drying, or evaporation, requires use of the heat of vaporization.    We Ship Our Industrial Process Heaters To OEM’s & Industry World Wide.

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