1. Define the process
Use a mean heat capacity for the material being heated. The water example is approximate.
Positive net duty means external heating is required. Negative net duty means cooling is required. Reaction heat and environmental heat gains can offset heating demand.
2. Include additional heat terms
Turn on only the terms that apply. Disabled terms are excluded from the balance.
Enter the overall molar reaction rate, not total stream flow or a rate per unit vessel volume. Divide a reactant’s molar consumption rate by its stoichiometric coefficient in the reaction as written. For a batch, enter the total reacted amount on the same basis.
Enter a positive magnitude; choose whether the reaction releases or absorbs heat.
Use ΔH for the same reaction and reference basis as the extent. In this simplified balance, ΔH is evaluated at the initial/inlet temperature, followed by heating the resulting material to the final temperature.
Use latent heat at the actual transition conditions. The default is an illustrative water vaporization value. cp must represent the sensible portions of the heating path, excluding latent heat.
Use conductance through all relevant resistances, including walls, insulation, and external heat transfer.
Temperatures use the selected °C/°F unit. For a batch, enter a time-average process temperature. Use a combined coefficient only when any radiation contribution is valid for these surroundings.
Positive: heat leaves the process. Negative: heat enters from surroundings.
This term excludes the heater/cooler being sized. Do not count the same loss again in another term. Negative temperature difference correctly produces environmental heat gain.
Enter process conditions and calculate.
3. External heating or cooling requirement
| Heat-balance term | Signed contribution (kW) | Effect |
|---|
Batch results are total energy and average duty over the entered duration. They do not predict peak reaction heat release, heat-up time at fixed power, or thermal runaway.
This is heat delivered to or removed from the process. Fuel/electrical input, refrigeration power, equipment margins, and utility efficiency are separate sizing steps. Use the Heat Exchanger Calculator to assess a suitable heat-transfer system.
Energy-balance method
Q̇surroundings = UA (Tprocess − Tambient), or a directly entered signed heat rate
Batch: Eexternal = m cp (Tfinal − Tinitial) + ξ ΔHreaction + m f ΔHphase + Q̇surroundings × time
Average batch duty = Eexternal / time
Exothermic ΔHreaction is negative; endothermic is positive. Vaporization or melting enthalpy is positive; condensation or freezing is negative. Heat loss to surroundings is positive. Reaction and phase directions supply these signs automatically.
Assumes a lumped process with one effective mass and heat capacity, no shaft work, negligible kinetic and potential energy changes, and constant representative properties. For reacting streams with changing composition, use a consistent enthalpy path: reaction at the initial/inlet reference temperature, then sensible heating of the products. If a single effective cp cannot represent that path, use a detailed species enthalpy balance. Do not add reaction heat if your stream enthalpies already include heats of formation.
Reaction extent must be known from conversion or measured reaction progress; kinetics are not predicted. No chemical-property database, equilibrium, vapor fraction, or latent heat is calculated automatically. Environmental exchange assumes the entered representative conditions persist, or represent the appropriate average.
References: LearnChemE: energy balances with reaction; Reaction-engineering energy-balance lecture notes.