Energy balance, properties, cycles and state-change calculations.
MODULE OVERVIEW
Thermodynamics in practical engineering work.
Thermodynamics tracks energy, work and heat across a defined system boundary. State properties must be evaluated at the correct temperature, pressure, phase and composition.
CORE PRINCIPLES
What to establish first
Energy is conserved across a closed system or control volume.
Specific heat relates sensible temperature change to energy for an appropriate range.
Phase change and real-fluid effects need property data beyond a constant-cp model.
DESIGN CONCEPTS
Terms worth checking
System boundary
Enthalpy
Sensible versus latent heat
Common applications: Tank heating · Thermal storage · Process energy balances
KEY RELATIONSHIP
Sensible heat
Q = mcₚΔT
m — mass, kg
cₚ — specific heat, kJ/kg·K
ΔT — temperature change, K
Use a property value suitable for the fluid and temperature range; do not apply it through a phase change.
Use the relationship with compatible units, then review the result against the stated design conditions.
WORKED EXAMPLE
Known values → substitution → interpretation
Known values
m = 100 kg; cₚ = 4.186 kJ/kg·K; ΔT = 30 K
Method
Q = 100 × 4.186 × 30
Interpretation
The sensible heat is 12,558 kJ, or about 3.49 kWh.
KEY DESIGN CHECKS
Confirm the conditions behind the number
Define the governing load case, duty cycle and required design life before using a simplified relation.
Use compatible units and material data for the actual condition, temperature and manufacturing state.
Compare the result with strength, stiffness, fatigue, safety, serviceability and applicable-code requirements.
COMMON ENGINEERING MISTAKES
Keep the model within its scope
Applying sensible heat outside the assumptions shown on this page.
Using a nominal condition while a peak, alternating, transient or environmental case governs the design.
Treating a calculated value as a final component selection without checking interfaces, tolerances and the current governing standard.
ReferenceY. A. Çengel and M. A. Boles, Thermodynamics: An Engineering Approach.ScopeRelationships are presented for the assumptions stated on this page and linked tool.Design reviewCheck material condition, loads, environment and the applicable current code.SafetyResults are educational/preliminary and do not certify safety or compliance.
