Thermodynamics

Overview

Thermodynamics is the branch of physics that describes the relationships between heat, work, temperature, and energy. In engineering practice, thermodynamic calculations are essential for designing power plants, refrigeration systems, chemical processes, and HVAC equipment. These tools provide access to accurate thermophysical property data and equilibrium calculations needed for rigorous engineering analysis.

All thermodynamic calculations are implemented using CoolProp, an open-source library providing high-accuracy equations of state for pure fluids and mixtures. CoolProp implements reference-quality equations from NIST and peer-reviewed literature, covering over 120 pure fluids and enabling calculations for refrigerants, hydrocarbons, cryogens, and common industrial fluids. The library is built on NumPy for efficient numerical operations.

Thermophysical Properties: The PROPS_SI tool is the primary interface for calculating fluid properties such as density, enthalpy, entropy, viscosity, thermal conductivity, and speed of sound. Given any two independent state variables (e.g., temperature and pressure, or pressure and enthalpy), it returns any desired thermophysical property. This enables calculations for pump work, heat exchanger sizing, pipe flow analysis, and thermodynamic cycle evaluation. The PHASE_SI tool identifies the phase (liquid, vapor, two-phase, supercritical) at any state point—critical for avoiding calculation errors when properties behave differently across phase boundaries.

Chemical Properties: For process engineering applications, CHEMICAL_PROPS retrieves fundamental substance data including molecular weight, critical temperature and pressure, acentric factor, normal boiling point, and triple point conditions. These properties are essential inputs for equation-of-state calculations, vapor-liquid equilibrium modeling, and experiment transport property correlations.

Humid Air and Psychrometrics: HVAC and drying applications require specialized treatment of moist air. The HA_PROPS_SI tool calculates psychrometric properties including relative humidity, wet-bulb temperature, dew point, humidity ratio, and specific enthalpy of humid air. These calculations follow the psychrometric relationships defined in ASHRAE standards, enabling accurate analysis of air conditioning, dehumidification, and evaporative cooling processes.

Mixture Calculations: Real industrial processes often involve fluid mixtures rather than pure components. The MIXTURE_STRING tool creates properly formatted mixture specifications from component lists and mole fractions, which can then be used with MIXTURE_FLASH to perform vapor-liquid equilibrium (VLE) flash calculations. Flash calculations determine the equilibrium phase compositions and fractions when a mixture is brought to specified temperature and pressure conditions—fundamental to distillation, absorption, and separation process design.

Practical Workflow: For pure fluid calculations, call PROPS_SI directly with the fluid name and state conditions. To verify you’re in the expected phase region, use PHASE_SI. For humid air applications, use HA_PROPS_SI with appropriate psychrometric inputs. For mixture work, first construct the mixture definition with MIXTURE_STRING, then perform equilibrium calculations with MIXTURE_FLASH.

Tools

Tool	Description
CHEMICAL_PROPS	Retrieve physical and thermodynamic properties for a chemical specimen.
HA_PROPS_SI	Calculate humid air properties using CoolProp psychrometrics.
MIXTURE_FLASH	Perform a flash calculation for a chemical mixture and return key properties.
MIXTURE_STRING	Create a formatted CoolProp mixture string from component fluids and mole fractions.
PHASE_SI	Identify the phase of a fluid at a given state using CoolProp.
PROPS_SI	Calculate thermophysical properties of fluids using CoolProp.