# Vuilleumier cycle

Thermodynamics :
The classical Carnot heat engine :
Branches
Classical
Statistical
Chemical
Quantum thermodynamics
Equilibrium / Non-equilibrium :
Laws
Zeroth
First
Second
Third :
Systems
Closed system
Open system
Isolated system
State
Equation of state
Ideal gas
Real gas
State of matter
Phase (matter)
Equilibrium
Control volume
Instruments
Processes
Isobaric
Isochoric
Isothermal
Adiabatic
Isentropic
Isenthalpic
Quasistatic
Polytropic
Free expansion
Reversibility
Irreversibility
Endoreversibility
Cycles
Heat engines
Heat pumps
Thermal efficiency :
System propertiesNote: Conjugate variables in italics
Property diagrams
Intensive and extensive properties
Process functions
Work
Heat
Functions of state
Temperature / Entropy (introduction)
Pressure / Volume
Chemical potential / Particle number
Vapor quality
Reduced properties :
Material properties
Property databases
Specific heat capacity 
$c=$
$T$$\partial S$$N$$\partial T$
Compressibility 
$\beta =-$
$1$$\partial V$$V$$\partial p$
Thermal expansion 
$\alpha =$
$1$$\partial V$$V$$\partial T$ :
Equations
Carnot's theorem
Clausius theorem
Fundamental relation
Ideal gas law
Maxwell relations
Onsager reciprocal relations
Bridgman's equations
Table of thermodynamic equations :
Potentials
Free energy
Free entropy
Internal energy $U(S,V)$Enthalpy $H(S,p)=U+pV$Helmholtz free energy $A(T,V)=U-TS$Gibbs free energy $G(T,p)=H-TS$ :
HistoryCulture
History
General
Entropy
Gas laws
"Perpetual motion" machines
Philosophy
Entropy and time
Entropy and life
Brownian ratchet
Maxwell's demon
Heat death paradox
Loschmidt's paradox
Synergetics
Theories
Caloric theory
Vis viva ("living force")
Mechanical equivalent of heat
Motive power
Key publications
An Inquiry Concerning the Source ... Friction
On the Equilibrium of Heterogeneous Substances
Reflections on the Motive Power of Fire
Timelines
Thermodynamics
Heat engines
ArtEducation
Maxwell's thermodynamic surface
Entropy as energy dispersal :
Scientists
Bernoulli
Boltzmann
Bridgman
Carathéodory
Carnot
Clapeyron
Clausius
de Donder
Duhem
Gibbs
von Helmholtz
Joule
Kelvin
Lewis
Massieu
Maxwell
von Mayer
Nernst
Onsager
Planck
Rankine
Smeaton
Stahl
Tait
Thompson
van der Waals
Waterston :
Other
Nucleation
Self-assembly
Self-organization
Order and disorder :
Category :
vte :
The Vuilleumier cycle was patented by a Swiss-American engineer named Rudolph Vuilleumier in 1918. The purpose of Vuilleumier's machine was to create a heat pump that would use heat at high temperature as energy input. The Vuilleumier cycle...
   utilize[s] working gas expansion and compression at three variable volume spaces in order to pump heat from a low to a moderate temperature level. The interesting characteristic of the Vuilleumier machine is that the induced volume variations are realized without the use of work, but thermally. This is the reason why it has a potential to operate at modern applications where the pollution of the environment is not a choice. It is a perfect candidate for such applications, as it consists only of metallic parts and inert gas. Using these units for heating and cooling buildings, large energy savings can be accomplished as they can be operated at small scale in common buildings or at large scale providing heat power to entire building blocks without using fossil fuels. The use of Vuilleumier machines for industrial applications or inside vehicles is also a feasible option. Another field where these machines have already been involved is cryogenics, as they are also able to provide refrigeration at very low temperatures like the very similar and well-known Stirling refrigerators.
The Vuilleumier cycle is a thermodynamic cycle with applications in low-temperature cooling. In some respects it resembles a Stirling cycle or engine, although it has two "displacers" with a mechanical linkage connecting them as compared to one in the Stirling cycle. The hot displacer is larger than the cold displacer. The coupling maintains the appropriate phase difference. The displacers do no work—they are not pistons. Thus no work is required in an ideal case to operate the cycle. In reality friction and other losses mean that some work is required.
Devices operating on this cycle have been able to produce temperatures as low as 15 K using liquid nitrogen to pre-cool. Without precooling 77 K was reached with a heat flow of 1 W.
The cycle was first patented by Vuilleumier in 1918 with patent US1275507, and again in Leiden by KW Taconis in 1951. In March 2014, the Vuilleumier Cycle was tested in application with updating conventional HVAC (heating, ventilation, and air-conditioning) systems by utilizing the cycle's proposed thermodynamic process of moving heat energy, and having results of increased output efficiencies coupled with a reduced carbon footprint. This work was completed by ThermoLift), a company based out of the Advanced Energy Research and Technology Center at Stony Brook University, with collaboration from the US Department of Energy and the New York State Energy Research and Development Authority (NYSERDA). This work culminated in the demonstration of the ThermoLift system at Oak Ridge National Laboratory in August, 2018. The demonstration showed that the ThermoLift technology (TCHP), is able to achieve coefficients of performance (COP) for the cycle that well exceeded the DOE’s target COPs for cold-climate heat pumps (although not at all exceeding Geothermal heat pump efficiencies). Furthermore, due to the nature of the TCHP, there is no significant capacity decrease as the inlet temperature to the cold HX decreases.