Computational Methods for Absorption Working Pairs: A Research Review

Version v1.2 · 2026-10-14

This is a living document. It is revised as further method sets are verified in the underlying reading programme; each revision is logged at the end. Statements that the underlying sources leave unresolved are marked [to be verified]. The review records methods side by side — their forms, validity ranges, reference states and verification status — and draws no ranking among them.

1. Introduction

Every absorption refrigerator or heat-pump calculation passes through the same narrow gate: the thermophysical properties of the working pair. A cycle model needs the solution vapour pressure Psol(T, ξ), the bubble-point and dew-point temperatures, and the specific enthalpy of the solution hsol at every state point; the generator, absorber and solution heat-exchanger balances are only as definite as the correlations behind these quantities.

Two practical difficulties recur throughout the literature surveyed here. The first is dispersion. For a single pair such as LiBr–H₂O, method sets coexist from journal papers, theses, handbooks and manufacturers' booklets spanning 1971–2025, fitted to different data batches, in different functional forms (per-property polynomials, Dühring-type relations, activity-coefficient models, single Gibbs-energy equations), and with three concentration conventions in simultaneous use (weight-percent numbers, mass fractions, mole fractions). The second is degradation in transmission: correlations are reprinted from paper to thesis to textbook, and along these chains coefficients acquire sign errors, lost exponents and altered values (Section 5); enthalpy reference states also differ between sets, so enthalpies from two sets cannot be compared — or combined — until their zero points are aligned.

This review compiles the method sets that an ongoing survey has located, transcribed and, where the sources permit, checked by recomputation. The pairs covered are listed in Section 2.1; the methods are organised by refrigerant and, within each refrigerant, by absorbent (Section 3), followed by the pure-fluid fits on which several pair models rest (Section 4), an account of the provenance and transcription-error auditing that accompanies the survey (Section 5), and a list of open gaps (Section 6).

2. Scope and method of this review

Census. A census of the published literature (begun 2026-09-28) admits a source as a method only if it prints explicit equations with numerical constants; sources giving data tables without fitted equations are registered as data-type leads. Each admitted pair is graded: A — bubble point and enthalpy both programmable; B — vapour–liquid equilibrium (VLE) only; C — candidates, gaps and exclusions.

Verification. Four forms of checking are used, and the review states which form stands behind each entry: (i) recomputation against the source's own measured points or printed tables; (ii) cross-implementation agreement between independent Python and C implementations of the same transcription; (iii) design-point and endpoint back-checks (for example, an enthalpy polynomial whose pure-refrigerant endpoint is structurally required to vanish); (iv) same-point comparison of two method sets against a third reference (CoolProp 8.0 in the cases reported here). A distinction is maintained throughout between a source's self-reported fit residuals and residuals recomputed in this survey.

Validity ranges and reference states. Every method is recorded with the temperature, pressure and composition range of its underlying data; implementations in the associated library refuse evaluation outside these ranges rather than extrapolating silently. Enthalpy reference states are recorded per set, because they differ (Section 3, passim).

Provenance. Each set is labelled original fit, compilation, transcription or re-fit, with the basis of the judgement recorded: equation-by-equation comparison, coefficient fingerprints, endpoint structure tests, or numerical back-checks (Section 5).

The associated library. Verified sets are built into an open-source library (MIT licence) with three implementations per pair — Python (reference), C, and Excel VBA worksheet functions — under a unified naming system: Psol, Pref, TdewByTsolXi, XiByTsolTdew, hgas, hliq, hsol, hlat = hgas − hliq, TsolByHsol. The VBA modules are ported line-by-line from the verified Python/C code but have not been compiled in a real Excel session; this caveat applies to every "built" status below.

Classification. This review organises the pairs by a two-level scheme: the first level is the refrigerant, the second the absorbent. Section 2.1 lists every pair covered, in that order, and Section 3 follows the same order. A derivative complex absorbent is registered under its own name within its parent absorbent family, and a binary refrigerant blend counts as one refrigerant entry.

2.1 Pairs covered by this review

The pairs covered are listed below in the classification order (refrigerant, then absorbent). The last column states, in one line, the method sets on record for the pair and their verification status; the full accounts are in Section 3. Pairs for which the census found no source printing explicit equations with constants are not listed; they appear as gaps in Section 6.

Second-level pages: NH₃ · H₂O · CH₃OH · Halocarbons and hydrocarbons · Pure fluids

Overview. Table 1 collects the principal sets. It is maintained as an extensible table: newly verified sets are added as rows in the same columns, in the classification order of Section 2.1, and a row's verification status is upgraded as checking progresses.

Table 1. Principal method sets by refrigerant and absorbent.

5. Provenance and transcription-error auditing

Because these correlations circulate by reprinting, the survey maintains a standing register of transcription and printing errors (entries TE-001 to TE-076 at the time of writing), each with the wrong and correct values, the detection method, the quantitative impact, and the disposition. Four detection methods recur: coefficient-by-coefficient comparison of two chains; endpoint structure tests; back-calculation from the source's own tables or figures; and numerical fingerprinting. Three confirmed cases and one falsification illustrate the scale of the effects.

TE-001 (transcription chain). In the SCIRP chain of the Ferreira NH₃–NaSCN set, the X³ coefficient of the enthalpy polynomial A is printed as −3.5137; the parallel Yin chain gives −295.67. The endpoint test decides: the Yin chain gives A(1) = −0.05 ≈ 0, the SCIRP chain A(1) = +292.11, which is physically impossible; and −3.5137 is identical, digit for digit, to the SCIRP chain's own B-polynomial X³ coefficient — the coefficient was copied from the wrong polynomial. The chain's enthalpies run 33–52 kJ/kg high at six comparison points; its enthalpy equation is excluded, while its bubble-point equation (within +0.014 to +0.016% of the Yin chain at six points) remains usable as corroboration.

TE-014 (original-paper misprint). In Pátek & Klomfar (2006), the 22nd of the 30 enthalpy coefficients is printed as 2.33910E1; back-calculation at the paper's own six Table 9 points reproduces both p and h only with 2.33910E−1 — a factor-of-100 exponent error in the original printing.

TE-015 (original-paper misprint). In Chua et al. (2000), Table 1, coefficient B₁₂ is printed as +3.12628E−16 without its minus sign (the glyph is clean at 800 dpi, so this is not a reading error). With the positive value, BD(30) = 336.8 against the ≈4.5 implied by the paper's Fig. 2; with the negative value Fig. 2 is reproduced. The library implements −3.12628E−16.

TE-050 (non-self-consistent parameter set). A 2014 thesis reports new VLE measurements for R161 + DMAC, R161 + NMP, R134a + DMAC and R134a + NMP with five-parameter NRTL correlations. Substituting the printed equations and parameters at one of its own points (R161 + DMAC, T = 303.15 K, x₁ = 0.4058; measured p = 0.3315 MPa) returns a bubble pressure of ≈0.000078 MPa — a factor of about 4000 from the measurement; the printed α values (5.935–18.97) also lie far outside the conventional NRTL span of 0.2–0.5. The parameter sets are marked [to be verified] and excluded from building; the measurement tables remain usable. The register exists so that such sets are documented and excluded rather than silently "corrected".

6. Gaps and open problems

• R124–NMP / R124–DMF solution enthalpy. Only VLE correlations have been published (Xu et al. 2017); no mixture-enthalpy, density or viscosity correlation for either pair has been found.
• Ferreira (1984) arbitration. The sign of the C-polynomial's first term in the NH₃–NaSCN enthalpy (two readings differing by up to ≈10 kJ/kg at 90 °C) awaits direct reading of the archived 1984 paper; the Delft reports K 91/K 92 have not been located publicly.
• NH₃–LiNO₃ viscosity. The only located correlation is typographically damaged in its source; the reconstruction in circulation is unverified.
• Equation faces to be settled against the originals: Schulz (1971); Kim & Ferreira (2006), including its reference-constant units [to be verified].
• (R32 + R227ea)/DMF has no published measured VLE and no solution-enthalpy model; its dossier is marked as having no experimental anchor.
• Full texts not yet obtained: Wang, Jia & Wang (2021) on R290 + oil (the one located source that may carry both bubble point and enthalpy for a hydrocarbon–oil pair).
• Missing literature: no source printing explicit equations with constants was found for R142b, R123, CH₃OH–LiCl or ethanol–salt pairs.
• Excel verification: all built VBA modules remain uncompiled in a real Excel session (Section 2).

7. References

Bibliographic fields not present in the survey materials are marked [bibliographic detail pending] rather than completed from memory.

1. Pátek, J., Klomfar, J. "Simple functions for fast calculations of selected thermodynamic properties of the ammonia-water system." International Journal of Refrigeration 18(4), 228–234, 1995.
2. Conde, M. Thermophysical Properties of NH₃+H₂O Solutions for the Industrial Design of Absorption Refrigeration Equipment. M. Conde Engineering, Zurich, 2004.
3. Schulz, S. C. G. "Equation of state for the system ammonia-water for use with computers." 1971. [bibliographic detail pending]
4. Patterson, M. R., Perez-Blanco, H. "Numerical fits of the properties of lithium-bromide water solutions." ASHRAE Transactions 94(2), 2059–2077, 1988.
5. Chua, H. T., et al. "Improved thermodynamic property fields of LiBr-H2O solution." International Journal of Refrigeration 23, 412–429, 2000.
6. Pátek, J., Klomfar, J. [LiBr–H₂O correlations.] International Journal of Refrigeration 29, 566–578, 2006. DOI 10.1016/j.ijrefrig.2005.10.007. [bibliographic detail pending: article title]
7. Kaita, Y. "Simulation results of triple-effect absorption cycles." International Journal of Refrigeration 25, 999–1007, 2002. (See also Kaita, Int. J. Refrigeration 24, 374–390, 2001; which of the two the transcribed set follows is [to be verified].)
8. Kim, D. S., Infante Ferreira, C. A. "A Gibbs energy equation for LiBr aqueous solutions." International Journal of Refrigeration, 2006. [bibliographic detail pending: volume and pages]
9. McNeely, L. A. [Dühring equilibrium equation for LiBr–H₂O.] 1979. [bibliographic detail pending]
10. Jia Mingsheng. [Correlation equations for the principal property parameters of lithium bromide aqueous solution.] Journal of Zhanjiang Ocean University 22(3), 52–58, 2002. (Title as recorded in Chinese in the survey notes.)
11. ASHRAE. ASHRAE Handbook — Fundamentals. 2009.
12. Infante Ferreira, C. A. "Thermodynamic and physical property data equations for ammonia-lithium nitrate and ammonia-sodium thiocyanate solutions." Solar Energy 32(2), 231–236, 1984.
13. Libotean, S., et al. [NH₃–LiNO₃ vapour pressure.] Journal of Chemical & Engineering Data 52, 1050–1055, 2007. [bibliographic detail pending: article title]
14. Libotean, S., et al. [NH₃–LiNO₃ specific heat, density, viscosity.] Journal of Chemical & Engineering Data 53, 2383–2388, 2008. [bibliographic detail pending: article title]
15. Amaris Castilla, C. F. Intensification of NH3 Bubble Absorption Process Using Advanced Surfaces and Carbon Nanotubes for NH3/LiNO3 Absorption Chillers. Doctoral thesis, Universitat Rovira i Virgili, 2014.
16. Cai Dehua. [Theory and experiment of a small air-cooled ammonia/salt non-adiabatic absorption refrigeration system.] Doctoral thesis, Huazhong University of Science and Technology, 2015. (Title as recorded in Chinese in the survey notes.)
17. Liang Xiao. [Micro-scale falling-film absorption enhancement of ammonia–salt working pairs in vertical tubes.] Doctoral thesis, Huazhong University of Science and Technology, 2022. (Title as recorded in Chinese in the survey notes.)
18. Yin Jiayuan. [Solar-driven NaSCN–NH₃ absorption refrigeration system.] Master's thesis, Huazhong University of Science and Technology, 2015. (Title as recorded in Chinese in the survey notes.)
19. Zehioua, R., et al. [R134a + DMF vapour–liquid equilibrium.] Journal of Chemical & Engineering Data, 2009. DOI 10.1021/je900440t. [bibliographic detail pending: article title]
20. Xu, S., et al. [R124 + NMP / R124 + DMF vapour–liquid equilibrium.] Journal of Chemical & Engineering Data 62, 3414–3422, 2017. [bibliographic detail pending: article title]
21. Borde, I., Jelinek, M., Daltrophe, N. C. [R124–DMAC correlations.] International Journal of Refrigeration 20(4), 1997. [bibliographic detail pending: article title and pages]
22. Ando, E., Takeshita, I. [R22–DEGDME correlations.] International Journal of Refrigeration 7(3), 1984. [bibliographic detail pending: article title and pages]
23. Nezu, Y., et al. [R134a + DMA/DMF/glyme-ether working pairs.] IIR Commissions B1/B2/E1/E2, Guangzhou, 2002. [bibliographic detail pending]
24. Chen, W., Bai, et al. [NH₃/[emim]Cu₂Cl₅ working pair.] Energy 112, 332–341, 2016. [bibliographic detail pending: article title]
25. Chen, et al. [NH₃/[bmim]Zn₂Cl₅, UNIFAC.] Fluid Phase Equilibria 360, 1–6, 2013. DOI 10.1016/j.fluid.2013.09.011. [bibliographic detail pending: article title]
26. Critoph, R. E., Rivero Pacho, et al. [Methanol–salt working pairs.] Energies 15(4), 1449, 2022. DOI 10.3390/en15041449. [bibliographic detail pending: article title]
27. El-Shamarka, S. [Methanol–inorganic bromide working pairs.] Doctoral thesis, Cranfield Institute of Technology, 1981. [bibliographic detail pending: thesis title]
28. Iedema, P. D. [Methanol–LiBr/ZnBr₂ working pairs.] Doctoral thesis, TU Delft, 1984. [bibliographic detail pending: thesis title]
29. Marcelino Neto, M. A., Barbosa, J. R. [R600a + POE oil.] International Journal of Refrigeration 31, 34–44, 2008. DOI 10.1016/j.ijrefrig.2007.08.004. [bibliographic detail pending: article title]
30. Haar, L., Gallagher, J. S. "Thermodynamic properties of ammonia." Journal of Physical and Chemical Reference Data 7, 635–792, 1978.

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