Heat transfer fluid (thermic oil) is the closed-loop heat carrier — heated in a boiler, circulated through process equipment, returned cool. Replaces steam where temperatures above 200 °C are needed at modest pressure. Three families: mineral oil (300 °C bulk), synthetic aromatic Therminol VP-1 class (400 °C), silicone Syltherm (extreme -75 to +400 °C). India market driven by textile dyeing, pharma reactor, food processing, chemical reactor. This guide gives the mineral thermic oil BOM and decision criteria vs synthetic. Thermic oil sits in a wider specialty-fluid portfolio alongside brake fluid formulation and power steering fluid formulation, which share QC and ashless-chemistry disciplines.
| Component | Function | % (m/m) | Indian Supplier |
|---|---|---|---|
| Group II 110N or hydrocracked premium base oil | Primary base — high thermal stability | 92.0% | HPCL Group II / Reliance hydrocracked |
| Methylene-bis-DTBP phenolic AO (low-volatility) | Primary high-temp AO | 2.0% | Albemarle Ethanox 4710 |
| Alkylated DPA aminic AO | High-temp secondary AO synergist | 1.5% | LANXESS Naugalube 438L |
| Sulphurised olefin (peroxide decomposer) | Hydroperoxide chain-terminator | 1.0% | Lubrizol Anglamol low-S |
| Alkenyl-succinic-acid CI | Ferrous rust (start-up condensation) | 0.3% | King K-Corr 200 |
| Thiadiazole CI | Yellow-metal protection | 0.2% | Vanderbilt Vanlube 887 |
| Silicone foam inhibitor | Foam control | 100 ppm | Dow Corning DC200 |
| Group II 220N diluent | KV / flash fine-tune | 2.99% | HPCL Group II |
| TOTAL | 100.0% | — | |
| CRITICAL: NO ZDDP, NO metallic detergent — ash deposit on heater tubes causes failure | |||
Process: blend Group II + diluent at 60 °C; charge ashless AO blend + peroxide decomposer + CI; foam inhibitor last. QC: KV40 32 cSt, flash point >220 °C (D92), pour <-15 °C, RPVOT D2272 >1,500 min, copper strip 1B, sulphur <300 ppm, distillation residue at 350 °C <5%. Ex-works cost ₹140-200 / L at 5 MT batch. Service limit bulk 300 °C / film temperature 320 °C. For service >300 °C bulk — recommend Therminol VP-1 / Dowtherm A synthetic. Each batch is released against ASTM lubricant & grease testing for RPVOT, flash point, copper strip and distillation residue.
Heat transfer fluid (thermic fluid, thermal oil) is the liquid heat-carrier used in closed-loop heating systems — heated in a boiler / heater, circulated through pipework to deliver heat to process equipment, returned cool. Replaces steam where temperatures above 200 °C are needed at modest pressure.
Three HTF families: mineral oil thermic fluid (Group I / II base, service to 300 °C bulk), synthetic aromatic (Therminol VP-1, Dowtherm A — 400 °C), silicone (Dow Corning Syltherm — extreme -75 to +400 °C). Used in textile dyeing, pharma reactor, food cooker, chemical reactor.
Mineral thermic oil ISO VG 32 BOM (%): Group II 110N or hydrocracked premium base 92%, methylene-bis-DTBP phenolic AO 2%, aminic AO 1.5%, sulphurised olefin peroxide decomposer 1%, ASA + thiadiazole CI 0.5%, silicone foam inhibitor 100 ppm, balance Group II diluent.
QC: KV40 32 cSt, flash >220 °C, pour <-15 °C, RPVOT >1,500 min, copper strip 1B, sulphur <300 ppm. Service limit bulk 300 °C / film 320 °C. Ex-works ₹140-200/L.
Therminol VP-1 / Dowtherm A / Diphyl is the eutectic 26.5% diphenyl + 73.5% diphenyl oxide — a specific chemistry. Melting point 12 °C, boiling 257 °C, bulk service to 400 °C. Cannot be 'formulated' from base oils — pure synthetic chemistry.
Indian sourcing via import (Solutia / Eastman, Dow). Lubechem custom for Therminol-class doesn't make sense — recommend client buy genuine Therminol VP-1. For service to 320 °C bulk, premium mineral (LC-THERMIC-300) is cost-effective alternative.
India thermic oil: (1) Textile dyeing — stenter, calender, dyeing kier — 220-280 °C, biggest segment. (2) Pharmaceutical reactor jacketing (Sun, Cipla, Dr Reddy's, Lupin, Aurobindo) — 150-280 °C. (3) Food processing — bakery oven, deep fryer, kettle — 180-260 °C. (4) Chemical reactor jacket — 200-320 °C. (5) Paper machine yankee dryer. (6) Solar thermal power plant (Therminol).
Volume ~80-120 ML/year. Brands: Mobiltherm 605 / 603, Shell Thermia B, Castrol Perfecto T, Therminol 55 / 66, IOCL Servotherm, BPCL Mak Therm Oil. ₹140-280 / L. A fast-growing adjacent thermal-management segment is EV fluid formulation, where dielectric coolants carry heat away from battery packs and e-axles.
Mineral thermic oil service life 3-6 years typical (24,000-50,000 hr). Degradation: (1) Thermal cracking at hot-spots gives low-MW species — viscosity decrease, flash drop. (2) Oxidation at O2-contaminated sections — viscosity increase. (3) Carbon deposit on heater tubes.
Annual oil analysis tracks KV40 (±5% of fresh), TAN (max 0.5), flash drop max 25 °C, distillation residue, particle count. When TAN >0.5 or flash drop >25 °C, oil change required.
Metallic additives (ZDDP, Ca / Mg detergent) deposit ash on heater tubes when thermic oil is heated to 280-320 °C film temperature. Ash insulates the tube, reduces heat transfer, eventually causes hot-spot and tube failure.
Thermic oil uses ASHLESS additive chemistry only — phenolic + aminic AO, sulphurised olefin peroxide decomposer (S burns to gas), ASA CI (organic), thiadiazole. ZDDP, detergents, polysulfide phosphate are excluded. Key chemistry constraint vs PCMO. Building a compliant ashless package is a dedicated additive package development exercise in its own right.
Share your service temperature, application (textile / pharma / food / chemical / solar), system volume and budget. We respond within one business day with the BOM and ex-works cost.