Reactor Thermal Oil Selection and Circulation Pump Guide

What operating data are needed before selecting reactor thermal oil?

The design guide supplied for this topic, labeled as published on September 11, 2026, provides a starting point for discussing expansion tanks, circulation and film temperature. Its publication date and original content have not been independently verified. This article therefore uses general heat-transfer principles and the supplied Chemie product data rather than treating the reference as verified recent industry news.

Chemical and pharmaceutical reactors often alternate between heating, holding and cooling, with heat duty changing between batches. First distinguish process material temperature from thermal oil temperature: the target batch temperature is not the required jacket supply temperature. The necessary temperature difference also depends on jacket area, process viscosity, agitation and fouling. Exothermic reactions require a separate assessment of cooling capacity and abnormal operating conditions.

Use a three-stage workflow: collect operating conditions, screen fluids, then verify the system. Gather supply and return temperatures, minimum shutdown ambient temperature, heating and cooling times, heat duty, allowable jacket pressure and heating method. Screen fluids by operating range, film temperature, pour point, flash point and viscosity. Then verify the circulation pump, heater, expansion tank, seal materials and protective interlocks.

How do operating temperature, film temperature, pour point and flash point differ?

Operating temperature refers to the bulk circulating fluid; film temperature refers to the local fluid layer next to a heated surface. Film temperatures near heater tubes or electric heating elements can exceed bulk temperature. Higher local heat flux, insufficient flow and fouling increase overheating risk. The equipment supplier should assess film temperature using heat flux, flow geometry and heat-transfer conditions, with an appropriate operating margin.

Pour point describes low-temperature flow behavior; it is not an allowable pump startup temperature. Flash point indicates the potential for vapor ignition under specified test conditions—not an operating-temperature limit or autoignition temperature. Where operating temperature exceeds flash point, assess containment, leak prevention, ventilation, hot-surface protection and applicable codes. A closed system does not eliminate fire risk.

The table supports initial screening. Direct viscosity comparisons require the same measurement temperature. Eurotherm 330 is shown at -30°C and should not be ranked directly against values measured at 40°C. Flash-point test methods are stated only where provided. Request viscosity-temperature curves, density, specific heat and vapor-pressure data separately.

How do startup viscosity and circulation flow affect pump selection?

During a cold start, increased viscosity generally raises circuit resistance and changes pump flow, head and efficiency. Motor load and suction conditions therefore need checking. Obtain viscosity at the actual startup temperature from the fluid supplier and ask the pump manufacturer to apply viscosity corrections. Kinematic viscosity at 40°C cannot substitute for winter startup data; confirm pumpability when approaching the fluid's lower operating limit.

For single-phase liquid circulation, using suitable mean fluid properties over an applicable temperature interval, estimate volumetric flow with Qᵥ = P / (ρ × cₚ × ΔT). Here, P is heat duty, ρ is density, cₚ is specific heat and ΔT is the supply-return temperature difference; use consistent units. At a given duty, a smaller temperature difference generally requires more flow. Design flow must also satisfy the heater minimum flow and jacket heat-transfer requirements. For parallel reactors, check flow distribution through each branch.

Check pump operating points under both cold and hot conditions, including total circuit pressure drop, control-valve losses, motor power, seal temperature capability and material compatibility. For hot operation, assess available net positive suction head using vapor pressure, inlet pressure, elevation head and suction losses. A larger pump is not automatically the solution: insufficient flow can raise film temperature, while excessive flow can increase pressure drop, energy use and jacket pressure loading.

How much expansion space does a closed thermal oil system need?

All listed Chemie fluids are for liquid-phase operation in closed systems requiring nitrogen blanketing or a cold-oil seal. Closed operation does not remove the need for pressure control. Establish operating conditions from vapor pressure at the highest working temperature, circulation losses, pump inlet requirements and equipment pressure limits, with suitable pressure relief and protective devices.

Base expansion calculations on the entire fluid inventory, including the heater, piping, reactor jackets, heat exchangers and associated vessels. For a fixed mass of fluid that can be treated as having a uniform temperature, estimate expansion using ΔV = Vcold × (ρcold / ρhot − 1). Calculate sections separately where their temperatures differ. Expansion-tank sizing must also allow for minimum operating level, normal level fluctuations, gas space and abnormal operating conditions. Calculated fluid expansion is not the required total tank volume.

Eurotherm 100 has an upper operating limit of 175°C and a listed boiling point/distillation value of 99°C. This illustrates why operating range alone cannot determine system pressure. For higher-temperature liquid circulation, obtain the vapor-pressure curve and establish the pressure needed to maintain the liquid phase. Check the expansion tank, pump inlet and overall equipment pressure ratings together; nitrogen blanketing is not a substitute for pressure design.

What maintenance checks and RFQ details should users prepare?

Before startup, follow equipment procedures to check system cleanliness, residual moisture, valve positions, fluid level and seals. Complete circulation, venting and any necessary dehydration before normal heating. Enable heating only after confirming adequate flow. During shutdown, normally stop heating first and maintain circulation as specified by the equipment supplier to dissipate residual heat. Interlock heating permission with circulation status and provide appropriate overtemperature, low-level and pressure protection.

Record supply and return temperatures, flow or differential pressure, pump current, expansion-tank level and makeup-fluid additions. A larger temperature difference at the same duty, unusual pump noise, pressure fluctuations or abnormal level changes can warrant checks for insufficient flow, entrained gas, leaks or fluid deterioration. In-service testing may include viscosity, acid number, moisture, flash point and insolubles. Set test scope and intervals according to operating conditions, baseline fluid properties and testing recommendations—not a universal oil-change interval.

Process RFQ checklist: target batch temperature; jacket supply and return temperature ranges; minimum ambient and startup temperatures; reactor count and simultaneous operation; working batch quantity and available thermal properties; heating and cooling times; normal and abnormal heat duties; exothermic reaction potential; whether one fluid serves both heating and cooling; and contamination-control or material-compatibility requirements.

Equipment RFQ checklist: fired or electric heater duty, heated-surface information and minimum flow; jacket design and allowable pressure; pipe diameters and lengths; valve, filter and heat-exchanger pressure drops; existing pump curves, motor and seal details; total fluid inventory; expansion-tank volume, levels and elevation; nitrogen-blanketing or cold-oil-seal arrangement; and the existing fluid, operating condition and residual-fluid removal plan. Submit these details through the Chemie Parameter Selection Tool at https://calculator.szchemie.com.cn/select or the AI Selection Tool at https://calculator.szchemie.com.cn/ai. Tool results support initial screening; equipment suitability and safety conditions still require engineering verification.

Which Chemie thermal oils suit different reactor duties?

Deep-cooling and wide-temperature-range reactors: consider Eurotherm 100 where the required operating envelope falls within -115 to 175°C, with particular attention to its low flash point, vapor pressure and closed-system requirements. For combined heating and cooling circuits requiring -50 to 330°C, assess Eurotherm 330 and check the circulation pump against actual low-temperature viscosity. Fluid temperature coverage does not establish the operating capability of existing equipment.

General synthesis and medium-to-high-temperature jacket heating: Eurotherm 320 is a candidate for -30 to 320°C service, with a maximum film temperature of 340°C. For duties not exceeding 310°C where circulation resistance and pump matching are priorities, compare Eurotherm HFT-LV, which has a kinematic viscosity of 6.2 mm²/s at 40°C. Any reduction in system energy use still depends on flow, piping resistance and pump efficiency.

Higher-temperature liquid-phase reactors: Eurotherm 350 offers an operating range of -30 to 350°C and a maximum film temperature of 380°C. Assess heat flux and film-temperature margin before selection. For pharmaceutical or fine-chemical applications requiring a food-grade medium, evaluate Eurotherm F301, with an operating range of -10 to 320°C and a kinematic viscosity of 39 mm²/s at 40°C. Confirm applicable compliance documentation and process suitability separately; food-grade status does not replace a pharmaceutical contamination-risk assessment.

After screening fluids, have process, equipment and fluid engineers jointly confirm operating range, film temperature, pump operating points, expansion space and protective logic. Contact Suzhou Chemie at +86-512-66560280 or kevin_leehtfs@szchemie.cn. For quotations or sample requests, visit https://www.szchemie.com.cn/contact-us. The scope of fluid-change, cleaning and in-service testing advice is subject to confirmation by a Chemie engineer.

FAQ

Sources

• JINHONG：Thermal Oil Heater System Design: Expansion Tank, Circulation and Film Temperature（2026-09-11）