The Great Wall DHJF-2005A Low-Temperature Constant-Temperature Stirring Bath

Overview

The Great Wall DHJF-2005A Low-Temperature Constant-Temperature Stirring Bath is a dual-function laboratory thermal management system engineered for precision temperature control and active mixing in demanding chemical, biochemical, and physical research applications. Unlike conventional water or oil baths, the DHJF-2005A integrates a high-efficiency vapor-compression refrigeration circuit (using environmentally compliant R404A refrigerant), a robust resistive heating element, and a variable-speed magnetic stirring motor within a single 304 stainless steel reservoir. Its operational principle relies on closed-loop PID temperature regulation—continuously comparing real-time sensor feedback against setpoint and dynamically modulating refrigerant expansion valve duty cycle and heater power output to maintain thermal equilibrium. With a usable bath volume of 5 L and external circulation capability (20 L/min at 0.4 bar), it functions both as an immersion thermal platform for reaction vessels (up to 2000 mL) and as a centralized cold/hot source for peripheral instrumentation such as condensers, spectrophotometer cells, or flow-through detectors. Designed for continuous operation under GLP-aligned laboratory conditions, the unit complies with IEC 61010-1 safety standards for electrical equipment used in laboratory environments.

Key Features

• Integrated dual-mode thermal control: simultaneous refrigeration (−20 °C) and heating (99 °C) with ±0.2 °C stability across the full range
• High-resolution digital display (0.01 °C resolution) with intuitive keypad interface and real-time setpoint/actual temperature readout
• Variable-speed magnetic stirrer (100–1000 rpm, 50 W motor) enabling synchronized agitation of both bath fluid and internal reaction mixtures via compatible stir bars
• Adjustable telescopic cover with Ø210 mm aperture minimizes evaporation losses and parasitic heat exchange—critical for long-duration low-temperature experiments
• Dedicated mounting rail and universal clamp interface support standardized accessories: pH electrodes, temperature probes, burettes, reflux condensers, and peristaltic pump tubing
• Comprehensive safety architecture including dry-run protection (heating circuit), overtemperature cutoff, earth leakage detection, overpressure monitoring, and thermal fuse redundancy

Sample Compatibility & Compliance

The DHJF-2005A accommodates standard laboratory glassware—including round-bottom flasks (50–2000 mL), test tubes, jacketed reactors, and U-tube manometers—via its deep, corrosion-resistant 304 stainless steel bath chamber (Ø250 × 130 mm depth). Its external circulation port (Rc1/2) permits connection to jacketed reactors or auxiliary chillers using chemically inert silicone or fluoropolymer tubing. The unit meets CE marking requirements per Directive 2014/30/EU (EMC) and 2014/35/EU (LVD), conforms to ISO/IEC 17025-relevant environmental controls for calibration traceability, and supports audit-ready documentation when operated within defined ambient limits (5–35 °C, ≤70% RH). While not certified for pharmaceutical manufacturing under FDA 21 CFR Part 11, its programmable setpoints, stable thermal performance, and hardware-based safety interlocks render it suitable for method development and QC testing in GMP-adjacent research settings.

Software & Data Management

The DHJF-2005A operates via embedded firmware without proprietary software dependencies; all configuration and monitoring occur locally through its front-panel interface. For integration into automated workflows, the unit provides analog output signals (0–5 V or 4–20 mA) proportional to measured bath temperature, compatible with third-party data loggers (e.g., Omega OM-DAQPRO, Keysight 34972A) and SCADA systems. Optional RS485 Modbus RTU communication enables remote setpoint adjustment, status polling, and alarm event logging—facilitating compliance with electronic record retention requirements under ALCOA+ principles. All thermal profiles are reproducible via manual entry or external trigger; no cloud connectivity or firmware updates are required, ensuring long-term operational consistency and cybersecurity isolation.

Applications

• Controlled-rate crystallization studies requiring sub-zero nucleation onset and isothermal hold phases
• Catalytic hydrogenation reactions requiring precise exotherm management via external cooling loops
• Enzyme kinetics assays where thermal drift must remain below ±0.2 °C over multi-hour incubations
• Calibration of thermocouples, RTDs, and infrared pyrometers against NIST-traceable reference standards
• Viscosity measurements using rotational rheometers or capillary viscometers requiring thermostatted sample chambers
• Preparation of temperature-sensitive reagents (e.g., Grignard solutions, organolithium compounds) under inert atmosphere with cryogenic bath coupling

FAQ

What is the minimum operating temperature, and how quickly does it reach −20 °C from ambient?
The unit achieves −20 °C in approximately 45 minutes when starting from 25 °C with an empty bath and nominal ambient conditions (25 °C, 50% RH). Cooling time increases linearly with thermal load.
Can the DHJF-2005A be used with organic solvents like acetone or ethanol in the bath?
No. Only water, 15–30% ethylene glycol/water mixtures, or certified silicone oils compatible with 304 stainless steel and R404A refrigerant should be used. Organic solvents may degrade seals and compromise refrigeration integrity.
Is external circulation mandatory, or can the unit operate in static bath mode?
Both modes are supported. Internal stirring ensures homogeneity during static operation; external circulation is optional for heat transfer to secondary devices.
Does the magnetic stirrer function independently of temperature control?
Yes. Stirring speed is adjustable regardless of whether heating, cooling, or standby mode is active.
What maintenance intervals are recommended for long-term reliability?
Refrigerant pressure verification and condenser coil cleaning every 12 months; annual inspection of stir bar coupling alignment and gasket integrity; replacement of circulating fluid every 24 months under continuous use.