Contractors & Architects

A – Application: Which Desiccator is Best for My Application?
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Cost vs. Control: Terra Desiccators Simplify Your Choice

You need to protect sensitive samples, but you don’t want to overpay. Below is a list of application descriptions to help choose the best desiccator storage system for your application and budget.

A1 - Critical Control Demands:

For applications that require not only a low-RH set point, but a system that recovers it quickly when doors open/close, allows a different set point in each chamber, and/or protects against static and particulate contaminants.

Typical Applications

• Low exposure tolerance: Microelectronic or pharmaceutical samples that degrade very quickly when exposed to moisture.
• High access frequency: Doors open/close before system can recover target set point level.
• Exposure testing: Requires a separate %RH monitor/control in each desiccator chamber.
• ESD-sensitive parts: Minute static discharge results in severe degradation, cuts yields.
• Sterile and/or Particle Sensitivity: Critical contamination requirements won’t tolerate materials that shed particles or corrode.

A2 - Moderate Control Demands:

Sensitive samples may require automatic low humidity set point control, but low access frequency minimizes the need for faster RH recovery time. Protection against ESD and/or particulate contaminants may also be required.

Typical Applications

• Low-Moderate exposure tolerance: Low humidity and automatic monitoring is required. Microelectronic or pharmaceutical samples that degrade when exposed to moisture.
• Moderate-High Access Frequency: Parts are accessed on a daily basis and/or are sensitive to moisture exposure when doors are opened.
• ESD-sensitive parts: Minute static discharge results in severe degradation, cuts yields.
• Sterile and/or Particle Sensitivity: Critical contamination requirements won’t tolerate materials that shed particles or corrode.

A3 - Minimal Control Demands:

You need occasional nitrogen purging or desiccant to bring down the RH, or you may only need a dust-free enclosure without humidity control.

• Moderate-High exposure tolerance: Low humidity and/or automatic monitoring is not required.
• Low Access Frequency/Extended Storage: If low humidity is required, fast recovery time is not, because doors are rarely opened: you stock the sample and come back for it days or weeks later.
• Moderate Static Protection: Availability of static-dissipative materials a plus, but ionization not required.
• Dust-Free Conditions: Samples require a clean environment, but chrome plating and adhesive seals are acceptable.

Additional Application Considerations:

For critical moisture control applications, relative humidity (RH) set-point recovery time is one of the most important considerations to achieving the required quality, safety, and shelf life of stored materials.

RH recovery is the time needed to reach an RH set point after a desiccator chamber or cabinet is accessed. A fast RH recovery time minimizes exposure of stored materials to harmful moisture levels. Thus, the ideal desiccator quickly and efficiently reaches and maintains the desired RH level.

Set-point recovery time depends on several variables listed below. Keep these factors in mind to choose the best desiccator storage system for your application and budget.

• Internal & External RH:

  The desired internal RH set point depends on industry and application. Extremely low humidity requirements (under 10% RH) are more difficult to achieve and generally call for a Smart controller option to optimize recovery time and efficiency.

  The greater the gap between required internal RH and ambient RH, the more time and inert gas will be needed to remove moisture from inside the desiccator. For example, a desiccator in a more humid ambient environment will have more moisture in the air to displace, and will therefore require more nitrogen gas or a more efficient humidity control system than one in a less humid environment.

• Access Frequency & Duration:

  RH set-point recovery time is affected by the need to access parts inside the desiccator cabinet. Each time a door is opened, moisture-laden air, often bearing particles, enters the exposed chamber. The longer a door is left open, the more ambient air can flow inside. Once the door is closed, depending on the cabinet design, moisture can migrate from chamber to chamber, raising the internal RH throughout the cabinet.

  During periods of frequent or prolonged access, a poorly configured desiccator may never attain the required RH set point, posing a serious threat to quality, safety, or shelf life of stored materials.

  Choosing an appropriate automatic RH control system and cabinet design will help mitigate problems caused by frequent access.

• Desiccator Cabinet Size & Chamber Configuration:

  The size or volume of your desiccator will determine how much ambient air needs to be displaced to reach your target RH set-point. Thus larger desiccators typically require more nitrogen or a more efficient RH control system, than smaller ones.

  Furthermore, the chamber configuration can have a significant effect on time to reach set-point. Isolated chambers tend to be more efficient, as opening one chamber will not expose other chambers in the cabinet to ambient air. Non-isolated chambers that share the same air space will generally take longer to recover after one door is opened, as ambient air can more easily circulate through the entire cabinet.

• Nitrogen Gas Expense:

  Users seek to achieve a low RH set-point as efficiently as possible to reduce wasteful gas consumption. Unfortunately, unassisted RH control systems require significantly higher consumption of nitrogen gas to reach the desired relative humidity set-point. This problem compounds with high access frequency.

  High nitrogen gas consumption drives up overhead cost and can lead to other operational problems. For instance, those who rely on gas canisters will need to plan for more frequent replacements and will be suseptible to dealing with supply shortages.

  A smart control system automates the process to conserve nitrogen and reduces costs by up to 78%. A nitrogen generator can also eliminate the supply shortage issues from dependence on pre-filled gas canisters.

• Cabinet Material Type:

  Material type can also affect relative humidity inside a desiccator cabinet. The more porous or hygroscopic a material, the easier it is for gases and moisture to transfer through. Many plastics such as acrylic may appear impermeable to the naked eye, however are porous enough at a molecular level to absorb moisture that can then permeate into the chamber. The diffusion or passage of moisture through acrylic can occur in a few ways listed below. The higher the difference between moisture levels, and the greater the exposed surface area, the higher the rate at which moisture will enter the chamber.

  1. Walls inside the cabinet can absorb moisture from ambient air already inside the cabinet, and then release the moisture after the cabinet is purged with a dry inert gas.
  2. Moisture can permeate through the walls from the outside (higher moisture) to inside (lower moisture).
  3. Walls can absorb moisture from direct contact with water (either inside or outside the cabinet).

  Critical moisture control applications concerned with moisture vapor transmission rate (MVTR) should consider a vapor impermeable cabinet material such as stainless steel to achieve the required quality, safety, and shelf life.

B – Nitrogen RH Control Systems:
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B1 – Nitroplex™ System: NitroPlex™, Terra’s most efficient humidity control solution, is designed for the most demanding critical moisture control applications. The system features multiple RH sensors modules to allow RH monitor & control to 0% RH in each isolated chamber. The modules use automatic binary (on/off) valves to quickly and efficiently direct N2 gas where and when it’s needed. The ability to establish separate humidity set points in each storage chamber allows for storage of parts with differing moisture sensitivities and conservation of N2 gas in chambers that are not in use.

B2 – IsoDry® System: IsoDry® upgrades the Dual Purge™ & NitroWatch™ system by adding twin dilution fans for drastically improved RH recovery & uniformity. The fans rapidly mix and circulate incoming nitrogen gas to accelerate moisture removal and achieve uniform RH throughout the entire cabinet. The door sensors de-activate the dilution fans when a door is open to minimize the spread of incoming moisture and contaminants throughout the cabinet.

B3 – Dual Purge™ & NitroWatch™: This system is designed for larger cabinets. Like the Smart® system, it features a single RH sensor for automatic RH set point control to 0%RH. The Dual Purge™ has two gas flow settings (high/low) to rapidly reach and then maintain the user-specified set-point. Door sensors trigger high gas flow when doors open to help protect against the entry of contaminants, and expedite set-point recovery. Because this system includes only 1 RH sensor, the displayed RH reading may not accurately reflect the RH in other chambers of the cabinet.

B4 – Smart® System: Terra’s Smart® desiccator system features a built-in RH Sensor to provide automatic RH set point control to 0% RH with binary (on/off) gas flow. The automatic RH set point control minimizes necessary supervision and increases efficiency of N2 gas consumption. The system is recommended for smaller cabinets with 1-2 chambers. This single gas inlet system can encounter inefficiencies with gas distribution and RH uniformity in larger cabinet systems.

B5 – Flow Meter: A manually controlled flow meter offers the lowest up-front cost for RH control. It is most suitable for smaller desiccators that do not require much nitrogen gas or those that require minimal supervision. Manual control means humidity control is more prone to human error and not as efficient with the consumption of inert gas, which can lead to damaged products and high operating costs.