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TRANG CHỦ Sản phẩm Parr Oxygen Bomb Calorimeters 6790 Detonation Calorimeter

Ordinary oxygen bomb combustion calorimetry is used to measure the heat of combustion or reaction of materials in oxygen or inert atmospheres. Even for high strength vessels, such as the Parr 1104 Oxygen Combustion Bomb, the conditions necessary to detonate small amounts of highly reactive materials are often difficult to achieve and can result in unpredictable consequences. For example, the conventional heat of combustion of pentaerythritol tetranitrate (PETN) [C5H8N4O12] in oxygen is 1957 cal/g while the heat of detonation in vacuum is 1490 cal/g (a 24% difference).

Additionally, it is well known that the degree of confinement of explosive materials significantly influences the released energy. For unconfined or lightly confined charges, the released energy is largely retained in the products. When the charge is heavily confined, the detonation energy, for the most part, is converted to kinetic and internal energy of the confining case. For example, the conventional heat of combustion of 2,4,6-trinitrotoluene (TNT) in oxygen is 3590 cal/g. The heat of detonation for TNT at a charge density of 1.53 g/cc is 1093 cal/g and at a charge density of 0.998 g/cc is 870 cal/g. In contrast, an unconfined reaction yields approximately 600 cal/g.

Precise fundamental information about the detonation process can be obtained by combining calorimetric and dynamic pressure measurements. These measurements can be used ultimately to predict explosives performance. The Parr Detonation Calorimeter has been designed to aid research in this area.

Parr Instrument Company’s new heat of detonation calorimeter accepts up to a 25 g high explosive charge with a nominal total energy release per charge of ~160 kJ. The detonation is initiated using a small commercial EBW style detonator incorporating 80 mg of PETN and 450 mg of RDX with a binder. Detonators are fired using a one-microfarad – 4000 V capacitance discharge firing set.  A complete calorimetric measurement can be made in a few hours with a precision of several tenths of a percent. The bomb can be optionally fitted with a high-speed pressure transducer that allows the user to gain further insight into the dynamics of the detonation process.


 

Major Subsystems

  Detonation Vessel

The distinctive spherical bomb is made of 3.2 cm thick stainless steel and has an inside diameter of 21.6 cm providing an internal volume of 5.3 liters. The 9 cm opening is covered by a lid 3.8 cm thick at the center. The lid is secured by 12, 1.3 cm diameter, high strength bolts inserted through the lid flange and sealed with an o-ring. The lid incorporates a bomb lift fitting at the center, surrounded by an inlet / outlet valve and two high-voltage style insulated electrodes. An optional port can be provided on the lid for a fast responding pressure transducer. The mass of the bomb (cylinder and lid) is 55 kg.

 

  Calorimeter Stand

The detonation calorimeter uses a classic design incorporating a compensated static jacket. The compensated static jacket approach has been used successfully for many years in two generations of Parr calorimeters (Models 1356 & 6100). The calorimeter stand houses the calorimeter jacket and also includes a bomb lift hoist as well as a conveniently placed bomb support and bomb head stand. The calorimeter lid is stored on the lower shelf, below the bomb workstation, when not in use.

6772 Precision Calorimetric Thermometer

The Parr 6772 Calorimetric Thermometer is used to record all temperature readings and fully sequence the calorimetric test. The thermometer is equipped with a color touch screen display, supporting an intuitive graphical user interface. The temperature of the stirred water surrounding the bomb, as well as the calorimeter jacket temperature, is recorded. Real-time heat leak corrections are performed during the test by the thermometer, resulting in a fully corrected temperature rise measurement for each test run. The thermometer can also be connected to an Ethernet network (LAN) and incorporates web, FTP, and VNC servers. The Parr Remote Interface Feature VNC server allows for remote operation of the calorimeter from a network connected PC running either MS Windows or a Linux operating system.

Dynamic Pressure Recording System

The Parr Dynamic Pressure Recording System can be used in conjunction with the detonation calorimeter in order to record the change in pressure in the bomb that accompanies a detonation.  This system is designed to allow users to study pressure changes typically associated with the fast decomposition of materials used as explosives and is comprised of the following subsystems:

  1. The first subsystem includes a fast-time response dynamic pressure transducer with the associated signal conditioning electronics. The transducer is capable of recording pressures up to 10000 psi.  The useable upper frequency limit for the transducer is 100 kHz. The minimum detectable pressure change is 0.5 psi. The accuracy is 1% of full scale. The time constant of the measurement system is on the order of 10 minutes. As a result, short-term static or “quasi-static” pressure measurements become feasible.
  2. The system also includes a high speed (200 kS/s), PC based (USB interface) data acquisition system, which is used to record the output of the transducer system. Data acquisition can be triggered or synchronized by the manual activation of the bomb ignition unit or firing set. Post triggered pressure data is saved to a PC disk file.
  3. A Windows™ based user interface program is provided with the system. The program is equipped to stream data to disk after the combustion event is initiated. The data can then be easily exported to a spreadsheet for further analysis and plotting.