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Large–Scale Freezing and Thawing of Biopharmaceutical Products
Published in Kenneth E. Avis, Vincent L. Wu, Biotechnology and Biopharmaceutical Manufacturing, Processing, and Preservation, 2020
Richard Wisniewski, Vincent Wu
There are several design considerations for the monitoring and control of the freezing process. Ideally, process control should be performed by a temperature sensor that measures the warmest point in the vessel to provide direct determination that freezing has been completed. If the freeze-thaw vessel is designed in such a way that the warmest area is at the top of the freezing bulk, then an infrared temperature sensor may be implemented. Since batch sizes vary, the infrared beam offers the advantage of being able to accommodate a range of liquid volumes in the vessel. If a temperature sensor cannot be located at the warmest point in the vessel, a welded, sidewall thermowell, used commonly in portable tanks, may be implemented for measuring the temperature of the bulk. The thermowell may have inserted into it a temperature sensor or thermocouple to monitor the temperature of the bulk during freezing and thawing for recording and control.
HVAC Controls
Published in Herbert W. Stanford, Adam F. Spach, Analysis and Design of Heating, Ventilating, and Air-Conditioning Systems, 2019
Herbert W. Stanford, Adam F. Spach
RTDs, thermocouples, and thermistors are all small devices with similar mounting techniques used for all of the types. Sensors for pipe and duct mounting are commonly sheathed in a stainless steel sheath of 1/8″–1/4″ diameter (larger and smaller diameters are available). Sensors for liquid piping systems may be mounted with direct immersion into the fluid or installed in a thermowell to allow removal without draining the piping system and to reduce the likelihood of leaks. Sensors installed in wells should be installed with a heat transfer compound filling the space between the sensor and the well to insure good thermal contact between the measured fluid and the sensor.
Introduction
Published in G. Vaidyanathan, Dynamic Simulation of Sodium Cooled Fast Reactors, 2023
For finalizing the LSSS, the response time of the different sensors is to be considered. Thermocouples at core outlet have a typical response time of 4+ 2s (Value for FBTR) (Vaidyanathan et al., 1987). These values are to be based on the tests carried out on the thermocouple-thermowell combination. A response time of 6 seconds is considered in the simulation. The sodium flow measurement using electromagnetic flow meters and related electronics has a response time of 1 second. Neutron flux measurements using boron counters in the low power range, fission counters in the intermediate power range, and compensated ion chambers in the power range up to full load have response times < 1 second. For the signals from the electrical contacts of the pumps in case of loss of power, though signal is instantaneous, the trip is initiated with a delay of ~3 seconds to avoid trips for short-duration power failures. There is a need to minimize the number of trips, as each shutdown gives a cold shock to the components. Also, the signals are triplicated with a 2/3 logic, with two out of three being sufficient to initiate the trip or safety system action. The requirement that two channels must both vote for a trip reduces the likelihood of spurious trips due to a single component failure. On the other hand, the reactor will still trip if required even if one channel is unavailable (failed unsafe). Finally, a single channel can be tested without tripping the reactor. Such a scheme allows testing of each channel without causing a trip, thereby improving availability. There is also the need to consider the response time of the shutdown system, which is ~1 second for FBTR in finalizing the LSSS.
Flow and heat transfer in narrow fixed beds with axial thermowells
Published in Numerical Heat Transfer, Part A: Applications, 2019
Fixed-bed reactors play an important role in the chemical industry. One long-standing problem is to obtain a good qualitative understanding and prediction of the fluid flow and heat transfer in the fixed-bed reactor. The temperature inside fixed-bed reactors is a crucial variable to know for safe reactor design. Several approaches have been developed, including radially inserted thermocouples, thermocouples embedded in particles, thermocouple crosses positioned both inside and outside the bed, and ladder-like structures to support an array of thermocouples. Temperature is frequently monitored at the laboratory scale [1] and at the pilot plant scale [2, 3] using thermowells. A thermowell comprises a thermocouple inserted inside a protective metal tube. It is an inexpensive and traditional solution to the problem of fixed-bed temperature measurement.
Measurement of Transient Fluid Temperature in a Pipeline
Published in Heat Transfer Engineering, 2018
Magdalena Jaremkiewicz, Jan Taler
Thermowells are tubular housings used to protect temperature sensors installed in the pipeline or pressure vessel [1, 2]. The wires that make up the thermocouple must be insulated from each other everywhere, except at the sensing junction. A thermowell is typically mounted in the process stream by way of a threaded, welded, sanitary cap or flanged process connection. The heat from the process fluid is transferred to the thermowell wall, which in turn transfers heat to the sensor through the air gap and optionally through ceramic beads. Since more mass is present and additionally thermal contact resistance is increased, the sensor's response to process temperature changes is damped and delayed. Consequently, the thermowell impacts thermometer accuracy and responsiveness of the thermometer negatively.