Temperature bulb, response

The three most important types of thermometers are expansion-type thermometers (pressure thermometers), electrical thermometers, and radiation thermometers. In expansion-type thermometers the primary sensing element is a bulb containing an expansible fluid. The bulb is connected to a pressure spring through capillary tubing. Expansion of the thermometric fluid with rising temperature causes expansion of the pressure spring, which in turn is converted to a mechanical displacement as the final measure of temperature. The response of these thermometers... 

A thermowell is required to protect the thermal element of a thermometer or temperature transmitter thermobulb from corrosion and erosion, to give it adequate support, and to permit its removal without interrupting the process. The use of the thermowell will unavoidably introduce a temperature time lag to the changes in the process temperature and response to the temperature relayed to the instrument. This is caused by the transmission of heat through the thickness of the metal well and the inevitable dead air space between the well and bulb. 

The temperature response of the measurement element shown in Fig. 2.13 is strictly determined by four time constants, describing a) the response of the bulk liquid, b) the response of the thermometer pocket, c) the response of the heat conducting liquid between the wall of the bulb and the wall of the pocket and d) the response of the wall material of the actual thermometer bulb. The time constants c) and d) are usually very small and can be neglected. A realistic model should, however, take into account the thermal capacity of the pocket, which can sometimes be significant. 

Step 1 Remove the electrode from its storage solution and rinse with purified water. Dab the electrode with tissue paper to remove excess water that could dilute the solution to be tested. Do not wipe the glass bulb. Place the electrode (and the temperature probe if applicable) into the first buffer to be tested. Wait for a stable response from the instrument. (Note If using a refillable electrode, open the fill-hole cover during calibration or any measurement to allow a uniform flow of electrode filling solution. Close the fill hole when the electrode is not in use.)... 

Plant operations personnel generally purchase cooling towers rather than construct them themselves. The philosophy behind this policy is that it makes available to operators a wealth of practical knowledge directly applicable in the field. The operator must specify the amount of water and the temperature range required to handle a specific set of process conditions. It is the fabricator s responsibility to propose a system that will meet the operator-furnished conditions for the 5% wet-bulb in the plant locality. This also means that the fan power with which the operation will be accomplished will be guaranteed. 

A solution of 150 mL of 1.6 M butyl-lithium in hexane under N2 was vigorously stirred and diluted with 150 mL petroleum ether (30-60 °C) and then cooled with an external ice bath to 0 °C. The addition of 26.7 g of veratrole produced a flocculant white precipitate. Next, there was added a solution of 23.2 g of N,N,N ,N -tetramethylethylenediamine in 100 mL anhydrous Et20 and the stirred reaction mixture was allowed to come to room temperature. The subsequent addition of 20.7 g of dimethyl disulfide over the course of several min produced an exothermic response, and this was allowed to stir for an additional 30 min. There was then added 10 mL EtOH followed by 25 0 mL of 5 % NaOH. The organic phase was washed first with 150 mL 5% NaOH, followed by 2x100 mL portions of 5% dilute HC1. The removal of solvent and bulb-to-bulb distillation of the residue provided 2,3-... 

Heat evolution during immersion processes involving surface rehydration has been found to occur over a 20- to 40-minute interval, so that high precision methods are required if immersion heats include a contribution due to rehydration. The immersion heat determinations were carried out in a microcalorimeter having a temperature sensitivity of 5 X 10 6° C., rapid thermal response, and carefully determined heat transfer characteristics. The calorimetric system has a demonstrated capability of handling heat input rates as low as 0.005 joule per second (15). Samples for immersion were contained in very thin-walled bulbs holding... 

Accuracy. Mercury-in-glass thermometers are relatively inexpensive and can be obtained in a wide variety of accuracy and temperature ranges. For example, between 0 and 100°C, thermometers with a 0.1°C graduation interval are readily available. Factors that affect the accuracy of the thermometer reading include changes in volume of the glass bulb under thermal stress, pressure effects, and response lag. With proper calibration by NIST [9,10] or traceable to NIST, an accuracy of from 0.01 to 0.03°C can be achieved. Table 16.5 summarizes... 

When thermowells are installed, in a vertical position in piping and equipment, various substances are used to increase the heat transmission and temperature response — one is mercury (see Figure 7-89c). Although mercury is probably the best substance from a thermal consideration, it must not be used when the process operating temperature approaches its boiling point (375°C or 674°F). Both the thermowell and bulb should be made of steel or ferrous alloy. A brass thermowell or bulb immersed in mercury would be destroyed by amalgamation. 

Figure 3. Onion pungency (umol pyruvate per ml of onion juice) in response to increasing growing temperatures. Solid line represents plants grown at (he tlifrerem temperatures for 35 days in a bulbing photoperiod. Dashed line represents plants grown to maturity at the different temperatures.

Initial experiments at the 286.5 atm charge pressure configuration indicated time responses of the order of 10 sec in the 6°-7 K temperature range. Due to the theoretical indication that the system was heat-transfer limited, the cold bulb was replaced with one of identical geometry but containing a loosely packed quantity of fine brass wool. The results obtained due to this modification are shown in Fig. 7. 

One method to limit the amount of hydration of a glass bulb in order to decrease response time has been to etch the glass bulb and then to hydrate it in strong acid. The etching of the bulb is done in 2% hydrofluoric acid in water for 2 minutes at room temperature it is then hydrated in dilute HCl for about I hour. This partially hydrated electrode is not suitable for use in aqueous solutions because further hydration will cause drift. Further hydration can be limited by storage in the organic solvent to be used, but the electrode must be immersed in water for a few minutes before use. This etching procedure does limit the electrode life and is normally not performed when response time is not critical. 

Since the resistance of the glass bulb approximately doubles for every TC decrease in temperature, the lower temperature limit of 5 C is stated only for glass electrodes with relatively low resistance. A slower response and noisier readings can be expected at lower temperatures. If the glass electrodes are used continuously at... 

---