5.6 Heat responsive element operating characteristics

5.6.1 Operating temperature test (see 4.3 ) [7.6]

Ten nozzles should be heated from room temperature to 20°C to 22°C below their nominal release temperature. The rate of increase of temperature should not exceed 20°C/min and the temperature should be maintained for 10 min. The temperature should then be increased at a rate between 0.4°C/min to 0.7°C/min until the nozzle operates.

The nominal operating temperature should be ascertained with equipment having an accuracy of ±0.35% of the nominal temperature rating or ±0.25°C, whichever is greater.

The test should be conducted in a water bath for nozzles or separate glass bulbs having nominal release temperatures less than or equal to 80°C. A suitable oil should be used for higher-rated release elements. The liquid bath should be constructed in such a way that the temperature deviation within the test zone does not exceed 0.5%, or 0.5°C, whichever is greater.

5.6.2 Dynamic heating test (see 4.4 )

5.6.2.1 Plunge test

Tests should be conducted to determine the standard and worst case orientations as defined in 2.4 and 2.5. Ten additional plunge tests should be performed at both of the identified orientations. The worst case orientation should be as defined in 4.14.1. The RTI should be calculated as described in 5.6.2.3 and 5.6.2.4 for each orientation, respectively. The plunge tests should be conducted using a brass nozzle mount designed such that the mount or water temperature rise does not exceed 2C for the duration of an individual plunge test up to a response time of 55 s. (The temperature should be measured by a thermocouple heatsinked and embedded in the mount not more than 8 mm radially outward from the root diameter of the internal thread or by a thermocouple located in the water at the centre of the nozzle inlet.) If the response time is greater than 55 s, then the mount or water temperature in degrees Celsius should not increase more than 0.036 times the response time in seconds for the duration of an individual plunge test.

The nozzle under test should have I to 1.5 wraps of PTFE sealant tape applied to the nozzle threads. It should be screwed into a mount to a torque of 15 ± 3 Nm. Each nozzle should be mounted on a tunnel test section cover and maintained in a conditioning chamber to allow the nozzle and cover to reach ambient temperature for a period of not less than 30 min.

At least 25 ml of water, conditioned to ambient temperature, should be introduced into the nozzle inlet prior to testing. A timer accurate to ±0.01 s with suitable measuring devices to sense the time between when the nozzle is plunged into the tunnel and the time it operates should be utilized to obtain the response time.

A tunnel should be utilized with air flow and temperature conditions^footnote at the test section (nozzle location) selected from the appropriate range of conditions shown in Table 2. To minimize radiation exchange between the sensing element and the boundaries confining the flow, the test section of the apparatus should be designed to limit radiation effects to within ±3% of calculated RTI values^footnote.

Table 2 Plunge Oven Test Conditions

Table 2 — PLUNGE OVEN TEST CONDITIONS
	Air temperature ranges¹			Velocity ranges²
Normal Temperature °C	Standard Response °C	Special Response °C	Fast Response °C	Standard Response m/s	Special Response m/s	Fast Response Nozzle, m/s
57 to 77	191 to 203	129 to 141	129 to 141	2.4 to 2.6	2.4 to 2.6	1.65 to 1.85
79 to 107	282 to 300	191 to 203	191 to 203	2.4 to 2.6	2.4 to 2.6	1.65 to 1.85
121 to 149	382 to 432	282 to 300	282 to 300	2.4 to 2.6	2.4 to 2.6	1.65 to 1.85
163 to 191	382 to 432	382 to 432	382 to 432	3.4 to 3.6	2.4 to 2.6	1.65 to 1.85
¹ The selected air temperature should be known and maintained constant within the test section throughout the test to an accuracy of +/– 1^oC for the air temperature range of 129^oC within the test section and within +/- 2^oC for all other air temperature.
² The selected air velocity should be known and maintained constant throughout the test to an accuracy of +/- 3 m/s for velocities of 1.65 to 1.85 and 2.4 m/s to 2.6 m/s and +/- 0.04 m/s for velocities for of 3.4 m/s to 3.6 m/s.

The range of permissible tunnel operating conditions is shown in Table 2. The selected operating condition should be maintained for the duration of the test with the tolerances as specified by footnotes 1 and 2 in Table 2.

5.6.2.2 Determination of conductivity factor (C) [7.6.2.2]

The conductivity factor (C) should be determined using the prolonged plunge test (see 5.6.2.2.1) or the prolonged exposure ramp test (see 5.6.2.2.2).

5.6.2.2.1 Prolonged plunge test [7.6.2.2.1]

The prolonged plunge test is an iterative process to determine C and may require up to twenty nozzle samples. A new nozzle sample must be used for each test in this section even if the sample does not operate during the prolonged plunge test.

The nozzle under test should have 1 to 1.5 wraps of PTFE sealant tape applied to the nozzle threads. It should be screwed into a mount to a torque of 15 + 3 Nm. Each nozzle should be mounted on a tunnel test section cover and maintained in a conditioning chamber to allow the nozzle and cover to reach ambient temperature for a period of not less than 30 min. At least 25 ml of water, conditioned to ambient temperature, should be introduced into the nozzle inlet prior to testing.

A timer accurate to ±0.01 s with suitable measuring devices to sense the time between when the nozzle is plunged into the tunnel and the time it operates should be utilized to obtain the response time.

The mount temperature should be maintained at 20 ± 0.5°C for the duration of each test. The air velocity in the tunnel test section at the nozzle location should be maintained with ± 2% of the selected velocity. Air temperature should be selected and maintained during the test as specified in Table 3.

Table 3 Plunge Oven Test Conditions for Conductivity Determinations

TABLE 3 – PLUNGE OVEN TEST FOR CONDUCTIVITY DETERMINATIONS
Nominal nozzle temperature, °C	Oven temperature, °C	Maximum variation of air temperature during test.°C
57	85 to 91	+/- 1.0
58 to 77	124 to 130	+/- 1.5
78 to 107	193 to 201	+/- 3.0
121 to 149	287 to 295	+/- 4.5
163 to 191	402 to 412	+/- 6.0
*If the value of C is determined to be less than 0.5 (m.s) ^0.5, a C of 0.25 (m.s) ^0.5 should be assumed for calculating RTI value.

The range of permissible tunnel operating conditions is shown in Table 3. The selected operating condition should be maintained for the duration of the test with the tolerances as specified in table 3.

To determine C, the nozzle should be immersed in the test stream at various air velocities for a maximum of 15 min ^footnote. Velocities should be chosen such that actuation is bracketed between two successive test velocities. That is, two velocities should be established such that at the lower velocity (u_l) actuation does not occur in the 15 min test interval. At the next higher velocity (u_h), actuation should occur within the 15-minute time limit. If the nozzle does not operate at the highest velocity, an air temperature from Table 3 for the next higher temperature rating should be selected.

Test velocity selection should insure that:

The test value of C is the average of the values calculated at the two velocities using the following equation:

where:

Δ Tg	=	Actual gas (air) temperature minus the mount temperature (Tm) in °C.
Δ Tea	=	Mean liquid bath operating temperature minus the mount temperature (Tm) in °C.
u	=	Actual air velocity in the test section in m/s.

The nozzle C value is determined by repeating the bracketing procedure three times and calculating the numerical average of the three C values. This nozzle C value is used to calculate all standard orientation RTI values for determining compliance with 4.14.1.

5.6.2.2.2 Prolonged exposure ramp test [7.6.2.2.2]

The prolonged exposure ramp test for the determination of the parameter C should be carried out in the test section of a wind tunnel and with the requirements for the temperature in the nozzle mount as described for the dynamic heating test. A preconditioning of the nozzle is not necessary.

Ten samples should be tested of each nozzle type, all nozzles positioned in standard orientation. The nozzle should be plunged into an air stream of a constant velocity of 1 m/s ± 10% and an air temperature at the nominal temperature of the nozzle at the beginning of the test.

The air temperature should then be increased at a rate of 1 ± 0.25 °C/min until the nozzle operates. The air temperature, velocity and mount temperature should be controlled from the initiation of the rate of rise and should be measured and recorded at nozzle operation. The C value is determined using the same equation as in 5.6.2.2.1 as the average of the ten test values.

5.6.2.3 RTI value calculation [7.6.2.3]

The equation used to determine the RTI value is as follows:

where:

t_r	=	Response time of nozzles in seconds
u	=	Actual air velocity in the test section of the tunnel in m/s from table 2
ΔT_ea	=	Mean liquid bath operating temperature of the nozzle minus the ambient temperature in °C
ΔT_g	=	Actual air temperature in the test section minus the ambient temperature in °C
C	=	Conductivity factor as determined in 5.6.2.2

5.6.2.4 Determination of worst case orientation RTI

The equation used to determine the RTI for the worst case orientation is as follows:

where:

t_r-wc

Response time of the nozzles in seconds for the worst case orientation

All variables are known at this time per the equation in 5.6.2.3 except RTI_WC (Response Time Index for the worst case orientation) which can be solved iteratively per the above equation.

In the case of fast response nozzles, if a solution for the worse case orientation RTI is unattainable, plunge testing in the worst case orientation should be repeated using the plunge test conditions under Special Response shown in table 2.