Archives: White papers

AUTHOR	DATE CREATED	VERSION	DOCUMENT NUMBER
Dr. Peter Marshall	9 February 2017	V1.5	CC11 – 00107

Introduction

This paper details investigations into the best glass to protect Ceramicx’s quartz cassette heaters allowing for best transmission of infrared radiation. A number of different glasses are available; however, these will have different characteristic transmission spectra due to differing compositions. By tuning the emission spectrum of the element to the transmission spectrum of the glass, the optimal combination for heating process energy efficiency can be identified.

Method

2.1 Materials

Five different quartz glasses were sourced, each with a thickness of 3mm. The first glass was Ceramicx standard protection Robax® glass. Two further glasses were obtained from Schott glass’s NextremaTM range (Materials 712-3 & 724-3). A further two glasses were sourced from another third party. These were transparent with a slight grey hue and a white, opaque colour or frosted appearance.

Each glass was mounted directly in front of a 500W, 230V HQE element (dimensions: 123.5 x 62.5mm). The heating coil was placed within 6 of the 7 available quartz glass tubes with the central tube left unheated. An image of each of the 5 glasses in-situ on the HQE heaters is shown in Figure 1

 

The data sheet for the three Schott glasses (NextremaTM 712-3, NextremaTM 724-3 & Robax^®) shows the infrared transmission spectra which are shown in Figure 2. This shows the NextremaTM 712-3 transmits little or no radiation in the visible spectrum, consistent with the dark colour of the material, whereas far more radiation is transmitted by the NextremaTM 724-3 (Figure 2Error! Reference source not found.) and Robax^® glasses. At longer wavelengths, the percentage radiation transmitted by the the NextremaTM 724-3 material is higher than the Robax^® glass.

The HQE 500W heater has a peak spectral power density (emission) in the waveband of 2 – 4.2μm as shown in the spectrum (Error! Reference source not found.). Therefore, it would be expected that the glass with the greatest transmission in this region will exhibit the greatest heat flux in the experiment. This is particularly important at lower wavelengths which are more energetic than longer wavelengths.

2.2 Method

The heaters were mounted within the Herschel platform and energised. The voltage was adjusted such that the power output was 500 ± 1 W. The heater was allowed to heat up for a 10 minute period prior to testing commencing. Each heater was tested three times to increase accuracy.

2.3 Herschel

Ceramicx Herschel heat flux robot examines the total heat flux (W.cm^-2) which is incident on the sensor. Heaters can be mounted in the Herschel and analysed using the 3D Infrared heat flux mapping routine. This automated system uses an infra-red sensor that is robotically guided around a pre-determined coordinate grid system in front of the heater emitter under test. The sensor has a maximum heat flux level of 2.3 W.cm^-2 and measures IR in the band 0.4-10 micrometres. The coordinate system is a 500mm cubic grid in front of the heating emitter, see Figure 3. The robot moves the sensor in 25mm increments along a serpentine path in the X- and Z- directions, while the heating emitter is mounted on a slide carriage which increments in 100mm steps along the Y- direction.

The results from the machine can be transformed into a percentage of total energy consumed returned as radiant heat flux from the heater. This decreases with increasing distance from the heater as the radiant heat flux diverges from the heater.

Results

The results of the test show some interesting data which must be interpreted alongside the transmission and emission spectra of glass and Ceramicx’s HQE heating elements, respectively. All contour plots were made using the same colour scale to ensure visual comparison is possible.

3.1 NextremaTM 712-3

This dark tinted glass displays little or no radiation transmission in the visible spectrum (Figure 2); however, at longer wavelengths it is more transparent. The transmission drops off to <10% in the waveband of ≈ 2.8 – 3.2 μm, but recovers to ≥40% in the 3.5 – 4.2 μm band region.

The results show that, at 100mm, there is a peak power density of 0.6 W.cm^-2, as shown in Figure 4. This shows that the peak heat flux, as expected, comes from the centre of the element and decreases concentrically with distance both from the centre of the element.

A similar plot can be produced for all distances from the heater; however, the general trend of decreasing heat flux from the element centre is the same.

Similarly, the percentage radiative heat flux recorded decreases as the distance from the element increases (along the y-axis) as indicated in section 2.3. The magnitude of this decrease is shown in Figure 5

3.2 NextremaTM 724-3

The transparent NextremaTM glass (724-3) displays a slightly higher heat flux output than the 712-3 glass. This is primarily due to its better transparency (≈90%) in the more energetic visible and near-IR regions (0.5 < λ < 2.8 μm). When combined with the emission spectrum of the quartz element, a better match is seen which is confirmed by the higher heat flux recorded in the map (Figure 6)

The decrease in energy detected as a function of distance from the heater is very similar to that which is shown in Figure 5 for the same element with 712-3 protection glass.

3.3 Robax^®

The Robax^® glass shows a distinctly higher heat flux at the central point of the element which is off the general scale which was applied, as shown in Figure 7. In this case, the peak radiative heat flux is 0.80 W.cm^-2. The higher heat flux at the centre is indicative of greater transmission due to higher source temperature (shorter IR wavelengths).

The reason for this slightly better performance is the increased IR transmission in the primary band (0.4<λ<2.8μm). For Robax® glass, the transmission drop occurs at a slightly longer wavelength which increases the output from the heater. The decreased and narrower bandwidth of transmission in the secondary band (3.2< λ<4.2μm) does not have the same influence as these wavelengths are not as energetic as the shorter wavelengths. The total heat flux recorded at 100 mm is, as expected, slightly higher than for the glasses examined in sections 3.1 and 3.2 due to the enhanced transmission properties of the glass. This is shown in Figure 8, below.

3.4 Frosted glass

The heat flux map for the frosted glass protected heater is shown in Figure 9. This shows a similar pattern of energy emission from the heater to those detailed above. The detected heat flux magnitude is higher than those with Nextrema^TM protection but lower than that of the Robax^® glass. As no transmission spectrum is available for this material, no insight can be given into the reasons behind this.

As the distance between the emitter and the heat flux sensor is increased, the detected heat flux falls off. The percentage heat flux detected at 100mm is lower than that of the Robax^® glass which is shown in Figure 7, but higher than the Nextrema^TM glasses.

3.5 Transparent glass

The heat flux map for the transparent glass is shown in Figure 11. This shows very little discernible difference to the frosted glass material which was examined in section 3.4, indicative of very little change in the transmission spectrum of the glass in the active waveband region (2-4.2μm).

The total heat flux is slightly elevated compared to that of the frosted glass; however, it is still below that of the Robax^® glass. Without transmission spectrum data, no explanation can be offered for this observation.

Table 1 shows the average maximum heat flux which was recorded for the element across the three conducted tests as well as the average percentage heat flux recorded at 100 and 200mm from the element surface. This indicates that the two Nextrema^TM and the Frosted glasses performed poorly, however, there is little to separate the Robax^® and the Transparent glasses.

A measurement phenomenon occurs during heat flux mapping whereby the initial reading taken is a reference value, designated zero and each recorded value is measured relative to this. At short separations, the heat flux can, therefore, be recorded as negative which gives rise to the uncoloured regions in the contour plots.

Normalising the raw data reveals that the Robax® and Transparent glasses are indeed the most efficient glass for transmitting the radiation as shown in Table 2.

Given no spectral data is available for the Transparent glass, it is not possible to give a definitive reason as to why the difference between this and Robax® occurs and whether it is the transparency level in the visible/near-IR (0.5 – 2.8μm) or in the medium wave region (≥3 μm).

It is noticeable that the maximum heat flux recorded for Robax^® is higher than for the Transparent glass. This may be indicative of a change in the infrared transparency as a function of temperature, with Robax^® becoming more transparent at the elevated temperatures seen in the central portion of the element.

Conclusion

The results of the experiment above show that the Robax^® glass, currently used by Ceramicx, to protect its heaters possesses one of the best IR transmission properties for the quartz cassette heaters. This is because the transmission spectrum for this glass is at a maximum in the active waveband of the heater.

For optimal heating, the transmission spectrum of the protection glass should be matched to the emission spectrum of the heater that it is protecting. In this case, the glass should be as transparent as possible in the 1 – 3.2 μm waveband.

It should be noted that the power density of the element and a variety of other factors will influence the results of this experiment. Should the power per unit area of the element change, the results will change. Moreover the results indicated in this experiment are not representative of a platen type configuration.

¹ A 1000W FQE and 500W HQE have the same power density and therefore similar emission characteristics

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Disclaimer

These test results should be carefully considered prior to a determination on which type of infrared emitter to use in a process. Repeated tests conducted by other companies may not achieve the same findings. There is a possibility of error in achieving the set-up conditions and variables that may alter the results include: the brand of emitter employed, the efficiency of the emitter, the power supplied, the distance from the tested material to the emitter utilised and the environment. The locations at where the temperatures are measured may also differ and therefore affect the results.

AUTHOR	DATE CREATED	VERSION	DOCUMENT NUMBER
Dr. Peter Marshall	8 April 2016	V1.1	CC11 – 00101

Introduction

CCP Gransden approached Ceramicx to build an infrared oven to heat thermoplastic carbon fibre prepreg materials for their forming operations. This testing work was carried out as part of functions defined in the sales proposal (CSP 000 008). Phase one involves the infrared heater assessment and selection for this project, with the stipulated minimum material temperature being 425°C.

Material description

Three samples of two materials were received in 230 x 230 x 1mm pieces. In these cases, the matrix was PEEK¹ and PPS². A smaller sample of PEKK³ with dimensions of 200 x 150 x 2mm was also received. The material was rigid, smooth with a glossy black finish. A small pattern was visible on the surface on the surface of the PEEK and PPS samples.

The PEEK and PPS samples were cut into 115 x 115 mm pieces. The PEKK material was cut into 100 x 75mm pieces.

Method

Two distinct heater families were evaluated; halogen (QH and QT) and black hollow ceramic (FFEH). In each case, the platens were mounted above and below the material sample with adjustable height.

FastIR

A mounting system was manufactured to allow two of Ceramicx’s FastIR 500 units to be mounted above and below the material. A FastIR 500 consists of seven heating elements mounted in parallel fashion within a 500 x 500 mm case. The spacing between these tubes is 81mm. 1500W and 2000W ‘long’ (total length: 473mm) elements were used giving a total output from the two units of 21 or 28kW respectively. The heater units were mounted such that the distance between the element surface and the sample was varied between 55mm and 95mm.

The experimental protocol used was as follows:

• Fans switched on
• Central three heating elements switched on, top then bottom
• Outside four heating elements switched on, top then bottom

An image of a sample between the two FastIR units is shown in Figure 1. Nothing was used to enclose the gap between the two heating units

Elements

Two types of element can be mounted in the FastIR unit; quartz halogen and quartz tungsten. These elements emit different peak infrared wavelengths; halogen at approximately 1.0 – 1.2μm and tungsten between 1.6 – 1.9μm. Each tube has a diameter of 10mm, a total length of 473mm and a heated length of 415mm.

Black Hollow

A custom heating platen was designed to incorporate a 2 x 7 matrix of Ceramicx’s 800W FFEH elements, giving each platen 11.2kW of power. This matrix was enclosed in a 510 x 510mm case and mounted in the same frame as the FastIR system detailed above. The experimental protocol was used; however, fans were not employed in these platens. The distance between these elements was 65mm.

Two different element-sample distances were used, 50 and 100mm. Again, the gap between the two heating units was left open

Elements

Ceramicx black hollow elements emit peak wavelengths in the medium to long regime (2 – 10μm). Each element has dimensions of 245 x 60mm (l x w). The longer wavelengths associated with ceramic elements is very efficient for heating many polymeric materials.

Instrumentation

Type K thermocouples were affixed to the surface of the sample using M3 screws. Ceramic cement was trialled however this did not adhere to the surface of the material. Given the high temperatures required, no available adhesive would remain stable, so mechanical fixation was deemed necessary. The thermocouples were located at the centre of each specimen and also 10mm (edge) and 30mm (quarter) from the edge as shown in Figure 2. This located the thermocouples directly over the tube elements and in the centre between the elements so that the maximum temperature difference would be recorded. The temperature data was recorded at single second intervals.

Sandwich testing

The sandwich tester is an advanced material thermal response testing machine as shown in Figure 2. Various types of infrared heaters can be mounted in two positions, facing vertically up and down. This ensures that the tested material can be heated from the top and/or the bottom. Four non-contact optical pyrometers are used to determine the top and bottom surface temperature of the tested material. The emitters are allowed to warm up to their operating temperature and the material is then brought under the emitter(s) for a predetermined period. This test was performed with both 1kW tungsten (QTM) and 800W black hollow elements (FFEH) mounted 75mm above the sample to determine which heater gave the best penetration through the material.

Results

FastIR

This section reports on the results found for tungsten and halogen tubes for the three materials in question. Tests were carried out with three different heater heights (55mm, 80mm & 95mm).

PEEK

Initial trials were conducted with a PEEK sample and the two FastIR heaters with 1500W quartz halogen tubes separated by 110mm. The results of this test, shown in Figure 4, indicate that the sample failed to reach the required temperature.

The elements were changed to 2000W shortwave halogen (QHL) tubes which showed that, at the same separation, the sample reached and exceeded the required temperature at one location. In this instance, the maximum temperature recorded was 485°C, however, significant temperature differences (up to 83°C) were also detected. The time required to reach the target temperature of 425°C was 99 seconds. This was achieved at two locations only

Quartz tungsten (QTL) tubes (2000W) were also examined at the three levels with maximum temperature falling off as heater distance increased. At 55mm, a maximum and minimum temperature of 520°C was detected. The target temperature, across the material sample was achieved in 206 seconds. Increasing the distance to 80mm, these reduced to 450°C and 415°C and at 95mm above the sample, the maximum and minimum temperatures of the sample were 407 and 393°C.

Figure 4 shows the variance in temperature that can occur across the sample due to the close proximity of the heaters to the sample as well as the time required to heat the material to 425°C (206 seconds for 2kW QT heater).
150°W tungsten tubes were not tested as it was deemed more operationally important to increase the heater distance than decrease the power of the elements used.

Figure 5 shows the visual difference in the sample before and after heating.

PEKK

PEKK was heated with 2000W tungsten heaters at 55mm only. The thermal response of the material was excellent with temperatures in excess of 500°C being recorded. The minimum stipulated temperature was achieved in 102 seconds with the maximum temperature recorded being in excess of 500°C.

It was noticeable that this sample appeared to show some splitting and delamination at the edges and also some surface distortions following heating as shown in Figure 7, possibly from moisture absorption during storage and the rapid heating which occurred.

PPS

The PPS material was tested with 2000W halogen and tungsten heaters. The halogen test was carried out with a separation of 55mm and the tungsten tests at 55mm and 95mm.
The data again showed that the tungsten tube was a better heater for this material (than the halogen heater) with higher temperatures being recorded at the 55mm separation and also greater uniformity of temperature across the sample. A variation of 38°C was recorded for the halogen heaters and 30°C for tungsten heaters. This recorded variation will be highly influenced by the location of the thermocouple relative to the tubes. Identical thermocouple locations are not guaranteed.

Tests with PPS were terminated soon after the material reached the required temperature of 425°C as there was a release of sulphur smelling fumes from the samples.
At a distance of 55mm, the target temperature was recorded after 66 and 88 seconds for halogen and tungsten heaters at 55mm respectively. When the tungsten heaters were mounted at 95mm from the sample, the target temperature was not achieved.

Black Hollow

Initial tests were conducted with an element-material separation of 50mm. The temperature rise of the material was very rapid for all materials. From a cold start, hollow elements take approximately 10-12 minutes to heat to steady operational levels (surface temperature of approx. 700°C). The material temperature increase was broadly similar to the heating curve of the heater, however, there was a time lag in this.

PEEK

A plot of the time taken to heat the sample of PEEK to reach the required processing temperature is shown below in Figure 9. This shows that the heating time to 425°C is approximately 185 seconds from when the heaters are turned on at 50mm. If the distance is increased to 100mm, the time is increased to 230 seconds. The sample was left between the two platens during heat up and removed for cooling.

PEKK

The time taken for PEKK to reach the minimum threshold was slightly longer than for PEEK. Two possible reasons exist for this: 1.) the material does not absorb the infrared radiation as well as PEEK and 2.) the thickness of the material being twice as large (1 and 2mm respectively). The time required to reach 425°C at 50mm was 181 seconds and at 100mm this increased to 244 seconds

PPS

PPS heated very successfully with the black hollow elements with 425°C being recorded in 171 seconds and 219 seconds at 50 and 100mm respectively. The heating curve for this material is shown in Figure 11. Again, a release of sulphur smelling smoke occurred, however the quantity of this was not as much as with the halogen heaters as detailed above. This may partially be due to the absence of fans on the back of the heating platen.

A summary of the times required to heat the materials, with halogen, tungsten and hollow ceramic elements, to the target temperature is shown below in Table 1. As mounting the halogen elements at longer distances than 55mm was not universally successful, these results were omitted from the table.

Material	Heater type (power)	Distance	Time to reach 425°C
PEEK	QHL (2kW)	55mm	99
	QTL (2kW)	55mm	206
	FFEH (800W)	50mm	185
	FFEH (800W)	100mm	230
PEKK	QTL (2kW)	55mm	102
	FFEH (800W)	50mm	181
	FFEH (800W)	100mm	244
PPS	QHL (2kW)	55mm	66
	QTL (2kW)	55mm	88
	FFEH (800W)	50mm	171
	FFEH (800W)	100mm	219

Sandwich testing

Sandwich testing was carried out to obtain information about the transfer of heat through the material. This was done by heating the sample from a single side, measuring the temperature on both sides and comparing the results. Tungsten tubes and black hollow elements only were examined, as based on the FastIR results, the shortwave halogen tubes are not suitable heaters for the materials in question.

The results for QTM elements show that there is no significant temperature difference between the top and bottom surface for PEEK and PPS materials, however PPS heats more quickly and the curves for this material are virtually indistinguishable. It must be noted that these two materials are very thin (≈ 1mm). As expected, the temperature difference for PEKK was larger (75±2oC) due to its thickness (≈ 2mm). These results are shown in Figure 12 below.

For operational reasons, the test terminates when a temperature of 300°C is detected by the pyrometers. The peak seen in the first 30 seconds of the test is reflectance and is not a true temperature reading.

These results demonstrate that good IR penetration of the material is possible for PEEK and PPS using the tungsten type heater. However the temperature equalisation for PEKK is not as good, demonstrated by the almost 75°C difference in temperature in the last 18 seconds of the test4.

It was not possible to move the material samples closer to the heater to analyse what effect this would have as the acute angle required for the pyrometer to see the material would distort the reading.

Heating of the samples with black hollow elements at the same distance (75mm) shows a similar trend with a larger temperature difference (45±2°C) being observed for the thicker PEKK material (compared with the thinner materials). The temperatures of the top and bottom surfaces of PEEK are virtually indistinguishable; however there is a difference in the temperature of PPS (25±2°C). This data is shown in Figure 13. This indicates that IR penetration of PPS with longer wavelength radiation is not as good as with shorter tungsten IR, however, the temperature equalisation of PEKK is better (but not ideal).

At 75mm separation, the highest temperatures and heating rates are obtained using the tungsten heater which appears to contradict the previous platen results. This however should not be used as a guide as only a single heater was used. Moreover, these characteristics will be improved by using an array of heaters as opposed to a single heater.

Conclusion

• The tests carried out and detailed above indicate that heating of the three thermoplastic carbon composite materials to a minimum of 425°C is possible with both medium-wave halogen and black hollow elements.
• Higher maximum temperatures are achievable using Ceramicx 800W black hollow element (FFEH).
• The time required to heat PEEK to 425°C was 206 seconds for 2kW tungsten tube heaters at 55mm and 230 seconds for FFEH elements at 100mm
• The time required to heat PEKK to 425°C was 102 seconds for 2kW tungsten tube heaters at 55mm and 244 seconds for FFEH elements at 100mm
• The time required to heat PPS to 425°C was 88 seconds for 2kW tungsten tube heaters at 55mm and 219 seconds for FFEH elements at 100mm
• The maximum temperatures, material heating rates achievable and surface temperature uniformity are a strong function of the distance at which the heaters are mounted from the material.
• Excellent IR penetration and therefore temperature equalisation, through the material thickness, of PPS and PEEK was achieved with medium-wave halogen (tungsten). The temperature equalisation achieved with PEKK was not as good as with the other materials.
• Excellent IR penetration and temperature equalisation was seen with PEEK using black hollow elements. This property was not as good as for PEKK and PPS.

Based on the test data above and the close element-material separations which are required to achieve the temperatures demanded to form the materials in question, it appears the best infrared emitter is Ceramicx 800W black full flat hollow element. While the times to achieve the required temperatures are slightly longer than the tungsten heaters, the closer proximity of the elements used will lead to better surface temperature uniformity. Furthermore, the ceramic elements were started from room temperature and required approximately 12 mins to reach operational levels. Therefore, this time could be significantly shorted by preheating the elements.

It should also be noted that these results are based on the samples which were made available for testing (i.e. 1mm and 2mm in thickness). Heating of thicker parts may require significant changes in heating technology to be investigated in order to ensure the temperature profile, across the material’s thickness, is uniform and suitable for subsequent forming operations.

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¹ Polyether ether ketone
² Polyphenylene Sulfide
³ Polyetherketoneketone
⁴ Average difference between top and bottom surfaces taken over the last 18 seconds of the test.

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Disclaimer

These test results should be carefully considered before a certain type of infrared emitter is determined to employ.
Repeat tests conducted by other companies may not achieve the same findings. Differences in the experimental conditions may alter the results. Other sources of error include: the brand of emitter employed, the efficiency of the emitter, the power supplied, the distance from the tested material to the emitter utilised and the environment. The locations at which the temperature is measured may be also cause variation in the results.

AUTHOR	DATE CREATED	VERSION	DOCUMENT NUMBER
Dr. Gerard McGranaghan	15 May 2015	V1.1	CC11 – 00065

Plancks Law describes the electromagnetic radiation emitted by a black body in thermal equilibrium at a definite temperature. It is named after Max Planck who proposed it in 1900.

Introduction

Plancks Law tells us that as the temperature of any emitting surface increases, more and more energy will be released as Infrared energy. The higher the object temperature, the greater the amount of infrared energy will be produced. As well as becoming more intense (Power) the emitted frequencies become wider and the peak wavelength becomes shorter. At very high temperatures not just infrared, but some shorter wavelength visible light will also be produced. This is first witnessed as a dull red glow, then to orange, yellow and finally white. Figure 1 shows typical Planck curves for a range of temperatures that have been plotted from 1050°C to 50°C.

The red curve corresponding to 1050°C exhibits the strongest output. It shows the highest power output and its peak is at around 2.5 microns. This is followed by the curve at 850°C where the peak energy is less than half of that produced at 1150°C. As the temperature decreases, the energy levels also drop, and the peak energy wavelength shifts to the longer wavelengths. The lowest temperatures from the 250°C, 100°C and 50°C curves cannot be seen in the graph.

When the graph is enlarged to see the lower temperature curves, this shift to the longer wavelengths is more apparent. However the power intensity drops significantly.

This is shown in Figure 2. At 250°C the blue curve can be seen to have an approximate peak around 6 microns, whereas at 100°C the peak wavelength is around 7.5 microns. Note also that the extent of wavelength is more evenly distributed and doesn’t exhibit the concentrated narrow peak seen at higher temperatures.

If we enlarge the same graph again and focus only on the lower temperatures as shown in Figure 3 we see that temperatures of 50°C and 25°C have peak wavelengths of around 9 and 10 microns respectively.

In the final graph shown in Figure 4, a curve showing the peak wavelength against temperature is shown. This is plotted from Wiens Law. The increase in peak wavelength as temperature drops is clearly seen.

Summary

Plancks Law describes the electromagnetic radiation emitted by a black body in thermal equilibrium at a definite temperature. When plotted for various heater (emitter) temperatures, the law predicts

1. the range of frequencies across which infrared heating energy will be produced
2. the emissive power for a given wavelength

When selecting an infrared emitter for a particular heating task, the target material absorption characteristics are of high importance. Ideally,the emitted infrared frequencies and the target material absorption frequencies should match to allow the most efficient heat transfer. However as can be seen from the previous graphs, at longer wavelengths, the amount of energy transferred will be lower due to the lower emitter temperatures, therefore heating times will usually take longer.

The shorter the wavelength, the higher the emitter temperature and the available infrared power increases rapidly.

AUTHOR	DATE CREATED	VERSION	DOCUMENT NUMBER
Dr. Gerard McGranaghan	10 July 2014	V1	CC11 – 00034

Introduction

AUTHOR	DATE CREATED	VERSION	DOCUMENT NUMBER
Conor Newman	9 July 2019	V1.1	CC11 – 00152

Introduction

Two tests were implemented for the purpose of this report:

1. Test 1 compares the performance of a 2 standard FFEH 800W (running at 400W each) when paired with various reflectors, and in turn when fitted with various grills as seen in an IRP4
2. Test 2 quantifies the ability of an IRP4 to heat a concrete slab from a set distance. It also moniters the internal and surface temperatures of the IRP4.

Test 1

The first test was carried on in Ceramicx’ Herschel heat flux robot. Two standard FFEH 800W elements were paired with three separate RAS 2 reflectors, and the emitted heat flux was mapped. The elements were a distance of 200mm from the sensor. It was determined that the aluminised steel reflector outperformed both the stainless steel and the bronzed stainless steel by approximately 6%.

The results were as follows:

Once the aluminised steel was determined as the optimum reflector, the Herschel was once again use, this time placing a grill in front of the elements. It was found that a stainless steel or a bronzed stainless steel grill would reduce the performance of the FTE by 20%, and the black coated stainless steel grill would reduce said performance by 26%.

The results were as follows:

Test 2

A concrete slab (dimensions 400mm x 200mm, 15mm thick) was placed on the tiled floor, 2.7m directly below the IRP4. A type K thermocouple was attached to the slab and the temperature was recorded. The tests were run for in excess of 6 hours. The following results were noted:

• The 1000W FTE set resulted in the highest slab temperature. The slab reached a temperature of 28°C.
• The 650W FTE and 800W PFQE yielded similar results, a slab temperature of approximately 26°C.
• Both FFEH sets, 800W and 600W led to the poorest results, slab temperatures of 24.5°C and 22.5°C respectively.

The results are displayed graphically in the figure below:

The internal and back surface temperatures were recorded while the IRP4 was in operation. The following results were observed:

• When fitted with either 4x650FTE,4x600FFEH,4x800WFTE,or4x800WPFQE, the internal temperature at the measured point ranged between 150-180°C, and the back surface ranged between 85-105°C.
• When fitted with 4 x 1000W FTE, the internal and back surface temperatures recorded were 240°C and 115°C respectively.

The results are displayed graphically in the figure below:

Conclusions

• Test 1 provides clear data highlighting the superior performance of an aluminised steel reflector when compared to stainless steel reflectors. The aluminised steel reflector outperformed both the stainless steel and the bronzed stainless steel by approximately 6%.
• The stainless steel grill, both standard and bronzed by heat treating, performed better than the black coated reflector. This was expected due to the high emissivity of a black coated surface. It was found that a stainless steel or a bronzed stainless steel grill would reduce the performance of the element by 20%, and the black coated stainless steel grill would reduce said performance by 26%.
• When used exclusively to heat a concrete slab 2.7m below the IRP4, the 4 x 1000W FTE array performed best. This was expected due to the higher power. However, when comparing FTE performance to FFEH performance within an IRP4, the FTE performed noticeably better. Further works will be carried out to better analyse these differences in performance.
• As expected, the internal and back surface temperatures were much higher when using the high powered 1000W FTE. Consideration would have to be given to the max operating temperatures of the IRP4’s internal components should high powered elements be used. FFEH elements resulted in marginally lower temperatures than the FTE’s.
• From a performance standpoint, the 800W PFQE elements in the IRP4 went largely unnoticed throughout these tests. The results were neither particularly high nor low with respect to the ceramic elements. The potential future benefits of using quartz elements in an IRP4 appear to be purely aesthetic.

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Disclaimer

These test results should be carefully considered prior to a determination on which type of infrared emitter to use in a process. Repeated tests conducted by other companies may not achieve the same findings. There is a possibility of error in achieving the set-up conditions and variables that may alter the results include the brand of emitter employed, the efficiency of the emitter, the power supplied, the distance from the tested material to the emitter utilised and the env