Results 1 - 10 of 80
Results 1 - 10 of 80. Search took: 0.021 seconds
|Sort by: date | relevance|
[en] Extensive convective heat transfer measurements have been collected in the Supercritical University of Ottawa Loop (SCUOL) with carbon dioxide at supercritical pressures flowing vertically upwards in tubular test sections having inner diameters equal to 22.0, 8.0, and 4.6 mm. Outer wall temperature was measured by a large number of thermocouples, from which the inner wall temperature and the local heat transfer coefficient were estimated. The measurements extend over wide ranges of conditions, which cover both the normal and deteriorated heat transfer modes. Experiments were conducted using all three test sections with the purpose of determining the tube diameter effects on the local heat transfer coefficient h for normal heat transfer. Measurements were collected for 15 different flow and heating conditions, all at P/Pcritical ≈ 1.13. The results showed that, in most cases, the corresponding h was higher for smaller diameter tubes. Nevertheless, for flows at low mass fluxes (G ≤ 400 kg/m2s), the h values from the 8 and 22 mm test sections were comparable, especially at high specific bulk enthalpies (Hb > 300 kJ/kg); for G = 300 kg/m2s, the h values from all three test sections in the high enthalpy range actually nearly coincided. At higher mass fluxes, however, the h values remained distinct for each test section over the full range of Hb values examined, with higher h values for smaller test section diameters.
[en] In data acquisition, it is necessary to improve the performance of the instrumentation system by developing a LabVIEW based data acquisition system, one of which is by ensuring that the data obtained is correct and reliable. The data must go through a calibration process. In this experiment, the calibration was done by comparing the results of the temperature measurements from the recorded thermocouples in the form of NI cDAQ 91 data acquisition with measurements of the standard Fluke digital thermometer that functions as a calibrator. The NI cDAQ 91 module used is channel 1 and channel 2. Each channel has two parts of data taken, namely for low temperatures with smaller ranges and higher temperatures with a greater range. The results of the calibration data will be processed and the results of the uncertainty will be searched. After going through the calibration process it turns out the data results are not much different because it does not reach a temperature of 1 °C means that the calibration data results can be trusted with errors less than 1 °C. (author)
[en] A heater tank was designed and fabricated to simulate behavior of nuclear core by using electrical heating rods. This paper reports the experimental results for six heat rods. These rods were tested at 40 degree Celsius in air at room temperature. Setup parameters were verified. The results suggest that its temperature profile follows the trend for a heat distribution profile in nuclear fuel element. (author)
[en] The two-thermocouple method was investigated experimentally to evaluate its accuracy for the measurement of local wall temperature and heat flux on a heat transfer tube with an electric heater rod installed in an annulus channel. This work revealed that a thermocouple flush-mounted in a surface groove serves as a good reference method for the accurate measurement of the wall temperature, whereas two thermocouples installed at different depths in the tube wall yield large bias errors in the calculation of local heat flux and wall temperature. These errors result from conductive and convective changes due to the fin effect of the thermocouple sheath. To eliminate the bias errors, we proposed a calibration method based on both the local heat flux and Reynolds number of the cooling water. The calibration method was validated with the measurement of local heat flux and wall temperature against experimental data obtained for single-phase convection and two-phase condensation flows inside the tube. In the manuscript, Section 1 introduces the importance of local heat flux and wall temperature measurement, Section 2 explains the experimental setup, and Section 3 provides the measured data, causes of measurement errors, and the developed calibration method
[en] Femtosecond laser is an effective and safe tool in many surgeries, but the studies of its effect on oral soft tissue ablation are insufficient. This study aimed to investigate the effect of soft tissue ablation with a 1030-nm femtosecond laser on temperature and depth. Twenty Sprague–Dawley rat tongue specimens were obtained and flat-mounted. The 1030-nm femtosecond laser was controlled by a computer system, with a set distance of 4.7 mm between the laser aperture and soft tissue surfaces. Ten specimens were ablated for > 1 min with or without air-cooling for temperature measurement, while the other 10 specimens were ablated for depth measurements, using the following parameters: (i) 3 W, 2000 mm/s; (ii) 3 W, 4000 mm/s; (iii) 5 W, 2000 mm/s; (iv) 5 W, 4000 mm/s; (v) 8 W, 2000 mm/s; (vi) 8 W, 4000 mm/s. Temperature changes were measured using a type-K thermocouple. The depth attained using different power and scanning speed settings was measured by a three-dimensional morphology measurement laser microscope. Laser power, scanning speed, and air-cooling effects were determined. Higher energy and lower speed induced higher temperatures (p < 0.05), which were significantly decreased by air-cooling (p < 0.05). The lowest ablation depth was obtained at 3 W and 4000 mm/s (72.63 ± 6.47 μm) (p < 0.05). The greatest incision depth was achieved at 8 W and 2000 mm/s (696.19 ± 35.37 μm), or 4000 mm/s (681.16 ± 55.65 μm) (p < 0.05). The 1030-nm femtosecond laser application demonstrates clinically acceptable ablation efficiency, without marked temperature damage, in a controlled manner.
[en] Semisolid processing of Al–4.3%Cu (A206) alloy was carried out using gas-induced semisolid (GISS) process in different conditions. The flow rate of inert gas, 1, 2, and 4 L min−1, starting temperature for gas purging (the temperature of superheated melt), 670, 660, and 650 °C, and the duration of gas purging, 10, 20, and 30 s, were three key process variables which were changed during this investigation. Thermal analysis was successfully implemented through CA-CCTA technique for GISS samples as well as conventionally cast sample. The two-thermocouple thermal analysis technique was utilized to determine the dendrite coherency point of GISS sample and conventionally cast sample. The results showed that gas purging into the melt led to temperature drop of the melt to its liquidus temperature. In fact, copious nucleation is induced by cooling effect of inert gas bubbles. GISS process delays the dendrite coherency point from 644.2 to 637.3 °C which leads to increase the solid percentage from 9 to 21% at this point and therefore enhance the casting characteristics. It is found that inert gas purging into the molten metal, regardless of the process parameters, leads to the microstructural modification from fully dendritic to globular structure. Microstructural evaluation showed that the best sample which included fine grains of 76 μm in average size and with high level of globularity of 0.86 was achieved from a semisolid sample in which the gas purging started at 670 °C and its duration time was 20 s with the gas flow rate of 4 L min−1.
[en] Heat generation and accumulation during working schemes of the lithium-ion battery (LIB) are the critical safety issues in hybrid electric vehicles or electric vehicles. Appropriate battery thermal management is necessary for ensuring the safety and continuous power supply of rechargeable LIB modules. In this study, thirty cylinder 18650-type cells were fabricated a 6S5P battery module with a 2-mm spacing between cells to evaluate exothermic trajectories. The modules, equipped with a forced-air cooling system, were charged at 1 C-rate and discharged at 1, 1.5, and 2 C-rates for three cycles in each test; thermocouples were connected to the cells to track the variances in temperature and voltage. The efficiency of the developed forced-air cooling system was estimated to be 73.0% in case 1 with the 1 C discharge rate, and the temperature difference (TD) was less than 5.0 °C. The maximum temperature (Tmax) of this case was maintained below 45.0 °C showing uniform heat distribution. Moreover, extreme heat accumulation developed inside the module and damaged the adjacent LIBs during fast 2 C discharge test. Our TD testing showed that a forced-air cooling system in the LIB module provides effective heat dispersion under normal discharge conditions.
[en] This paper describes on the temperature measurement technique using ultrasonic wave as a noncontact-type. Because high-speed and high-resolution temperature measurement is required to diagnose combustion status of gas turbine, particularly combustion instability, a fast-responding ultrasonic wave measurement approach was adopted in this research. To validate the possibility of this approach, a fundamental experiment was conducted in a circular pipe, with the ultrasonic transmitter and the receiver were installed at both ends. A continuous 40 kHz sinusoidal ultrasonic wave was transmitted at one end and this signal was received at the other end at the rate of 1MHz. The time-of-flight in a circular tube was calculated to derive the temperature, and the temperature was simultaneously measured using thermocouples. The ultrasonic temperature measured by this method was corrected using the temperature fitting equation, and the error between the thermocouple and ultrasonic data was reduced to 1% level thus confirming that very accurate temperature measurement is possible.
[en] Urban heat island (UHI) is one of the adverse effects of densely populated cities. Therefore, studying the causes of temperature variations and UHI formation in urban area has become more important as a significant stage in improving urban health and development. Toward this end, impacts of urban Land Use/Land Cover (LULC) characteristics and spatiotemporal pattern of Land Surface Temperature (LST) under different weather conditions were investigated for determining the area with high potential of UHI formation in Tehran. Furthermore, LST of six different land covers was recorded with 15-min time intervals using 2channel-thermocouples with six PT100 sensors. In addition, SHRP model that can effectively predict LST using air temperature were developed for different weather conditions. Then, the accuracy of the model was determined by actual measured LST. Results indicate that temperature of land surface corresponds exactly to the distinct LULC types. The temperature of water bodies and vegetated area ranges between 12–14 °C and 8–10 °C lower than the surface temperature of roads and built-up areas in summer and winter times, respectively. Hence, bare lands, built-up areas and roads with average surface temperature of 48.5, 47.2, and 46.1 °C are the hottest places of the city with high potential of UHI formation. Also, results illustrate that SHRP model has high degree of accuracy for estimating the LST using air temperature when direct observations and measurement of LST are unavailable (r = 0.95).
[en] This study presents the micro thermoelectric infrared (IR) sensor consisting of the heat transduction absorber and the serpentine structure with embedded thermocouple using the TSMC 0.18 µm 1P6M standard CMOS process and the in-house post-CMOS MEMS process. The proposed IR absorber design has an umbrella-like structure with a post anchor to the serpentine suspension with embedded thermocouple. Compared to the reference design (IR sensor consisted of only the serpentine structure with embedded thermocouple), a better heat-flow path is achieved and the temperature difference between the hot and cold junctions is increased. Moreover, the umbrella-like structure has higher IR absorption area compared with the serpentine structure. In addition, the Seebeck coefficients of poly-Si films with and without silicide are respectively characterized. The poly-Si with no silicide has a much higher Seebeck coefficient (56-fold), and is employed in this study as the thermocouple material. Experiment results indicate the detectivity of proposed design is 2–2.6 fold higher than that of the reference one at 200 mTorr. Experiment also show that the responsivity enhancement of proposed design is further increased as the sensor size is reduced in area. (paper)