Comparative Performance of K, E, and J-Type Fast Response Coaxial Probes for Short-Period Transient Measurements

2020 ◽  
Vol 13 (3) ◽  
Author(s):  
Sanjeev Kumar Manjhi ◽  
Rakesh Kumar
Keyword(s):  
Heat Flux ◽  
Surface Heat Flux ◽  
Continuous Wave ◽  
Surface Heat ◽  
Laser Source ◽  
Average Error ◽  
Transient Temperature ◽  
Thermal Coefficient ◽  
Thermal Product ◽  
Short Period

Abstract In many engineering applications, the heating condition changes in a millisecond or less, thus to study such conditions, the coaxial thermocouples (CTs) are used because they have fast responding capability. The present study reveals the construction of K, E, and J-type of coaxial thermocouples and comparative investigation of performance parameters such as determination of thermal coefficient resistance, sensitivity, thermal product (TP), transient temperatures, surface heat flux, response time, and the comparative analysis are performed. These coaxial thermocouples are exposed to four different step heat loads (5 kW/m2, 25 kW/m2, 50 kW/m2, and 70 kW/m2) supplied by a continuous-wave type laser source. Subsequently, the transient temperature histories have been captured for 1.5 s, as well as the thermal product and the surface heat flux are assessed through one-dimensional heat conduction modeling for a semi-infinite body. For the known wattage input heat load, the finite element and analytical study have been done to compare the experimental outcomes. The experimental results have reasonable accuracy with the numerical and analytical results. The average error calculated for transient temperatures and evaluated heat flux are ±0.25% and ±2.5%, and the response times of these coaxial thermocouples are calculated as 40 µs, 36 µs, and 46 µs for K, E, and J-type, respectively, which shows the measuring capability of these CTs for short-duration measurements.

Heat Transfer During Liquid Contact on Superheated Surfaces

1995 ◽  
Vol 117 (3) ◽  
pp. 693-697 ◽  
Author(s):  
J. C. Chen ◽  
K. K. Hsu
Keyword(s):  
Heat Flux ◽  
Atmospheric Pressure ◽  
Surface Heat Flux ◽  
Temperature Data ◽  
Surface Heat ◽  
Transient Temperature ◽  
Time Varying ◽  
Wall Superheat ◽  
Hot Surface ◽  
Better Than

Several boiling regimes are characterized by intermittent contacts of vapor and liquid at the superheated wall surface. A microthermocouple probe was developed capable of detecting transient surface temperatures with a response time better than 1 ms. The transient temperature data were utilized to determine the time-varying heat flux under liquid contacts. The instantaneous surface heat flux was found to vary by orders of magnitude during the milliseconds of liquid residence at the hot surface. The average heat flux during liquid contact was found to range from 105 to 107 W/m2 for water at atmospheric pressure, as wall superheat was varied from 50 to 450°C.

Transient Response Characteristics of a Surface Junction Probe

2019 ◽  
Author(s):  
Anil Kumar Rout ◽  
Niranjan Sahoo ◽  
Pankaj Kalita ◽  
Vinayak Kulkarni
Keyword(s):  
Heat Flux ◽  
Transient Response ◽  
Time Scale ◽  
Surface Heat Flux ◽  
Scale Up ◽  
Surface Heat ◽  
Temperature History ◽  
Transient Temperature ◽  
Time Data ◽  
Response Characteristics

Abstract The present work highlights the transient response phenomena captured by a coaxial surface junction thermocouple (CSJT) and subsequent use of the thermal probe for prediction of surface heat flux. To accomplish the objective, an E-type CSJT has been fabricated in-house in a laboratory scale from its thermo-elements with constantan (0.91mm diameter and 15mm length) serving as the inner element and chromel as outer element (3.25mm diameter and 10mm length). Both the thermo-elements are clubbed together coaxially which are separated by a thin layer of insulation in between them along the length. The junction between the thermo-elements is created at the surface through abrasion technique which forms a firm contact through formation of cold weld. The junction feature is then examined through a field emission scanning electron microscope (FESEM). The sensitivity of the probe is found experimentally to be 59 μV/°C. The transient response characteristics are observed through water plunging and water droplet tests at 55°C for 20ms and 2s time scale. The voltage time data is recorded and with the help of sensitivity value, the temperature history is calculated. The temperature histories from plunging and droplet experiments are used for calculation of heat flux by analytically modeling the sensor as semi-infinite substrate and assuming heat conduction through it is one dimensional. The heat flux is also calculated from the same temperature history by using numerical analysis and compared with the previous one. The measured data provides substantial evidence for usage of these CSJT probes in transient temperature and surface heat flux recoveries within experimental time scale up to 2s with reasonable accuracy.

Analysis of significant measures for thermal conductivity

2020 ◽  
pp. 35-42
Author(s):  
Yuri P. Zarichnyak ◽  
Vyacheslav P. Khodunkov
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Surface Heat Flux ◽  
Heat Flux Density ◽  
Measurement Method ◽  
Conductivity Measurement ◽  
Surface Heat ◽  
Measuring Instrument ◽  
New Class ◽  
Achievable Accuracy

The analysis of a new class of measuring instrument for heat quantities based on the use of multi-valued measures of heat conductivity of solids. For example, measuring thermal conductivity of solids shown the fallacy of the proposed approach and the illegality of the use of the principle of ambiguity to intensive thermal quantities. As a proof of the error of the approach, the relations for the thermal conductivities of the component elements of a heat pump that implements a multi-valued measure of thermal conductivity are given, and the limiting cases are considered. In two ways, it is established that the thermal conductivity of the specified measure does not depend on the value of the supplied heat flow. It is shown that the declared accuracy of the thermal conductivity measurement method does not correspond to the actual achievable accuracy values and the standard for the unit of surface heat flux density GET 172-2016. The estimation of the currently achievable accuracy of measuring the thermal conductivity of solids is given. The directions of further research and possible solutions to the problem are given.

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