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Title: The effect of heat transfer on temperature measurement and its applications to study microchannel heat sinks
Author: Al-Waaly, Ahmed
ISNI:       0000 0004 5368 942X
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 2015
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Analytical, numerical and experimental analyses have been performed to investigate the effects of thermocouple wire electrical insulation on the temperature measurement of a reference surface. Two diameters of K-type thermocouple, 80μm and 200μm, with different exposed stripped wire lengths (0 mm, 5mm, 10mm, 15mm and 20mm) were used to measure various surface temperatures (4oC, 8oC, 15oC, 25oC and 35oC). Measurements were made when the thermocouple probe is in direct contact with the surface and the wires are extended vertically and exposed to natural convection from outside environment. Experimental results confirmed that the thermal effect from the electrical insulation on temperature measurement was within -0.5oC and therefore it can be neglected. Moreover, the experimental results agree well with those obtained by both the analytical and numerical methods and further confirm that the diameter of the thermocouple has an impact on the temperature measurement. Analytical results of the thermocouple wire with insulation confirm that there is no specific value for the critical radius and the rate of heat flux around the thermocouple wire continuously increases with the wire radius even when this is larger than the critical radius. Experimental and numerical analyses have been performed to investigate the heating impact of using thermocouples for the temperature measurement of small volumes of cold water. Two sizes of K-type thermocouple have been used: 80μm and 315μm to measure the temperature of the cold water inside a small chamber while the thermocouple wires were extended vertically in the outside environment. For this study, the chamber temperature was adjusted to 4oC. The results show that the heating effect of the thermocouple decreases for the greater depth measurements and this effect is eliminated when the thermocouple junction is close to the chamber bottom surface. The increase in the thermal resistance between the bottom surface and the thermocouple junction raises the heating effect of the thermocouple impact. Moreover, the exposed length of thermocouple wires to the environment has no effect over a specific length where the wire end temperature is equal to that of the environment. Experimental and numerical analyses have been carried out to study the effect of using subchannels in heat sink to minimise the effect of hotspots generated on a chip circuit. Two devices of heat sink – with and without subchannels – were fabricated in order to investigate this effect. The first device was manufactured with a normal parallel channel while the second one was designed to extract more heat by dividing the main channels above the hotspot into two subchannels. A hotspot heat flux (16.7×104 [W/m2]) was applied at the centre of the channels while a uniform heat flux (4.45×104 [W/m2]) was applied at upstream and downstream of the channels. Five mass flow rates have generated under gravity force to investigate the performance of devices under different operating conditions. The results showed the maximum surface temperature was reduced by 4oC the temperature uniformity was improved. Moreover, thermal resistance was reduced by 25% but the pumping power was increased as a result of the presence of the subchannels.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TJ Mechanical engineering and machinery ; TK Electrical engineering. Electronics Nuclear engineering