Browsing by Author "Mahmud, Md. Almostasim"

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    Analysis of heat transfer and fluid flow in an evaporating sessile droplet for evaporative cooling applications
    (2015-08-01) Mahmud, Md. Almostasim; MacDonald, Brendan
    Cooling is of critical importance for a number of fields, particularly in microelectronic devices and other miniaturized technology. The evaporation of the sessile liquid droplet facilitates the phase change of that liquid and provides cooling to the system, because a large amount of latent heat is required to change the phase. Evaporation takes place at the liquid-vapour interface, so to enhance the phase change process, it is essential to understand the interfacial energy transport mechanisms involved in transporting energy to the liquid-vapour interface from the solid substrate and the vapour surrounding. A series of experiments were conducted under different experimental conditions to understand interfacial energy transport in an evaporating sessile droplet. The experimental results demonstrate the effect of the ambient and substrate temperature on the evaporation process and the relative contributions of the conduction energy transport and other modes of energy transport in the total energy required for the phase change process.
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    Miniaturization of features in microfluidic paper-based analytical devices for user-friendly testing and diagnosis using small sample volumes
    (2019-04-01) Mahmud, Md. Almostasim; MacDonald, Brendan
    Microfluidic paper-based analytical devices (µPADs) are a promising platform for analytical testing, particularly for medical diagnosis. One of the main advantages of µPADs is the capacity for inexpensive, portable and user-friendly diagnostic devices for people who do not have access to traditional lab-based medical diagnosis. Miniaturization of µPADs can further reduce the material cost, reagent cost, and enhance the user-friendliness of the device. However, it is challenging to produce inexpensive and miniaturized µPADs using existing fabrication techniques because the techniques that offer high-end fabrication resolution are expensive, require multiple steps in fabrication, and are not suitable for mass production. Based on this research need, I have developed an inexpensive and high-resolution fabrication technique that enabled the fabrication of user-friendly miniaturized µPADs. The technique is rapid, capable of mass production, and offers the highest fabrication resolution compared to existing fabrication techniques. Small-scale paper channels are fabricated using a wide range of commercially available paper materials and it is found that the fibre width of the paper materials is the dominant parameter in creating the smallest features with the capability of fluid flow. The capillary flow speeds through small-scale paper channels are investigated to provide an understanding to predict fluid flow in miniaturized µPADs. Two different types of miniaturized µPADs are developed using the newly developed fabrication technique: (a) compact µPAD for multiplexed testing and (b) lateral flow assay (LFA)-type µPAD for semi-quantitative test readout. The compact multiplexed µPAD enables detection of eight analytes using 2 µL of samples and the efficacy of this device is demonstrated by performing dye tests and glucose tests. The LFA-type µPAD enables analytical tests using sub-microlitre volume of samples and provides user-friendly semi-quantitative test readouts. The efficacy of the LFA-type µPAD is demonstrated by performing dye tests, glucose tests, and human immunoglobulin E (IgE) tests. Thus, the fabrication technique demonstrates its capability in the development of functional miniaturized µPADs and such devices are able to provide inexpensive and user-friendly diagnostic tests.