In this paper, we present our experimental results on the determination of the thermal conductivity of biological tissues using a transient technique based on the principles of the cylindrical hot-wire method. A novel, 1.45 mm diameter, 50 mm long hot-wire probe was deployed. Initial measurements were made on sponge, gelatin and Styrofoam insulation to test the accuracy of the probe. Subsequent experiments conducted on sheep collagen in the range of 25 • C < T < 55 • C showed the thermal conductivity to be a linear function of temperature. Further, these changes in the thermal conductivity were found to be reversible. However, when the tissue was heated beyond 55 • C, irreversible changes in thermal conductivity were observed. Similar experiments were also conducted for determining the thermal conductivity of cow liver. In this case, the irreversible effects were found to set in much later at around 90 • C. Below this temperature, in the range of 25 • C < T < 90 • C, the thermal conductivity, as for sheep collagen, varied linearly with temperature. In the second part of our study, in vivo measurements were taken on the different organs of a living pig. Comparison with reported values for dead tissues shows the thermal conductivities of living organs to be higher, indicating thereby the dominant role played by blood perfusion in enhancing the net heat transfer in living tissues. The degree of enhancement is different in different organs and shows a direct dependence on the blood flow rate.
In this paper, we present recent experimental results on forced convective heat transfer in novel finned metal foam heat sinks. Experiments were conducted on aluminum foams of 90 percent porosity and pore size corresponding to 5 PPI (200 PPM) and 20 PPI (800 PPM) with one, two, four and six fins, where PPI (PPM) stands for pores per inch (pores per meter) and is a measure of the pore density of the porous medium. All of these heat sinks were fabricated in-house. The forced convection results show that heat transfer is significantly enhanced when fins are incorporated in metal foam. The heat transfer coefficient increases with increase in the number of fins until adding more fins retards heat transfer due to interference of thermal boundary layers. For the 20 PPI samples, this maximum was reached for four fins. For the 5 PPI heat sinks, the trends were found to be similar to those for the 20 PPI heat sinks. However, due to larger pore sizes, the pressure drop encountered is much lower at a particular air velocity. As a result, for a given pressure drop, the heat transfer coefficient is higher compared to the 20 PPI heat sink. For example, at a Δp of 105 Pa, the heat transfer coefficients were found to be 1169W/m2-K and 995W/m2-K for the 5 PPI and 20 PPI 4-finned heat sinks, respectively. The finned metal foam heat sinks outperform the longitudinal finned and normal metal foam heat sinks by a factor between 1.5 and 2, respectively. Finally, an analytical expression is formulated based on flow through an open channel and incorporating the effects of thermal dispersion and interfacial heat transfer between the solid and fluid phases of the porous medium. The agreement of the proposed relation with the experimental results is promising.
Testing of groundwater used for drinking for arsenic has been undertaken more widely by state governments in several states of India in recent years with the support of UNICEF. Available data for five states are collated in this paper and this provides the most up-to-date picture of areas known to be affected by arsenic in groundwater in the Indian portion of the Ganges-Brahmaputra river basin. In West Bengal, water from 132,262 government installed handpumps in 8 districts has been tested and overall 25.5% of samples were found to contain arsenic at concentrations greater than 50 microgL(-1) and 57.9% at concentrations greater than 10 microgL(-1). On the banks of the Brahmaputra in Assam, to date, samples from 5,729 government handpump sources in 22 districts have been tested for arsenic. Overall, samples from 6.3% of sources were found to contain arsenic at concentrations greater than 50 microgL(-1) and 26.1% at concentrations greater than 10 microgL(-1). In Bihar, on the River Ganges upstream of West Bengal, 66,623 sources from 11 districts have been tested and water samples from 10.8% of sources were found to contain arsenic at concentrations greater than 50 microgL(-1) and 28.9% at concentrations greater than 10 microgL(-1). Upstream of Bihar in Uttar Pradesh, home of the Taj Mahal, to date water samples from 20,126 government-installed handpump sources have been tested. As a result 2.4% of the samples tested were found to contain arsenic at concentrations greater than 50 microgL(-1) and 21.5% at concentrations greater than 10 microgL(-1). Finally in one district of Jharkhand, lying on the Ganges alluvial plain between Bihar and West Bengal, 9,007 sources have been tested and water samples from 3.7% of sources were found to contain arsenic at concentrations greater than 50 microgL(-1) and 7.5% at concentrations greater than 10 microgL(-1). State governments have adopted different sampling strategies and these are described in this paper. Testing is ongoing in several states and the complete picture is yet to emerge in some areas.
In this paper, we investigate a novel alternating current electrothermal (ACET) micromixer driven by a high efficiency ACET micropump. The micromixer consists of thin film asymmetric pairs of electrodes on the microgrooved channel floor and array of electrode pairs fabricated on the top wall. By connecting electrodes with AC voltage, ACET forces are induced. Asymmetric microgrooved electrodes force the fluids along the channel, while lateral vortex pairs are generated by symmetric electrode pairs located on the top wall. Waviness of the floor increases contact area between two confluent streams within a narrow confinement. An active mixer operates as a semi active semi passive mixer. Effects of various parameters are investigated in details in order to arrive at an optimal configuration that provides for efficient mixing as well as appreciable transport. It is found that using a specific design, uniform and homogeneous mixing quality with mixing efficiency of 97.25% and flow rate of 1.794μm2/ min per unit width of the channel can be achieved.
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