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Improving Your Pressure Pump

1. You are designing a microfluidic device and want to achieve a 50% increase in flow rate through a channel. Which of the following approaches would be most suitable? a. Increase the radius by 10% b. Decrease the change in pressure by 50% c. Increase the length by 50% d. Decrease the flow speed by 25%

Explain the answer you have selected, and why the other answers will not achieve the desired changed in volume flow rate. (8 marks)

2. Thin films are layers of materials between 2nm and 1μm thick. This corresponds to a few several hundred atomic layers. Since thin films are so fragile, they are often formed on and supported by a substrate, which acts as a rigid base. To create the thin film, the substrate can first be covered with a thin metal coating, or an electrode. The thin film is built on top of this to the desired thickness, and then covered with a second metal electrode. This effectively forms a parallel-plate capacitor with the thin film acting as the dielectric and the electrodes acting as the parallel plates. Figure 1 shows this thin film device.

Some thin films are pyroelectric. These are materials that respond to a change in temperature by generating a small current across the opposite faces of the thin film. The magnitude of the current generated by the pyroelectric material is determined by the following equation: ???? = ???? ???? ????? ?

Where i is the current, p is the pyroelectric coefficient, A is the area of the electrodes, ΔT is the change in temperature and t is the time. The pyroelectric coefficient is a measure of the performance of the pyroelectric material; the higher the coefficient, the higher the efficient the material is. The pyroelectric thin film used here has a thickness of 1μm and a pyroelectric coefficient of 20x10- 6C/m2 ? ?C. The area of the metal electrodes is 3x10-4 m

Note: the condition for maxmum intensity of light reflected off a thin film is 2???????? = (???? + 1 2 )?

Where m is an integer ≥ 0, n is the index of the refraction of the film, d is the thickness of the film, and λ is the wavelength of light.

Answer each of the following questions by selecting the most appropriate answer. Explain your choice.

(4 marks) Which of the following would increase the magnitude of the current generated by the pyroelectric thin film? I. Increasing the rate of change in temperature II. Increasing the area of the electrodes III. Increasing the thickness of the film

a. I only b. I and II only c. II and III only d. I, II and III

(4 marks) The current i generated by the pyroelectric is equal to Q/t, where +Q and -Q are equal to the charge deposited on the positive and negative electrodes, respectively. If a pyroelectric material is charged up and then connected in parallel to a resistor, what will the maximum voltage across the resistor be? (Note the capacitance of the pyroelectric is C and the resistance of the resistor is R): a. pA(ΔT)/RC b. pA(ΔT)/C c. pA(ΔT)/R d. pA(ΔT) RC Hint: consider the equation relating charge and voltage on a capacitor.

(4 marks) Which of the following graphs best illustrates the relationship between the thickness and the capacitance of the thin film? Hint: consider equation for capacitance of a parallel plate capacitor.

(2 marks) If the area of the electrodes and the thin film are doubled, the dielectric constant of the thin film will then: a. Be reduced by half b. Remain unchanged c. Double d. Quadruple.

(3 marks) A thin film of unknown thickness and an index of refraction n = 1.5 is not in contact with any electrodes or substrate. Monochromatic light of variable wavelength is incident on the film. If the reflected light is maximum for a wavelength of 480nm, what is the minimum thickness of the film? a. 80nm b. 160nm c. 240nmm d. 480nm0.

Improving Your Pressure Pump

Introduction

Microfluidic device. (kabayishi, 2009)These are devices which are normally used in biology and bio-techniques for diagnosis, most of these devices may be categorized either passive or active device. Both active and passive have several parts. Active micro fluids consist of microfluidic valves that pump automatically while passive consists of mixers, rich chambers gradient generator splitters and mixers.

Improving your pressure pump.

Increase in pressure pump increases the rate of flow in microfluidic and pulse flow where device in pressure pump reduces rate of pulse flow in microfluidic. (Thorsen,2009) Microfluidic have no moving parts hence pressure device flows is much more smooth. Pressure increases in the liquid depending on the speeding  of  the liquid  hence enable faster flow rate.

Increase radius by 10%

When micrometric diameter of the tube is increased more air bubbles are formed inside the microfluidic device. (Chung, 2010)This are the bubbles, which are very detrimental and very difficult to remove during experimental set up. Due to air bubbles there will be high range of solution in microfluidic device. The presence of air bubbles inside microfluidic device will cause flow rate instability and this increases the pressure equilibrium in microfluidic device. This is because air will absorb some of the pressure inside the microfluidic device.

By increasing the length by 50%-this is the best method to be used

When the length of a microfluidic device for example increases  the Reynold number will be high and the flow will also be high hence mass becomes smaller (Yang,2006). When the length is reduced, the Reynold number decreases and flow will become laminar and mass increases.

Decrease the flow speed by 25%

Decreasing the flow speed of the fluid will reduce the strength of micro fluid. The rate at which micro fluid will move will determine the rate flow. Mellor’s (2010) At a low rate of speed flow, the air bubble will accommodate in microfluidic device which will reduce the rate of pulse flow in the microfilm.

Question 2

  • (i) (Lagally,2010). Increase in the rate of change in temperature will increase the magnitude of the film. The heat flow across the thin film layer of the microfilm enhances magnitude increase. The temperature variations of layer is the heat capacity of thermal-conduct of the microfilm layer. Whenever there is a thin film there is consequently increase in magnitude of the microfilm.
  • (ii) Wavelength is inversely proportional to frequency.

Question

Current=I=PA AT/t

Current=PA AT/t

P=pyroelectric coefficient. 20×10-6cm/m2

A=Area of electrode. 3×10-4m2

T=change in temperature

t=Time

PA(AT)/RC

And whenever there is thick film there is less magnitude. This implies that temperature also depends upon thickness of the film.

??α???V

??constant(c)

Where speed c= speed of light

Vα€

Or €αV

€=hV where h constant

(a)PA(AT)/RC

1=PA  AT/t

PACAT/

3×10-4m×20×106cm/m2

=60×102 

(iii)Explain relationship between thickness and capacity capacitance of the film. 

(v)    The relationship between the thickness and capacity of the thin film is inversely proportion to each other. When the thickness is higher the capacitance becomes lower while when capacity becomes higher the thickness of film decreases. (Chung,2008) Thickness of a film will dictate how much electric field flux will develop a certain amount of electric field force. The greater the plate, the greater the capacitance.Relationship between dialectic constant of the thin film and area of the thin film.

(iv)   when you double layer of the capacitance there will be double electrical effect. This will obscene between a conductive electrode and an adjacent liquid. At this point of two layer of ions with opposing polarity form if voltage is applied. (Kobaiyishi, 2010)The two layer is normally separated by single layer of a molecular which is solvent and adhere to the surface of the electrode which later acts like a di electric in the capacitor conventional, hence the amount of electric charge stored in a double layer is directly proportional to the applied voltage dependence to the electrode surface. 

References

 Chung, B.G., Flanagan, L.A., Rhee, S.W., Schwartz, P.H., Lee, A.P., Monuki, E.S. and Jeon, N.L., 2008. Human neural stem cell growth and differentiation in a gradient-generating microfluidic device. Lab on a Chip, 5(4), pp.401-406.

Hosokawa, K., Fujii, T. and Endo, I., 1999. Handling of picoliter liquid samples in a poly (dimethylsiloxane)-based microfluidic device. Analytical chemistry, 71(20), pp.4781-4785.

Kobayashi, J., Mori, Y., Okamoto, K., Akiyama, R., Ueno, M., Kitamori, T. and Kobayashi, S., 2009. A microfluidic device for conducting gas-liquid-solid hydrogenation reactions. Science, 304(5675), pp.1305-1308.

Lagally, E.T., Medintz, I. and Mathies, R.A., 2010. Single-molecule DNA amplification and analysis in an integrated microfluidic device. Analytical chemistry, 73(3), pp.565-570.

Mellors, J.S., Jorabchi, K., Smith, L.M. and Ramsey, J.M., 2010. Integrated microfluidic device for automated single cell analysis using electrophoretic separation and electrospray ionization mass spectrometry. Analytical chemistry, 82(3), pp.967-973

Thorsen, T., Roberts, R.W., Arnold, F.H. and Quake, S.R., 2009. Dynamic pattern formation in a vesicle-generating microfluidic device. Physical review letters, 86(18), p.4163.

Wheeler, A.R., Throndset, W.R., Whelan, R.J., Leach, A.M., Zare, R.N., Liao, Y.H., Farrell, K., Manger, I.D. and Daridon, A., 2012. Microfluidic device for single-cell analysis. Analytical chemistry, 75(14), pp.3581-3586.

Yang, S., Ündar, A. and Zahn, J.D., 2006. A microfluidic device for continuous, real time blood plasma separation. Lab on a Chip, 6(7), pp.871-880.

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