A rapid and simple thermally-solvent assisted method of bonding was introduced for poly(methyl methacrylate) (PMMA) based microfluidic substrates. The technique is a low-temperature (), and rapid () bonding technique; in addition, only a fan-assisted oven with some paper clamps are used. Two different solvents (ethanol and isopropyl alcohol) with two different methods of cooling (one-step and three steps) were employed to determine the best solvent and method of cooling (residual stresses may be released in different cooling methods) by considering bonding strength and quality. In this bonding technique, a thin film of solvent between two PMMA sheets disperses tends to dissolve a thin film of PMMA sheet surface, then evaporate, and finally reconnect monomers of the PMMA sheets at the specific operating temperature. The operating temperature of this method comes from the coincidence of the solubility parameter graph of PMMA with the solubility parameter graph of the solvents. Different tests such as tensile strength test, deformation test, leakage tests, and surface characteristics tests were performed to find the optimum conditions for this bonding strategy. The best bonding quality and the highest bonding strength () occurred when 70% isopropyl alcohol solution was employed with the one-step cooling method. Furthermore, the bonding reversibility was taken into account and critical percentages for irreversible bonding were obtained for both of the solvents and methods. This method provides a perfect bonding quality for PMMA substrates, and can be used in laboratories without needing any expensive and special instruments, because of its merits such as lower bonding time, lower-cost, and higher strength etc in comparison with the majority of other common bonding techniques.

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An effective approach in suppressing stall is mass injection upstream of the tip of an axial flow compressor. Developing reliable injection systems for high pressure ratio compressors requires an understanding of the effects of injection parameters, for example, injection angle, on the compressor stability and performance. This paper reports on a numerical investigation of injection angle on the operability of a high-speed compressor rotor. The injection port is set to be choked for all of the injection cases. Simulations indicate that injection angle has a significant impact on stability improvement. Maximum range extension is obtained when an injection yaw angle equal to 30 deg is applied. At this injection angle, the stalling mass flow coefficient was reduced by 17.4% by using an injected mass flow equivalent to 1.55% of the baseline annulus flow. Results also indicate that the best injection case creates an incidence angle of about 0 deg over the tip of the blade and adds the highest momentum in the relative frame of reference.Nomenclature A = area a = annulus adb = adiabatic amb = ambient DF = diffusion factor in = blade inlet j = jet out = blade outlet P 0 = total pressure rel = relative frame of reference T 0 = total temperature t = tip U, V = velocity x = axial component y = nondimensional wall distance = efficiency = tangential component = momentum = density = solidity = flow coefficient

This paper reports on a theory for poststall transients in contra-rotating fans, which is developed from the basic Moore–Greitzer theory. A second-order hysteresis term is assumed for the fan pressure rise, which gives the theory more capabilities in predicting the fan instabilities. The effect of the rotational speed ratio of the two counter rotating rotors on the fan performance during the occurrence of surge and rotating stall are studied (the rotational speed of the front rotor is assumed to be kept constant whereas the speed of the rear rotor is variable). One of the new capabilities of the current model is the possibility of investigating the effect of the initial slope on the fan characteristic. Results reveal that unlike the conventional fans and compressors, in the current contra-rotating fan stall cannot be initiated from the negative slope portion of the fan pressure rise characteristic curve. One of the important advantages of the developed model is that it enables investigation of the effect of the rate of throttling on the instabilities. Results show that more the rotational speed of the rear rotor, the more robust to surge (caused by throttling) the fan is.

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