Electrospun natural-synthetic composite nanofibers, which possess favorable biological and mechanical properties, have gained widespread attention in tissue engineering. However, the development of biomimetic nanofibers of hybrids remains a huge challenge due to phase separation of the polymer blends. Here, aqueous sodium hydroxide (NaOH) solution is proposed to modulate the miscibility of a representative natural-synthetic hybrid of gelatin (GT) and polycaprolactone (PCL) for electrospinning homogeneous composite nanofibers. Alkali-doped GT/PCL solutions and nanofibers examined at macroscopic, microscopic, and internal molecular levels demonstrate appropriate miscibility of GT and PCL after introducing the alkali dopant. Particularly, homogeneous GT/PCL nanofibers with smooth surface and uniform diameter are obtained when aqueous NaOH solution with a concentration of 10 m is used. The fibers become more hydrophilic and possess improved mechanical properties both in dry and wet conditions. Moreover, biocompatibility experiments show that stem cells adhere to and proliferate better on the alkali-modified nanofibers than the untreated one. This study provides a facile and effective approach to solve the phase separation issue of the synthetic-natural hybrid GT/PCL and establishes a correlation of compositionally and morphologically homogeneous composite nanofibers with respect to cell responses.
Three different structural types of closed cooling tower (CCT) and two cooling water flow directions were considered. The experimental study were done on the cooling performance of influences of inlet air dry and wet bulb temperature, cooling water flow rate and inlet temperature, air flow rate and spray density. The experimental results show that the cooling performance of CCT with packing is obviously better than non-packing cooling tower in 7%~18.4%. And the cooling performance of CCT with packing on top and coil underneath is slightly better than CCT with coil on top and packing underneath in 4.9%. In the same conditions the cooling performance of CCT with packing under cooling water cocurrent-flow is better than that cooling water countercurrent-flow in 3.2%~9.6%. Therefore, the closed cooling tower structure with the cooling water path in bottom and out top, and with packing on top and coil underneath is recommended.
The initial ground temperature (IGT) is one of the most important parameters in designing a ground source heat pump (GSHP) system and evaluating its performance. In this paper, three initial ground temperature test methods are introduced. Except the shallow zone, the ground temperature distribution measured from direct and indirect testing method has very small difference. In direct test, the temperature sensor must be embedded when burying the tube in the borehole which is hard to operate in engineering applications. Thus the direct testing method is suggested to be applied in the scientific research. The indirect testing method could be used in engineering applications. The mean ground temperature could be calculated from temperature distribution except the shallow zone temperature. The results from three calculating methods have a quite small difference. Therefore, the arithmetic average method is suggested for scientific and engineering application to calculate the mean ground temperature. The mean ground temperature is also gotten in TRT conveniently. In the condition of velocity 0.7m/s, water was circulated in the tube system with no heat source for 30 minutes. The average water temperature could be regard as the mean ground temperature with sufficient accuracy.
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