Design and Manufacture of a Micro-Ejector and the Testing Stand for Investigation of Micro-Ejector Refrigeration Systems.

This paper describes the procedure of design and manufacture of a micro-ejector proposed for miniature ejection refrigeration systems. It describes the procedure of design, fabrication, and experimentation on supersonic micro-ejectors and makes the case for isobutane as a working fluid for such systems. It was demonstrated that it is possible to design and fabricate a micro-ejector with a cooling capacity of approximately 3 W. The discussed micro-ejector was driven by a heat source with temperature below 60 °C. The evaporation temperature was approximately 15 °C. For these operating parameters, the reported entrainment ratio was approximately 0.20. The difficulties in fabricating the micro-ejector due to its small dimensions are discussed in the paper. Additionally, the potential difficulties and solutions related to ensuring and maintaining stable operation of the testing stand are presented. The performance of the proposed system is demonstrated and discussed, including relations between mass entrainment ratio, compression ratio, cooling capacity, and temperature.

The Influence Of Intrauterine Pressure On Embryo Retention In A Catheter After Embryo Transfer.

The retention of the embryo in the transfer catheter after embryo transfer (ET) during in vitro fertilization is a very common phenomenon, encountered by even the most experienced operators, and embryos retained in the transfer catheter or its sleeve require a repeat transfer. The exact mechanism of embryo retention has not been explained. Therefore, the present study aimed to investigate the mechanism of embryo retention in the catheter during embryo transfer by using a transparent uterus model equipped with pressure sensors and a video recorder. The results indicate that pressure changes in the uterine cavity during ET can influence the distribution of the transferred fluid containing the embryo. Under certain conditions, the transferred fluid can flow backward in the catheter, which may lead to retention of the embryo in the catheter.

Fluid dynamics during embryo transfer.

OBJECTIVE: To study fluid dynamics during ET. DESIGN: Computational fluid dynamics were applied to calculate fluid velocity changes, dynamic pressure differences, and shear stress in the transferred load for the following injection speeds: 0.1, 1, 6, 12, and 20 m/sec. SETTING: Academic research institute of mechanical engineering and reproduction biotechnology and private centers of reproductive medicine. PATIENT(S): None. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Fluid velocity, dynamic pressure, and shear stress during injection of the transferred load. RESULT(S): An increase of injection speed for the transferred load increased the shear stress, dynamic pressure, and velocity differences acting on the embryo. The narrowing of the catheter lumen diameter by 20% amplified the transferred fluid velocity by 78%. An embryo positioned in proximity to the catheter's wall was exposed to considerably higher shear stress, dynamic pressure, and velocity difference than an embryo in the center of the catheter's lumen. CONCLUSION(S): The transfer of an embryo should be conducted gently and with minimal injection speed. Any narrowing of the catheter lumen should be eliminated. Preferably the embryo should be kept far from the catheter's wall during injection of the transferred load.

Pressure changes during embryo transfer.

OBJECTIVE: To investigate the pressure changes in the transferred load during mock ET. DESIGN: Experimental setup. SETTING: Academic Research Institute of Mechanical Engineering and private centers of reproductive medicine. PATIENTS(S): None. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Laboratory simulations of ET into a rigid transparent uterine model equipped with a pressure sensor. RESULT(S): Injection of a transferring load during mock ET could increase pressure locally up to 155 mm Hg in <0.1 seconds. The recorded pressure increase slope reached values as high as 72,000 mmHg/s, and the pressure decrease slope reached 144,000 mmHg/s. The pressure buildup in the transferred liquid was proportional to the ejection speed of the transferred load. CONCLUSION(S): ET can cause rapid pressure fluctuations in the transferred liquid. Therefore, it is advisable to transfer the embryo gently with minimum ejection speed, to avoid exposing the embryo to the steep pressure gradient.