5 research outputs found
Exploratory Research on MEMS Technology for Air-Conditioning and Heat-Pumps
This report details the efforts to exploit micro-electrical-mechanical-systems (MEMS)
and micro device technologies to improve control of multi-channel evaporators by
reducing maldistribution among channels, and increase capacity and efficiency of
current vapor-compression refrigeration chillers and heat-pumps. Besides
summarizing the market potential of MEMS technology for use in evaporators and
micro-heat-pumps, the report describes the accomplishments of an experimental
investigation of refrigerant-side maldistribution in multi-channel plate heat exchangers
(PHE's). A special test facility designed for the purpose of studying the
maldistribution of refrigerant in evaporators is described in the report. The facility
allows maldistribution caused by either normal superheat temperature control, or
induced by the user in controlled amounts, to be measured and quantified. Four
different techniques were used to detect the presence of liquid droplets in the stream of
superheated vapor at the evaporator exit, an indication of maldistributed flow. They
are: Helium-Neon laser, beaded thermocouple, static mixer and newly designed heated
MEMS sensor. Comparison of the four techniques shows that the MEMS sensor
designed and fabricated in this project has the highest potential for indicating
maldistribution, manifested by entrained liquid droplets, in multi-channel evaporators.
A complete set of test results in the time and frequency domain is show in graphical
form in the appendices. The design, fabrication, calibration, and testing of the MEMS
serpentine resistance sensor is also reported, along with a control scheme and strategy
for implementing the MEMS sensor in multi-channel evaporator systems
Exploratory Research on MEMS Technology for Air Conditioning and Heat Pumps
This report presents an experimental investigation of refrigerant liquid mass fraction (LMF) in the exit
flows of plate evaporators. The objective is to identify a sensor that is capable of measuring small amounts of
refrigerant liquid in the superheated vapor at evaporator exits. This sensor should have the potential to be combined
with an active control scheme that increases the fill factor of the evaporator while simultaneously reducing superheat
temperature at the evaporator exit. Four methods were used to detect refrigerant droplets in the superheated vapor
stream exiting a plate evaporator: (1) an energy balance calculation, (2) a microfabricated thin-film resistance sensor
developed specifically for this project, (3) an exposed beaded thermocouple, and (4) photodiodes that detected laser
light scattered by droplets. The design, fabrication, calibration procedures, and theory of operation of the MEMS
thin-film resistance sensor are also presented in this report. Experimental results indicate that a MEMS thin-film
resistance sensor is more sensitive than a beaded thermocouple to LMF of non-equilibrium evaporator exit flows.
The MEMS sensor accurately detected refrigerant LMF as low as 1.5% in superheated evaporator exit flows
Vascular incorporation of endothelial colony-forming cells is essential for functional recovery of murine ischemic tissue following cell therapy.
OBJECTIVE: Cord blood-derived human endothelial colony-forming cells (ECFCs) bear a high proliferative capacity and potently enhance tissue neovascularization in vivo. Here, we investigated whether the leading mechanism for the functional improvement relates to their physical vascular incorporation or perivascular paracrine effects and whether the effects can be further enhanced by dual-cell-based therapy, including mesenchymal stem cells (MSCs). METHODS AND RESULTS: ECFCs or MSCs were lentivirally transduced with thymidine kinase suicide gene driven by the endothelial-specific vascular endothelial growth factor 2 (kinase insert domain receptor) promoter and evaluated in a hindlimb ischemia model. ECFCs and MSCs enhanced neovascularization after ischemic events to a similar extent. Dual therapy using ECFCs and MSCs further enhanced neovascularization. Mechanistically, 3 weeks after induction of ischemia followed by cell therapy, ganciclovir-mediated elimination of kinase insert domain receptor(+) cells completely reversed the therapeutic effect of ECFCs but not that of MSCs. Histological analysis revealed that ganciclovir effectively eliminated ECFCs incorporated into the vasculature. CONCLUSIONS: Endothelial-specific suicide gene technology demonstrates distinct mechanisms for ECFCs and MSCs, with complete abolishment of ECFC-mediated effects, whereas MSC-mediated effects remained unaffected. These data strengthen the notion that a dual-cell-based therapy represents a promising approach for vascular regeneration of ischemic tissue