Feasibility of Pulmonary Airway Tissue Engineering and Repair Using a Cell Spraying Device and Decellularized Porcine Trachea

University of Minnesota M.S. thesis. August 2019. Major: Biomedical Engineering. Advisor: Angela Panoskaltsis-Mortari. 1 computer file (PDF); vii, 62 pages.Methods for tracheal repair and regeneration are necessary due to the limitations of tracheal resection and reconstruction for certain disorders such as tracheal stenosis, tracheomalacia, and tracheal tumors. Additionally, pulmonary injuries such as airway burns do not have effective treatment options aside from supportive care. The feasibility of a cell spraying device is investigated here as a system for applying human bronchial epithelial cells (HBECs) to decellularized porcine trachea matrices for creation of engineered grafts or as a minimally invasive method for delivering cells for wound healing. HBECs show viability greater than 90% after spraying onto cell culture media or tissue culture plastic. Similarly, one day after spraying onto decellularized trachea, viabilities are seen to be around 90%. Around day three, viabilities were slightly decreased to around 80%. After culturing for over one week, HBECs sprayed onto decellularized trachea displayed a basal cell marker (cytokeratin-5, CK5) and a club cell marker (uteroglobin). Markers for ciliated cells and goblet cells that are crucial for tracheal epithelium could not be found, but this needs to be investigated further. To validate the mechanical performance of the decellularized trachea, compressive resistance testing was performed before and after decellularization of tracheal rings. Results were generally inconclusive with high degrees of variability. A paired sample test conducted with 4 tracheas provided the most interesting results and showed that the decellularization process produced a significantly different compressive resistance compared to the native samples. In practice though this did not seem to be noticeable as the variability found within tracheal samples masked the difference. This would suggest that the decellularization process is not detrimental to the compressive resistance of trachea rings. Based on the results reported here, using a cell spraying device for engineering tracheal grafts and airway epithelial repair seems achievable

HVAC Systems with Low Global Warming Potential Refrigerants: A Case Study

The objective of this case study is three-fold: (1) identify promising alternative refrigerants with lower global warming potential (GWP); (2) among those, select refrigerant(s) that could be “drop-in” replacements for R-410A and would not require significant system redesign or compressor changes — with the exception of minimal changes such as lubricating fluid and expansion valves; (3) evaluate the impact of another easy-to-implement option: replacing lower-efficiency, permanently split capacitor (PSC) condenser fans and evaporator blower motors with electronically commutated motors (ECM) for additional system efficiency improvements. This study leverages the steady-state heat pump design model (HPDM) developed by the Department of Energy (DOE) and the Oak Ridge National Laboratory (ORNL) to demonstrate three key findings: (1) two popular refrigerant replacement candidates with a GWP less than 750, R-32 and R-454B; both have system performance equal to or better than R-410A; (2) the lower-GWP refrigerant options with a GWP below 300 all underperform compared to R-410A; however, heat exchanger optimization may improve system performance; (3) using an ECM instead of a PSC evaporator blower motor increased system seasonal energy efficiency ratio (SEER) performance ~8% for all refrigerants evaluated

Simulation Model of an Automatic Commercial Ice Machine

Automatic commercial ice making machines that produce a batch of cube ice at regular intervals are known as “cubersâ€. Such machines are commonly used in food service, food preservation, hotel, and health service industries.  Machines are typically rated for the weight of ice produced over a 24 hour period at ambient air temperatures of 90°F and water inlet temperature of 70°F. These cubers typically utilize an air-cooled, vapor-compression cycle to freeze circulating water flowing over an evaporator grid. Once a sufficient amount ice is formed, a valve switches to enable a harvest mode, where the compressor’s discharge gas is routed into the evaporator, thereby releasing ice into a storage bin. The U.S. Department of Energy has set a target of reducing energy usage by 10 – 15% by 2018.  Engineering models are not publicly available to assist designers in achieving the new energy regulations. This paper presents an engineering simulation model that addresses this need. This model simulates the transient operation of a cuber ice machine based on fundamental principles and generalized correlations. The model calculates time-varying changes in the system properties and aggregates performance results as a function of machine capacity and environmental conditons.  Rapid “what if†analyses can be readily completed, enabling engineers to quickly evaluate the impact of a variety of system design options, including the size of the air-cooled heat exchanger, finned surfaces, air / water flow rate, ambient air and inlet water temperature, compressor capacity and/or efficiency for freeze and harvest cycles, refrigerants, suction/liquid line heat exchanger and thermal expansion valve properties. Simulation results from the model were compared with the experimental data of a fully instrumented, standard 500 lb capacity ice machine, operating under various ambient air and water inlet temperatures. Key aggregate measures of the ice machine’s performance are: (1) cycle time (duration of freeze plus harvest cycles), (2) Energy input per 100 lb of ice, and (3) Energy usage during 24 hours. For these measures, the model’s accuarcy is within 5% for a variety of operating conditions.

Steady-State Modeling of Condensing Units with an Economizer Loop

This paper presents an engineering model that simulates the steady-state operation of air-cooled condensing units. Packaged, air-cooled, condensing units includes a compressor, condensing coil, tubing, and fans, fastened to a base or installed within an enclosure. To increase capacity, modern condensing units are being equipped with a brazed-plate heat exchanger for an economizer loop, configured in either upstream or downstream extraction schemes