Critical Radius of Insulation

The critical radius of insulation is a counterintuitive concept within the study of heat transfer. The theory states that adding insulation to a cylindrical or spherical object will increase the rate of heat loss rather than decrease it, if the radius (thickness) of the insulation is at its “critical” value. The Critical Radius of Insulation Senior Project is designed to demonstrate this phenomenon to Heat Transfer students via a portable apparatus. The concept will be demonstrated with a cylindrical object which is heated by way of a separate voltage source. Thermocouples will display the temperature of the cylinder while insulation is added along with ambient air temperature, showing a distinct decrease in temperature caused by the addition of insulation. The design team conducted preliminary experiments using 1Ω, 2Ω, and 10Ω power resistors in an attempt to demonstrate the critical radius theory and evaluate the viability of using power resistors as the heated cylinder. The experiments were unsuccessful in demonstrating the critical radius theory but showed that the prototype setup was a viable design that could demonstrate this theory if the insulation material, insulation thickness, and power resistor diameter were properly modified. Based on the preliminary testing and analysis, a conceptual prototype model was developed. After further testing, the team determined that power resistors would take too long to reach steady state temperatures for a short classroom demonstration and that the diameters of the resistors were too large to demonstrate this theory with the appropriate experimental margin. Other studies were conducted using different heated cylinders starting with Calrod® heating elements. Testing was conducted with these heaters and 3D printed PLA insulation with great success. The heat loss for this setup was greater with the insulation than without, so the team used this heater and insulation combination to create a functioning structural prototype. Once the structural prototype was constructed and thoroughly tested, the team was able to successfully create a portable demonstration apparatus that physically shows the critical radius of insulation theory at work. This document details the iterative design process used to achieve the final design, the final design description, the manufacturing process used to build the final design, the verification and testing process, and conclusions about the overall project and the teams experience. The team’s overall objectives for this project are to first understand the concept of the critical radius of insulation and the experimental variables and assumptions that are important to proving it. The next step is to design and build an apparatus that can be used as a classroom demonstration and test this apparatus to ensure it is safe, easy to use, and clearly demonstrates critical radius theory. A supplemental handout also needs to be created to simply describe the theory to Heat Transfer students that will be witnessing this demonstration

Segmental mandibular reconstruction in patients with poor lower extremity perfusion, vessel-depleted necks and/or profound medical frailty

PURPOSE OF REVIEW: Options for segmental mandibular reconstruction in patients poorly suited to undergo fibula free flap (FFF). RECENT FINDINGS: Although FFF is the current \u27gold standard\u27 for segmental mandibular reconstruction, other reconstructive options must be considered when FFF is contraindicated or disfavoured and/or patient frailty precludes a lengthy anaesthetic. In addition to various nonvascularized and soft tissue only reconstructions, excellent osseous free flap alternatives for functional segmental mandibular reconstruction may be employed. The subscapular system free flaps (SSSFF) may be ideal in frail and/or elderly patients, as SSSFF allows for early mobility and does not alter gait. In extensive and/or symphyseal defects, functional mandibular reconstruction in lieu of a free flap is extremely limited. Pedicled segmental mandibular reconstructions remain reasonable options, but limited contemporary literature highlights unpredictable bone graft perfusion and poor long-term functional outcomes. SUMMARY: There are several excellent free flap alternatives to FFF in segmental mandibular reconstruction, assuming adequate cervical recipient vessels are present. On the basis of the current literature, the optimal mandibular reconstruction for the medically frail, elderly and/or patients with extreme vessel-depleted necks is limited and debatable. In qualifying (i.e. limited, lateral) defects, soft tissue only reconstructions should be strongly considered when osseous free flaps are unavailable