Open Source High-Temperature RepRap for 3-D Printing Heat-Sterilizable PPE and Other Applications

Thermal sterilization is generally avoided for 3-D printed components because of the relatively low deformation temperatures for common thermoplastics used for material extrusion-based additive manufacturing. 3-D printing materials required for high-temperature heat sterilizable components for COVID-19 and other applications demands 3-D printers with heated beds, hot ends that can reach higher temperatures than polytetrafluoroethylene (PTFE) hot ends and heated chambers to avoid part warping and delamination. There are several high temperature printers on the market, but their high costs make them inaccessible for full home-based distributed manufacturing required during pandemic lockdowns. To allow for all these requirements to be met for under $1,000, the Cerberus – an open source three-headed self-replicating rapid prototyper (RepRap) was designed and tested with the following capabilities: i) 200oC-capable heated bed, ii) 500oC-capabel hot end, iii) isolated heated chamber with 1kW space heater core and iv) mains voltage chamber and bed heating for rapid start. The Cereberus successfully prints polyetherketoneketone (PEKK) and polyetherimide (PEI, ULTEM) with tensile strengths of 77.5 and 80.5 MPa, respectively. As a case study, open source face masks were 3-D printed in PEKK and shown not to warp upon widely home-accessible oven-based sterilization.

Generalized Heat Flow Model of a Forced Air Electric Thermal Storage Heater Core

Electric thermal storage (ETS) devices can be used for grid demand load-leveling and off-peak domestic space heating (DSH). A high-resolution three-dimensional finite element model of a forced air ETS heater core is developed and employed to create a general charge/discharge model. The effects of thermal gradients, air flow characteristics, material properties, and core geometry are simulated. A simplified general stove discharge model with a single time constant is presented based on the results of the numerical simulations. This simplified model may be used to stimulate economic/performance case studies for cold climate communities interested in distributed thermal energy storage.

The Design and Realization of Micro Induction Heater for the Thermal Bubble Generation

This paper presents a micro induction heater based on the principle of induction heating. The liquid contact with the micro heater core directly and heated by the eddy current effect. The heating effect of the micro heater is simulated with the software of COMSOL. The simulation results indicate that the temperature of the micro heater core can reach to 540K in 0.9s while the current is 0.7A and the power frequency is 200 kHz. The relations between the heating effect and the micro induction heaters parameters such as the current, the AC power frequency and the coils parameters are studied in the simulation respectively. The prototype of the micro heater has been fabricated and the experimental test has carried with the micro heater. The experiments indicated that the micro heater can generate thermal bubble in 0.3s while the 1.0A high frequency current passes through the heater coil. The micro induction heater can be applied to a variety of thermal bubble devices, such as micro injector, micro switch and micro pump.

Evaluation of Heat Transfer and Pressure Drop for the Heater-Core in an Automotive Heat Pump System

The heat transfer and pressure drop results for a heater-core of an automotive system are presented and discussed in this article. The heater-core is a type of compact heat exchanger that is used as part of an automobile heating-cooling system for heating the passenger cabin on cold seasons. The automotive heating-cooling system in this study includes a standard refrigeration cycle consists of a condenser, an evaporator, a compressor and an expansion valve using the refrigerant R134a as the working fluid. Furthermore, the system uses two separate secondary fluid loops using a 50% glycol-water mixture to exchange energy with the main refrigeration loop. During the cold weather season, the system is operated in the heat pump mode and one of the fluid loops is used to transfer heat from the condenser to the heater-core for heating the passenger cabin. The heat transfer from the heater-core to the passenger cabin is accomplished using air flow through the heater-core openings in an unmixed and cross-flow fashion. The air-side of the heater-core has a unique louver system that is intended to enhance the air-side heat transfer while the glycol-side has a twisted wire inserts to enhance flow turbulence and heat transfer. Semi-empirical correlations for the heat transfer and pressure drop for both glycol-water mixture and air flows in the heater-core are proposed. The flow of the glycol-water mixture in the heater-core is a single-phase flow within a bundle of parallel circular tubes with the twisted wire inserts. The flow of air through the heater-core is approximated as a flow across a finned-tube compact heat exchanger with continuous plate-fins. A modified Wilson plot technique is applied to determine correlations for heat transfer on both glycol-water mixture and air sides. The frictional pressure drop on the glycol-side is calculated from the total measured pressure drop and adjusted for pressure drops within manifolds and inlet/outlet ports. The results for the heat transfer and pressure drop analyses are finally plotted, discussed and compared with the relevant previous studies. These results show that the heat transfer rate is increased in the glycol-side due to the twisted wire inserts, in comparison with the smooth circular tubes. The air-side heat transfer rate is also enhanced due to the louvers in the air passages, as compared to flat-plate fins in compact heat exchangers.