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During the drying phase of a dishwasher, water evaporation and condensation phenomena take place. Some wet surfaces inside the dishwasher are above the local air dewpoint and will experience evaporation, while other surfaces are below the local air dewpoint and will experience condensation. In this study, the evaporation mass transfer resistance of a standard load used in a household dishwasher was experimentally measured. The standardized load measurements were taken in situ during a regular drying phase after the ordinary washing was complete. To determine the mass transfer resistance of condensation, a tub wall sample was cut from the interior of a commercially available dishwasher. The wall samples were tested ex-situ in a benchtop psychrometric chamber to determine the condensation heat and mass transfer coefficient. The wall samples were locally cooled using a thermoelectric module. The experimental results were compared to those from a heat and mass transfer resistance correlation. The measured evaporation and condensation mass transfer coefficients can be used to model the drying process in a humid and stagnated environment.

By employing the high temperature heat source to directly generate the electricity needed to power auxiliary systems in a natural gas furnace, boiler or hot water heater, a “self-powered” heating system can provide several benefits. Compared with a traditional furnace, boiler or hot water heater, when overall fuel utilization is kept constant, the self-powered system will have a higher primary energy efficiency, lower operating costs, and dramatically improved building safety and resilience during electric grid outages. Furthermore, a self-powered heating system only has a single utility connection – natural gas, without an electric connection – thus simplifying installation. A thermoelectric generator can be used for direct energy conversion of thermal energy to electricity with no moving parts, which offers a very simple means to provide power for the self-powered heating system, and the operation is without noise or vibration and can thus provide a very long system life. This paper provides an analysis focused on materials selection and the thermal power requirements for a thermoelectric generator (TEG) for use in a self-powered heating system. The dimensionless figure of merit for thermoelectric materials, zT, is used to estimate the optimal efficiency that can be achieved with a TEG to produce the electric power required in such an application. Comparisons of the predicted efficiency, the required heat transfer rate to the TEG and the heat transfer area needed for sustained operation under thermal conditions relevant to the self-powered heating application are made for several potential thermoelectric materials. This analysis was used to develop system requirements for a self-powered hot water heater using a TEG for electric power generation.