No abstract

Ejector driven systems have the ability to operate at high efficiencies, utilizing recycled thermal energy as a power source. For a typical ejector heat pump system, the increase of the condenser temperature reduces the coefficient of performance (COP). In addition, if the condenser temperature is higher than the critical temperature, the ejector may not function. In this situation, the condenser temperature must be reduced, and an additional heater will be utilized to heat the production water from the condenser temperature to the desired temperature. In this investigation, a single-stage gas-fired ejector heat pump (EHP) is investigated and thermodynamically modeled in order to optimize the system COP for the purpose of heating water by utilizing the thermal energy from the ambient air. The effects of the high-temperature evaporator (HTE) and low-temperature evaporator (LTE) temperatures on the ejector critical back pressure and the EHP system performance are examined for a HTE temperature range of 120-180 °C and LTE temperatures of 15.5, 17.5, and 19.5 °C. Results show that an optimized COP of the EHP system exists which depends on HTE and LTE temperatures, primary nozzle throat diameters. In addition, it is found that the EHP COP is independent of the ejector COP. From this investigation a maximum EHP COP of 1.31 is able to be achieved for a HTE temperature of 160 °C and a LTE temperature of 19.5 °C with a total heating capacity of 15.98 kW.

An oscillating heat pipe (OHP) charged with a hybrid fluid is investigated. This hybrid fluid uses an emulsion-based mixture of liquid metal gallium microdroplets suspended in an ethanol solution. The gallium microdroplets are fabricated using an ultrasonication technique. The OHP is fabricated from a copper plate and contains a six-turn channel with a 3 × 3 mm2 cross-section. The heat transfer performance of the OHP was investigated experimentally with different concentrations of gallium at a 50% filling ratio. Steady-state oscillating motion was achieved with weight concentrations of gallium up to 20%. The experimental results show that using gallium-in-ethanol hybrid fluid emulsion as the working fluid can increase the heat transfer performance of the OHP by up to 7.8% over pure ethanol at 300 W. The mass of gallium needed to achieve this magnitude of heat transfer improvement is drastically reduced compared to previous research.