Papers by Jiazhen Ling:

Title: Duty Cycle for Low Energy Operation of a Personal Conditioning Device
Authors: Rohit Dhumane, Jiazhen Ling, Vikrant Aute and Reinhard Radermacher
Abstract:The Roving Comforter (RoCo) is an innovative personal thermal management technology that provides ultimate personal thermal comfort for individuals in inadequately or even unconditioned environments. It is a miniature heat pump system mounted on a robotic platform capable of autonomously following individuals to deliver comfort by directing hot or cold air through automatically controlled nozzles. This allows buildings to relax their thermostats upto 4 degrees Fahrenheit without sacrificing occupant comfort, leading to energy savings anywhere between 10 to 30% depending on climatic conditions. RoCo, a portable device, operates fully on an onboard battery pack which therefore has to be carefully designed to balance power output, operating time and weight. To address this challenge, a multi-physics model that is capable of simultaneously simulating thermodynamics, electricity and mechanics of RoCo is developed and two duty cycles are analyzed. By observing and analyzing the simulation results, control strategies related to RoCo operation are proposed.
Links: Full paper

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Title: Modeling of a Thermosiphon to Recharge Phase Change Material Based Thermal Battery for a Portable Air Conditioning Device
Authors: Rohit Dhumane, Jiazhen Ling, Vikrant Aute and Reinhard Radermacher
Abstract:Closed loop two phase thermosiphons have a wide range of applications due to their simplicity, reliability, low cost and the ability of dissipating high heat fluxes from minimal temperature differences. The present study focuses on one thermosiphon operation which solidifies a phase change material (PCM) based thermal battery for a portable air conditioner called Roving Comforter (RoCo). RoCo uses vapor compression cycle (VCC) to deliver cooling and stores the heat released from the condenser into a compact phase change material (PCM) based thermal battery. Before its next cooling operation, the PCM needs to be re-solidified. This is achieved by the thermosiphon, which operates within the same refrigerant circuitry with the help of a pair of valves. The molten PCM which acts as heat source affects the dynamics of the thermosiphon which in turn affects the solidification process. Thus the dynamics of both the PCM and thermosiphon are coupled. For accurate transient modeling of this process, the PCM model considers the solidification over a temperature range, variable effects of conduction and natural convection during the phase change and variable amounts of heat release at different temperatures within the temperature range of phase change. The paper discusses component modeling for this transient operation of thermosiphon and its validation with experimental data.
Links: Full paper