Research On Gravity-Powered Heating Terminal Device And Operating Characteristics

Reducing energy comsumption from building heating, utilizing industrial wasteheat or renewable energy, and therefore realizing the cascade utilization of energy areseveral major important research subjects in current building energy field. In China, alarge amount of low temperature hot water which is produced from low temperatureresources has a great potential to be reused for building heating. However, current studyon low temperature heating devices is relatively rare, and the products are limited inapplication. The newly developed gravity-powered heating terminal device consists of aseries of capillary tubes in which the running water for heating is as low as30℃, so itcould fully utilize the low-grade heat resoureces which are unusable by other heatingterminal devices. Meanwhile, there are so many subjects should be studied and solvedfor this device from theory to application. For instance, the size of capillary tube isbetween conventional and micro tubes, of which resistance characteristic is unclear. Inadditon, the mechanism of heat transfer is extremly complex especially when thestorage effect has to be considered when the phase change material is added. Lastly, theperformance parameters such as total heat transfer and flow resistance for the wholedevice set are unknown.This thesis studies several operating characteristics of the device firstly. Thecritical Reynolds number in the capillary tube indicating the transition from laminarflow to turbulent flow is obtained by experiment and the flow resistance characteristicof capillary single tube is comparable with typical normal tube. Further, a series ofexperiments on the resistance, heat dissipation, cooling characteristics and heat transferlaw for sample device were conducted. The resistance experiment shows that the devicehas higher resistance, so the width of capillary network should not be more than1m; thecooling characteristic experiment obtains the cooling data when the sample device coolsusing high temperature chilled water, which provides theoretical basis for furtheroptimization; the analysis of heat transfer law shows that the internal temperature fieldand air inlet and outlet have consistency in the width direction during the sample devicerunning, and this characteristic could help to simplify computation model.The characteristics of internal temperature distribution within the device and heatdissipating capacity are obtained through the method of numerical simulation in theparameter optimization research for device structure. Also, this thesis proposes theoptimal parameters such as device enclosure height, enclosure width, inlet size, outletsize, and distance between neighboring capillary tubes, and fits the relations aboutRayleigh number based on these parameters for heat dissipating capacity. Based on theoptimization of structure parameters, an optimal device is designed and applied in the projects to testify the optimization results. Test results show that the improved devicehas reasonable structure, effctive application, and could satisfy the room heatcomsumption. Based on the device operation characterics and heating effect, thestandard condition and ecnomical index are proposed.During the research on device heating and cooling characteristic and application, itindicates that this device is suitable to use by combing with heat pumps. And if storageequipment is added, the device could store heat at night when the power demand is lowand could release heat during daytime when the power demand is high. In this way, thisdevice could balance the power demands, hence reduce cost. This study uses capric acidand high density polyethylene as material, which has the characteristics such as lowerphase change temperature and immobilization during heat storaging, and it has gooduniformity and stability. To integrate the phase change material to gravity-poweredheating terminal device, aluminum alloy plates are used as the frame, and a proto typeof phase change board is fabricated and filled with the device.This thesis studies the heat storage characteristic of the device. The heat storagingand releasing mechanism and characteristics of the gravity-powered heating terminaldevice with phase change plate are extremly complex. Convective heat transfer,radiation, heat conduction and phase change heat transfer occur simultaneously. In orderto study and optimize the device heat storage characteristic, this work obtains theoperation characteristics when the device is storaging heat through mathematicalmodeling and procedure, and optimizes the thickness of phase change plate with theconstraint of heat storage time.In order to study region applicability of the heat storage effect, this thesis studiesthe operating characteristics in hot summer and cold winter regions as well as coldregions through mathematical modeling. Results show that this device is more suitablein hot summer and cold winter regions, and also this study obtains the operation schemeand economical analysis results for this kind of region.Gravity-powered heating terminal device could heat with hot water of lowtemperature and cool with cold water of high temperature, and is capble of storing heat.The development of this device offers a new choice for the application of lowtemperature terminal, and expands the space of the use of low temperature heat sourcefor heating. The works in this thesis provide both theoretical and practical basis for thefurther research and application of new low temperature heating terminal device, andpromote the engineering application of this device.