Experimental Study Of Cooling Humidification System Based On Utilization Of Natural Cool Resource

The northern part of China was characterized by its harsh and long winter, hot and short-lived summer. If the climatic feature could be made full use of, namely storing ice during winter and using them to freeze seafood,agricultural products in order to preser ve food during summer. If so, energy can be conser ved considerably. Currently, refrigerating storeroom is driven by electric ity, the use of refrigerant caused environmental pollution and a great amount of energy had been wasted. Confronted with the deepening energy crisis as well as environmental pollution, taking advantage of freezing natural resour ces, which proved to be clean green energy, to keep vegetables and fruits fresh would not only conser ve resources but protect the environment as well. It was essential to resolve the shortage of energy and pollution issues by properly replacing conventiona l consumption energy with clean renewable energy.The paper made a analysis of domestic and overseas cutting-edge technology applied by Natural Cool Resource, combined with northern climatic characteristics as well as experimental conditions, then designed a set of cooling, humidifying devices by introducing Natural Cool Resource: storing ice during winter and releasing cooling capacity before the ice was transferred into water. The mechanism of the new de vice replaced the conventional refrigerant by exchan ging heat indirectly and cooling in internal circulation that substantially improved the air quality, reduced pre-cool time and separated ice storage room from fresh storage room. Moreover, an auto-control system of air-conditioned environment for the de vice had been de veloped by Labview, achie ving the goal of auto controlling the temperature, humidity and cooling down simultaneously for multiple spots.The primary contents and conclusion were listed as follows:(1)Performing an overall design for auto-controlling system of fresh storage room. Based on virtual instrument technology, measurement and control system could be established, environmental parameters could be collected, stored, displayed by applying PCI-6225 DAQ Card, remote analog output module RM441, temperature and humidity sensor, CO2 concentration sensor, leakage protector as well as computer and so forth. The measurement and controlling of the temperature, humidity, CO2 concentration as well as other physical parameters was able to be achie ved. The data pre viously collected could be stored, retrieved, inquired, deleted by making use of powerful functions of database management on the basis of communication between LabVIEW and Microsoft Access.(2)Design was based on the system of ice-water mixed indirect heat transfer with natural cool resource. Then calculations were performed on the parameters with regard to the core part of the system: Fin-and-tube heat exchanger. According to the cooling capacity required by fresh storage room, The size of the face area of four fin-and-tubes heat exchanger is supposed to be 0.16m2, entire heating transfer area is 8.6 m2, the length of heat exchange tube is 25.5m. Analysis regarding the influence on cooling capacity and pressure drop imposed by head wind velo city, ice water flow, pipe length was conducted, based on CCD approach in Design-expert 8.0. Then regression model would be established, leading to the best set of parameters with the optimum cooling capacity and lowest pressure drop: Head wind ve locity 2.86m/s, ice water rate of flow 0.85m3/h. the length of heating transfer pipe 24.36 m. E ventually, the optimum value of cooling capacity was 4.92 Kw, the pressure drop was 56.98 Pa.(3)ANSYS FLUENT would be used to perform a numerical simulation and validation on the air side heat transfer and flow characteristics of Fin-and-tube heat exchanger. Then distribution pattern of temperature field, velocity field, pressure field, average field synergy angles could be gained. After that, Analysis would be made on Head wind velocity, air inlet direction, air inlet temperature’s impact on flow and heat transfer. The results manifested the heat wind velocity had a considerable influence on heat transfer. When the head wind velocity defined as six different va lues ranging from 1.5m/s to 4m/s, heat transfer coefficient would be increased by 133%, pressure drop would be increased by 428%. Air inlet direction had a major impact on the air flow distribution at the flank of the Fin, overlarge or exceedingly small air inlet direc tion would result in vortex as well as une ven air flow distribution, and further affect heat transfer performance. When the air inlet direction changed from 0 to 30, the heat transfer coefficient would be increased accordingly. In other words, when the hea d wind velocity declined gradually along the flow of ice water, it would be benefic ial to heat transfer. Then another analysis was performed on the heat transfer performance of Flat Fin-and-tube heat exchanger on the basis of field synergy. When the head wind velocity was within the range from 1.5m/s to 3.5 m/s, average field synergy angles would be increased as it became higher, as a result, the a verage field synergy angles were increased by 12%. The difference in variation of the synergy degree between ve locity field and temperature field was adverse to the heat transfer. When the wind velocity reached 3.5m/s, synergy angles would almost hold steady. Therefore, the optimum head wind velocity should be within the range from 2.5m/s to 3m/s.(4)Natural cool resource was introduced based on the comprehensive analysis on conventional humidicool system, the water spraying air-cooler humidicool system had been designed afterwards. There were “three circulations” existing in the system, which included water spray circulation, ice water circulation, humid air circulation. The amount of water spray, head wind velocity as well as wet bulb temperature’s influence on refrigeration performance of the humidicool system was also analyzed and tested.The results re vealed that head wind ve locity along with spray water amount were two primary factors affecting humidicool system, the heat transfer coeffic ient would rise with the increase of head wind velocity and spray water. When reaching the optimum value, it would hold steady. When spray water increased from 0.08 m3/h to 0.2 m3/h, the average rate of change for cooling capacity would rise by 60.7%, then the minimum spray water amount should be 0.14 m3/h, head wind ve locity was ranging from 1.5m/s to 4m/s, the heat transfer coeffic ient increased by 46%, the air mass transfer coefficient increased by 43%, the energy effic iency ratio increased by 5%. When the head wind velocity was 3m/s, spray water amount was 0.14 m3/h, the heat transfer coeffic ient would reached its maximum va lue 114.78w/(m2·k), the temperature of spray water exerted almost no influence on the drop of the air temperature. Furthermore, Cooling capacity and EER would decrease as the web-bulb temperature increased, when the air web-bulb temperature increased from 12℃ to 24℃, cooling capacity and EER would decrease by 5% and 5.3% respective ly. High web-bulb temperature was adverse to heat transfer. Consequently, the humidicool system was a great fit for the dry northern areas. The total heat transfer coefficient in dry working condition would decline by 75% in comparison to the one in spray working condition. With short pre-cool time, the humidicool system managed to create a low-temperature(3.8℃), high-humidity(92%RH-100%RH) and relative ly stable fresh environment.(5)The minimum temperature in ice water fresh storage room was around 4 ℃,howe ver the fresh-keeping temperature of most vegetables and fruits were between 0 ℃ to 4℃. The temperature of the fresh storage room could be reduced and the temperature range of stori ng ve getables and fruits could be expanded by using salt water freeze. Analysis could be performed on head wind velocity, concentration of salt solution, tube row number ’s influence on the temperature in fresh storage room by applying BBD method in Design-expert8.0. By analyzing these three parameters, it could be concluded that regarding the lowest temperature as the optimum target, the optimum parameters would be 3.5m/s of head wind velocity, 10% of salt water concentration, 5-tubes heat exchanger, then the lowest temperature was-1.12℃.(6)An example was provided here, suppose there was a storage of 2 t tomatoes in fresh storage room, the annual cooling energy and ice consumption could be calculated. Calculations regarding cost-effectiveness were performed on the basis of these three systems including humidicool system, traditional humidicool system as well as the house in mechanical refrigeration. The initial construction costs of these three systems were 61.1k ￥, 80.6k￥, 8.6k￥ respective ly, the annual electricity costs were 1.9k￥, 3.8k￥, 7.7k￥. The newly designed humidicool system was able to reduce CO2 emission by 0.4t. Consequently, there was e very e vidence that bringing natural cool resource into vegetables and fruits fresh storage room would substantially reduce initial construction cost as well as operation cost, which also reduced the CO2 emission dramatically, made a marked improvement in environmental and economic effectiveness. Therefore, the humidicool system possessed broad space for deve lopment.