Experimental Study On Heat Pipe Type Two-stage Evaporative Cooling Air-conditioning System

In this dissertation, heat pipe type evaporative cooling technology was reviewed. The main system forms were summarized and individual characteristic was analyzed. Based on some experiments done by the former graduate, converters, digital thermo/humidity sensors, indoor cooling equipments and heat insulation measurements were added. Heat pipe type two-stage evaporative cooling air-conditioning system was put forward.The important component was heat pipe heat exchanger. A flat wick Al-NH3 heat pipe heat exchanger was designed and its evaporation section and condensation section didn't need to be switched whether in summer or in winter. The heat exchanger was composed of 96 heat pipes, which were arranged with staggered layout and the outline dimension was 1400×800×950mm (length×width×height).Heat pipe heat exchanger could be used for energy recovery between fresh and exhaust air. In order to enhance elimination of heat of condensation section, evaporative cooling technologies were adopted at exhaust air side. There were four elimination modes, mode 1 is: exhaust air→condensation section→outdoor; mode 2 is: exhaust air→air washer→condensation section→outdoor; mode 3 is: exhaust air→pad direct evaporative cooler→condensation section→outdoor; mode 4 is: exhaust air→spraying water directly at the top of condensation section→outdoor. Fresh air flowed across evaporation section, then it was further cooled down by a pad direct evaporative cooler, which is aim to increase temperature difference of fresh air.According to a series of experiments in summer, some conclusions were drawn as followings:(1) The best effect of processing fresh air was mode 4;(2) The optimum flow ratio of exhaust and fresh air was 0.9;(3) When the inlet dry-bulb temperature of fresh air was 32.9℃, fresh air dry-bulb temperature difference between inlet and outlet of mode 4 was 9.5℃and the heat exchange efficiency was 67.6%. It increased 2.4℃, 16.2% respectively compared to mode 1;(4) When the inlet wet-bulb temperature of fresh air was 22.3℃, the outlet dry-bulb temperature of fresh air of mode 4 was 20.8℃. It decreased 2.8℃compared to mode 1. The heat exchange efficiency of mode 4 was maximal, above 68.0%;(5) When the inlet dry-bulb temperature of exhaust air was 22.0℃, fresh air temperature difference between inlet and outlet of mode 4 was 9.3℃and the heat exchange efficiency was 65.7%; (6) When the inlet wet-bulb temperature of exhaust air was 19.2℃, the heat exchange efficiency of mode 4 was maximal, reached 65.0% which is 23.3% higher than mode 1.The experimental results of heat recovery in winter showed:(1) The optimum flow ratio of exhaust and fresh air was 1.0;(2) When the inlet dry-bulb temperature of fresh air was 1.5℃, the outlet dry-bulb temperature of fresh air was 14.3℃and the heat exchange efficiency was 74.3%;(3) When the inlet dry-bulb temperature of exhaust air was 22.6℃, the outlet dry-bulb temperature of fresh air was 18.6℃and the heat exchange efficiency was 76.8%.The observations in this work will provide a reference to comprehend heat pipe type two-stage evaporative cooling air-conditioning system and offer a theoretical gist for mastering system performance. It is also useful to develop heat pipe type evaporative cooling air-conditioning unit, which could save energy consumption of fresh air, improve indoor air quality (IAQ) and reduce destruction of ozonosphere.