دانلود رایگان مقاله انگلیسی شبیه سازی یک سیستم خنک کننده هوای غالب منفعل - IEEE 2018

Abstract

Climate control is an everyday challenge. With the rapid surge in electricity prices over the past few years, air conditioning operating expenses necessarily increased. The effects, furthermore, of global warming result in increased cooling, and therefore, energy demand. The purpose of this paper is to propose two models that simulate a natural air cooling system. The first model simulates cooling through an earth to air heat exchanger, utilising the soil as a heat sink. The second model simulates the transient cooling of a control volume, which receives cooled air and is open to the environment. A scale model of an earth-to-air heat exchanger system was designed, constructed and used to verify results from the proposed models. Following verification, a real-life size heat exchanger was simulated in order to cool down a room of 60 m3 within one hour, using only the underground soil as a heat sink. Results showed that a room at an initial 30 °C can be cooled down to 20.5 °C with a 1.2 m underground heat exchanger and down to 17.8 °C if the length is increased to 2.0 m. Only fan power is needed to increase the air’s dynamic pressure, resulting in flow conditions. As a result a coefficient of performance between 60 and 80 can be achieved.

4.3 Experimental testing and validation of transient cooling model

Experiments were performed on the cooling of the control volume. The control volume was heated up while steady state conditions were reached by the heat exchanger. During this time a natural flow of air developed within the control volume. At a temperature of 30.3 °C the heat source was removed, so that only cooled air could enter the wellinsulated control volume. Temperature readings within the control volume were logged every second.

Figure 3 shows the transient simulated air temperatures of the control volume, together with the experimentally obtained values. The heat exchanger simulation indicates that cooled air at 21.14 °C enters the control volume. Results from the transient simulation indicates that just after 150 s (163 s), the air mixture inside the control volume should be at 22.00 °C, provided a continuous uniform mixture of molecules.

From Fig. 3 it is evident that the theoretical results initially under predict the control volume’s temperature and that a larger change in temperature is observed. It should be noted that the colder air, with a higher density, enters the control volume at the bottom, whereas air is discarded into the surrounding environment at the top. The warmer, lower density, air is therefore initially forced out of the control volume through the natural convection, without uniformly mixing with the incoming stream. As a result, the transient model initially under-predicts the heat rejection.