CFD-SIMULATION OF A HEAT-PIPE-HEAT-EXCHANGER EFFECT ON A TUBULAR AIR-COOLED CONDENSER

摘要

Continuous increase in electricity tariff and its power consumption has brought an alteration towards the development of cooling technologies. Cooling technology with normal vapor compression cycle rely on electricity to increase and decrease the pressure, hence the temperature, within its cycle. Alternative technology such as passive cooling, using heat pipe heat exchangers is being applied to the refrigeration cycle components to assist in temperature reduction of the cooling process. The supply and return air temperatures of an evaporator and condenser are being precooled by passive cooling equipment to assist in reducing the compressor work done. The objective of this study is to investigate and simulate a force-ventilation of an air around a circular air-cooled-condenser tube for an air conditioning system. The incoming air supplied to the condenser is assisted by air that had been precooled by a heat pipe heat exchanger attached 100mm from the condenser. This study investigates the effect of the heat pipe heat exchanger in removing the energy and its temperature, in assisting the condenser heat removal process. In a normal refrigeration cycle, the heat of a condenser at a constant pressure at 109200Pa and a temperature of 319K are reduced by the force convection ventilation to 315K. The temperature of the refrigerant in the tube is being reduced at constant pressure of 5K by a heat transfer exchange of ambient air and the condenser tube. This simulation showed the effect of a heat pipe heat exchanger attached before the condenser by using the computational fluid dynamic software. A condenser from a refrigeration cycle with refrigerant R134a is being simulated using CFD software. The condenser tube is a row of 5 copper tubes (9.5mm OD) in a vertical straight line exposed to an ambient air of 300K. A hot vapor refrigerant temperature leaving a compressor enters a condenser inlet at 319K and exit the outlet tube at a liquid temperature of 315K. The inlet and outlet pressures of the condenser tube are assumed constant throughout the process at 109200Pa. Using a computational fluid dynamic simulation, a normal condenser inlet and outlet air is being studied. The simulation results are then compared to a simulation of a condenser tube which had been attached to a heat pipe heat exchanger at the air inlet section. A 100mm air gap between the heat pipe heat exchanger and the condenser where the simulation of heat transfers is assumed to be the key process is discussed. The end result of the air outlet of the condenser and the effect of the heat pipe heat exchanger attached to it is discussed. ANSYS Fluent and CFD ACE+ software are being used to run the simulation and the results are presented in terms of the temperature contour, velocity vectors and flow patterns. It is found that the outlet temperature of the condenser reduced when a heat pipe heat exchanger is attached before the condenser. It is an advantage to use a heat pipe heat exchanger to increase the temperature difference between a refrigerant fluid at the inlet and outlet of the condenser. By increasing the heat transfer rate of the heat pipe and the condenser tube, hence lowering the condenser temperature output, the system capacity will increase.