STUDY OF HEAT TRANSFER CHARACTERISTICS OF COMPACT HEAT EXCHANGER DURING START UP

 Compact heat exchangers have been widely used in various applications in thermal fluid systems including automotive thermal management systems. Radiators for engine cooling systems, evaporators and condensers for HVAC systems, oil coolers, and intercooler which are typical examples of the compact heat exchangers that can be found in ground vehicles. Compact heat exchangers are used in low heat transfer rates of gasliquid systems because of the high surface area per unit volume of this device.Itis used to transfer heat in system characterized by low heat transfer coefficient.In this work, a compact heat exchanger of 20x19x5cm has been used with hot water of 60˚C flowing inside the heat exchanger and air at room temperature flowing across it. A fan is located with a small tunnel adjacent to the heat exchanger. The velocity of fan can be controlled by a Voltage switch. Changing velocity of air by controlling the velocity of the fan which increase flow rate of air flowing. Three different velocities have been studied in this work with constant water velocity. Thermometers are used to register  temperature variation with time for outlet streams.It is found that the main factor which affects the heat transfer is the heat transfer
coefficient of air side which can be increased by increasing the flow rate of air while water flow rate has minor effect on the heat transfer operation. The effectiveness also behaves in the same way and it could be increased as well by increasing the air flow rate. Studying the dynamic response of the system revealed that the time constant for such system could be decreased by increasing flow rate of air, which means faster dynamic temperature response. The dead time drops steeply as the flow rate of air increases.