Investigation on dynamic behaviour of condensation heat transfer in indirective evaporative cooler

Indirect evaporative cooling is a rapidly developing air-handling technology and has great application potentials for energy recovery in hot and humid regions. The condensation in dry channels of an indirect evaporative cooler (IEC) occurs when the dew point temperature of outdoor air is high. However, the dynamic heat transfer performance of an IEC during the process of condensation evolution was rarely discussed. This paper aims to experimentally investigate the dynamic behaviour of primary air condensation and its effects on the convective and total heat transfer rate of an IEC. A transparent cover plate is placed outside an aluminium heat exchanger plate to visualize the evolution process of droplets retained on the surface. The droplets' falling frequency was recorded and the accumulated condensate mass was correlated based on an analytical method taking into account the contact angle and droplet volume. Results showed that the dynamic dehumidification performance can pose great influences on the convective heat transfer in IEC. The gradually diminished dropwise regions and increase of filmwise regions deteriorate the wet-bulb effectiveness of IEC by 14.8%. The convective heat flux keeps decreasing with the accumulation of condensate retention until a dynamic equilibrium is achieved between the retained and falling droplets.

Development of User-Friendly Software to Design Dairy Heat Exchanger and Performance Evaluation

The paper proposes a calculation algorithm and development of a software in Visual Basic(Visual Studio 2012 Express Desktop) used in heat transfer studies when different heat exchangers are involved (e.g. Helical Type Triple Tube Heat Exchanger , Plate Type Heat Exchanger).It includes the easy calculation of heat transfer co-efficient and followed by the design and simulation of heat exchanger design parameter by inputting general known parameters of a heat exchanger into the developed software-DAIRY-HE. A parametric study is conducted using the software interface to determine the length of tubes or dimensions of heat exchanger.

Decreasing the Fouling of Heat Exchanger Plates Using Air Bubbles

The heat transfer performance of heat exchanger plate decreases as time goes by. The main reason for this phenomenon is the fouling of the heat exchanger plates. To remove the fouling, we have usually cleaned the plate of heat exchanger using chemicals or polishing brush or cloth with hand after stopping the equipment and disassembling the heat exchanger. However, to clean the plate using these methods, the heat exchanger equipment needs to be stopped and disjointed. In addition, it must be re-jointed after cleaning. Especially, the concern of environmental pollution happens in case of using chemicals. Therefore, we need to develop an automatic fouling removal equipment which can continuously keep high heat transfer efficiency and solve the problem of environmental pollution. So, in this paper, we developed and tested the equipment which can clean the fouling on heat exchanger plates automatically per constant period and interval using air bubbles. The total heat transfer coefficient decreased with a slower tendency when using air bubbles compared to the existing methods. There was 10% higher heat transfer effect air bubbles every 10 minutes for 2 hours to remove the fouling ingredients on the heat transfer surface area concerned to the case without air bubbles after 192 hours.