This paper reported a review based study into the Indirect Evaporative Cooling (IEC) technology, which was undertaken from a variety of aspects including background, history, current status, concept, standardisation, system configuration, operational mode, research and industrialisation, market prospect and barriers, as well as the future focuses on RD good distribution of the water stream across the wet surface of the exchanger plate (tube) and adequate (matching up the evaporation) control of the water flow rate are critical to achieving the expected system performance. It was noticed that the IEC devices were always in combined operation with other cooling measures and the commonly available IEC related operational modes are (1) IEC/DEC system; (2) IEC/DEC/mechanical vapour compression system; (3) IEC/desiccant system; (4) IEC/chilled water system; and (5) IEC/heat pipe system. The future potential operational modes may also cover the IEC-inclusive fan coil units, air handle units, cooling towers, solar driven desiccant cycle, and Rankine cycle based power generation system etc. Future works on the IEC technology may focus on (1) heat exchanger structure and material; (2) water flowing, distribution and treatment; (3) incorporation of the IEC components into conventional air conditioning products to enable combined operation between the IEC and other cooling devices; (4) economic, environment and social impacts; (5) standardisation and legislation; (6) public awareness and other dissemination measures; and (7) manufacturing and commercialisation. All above addressed efforts may help increase the market ratio of the IEC to around 20% in the next 20 years, which will lead to significant saving of fossil fuel consumption and cut of carbon emission related to buildings.

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Indirect evaporative cooling : Past, present and future potentials

Comparative study of the performance of the M-cycle counter-flow and cross-flow heat exchangers for indirect evaporative cooling – Paving the path toward sustainable cooling of buildings

A desiccant-enhanced evaporative air conditioner: Numerical model and experiments

The Maisotsenko Cycle (M-Cycle) is a thermodynamic conception which captures energy from the air by utilizing the psychrometric renewable energy available from the latent heat of water evaporating into the air. The cycle is well-known in the air-conditioning (AC) field due to its potential of dew-point evaporative cooling. However, its applicability has been recently expanded in several energy recovery applications. Therefore, the present study provides the overview of M-Cycle and its application in various heating, ventilation, and air-conditioning (HVAC) systems; cooling systems; and gas turbine power cycles. Principle and features of the M-Cycle are discussed in comparison with conventional evaporative cooling, and consequently the thermodynamic limitation of the cycle is highlighted. It is reported that the standalone M-Cycle AC (MAC) system can achieve the AC load efficiently when the ambient air humidity is not so high regardless of ambient air temperature. Various modifications in MAC system design have been reviewed in order to investigate the M-Cycle applicability in humid regions. It is found that the hybrid, ejector, and desiccant based MAC systems enable a huge energy saving potential to achieve the sensible and latent load of AC in humid regions. Similarly, the overall system performance is significantly improved when the M-Cycle is utilized in cooling towers and evaporative condensers. Furthermore, the M-Cycle conception in gas turbine cycles has been realized recently in which the M-Cycle recuperator provides not only hot and humidified air for combustion but also recovers the heat from the turbine exhaust gases. The M-Cycle nature helps to provide the cooled air for turbine inlet air cooling and to control the pollution by reducing NOx formation during combustion. The study reviews three distinguished Maisotsenko gas turbine power cycles and their comparison with the conventional cycles, which shows the M-Cycle significance in power industry.

Overview of the Maisotsenko cycle – A way towards dew point evaporative cooling

An improved method and apparatus for indirect evaporative cooling of a fluid stream to substantially its dew temperature. Plate heat exchanger has perforations (11) and channels (3, 4 and 5) for gas or a low temperature for liquids on a dry side and wet side. Fluid streams (1) flow across the dry side (9), transferring heat to the plate. Gas stream (2) flows across the dry side and through perforations to channels (5) on wet side (10), which it then cools by evaporative cooling as well as conductive and radiative transfer of heat from plate. A wicking material provides wetting of wet side. In other embodiments, a desiccant wheel may be used to dehumidify the gas, air streams may be recirculated, feeder wicks (13) and a pump may be used to bring water form a water reservoir, and fans may be used either force or induce a draft.

Method and plate apparatus for dew point evaporative cooler

The within invention improves on the indirect evaporative cooling method and apparatus by making use of a working fluid that is pre-cooled with and without desiccants before it is passed through a Wet Channel where evaporative fluid is on the walls to take heat and store it in the working fluid as increased latent heat. The heat transfer across the membrane between the Dry Channel and the Wet Channel may have dry, solid desiccant or liquid desiccant and may have perforations, pores or capillary pathways. The evaporative fluid may be water, fuel, or any substance that has the capacity to take heat as latent heat. The Wet Channel or excess cooled fluid is in heat transfer contact with a Product Channel where Product Fluid is cooled without adding any humidity. An alternative embodiment for heat transfer between adjacent channels is with heat pipes.

Method and apparatus of indirect-evaporation cooling

The operating efficiency of indirect evaporative cooling processes and indirect evaporative cooling apparatus employing a dry side channel and a wet side channel (16) separated by a heat exchange plate (3) are improved by placement of holes (H1, H2, H3 ... HN) in the heat exchange plate (3). Further improvements are obtained when the flow direction in the wet side channel is cross- current to the flow direction (2A) in the dry side channel. Placement of desiccant materials in the dry side channel (15) also serve to improve the operating efficiencies of these processes and apparatus.

Method of evaporative cooling of a fluid and apparatus therefor

The present invention relates to methods for indirect evaporative air cooling with the use of plates, heat exchangers and feeder wicks on the indirect evaporative type. Several components for an indirect evaporative heat exchanger described as follows: A plate for an indirect evaporative heat exchanger where the plate is made of laminate material comprising one sheet of wicking material for wet zone(s) and the other of a water proof plastic material for the dry zone(s). An evaporative heat exchanger is created by assembling the plates forming spacing for wet channels, (they are created by the wet zone of the plates,) and dry channels, (they are created by the dry zone of the plates,) with channel guides or corrugated plates. The spacing between the plates is defined to reduce pressure drop for increased airflow. A feeder wick system creates the wetting of the wet channels without excess water. Sometimes the wet zone of the plate can be made of a membrane material where the opposite side of this membrane material is covered by a solid desiccant creating the wet zone of this desiccant plate. An indirect evaporative heat exchanger that is created by assembling both wick coated with plastic plates and desiccant plates, can realize not only the evaporative cooling but also the dehumidification of air.

Indirect evaporative cooling mechanism

A power system (90) includes a device (3, 43, 300) for extracting energy from a hot gas stream to power a driveshaft (4a). An evaporative duplex counterheat exchanger (5, 9, 24, 59, 60, 130, 202) is disposed in flow communication with the energy extracting device. The duplex exchanger includes a first heat exchanger (72) having a first main flow channel (80a), and a counterheat channel (82a, b) joined in flow communication therewith. A second heat exchanger (74) includes a second main flow channel (80b) adjacent the counterheat channel (82a, b). And, a evaporative fluid is injected into the counterheat channel to evaporatively cool the flow through both main flow channels.

Alan D. Gillan

Papers

Method and plate apparatus for dew point evaporative cooler

Method and apparatus of indirect-evaporation cooling

Method of evaporative cooling of a fluid and apparatus therefor

Indirect evaporative cooling mechanism

Power system and method