DE102008035941A1 - Method for heat/material transport between fluids for recooling of sorption refrigerating machine, involves transferring heat from air to damped cooled water on large surface of filling body before pre-cooled air enters into heat carrier - Google Patents

Abstract

The method involves utilizing adiabatic air moistening for indirect cooling of a fluid e.g. cooling water, in a closed circuit. A lamella heat carrier is arranged in an air flow. A heat transfer from the fluid to be cooled to air takes place. A filling body (9) is arranged before the heat carrier in an air flow direction in a suitable form, where water e.g. sea water, for adiabatic air moistening is distributed over the filling body. Heat is transferred from the air to damped cooled water on a large surface of the filling body before the pre-cooled air enters into the heat carrier.

Description

The The invention relates to a method for cooling fluids in closed hydraulic systems with ambient air, optionally taking advantage of Evaporative cooling, according to the preamble of claim 1.

chillers as a special form of heat pumps need a recooling, d. H. a method for removal the heat, the one to be cooled Room is deprived, to the environment. Heat can only be from "warm to flow cold, the Heat in Room flows therefore in a heat sink, whose temperature is below room temperature. This amount of heat then gets up from a heat pump a temperature level over lifted from the environment and can thus have a suitable heat exchanger drain into the environment. Additionally falls at the thermal drive of adsorption and absorption refrigeration systems, a relatively large amount to process heat which also over the recooler be discharged got to.

Development of a recooling process, in particular for example for solar / thermal cooling systems of low power:
The aim of the recooling is to deliver the dissipated heat with minimal energy consumption at the lowest possible temperature level to the environment. This temperature level must be above the ambient temperature, the temperature difference to be maintained is defined by the size of the heat transfer surface and the amount of media flowing past. Especially in sorption refrigerators, great attention is paid to the lowest possible recooling temperatures.

Should these can even be lowered below the ambient temperature you get the so-called wet recooling. in this connection becomes the cooling water brought into direct contact with the air flow, being part of the Water evaporates and the heat of evaporation required for this Fluids is removed. The achievable cooling is limited by the so-called wet bulb temperature. For example, at the design state used in Germany (32 ° C, 40% rh, 12 g / kg) is the same at about 21.5 ° C.

purpose The development is in both the dry and the wet recooling in a device Unite the disadvantages of both technologies in this combination as described below most To get picked up. A machine should for example for use with sorption chillers be optimized, so especially minimal electrical power consumption cause and as possible low cooling water temperatures enable. Especially for solar cooling used in the small power range, the cooling tower should also visually be suitable for example in the garden of a detached house.

Usual and available in the market are the following techniques:

1. dry cooler

dry Chillers exist mostly from laminated heat exchanger packages is blown or sucked through the air with fans and the of cooling water flows through become. Compared to use with ordinary chillers, these must in sorption chillers significantly larger. To have enough air for heat exchange to disposal are also larger fans whose power consumption is the energy efficiency of the overall system impaired.

A clever hydraulic connection of the cooling water pipes inside the cooler is necessary, by as possible low pressure losses in the cooling water circuit to keep the electric drive energy of the pumps small. The Most of the coolers currently in use are in this regard not optimized.

moreover causes the cost of materials for finned heat exchanger size Costs. This conventional Dry chillers are designed so that they can be modularly combined in large numbers can, to large-scale Recooling plants. hereby is a mostly rectangular design conditionally. Lamella packages become mostly installed in the horizontal, while the fans arranged above it to suck in the air from below. That's why these models are not visually nice, need relatively a lot of parking space and usually cause considerable noise pollution.

2nd wet cooler

The So far, for example, in solar cooling with sorption refrigeration machines most widely used solution put so-called wet coolers Here, some of the cooling water from the recooling circuit evaporates, whereby the remaining water is cooled. The main advantage This technology is the big one capacity in a relatively small size or can thus very low recooling temperatures be achieved. Lower needed Air mass flows offer the advantage of lower fan power and thus one improved energy efficiency.

Disadvantages are the high water consumption (eg in Germany about 40 l / h at 30 kW recooling) and the danger for example of legionella education. Due to the open system, there are usually high hydraulic pressure losses in filters used. Also high pressure losses cause the most commonly used nozzles for the distribution of cooling water for evaporation.

3. Hybrid cooler

a The middle ground between the two technologies is the so-called hybrid cooling tower. This is ideally a full dry cooler, the at too high outside temperatures or larger performance requirements at the same time uses the effect of evaporative cooling. Usually this will be by the wetting of heat exchanger surfaces with Water realized. Compared to the wet cooling tower here is less water needed. However, such devices are so far, if at all, then technically inadequate or very expensive for the small power range realized. Size Problems can here especially by corrosion or calcification of wetted lamellae the cooler occur.

technical description

Since the use of a water-air heat exchanger with direct water wetting of the heat exchange surface is associated on the one hand with high material wear and on the other hand with high material costs, an alternative concept should be pursued here:
There are simple disk packs ( 8th ) used for the dry cooling of the water.

The cooling water is in a closed circuit.

In the air flow in front of these coolers are filler ( 9 ), which are wetted with water if necessary.

An internal fan ( 1 ) draws or blows the air first into the packing ( 9 ), there is a mass transfer to the enlarged surface of the packing instead. Part of the water evaporates, with the remaining water cooling off. Furthermore, a heat exchange between the air and the cooled water takes place on the large surface of the packing. The air is therefore pre-cooled adiabatically before it enters the dry cooler.

The water becomes, after it from the packing ( 9 ) exits in a tub ( 4 ) collected. Here is a water-water heat exchanger ( 6 ), which is the final stage of the recooler, as it collects water at a low temperature near the wet bulb temperature, much cooler than the ambient air. The cooling water in the closed system thus flows first through the upper (air outlet side) water-air heat exchanger ( 8th ), then through the lower (air inlet side) and at the end through the water-water heat exchanger ( 6 ) in the tub.

The water for adiabatic cooling is in a separate circuit and z. B. from a fresh water line ( 12 ) nachgepeist. The water is trickled over the above-mentioned filler, this only the difference in height between sump ( 4 ) and distribution device ( 10 ) by a pump ( 2 ) are overcome low electrical power consumption.

Since a part of the circulating cooling water evaporates, water must be constantly refilled. To do this, place in the underlying collection trough ( 4 ) via a float valve ( 5 ), here the level is kept constant.

Around Contamination and lime concentration in the water is limited the tub contents in existing systems, eg. B. by an electrical conductivity measurement controlled or emptied at regular intervals. This sludge means additional Water consumption.

The present development is based on a low water content of the system (eg with 30 kW return cooling capacity: less than 20 l), which means that it can be emptied after each operation without separate regulation. This is achieved above all by suitable design of the heat exchanger ( 6 ) in the drip tray ( 4 ).

- Regulation the circuit for evaporative cooling:

A request signal switched by a higher-order control only opens a solenoid valve for wet operation of the cooler ( 3 ) in the water supply. Through the float switch ( 5 ) in the lower tub, the refill is regulated. The level in the lower tank ( 4 ) is thus kept approximately constant during operation. After each operating phase with adiabatic humidification of the air, the open system should be emptied. For this purpose, a blow-down opening ( 11 ) intended. This opening must have a sufficiently large cross-section to drain limescale and dirt, and open automatically after shutdown.

It open-circuit materials are used that are corrosion-resistant and lime insensitive. In particular, the water-water heat exchanger in the tub must be large enough and insensitive against deposits, because in the tub, so on the side of the Open circuit only very low flow rates occur should. As a result, pressure losses and thus the pump power kept low.

With this combination of adiabatic pre-cooling of the air and wet cooling cycle with separate systems, the effect of evaporative cooling should be fully utilized be a coordinated interpretation of the heat exchangers used is required.

Through the serial connection of packing and dry coolers in the air volume flow increased flow losses occur, which also remain in dry operation. To compensate for these losses, dry coolers are used with a small sipe depth, the flow resistance is thus relatively small, based on the inlet surface. However, it still requires the large heat exchange surface of a conventional dry cooler. This shows a great advantage of small radiator elements (for example, motor vehicle radiator). Due to their small size they can be brought in a large number of very flexible in a desired geometric arrangement. With a suitable installation, it is possible to connect many of these coolers in parallel on the air side and at the same time reduce the size of the recooler to a minimum, see also 2 and 3 ,

One Another approach of the concept is to put the fan in the interior to integrate the recooler. The cooler packages are arranged so that these in the air flow both before, as well as behind the fan. The fan is thus Completely through housing and cooler packages from the environment separately. The biggest source disturbing operating noise sets the strongly accelerated air with its turbulences the fan blades and the fan nozzle Through the casing of the recooler cooler packages and housing The aim is to reduce the noise level in the environment of the recooler. Consequently This development can significantly contribute to the acceptance of the recooler noise-sensitive Environments such. B. Housing estates contribute.

Claims (13)

Process for heat / mass transfer between two fluids over Packing and / or Laminated heat exchanger with following features: a) Use adiabatic humidification for indirect cooling a fluid in a closed circuit: moistening the air with in the air flow from above distributed water. cooling to be cooled Fluids over a heat exchanger, on the secondary side the excess, cold water the evaporative cooling flows. b) advancement of water for adiabatic humidification in the open system a drip pan in a pressureless distribution system above the Packing / heat exchanger. c) Arrangement of the component for heat transfer of to be cooled Fluid on the excess water of evaporation in the drip pan of the water, being in the open system for the promotion of water for adiabatic humidification a negligible low flow resistance arises. d) refill of water for adiabatic humidification from a water supply via a Level control valve in the drip tray. e) From that too cooling Fluid flowed through Lamella heat exchangers are in the air flow arranged. A heat transfer from the fluid to be cooled Air can therefore also take place without adiabatic humidification. Likewise Both operating modes are combined: For this purpose, in the flow direction the air in front of these heat exchangers respectively arranged in a suitable form a filler over the the water can be distributed for adiabatic moistening. On whose greater surface can heat transferred from the air to the trickled, cooled water be before the so pre-cooled Air enters the finned heat exchanger. Method according to claim 1 characterized in that that the entire open subsystem of adiabatic humidification at each end of the adiabatic cooling operation by an automatically opening drainage device is emptied. Method as in claim 1, characterized in that that several finned heat exchanger with small thickness (length in the air flow direction) be arranged so that they allow the air as large a cross-sectional area as possible to the flow direction Offer. A method as in claim 3, characterized by a star-shaped arrangement of the individual fin heat exchangers and in each case adapted arrangement of the packing (see 2 ). Process as claimed in any one of the preceding claims in that the to be cooled Medium only the lamella heat transfer and then the heat exchanger in the Traps traversed. Method according to one of the preceding claims, characterized in that in the flow direction the air both before and after the fan filler and / or Laminated heat exchanger arranged are. Method according to claim 5 characterized in that that to be cooled Medium first the lamellar heat exchanger in the direction of air flow the fan, then the lamella heat exchangers in front of the fan and Last, the heat exchanger in the Traps traversed. Method according to one of the preceding claims, characterized in that the fluid in the closed system cooling water is. Method according to one of the preceding claims, characterized in that the fluid in the closed system is a mixture of Cooling water and Antifreeze is. Method according to one of the preceding claims, characterized in that the fluid in the closed system is a refrigerant or refrigerant-solvent mixture is. Method according to one of the preceding claims, characterized in that the water for adiabatic humidification seawater (salted or desalted). Method according to one of the preceding claims, characterized in that the water for adiabatic humidification rainwater is. Method according to one of the preceding claims, characterized in that the water for adiabatic humidification fresh water (for Example from wells, cisterns, rivers, lakes) is.