DE2813682A1 - Protective cabinet for electronic circuits - has inbuilt air-air heat exchanger distributed around rear and side walls to reduce pressure loss - Google Patents

Abstract

The cabinet, for electronic circuits, has a built-in heat exchanger with air-to-air heat transfer. Pressure loss is reduced by distributing the heat exchanger along the rear and side walls of the cabinet and by designing it so that both air flows are laminar. The air flows are separated by pipes. The cabinet has an outer skin with inlet and outlet holes for cold external air and an inner skin enclosing the circuits and with holes to allow internal air to circulate around the pipes between the two skins. The cabinet provides protection against corrosive atmosphere.

Description

Control box with integrated heat exchanger to accommodate

electronic circuits in protection class IP 54 The invention relates to an equipment box to accommodate electronic circuits in protection class IP 54 integrated heat exchanger to dissipate the heat losses that arise in the equipment box.

The use of electronic circuits in industrial plants makes one Protection of these circuits from environmental influences such as dust, moisture or corrosive substances Atmosphere necessary. The dust- and splash-proof housing of the electronic Assemblies are therefore essential. On the other hand, the Excess heat is often not sufficiently dissipated through the walls of the house. the The electronic circuits must therefore be cooled with the aid of a heat exchanger take place.

It is known that heat exchangers are housed in a dust-tight manner for cooling Electronic circuits in the form of flat ones that can be screwed onto control cabinet doors To use cuboids (Siemens-Zeitschrift 46 (1972) issue 8, p. 699 ff; prospectus from Autz + Herrmann, Heidelberg, Karl-Benz-Str. 10-12 (1976); magazine "Schroff Information" No. 25, April 1977, p. 5). These heat exchangers are air-to-air exchangers, work according to the countercurrent principle and in the area of turbulent flow. As a partition folded sheet metal or PVC is used between the inside air and outside air.

The design, arrangement and mode of operation of these heat exchangers require different ones Disadvantages: 1. Operation in the area of turbulent flow requires fans with high Connection power to achieve the necessary flow speeds and to compensate for the associated pressure loss in the exchanger.

2. Supply and exhaust air ducts are to be generously dimensioned to avoid further pressure losses and to prevent uneven flow through the exchanger. These channels enlarge the exchanger considerably.

3. There are none at the level of the intake and exhaust air openings of the exchanger Assemblies (e.g. 19 "plug-in units) are arranged; this would reduce the flow of the exchanger impair 4. The one on the sides of the 19 "racks Space up to the wall unit with 600 mm wide standard cabinets must be sealed off in order to Prevent bypass flow.

5. The cost of tools to produce folded metal sheets or plastic sheets are high, so that this version of the separating elements is unsuitable for small series is.

The invention is based on the object of an air-to-air heat exchanger to be integrated into an equipment cabinet to be constructed with a standard width of 600 mm so that that a minimum of usable space is lost inside the cabinet, fans The lowest possible connected load and with a low noise level can be used no special tools are required to manufacture the exchanger.

According to the invention, this object is achieved in that the heat exchanger on the back wall and both. Side walls of the equipment cabinet is distributed, commercially available Pipes to separate the indoor and outdoor air are used by the exchanger in the area laminar flow and therefore works with low pressure losses.

The cold outside air flows vertically through the from bottom to top Pipes and is sucked off by a fan in a collecting space on the top of the housing.

The indoor air exits horizontally at the lower end of the equipment cabinet into a collecting space used as a cable duct from the exchanger and flows vertically through the assemblies upwards. Above the last assembly is the heated one Air is sucked off by a sealed fan and passes horizontally to the Tube bundle of the exchanger, from where it goes vertically down between the tubes in the Countercurrent to the outside air flows.

The laminar flow in the exchanger results from the laws of Fluid mechanics.

The advantages achieved by the invention are that - in commercial standard cabinets with a width of 600 mm unused space for the installation of the heat exchanger is used, - by operating in the laminar flow range and large-area inlet and outlet air openings of the exchanger, low pressure loss results and thus fans with a low connected load and at a low price can be used - Expensive special tools are no longer required due to the use of commercially available tubes.

An embodiment of the invention is shown in the drawings and described in more detail below.

Fig.1 shows a cross section from above through the equipment box. the Heat exchanger tubes (3) are attached between the inner (2) and outer casing (1). At the lower end of the inner jacket, Luftleithlethe (4) are spotted. The pipes are arranged in three rows on three sides of the equipment cabinet.

Fig. 2 shows a longitudinal section through the equipment cabinet with a view from the beginning. The exchanger tubes (3) are 80 mm longer than the top and bottom the inner casing shell (2). At the upper end of the inner shell is an end plate (5), which carries the fan (8) for the indoor air. At the bottom The air baffles (5a) of the inner jacket are spotted. The lower end of the housing form the guide (6a) and retaining plates (6b) for the exchanger tubes (3), whereby the retaining plates are screwed on and can be easily dismantled so that the pipes can be removed for cleaning.

can. Between the top of the inner shell and the cabinet lid are the upper guide (4a) and retaining plates (4b) point, on which a partition plate is welded, which separates the inner from the outer air flow. Above this partitioning sheet is the collecting space for the outside air. The fan is in the middle of the cabinet lid (7) mounted for the outside air.

Fig. 3 shows the attachment of the exchanger tubes. The upper (4a) and The lower (6a) guide plates are spotted on the outer casing (1) of the equipment cabinet and have holes with the outer diameter of the exchanger tubes (3). Direct on the upper guide plate (4a) is the upper retaining plate (4b) with holes of the Inside pipe diameter attached. The lower holding plate (6b) is attached from below the lower guide plate is screwed on and has the same perforations as that upper end plate (4b). So the guide plates prevent radiole and the conclusion sheet axial movements of the exchanger tubes.

In the exemplary embodiment, the laminar flow of the outside air is thereby achieves a volume flow of 6.10 -2m3sec sec through 247 pipes with an inner diameter of 9 mm is directed.

The flow velocity (u) in the pipes is thus: The associated Reynolds number (Re) is calculated using the inner diameter d. of the pipes and the kinematic viscosity of the air.

di = 9.10-3m γ = 1.786-10-5m2sec-1 The critical Reynolds number for pipes through which there is a flow is 2320. With a Reynolds number of 1924, laminar flow is guaranteed.

The pipe division in the heat exchanger was made so that a hydraulic Diameter of 9.8 mm was achieved.

With a volume flow of 6.10 m3sec for the indoor air, the flow velocity u was 2.44 msec 1. The associated Reynolds number is therefore This means that the flow around the outside of the pipes is also laminar.

Claims (4)

Claims: 1. Equipment box to accommodate electronic circuits In protection class IP 54 with integrated air-to-air heat exchange, characterized in: 1 that to achieve low pressure losses of the heat exchanger to the rear wall and both Side walls of the equipment cabinet distributed and designed such that both air flows are laminar in the heat exchanger. 2. Device box according to claim 1, characterized in that for separation of the two air streams tubes are used. 3. Eerätekasten according to claim 1 and 2, characterized in that the equipment box has an outer jacket (1) with inlet and outlet openings for the cold outside air and an inner jacket (2) to accommodate the circuits with openings for circulating the indoor air and heat exchanger tubes (3) and the two Air flows through the exchanger tubes (3) and guide (4a), (6a) and retaining plates (4b), (6b) are separated. 4. Serätekasten nacti claim 1 to 3, characterized in that the exchanger tubes are held at both ends in perforated guide plates (4a), (6a) and secured against axial displacement by perforated retaining plates (4b), (6b) The diameter of the holes in the retaining plates is equal to the inner diameter the pipes is.