GB2456741A - Thermosiphon Enclosure Surrounding an Evaporator Pipe - Google Patents

Abstract

An absorption refrigeration system 5 has an evaporator pipe 4 surrounded by and in thermal contact with a fluid filled enclosure 3, such that thermosiphon of the fluid within the enclosure increases the evaporator pipe heat transfer performance. The fluid filled enclosure may have one or more filling points and a vent to prevent build-up of hydrogen gas. The refrigeration system may be used to cool electrical or electronic components, such as back-up batteries, housed within a temperature controlled space bounded by walls. The fluid filled enclosure may be attached to the walls of the space by way of welding, gluing or other mechanical fixings 2, and the wall may include insulation means 9.

Description

IMPROVEMENT TO EVAPORATOR HEAT TRANSFER IN DIFFUSIOI

ABSORPTION CYCL}S The present invention relates generally to temperature controlled enclosures and specifically to improvements in performance in temperature controlled enclosures containing electrical and electronic equipment using diffusion absorption refrigeration cycles.

Many items of electrical and electronic equipment have increased susceptibility to failure, malfunction or generally accelerated degradation and shortened lifespan when exposed to large variations in temperature, humidity and other ambient conditions.

The problem is particularly significant for items of equipment that must be left for extended periods of time in environments that are relatively unprotected from atmospheric conditions.

One example is items of control equipment, and in particular, the standby or backup battery power supplies thereof. Such control equipment may be found in power distribution, telecommunication, transport and security systems and may often be situated in isolated and exposed outdoor and indoor locations. Installing such equipment in an enclosure for protection from rain or other precipitation can often increase temperature variations, in that sunlight on the enclosure will tend to heat the contents of the enclosure to far higher temperatures than would otherwise be the case.

Additionally, in some applications, heat emitting equipment situated close to the sensitive equipment may add to the thermal stress. Thus, there is a requirement to provide cooling or air conditioning to the most temperature sensitive items.

In particular, battery back-up power supplies for power distribution control systems and telecommunication systems in the field have been observed to have a service life substantially lower than expected largely due to degradation caused by temperature and/or humidity variation. Solutions in the prior art have provided temperature controlled enclosures for the sensitive equipment ranging from a simple ventilated enclosure through to complete air conditioning systems. These solutions and systems incorporate technologies such as thermoelectric devices, forced convection, heat pipes, phase change material and vapour compression cycles.

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A problem to be addressed in such temperature controlled enclosures is to make them as thermally efficient as possible, whilst at the same time developing devices that have no moving components which removes the need for regular and expensive maintenance due to the failure of those components as a result of mechanical wear and tear. Components which can be removed include mechanical parts such as fans, pumps and compressors and consumables such as filters.

An alternative refrigeration cycle or cooling mechanism to those noted which can be adapted to be used with electronic and electrical equipment is the diffusion absorption cycle. This cycle completely avoids the need for mechanical energy as used in vapour compression and instead relies on direct thermal energy to drive the cycle. This cycle also uses environmentally benign working fluids, is reliable, silent and relatively inexpensive to build and have no moving parts. However they have relatively low refrigeration coefficient of performance (COP') which needs to be improved so that electronic and electrical equipment such as industrial batteries can efficiently be cooled.

Specifically inside the temperature controlled enclosure the evaporator pipe of the diffusion absorption refrigeration cycle builds up ice when cooling which introduces safety issues in the temperature control of electrical and electronic equipment. In addition the ability to spread cool throughout the cabinet is limited because the surface area of the evaporator pipe is often small when compared to the contents of the temperature enclosure.

It is an object of this present invention to provide temperature controlled enclosures for electrical and electronic components using an improved diffusion absorption refrigeration cycle leading to lower cost, and greater efficiency at a wider range of ambient temperatures.

The improvement in the diffusion absorption cycle comes from improving the distribution of the cooling effect throughout the enclosure and ensuring that there is no ice build up on the evaporator pipe coming into contact with any of the contents of the enclosure.

According to one aspect, the present invention provides an additional piece of equipment enclosing the evaporator pipe located within the temperature enclosure: A fluid filled evaporator thermo siphon surrounding the evaporator pipe on a diffusion absorption refrigerator cycle The thermo siphon being sealed in all aspects to avoid fluid escaping from the enclosure to the environment The thermo siphon being attached or embedded by various methods which may include gluing, welding and mechanical fixing to the enclosure wall, ceiling or floor thereby providing the opportunity for one or more sides of the thermo siphon to be made of different materials.

The thermo siphon being made from such material and in such dimensions to optimise and improve convection around the evaporator pipe and provide additional surface area from which to transfer heat The thenno siphon is located and shaped to increase energy transfer from convective flows around the evaporator pipe thereby improving heat transfer from the contents of the temperature controlled enclosure.

The size of the thermo siphon is optimised to provide a balance between thermal efficiency in dissipating heat, heat transfer and convection, cost of manufacture, fit with the refrigeration cycle and weight of fluid.

The fluid filled evaporator thermo siphon secures the following improvements in the performance of the diffusion absorption cycle; Improvement in thermal performance of the diffusion absorption cycle-specifically providing a larger surface area internal to the temperature controlled enclosure for transferring heat Cost benefits as a standard diffusion absorption is only modified by the addition of the thermo siphon which can be undertaken post manufacture of the cycle by enclosing the evaporator pipe.

The thermo siphon may be made from one or a limited number of pieces of material which improves the ease of manufacture of the enclosure and the ease of installation around the evaporator pipe.

No moving parts have been added such as fans which would increase the maintenance costs of the equipment. Heat transfer from the evaporator pipe is being achieved more effectively with no forced convection.

Ice no longer builds up on the evaporator pipe enabling electrical and electronic components to be safely cooled.

Contents which are held in different locations in the temperature controlled enclosure can be cooled Testing has indicated that iTs, between the temperature of the contents of a controlled enclosure.. .in this case industrial batteries.., and external ambients, in the region of 5°C can be obtained using standard 80W diffusion absorption cycles. In addition the temperature of the contents can vary by over 10°C between the top and the bottom of the enclosure. Using the improvement in heat transfer with this fluid filled enclosure around the evaporator this variation has been brought down under 5°C.

This enables the cycle to be used in ambient temperatures (well above domestic room' temperatures) up to 60°C and to maintain all the contents at least below 50°C and to reduce the variation of temperature within the enclosure; An effective minimum iT of 10°C for all contents down to room temperature ambients.

Embodiments of the present fluid filled enclosure will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a cross sectional view of a diffusion absorption cycle with a fluid filled thermo siphon on its evaporator pipe.

With reference to figure 1 a diffusion absorption refrigeration cycle 5 is attached to structural insulation or a material enclosing insulation 9. The evaporator pipe 4 which removes heat from the inside of the temperature controlled enclosure 8 is part of the diffusion absorption refrigeration device 5 and is separated from outside the temperature controlled enclosure 7 by structural insulation or a material enclosing insulation 9. The fluid filled thermo siphon 3 is attached to the inside of the temperature controlled enclosure 8 to form a sealed vessel 3 which incorporates, inside the vessel 3, the evaporator pipe 4 of the diffusion absorption cycle 5. The sealed thermo siphon also has one or more filling points which are used to introduce fluid to the vessel once it has been fixed in place around the evaporator pipe 4. The fluid filled enclosure may be attached to the structural insulation or a material enclosing insulation 9 by the way of welding, gluing or other mechanical fixing methods 2. The thermo siphon has one or more sides that utilise the structural insulation or a materiaL enclosing insulation 9 and therefore the thermo siphon 3 may be made of more than one material. The external surface of the thermo siphon 6 may or may not be in direct contact with the contents of the temperature controlled enclosure. In addition a hydrogen vent is added to the enclosure to ensure that hydrogen is dissipated to the external environment to avoid any explosive build up of hydrogen gases within the enclosure.

Other embodiments are intentionally within the scope of the accompanying claims.

Claims (5)

1. A fluid filled thermo siphon surrounding the evaporator pipe on a diffusion absorption refrigerator cycle.

2. A temperature enclosure for sensitive electronic and electrical equipment being cooled by a diffusion absorption refrigeration cycle with the thermo siphon of claim 1

3. The thermo siphon of claim I incorporating structural insulation or a material enclosing insulation as part of its physical construction which may be different in material from that of the remaining part of the thermo siphon

4. The enclosure of claim I has one or more filling points.

5. A fluid filled enclosure substantially as described herein with reference to the accompanying drawings.