Wells – Processes – Heating – cooling or insulating
Reexamination Certificate
2002-12-11
2004-08-03
Bagnell, David (Department: 3672)
Wells
Processes
Heating, cooling or insulating
C166S057000, C062S259200, C165S045000
Reexamination Certificate
active
06769487
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
This invention relates to an apparatus and method for cooling Instrumentation in an apparatus exposed to high temperature environments. In particular, this invention relates to active cooling of instrumentation, such as electronics in a downhole tool positioned in a wellbore.
2. Background Art
The environment encountered by downhole oil exploration tools can be very severe. Temperatures up to and in excess of 200 degree C. and pressures up to 1.38×10
8
Pa are not uncommon. Consequently, producers of oil exploration tools must design robust tools that can operationally sustain these harsh conditions for extended lengths of time. Perhaps the most challenging of all conditions to design electronics that can reliably operate in high temperature environments. Standard electronic components are usually rated to operate only up to approximately 125 degree C. Thus, it becomes necessary to create or experimentally find electric components that can survive the high temperatures existing downhole. Since the components are constantly changing via new manufacturing techniques, updates, etc., this process of creating electronic components is expensive, time consuming, and never ending. In an effort to combat the high temperature requirement of electronics, the chassis or electronics compartments in downhole tools could be kept at or below 125 degree C.
Today, tools rated to 175 degree C. are sometimes inserted into Dewar Flasks when exploring boreholes in excess of 175 degree C. Dewar Flasks act to insulate the tool electronics and to slow the heating of the electronic chassis similar to a large “thermal bottle”. The flask is a passive system that extends the downhole residence time of the tools by approximately four to six hours. Often the downhole residence times required for exploration are much greater than those offered by the expensive Dewar Flask system.
The problem at hand points toward the need for an active cooling system that can maintain the electronic chassis below 125 degree C. for extended lengths of time. Standard electronics could then be used without the need for the expensive high temperature components.
Active cooling systems already exist for a variety of applications such cooling food products, motor vehicles and buildings. These active cooling systems, better known as air conditioners and refrigerators, can effectively operate for extended periods of time with little to no maintenance. A cooling system makes heat move. It takes heat from one location and moves it to another location. The location from which heat was removed obviously becomes colder. For example, a refrigerator takes heat out of the inside and moves it to the outside. The heat flows into the air and the inside, having lost heat, becomes colder.
Vapor compression active cooling systems work by evaporation. When a liquid turns into a vapor, it loses heat and becomes cooler. This change is because the molecules of vapor need energy to move and leave the liquid. This energy comes from the liquid; the molecules left behind have less energy and so as a result, the liquid is cooler.
For an active cooling system to work continuously, the same cooling agent (etc., Freon) must be repeatedly used for an indefinite period. These cooling systems have three basic patterns: the vapor-compression system, the gas-expansion system and the absorption system. The vapor-compression system is typically more effective and is used more extensively than the other arrangements. The vapor-compression system consists of four main elements: an evaporator, a compressor, a condenser and an expansion device.
Referring to
FIG. 1
, in the evaporator
1
, the cooling agent boils (evaporates) at a temperature sufficiently low to absorb heat from a space or medium that is being cooled. The boiling temperature is controlled by the pressure maintained in the evaporator, since the higher the pressure the higher the boiling point. The compressor
2
removes the vapor as it is formed, at a rate sufficiently rapid to maintain the desired pressure. This vapor is then compressed and delivered to a condenser
3
. The condenser dissipates heat to circulating water or air. The condensed liquid cooling agent, which is now ready for use in the evaporator
1
, is then sharply reduced in pressure by passing it through an expansion valve
4
. Here, the pressure and temperature of the cooling agent drop until they reach the evaporator pressure and temperature, thus allowing the cooling cycle to repeat.
During expansion some of the liquid of the cooling agent flashes into vapor so that a mixture of liquid and flash vapor enters the evaporator. In a cooling system, the low pressure in the evaporator is set by the cooling temperature which is to be maintained. The high pressure maintained in the condenser is determined ultimately by the available cooling medium (e.g., the temperature of circulating water or the atmosphere air temperature). The process is one in which the cooling agent absorbs heat at a low temperature and then under the action of mechanical work, the cooling agent is compressed and raised to a sufficiently high temperature to permit the rejection of this heat. Mechanical work or energy supplied to the compressor as power is always required to raise the temperature of the system.
To further explain the cooling process, the four major components are examined in greater detail The evaporator
1
is the part of the cooling system in which the cooling is actually produced. The liquid cooling agent and vapor from the expansion valve
4
are introduced into the evaporator. As the liquid vaporizes, it absorbs heat at low temperature and cools its surroundings or the medium in contact with it. Evaporators may be direct expansion (acting directly to cool a space or product) or they may operate as indirect-expansion units to cool a secondary medium, such as water or a brine which in turn is pumped to a more distant point of utilization. A domestic refrigerator, for example, is a direct-expansion unit in that its evaporator directly cools the air in the food compartment and also directly contacts the water trays used for making ice. Evaporators vary greatly in design, with those used for cooling air often made as continuous pipe coils, with fins mounted outside the pipes to give greater surface contact to the air being chilled. For cooling liquid, such as a brine water, the shell and tube arrangement is common in this case, the brine passes through tubes surrounded by the boiling (evaporating) cooling agent, which is contained in a larger cylindrical shell. The brine tubes, in turn, are welded or rolled into tube sheets at the end of the shell to prevent leakage of the cooling agent from the shell or into the brine circuit.
The expansion valve
4
that feeds the evaporator must control the flow so that sufficient cooling agent flows into the evaporator for the cooling load but not in such excess that liquid passes over to the compressor, with the possibility of causing damage to it.
The compressor
2
, the key element of the system, can be powered by means such as electric motor, steam or internal combustion engine, or steam or gas turbine. Most compressors are of the reciprocating (piston) type and range from the fractional-horsepower size, such as those found in domestic refrigerators or in small air-conditioning units, to the large multi-cylinder units that serve large industrial systems. In these large multi-cylinder units, capacity can be controlled with automatic devices that prevent the in certain cylinders from closing. For example, in a six-cylinder unit, if the valves are held open on two of the cylinders to keep them inoperative, the capacity of the machine is reduced by one-third when operating at normal speed.
Centrifugal compressors are used for large refrigeration units. These compressors employ centrifugal impellers that rotate at high speed. Centrifugal compressors depend for their compression largely on the dynamic action of the gases themselves as they flow in the diffusion pa
Bagnell David
Jeffery Brigitte L.
Ryberg John
Schlumberger Technology Corporation
Segura Victor H.
LandOfFree
Apparatus and method for actively cooling instrumentation in... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus and method for actively cooling instrumentation in..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus and method for actively cooling instrumentation in... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3294370