The challenges of underground vehicle cooling systems.
As the cooling system components are typically packaged within enclosed engine cabinets, radiator cooling air is "preheated," and close proximity to exhaust system components and engine heat also can result in higher temperatures. And since the mine environment is typically extremely dirty, the system must resist clogging and allow for easy cleaning.
Several configurations can be used to address the challenges of cooling underground vehicles.
The side-by-side radiator configuration [ILLUSTRATION FOR FIGURE 1 OMITTED] houses multiple cores in one framework. This type of system has the ability to be designed with the least thickness and framework cost. One disadvantage is that typically the overall height and width must be larger than the full-face variety. Most underground radiators are built in a crossflow configuration - tanks on end with horizontal tubes. Therefore, by placing the radiator at the bottom of the assembly, the surge tank can be mounted lower in the vehicle just above the top of the engine.
While the side-by-side radiator assembly is a convenient package to mount into the vehicle, it is often limited size-wise by air and water pressure drop. The quantity of tubes and number of rows must be selected to meet cooling specifications, turbo air pressure drop limitations, and water pump maximum external head specifications. Each custom design may be different and should be checked.
The front-to-back radiator configuration [ILLUSTRATION FOR FIGURE 2 OMITTED] is composed of two complete assemblies (radiator and charge-air cooler, for example) with frameworks fastened together. The biggest advantage to this assembly is that it typically requires less height and width in the core. The full-face assembly also tends to provide more uniform airflow distribution and more efficient performance when used with a blower fan. Airside and waterside pressure drops are often less of a problem.
The main disadvantage to the front-to-back configuration is that it requires more space in the thickness dimension. This type of assembly will also cost more due to the extra framework required.
Depending on the customer's requirements, cooling packages are designed to be used with blower (pusher) or sucker fan arrangements. Blower fans are the standard preference in many underground mining machines in order to push the hot engine air away from the operator. A disadvantage to blower fans is that they lower the radiator performance by directing preheated engine air across the core. In cases where the engine and radiator are tightly installed into the vehicle, we have noted that blower fans have decreased airflow efficiency and performance. Maintaining a maximum charge-air cooler outlet temperature of 150 [degrees] F (specified) is one of the largest challenges in designing a system for use with a blower fan. It is difficult to maintain 150 [degrees] F air outlet when the charge-air cooler sees an entering air temperature of 130 [degrees] F (120 [degrees] F ambient + 10 [degrees] F engine preheat).
Sucker fans are most popular in high ambient environments or in vehicles with full cabs to protect the operators. The advantage to sucker fans is that the air they draw across the radiator is not preheated by the engine, therefore performance is increased.
As entrained air is an enemy of effective heat transfer, there are several methods used to remove air from coolant in heavy equipment cooling systems. The secret to deaeration is to slow the coolant down to allow the air to escape from the coolant. All top tanks must meet the following design criteria in order to operate correctly:
* Every cooling system must remove entrained air and deaerate within a given amount of time or at a specified rate. Upon completion of this deaeration the water loss or level in the top tank must not exceed a given amount.
* There must be provisions for coolant expansion.
* The system must vent during fill and be capable of being filled at a specified rate.
* Provisions must be made for the minimum drawdown capability (drawdown being reserve volume in the top or surge tank).
The use of surge tanks can provide several advantages to the cooling system. Space is conserved in the machine envelope since less volume is required in the top tank. Crossflow configurations using horizontal tubes can be implemented. Multiple pass cores can also be used, increasing cooling efficiency.
To ensure the fewest amount of problems, operators of underground equipment should maintain a regular cleaning schedule of their cooling system. To wait until the unit is overheating is a mistake, as damage can occur at that point. Severely plugged cores may have to be cleaned by removing the outside rows to gain access to the plugged internal rows.
During routine maintenance and major engine work, the radiator unit should receive a thorough exterior cleaning and inspection. A few tubes on the air inlet side should be removed and inspected for signs of contamination. The removed tube can be split open like a peeling of a banana to inspect for interior contaminants. Any contamination found can be analyzed to help find the cause and take corrective action.
Should an overheat situation occur, there are several steps that should be taken. First, temperature gauges must be tested for accuracy to ensure an actual overheat has occurred. Check to make sure the core is clean. The worst plugging can be in the interior rows. Inspection may be done by moving first row tubes sideways to see the interior easier and with a light from the opposite side.
Check for loose belts that could make the fan run slower and make sure the system has the appropriate amount of coolant. Inspect the fan and shroud for damage as well as fan placement in the shroud. Thermostats and pressure caps should also be inspected.
Solving the overheat problem is a matter of determining what is actually happening compared to the expected temperatures. This is done by measuring water in and out as well as air in and out temperatures.
Tom Haapoja is applications engineer at L&M Radiator, Inc., the Hibbing, Minn., manufacturer of heat transfer components and systems.
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|Title Annotation:||for underground mining vehicles|
|Comment:||Underground mining vehicles provide a number of unique challenges for the cooling system designer.|
|Publication:||Diesel Progress North American Edition|
|Date:||Apr 1, 1997|
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