ACR Journal

CMYK / .ai CMYK / .ai CMYK / .ai acrjournal.uk In a two-part article, Brad Bray of Evomart delves into the importance of filter driers on the life and efficiency of air conditioning, refrigeration and heat pump systems, and outlines new cost-effective product innovations. 21 SYSTEM LUBRICANTS Safeguarding your future: tiny drier, major potential! want to create equilibrium (balance) on both sides. On one side, we have carboxylic acids + alcohol, once heated and mixed, this creates our ester ‘product’, but it too creates water. When both sides are satisfied this creates equilibrium, see above: Hydrolysis – reverse reactions POE lubricants are known as hygroscopic, meaning they are prone to absorbing water. Water sits on the ester side of our scale’s analogy. As esters are formed during esterification, hydrolysis is the reversal of this reaction. POE lubricants are hydrolysed (broken down by reaction) by water. If we use a refrigeration system as an example, if water is present within the circulating refrigerant, then the reverse reaction may begin, be-it very slowly, without much noticeable impact on the systems performance. If moisture is present within the cycle, this will eventually begin to produce carboxylic acid compounds and alcohol, by reverse reactions as the POE lubricant is hydrolysed by water, see top right: The catalyst in this case is the hydroxonium ion, H3O+ , which is present in all solutions of acids in water. More acids that form accelerate the hydrolyses effect. In principle, hydrolysis becomes self- catalysing, driving the equilibrium back the other way, into the base compounds that from the ester product. The catalyst acid forms and if left unchecked/treated, then these smaller reactions will begin Filters driers are small but relatively understated, with the perception of being insignificant. While simple in application, they provide protection to HVAC systems the world over. They sit under the radar, acting as a watchman within a system that runs 24/7. To understand the importance of this component, we need to understand what its purpose is and how it safeguards HVAC systems and maintains lubricant stability. POE (poly olester synthetic oil) is commonly referred to as a universal oil. This oil serves as a lubricant to reduce friction and overheating of mechanical components, such as a compressor. Ensuring the compressor remains lubricated is vital. A compressor is known as the heart of a system, which fulfils two major functions: 1. Circulates refrigerant: For a fridge system to function, it requires a cooling medium to circulate around the system with the aim on moving heat energy from one source to another. 2. Applies pressure: HVAC systems rely on the pressure/temperature relationship to provide the necessary conditions for heat energy to move. If a compressor fails, this is known as a burnout. Maintaining the life of the compressor is a refrigeration engineer’s immediate priority, if this fails, everything will fail, resulting in a very costly repair. Lubricants are used in systems with moving mechanical components, as the means of reducing friction and overheating which in turn may lead to component failure. HVAC systems may suffer a compressor burnout, which is where lubricant is unable to make its way back to the compressor or the oil has become sufficiently degraded where the lubricant is unable to provide its lubricating properties. There are different types of lubricants: Mineral, PAG, Alkylbenzene and POE. For the purpose of this article, we are focused on POE. How are POE lubricants made? What is the impact of moisture has on the base lubricant? How does acid form within a system containing POE lubricants? Let’s take a look at what POE is made-up form… Esterification – “A chemical reaction resulting in the formation of at least one ester product.” The ester lubricant base is created with a parent carboxylic acid, which is heated with an appropriate alcohol with an acid catalyst (catalyst used to increase rate of chemical reaction). The occurring reaction is called esterification. Esterification is an equilibrium reaction of acids and alcohols that form an ‘ester-product’ + water. To complete ideal equilibrium (to maintain the ester product), water must be removed, otherwise a reverse reaction may trigger, called hydrolysis. As with a set of scales, these reactions As with a set of scales, these reactions want to create equilibrium (balance) on both sides. On one side, we have carboxylic acids + alcohol, once heated and mixed, this creates our ester ‘product’ , but it too creates water. When both sides are satisfied this creates equilibrium, see below: <subhead> Hydrolysis – reverse reactions POE lubricants ar known as hygroscopic, meaning they are prone to absorbing water. Water sits on the ester side of our scale’s an logy. As esters are formed during esterification, hydrolysis is the rev rsal of this reaction. POE lubricant are hydrolysed (broken do n by reaction) by wate . If we use a refrigeration system as an example, if water is present within the circulating refrigerant, then the reverse reaction may begin, be-it very slowly, without much noticeable impact on the systems performance. If moisture is present within the cycle, this will eventually begin to produce carboxylic acid compounds and alcohol, by reverse reactions as the POE lubricant is hydrolysed by water, see below: The catalyst in this case is the hydroxonium ion, H 3 O + , which is present in all solutions of acids in water. More acids hat form a celerate the hydrolyses effect. In principle, hydrolysis becomes self-catalysing, driving the equilibrium back the other way, into the base compounds that from the ester product. The catalyst acid forms and if left unchecked/treated, then these smaller reactions will begin to accelerate, ultimately resulting in a compressor burnout. Engineers are encouraged to perform acid checks regularly. This is where a sample of the system oil is removed and tested for traces of acids. If acids are present, then this needs to be addressed immediately, as to maintain oil stability and system health. The reverse reaction may be slow at first, then as equilibrium is achieved, the reverse reaction accelerates considerably. This is like starting at the top of the slide, as yo proceed down the slide your speed increases, until you hit t bott m and fly off. <subhead> Effect of moisture on an HVAC system. Brad Bray