Hóa học - Dầu khí - Chapter 2: Refrigerant and coolant

CHAPTER 2: REFRIGERANT AND COOLANT 12/2015 Chapter 2 : Refrigerant 1 OBJECTIVES Student can: - Understand the requirements of refrigerant and coolant - Understand the thermodynamic and property of some refrigerants - Use the refrigerant chart to display refrigeration cycle 12/2015 2Chapter 2 : Refrigerant REFRERENCES [1] Refrigerant and Air Contioning A R Trott. - . . and T. Welch [2] Danfoss document. 12/2015 3Chapter 2 : Refrigerant CONTENTS REFRIGERANTS COOLANT REFRIGERANT CHART ANALYST 12/2015 4Chapter 2 : Refrigerant REFRIGERANT 1. Ideal properties for a refrigerant: (page28,[1]) It ill b f l t i d l f thw e use u o rem n ourse ves o e requirements for a fluid used as a refrigerant. A hi h l t t h t f i ti• g a en ea o vapor za on • A high density of suction gas N i t i d fl bl• on-corros ve, non- ox c an non- amma e • Critical temperature and triple point outside the kiwor ng range • Compatibility with component materials and l b i ti ilu r ca ng o • Reasonable working pressures (not too high, or b l 12/2015 5 e ow Chapter 2 : Refrigerant REFRIGERANT • Low cost E f l k d t ti• ase o ea e ec on • Environmentally friendly N i l fl id h ll th ti do s ng e u as a ese proper es, an meets the new environmental requirements, but this h t ill h th d l t th t t kic ap er w s ow e eve opmen s a are a ng place in influencing the selection and choice of a f i tre r geran . 12/2015 6Chapter 2 : Refrigerant REFRIGERANT 2. Ozone depletion potential (ODP): Th l i t he ozone ayer n our upper a mosp ere provides a filter for ultraviolet radiation, which can b h f l t h lthe arm u o our ea . The Montreal Protocol in 1987 agreed that the d ti f th h i l ld b h d tpro uc on o ese c em ca s wou e p ase ou by 1995 and alternative fluids developed 12/2015 7Chapter 2 : Refrigerant REFRIGERANT R22 is an HCFC and now regarded as a t iti l f i t i th t it ill b l t lrans ona re r geran , n a w e comp e e y phased out of production by 2030, as agreed under th M t l P t le on rea ro oco . 12/2015 8Chapter 2 : Refrigerant REFRIGERANT 12/2015 9Chapter 2 : Refrigerant REFRIGERANT 3. Global warming potential (GWP): Gl b l i i th i i f th ld’- o a warm ng s e ncreas ng o e wor s temperatures, It i d b th l i t th t h- s cause y e re ease n o e a mosp ere of so-called ‘greenhouse’ gases, which form a bl k t d fl t h t b k t th th’ fan e an re ec ea ac o e ear s sur ace, or hold heat in the atmosphere. Th t i f h i b- e mos n amous green ouse gas s car on dioxide (CO2), which once released remains in the t h f 500 th i t ta mosp ere or years, so ere s a cons an build-up as time progresses. 12/2015 10Chapter 2 : Refrigerant REFRIGERANT Table 3.3 shows that the newly developed f i t l h l b l ire r geran gases a so ave a g o a warm ng potential if released into the atmosphere. F l R134 h GWP f 1300 hi hor examp e, a as a o , w c means that the emission of 1 kg of R134a is i l t t 1300 k f COequ va en o g o 2. 12/2015 11Chapter 2 : Refrigerant REFRIGERANT 12/2015 12Chapter 2 : Refrigerant REFRIGERANT + Note : 12/2015 13Chapter 2 : Refrigerant REFRIGERANT 12/2015 14Chapter 2 : Refrigerant REFRIGERANT 4. Ammonia and the hydrocarbons: Th fl id h i t ll ODP d- ese u s ave v r ua y zero an zero GWP when released into the atmosphere and th f t f i dl i t lere ore presen a very r en y env ronmen a picture. Ammonia has long been used as a f i t f i d t i l li tire r geran or n us r a app ca ons. - Ammonia cannot be used with copper or copper ll f i t i i d t h ta oys, so re r geran p p ng an componen s ave o be steel or aluminium. It l b ili i t i 33 °C A i h- s norma o ng po n s – . mmon a as a characteristic smell even in very small t ti i i 12/2015 15 concen ra ons n a r. Chapter 2 : Refrigerant REFRIGERANT - It cannot burn, but it is moderately explosive h i d ith i i l t f 13 tw en m xe w a r n a vo ume percen age o o 28%. U d i i d t i l t- se n n us r a sys em 12/2015 16Chapter 2 : Refrigerant REFRIGERANT Fluorinated refrigerants always carry the d i ti “R” f ll d b b R22es gna on o owe y a num er, e.g. , R134a, R404A and R407C. The fluorinated f i t ll h th f ll i f tre r geran s a ave e o ow ng ea ures: - Vapour is smell-free and non-irritant. E t i l i I th f- x ens ve y non-po sonous. n e presence o fire the vapour can give off fluoric acid and h hi h ip osgene, w c are very po sonous. - Non-corrosive. N fl bl d l i- on- amma e an non-exp os ve. 12/2015 17Chapter 2 : Refrigerant REFRIGERANT +The most common fluorinated refrigerants are: R134 hi h i b t f th tha, w c s a su s ance o e e ane group with the formula CH2FCF3 and has a normal b ili i t f 26 1°C It th d io ng po n o – . . s ermo ynam c properties make it suitable as a refrigerant for di t t li ti h d time um empera ure app ca ons suc as omes c refrigerators. 12/2015 18Chapter 2 : Refrigerant REFRIGERANT R22, which is a substance of the methane ith th f l CHF CI d h b iligroup w e ormu a 2 an as a o ng point of –40.8 °C. Its thermodynamic properties k it it bl f i t f id fma e su a e as a re r geran or a w e range o applications in commercial refrigeration and air diti i R22 i b i h d t f i tcon on ng. s e ng p ase ou as re r geran in many countries due to its ozone depleting t ti lpo en a . 12/2015 19Chapter 2 : Refrigerant REFRIGERANT R32 is difluoromethane (methylene fluoride) and it i HFC t f i t R32 h b d fs an ype re r geran . as een use or many years as a component of both R407C and R410A It i fl bl it b t t h. s amma e on s own, u no w en mixed with the other components of these blends. 12/2015 20Chapter 2 : Refrigerant REFRIGERANT 5. Refrigerant blends: M f th lt ti f i t- any o e new, a erna ve re r geran s are ‘blends’, which have two or three components, d l d f i ti d l teve ope or ex s ng an new p an s as comparable alternatives to the refrigerants being l drep ace - They are ‘zeotropes’ with varying evaporating or d i t t i th l t t h t fcon ens ng empera ures n e a en ea o vaporization phase, referred to as the ‘temperature lid ’g e . 12/2015 21Chapter 2 : Refrigerant REFRIGERANT 12/2015 22Chapter 2 : Refrigerant REFRIGERANT 12/2015 23Chapter 2 : Refrigerant REFRIGERANT 12/2015 24Chapter 2 : Refrigerant REFRIGERANT - To compare the performance between single t f i t d bl d it ill bcomponen re r geran s an en s w e necessary to specify the evaporating temperature of th bl d t i t A th di d the en o po n on e agram an e condensing temperature to point B. A bl i t d ith bl d i th t- pro em assoc a e w en s s a refrigerant leakage results in a change in the t t ti f th f i tcomponen concen ra on o e re r geran . however, tests indicate that small changes in t ti ( l th 10%) h li iblconcen ra on say ess an ave a neg g e effect on plant performance. 12/2015 25Chapter 2 : Refrigerant REFRIGERANT The following recommendations apply to the use f bl do en s: • The plant must always be charged with liquid f i t th t t ti illre r geran , or e componen concen ra ons w shift. Si t bl d t i t l t• nce mos en s con a n a eas one flammable component, the entry of air into the t t b id dsys em mus e avo e . • Blends which have a large temperature glide, t th 5K h ld t b d f fl d d tgrea er an , s ou no e use or oo e - ype evaporators. 12/2015 26Chapter 2 : Refrigerant REFRIGERANT 12/2015 27Chapter 2 : Refrigerant REFRIGERANT 12/2015 28Chapter 2 : Refrigerant REFRIGERANT R404A/R507A (also known as R507), which is a mixture of the refrigerants R125 (CHF2CF3) and R143a (CH3CF3) with a boiling point at (–46.7 °C) which is slightly lower than for R22. Its thermodynamic properties makes it suitable as a refrigerant for low and medium temperature applications in commercial refrigeration (e.g. supermarkets). 12/2015 29Chapter 2 : Refrigerant REFRIGERANT R407C, which is a mixture of the refrigerants R32 (CH2F2), R125 (CHF2CF3) and R134a (CH2FCF3) with a boiling point at (–43.6 °C) which is slightly lower than for R22. Its thermodynamic properties make it suitable as a refrigerant for medium and high temperature applications in residential and commercial air conditioning. 12/2015 30Chapter 2 : Refrigerant REFRIGERANT R410A, which is a mixture of the refrigerants R32 (CH2F2) and R125 (CHF2CF3) with a boiling point at (–51.4 °C) which is lower than for R22. Its thermodynamic properties make it suitable as a refrigerant for medium and high temperature applications in residential and commercial air conditioning. 12/2015 31Chapter 2 : Refrigerant REFRIGERANT Except for R22, systems with fluorinated hydrocarbons are in general lubricated with polyol ester oils (POE). These oil types are much more sensitive to react chemically with water, the so- called “hydrolysis” reaction. For that reason systems today are kept extremely dry with filter driers. 12/2015 32Chapter 2 : Refrigerant COOLANT The refrigerants mentioned above are often designated “primary refrigerants”. As an intermediate link in heat transmission from the surroundings to the evaporator, the so-called “secondary refrigerants” can be used, e.g. water, brine, atmospheric air etc. 12/2015 33Chapter 2 : Refrigerant COOLANT 12/2015 34Chapter 2 : Refrigerant COOLANT 12/2015 35Chapter 2 : Refrigerant COOLANT 12/2015 36Chapter 2 : Refrigerant REFRIGERANT CHART ANYLYST - The diagram is arranged so that it displays the liquid, vapour and mixture regions for the refrigerant. Liquid is found to the left (with a low energy content) - vapour to the right (with a high energy content - In between you find the mixture region. The regions are bounded by a curve - called the saturation curve. The fundamental processes of evaporation and condensation are illustrated. 12/2015 37Chapter 2 : Refrigerant REFRIGERANT CHART ANYLYST Diagrams are still used as the main tool for analysis of refrigeration processes. Subcool De-Superheat Superheat 12/2015 38Chapter 2 : Refrigerant REFRIGERANT CHART ANYLYST 12/2015 39Chapter 2 : Refrigerant REFRIGERANT CHART ANYLYST 12/2015 40Chapter 2 : Refrigerant REFRIGERANT CHART ANYLYST 12/2015 41Chapter 2 : Refrigerant REFRIGERANT CHART ANYLYST If a refrigerant at the same temperature as ambient is allowed to expand through a hose with an outlet to atmospheric pressure, heat will be taken up from the surrounding air and evaporation will occur at a temperature corresponding to atmospheric pressure. 12/2015 42Chapter 2 : Refrigerant REFRIGERANT CHART ANYLYST If in a certain situation pressure on the outlet side (atmospheric pressure) is changed, a different temperature will be obtained since this is analogous to the original temperature - it is pressure dependent. ( Open R22 thermodynamic table ) 12/2015 43Chapter 2 : Refrigerant REFRIGERANT CHART ANYLYST When the refrigerant coming from the evaporator is fed to a tank the pressure in the tank will rise until it equals the pressure in the evaporator. Therefore, refrigerant flow will cease and the temperature in both tank and evaporator will gradually rise to ambient. 12/2015 44Chapter 2 : Refrigerant REFRIGERANT CHART ANYLYST To maintain a lower pressure, and, with it a lower temperature it is necessary to remove vapour. This is done by the compressor, which sucks vapour away from the evaporator. In simple terms, the compressor can be compared to a pump that conveys vapour in the refrigeration circuit. 12/2015 45Chapter 2 : Refrigerant REFRIGERANT CHART ANYLYST In a closed circuit a condition of equilibrium will always prevail. To illustrate this, if the compressor sucks vapour away faster than it can be formed in the evaporator the pressure will fall and with it the temperature in the evaporator. Conversely, if the load on the evaporator rises and the refrigerant evaporates quicker, the pressure and with it the temperature in the evaporator will rise. 12/2015 46Chapter 2 : Refrigerant REFRIGERANT CHART ANYLYST Refrigerant leaves the evaporator either as saturated or weak superheated vapour and enters the compressor where it becomes compressed. Compression is carried out as in a petrol engine, i.e. by the movement of a piston. The compressor requires energy and carries out work. This work is transferred to the refrigerant vapour and is called the compression input. 12/2015 47Chapter 2 : Refrigerant REFRIGERANT CHART ANYLYST The refrigerant gives off heat in the condenser, and this heat is transferred to a medium having a lower temperature. The amount of heat given off is the heat absorbed by the refrigerant in the evaporator plus the heat created by compression input. 12/2015 48Chapter 2 : Refrigerant REFRIGERANT CHART ANYLYST Liquid from the condenser runs to a collecting tank, the receiver. To reduce pressure to the same level as the evaporating pressure a device must be inserted to carry out this process, which is called throttling, or expansion. Such a device is therefore known either as a throttling device or an expansion device. 12/2015 49Chapter 2 : Refrigerant REFRIGERANT CHART ANYLYST There are many different temperatures involved in the operation of a refrigeration plant since there are such things as subcooled liquid, saturated liquid, saturated vapour and superheated vapour. There are however, in principle, only two pressures; evaporating pressure and condensing pressure. The plant then is divided into high pressure and low pressure sides, as shown in the sketch. 12/2015 50Chapter 2 : Refrigerant REFRIGERANT CHART ANYLYST High and low pressure sides of the refrigeration plant 12/2015 51Chapter 2 : Refrigerant REFRIGERANT CHART ANYLYST Refrigeration process, pressure/enthalpy diagram Note : + C-C1 : Superheat , po=const, tC1>tC + D-E : Desuperheat A A1 S b l+ - : u coo 12/2015 52Chapter 2 : Refrigerant REFRIGERANT CHART ANYLYST Survey this R134a refrigeration system and display points on chart 12/2015 53Chapter 2 : Refrigerant