制冷外文期刊.docx

1、制冷外文期刊制冷-外文期刊Jonrnal of Applied Sciences (8):788-794,2008ISSN 1812-56542008 Asian Network for Scientific InformationDesigning of Cold Stores and Choosing of System ElementsS.AkdemirAir-Condition and Refrigeration Programme, Vocational School,Namik Kemal University, 59030 Tekirdag, TurkeyAbstract: In

2、 this study, calculation of cooling load and choosing of the cooling system elements such as compressor, condenser and evaporator were explained for designing of the cold storage. Transmission heat (q1), infiltration heat (q2), product heat (q3),heat of other sources (q4) and unknown and unexpected

3、heat (q5) which is components of the cooling load were calculated. In addition, amount of the cooling fluid was calculated and choosing of the compressor, the condenser and the evaporator were explained.Key words: Cold storage, cooling load, compressor, condenser, evaporatorINTRODUCTIONCooling can b

4、e defined as the decrease of temperature of a substance or medium below temperature of its environment (Anonymous, 2001). Refrigeration is a process of lowering the temperature and maintaining it in a given space for the purpose of chilling foods, preserving certain substances, or providing an atmos

5、phere conductive to bodily comfort. Storing perishable foods, pharmaceuticals, or other items under refrigeration is commonly known as cold storage. Such refrigeration checks both bacterial growth and adverse chemical reactions that occur in the normal 1999 ). Taner (1987) and Aybers (1992) stated t

6、hat the choice of the ideal cooling system requires good calculation load and all sources of cooling load must be take into consideration. According to Erol (1993), determination of all inputs of cooling load would not be possible, for this reason there may be some deviations in the cooling load and

7、 the focus point must be minimizing the deviation.It is explained that the ambient temperature of cold storage, the situation of stored product before entering to the cold store, the daily working hours and the determination of which product will be stored are important for calculation of the coolin

8、g load (Anonymous, 1994). The capacity of the compressor must be enough to suck and to pump the cooling gas to the compressor (Savas, 1987).Preparing of an investment plan and feasibility analyses for the cold storage must be first to design a cold store. The location of the cold storage, the distan

9、ce of the storage to the stored product, transportation, distance to market, the decision about products to be stored and aim of the cold storage must be determined. The objectives of constructing a cold storage must be to design it not only for a specific product but also for different kind of prod

10、ucts. The design of some small cold rooms instead of a big cold storage a due to the impossibility of cold storage of more than one product minimizes the energy cost and unforeseen.For the calculation of the cooling load of the environment, detailed construction design information used as cold store

11、 and meteorological conditions are required. The steps given below must be followed (Anonymous, 1998c).Data collection: Building characteristics (construction materials, building size, colour of the outside of the building and shape), location of building (obtained from the construction plan), outsi

12、de environment conditions, meteorological data, approved outside environment conditions for the project), interior environmental project conditions (dry and wet thermometer temperatures, amount of the ventilation), management strategy, operating date and time must be selected.J. Applied Sci., 8 (5):

13、 788-794,2008Data usage: After collecting the related data, the cooling load may be calculated according to the determined environmental conditions.In this study, the way of calculation of the cooling load for the design of cold storage and the selection of the cooling system elements are tried to b

14、e explained. How to design a cold storage is explained by the use of different literatures. CALCULATION OF COOLING LOADWhile determining the outside temperature for calculation of cooling load, the average temperature of the hottest month in the year is taken into account. In order to calculate the

15、heat load in cold storage, the heat amount of the produced heat by all sources should be determined and summed. The load of the heat consists of the transmission heat( q.), infiltration heat( ), products heat( q.), other heat sources (q4) and unknown and unexpected heat (q5) for the calculation of t

16、he cooling load (Ozkol, 1999). Calculations were realized according to the above given explanations. Transmission heat (ql): The calculation of the transmission heat created by walls, floor and ceiling requires information on thickness and type of isolation material used in construction of cold room

17、, construction of building, physical specifications of the cold storage volume, inside and outside environment temperatures and the effect of sunshine. Following equations were used to calculate transmission heat (Taner, 2005; Anonymous, 1996b, 2001). Where: = Heat transmission at flat surface (W) K

18、 = Total heat transmission coefficient () A = Area of heat transmission () = Temperature of outside or neighbour volume (K) = Inside volume temperature (K) （2） Where: = Coefficient of heat transmission of outside surface()= Coefficient of heat transmission of inside surface () = Material thickness (

19、rn) = Thermal conductivity ()Heat transmission coefficients can be selected from different literatures such as Ozkol (1999) and Anonymous (2001 ). Following equation is used for practical calculations (Taner, 2005). (3)Main effective factor on overall heat transmission coefficient (K) is thermal con

20、ductivity () and material thickness. The effect of other factors can be generally neglected. Thicknesses of isolation materials determine due to investment and management costs. K overall heat transmission coefficient can be taken between 0.25 and 0.06. The calculation of outside temperature is dete

21、rmined according to the hottest month of the year. However, a smaller value of the outside temperature may take into account because of economical reasons. Through benefiting from the information of long-term temperature data, calculated outside temperatures, wet and dry temperature data are also gi

22、ven by Ozkol (1999). Infiltration heat ():The infiltration heat load is defined as the value obtained through the entrance of the air with a higher enthalpy to the cold stoeage.Some structural deformations such as windows, doors and walls, which cause to air leakage may occur. Air leakage create add

23、itional heat load during the cold storage. This heat load can be calculated by using following equation (Erol, 1993; Anonymous, 1998c). (4)Where: = Heat produced by air changing and leakage air () = Specific heat of humid air (1300) (Erol, 1993) = Daily number of air exchanging (Erol, 1993; Anonymou

24、s, 2001) = Volume of cold storage () = Storage temperature (K) Product heat (): The most important factor for the determination of the inside temperature is the purposeof the cold storage use. Inside temperature required for cooling is defined as storage temperature (Erol, 1993).The fact that some s

25、tored products contain water in their structure, cause to some changes such as the decrease of the temperature during storage, the condensation of water vapour, water and liquid freezing, heat outcome if any chemical reaction takes place.J. Applied Sci., 8 (5): 788-794,2008Stored product which conta

26、in water in their structure create heat load by losing their latent heat while condensation or freezing.It is known that stored products especially fruits, vegetables continue their vitality after harvesting and they diffuse heat as a result of some chemical reactions to their environment during thi

27、s period (Erol, 1993; Anonymous, 1998b; Cemeroglu et al., 2001). If cold stored materials are placed into plastic or wooden boxes, heat load of these boxes must be taken into consideration. Equation 5 calculates heat load created by cold stored product (Cemeroglu et al., 2001). （5）Where: = Heat prod

28、uced by cooling above freezing points (W) = Heat must be taken during freezing (W) = Deep cooling after freezing of cold stored product (W) = Maturation heat (W)Cooling may be classified as short-term cold storage and long-term cold storageCalculation of heat load pre-cooling above freezing point ()

29、: Pre cooling lengthen storage time after making the product wait for 24 h in a cold room. The amount of heat, which must be taken from stored product to decrease its temperature to cold rooms temperature and heat used to decrease temperature of stored product from t1 to t2, can be calculated with t

30、he following equation.Where:q31 Heat produced by cold stored product (W) G Amount of the stored product (kg) CI Specific heat up to product freezing (kJ kg-I K) (Anonymous, 1998b, 2001)T cut Outside temperature (K) T, Inside temperature (K) M, Cooling time (h) LF Loading factor Products may be place

31、d into pre-cooling rooms before being placed into storages. The great differences between the temperature of the product and the storage cause to excessive work of evaporators. This is taken into consideration as loading factor during the calculation of cooling load. The loading Factor is only requi

32、red for cold stores which has a pre-cooling room. Weight of the daily boxes entered to cold store is calculated as follows: (7)Where: = Total number of boxes for a cold store = Weigh of a box (kg)Heat produced while freezing (q32)Where:Heat produced while freezing (W) Freezing heat of stored product (J kg-I) Freezing time (h) (Anonymous, 1998a) Deep cooling after freezing (q33)Where:q3J Deep fr