Thermodynamic (energy-exergy) analysis of pre-cooled linde system

Transcription

1 International Journal of Research in Engineering and Innovation Vol-1, Issue- (17), 1-6 International Journal of Research in Engineering and Innovation (IJREI) journal home page: ISSN (Online): 6-69 Thermodynamic (energy-exergy) analysis of pre-cooled linde system R. S. Mishra, Devendra Kumar Department of Mechanical, Production & Industrial and Automobiles Engineering, Delhi Technological University, Delhi, India Abstract The present studies concern on detailed thermodynamic (energy and exergy analyses) of Pre cooled Linde cryogenic system up to their sub component level. This parametric study is conducted to investigate the effects of variation of various system input parameters such as ratio, expander mass flow ratio, compressor output temperature on different performance parameters like COP, work input,liquefaction rate,specific heat and exergy. The numerical computations have been carried out for Claude system are study with six different gases for liquefaction like oxygen, argon, methane, fluorine, air and nitrogen respectively. It was observed that methane has better thermal performances (first law performance i.e. COP) and exergetic efficiency (second law performance) as compared to other gases. The total net work done decreasing. 17 ijrei.com. All rights reserved Keywords: Thermodynamics Analysis, Collin Cryonic System, Energy-Exergy Analysis, First and second Law Analysis 1. Introduction The term cryogenic is derived from the Greek word Kryos which means cold or frost. It is frequently applied to very low temperature refrigeration applications such as in the liquefaction of gases and in the study of physical phenomenon at temperature approaching absolute zero. The first low temperature refrigeration system was primarily developed for the solidification of carbon dioxide and the liquefaction and subsequent fractional distillation of gases such as air, oxygen, nitrogen, hydrogen and helium. Cryogenic process to liquefy air which is further extent to extract various particular gas like oxygen, nitrogen, feron etc. Always various analyses is done to identify the loop hole of process and to rectify it to their upper level. electro caloric cooling is a transiting to new cooling principle s is critical and one of the most promising alternatives may be [1].Various particular part are taken under study to increase overall performance of cryogenic system e.g. A good exergetic design of a heat exchanger would allow for an increase in the global efficiency of the process, by defining a thermodynamic cycle in which the exergetic losses would be limited [] apart from this other parts like expander, mass ratio and input variables are considered to improve cryo systems. Pre-cooled Linde Hampson system is advanced stage old simple Linde Hampson system.in this system vapour compression evaporator having R1 a refrigerant is taken as additional equipment to fill the gap of simple Linde system. In Fig.1 (a&b) shows the detail block diagram and T-S diagram of Pre-cooled Linde system. Vapor compression system lower down the temperature of gases coming through the compressor which is desirable for better performance of system. The method of cooling the gas after the compression or before the entrance to the heat exchanger is called as precooling. The precooling limit of the precooling cycle is governed by the boiling point of refrigerant at its suction this increment in the yield is dependent on the The change in enthalpy values from (h d h a )of the refrigerant. Refrigerant flow rate (m r ). the heat of compression Q R can be obtained by using nd Law for an isothermal compression. Corresponding author: R.S. Mishra Id:rsmishradtu@gmail.com 1

2 P a = 1.1 P b = 1.1 Adiabatic Compression P c = P b, T a =, T b = 7, T c =,h a = 78, h b =.9, h c = 89.7 "Boiling Temperature of Refrigerant" T d = 7.1 Control Vol having HT, J-T, Separator "Energy Balance by First Law" = r, r =.8 m r m m r h d + m h = m r h a + (m m f ) h 1 + m f h f y = m f m Control Vol having HT,J- T,Seperator Figure 1(a): Schematic of Pre-cooled linde system m h = m f h f + (m m f ) h 6 y max = h 6 h h 6 h f W total = W c1 + W c Compressor work per liquefaction of system E in = E out E in = m h 1 W c1 E out = m h Q R Q R = m T 1 (s s 1 ) Compressor work of ref system Figure 1(b: T-S diagram of Pre-cooled linde system. Mathematic Modelling of "Pre-Cooled Linde Hampson Cycle Working Fluid Properties R$ = oxygen P 1 = 1.1, T 1 = 98, T 1 = T, P = 1, T = T 1 P f = P 1, x =, x 1 = 1, T f = T g, Refrigerant Properties R1 a m r h a W c = m r h b = Z W total m f W total = abs ( T 1 (s 1 s ) m (h 1 h ) + r (h b h a ) ) W i = T m 1 (s 1 s f ) (h 1 h f ) W i = K m f FOM = Z K COP = ( h 1 h f W total ) Eta nd% = abs (( (h f h 1 ) T (s f s 1 ) W total m f ) 1) First Heat Exchanger ( HX_1) analysis TypeHX 1$ = counterflow epsilon HX1 =.8 T co = 9, T hi = T 1, T 1 = T co m hhx1 = m, m chx1 = m m f T ho = T, T ci = T 9 C hhx1 = m hhx1 cp fluidhx1 C chx1 = m chx1 cp fluidhx1 q HX1 = C hhx1 (T hi T ho ) q HX1 = C chx1

3 q_max _HX1 = C_min _HX1 (T_h_i T_c_i) epsilon_hx1 = q_hx1/q max. HX1 Ntu HX1 = HX(TypeHX 1$, epsilon HX1, C hhx1, C chx1,. Ntu ) Ntu_HX1 = (G_HX1)/C min. HX1 Ed HX1 = (T ((s + s 9 ) (s + s 1 ))) Second Heat Exchanger (HX_) analysis TypeHX $ = counterflow epsilon HX =.8 m hhx = m m chx = m m f C hhx = mh HX cp hotfluidhx C chx = m chx cp coldfluidhx q HX = C hhx (T T ) q HX = C chx (T 9 T g ) q_max _HX = C_min _HX (T_ T_g) epsilon_hx = q_hx/q max. HX Ntu HX = HX(TypeHX $, epsilon HX, C hhx, C chx,. Ntu ) Ntu_HX = (G_HX)/C min. HX Ed HX = (T ( (s + s g ) (s + s 9 ) )) In Non-ideal gas any variable can be defined by two other dependent variable on them a non ideal gas = fx(b, c) Table: 1 Variable Table (Pre-cooled Linde system) Variable (a) Gas Variable (b) Variable (c ) h R$ T P 1 h 1 R$ T 1 P 1 h R$ T P s R$ T P 1 s 1 R$ T 1 P 1 s R$ h P s f R$ x f T f T f R$ x P 1 h f R$ x f T f s g R$ x 1 P 1 h g R$ x 1 T g s R$ T P h R$ T d P s 9 R$ T 9 P 1 s 1 R$ T 1 P 1 cp(fluid) HX1 R$ T P cp(cf) HX1 R$ T 8 P 1 C min - C hot_hx1 C cold_hx1 cp(hf) HX R$ T P cp(cf) HX R$ T g + 1 P 1 C min - C hot_hx C cold_hx h 6 R$ h d P 1 s R$ T P s R$ T P. Result and Discussion Fig. illustrates the variations in COP and second law efficiency with compressor. It has been observed that methane has the highest COP and second law efficiency among the other gases, i.e at bar and 7.7% at bar. Fig. illustrates the variations in liquefaction mass flow rate with the compressor from to bar. It has been noticed that methane has the highest liquefaction mass flow rate, i.e..78kg/s to.kg/s followed by other considered gases COP m f (Liq mass)(kg) Figure : Variation in COP and second law efficiency with the compressor COP oxygen COP argon COP methane COP Nitrogen h nd,% oxygen h nd,% Argon h nd,% Nitrogen m f (Oxygen) m f (Methane) m f (Argon) m f (Fluorine) m f (Air) m f (Nitrogen) Air COP h nd,% Methane h nd,% Fluorine h nd,% Air COP Fluorine Figure : Variation in liquefaction mass flow with compressor hnd,%

4 cp hf(hx1) (kj/kg-k) W total (Net work done)(kj/kg) W net (Oxygen) W net (Argon) W net (Methane) W net (Fluorine) W net (Air) W net (Nitrogen) Figure : Variation in total net work done with compressor cp hot,fluid,hx1 (Oxygen) cp hot,fluid,hx1 (Argon) cp hot,fluid,hx1 (Methane) cp hot,fluid,hx1 (Fluorine) cp hot,fluid,hx1 (Air) cp hot,fluid,hx1 (Nitrogen) 1 Figure : Variation in specific heat of hot fluid in HX1 with compressor cp hf(hx) (kj/kg-k) NTU HX cp hot,fluid,hx (Oxygen). cp hot,fluid,hx (Argon).8 cp hot,fluid,hx (Methane).6 cp hot,fluid,hx (Fluorine). cp hot,fluid,hx (Air) 1.8 cp hot,fluid,hx (Nitrogen) Figure 6: Variation in specific heat of hot fluid in HX with compressor NTU HX1 (Oxygen) NTU HX1 (Argon) NTU HX1 (Nitrogen) NTU HX1 (Air) NTU HX1 (Methane) NTU HX1 (Fluorine) Figure 7: Variation in NTU in HX1 with compressor

5 NTU HX Table (a) Various performance parameters on optimum Temperature (K) and P_ (1 bar) Gases COP Eff. ηnd % Table (b) Various performance parameters on optimum Temperature (K) and P_ (1 bar) Table (c) Various performance parameters on optimum Temperature (K) and P_ (1 bar) Edest (HX1) (kj/kg) Edest (HX) (kj/kg) Oxygen Argon Methane Fluorine Air Nitrogen Gases COP Efficiency m_f kg/s FOM ηnd % Oxygen Argon Methane Fluorine Air Nitrogen Gases COP Efficiency ηnd % NTU (HX1) NTU (HX) Oxygen Argon Methane Fluorine Air Nitrogen NTU HX (Argon) NTU HX (Air) NTU HX (Methane) NTU HX (Fluorine) NTU HX (Nitrogen) Figure 8: Variation in NTU in HX with compressor Ed HX1 (kj/kg) Ed HX (Oxygen) Ed HX (Argon) Ed HX (Methane) Ed HX (Fluorine) Ed HX (Air) Ed HX (Nitrogen) Figure 9: Variations in exergy destruction in HX1 with compressor Ed HX (kj/kg) 1 1 Ed HX (Oxygen) Ed HX (Argon) Ed HX (Methane) Ed HX (Fluorine) Ed HX (Air) Figure 1: Variation in exergy destruction in HX with compressor

6 The optimum performance parameters at optimum temperature at optimum are shown in Table- respectively. Fig. shows the variation in net work done with the compressor and it has been observed that total net work done decreases with the compressor, and argon has the highest value among other gases. Fig. illustrates the specific heat of hot fluid in HX1 and methane has the largest value of specific heat among the other gases i.e..61kj/kg-k at bar. Fig.6 demonstrates that methane has the highest value of specific heat of hot fluid in HX among the other considered gases, i.e..6kj/kg-k at 16bar. Fig.7 shows that NTU in HX1 continuously decreasing and fluorine has the highest value of NTU among the other gases, i.e..77 at bar. Fig.8 shows the NTU in HX and it has been seen that all the gases has the decreasing trend except air between the prescribed the temperature range of bar to bar. Fig.9 illustrates the exergy destruction rate in HX1 and it has been seen that methane shows the highest value of exergy destruction rate, and its graph first increasing then shows the decreasing trend. Alternatively, all the other gases shows the increasing trend. Fig.1 shows the exergy destruction rate in HX and it has been seen that methane has the highest value, and it is decreasing first up to a certain and then increasing followed by other considered gases. Conclusions Methane has the highest first law efficiency (i.e. COP) and second law efficiency (i.e. exergetic Efficiency) among the other gases. Methane has the highest liquefaction mass flow rate, followed by other considered gases. The total net work done decreases with the compressor, and argon has the highest value among other gases. NTU in the third heat exchanger (HX) for all gases has the decreasing order. Methane shows the highest value of Exergy destruction rate in first heat exchanger (HX1). Methane has the highest value of specific heat of hot fluid in HX among the other considered gases. Exergy destruction rate of methane in the third heat exchanger (HX) has the highest value, and it is decreasing first up to a certain and then increasing followed by other considered gases. Total net work done decreases with the compressor, and argon has the highest value among other gases. References [1] Yu. V. Sinyavskii, Electro caloric refrigerators: A promising alternative to current low-temperature Apparatus, Chemical and Petroleum Engineering, 1(6), 199, 9-6. [] R. Agrawal, D. W. Woodward, Efficient cryogenic nitrogen generators: An exergy analysis, Gas Separation & Purification, (), 1991,