Design, Manufacturing of Chilled Water System for Process Cooling Application

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IJSTE - International Journal of Science Technology & Engineering Volume 2 Issue 11 May 2016 ISSN (online): 2349-784X Design, Manufacturing of Chilled Water System for Process Cooling Application

1 IJSTE - International Journal of Science Technology & Engineering Volume 2 Issue 11 May 2016 ISSN (online): X Design, Manufacturing of Chilled Water System for Process Cooling Application Prof. Gaffar G. Momin Akshay Gawade Vikram Jadhav Rohan Chaskar Abstract Our aim is to design a custom built water chiller system. The concept or methodology used in the design of water chiller. In vapor compression system there are four major components: evaporator, compressor, condenser and expansion device. Power is supplied to the compressor and heat is added to the system in the evaporator, whereas in the condenser heat rejection occurs. Heat rejection and heat addition are dissimilar to different refrigerants. A standard vapor compression cycle consists of four processes reversible adiabatic compression from the saturated vapor to the compressor pressure followed by a reversible heat rejection at constant pressure causing de-superheating and condensation. This is further extended to an irreversible expansion at constant enthalpy from saturated liquid to evaporator pressure and there after a reversible heat addition at constant pressure causing evaporation to saturated vapor. The main advantages of this design system are that the flow of water can be controlled. Keywords: Vapour Compression cycle, Evaporator, ScrollCompressor and Condenser,COP I. INTRODUCTION A chiller is a machine that removes heat from a liquid via a vapour-compression or absorption refrigeration cycle. This liquid can then be circulated through a heat exchanger to cool air or equipment as required. Vapour compression chillers are popular for wine and water chilling. Concerns in design and selection of chillers include performance, efficiency, maintenance, and product life cycle environmental impact. II. DESIGN Evaporator A plate heat exchanger is composed of a number of plate elements each of which comprises two thin nested plates, the elements defining flow spaces between them, adjacent elements being joined around their periphery by brazing bent edge portions, there being brims extending from the edge portions of each plate element, each brim being spaced from the brims of adjacent plate elements. Fig. 1: Plate type heat exchanger (Evaporator) All rights reserved by 289

2 Given Specifications:- REFRIGERANT USED : R-22 WATER TEMPRETURE REQUIRED T= 4 DEGREES FLOW RATE :12,323 LPH CAPACITY : 25,293 WATT EACH COMPRESSOR : SCROLL TYPE CONDENSER : SHELL AND TUBE (WATER COOLED) EVAPOURATOR : BRAZED PLATE HEAT EXCHANGER REFRIGERANT CHARGED :16.7 kg STEP 1:- R22 inlet temperature - 2 Temperature reduction ( t) 4K Energy balance equation is given by, Design, Manufacturing of Chilled Water System for Process Cooling Application Q = m wcpw (Twi Two) Q = KW Q = 16.30TR 16TR Q = 57 KW Q = m c c pc (T co T ci) 57 = (T co (-2)) T co = -0.5 Logarithmic mean temperature difference (LMTD), Condenser design: Refrigerant R22 Evapourating temperature -2 Condensing temperature 40 Inlet temperature of water 32 Outlet temperature of water 36 For preliminary design, the assumed values for the shell and tube condenser are No. of passes 4 No. of tubes 36 I.D. of copper tube -16mm O.D. Of copper tube- 19mm p-h Diagram For the refrigeration cycle of the designed evaporator, p-h and T-s diagrams were created. They were created using the values calculated above and are shown below. All rights reserved by 290

3 Fig. 2: p-h Diagram Heat rejection ratio = Heat Rejected to Condenser is given by, = (16+3) = KW Condensing coefficient is given by, h cond= the density and latent heat of vapourizationh fg at kg/m 3 h fg= J/kg K= W/mK = pa-s Pr = t = 40 2 = 6 0 C The average no. of vertical tubes in a vertical row N is given by, =3.6 h cond= = W/m 2 K Conductivity of copper is 390 W/mK and resistance of tube is Fouling factor is given by, Water Side Coefficient: The Flow Rate of Water = x 10-6 m 2 K/w K/w Volume flow rate is = 4.1 kg/s Velocity of water through tubes = m 3 /sec All rights reserved by 291

4 V = Properties of water at 29 /m3 = 8.15 x 10-4 pa-s C p = 4180 J/kg.K K= W/mK Water Side Heat Transfer Coefficient Is Given by, =2.23 m/s hw Overall Heat Transfer Coefficient is, h w= W/m 2 K Logarithmic Mean Temperature Difference is Outside Tube surface area is, = W/m 2 k LMTD = = = U 0A 0 Length of tubes are A =10 m 2 = ft 2 L = For condenser, Shell diameter No. of tubes Outer tube diameter Length of tube L=5 m COP calculation: Inner tube diameter L = = 4.64m = 16 ft COPcarnot = COPsystem = = = = 5.36 Since the theoretical coefficient of performance is less than Carnot coefficient of performance, the design unit is achievable. All rights reserved by 292

A scroll is an involutes spiral mounted on a flat plate.

5 Compressor Fig. 3: Shell & Tube condenser The compressor used in our system is hermetically sealed scroll compressor. The scroll compressor is a rotary positivedisplacement machine used at present in small (535kW) air conditioning and heat pump units, and car air conditioning systems. A scroll is an involutes spiral mounted on a flat plate. The scroll set comprises two scrolls: one is fixed and the other, phased 180 C from the first, moves around a fixed point on the fixed scroll (translates). As the moving scroll translates, gas enters the space between the scrolls at the edge of the scroll set. Further motion traps the gas in a crescent-shaped pocket formed between scrolls and propels the gas towards the centre of the scroll set. As the gas moves inwards, the volume of the pocket is reduced and the gas is compressed. Eventually the discharge port is uncovered and compressed gas is discharged. As several compression processes are in progress all the time, the gas flow is much smoother than in a piston type where the process is discontinuous. Small scroll compressors offer several important manufacturing as well as performance advantages over reciprocating compressors. This is reflected in the worldwide trend to substitute reciprocating by rotary compressors in small capacity air-conditioning, heat pump systems and supermarket compressor packs. Fig. 4: Scroll Compressor All rights reserved by 293

6 Assembly Drawing Fig. 5: Assembly Actual Assembly Fig. 6: Assembly Photograph III. CONCLUSIONS The main perspective of the project was to design a custom built unit which could achieve temperature as low as 100C without the making the system design intricate. We have achieved the required temperature with the help of conventional vapour compression system concept. In the newly designed system we have replaced the shell and tube type evaporator with plate type evaporator. This system allows to control the flow of water as per company requirement. This in turn helps in improving the efficiency and productivity of the company All rights reserved by 294

7 The existing system works on R22 currently, considering the present scenario of global warming potential and Montreal Protocol, the refrigerant production is estimated to stop by 2020, hence other compatible refrigerants such as R417a, R404a, R438a could be used. One advantage of the system is that, we do not require to change the components of system to a major extent, only a few minor changes in the system will make it ready for use in case of the retrofit refrigerant. Lastly optimization of material weight and cost would make the energy savings and take the system performance to new heights. REFERENCES [1] Kern, D.Q., Process Heat Transfer, McGraw-Hill, New York, [2] Taborek, J., Evolution of heat exchanger design techniques, Heat Transfer Eng. 1, No. 1, (1979). [3] Perry, R.H., Green, D.W., Eds. Perry s Chemical Engineers Handbook, 7th Edition, McGraw-Hill, New York, [4] Phadke, P.S., Determining tube counts for shell-and-tube exchangers, Chemical Engineering, September 3, 1984, pp [5] Effectively Design Shell-and-Tube Heat Exchangers FEBRUARY 1998 Copyright 1997 American Institute of Chemical Engineers [6] NPTEL Chemical Engineering Chemical Engineering Design - II Joint initiative of IITs and IISc Funded by MHRD- Module #1 PROCESS DESIGN OF HEAT EXCHANGER: TYPES OF HEAT EXCHANGER, PROCESS DESIGN OF SHELL AND TUBE HEAT EXCHANGER, CONDENSER. [7] Keshwani, H.B. and Rastogi, K.V., Optimum inter-cooler pressure in multistage compression of refrigerants, All India Symposium on Refrigeration, Air- Conditioning and Environmental Control in Cold Storage Industry, (1968), pp. E [8] Arora, C.P. and Dhar, P.L., Optimization of multistage refrigerant compressor, Progress in Refrigeration Science and Technology, XIII International Congress of Refrigeration (IIR), (1973), pp [9] Prasad, M., Optimum interstage pressure for two stage refrigeration system,ashrae Journal, Vol. 23, (1981), pp [10] Kumar, S., Prevost, M. and Bugarel, R., Exergy analysis of a compression efrigeration system, Heat Recovery Systems and CHP, Vol. 9(2), (1989), pp [11] McGovern, J.A. and Harte, S., An exergy method for compressor performance analysis, International Journal of Refrigeration, Vol. 18(6), (1995), pp All rights reserved by 295

Gandhinagar Institute of Technology Mechanical Engineering (Thermal Engineering) Semester II. Design of Heat Exchange Equipments [ ]

Gandhinagar Institute of Technology Mechanical Engineering (Thermal Engineering) Semester II. Design of Heat Exchange Equipments [ ] Experiment 1 Study of fundamentals of Fluid Flow and Heat Transfer associated with Heat Exchangers Review questions (1) Significance of dimensionless numbers. (2) Define overall heat transfer coefficient.