Liquid Cooling System

Liquid Cooling System Akshaykumar Govind Wanjari 1 Student, Dept. of Mechanical Engineering, Jawaharlal Darda Institute of Engineering & Technology, Yavatmal, India. E-mail:akshaywanjari15@gmail.com Ashish Satish Wankhade 2 Student, Dept. of Mechanical Engineering, Jawaharlal Darda Institute of Engineering & Technology, Yavatmal, Maharashtra, India. E-mail: aashish.w23@gmail.com Abstract Advancement of technology in electronics leads to reduced size of system and machinery which also leads to an increased heat flux density of the components of the system. Traditionally used techniques of coping up with the increased heat flux and cooling the system like the forced air techniques prove to be unreliable and also costly. There are advanced techniques and options available in the form of Liquid cooling systems for appliances like desktop computers. Usage of liquids with high specific heat capacity like water can absorb a very large amount of heat with relatively low rise of temperature. Liquid coolants are much more effective and efficient way of cooling and are reliable in terms of care and safety of components of the appliances. Efficiency of this technique is checked at various levels to determine the minimum, maximum and average cooling requirements. This paper gives details about the experimental analysis and study of Liquid Cooling System and its applications. Keywords: Electronic, CPU, Heat Exchanger, Motherboard, Reservoir, Cooling, Pump, Processor, Tubes. 1. INTRODUCTION: With the rapid development of electronic technology, electronic appliances and devices now are always ever-present in our daily lives. However, as the component size shrinks the heat flux per unit area increases dramatically. The working temperature of the electronic components may exceed the desired temperature level. There are a number of methods in electronics cooling, such as jet impingement cooling [1,2] and heat pipe [3-5]. Conventional electronics cooling normally used forced air cooling with heat sink showing superiority in terms of unit price, weight and reliability while liquid cooling systems show superiority in terms of performance. At present, heat released by the CPU of a desktop and server computer is 80 130 W and of notebook computer is 25 50 W [6]. In the latter case, the heating area of the chipset has become as small as 1 4 sq.cm. This problem is further complicated by both the limited available space and the restriction to maintain the chip surface temperature below 100 C [7]. It is expected that conventional cooling fan system will not be able to meet the thermal needs of the next generation computers. Every component in a computer consumes electric power. In general, the faster a component performs its function, the more electric power it needs. But computer components consume the electric power very inefficiently, and the majority of the power input is wasted as heat with only a small portion being used for data generation [8]. 98

The speed of the central processor (CPU), 3D-graphic card, and hard disk drive (HDD) has continually increased in the last few years. And, HDD has reached a speed of 15,000 RPM, and every component of the computer has to deal with heat dissipation to some extent [9]. The heat generation in all computer chip-sets occurs due to switching between 0 and 1, which requires power consumption. On the other hand, heat is generated by the rotational motion in HDD and CD-ROM devices [10]. Nowadays, as the sizes of chipsets are being reduced, the rate at which the heat has to be transferred per unit area has also increased. Hard disk drive, CD-ROM, Graphics card, Sound card and Processor are the major heat sources inside the CPU. The cooling system includes the basic design components of the system include a heat exchanger, reservoir, micro-pump, tubing, fan and coolant. In this paper the various mathematical calculations are used. In this paper the different types of cooling systems were studied and compared as well. The liquid cooling system was studied in terms of performance as well as in terms of design, cost and reliability. A simple, reliable and economical cooling system was designed to meet the cooling requirements of a desktop computer. Measurements of the temperature distributions of different heat sources inside a computer system have been studied in this paper. Also an investigation of the optimum cooling condition for the computer system has also been made. Various Thermal Performance Parameters have been calculated as presented herein. In this paper the Prandtl number, Reynolds number as well as Nussels number are also studied in order to achieve the required cooling systems. In this paper the various components of the liquid cooling systems are studied as well as used in the systems. Also the working of the various cooling components are studied as well as given in the paper with the brief explanation as well as the Fig. 2.1. In this type of liquid cooling system separate flexible connecting tubes (1/2 ) to be used in connecting the different components. The separate flexible connecting tubes are of copper tubes.preferred option for the assembly of cooling system was to use a single copper tube to make the part of the system inside the CPU. This method obviates the problem of leakage and elimination of joints, leads to smooth flow with lower frictional head loss. Also there are advanced techniques and options available in the form of Liquid cooling systems for appliances like desktop computers. Usage of liquids with high specific heat capacity like water can absorb a very large amount of heat with relatively low rise of temperature. Liquid coolants are much more effective and efficient way of cooling and are reliable in terms of care and safety of components of the appliances. Also the use of liquid coolants is that their high specific heat capacity is of importantly used in this system. Efficiency of this technique is checked at various levels to determine the minimum, maximum and average cooling requirements. Hence, by using this technique liquid cooling system is studied. So this cooling system gives details about the experimental analysis and study of Liquid Cooling System and its applications. 99

2. COOLING SYSTEM DESIGN: The cooling system design is elaborated as follows: 2.1. COMPONENTS OF LIQUID COOLING SYSTEM: The basic design components of the system include a heat exchanger, reservoir, micro-pump, tubing, fan and coolant. A submersible type of the pump, having a head of 2-3m and inlet and outlet diameter of 0.5 is selected to fulfill the required design criteria. A flexible leak proof tubing of diameter 3/16 is selected which should adjust to passages in the motherboard. A fin type radiator of small size having high effectiveness has been selected so that it can allow the heat exchange between air and coolant. A high speed fan of 2000rpm having diameter of 10-12cm has been selected. A leak proof reservoir is selected to house the pump. Fig. 2.1: Components of Liquid Cooling System Going through the various literatures, this type of heat exchanger design has been selected for the cooling system in desktop. 2.2. THE WORKING OF LIQUID COOLING SYSTEMS: Fig. 2.2: Design of Pipe For fulfilling the requirement of fan in radiator, the CPU fan was used. Water was chosen as the coolant to be used in the present design model. Submersible axial micro pump was chosen because 100

it was easily available in the market and at a reasonable price and it was suitable for our design. Submersible pump was chosen because it would be kept in the reservoir and thus would require less space. Copper tubes (3/16 ) are used in critical heat source areas because of its high thermal conductivity. Separate flexible connecting tubes (1/2 ) to be used in connecting the different components. The number of passes around the heat source areas would be maximized to effect greater cooling. Preferred option for the assembly of cooling system was to use a single copper tube to make the part of the system inside the CPU. This method obviates the problem of leakage and elimination of joints, leads to smooth flow with lower frictional head loss. 3. SPECIFIC HEAT CAPACITY AND USAGE OF WATER: Every material has a tendency to absorb the surrounding heat and increase its temperature. The amount of heat energy a unit mass of the substance absorbs for a rise of 1 degree Kelvin of its absolute temperature is called as the specific heat capacity of that substance.the more is the value of Specific heat capacity of a substance, the more energy it requires to raise its temperature by a degree Kelvin. Fig. 3: Set Up Of Liquid System The specific heat capacity of water is very high, and is 1 cal/g-degc. Hence usage of water as a coolant in the Liquid cooling system enables absorption of a very large amount of heat without much rise in the temperature. The copper pipes being flexible and thin, the transport of heat by conduction from the outer surface to the inner one and then to the water becomes easy and effective. 4. MATHEMATICAL CALCULATIONS: Mathematical Calculations for thermal parameters: Diameter of copper tubes, d= 3/16" = 0.0047625 m Radius of copper tubes, r = d/2 = 0.00238m Cross-sectional area of tube, A = r 2 = 0.0000178 m 2 Calculation of water velocity in tubes: Q = A x v (4.1) v = Q/A = 0.295 m/s Calculation of Reynolds number for flow inside the tube: Properties of water:- Density = 1000 kg/m 3 Dynamic (absolute) viscosity, μ = 0.001 N-s/m 2 Reynolds number, Re = vd/μ = (1000 x 0.295 x 0.0047625)/0.001 = 1404.9375 (4.2) 101

As the value of Re < 2000, thus, the flow is laminar. Calculation of Frictional head loss inside tube Darcy friction factor for laminar flow is given by, Laminar = 64/ Re = 0.04555 The frictional head loss in the copper tubes is given as, phf = (laminar x L x v2 )/(2gd) = 0.2325 m (4.3) Calculation of heat absorbed by the water flowing in the tubes: Q = m x c x T = 65.9604 J/s (4.4) Calculation of Inner and Outer surface temperatures of the pipe: For Internal flow of water inside the copper tube, we have, Nussle s number Nu, for fully developed laminar thermal layer = 3.66, Thermal conductivity of water, k = 0.667 W/m-K hw = Nu x k/d = 512.592 W/m 2 -K (4.5) For external flow of air over the tubes we have, Air flow rate= 0.0046 m3/sec (Obtained from fan specifications), Diameter of fan=6cm; Swept area of fan = 0.00283 m 2 Re over pipe=vl/μ= 1.85 x 104 (4.6) Nu = c RemPr0.333; Where, c= 0.193; m=0.618 Prandtl Number, Pr= μcp/k (4.7) Where, μ= 1.846 x 10-5 kg/m-sec; Cp= 1.008 KJ/kg-K; k= 0.0262 W/m-1K-1; Pr= 0.707 Nu = c RemPr0.333=0.193 x (1.85 x 104)0.618 x 0.707 0.333= 74.563 ha = Nu x k/d = 410 W/m 2 -K (4.8) Conduction equation for hollow cylindrical pipe: hw x Ai x (Ti-Tw) = ha x Ao x (Ta-To) = k x 2_L x (To-Ti) (4.9) Where, Tw is average temperature of water (300.5 K), Ta is temperature of air (308 K), Ai = 2_riL, Ao = 2_roL, L is length of heat exchanger tube (2.13m). From the above eq., Ti and To, were found out to be 31.51 C and 31.51 C respectively. Calculation of heat flow from air into tube: Q= ha x Ao x (Ta-To) = 64.65 W (4.10) COP of the system is given by: COP = (heat removed by the system / Power used by the pump) = 64.65/12 = 5.387 (4.11) 5. SUMMARY/RESULT: The experimentation was conducted on a computer system having specifications as Model: HP-dx2280 MT (RR043Av), Chipset: Intel, Processor: Pentium D 2 CPU 3.4 GHz and 2.37 GHz, Physical Memory: 1.49 GB RAM, Hard disk: 160 GB and Graphics: VGA integrated. The following observations are noted before the inclusion of the cooling system in the CPU and after inclusion of the cooling system in the CPU. The data has been tabulated at high loading condition (CPU usage 75-85 %) and comparison is shown. 102

SR. NO TABLE I COMPARISON OF MOTHERBOARD HEAT SINK TEMPERATURES TEMPERATURE WITHOUT COOLING SYSTEM (DEG CELSIUS) Temperature with cooling system (DegCelcius) 1 39.0 33.4 2 42.3 32.2 3 41.6 34.5 4 40.2 33.6 5 43.5 34.0 6 41.3 32.0 AVERAGE 41.32 33.45 TABLE II COMPARISON OF PROCESSOR CORE TEMPERATURES SR. NO TEMPERATURE WITHOUT COOLING SYSTEM (DEG. CELCIUS) TEMPERATURE WITH COOLING SYSTEM (DEGCELCIUS) CORE 1 CORE 2 CORE 1 CORE 2 1 48.0 52.3 36.7 38.4 2 51.0 50.6 35.8 36.5 3 50.4 51.0 38.2 38.2 AVERAGE 49.8 51.3 36.9 37.7 SR. NO TABLE III COMPARISON OF HARD-DISK TEMPERATURES TEMPERATURE WITHOUT COOLING SYSTEM (DEGCELCIUS) TEMPERATURE WITH COOLING SYSTEM (DEGCELCIUS) 1 52.0 41.2 2 53.4 41.5 3 49.8 39.9 4 48.5 40.2 AVERAGE 50.93 40.7 SR. NO TABLE IV COMPARISON OF PROCESSOR HEAT SINK TEMPERATURES TEMPERATURE WITHOUT COOLING SYSTEM (DEG CELSIUS) TEMPERATURE WITH COOLING SYSTEM (DEG CELSIUS) 1 49.6 41.3 2 50.2 41.5 3 48.9 42.3 4 49.0 43.4 AVERAGE 49.43 42.13 103

SR. NO. TABLE V COMPARISON OF RAM TEMPERATURES TEMPERATURE WITHOUT COOLING SYSTEM (DEG CELSIUS) TEMPERATURE WITH COOLING SYSTEM (DEG CELSIUS) 1 38.3 36.7 2 40.2 32.0 3 39.4 35.3 4 38.0 36.2 AVERAGE 38.98 35.05 It is evident from the above tables that there is great reduction in the temperature achieved in all heat sources of CPU after using the properly designed cooling system. It is a great achievement that after inclusion of the cooling system in the CPU of desktop, huge reduction of Hard disk temperature was found. 6. CONCLUSIONS: Different types of cooling systems were studied and compared. Liquid cooling systemwas found to be most effective in terms of performance but not in terms of design, cost and reliability. A simple, reliable and economical cooling system was designed to meet the cooling requirements of a desktop computer. Measurements of the temperature distributions ofdifferent heat sources inside a computer system have been made. An investigation of the optimum cooling condition for the computer system has also been made. Various Thermal Performance Parameters have been calculated as presented herein. There was a significant improvement in the thermal conditions inside the computer that lead to an ameliorated performance. A noticeable temperature drop in hard disk was attained with the help of the cooling system. 7. REFERENCES: [1] Y. Chung and K. Luo, Unsteady heat transfer analysis of an impinging jet, J. Heat Transfer, 124 (2002) 1039-48. [2] K. Nishino et al., Turbulence statistics in the stagnation region of an axis symmetric impinging jet flow, Int. J. Heat Fluid Flow, 17 (1996) 193-201. [3] K. Kim et al., Heat pipe cooling technology for desktop PC CPU, Appl. Therm. Eng. 23 (2003) 1137-44. [4] Y. Wang and K. Vafai, An experimental investigation of the thermal performance of an asymmetrical flat plate heat pipe, Int. J. Heat Mass Transfer, 43 (2000) 2657-2668. [5] Z. Zhao and CT. Avedisian, enhancing forced air convection heat transfer from an array of parallel plate fins using a heat pipe, Int. J. Heat Mass Transfer, 40 (13) (1997) 3135-47. [6] Mochizuki M, Saito Y, Wuttijumnong V, Wu X, Nguyen T (2005) Revolution in fan heat sink cooling technology to extend and maximize air cooling for high performance processors in laptop/desktop/server application. In: Proceedings of IPACK 05, San Francisco [CD ROM] [7] Saucius I, Prasher R, Chang J, Erturk H, Chrysler G, Chiu C, Mahajan R (2005) Thermal performance and key challenges for future CPU cooling technologies. In: Proceedings of IPACK 05, San Francisco [CD ROM] [8] E. van Ballegoie, Fast graphics-cooling, (2000) 104. [9] S. S. Lee, Zero & One, Hello PC, (July, 2000). [10] D. H. Min, HDD and VGA Cooling Solution, Korea Benchmark, (February, 2000). [11] M.M. Shete and Prof. Dr. A. D. Desai, Design and Development of Test-Rig to Evaluate Performance of Heat Pipes in Different Orientations for Mould Cooling Application, International Journal of Mechanical Engineering & Technology (IJMET), Volume 3, Issue 2, 2012, pp. 360-365, ISSN Print: 0976 6340, ISSN Online: 0976 6359. 104

[12] Kapil Chopra, Dinesh Jain, Tushar Chandana and Anil Sharma, Evaluation of Existing Cooling Systems for Reducing Cooling Power Consumption, International Journal of Mechanical Engineering & Technology (IJMET), Volume 3, Issue 2, 2012, pp. 210 216. AUTHOR S BRIEF BIOGRAPHY: Ashish Satish Wankhade, Student of Mechanical Engineering at Jawaharlal Darda Institute of Engineering and Technology, Yavatmal. He has presented several papers at National and International conferences. He is member of several bodies such as ISTE, MESA. Akshaykumar Govind Wanjari,Student of Mechanical Engineering at Jawaharlal Darda Institute of Engineering and Technology, Yavatmal. He has presented several papers at National and International conferences. He is member of several bodies such as ISTE, MESA. 105