Processor Cooling. Report for the practical course Chemieingenieurwesen I WS06/07. Zürich, January 16,

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1 Proceor Cooling Report for the practical coure Chemieingenieurween I WS06/07 Zürich, January 16, 2007 Student: Francico Joé Guerra Millán fguerram@tudent.ethz.ch Andrea Michel michela@tudent.ethz.ch Aitant: Max Wohlwend HCI D182.5 Neil Oterwalder HCI E105 Abtract Overheating i nowaday a huge challenge for the computer indutry. Without a cooling ytem, working on a computer would be barely impoible, due to the ytem crahing down continuouly. The aim of thi experiment wa to tudy the heat tranfer phenomenon by cooling an Intel c Celeron c D 2.8Ghz proceor by different mean. Thi proceor emitted 17,48 J and 31,95 J and had an efficiency of 76,15% and 70,69% at normal and full load repectively. 1 Two fan cooler (an Intel c original and a Super-Silent), a ThermalTake c heat exchanger, two radiator (black and white) and a water cooling ytem (operated at different flow) were ued. A for the water ytem, a expected, increaing the water flow reult on higher convection coefficient, meaning that the cooling capacity alo increae. It wa alo poible to ee the linear dependency between the flow and the coefficient. Water i by far the bet cooling ytem. After analyzing different cooling device, the Intel c original fan cooler reulted the bet one, followed by a Super-Silent c fan cooler. Surpriingly, a black radiator had a better cooling effect than a ThermalTake c heat exchanger with an implemented fan. 1 Value obtained with the block of copper.

2 Content 1 Introduction and Theory 3 2 Experimental Procedure 5 3 Reult and Dicuion Block of copper Water Cooling Sytem Cooling Device Comparion Concluion and Outlook 11 F. Guerra, A.Michel 2

3 1 Introduction and Theory Overheating i nowaday one of the mot important problem. Not only a a global matter, but alo in our daily live. A an example, computer proceor can reach extremely high temperature and repreent a phyical danger for the final uer. To avoid fire and other damage, computer are programmed to crah down when the proceor reache a certain temperature, cauing coniderable lo of information. Therefore, CPU (Central Proceing Unit) cooling device are eential for computer manufacturer to offer an optimal performance. The aim of thi experiment wa to compare different CPU cooling device by meauring the heat emitted by the proceor at normal and full CPU load. To compare the different heat exchanger, the overall heat tranfer coefficient wa calculated for each device. By uing different cooler it i alo poible to oberve the three different heat tranfer mechanim, known a conduction, convection and radiation. Conduction9 i decribed a the flow of thermal energy through a olid from a higher- to a lower-temperature region. Heat conduction occur by atomic or molecular interaction. Steady-tate conduction i aid to exit when the temperature at all location in a ubtance i contant with time, a in the cae of heat flow through a uniform wall. It can be expreed with the following equation: Q t = ka T (1.1) x where: Q = heat J t = time k = conductivity contant W mk A = tranveral urface area m 2 T = temperature K x = thickne of the body through which the heat i paing m 2 Convection7 i heat energy tranfer between a olid phae and a fluid phae when there i a temperature difference between the fluid and the olid. Convection i a combination of conduction and the tranfer of thermal energy by circulation or movement of the hot particle to cooler area in a material medium. Thi movement occur from, to or within a fluid. Convection occur in two form: natural and forced convection. It can be decribed a follow: where: q = heat flux rate J h = convection coefficient W m 2 K T = urface temperature K T = ambient temperature K q = h (T T ) (1.2) F. Guerra, A.Michel 3

4 Radiation4 i tranfer of heat through electromagnetic radiation in the heat pectrum. All object radiate heat, unle they are at abolute zero. No medium i neceary for radiation to occur; radiation work even in a perfect vacuum. A prime example of thi i the energy of the Sun, which travel through the vacuum of pace before warming the earth. The energy radiated i given by the Stefan-Boltzmann Law: P r = eσa ( T 4 Tc 4 ) (1.3) where: P r = net radiated power J e = emiivity σ = Stefan-Boltzmann contant = T c = temperature of urrounding K W m 2 K 4 A general temperature profile i hown in Figure 1.1. The temperature profile i normally linear. The heat flow occur from the highet to the lowet temperature zone. Therefore, to calculate the heat tranfer we baically only need a temperature difference. Figure 1.1: General temperature profile for heat tranfer. To calculate the heat emited by the proceor, equation (1.4) wa ued. For implification purpoe, it i aumed that the pecific heat capacity i temperature independent. T Q = m c p dt (1.4) T 0 where: m = ma of the olid kg c p = pecific heat capacity J kgk The efficiency of a determinate heat exchanger i calculated with the equation below: η = P tot q 100 (1.5) P tot where: η = efficiency % P tot = overall computer power J F. Guerra, A.Michel 4

5 2 Experimental Procedure To analyze the heat tranfer phenomenon, a CPU with an Intel c Celeron c D 2.8Ghz proceor wa given. It wa poible to fit different cooler ytem over the proceor. Four thermometer to meaure the proceor and ambient temperature were alo provided. With a computer program called LabView c, the temperature were graphed on-creen live and the load for the proceor could be witched between normal (almot no CPU activity) and full (100% CPU activity). With another ingle-purpoe application, it wa poible to ee the CPU and Main Board temperature. Thi were meaured internally and due to the lack of information, it wa unure where exactly they were taken. A an advice from Mr. Wohlwend thoe meaurement were een a doubtful and were not ued for the calculation of the reult. A power meter wa alo ued to meaure the power conumption of the computer. All the data gathered by the computer wa exported to an Excel c file for further ue. Due to the fat overheating of the proceor, almot immediately after turning on the computer a cooler had to be placed over the proceor to avoid a udden crah-down. All meaurement (except where indicated) were taken at normal and full load. A a firt tep, the heat emitted wa meaured with a block of copper. Thi tep had to be preformed quite fat, becaue the copper can get extremely hot very oon. After that, different cooling ytem were analyzed; an Intel c Original fan cooler, a Super-Silent c fan cooler, a ThermalTake c heat exchanger (without and with an implemented fan), a black and a white radiator and a water cooling ytem (operated at different flow). After placing a determinate cooler and finihing with it meaurement, the next one could be placed without turning off the computer. It important to mention, that thi had to be done quickly, to avoid a crah-down, due to the proceor temperature going over 110 C. If thi happened, the computer had to be tarted again. Figure 2.1: Schematically draw of the experiment layout. Figure 2.1 how a chematically repreentation of the different cooler ued in thi experiment. A tay for the Intel c and Super-Silent c fan cooler, B repreent the ThermalTake c without ventilator, C how the black radiator and D picture the water cooling ytem. In the cae of both fan cooler the temperature were meaured in the rib and in the metallic cae of the computer. For the cae of the ThermalTake c and the radiator, they were meaured near the proceor and in the coolet extreme of the device. For the water cooling F. Guerra, A.Michel 5

6 ytem temperature were taken before and after the water had gone through the plate over the proceor. 3 Reult and Dicuion With the help of Microoft Excel c and the equation (1.2), (1.4) and (1.5) the folowing reult were obtained. The area of the heat tranfer urface wa A = m Block of copper With the pecific heat (c p = J gk 10), the ma of the block of copper (m = g) and equation (1.4), it wa poible to calculate the heat tranfer rate. Equation (1.5) wa ued to calculated the efficiency. Table 3.1 how the obtained reult for normal and full load. The efficiency obtained i urpriingly high, conidering that no more than 30% of the power get lot in form of heat, while an engine looe approximately 70% to 80% of the energy provided 8. Table 3.1: Reult for η baed on the heat tranfered to a block of copper. CPU mode Power q η W J % normal load full load It i clear to ee, that the amount of heat tranfered increae at full load. Thi i, due to the higher power conumption of the computer while working at full load. Figure 3.1 how the temperature profile at normal and full load. It how the linear dependency between the temperature and the time. Therefore, adding a trend-line allow u to calculate the heat per unit of time. The value of R 2, cloe to 1 indicate that our reult are reliable. 3.2 Water Cooling Sytem The implemented water cooling ytem operated at the flow rate hown in Table 3.2 and 3.3. Uing equation (1.2) the convection coefficient h and the parameter ha were calculated. It i important to mention, that the obtained value are calculated with the temperature difference of the water, but doe not conider the temperature of the plate where the real heat tranfer take place. The reult are hown in Table 3.2 and 3.3. At normal load (Table 3.2) h and ha clearly increae proportional to the water flow. A expected, with a larger flow, the proceor get better cooled. Neverthele, at ome point, thi cooling capacity hould reach a top value, becaue the water can only take a determinate amount of heat. At full load (Table 3.3) the trend for the value of h and ha i the ame than at normal load (Table 3.2). For thi cae, one could alo expect a top value for F. Guerra, A.Michel 6

7 Figure 3.1: Temperature profile for the block of copper at normal and full load. Table 3.2: Reult for the water cooling ytem at normal load. Flow h ha ml W W m 2 K K the cooling capacity of the water ytem. The reult how that thi wa not yet reached. Comparing Table 3.2 and 3.3 it i poible to ee, that the convection coefficient get bigger at full proceor load. An exception to thi affirmation i found at the flow rate of 1.73 ml. From the Table 3.2 and 3.3 it i poible to determine, that a higher value of h or ha repreent a better cooling effect. Figure 3.2 how the convection coefficient a a function of the water flow. A aid, h grow proportionally to the flow, but with the help of a trend-line it i alo poible to confirm that it i linearly proportional. The value of R 2 near to 1 give a certain reliability to the aumption. Neverthele it i poible to ee, that at normal load the trend could be reaching the mentioned top value. It i not really poible to determine if the variation of the fourth point of the curve i merely an experimental error or a reliable value. If the trend for normal and full load are compared and detailed analyzed, it i poible to conclude at firt ight that the cooling effect i better at full load. Having aid that a higher value of h repreent a better cooling, the line with the highet value hould be for the better cooling effect. Thi could alo be interpreted on a different way. F. Guerra, A.Michel 7

8 Table 3.3: Reult for the water cooling ytem at full load. Flow h ha ml W W m 2 K K Figure 3.2: Convection coefficient a a function of the water flow. The reult obtained are baed on the temperature difference between the water going into the heat exchange urface and the water going out of that area. The real heat exchange between the proceor and the implemented cooling ytem (at the metal plate) i not being taken on account. Obviouly, at full load, the heat tranfered from the proceor to the convection plate will be higher. Thi caue the water to get warmer at full load and therefore the T reult bigger. When entered into equation (1.2) the reulting value get bigger.thi doe not trictly mean that the the proceor had a lower temperature. With the pecific heat (c p = J gk 5), the flow rate and equation (1.4), it wa alo poible to calculate the heat emitted by the proceor per unit of time. Equation (1.5) wa ued to calculated the efficiency. Table 3.4 ummarize the reult for the efficiency of the ytem baed on the water. For each flow the heat emitted and the efficiency were calculated. Interetingly the reult at 1.73 ml eem to be quite different than all the other flow, but are very imilar to the reult obtained with the block of copper (Table 3.1). Therefore it i aumed, that the mot confident reult are obtained at lower flow. Thi deviation on the value can be becaue at a lower flow rate the ytem work with a more accurate T. A mean efficiency wa calculated F. Guerra, A.Michel 8

9 Table 3.4: Reult for the efficiency baed on the heat tranfered to the water. normal load full load Flow Power q η Power q η ml W J % W J % Mean at normal and full load. Thi value are lower than thoe obtained with the block of copper, but thi get a little cloer to the tatement that an engine looe approximately 70% to 80% of the energy provided 8. For comparion purpoe, all the heat coefficient h and ha are calculated baed on the reult obtained with the block of copper. 3.3 Cooling Device For thi part, different cooling device were compared. All of them work thank to the convection phenomenon and therefore equation (1.2) wa ued for the calculation. It i important to mention, that in all cae, the heat tranfer wa trictly done with the ambient air. For the fan cooler, the T wa meaured between the rib of the device and a temperature taken at the metallic cae of the computer. For the heat exchanger and the radiator the two temperature were meaured at the nearet point poible to the proceor and the oppoite extreme of the device. The fan implemented for the ThermalTake c wa a 12V fan opperated at 4V. Table 3.5 and 3.6 how the obtained reult. Table 3.5: Reult for the different cooling device at normal load. Cooler h ha W W m 2 K K Intel c Super-Silent c ThermalTake c ThermalTake c w/fan White radiator Black radiator Like previouly mentioned, a high value of h or ha indicate a better cooling capacity. A hown in Table 3.5 urpriingly, the original Intel c cooler i the bet one. Neverthele it i clearly viible, that the two fan cooler are by far the bet. One can alo notice, that the ThermalTake c work, a expected, better with a fan. The ThermalTake c ued hould theoretically be placed with F. Guerra, A.Michel 9

10 the proceor in an upright poition (which wa not the cae). Being placed horizontally, the convection effect within the rib cannot take place a expected for an optimal performance. Uing a little fan, help the air flow through the rib and provide the ytem with freh air. A for the radiator, the heat tranfer take place through the whole urface. It i well known, that the white color aborb more energy than the black. Therefore it i clearly viible, that the black radiator ha a better cooling effect. Interetingly the cooling capacity of the black radiator i more or le the ame than the one from the ThermalTake c with fan. Table 3.6: Reult for the different cooling device at full load. Cooler h ha W W m 2 K K Intel c Super-Silent c ThermalTake c w/fan Black radiator Table 3.6 preent the reult obtained for the different cooler at full CPU load. The ThermalTake without the implemented fan and the white radiator were not analyzed. In the cae of the ThermalTake c, the ventilator wa ued to imulate the optimal upright poition. The meaurement taken without it were only to confirm the performance decreaing. A for the white radiator, advied by Mr. Wohlwend, we kipped thoe meaurement. Apparently, the cooling effect i not trong enough, and reaching teady tate would be rather difficult, due to the ytem crahing down jut before getting table. The reult obtained at full load correpond to thoe obtained at normal load. Once again, the Intel c fan cooler i the bet one, followed by the Super-Silent. Thi two are coniderable uperior than the other. At full load it i poible to ee, againt the expectation, that the black radiator work quite better than the ThermalTake c. 3.4 Comparion To have a better overview of the reult, all the cooling device were compared ide by ide at normal and full load. The water cooling ytem i by far the bet cooling method. Therefor only the reult at the lowet flow were included in the cooler device comparion chart. Figure 3.3 compare the cooling capacity of the different cooler analyzed and the water cooling ytem at a flow rate of 1.73 ml, baed on the convection coefficient. A higher value repreent a higher cooling capacity and wa obtained due to a larger T. Like previouly aid, apart form the water, in normal and full load, the Intel c original fan cooler i the bet one. Once again, the convection coefficient at full load i much bigger than at normal load. It i important to remember, that it i due to the larger temperature difference. While the proceor get much warmer at full load and the ambient air temperature remain more or le contant, the temperature gradient i bigger. A bigger gradient induce a greater heat tranfer. Thi doe not repreent in any matter, F. Guerra, A.Michel 10

11 Figure 3.3: Comparion chart for the different cooler device at normal and full load. that the proceor temperature i lower. It i worth to mention that unlike the other cooler device, the convection coefficient for the water get lower at full proceor load. Thi i, a previouly aid, an exception that only appear at thi flow rate. 4 Concluion and Outlook Cooling i not an eay tak. Neverthele it i a huge challenge for the future. In thi experiment it wa poible to tudy the heat tranfer phenomenon by cooling a proceor in different way. Although different device and a water cooling ytem were ued, at the end, the medium that receive the heat i the air. Alo for the water cooling ytem, the heat exchange wa made between the water and the ambient air. Thi give an idea of the limitation to improve cooling ytem. Liquid nitrogen and acetone cooling ytem are often mentioned, but when implemented for real-life application, the expectation get lot. Thi technique only work for hort period of time. A for future experimentation, it would be intereting to tudy the ThermalTake c placed at it recommended poition, to ee if it performance really improve coniderably. Reference 1 Anwer Corporation. heat conduction. 06/07. December-January 2 efunda. Convection Theory in Heat Tranfer. tranfer/convection/overview conv.cfm, December-January 06/07. F. Guerra, A.Michel 11

12 3 QUICK-OHM Küpper & Co. GmbH. QUICK-COOL. December-January 06/07. 4 R. Nave. Stefan-Boltzmann Law. December-January 06/07. 5 R.H. Perry and D.W. Green. Perry Chemical Engineer Handbook. McGraw-Hill, Inc., 7th edition, Unknown. Fourier Law. uli/teaching/heat/fourierlaw.html, December-January 06/07. 7 Wikipedia. Convection. December-January 06/07. 8 Wikipedia. Engine efficiency. efficiency, December-January 06/07. 9 Wikipedia. Heat conduction. conduction, December-January 06/ Wikipedia. Specific heat capacity. heat capacity, 06/ Wikipedia. Stefan-Boltzmann law. law, 06/07. December-January December-January 12 Wikipedia. Wärmeleitung. December-January 06/ M. Wohlwend and N. Oterwalder. Kühlung eine Prozeor, WS 06/07. F. Guerra, A.Michel 12