Two-phase cooling systems based on the thermosyphon operating principle exhibit excellent heat transfer performance, reliability, and flexibility, therefore can be applied to overcome thermal challenges in a wide range of electronic cooling applications and deployment scenarios. However, extremely complex nature of two-phase flow physics involving flow patterns and phase transitions has been the major challenge for technology adoption in industry. This paper demonstrates a machine learning (ML) based model for evaluating the thermal performance and refrigerant mass flow rate, of a thermosyphon cooling system for telecom equipment. Unlike conventional laboratory approach that requires numerous sensors attached to a cooling system to capture their thermal performance, the new model requires a minimum number of sensors to monitor the health of a thermal management solution. Using the proposed model, a system control module can be further developed which could identify optimal operating parameters in real-time under dynamically changing heat load conditions and actively maintain safety and thermal requirements.

This paper advances the state-of-the-art in novel passive two-phase systems for more efficient cooling of datacenters and telecom central offices compared to the traditional air-based cooling solutions (e.g. aisle-based containment systems). The proposed passive two-phase technology uses numerous server-level thermosyphons to dissipate the heat generated by critical components, such as central processing units, accelerators, etc., with the flexibility of selecting the rack-level and room-level cooling elements depending on the deployment scenarios. The main goal of this paper is to experimentally investigate the thermal performance and maximum heat removal capability of a server-level thermosyphon for cooling compact servers. The experimental apparatus, built at Nokia Bell Labs, incorporates a single 7-cm high liquid-cooled thermosyphon that fits within a 2U server (smaller form factors can be achieved by a proper design that would further reduce the thermosyphon’s height). The heat source is represented by a pseudo-chip, composed of six parallel cartridge heaters installed in a copper block that incorporates local temperature measurements and is able of dissipating a total power of ≈ 500 W over a footprint area of 3.5 cm × 3.5 cm (corresponding heat flux of ≈ 41 W/cm 2 ). Steady-state experiments were carried out at various heat loads up to 240 W (corresponding heat flux of ≈ 20 W/cm 2 ), filling ratios and secondary side inlet conditions (coolant temperatures and mass flow rates), using R1234ze(E) and deionized water as the working fluids on the primary and secondary side, respectively. Test results demonstrate high heat transfer performance of the server-level thermosyphon over a wide range of conditions, and operating points are identified and classified into an operational map. Thermosyphon-based cooling systems across multiple length scales can significantly improve operation in terms of lowering energy consumption, allowing for higher hardware density, increased processing speed and reliability.

Frost formation on evaporators negatively affects the cooling performance of refrigerators. It increases the thermal resistance between the refrigerant and air leading to a reduction in the system cooling capacity. In this study, the effect of frost accumulation over a bare and finned surface on the convective thermal resistances has been experimentally investigated under impinging flow conditions. The surfaces are vertically positioned in a horizontal wind tunnel. The convective resistances have been measured with an in-house developed heat flux measurement system. Finally, the effectiveness of the finned surface was derived from the measurements for dry, condensing flow and as well as for frosting conditions. Under frosting conditions, the effectiveness of the finned surface is measured as 1.4 that is by a factor of 2X lower compared to the effectiveness of the same finned surface operating under dry conditions. It has been observed that the frost accumulation initially takes place at the tip of the fins and leads to a 45% drop in the heat transfer rate when the fin tips are completely covered with frost. Further frost accumulation on the fin base does not result in an additional drop in the heat transfer rate. In this regard, the study emphasizes the importance of the fin tip design for the heat sinks operating under frosting conditions.

The present study is focused on the experimental characterization of two-phase heat transfer performance and pressure drops within an ultra-compact heat exchanger (UCHE) suitable for electronics cooling applications. In this specific work, the UCHE prototype is anticipated to be a critical component for realizing a new passive two-phase cooling technology for high-power server racks, as it is more compact and lighter weight than conventional heat exchangers. This technology makes use of a novel combination of thermosyphon loops, at the server-level and rack-level, to passively cool an entire rack. In the proposed two-phase cooling technology, a smaller form factor UCHE is used to transfer heat from the server-level thermosyphon cooling loop to the rack-level thermosyphon cooling loop, while a larger form factor UCHE is used to reject the total heat from the server rack into the facility-level cooling loop. The UCHE is composed of a double-side-copper finned plate enclosed in a stainless steel enclosure. The geometry of the fins and channels on both sides are optimized to enhance the heat transfer performance and flow stability, while minimizing the pressure drops. These features make the UCHE the ideal component for thermosyphon cooling systems, where low pressure drops are required to achieve high passive flow circulation rates and thus achieve high critical heat flux values. The UCHE’s thermal-hydraulic performance is first evaluated in a pump-driven system at the Laboratory of Heat and Mass Transfer (LTCM-EPFL), where experiments include many configurations and operating conditions. Then, the UCHE is installed and tested as the condenser of a thermosyphon loop that rejects heat to a pumped refrigerant system at Nokia Bell Labs, in which both sides operate with refrigerants in phase change (condensation-to-boiling). Experimental results demonstrate high thermal performance with a maximum heat dissipation density of 5455 (kW/m 3 /K), which is significantly larger than conventional air-cooled heat exchangers and liquid-cooled small pressing depth brazed plate heat exchangers. Finally, a thermal performance analysis is presented that provides guidelines in terms of heat density dissipations at the server- and rack-level when using passive two-phase cooling.

With the current ozone depletion and global warming issues, it is critical to develop systems with better heat transfer performance and nontoxic refrigerants. An experimental investigation was performed to evaluate convective condensation and evaporation heat transfer characteristics using R410A at low mass fluxes. Experiments were conducted in a 12.0-mm O.D. horizontal smooth tube, and three enhanced tubes: 2EHT1 tube, 2EHT2 tube and 1EHT1 tube (O.D. 12.7 mm), with different sizes and shapes of dimple/protrusion and petal arrays. Refrigerant inlet quality varied in this study. Single phase experiment was conducted before the two-phase flow measurement. In-tube evaporation measurements of R410A were reported for saturation temperature at 6°C with vapor quality in the range of 0.2 to 0.9, and mass flux varied from 60 to 200 kg/m 2 s. Condensation tests were performed at saturation temperature of 45°C, vapor quality of 0.9 to 0.2, and mass flux of 60 to 260 kg/m 2 s. For evaporation with mass flux less than 200 kg/m 2 s, heat transfer coefficient of the 2EHT2 tube, 2EHT1 tube and 1EHT1 tube were greater than the experimental HTC (heat transfer coefficient) of smooth tube results by an average factor of 1.71, 1.69 and 1.87, respectively. Pressure drop in the 2EHT2 tube was 5% higher than the 2EHT1 tube and 1EHT1 tube. For condensation, when mass flux was less than 200 kg/m 2 s, the 1EHT1 tube showed obvious enhancement in heat transfer coefficient, while the pressure drop in the 1EHT1 tube was slightly 3–5% higher than that of the 2EHT1 tube and the 2EHT2 tube. In conclusion, for mass flux below 200 kg/m 2 s, the 1EHT1 tube presented the best heat transfer performance among others with R410A as the refrigerant.

As modern day electronics develop, electronic devices become smaller, more powerful, and are expected to operate in more diverse configurations. However, the thermal control systems that help these devices maintain stable operation must advance as well to meet the demands. One such demand is the advent of flexible electronics for wearable technology, medical applications, and biology-inspired mechanisms. This paper presents the design and performance characteristics of a proof of concept for a flexible Electrohydrodynamic (EHD) pump, based on EHD conduction pumping technology in macro- and meso-scales. Unlike mechanical pumps, EHD conduction pumps have no moving parts, can be easily adjusted to the micro-scale, and have been shown to generate and control the flow of refrigerants for electronics cooling applications. However, these pumping devices have only been previously tested in rigid configurations unsuitable for use with flexible electronics. In this work, for the first time, the net flow generated by flexible EHD conduction pumps is measured on a flat-plane and in various bending configurations. In this behavioral characteristics study, the results show that the flexible EHD conduction pumps are capable of generating significant flow velocities in all size scales considered in this study, with and without bending. This study also proves the viability of screen printing as a manufacturing method for these pumps. EHD conduction pumping technology shows potential for use in a wide range of terrestrial and space applications, including thermal control of rigid as well as flexible electronics, flow generation and control in micro-scale heat exchangers and other thermal devices, as well as cooling of high power electrical systems, soft robotic actuators, and medical devices.

High heat flux from electronic devices remains a continuing challenge for cooling of electronics hardware in radar antenna applications pertaining to the defense industry. Cooling methods for such applications have varied from conduction cooling approaches for the cooling of circuit card assemblies, to advanced convection cooling using two phase flow (with pumped refrigerant) for the high heat flux devices used in transmit / receive modules. It is found that the limiting parameter in such applications is usually the heat flux from the electronic device. This paper provides an overview of the cooling techniques used for defense electronics, as well as current modeling tools and analytical methods used for thermal design during the product development phase. The role of thermal interface materials used in the material stack up for the thermal design solutions will also be touched upon. Additionally, the importance of using experimental techniques to characterize the heat transfer coefficient for the pumped refrigerant two phase flow will be discussed.

Two-phase microchannel heat sink is promising in cooling high power electronics with dielectric fluids. Compared to water, dielectric fluids can assure system safety in case of working fluid leakage. However, two-phase heat transfer of these hydrofluorocarbon refrigerants is restricted by their relatively low thermal conductivities and low latent heats. Numerous nanoscale/submicron structures have been developed to enhance the single and two-phase heat transfer in microchannels; but these techniques usually require nanoparticle seeds in multi-step wet processes or nanolithography to integrate these nanostructures. Therefore, most of these techniques were time-consuming and costly. In this study, we present a plasma etching method using a modified Bosch process to create silicon tips with nanoscale scallops in microchannels. This is a rapid and cost-effective method to integrate large density of nucleation sites without involving nanolithography method or using nanoparticle seeds. Then, these silicon tip arrays were aligned with side walls of microchannels. As a result, flow boiling heat transfer of a dielectric refrigerant, HFE-7000, is substantially enhanced in a microchannel heat sink (five parallel channels: 10 mm L × 220 μm W × 250 μm H). Compared to plain-wall microchannels, the average junction temperature can be reduced up to 10 °C at a heat flux of 55 W/cm 2 and the equivalent thermal resistance of microchannel heat sink is reduced up to 31% at a mass flux of 1018 kg/m 2 ·s.

The cross flow heat exchanger is at the heart of most cooling systems for data centers. Air/Water or air/refrigerant heat exchangers are the principal component in Central Room Air Conditioning (CRAC) units that condition data room air that is delivered through an underfloor plenum. Liquid/air heat exchangers are also increasingly deployed in close-coupled cooling systems such as rear door heat exchangers, in-row coolers, and overhead coolers. In all cases, the performance of liquid/air heat exchangers in both steady state and transient scenarios are of principal concern. Transient scenarios occur either by the accidental failure of the cooling system or by intentional dynamic control of the cooling system. In either scenario, transient boundary conditions involve time-dependent air or liquid inlet temperatures and mass flow rates that may be coupled in any number of potential combinations. Understanding and characterizing the performance of the heat exchanger in these transient scenarios is of paramount importance for designing better thermal solutions and improving the operational efficiency of existing cooling systems. In this paper, the transient performance of water to air cross flow heat exchangers is studied using numerical modeling and experimental measurements. Experimental measurements in 12 in. × 12 in. heat exchanger cores were performed, in which the liquid (water) mass flow rate or inlet temperature are varied in time following controlled functional forms (step jump, ramp). The experimental data were used to validate a transient numerical model developed with traditional assumptions of space averaging of heat transfer coefficients, and volume averaging of thermal capacitances. The complete numerical model was combined with the transient effectiveness methodology in which the traditional heat exchanger effectiveness approach is extended into a transient domain, and is then used to model the heat exchanger transient response. Different transient scenarios were parametrically studied to develop an understanding of the impact of critical variables such as, the fluid inlet temperature variation and the fluid mass flow rate variation, and a more comprehensive understanding of the characteristics of the transient effectiveness. Agreement between the novel transient effectiveness modeling approach and the experimental measurements enable use of the models as verified predictive design tools. Several studies are designed based on the practical problems related to data center thermal environments and the results are analyzed.

A key component of the MEMS cryogenic cooling systems we are developing is a MEMS compressor. Its function is to compress the refrigerants used in the cooling cycle. Layers of polyimide are stacked and patterned on a silicon wafer to create micro check-valves and a compression chamber over which a diaphragm is suspended. To achieve the high (4:1) pressure ratio needed for the refrigeration cycle, the polyimide diaphragm needs to be fabricated with minimal dead volume beneath it, hence the need for a sacrificial layer with thickness of 100–300 nm. The topography created by the check-valves and valve-seats makes atomic layer deposition (ALD) ideal due to its conformality. Furthermore, following sacrificial layer release, the inside of the compression chamber will also need to be coated with a hermetic moisture barrier layer to enable the device to operate at 4 atmospheres without leaking. ALD is therefore also ideal for the final internal coating because it does not require line-of-sight. Towards this end, we demonstrate here the concept of using ALD TiO 2 as a sacrificial layer to create a 5 mm × 5 mm × 20 m-thick polyimide membrane, suspended by ∼ 100–350 nm above a silicon wafer, followed by a second thinner ALD coating of the interior surfaces bounded by wafer and membrane. The air gap under the membrane, defined by the released sacrificial layer, was measured at about 130–370 nm using two independent methods: reflectometry, and FIB cross sectioning followed by SEM imaging of the air gap’s cross section. The membrane was removed from one chip and the thickness of the internal coating on the underlying silicon was measured with the reflectometer to be about 40 nm. We thus demonstrate the use of ALD TiO 2 as both a sacrificial layer for fabricating nanoscale gaps, as well as for coating nanoscale internal cavities and channels.

A number of small electronic devices benefit from micro-scale low temperature operation. Recently we have developed micro cryogenic coolers (MCCs) using a low-pressure, mixed-refrigerant Joule-Thomson cycle. The cryocoolers utilizes a MEMS-enabled gas compressor coupled to a micro cold stage. Two cold stages have been developed: one which uses a fiber-enabled heat exchanger assembled to a micro-machined throttling valve, and another which uses a MEMS-based heat exchanger. A microcompressor has been developed which uses MEMS-based check valves coupled to a membrane, which is actuated with a mechanically amplified piezoelectric amplifier. The compressor measures a volume 15 mL, can generate a pressure ratio of 6:1 and a maximum flow-rate of 60 standard mL/min. The complete cryocooler has reached low temperatures of 177 K, although temperature instability has been an issue, due to 2-phase flow through the micro-channels. This paper will cover the development and testing of the micro cryogenic cooler, as well as an analysis of the micro channel flow. A proper understanding of the micro-channel flow allows us to design refrigerant mixtures to improve the cooling power, and modify the cooler to eliminate temperature instabilities.

The continued demand for high performance electronic products and the simultaneous trend of miniaturization has raised the dissipated power and power densities to new unprecedented levels in electronic systems. Thermal management is becoming increasingly critical to the electronics industry to satisfy the increasing market demand for faster, smaller, lighter and more cost effective products. Utilization of waste heat for the purpose of cooling chip is a promising area for enhancing the thermal management and net energy efficiency of the system. This paper focuses on the development of a tubular microgrooved evaporator and its performance characterization based on heat transfer coefficients and pressure drop measurements. Channel with aspect ratio of 3:1 (channel width – 100 μm, channel height – 300 μm) microgrooved structure was used in the evaporator. The system has been tested with R134a as refrigerant for refrigerant flow rate range of 0.005–0.02 kg/s and water flow rate range of 0.25–0.65 kg/s. Very promising results has been obtained in preliminary investigation. Heat transfer coefficient as high as 13,500 W/m2k has been obtained which is almost five times higher than comparative state of art technologies. The associated pressure drop is quite modest and much less than state of the art conventional evaporators.

In 2005, IBM released a water cooled heat exchanger product that significantly enhanced data center cooling capability while also demonstrating substantial energy savings. In 2008, IBM released an enhanced water less solution to cool the electronic racks via a R410A refrigerant based vapor compression system, which is the focus of this paper. The paper provides a detailed description of device and coolant loop construction, the experimental thermal data collected, as well as a discussion of its’ cooling energy efficiency relative to both typical air cooled facilities and water cooled heat exchangers, respectively. A data center level case study was performed with experimental measurements collected and discussed herein. Significant energy savings were realized even when the heat exchanger devices were implemented on a small part of the data center. Based on the test data and the experimental data center study, the CRAC units based loops have a COP of 1.95, while the refrigerant refrigerant heat exchanger loop has a COP of 5.0.

Flow in three horizontal channels for subcooled and saturated boiling characteristics are reported in this study. An experimental setup composed of heating elements provided heat flux variations on the channels. The heat transfer coefficient was found to be dependent on both the heat flux as well as mass flux levels. Results show that micro-coil inserts enhanced the heat transfer performance over that in smooth channels by 25% as compared to correlations for wire-coil inserts and 30% as compared to correlation for convective boiling process.

Nanotechnology quantum well thermoelectric materials have been developed that have high Figures of Merit and that can attain very high coefficients of performance (COP) to satisfy the requirements for cooling room temperature detectors. Hi-Z Technology, Inc. (Hi-Z) has developed Si/SiGe solid state quantum well (QW) thermoelectric (TE) materials that have demonstrated a Seebeck coefficient and thermoelectric properties that provide >4X higher conversion efficiencies than the current bulk TE materials. With the new Si/SiGe QW materials, cooling systems can be designed that are much smaller, quieter, lighter weight, and that have much reduced power requirements than current TE materials or presently used vapor-compression systems. On-going development for these new QW TE materials has demonstrated high-efficiency TE materials for power generation applications ranging from providing power for wireless sensors to converting waste heat from diesel engine exhaust directly to electricity and thus reducing the load on the alternator and reducing fuel consumption. Now, cooling devices with a high coefficient of performance (COP) are feasible and are being designed for room temperature detector cooling applications. Multi-layer nanocomposite QW films (each 10 nm thick) were fabricated to demonstrate that Si/SiGe QW materials can be deposited on a low thermal conductivity substrate and provide at least the desired COP over the required temperature range of 250K to 350K in a single-stage nano cooler. These QW thermoelectric materials can also be implemented into commercial equipment in the air conditioning and refrigeration applications, thus eliminating fluids, ozone-impacting refrigerants and compressors. Thermoelectric properties of QW thin-film materials have been measured at Hi-Z, several universities and national labs. The conversion efficiency of QW materials has been measured at Hi-Z in two different test couples and in a two-couple device. In all cases, good agreement was obtained between the measurements and prior analytical predictions. Cooling performance was measured in a test with one QW TE element and good agreement was obtained between measurements and analytical predictions. TE properties of the Si/SiGe QW material used in the analysis and design of the subject TE nano cooler were recently independently verified at University of California San Diego (UCSD) and the U.S. National Institute of Standards and Technology (NIST). This paper deals with the analysis of a high COP QW TE single-stage nano cooler for room temperature detectors and with the improved TE properties obtained with the QW thin-film materials resulting in such high COP designs.

A compact flow boiling module was developed for cooling a 100-W class package of about one-inch square in size. The cold plate, where heat is transferred from the package was made with a porous plating inside to augment boiling heat transfer. Heat transfer increased by a maximum of 50 percent when an organic refrigerant HFE-7100 was used, while the conditions for heat rejection to the ambient were kept unchanged. The heat rejection was achieved with an 80-mm fan with a matching corrugated fin radiator, whose effectiveness limits the overall size of the cooling module. The microscopic structure in the cold plate negatively influenced boiling of water, holding large patches of vapor bubbles on the surface. When the convective effect was increased by decreasing the cross sectional area of the channel by 10 times, heat transfer was further augmented approximately by 2 folds, making the use of the organic refrigerant an attractive option as the working fluid.

The average equipment rack in most of today’s high-performance data centers is limited to 1–3 kW with a typical overall heat load density of less than 100 W/ft 2 . Near-future racks, however, will dissipate up to 15 kW; in 2–4 years, computer and communications rack heat loads are projected to balloon to 30 kW with heat load densities exceeding 500W/ft 2 . Handling these heat loads is becoming increasingly difficult and expensive using traditional rack and data center cooling approaches. Based on an analysis of a realistic data center expansion plan, the current paper compares capital and operating costs associated with three alternative cooling approaches: (1) a business-as-usual approach, (2) employment of cooling augmentation systems based on chilled water and refrigerant-based heat exchangers, and (3) deployment of water- and refrigerant-based device-level cooling for some of the heat load. A major conclusion of the work is that challenging current industry norms can result in significant energy savings while allowing the benefits associated with increased functional density.

There is a strong need to improve our current capabilities in thermal management and electronic cooling, since estimates indicate that IC power density level could reach 500 W/cm 2 in near future. This paper presents several possible closed and open loop cooling schemes for thermal management of electronic equipment in data centers. To be able to identify the overall energy consumption impact, a thermodynamics coefficient of performance (COP) analysis for a data center under each one of the proposed schemes is presented. A limited condition condition 2 nd law of thermodynamics thermal efficiency (η II ) analysis of the proposed open-loop schemes is also presented. Using available performance data, the overall data center COP of open and closed-loop cooling schemes is evaluated. Also, the 2 nd law efficiency of open-loop schemes is evaluated. To properly design and size the components of a liquid or refrigeration-assisted open or closed-loop cooling scheme requires heat exchanger modeling that need to be incorporated in existing CFD simulation models. For that, analytical modeling of two kinds of direct expansion refrigeration cooling evaporator and a secondary liquid cooling fan coil heat exchanger in conjunction with a computational fluid dynamics (CFD) model to analyze a refrigeration cooled high heat density electronic and computer data center installed on a raised floor is presented. Both models incorporate an accurate tube-by-tube thermal hydraulic modeling of the heat exchanger. The refrigeration coil analysis incorporates a multi region heat exchanger analysis for a more precise modeling of two phase refrigerant flow in the evaporator. The single phase secondary loop fan coil heat exchanger modeling uses an effectiveness method for regional modeling of the spot-cooling coil. Using an iterative method, results of the heat exchanger modeling is simultaneously incorporated in the CFD model and an optimal design of spot cooling heat exchanger is developed. The presented cooling schemes, theoretical thermodynamics analysis along with the detailed thermal-hydraulic heat exchanger simulation in conjunction with the state-of-the-art CFD simulation code should enable data center designers to be able to handle expected increased in heat density of the future data centers.

The design of a thermal management system for an airborne, infrared, optical telescope system is described. This system provides transient thermal management for the optical elements of the system beginning at a high-temperature soak condition of 71°C (159.8°F) on the ground to a low-temperature operating condition of −30°C (−22°F) to −40°C (−40° F) within 45 min after aircraft takeoff. An active cooling system is employed to enable this rapid cooldown. In addition to the low-temperature requirement, the mirrors and lenses must be cooled so that temperature gradients across the optical elements are on the order of 1°C (33.8 °F) to 2°C (35.6 °F). The ambient air available for ground cooling is specified by the military environment to be 55°C (131.0 °F). As the aircraft takes off and climbs to an altitude of 11,582.4 m (38 kft), the ambient air temperature decreases to a low-temperature of −22°C (−7.6 °F) for steady, level flight at at Mach 0.9, this ambient air temperature results in a ram air inlet temperature on the order of 13.5°C (56.3 °F), after the air is captured and diffused to Mach 0.2 prior to entry into a ram air heat exchanger. This ram air heat sink is used to provide a chilled liquid for cooling of optical elements and the turret housing the system. The low temperatures required for this system, which are on the order of −30°C (−22 °F) to −40°C (−40 °F), make the use of forced-convection, liquid-cooling problematic because of the tendancy of liquids to become quite viscous as they approach these low temperature levels. Furthermore, the use of a single-phase heat transfer process will result in temperature gradients within the system. For these reasons, cooling concepts employing single-phase cooling using chilled-liquids have been eliminated from consideration. A low-temperature, low-pressure refrigerant, R-404a, is used as the working fluid. The themal management system uses the optical elements as the evaporator of a two-phase cooling system. The liquid refrigerant is introduced into the optical elements at the saturation temperature and saturation pressure of the liquid. The flow rate of the refrigerant will be controlled in such a manner that all of the heat transfer takes place in the liquid-vapor mixture region of the thermodynamic diagram for R-404a with the refrigerant exiting the elements at an arbitraily determned quality of approximately 0.8. This will assure that all of the heat transfer will be by boiling heat transfer and will take place at a constant temperature and essentially a constant pressure. Since the heat transfer coefficients are large and the process takes place at essentially a constant temperature, the optical elements will be controlled at the saturation temperature of the refrigerant and will be essentially a constant temperature across the expanse of the optical surface. The thermal management system is comprised of an array of TECs configured as a condenser HX. This TEC HX uses ram air as the eventual heat sink and will provide chilled-liquid produced by a liquid-to-ram air HX as the heat sink for the hot side of the TEC array. This system utilizes the system mass as the evaporator and a TEC HX as the condenser in a two-phase heat transfer process to provide rapid cooldown of the system mass to low temperatures in a short period of time and maintain that mass at proper operating temperatures with essentially zero temperature gradients throughout the system.

In this study the capillary pumped loop was manufactured as a cooling device for the tower-type personal computer and the heat transport characteristics of this cooling device was investigated. The experimental equipment consisted of the evaporator, the condenser, the liquid tube, the vapor tube and the reservoir. The length and the diameter of the evaporator were 150mm and 27mm respectively and had capillary wick in it with equivalent diameter of 5μm. In the experiment, the heat flux to the evaporator and the cooling water temperature were changed. And the effects of enclosed quantity of the working fluid (R134a) in the reservoir and the evaporator height above the condenser on heat transport rate were also investigated. Experimental results shown that this capillary pumped loop was able to transport heat rate of 15 to 95W (heat flux of 995 to 6051 W/m 2 ) with highest temperature of 343K and that the temperature difference in the loop was 16.7 to 43.9 K in the case of 2500mm in its heat transport length and cooling temperature of 293K. And it was derived that the working fluid enclosed rate affected the maximum heat transport rate. The computer code was also developed to evaluate the effect of the refrigerant enclosed rate and the wick thickness on the heat transport rate considering the pressure drop to the circumference direction in the wick.