Heat Dissipation Unit Research Articles

Thermal performance of pin fin heat sinks with phase change material for electronic devices thermal management

In the present paper, an experimental and numerical study is conducted to analyze various factors affecting the thermal performance of a heat sink with phase change material (HS-PCM). In order to maintain the chip below the limit temperature of 80 °C, ZDJN-35 with a phase change temperature of 37 ∼ 45 °C is selected as the energy storage material. Under different PCM filling volume fractions, heat fluxes, and operation modes, the study evaluates the thermal performance of the HS using chip temperature and the effective time extension coefficient. The volume fractions of PCM are 0 vol%, 30 vol%, 60 vol%, and 90 vol%. Under heat fluxes of 4000 ∼ 14000 W/m2, the results indicate that under continuous operation, the HS without PCM reaches the limit temperature within 18 min at heat flux of 8000 W/m2. In contrast, the time to reach the limit temperature for HS with 30 vol% PCM, 60 vol% PCM, and 90 vol% PCM extends by 12 min, 19 min, and 26 min, respectively. Compared to the HS without PCM, the peak temperatures reduce by 4.8 %, 10.5 %, and 12.8 % for the HS with 30 vol% PCM, 60 vol% PCM, and 90 vol% PCM under intermittent operation. Moreover, under intermittent operation, temperature fluctuations decrease by 27.3 %, 36.0 %, and 37.3 %, respectively. Finally, the numerical results show that the optimization of pin fin diameter is opposite for passive and active cooling modes, and a heat dissipation unit height of 25.5 mm is recommended.

A graphene nanoflake-based flexible composite phase change material for enhanced heat dissipation in chip cooling

Efficient heat dissipation is a key requirement for stable performance retention and failure prevention of microelectronic components. In practical applications, the interface thermal resistance between the component and the heat dissipation unit affects the heat dissipation effect. Thermal interface materials (TIM) are used to fill the voids at the solid interface between the device and the heat sink to create a thermally conductive path for heat dissipation. Phase change materials (PCMs) are candidates as TIM for next-generation electronic devices due to their excellent latent heat storage. However, some inherent problems of PCMs, such as low thermal conductivity, high solid-state rigidity, and easy leakage, also limit their application in the thermal management of electronic equipment. This study prepared a biomass cotton cloth substrate with a woven structure attached to graphite nanosheets and further constructed a thermally conductive matrix through drying or high-temperature carbonization. Through the composite of thermally conductive matrix and paraffin wax (PW), a flexible phase change thermal interface composite material was obtained. The phase change enthalpy of composite materials is as high as 157.7 J/g. The thermal conductivity of the composite material is 293.7 % higher than that of pure PW. On its excellent flexibility and structural strength, the composite material can better adapt to the thermal interface, reduce contact thermal resistance, and thus achieve good leakage resistance. The flexible phase-change TIM developed in this study have broad application prospects in the fields of chip heat dissipation and thermal management of wearable electronic devices.

Research on thermal radiation reflection coating of wearable air conditioner

As a special wearable system, wearable air conditioner can enhance the human body’s ability to adapt to the environment. In the actual study, the heat dissipation unit of the wearable air conditioner is prone to radiation interference from nearby heat sources, thus affecting the refrigeration efficiency and resulting in power attenuation due to the adverse heat dissipation of the system itself. In this paper, kirchhoff’s thermodynamic principle is applied to study the microphysical state of black, white and mirror, and a theory of coating mode conduction or obstruction of heat radiation propagation is provided. As a kind of extension and enhancement of heat dissipation under non-Fourier’s Law in practical application, the cooling efficiency of wearable air conditioner can be improved to the greatest extent.

Heat dissipation characteristic in the intake grille and radiator of a fuel cell vehicle

ABSTRACT In this study, a three-dimension (3D) computational model was proposed to investigate the flow and heat transfer characteristics of the intake grilles of two different fuel cell vehicles. The models of the intake grilles were constructed according to the actual sizes of two vehicles, namely, Roewe 950 and Toyota Mirai, considering the heat dissipation unit to simplify the heat transfer model of the vehicle. The results showed that relative to Roewe 950, Mirai intake air flow rate was approximately 10% higher, the heat transfer capacity was approximately 7% higher, and the intake grille area was larger. The coolant outlet temperature of Mirai was lower than that of Roewe 950, which was beneficial for the long term and stable operation of a fuel cell. This comparative study provided guidance for the intake grille and radiator design of fuel cell vehicles. The only difference between fuel cell vehicles on the market and conventional vehicles was that in the former, the internal combustion engine was replaced with a fuel cell stack, which had insufficient heat transfer capacity because of the reducing temperature difference. Increasing the intake grille area and the heat exchange capacity of the radiator were the key issues for the development of fuel cell vehicles. In this study, an optimal window opening angle of the radiator fin of 23° provided a maximal heat transfer coefficient.

Experimental Performance of a Cooler Box with Heat Dissipation Unit Variations

Experimental Performance of a Cooler Box with Heat Dissipation Unit Variations

Unjuk Kerja Kotak Pendingin Peltier dengan Unit Pembuang Panas Heat Sink Fin-Fan dan Double Fan Heat Pipe

Nowadays, technology is growing rapidly. A refrigerator is one of the technology applications by using heat transfer phenomena. However, the existing refrigerators in big size, need large power, and able to damage the ozone because most of the refrigerators utilize CFC. It is necessary to create a compact refrigerator with low energy needed and environmental friendly. In this study, a small cooler box of 24.5 cm x 20 cm x 28.5 cm with 2 modules Peltier SP 1848-27145 type arranged in cascade was used as a refrigerator. The data were logged by using the data logger DAQ MX 9714 NI that was connected to the PC by using LabView. In this experiment, 22 Watt of the electric power was used and 350 ml water was placed on the cooler box room. The results show that the temperature of the cooler box room with a single fan heat pipe is lower than the heat sink fin-fan. Furthermore, the temperature of the cooler box room with the single fan heat pipe where 350ml water was placed is lower than the cooler box room without the single fan. Moreover, the COP of the cooler box is significantly affected by the heat dissipation unit.

Experimental Investigation of the Feasibility of Using a Liquid Metal as a Variable Conductance Radiator for Space Applications

The feasibility of using a liquid metal with a high thermal conductivity as a functional fluid for realizing a variable conductance radiator (VCR) for space applications was proposed and investigated. The variable thermal conductivity of the radiator can be achieved by moving the liquid metal using a magneto-hydraulic pump between the two reservoirs in accordance with the temperature requirements of the on-board equipment. The liquid metal radiator proposed in this study is much more effective for saving heater power under cold condition while effectively dissipating heat to deep space under hot condition. The thermal behavior of the liquid metal radiator was demonstrated using the ambient thermal tests under cooling and insulation modes of the radiator. The performance of the proposed VCR was evaluated by comparing it with that of the conventional radiator whose conductivity value is fixed. The proposed radiator using the liquid metal was more effective than conventional radiator for suppressing the rate of increase of temperature for the heat dissipation unit in the cooling mode and for saving additional heater power by removing the liquid metal in the insulation mode.

Molecular Cooling Fan: Factors for Optimization of Heat Dissipation Devices and Applications

A molecular cooling fan (MF) is a nanocomposite coating technology, where the quantized lattice motions in nanomaterials are assembled to absorb heat from the heat source, promote to higher vibration states, and emit excess energy by radiation. Using a factorial design technique, seven factors were investigated to optimize MF cooling performance and efficiency. The results show that a MF coating prepared with 8 nm sized multiwalled carbon nanotubes can cool down 4 °C lower than that assembled with 50–80 nm due to higher activity of lattice motions. The MF makes equilibrium temperature cool down by 10 and 20 °C at input operation voltages of 35 and 55 V on the same heat dissipation unit (HDU). Using the optimal factors, a MF coating was applied on commercial HDUs. The results demonstrated that molecular fan action can reduce the size and mass of the heat-sink module, offering a low cost LED light unit.

HDU를 이용한 적외선 LED CCTV의 LED 수명 향상을 위한 방열설계에 관한 연구

Department of Printed Electronics Engineering, Sunchon National University, Suncheon 540-742, Korea(Received July 21, 2014; Revised August 28, 2014; Accepted September 11, 2014)Abstract: In this paper, thermal analysis of HDU (Heat Dissipation Unit) for infrared CCTV is performed by using SolidWorks Simulation (Thermal analysis) package, in order to change the part materials and HDU shape is optimized. Furthermore, HDU disperses the aggregated heat around the LED inside the housing. The junction temperature of infrared LED checked by HDU check was 65.83℃, 42.02℃, respectively. In addition, the Thermoelement by changing the shape of the HDU was possibly designed and equipped with. Comparison with simulation and prototype measurement results, without HDU model was 65.83℃, 61.99℃, respectively. In addition to with HDU model was 42.02℃, 39.01℃, respectively. Only HDU mounted into infrared CCTV is usable in the ordinary house or outdoors. Also HDU with thermal element, fan mounted into infrared CCTV is usable in a blast furnace workplace or high temperature workplace.Keywords: IR CCTV, CCTV, IR LED, Thermal dissipation

Research on Thermal Resistance of Micro Heat Pipe with Sintered Wick

As a highly efficient heat dissipation unit, a micro heat pipe is widely used in high heat flux microelectronic chips, and its thermal resistance is crucial to heat transfer capacity. Through analyses of the structure and heat transfer performance of a circular heat pipe with sintered wick, the theoretical model of total thermal resistance was established on heat transfer theory, and then simplified, finally a testing platform was set up to test for total thermal resistance performance. The testing results show that when the micro heat pipe is in optimal heat transfer state, its total thermal resistance conform well with that from the theoretical model, and its actual thermal resistance is much lower than that of the rod made of the material with perfect thermal conductivity and of the same geometric size. With the increment of heat transfer capability, the total thermal resistance of a micro heat pipe with sintered wick decreases first, then increases and reaches the minimum when it is in the optimal heat transfer state. The greater total thermal resistance in low heat transfer performance is mainly caused by too much working fluid accumulating in evaporator and the lower velocity in vapor cavity, and the greater total thermal resistance in high heat transfer performance is mainly due to the working fluid drying up in condenser. Total thermal resistance is related to many factors, such as thermal conductivity of tube-shell material, wall thickness, wick thickness, copper powders grain size and porosity, the lengths of condenser and evaporator, and the diameter of vapor cavity etc.. Therefore, the structure parameters of a micro heat pipe with sintered wick should be reasonably designed according to the specific conditions to ensure its heat transfer capacity and total thermal resistance to meet the requirements.

Sensor and Numerical Simulator Evaluation for Porous Medium Desiccation and Rewetting at the Intermediate Laboratory Scale

Soil desiccation, in conjunction with surface infiltration control, is considered at the Hanford Site as a potential technology to limit the flux of technetium and other contaminants in the vadose zone to the groundwater. An intermediate‐scale experiment was conducted to test the response of a series of instruments to desiccation and subsequent rewetting of porous media. The instruments include thermistors, thermocouple psychrometers, dual‐probe heat pulse sensors, heat dissipation units, and humidity probes. The experiment was simulated with the multifluid flow simulator STOMP, using independently obtained hydraulic and thermal porous medium properties. All instrument types used for this experiment were able to indicate when the desiccation front passed a certain location. In most cases the changes were sharp, indicating rapid changes in moisture content, water potential, or humidity. However, a response to the changing conditions was recorded only when the drying front was very close to a sensor. Of the tested instruments, only the heat dissipation unit and humidity probes were able to detect rewetting. The numerical simulation results reasonably match the experimental data, indicating that the simulator captures the pertinent gas flow and transport processes related to desiccation and rewetting and may be useful in the design and analysis of field tests.

Predicting the efficacy of convection warming in anaesthetized children

We previously described a convection warming technique (Cassey J, Armstrong P, Smith GE, Farrell PT. Paediatr Anaesth 2006; 16: 654-62). This study further analyses the children in that original study with three aims: (i) to investigate factors purported to influence children's heating rates, (ii) to describe the most effective usage of this warming technique, and (iii) to understand better the physiology of convection warming. Children having anaesthesia for elective surgery lasting longer than 90 min in ambient temperature 21 degrees C were warmed by a 'Bair Hugger' attached to a custom-built heat dissipation unit. Relationships between child and procedure characteristics and various thermal measures were analysed, and a thermodynamic model was evaluated. Thirty-nine children (aged 2 days to 12.5 yr) were studied. There were statistically significant correlations between a number of factors (e.g. height and weight) and heating efficacy. Our model demonstrated the impact of changing patient characteristics on temperature profiles. Neither the morphological characteristics nor our model could predict an individual's T(core) behaviour. (i) Although the effectiveness of this warming technique is influenced by patient/procedure characteristics, these do not predict normothermia (uncertainty +/-28 min). Effectiveness is independent of simple thermal measures. (ii) Previously described measures of vasoconstriction are not valid in children. (iii) Our model shows children's thermal properties change with their T(core). However, key factors are unknown for an individual and our model does not predict heating efficacy. (iv) To minimize the risk of hyperthermia, we recommend continuous measurement of T(core) during convection heating. The device air temperature should be turned to medium (38 degrees C) as T(core) approaches 37 degrees C.

Convection heating in pediatric general surgery – a comparison of warming alternatives in a mannequin study

Numerous methods of patient warming are used to prevent intraoperative hypothermia in children. Commercially available forced air warming blankets are effective, but are single-use items. We tested a custom-designed heat dissipation unit (HDU) against one such commercially available blanket. Air temperatures at various points around a mannequin under simulated operating conditions were recorded using thermistors and thermal imaging. The only variable changed was the heating method: a forced air blanket or a customized HDU with two draping techniques - cotton drapes with and without a plastic 'undersheet'. The three methods produced similar temperature increases and plateaux across the 11 thermistor points measured. There were no significant differences between temperatures at 1 h. A plastic sheet did not appear to enhance the effectiveness of the HDU in this study. Thermal imaging photography suggested more uniform heating of the mannequin with the HDU arrangements. The custom-built HDU compares favorably in our mannequin study with a Bair Hugger forced air warming blanket. As it is reusable, it offers considerable potential savings.

Study on the natural air cooling of electronic equipment casings: Effects of the outlet vent and the power heater locations on the cooling capability

This paper is concerned with the natural cooling of electronic equipment casings. Effects of the size and the location of the outlet vent as well as the relative distance from the outlet vent location to the power heater position on the flow resistance have been investigated experimentally by using a simple model casing simulated for practical natural air cooled electronic equipment casings. The result shows that the mean temperature rise inside the casing increases with increase in the heater input power, but decreases linearly with increase in the vent porosity coefficient in logarithmic coordinates. As the heater approaches the outlet vent, the temperature rise increases linearly in the logarithmic scale. By defining a new dimensionless parameter called the equivalent Reynolds number, involving the Reynolds number and the porosity coefficient, the flow resistance coefficient is found to have a close logarithmic linear correlation, K = kxχ−1.5, with the equivalent Reynolds number. Its validation has been proved by the good agreement with experimental results. The result indicates that the relative distance from the outlet vent to the heat dissipation unit can be considered as a chimney height in the practical engineering design. Although further more detailed validations are needed, a useful correlation between the flow resistance coefficient, the Reynolds number and the porosity coefficient has been presented for the design application of natural cooling electronic casings.

Experimental investigation of air cooling of a conductive calorimeter

The spatial inhomogeneity of thermal fluxes on the surface of the heat-dissipation unit of a KTS-2 calorimeter and a system consisting of an additional thermistor and stepped turbulizers for equalization and intensification of the heat transfer are investigated experimentally.