Heat Pipe Array Research Articles

Experimental Study of a Novel PV/T- Air Composite Heat Pump Hot Water System

Solar energy utilization and heat pump are common technologies of renewable energy utilization for solving the problem of energy crisis and environmental pollution in present. This paper proposed a novel PV/T-air composite heat pump hot water system. The system was comprised of independently developed flat plate solar PV/T collector based on micro-channel heat pipe array and air source heat pump, which were combined by a new composite evaporator. The performance of the system were experimentally studied, COP of heat pump reduced from 5.61 to 1.69 and the average was 3.03. Comprehensive COPsys of PV/T-air composite heat pump system ranged from 6.07 to 1.33, the average was 2.99. The result showed the system was worthy of promotion and application.

Experimental Investigation of Thermal Performance of a Unique Heat Pipe Array

A novel heat pipe array with multi-evaporators and a shared horizontal exocentric tube condenser was developed and experimentally investigated on its thermal performance and reliability. This uniquely designed heat pipe array was expected to have extensive applications in the fields of solar heat collecting, multichip cooling, waste heat recovery systems, etc. This unique heat pipe array was fabricated with five evaporator tubes vertically arranged in parallel sharing an exocentric horizontal condenser tube. The test facility had been setup and experiments were conducted to investigate the thermal performance of the proposed heat pipe array systematically. Experimental results showed that the heat pipe array had a good thermal performance and an excellent operating stability. Furthermore, the uniquely designed configuration of an exocentric tube condenser and multi-evaporators not only improved vapor–liquid two-phase flow and phase-change heat transfer in the horizontal direction, but also extended the area of condenser and evaporator. The average thermal resistance decreased and the maximum heat transport capacity increased when increasing the length of evaporators. The experimental results also indicated that a maximum thermal performance of the heat pipe array appeared with an evaporator length of 270 mm at an inclination angle of 60 deg and operating temperature of 80°C. In addition, the minimum average thermal resistance and maximum heat transport capacity of this heat pipe array could achieve up to and 1098 W, respectively.

Experimental investigation of the thermal performance of a novel concentric condenser heat pipe array

A novel concentric condenser heat pipe array is developed and expected to be utilized in integrated waste heat recovery equipment with higher heat transfer efficiency at lower temperature heat sources. The investigation of the overall thermal performance of the concentric condenser heat pipe array was experimentally conducted in this work. The parameters considered in this study are operating temperature, input power, inclination angle, and the length of evaporator section. The results showed that the maximum heat transport (Qmax) increased with the augment of the operating temperature, the length of evaporator section, and condensation area, while decreased with increasing the inclination angle. The present investigation also discovered that, when the inclination angle was 60° and the length of evaporator section was 270mm, the novel waste heat recovery equipment (concentric thermosyphon heat pipe array) delivered a better heat transfer performance.

A Study on the Micro Heat Pipe Array Based Flat Plate Solar Heating System

The application system of solar energy comprises: solar water heating system, solar heating system and solar photovoltaic system, etc. The data monitoring system used in the solar water heating system consists of measuring and monitoring equipment, data acquisition appliances and data-center softwares. The measuring and monitoring equipment includes outdoor temperature sensor, total solar irradiance sensor, water inlet and outlet temperature sensor of heat collecting system, circulating flow sensor of heat collecting system and the electric meter for supplementary heat source, etc.. The data monitoring system used in the solar photovoltaic system consists of measuring and monitoring equipment, data acquisition appliances and data-center softwares. The measuring and monitoring system is composed of outdoor temperature sensor, total solar irradiance sensor, the sensor for the surface temperature of back panel of solar photovoltaic modules and electric meter for the monitoring of power generation of solar photovoltaic system, etc.

The Experimental Research on Instantaneous Efficiency of PV/T Module Based on Micro Heat Pipe Array

A novel photovoltaic /thermal (PV/T) module is invented, which use micro heat pipe array (MHPA), a flat heat pipe, to cool the solar cell. The PV/T module can achieve the purpose of cogeneration by collecting and utilizing waste heat while cooling the solar cell and improving power efficiency. In order to test the performance of PV/T module based on MHPA, instantaneous thermal efficiency test was performed. The intercept of measured instantaneous thermal efficiency curve can reach 41.4%, the slope is 3.95. The temperature of PV module is the key factor of the influencing electric efficiency. The PV/T modules electric efficiency is kept between 10.5% and 12.3% during the test. Solar energy utilization total efficiency at 20°C inlet temperature can reach more than 50%, and comprehensive performance efficiency can reach above 70%.

The Experimental Study on Fresnel Lenses Concentrator Solar Cell Cooling by a Novel Micro Flat Plate Heat Pipe

A novel micro flat plate heat pipe, micro heat pipe array, was used as heat transfer element in Fresnel lenses concentrator solar cell cooling based on its temperature uniformity and the high thermal conductivity. The contrast experiment was carried out in September in Beijing and the cell performance had been studied for difference cooling means, respectively by ordinary fin and "heat pipe and fin". Experimental results show that compared with cooling by the ordinary fin, for "heat pipe and fin" cooling cell the cell temperature is reduced by maximum 8.2% and maintained at about 55°C. The maximum power is 13.21 W, increases by 7.6%. And the photoelectric conversion efficiency improves 6.1%, with maximum efficiency of 24.13%.

Experimental investigations on the heat transfer characteristics of micro heat pipe array applied to flat plate solar collector

This paper introduces a novel flat plate solar collector (FPC) using micro heat pipe array (MHPA) as a key element. To analyze the thermal transfer behavior of flat plate solar collector with micro heat pipe array (MHPA-FPC), an indoor experiment for thermal transfer characteristic of MHPA applied to FPC was conducted by using an electrical heating film to simulate the solar radiation. Different cooling water flow rates, cooling water temperatures, slopes, and contact thermal resistances between the condenser of MHPA and the heat exchanger were tested at different heating powers. The experimental results indicate that MHPA-FPC exhibits the enhanced heat transfer capability with increased cooling water flow rate and temperature. Total thermal resistance has a maximum decline of approximately 10% when the flow rate increases from 180 L h−1 to 360 L h−1 and 38% when the cooling water temperature increases from 20°C to 40°C. When the inclination angle of MHPA-FPC exceeds 30°, the slope change has a negligible effect on the heat transfer performance of MHPA-FPC. In addition, contact thermal resistance significantly affects the heat transfer capability of MHPA-FPC. The total thermal resistances lowers to nearly half of the original level when contact material between the condenser of MHPA and the heat exchanger changes from conductive silicone to conductive grease. These results could provide useful information for the optimal design and operation of MHPA-FPC.

Performance experiments for flat plate solar water heater based on micro heat pipe array

A novel flat plate solar water heater based on the micro heat pipe array (MHPA) was invented, and the experiments were carried out on the MHPA heat collector and water heater to test their thermal performance. Owing to its distinctive structure, the MHPA has good heat transfer ability, high reliability, high compressive strength and low cost. The structure and character of the novel collector with MHPA as the high-efficiency heat transfer element are as follows. First, the contact surface between the absorber and the MHPA is so large that the heat resistance is smaller than the traditional one, thus its thermal transfer capability is greatly improved. Second, the condenser section of the MHPA is connected closely to the heat exchanger with dry type. The heat pipes do not contact with water, which precludes scaling and leakage in the collector. Third, the MHPA uses low freezing points of the refrigerants, which makes the collector more suitable for extremely cold areas. Fourth, the MHPA is made of aluminum instead of copper, which could reduce the fabrication cost significantly. Fifth, the unique heat exchanger could exclude water easily, which could prevent the frozen cracking of the collector in winter. Consequently, compared with other conventional evacuated glass tube solar water heaters, the novel flat plate solar water heater offers the additional benefits of high compressive strength, light weight, high reliability and durability, easy integration into buildings, and resistance to freezing during the winter months. Compared with traditional sheet-and-tube structure flat plate solar water heaters, this novel solar water heater also demonstrates many advantages: lower cost, absence of welding, resistance to freezing. The experiments focused on the novel collector's instantaneous efficiency. The test results for the collector's instantaneous efficiency show that the slope and intercept of the instantaneous efficiency curve are 4.7 and 0.80 respectively, which are 11.0% and 22.3% superior to the technical data of the Chinese national standard. The high maximum instantaneous efficiency can be attributed to high transmittance of the glass cover and good absorption of the absorber, as well as great performance of micro heat pipe array. Due to the excellent isothermal characteristic of the MHPA, the absorber have uniform temperature field so that the heat loss by natural convection in the collector is reduced, thus the novel flat plate solar collector have relatively low heat loss factor. The low emissivity of absorber film also reduces the radioactive heat transfer between the absorber and glass cover. Finally, a detailed experimental study focusing on the thermal performance for the novel flat plate solar water heater based on the MHPA is conducted during daytime over several days. The test results show that the effective heat gain per contour aperture area for the novel flat plate solar water heater are higher than that of the Chinese national standard, and all of the average daily thermal efficiency are higher than 60%. Therefore, the flat plate solar water heater based on the MHPA has the broad application prospect because of its excellent performance.

Experimental investigation of performance for the novel flat plate solar collector with micro-channel heat pipe array (MHPA-FPC)

A novel flat plate solar collector with micro-channel heat pipe array (MHPA-FPC) is presented in this paper. Firstly, a preliminary test was conducted to investigate the thermal performance of the MHPA. It has been found that the surface temperature along the length of MHPA can get stable within 2 min. The temperature difference between the evaporator and condenser sections was less than 1 °C, which indicates that the MHPA has excellent isothermal ability and quick thermal respond speed. Based on these advantages, the MHPA was applied to the development of a novel solar collector. The performance test was conducted following the Chinese standard GB/T4271-2007, and a linear correlation between the instantaneous efficiency η and the reduced temperature parameter (Twi−Ta)·I−1 was established. The maximum instantaneous efficiency was found to be 80%, and the slope was −4.72. These values are 11.4% and 21.3% superior to the technical required values of the Chinese national standard. Test results were further compared with 6 groups of 15 samples coming either from either open literature or commercial products. The comparisons indicated that the maximum instantaneous efficiency of the MHPA-FPC surpassed 25% over the average level of those selected samples and better thermal insulation ability was presented by the MHPA-FPC. These results from this study demonstrate that the novel MHPA-FPC is one of the top level solar collectors among the current products.

Experimental field evaluation of novel concentrator augmented solar collectors for medium temperature applications

This paper looked at the development and experimental characterisation of the solar collector components termed novel “concentrator augmented solar collector array”. The “concentrator augmented solar collector array” being a combination of evacuated tube heat pipes with either an external or internal concentrator having a heat pipe or direct flow absorber as the last tube of the array. The performance of a novel designed and fabricated collector arrays augmented with an internal concentrator with either a heat pipe absorber (EICPC-HPA) or direct flow absorber (EICPC-DFA) and an evacuated tube heat pipe array (ETHPA) to be used for solar driven cooling systems is analysis and compared using a pressurised closed loop water system. Higher collector output temperatures with larger temperature differential, substantial improvement in efficiency and thermal performance produced by the EICPC-HPA collectors implies that higher coefficient of performance (COP) is possible when used to power solar driven cooling systems.

The potential applications and advantages of powering solar air-conditioning systems using concentrator augmented solar collectors

Non-concentrated evacuated tube heat pipe solar collectors have been reported to show higher fluid temperatures with improved thermal performance in the low to medium temperature range (⩽60°C) due to low heat losses but suffer higher heat losses at the medium to higher temperature range (⩾80°C) which reduces their efficiency compared to concentrated evacuated tube heat pipe solar collectors. To operate as stand-alone systems capable of attaining temperatures in the range of 70–120°C, an innovative concentrator augmented solar collector can be an attractive option. The performance of a combined low-concentrator augmented solar collector in an array of evacuated tube heat pipe solar collectors defined as concentrator augmented evacuated tube heat pipe array (CAETHPA) and an array of evacuated tube heat pipe collectors (ETHPC) were tested and compared and results presented in this paper. The analysis of the experimental data allows concluding that the use of a CAETHPA is a more efficient alternative for integrating renewable energy into buildings with higher fluid temperature response, energy collection and lower heat loss coefficient compared to the use of evacuated tube heat pipe collector array (ETHPA).

Thermal Management of a 15 kV/100 kVA Intelligent Universal Transformer

The thermal management of power electronics presents a significant challenge to thermal engineers due to high power loads coupled with small footprints. Inadequate thermal dissipation of these loads can lead to excessively high equipment temperatures and subsequent system failure. In this study, a unique power electronics-based transformer, called the intelligent universal transformer (IUT), is thermally analyzed using the computational fluid dynamics software ICEPAK. The objective of this work is to examine the use of a finned heat pipe array for the power electronics in the IUT. A design sensitivity study was performed to determine the effect of the number of fins attached to the heat pipe array, the number of heat pipes in the heat pipe array, and the fin material on the steady-state operating temperature of the power electronics. It was determined that a set of 33 copper fins attached to an array of 36 heat pipes on each side of the containment unit is sufficient for continuous operation of the power electronics. This analysis and thermal management solution will be applicable not only to this situation but also to other high density power electronics applications.

Experimental Investigation of Solar Panel Cooling by a Novel Micro Heat Pipe Array

A novel micro heat pipe array was used in solar panel cooling. Both of air-cooling and water-cooling conditions under nature convection condition were investigated in this paper. Compared with the ordinary solar panel, the maximum difference of the photoelectric conversion efficiency is 2.6%, the temperature reduces maximally by 4.7℃, the output power increases maximally by 8.4% for the solar panel with heat pipe using air-cooling, when the daily radiation value is 26.3 MJ. Compared with the solar panel with heat pipe using air-cooling, the maximum difference of the photoelectric conversion efficiency is 3%, the temperature reduces maximally by 8℃, the output power increases maximally by 13.9% for the solar panel with heat pipe using water-cooling, when the daily radiation value is 21.9 MJ.

The performance of micro heat pipes measured by integrated sensors

This study deals with silicon micro heat pipe (MHP) arrays which are powerful thermal devices for the cooling of microelectronic components. MHP arrays, consisting of non-circular hermetically sealed channels, are passive cooling systems. Their working principle is based on two-phase heat transfer. We report in this work on the fabrication and the characterization of all-silicon MHP arrays using integrated temperature sensor arrays. The MHP arrays consist in series of several tens of triangular shaped channels hermetically sealed using Si–Si direct bonding. We first show how we proceeded to integrate sensor arrays consisting of polycrystalline silicon thermistors in the all-silicon MHP arrays using simple and reliable microfabrication steps. Then, experimental thermal performances obtained using methanol as the working fluid are presented when varying the liquid charge, the heat sink temperature and the input power.

A new concept for integrating a thermal air power tube with solar energy and alternative, waste heat energy sources and large natural or man-made, geo-physical phenomenon

A method for power generation combining a solar concentration system and a pneumatic power tube system in a large open pit is described. Solar energy is concentrated by a plurality of heliostat mirrors placed along the embankment of the pit, which tends to be spherical in contour. The pneumatic tubes recover waste heat energy from the solar Rankine power cycle system and from a variety of sources that originate from or are in close proximity to the very deep, man-made open-pit mine or from other naturally occurring geo-physical chasms. The man-made or naturally formed chasms provide structural support for the pneumatic power tubes. The air in the tubes is heated by the recovered waste energy, and in so doing, its density is sufficiently reduced so as to produce air drafts from which mechanical power can be recovered from wind turbines and converted into electrical power by suitable electric generators. The deep chasms can be from a man-made phenomenon such as commissioned, open-pit mines or from naturally occurring fissures in the earth. The waste heat can be from solar energy, ground source energy or products of combustion from waste products that are to be mitigated or destroyed. The concept is novel in its integration of a solar powered heat engine with recoverable waste heat via the proposed pneumatic power tube as well as in the means of structural support that the geo-physical phenomenon provides and the modularity (for ease in manufacturing and installation) that makes the pneumatic power tube economically viable. The complete system uses state-of-the art wind turbine power recovery, solar reflective surfaces for solar energy collection, heat pipe arrays for ground source heat recovery, and air diffuser subsystems for enhanced wind turbine efficiency.

Hydrodynamic and Thermal Study of a Water-Filled Micro- Heat-Pipe Array

A detailed mathematical model for predicting the heat transport capability and the temperature distribution along the axial direction of a 55-micro-heat-pipe array, filled with a polar fluid (water), has been developed. This steady-state model combines hydrodynamic flow equations with heat transfer equations in both the condensing and evaporating thin films. The velocity, pressure, and temperature distributions in the vapor and liquid phases are calculated. Various boundary conditions fixed to the micro-heat-pipe evaporator and condenser have been simulated to study the thermal performance of the micro-heat-pipe array below and above the capillary limit. The effect of the dryout or flooding phenomena on the micro-heat-pipe performance, according to boundary conditions and fluid fill charge, can also be predicted.

Réalisation de microcaloducs en silicium pour le refroidissement de l'électronique

Click to increase image sizeClick to decrease image sizeIn this study, micro heat pipe arrays etched into silicon wafers were investigated, for electronic cooling purposes. Micro heat pipes of triangular cross-section (230 µm width) and with liquid arteries were fabricated by wet anisotropie etching in a KOH solution. The microchannels were closed by molecular bonding of a plain wafer with the grooved one. Two test benches were developed for the micro heat pipe filling and thermal characterisation. The temperarure profile at the silicon surface was deduced from experimemal measurements and a 3D numerical simulation. The results have shown that with the artery micro heat pipe array, the effective thermal conductivity of the silicon wafer was improved by 330 %.

Temperature control of electrohydrodynamic micro heat pipes

Active thermal control was achieved by using an electrohydrodynamically (EHD) assisted micro heat pipe array. A simulation model of temperature control of EHD micro heat pipes was established in a Matlab Sinulink environment. An experimental model was designed and fabricated to verify the model and identify the factors most influential to the thermal control via EHD micro heat pipe array. Good correspondence between simulations and experiments was achieved. Electric field intensity, set-point temperature and the gap between the upper and lower set-point temperatures were shown to have a dramatic influence on the temperature control.

Integrated micro-heat-pipe fabrication technology

This paper presents the design and fabrication of an integrated micro-heat-pipe system consisting of a heater, an array of heat pipes, temperature and capacitive sensors. Taking advantage of the large difference between the dielectric constants of liquid and vapor, the integrated capacitor can be used for void-fraction measurements in two-phase flows. Both CMOS-compatible and glass-based fabrication technologies are reported. In the CMOS-compatible technology, the heat pipes are capped by a thin nitride layer utilizing wafer bonding and etch back technique. In the glass-based technology, the heat pipes are covered by a glass substrate using die-by-die anodic bonding to allow visualization of the two-phase flow patterns. This approach also results in a significant reduction of the parasitic capacitance, thus enhancing the sensitivity of the capacitance sensor. A few particular problems related to this technology are discussed and proper solutions are proposed.

Fabrication and experimental investigation of silicon micro heat pipes for cooling electronics

An experimental investigation was conducted to determine the thermal behaviour of micro heat pipe (MHP) arrays micromachined in silicon wafers. Two types of MHP arrays were tested, one with triangular channels, 230 μm wide, 170 μm deep, and the other with triangular channels, 500 μm wide, 340 μm deep, coupled with arteries. Both types of arrays were fabricated using an anisotropic etching process. Once fabricated, a plain Si wafer was used to seal the pipe array hermetically. Two working fluids were tested, ethanol and methanol. A polysilicon heater was used to supply the heat input, and cooling water flowing through the condenser was used as a heat sink. Fill charges from 0% up to 66% were tested. The axial temperature variation along the length of the pipe was measured using T-type thermocouples connected to a data acquisition system. The effective thermal conductivity was evaluated using the experimental temperature profiles and 3D thermal modelling. The results show a maximum improvement of 300% in effective thermal conductivity at high heat flux, which demonstrates enhanced heat transfer in a prototype with liquid arteries.