Experimental Investigation Of Thermal Performance Research Articles

Experimental investigation of thermal performance of three configurations evaporative cooling systems (ECS) using synthetic grass wet media materials

Space cooling of buildings using evaporative cooling is a passive strategy that can provide thermal comfort for occupants and conserve energy. In this paper, an innovative evaporative cooling wet media material in the form of synthetic grass fibre mat was introduced to evaluate experimentally its effectiveness in Direct Evaporative Cooling (DEC), Indirect Evaporative Cooling (IEC), and Dew point evaporative cooling (DPEC). A laboratory evaporative cooling module was constructed and tested using a fully instrumented test rig and was subject to environmentally controlled conditions of air temperature and relative humidity (RH) commensurate to those prevailing in hot and dry climates like the Middle East. The wet bulb effectiveness and cooling capacity of evaporative coolers equipped with the new wet media material were evaluated experimentally. The results show that these evaporative coolers performance correlate well with current technology. For instance, the ambient air temperature is reduced by as much as 12.9 °C, 10.2 °C, and 10.3 °C for direct, indirect, and dew point modes, respectively. It was also shown that DEC achieved effectiveness 20 % higher than indirect evaporative coolers. The work demonstrated that the new wet media can be a viable alternative to organic and non-organic counterparts.

Experimental investigation of thermal performance of vertical multitube cylindrical latent heat thermal energy storage systems.

The multitube design in the shell-and-tube type latent heat thermal energy storage (LHTES) system has received intensive attention due to its promising benefits in enhancing heat storage efficiency. In this paper, single and multi-tube shell LHTES systems were experimentally investigated. First, this study experimentally compared the thermal characteristics between a multiple-tube heat exchanger (MTHX) and a single-tube heat exchanger (STHX). The STHX's geometrical parameters coincided with a virtual cylindrical domain in the MTHX, being similar to the single-tube model formulated by simplifying the numerical solution to investigate the MTHX. The experimental data was then used to validate the simplified numerical model commonly used in the literature that converted the multi-tube problem to a single-tube model by formulating a virtual cylindrical domain for each tube in the MTHX system. The results showed that there was a noticeable difference in the thermal characteristics between the actual STHX and the virtual cylindrical STHX domain in the MTHX system. The comparison indicated that the simplified numerical model could not accurately reflect the thermal performance of the MTHX system. An experimental study or three-dimensional numerical modelling was required for the thermal analysis of the multi-tube problems. Second, the effect of tube number in the MTHX was experimentally investigated. It was found that an increase in tube number boosted both charging and discharging rates without inhibiting the natural convection. The five-tube configuration decreased the total charging and discharging duration by 50% compared to the two-tube one. Finally, the effect of heat transfer fluid (HTF) operating parameters on the system performance was evaluated on the five-tube MTHX system. The results revealed that the adoption of higher HTF temperature considerably improved the charging performance. The charging time decreased by up to 41% with the HTF temperature increasing from 70 to 80°C. Meanwhile, a variation in the HTF flow rate from 5 to 20 L/min showed a more pronounced influence on charging than on discharging due to the different dominant heat transfer mechanisms.

Experimental investigation of thermal performance of novel type vortex generator in rectangular channel

Vortex generators are objects with geometries specifically designed to increase heat transfer. In this study, the thermal performance of a novel vortex generator that can generate longitudinal vortices in a common flow-down pattern was experimentally investigated with Reynolds numbers in the range of 5000–25,000. The vortex generators were placed on the base surface of the channel in such a way that they were mirror images of each other according to the geometric symmetry plane in the main flow direction. At a fixed inclination angle, the effects of the ratio of the transverse distance between two vortex generators in a row to the channel width (transverse pitch ratio) and the ratio of the longitudinal distance between two vortex rows to the channel height (longitudinal pitch ratio) on heat transfer were analyzed. First, the experiments were performed for a single row by increasing the number of the vortex generators in the row (2, 4, 6, and 8) so that the transverse pitch ratios were 0.50, 0.25, 0.16, and 0.12. According to the results, as the transverse pitch ratio decreased, the Nusselt number and friction factor increased, so the highest increases were realized at the transverse pitch ratio of 0.12, reaching 1.44 and 2.07 times greater values compared with the smooth channel, respectively. However, the highest thermal enhancement factor was obtained at the transverse pitch ratio of 0.16. Then, vortex generators were placed with an inline arrangement keeping the transverse pitch ratio of 0.16 constant, and the experiments were executed for longitudinal pitch ratios of 1, 1.5, 3, and 5. The results revealed that the Nusselt number and friction factor increase with the decrease in longitudinal pitch ratio, but the highest thermal enhancement factor value (1.59) was obtained at the longitudinal pitch ratio of 1.5. In addition, the experiments were also performed using a staggered arrangement, but the inline arrangement proved to be more efficient than the staggered arrangement in terms of thermal performance. The maximal thermal enhancement factor was achieved for the inline vortex arrangement at the transverse pitch ratio of 0.16 and longitudinal pitch ratio of 1.5.

Experimental investigation of thermal performance of single pass solar collector using high porosity metal foams

The previous literature showed that there have been many studies focusing on some specific aspects of single-pass solar air collectors, such as the effects of the number of passes, the shape of fins, and their effects on thermal performance. Also, the effect of thermal efficiency accompanied by the existence of these fins has been the interest of many studies. A few research types are dealing with using porous materials (Metal foam) to improve thermal performance. Therefore, an experimental apparatus was designed and fabricated to study the effect of Metal Foam (MF) on the performance of solar air collectors. The experiments were held in Iraq, Al Ramadi climate conditions. A comparison of three configurations of absorber plates of solar air heaters with and without MF is presented and evaluated. The results showed that by including MF fins in the absorber plate, the absorber plate's surface area was increased, increasing heat transmission compared to a flat plate (without MF). Moreover, utilizing MF at the tilted angle of 45° (MFθ=45o) increased turbulence intensity, which improved the mixing of cold and hot air. The MFθ=45o layout had the best thermal efficiency of the three employed configurations (94.8%), followed by the MFθ=0o configuration (62.6%) and the flat plate configuration (33.8%), all with the same mass flow rate. Finally, when using MF fins with a tilted angle of 45°, the air temperature differential is bigger compared to MF fins with a tilted angle of 0° or a flat plate collector.

Experimental Investigation of Thermal Performance of a Novel Alternating Cross-Section Flattened Tube Heat Exchanger

The air-side performance of a novel alternating cross-section flattened (ACF) tube heat exchanger was experimentally investigated. Three heat exchangers with an in-line tube arrangement and two tube rows were used as the test sections. The tube configuration is the highlight of the research work. ACF tubes with hydraulic diameters of 4.16, 4.75, and 5.20 mm were assembled as the heat exchanger. The experimental results showed that the ACF tube heat exchangers exhibited a prominent heat transfer characteristic with a reasonable pressure loss penalty. Performance evaluation criteria, as a nondimensional parameter, were employed to assess the heat exchanger performance. Finally, the j and f of the ACF tube heat exchanger were compared with those obtained from various shapes of noncircular tube and fin tube heat exchangers. All the details are examined and discussed in this study.

Experimental investigations of thermal performance for flat and dimpled plate solar air heater under turbulent flow conditions

Conversion of solar energy into useful thermal energy through solar air heaters (SAH) enhances the practical application of the available solar energy. A comparative thermal analysis of two SAH’s having different absorber plates is elucidated here. Experiments were conducted on a flat plate solar air heater (FPSAH) as well as on dimpled plate solar air heater (DPSAH) during bright and sunny days from 0930 am to 1430 pm at IIT (ISM) Dhanbad on six different days for six different flow rates between 0.028 kg /sec to 0.051 kg /sec (i.e. Re value = 5500 to 10300). For these two SAH’s, different parameters and thermal properties were evaluated and compared. Quantitively, it is shown that the temperature difference, average extracted power, heat transfer coefficient, instantaneous efficiency and the effective efficiency of the DPSAH is higher than the FPSAH. Subsequently, it has been also observed that, the rise in effective efficiency of DPSAH at higher mass flow rates (MFR) is not significant; hence it is less suitable for high flow rate operations.

Experimental investigation of thermal performance in a rectangular channel using compound structure

An experimental study was conducted to measure the heat transfer and pressure drop in a rectangular channel emphasizing a compound structure to improve the cooling performance of gas turbine blades. W shaped, semicircular, and multi semicircular shaped ribs with dimples are studied and applied to a lower surface of a channel. The experiment was carried out at a Reynolds number ranging from 10,000 to 32,000 and the ratio of pitch (P) to height (e) of the rib was 10. Also, the ratio of rib height (e) to channel hydraulic diameter (Dh) was 0.187 and the dimple depth (δ) to dimple diameter (D) ratio was 0.2. It was observed that the combination of ribs and dimple channel (compound channel) has an average of 23 % more heat transfer than the ribbed channel. W rib compound channel shows the highest thermal performance and enhanced up to 30 % more heat transfer than semi and multi-semicircular compound channel. friction rise was observed in the compound channel compared to the ribbed channel.

Numerical and experimental investigation of thermal performance in data center with different deflectors for cold aisle containment

The rapid development of data center (DC) construction and its high energy consumption problem has caused widespread concern all over the world. Effective airflow management is considered to be a reliable method to improve the utilization of cooling capacity and energy saving of air conditioning system (ACS) in DC. An innovative method of airflow optimization applying deflector in cold aisle containment (CAC) is proposed to improve the uniformity of airflow distribution in this paper. It is found that, in numerical simulation the application of deflector can improve the cooling efficiency of airflow, and the application of convex deflector with height of 1700 mm can obtain the best thermal environment. Meanwhile, the hotspot area of the rack is greatly eliminated and the uniformity of airflow distribution is improved. Furthermore, the thermal performance of DC is compared between the basic and optimal cases under five rack power (1.8 kW, 2.4 kW, 3 kW, 3.6 kW, and 4.2 kW) and three operating parameters (18 °C, 3.5 m3/s; 20 °C, 4.4 m3/s; 22 °C, 5.4 m3/s), and the accuracy of the numerical simulation is verified by field experiments. It is found that the application of the deflectors can reduce the heat accumulation of the rack in different scenarios, avoid the damage to the servers, improve the utilization of cooling capacity, and improve overall thermal environment. Results show that the deflector with optimal structure has wide applicability.

Experimental Investigation of Thermal Performance of Aluminum Foil Coated with Polyester in a Direct Evaporative Cooling System

An experimental study was carried out for an evaporative cooling system in order to investigate the effect of using an aluminum pad coated with fabric polyester. In the present work, it was considered to use a new different type of cooling medium and test its performance during the change in the wet-bulb temperature and dry-bulb temperature of the supply air outside of the pad, the relative humidity of the supply air, the amount of air supplied (300-600) CFM and also the change of the amount of circulated water (1.75, 2.5, 4.5) liter per minute. A decrease in the WBT of the air was obtained, whereas the WBT of the air entering the pad was 26.5 . In contrast, the WBT of the outside air had reached 23 even though evaporative cooling is an adiabatic process which makes the WBT of the air that comes out of the pad is equal to the entering air WBT. The decrease in DBT is by changing the amount of air and water passing through the aluminum pad, whereas the DBT of the air entering the pad was 45 , while the DBT of the outside air had reached 29 . Also, an essential thing was obtained as this rise in the relative humidity of the air is very small 57%RH compared to the conventional pads, and this gives a positive impression as the air supplied from this pad has less moisture and its ability to carry moisture is much higher than that of air supplied from other pads. This gives a positive impression because the air supplied from this pad has lower humidity and its ability to hold moisture much higher than the air supplied from other traditional pads.

Experimental investigation of thermal performance for pulsating flow in a microchannel heat sink filled with PCM (paraffin/CNT composite)

A novel microchannel heat sink, which includes a heat exchange cavity with pyramid pin-fins and a PCM (phase change material) cavity with square pin-fins, is designed. The CNT (carbon nanotube) is added to paraffin to enhance thermal conductivity. GOPs (Graphene oxide particles) nanofluids pulsating flow driven by square wave are used to improve the thermal performance. The PCM cavity is filled with CNT/paraffin composite material to absorb and store the heat on the heating surfaces and to transfer the heat through the exchange chamber to achieve cooling. The results show that the microchannel heat sink’s thermal performance can be significantly improved using PCM composite and GOPs nanofluids. Under steady flow conditions, the total thermal resistance decreases significantly when the proportion of carbon nanotubes is approximately 20%; and, the maximum increase of Nusselt number reaches 34.9%. The thermal performance reaches the maximum enhancement under pulsating flow as the pulsating frequency is around 6 Hz. The total thermal resistance decreases by 19%, and the Nusselt number increases by 15.2%. The enhanced effects of pulsating flow and PCM composite on thermal performance are also affected by pump power and heating load. The higher heating power plays an active role in the enhancement effect, whereas the higher pump power has the opposite effect.

Experimental investigation of thermal performance of novel cold plate design used in a Li-ion pouch-type battery

• Thermal performance of serpentine tube and mini channel cold plates are compared. • Transient average battery temperature change is examined at the various conditions. • The effect of cold plate design on the battery temperature homogeneity is studied. • Low fluid inlet temperatures adversely affect battery temperature uniformity. The world's tendency towards electric vehicles has accelerated and the thermal management of them are critical part of the actual studies. Liquid-based cooling is known as the most common one among other cooling techniques. However, there is still need on the use of various heat transfer enhancement techniques to reduce the maximum temperature and maintain homogenous temperatures. This study experimentally investigated thermal performance of water-cooled cold plates used in thermal management of batteries by using conventional serpentine tube and a novel mini channel designs including a lithium-ion phosphate battery under certain discharge rates from 1C to 5C. Experiments are conducted for different water flow rates from 0.1 to 1.1 L/min as the coolant with inlet temperatures from 15 to 35 °C. Experimental results show that lower coolant inlet temperature causes the largest maximum temperature difference on battery surface. The use of mini channel cold plate resulted in 5.7 °C reduction in the maximum average battery surface temperature compared to serpentine one. Battery surface temperature homogeneity is improved up to 40% for operating conditions for mini channel cold plate usage. Thus, enhancement on thermal performance of proposed new mini channel cold plate is accomplished by temperature measurements.

Experimental investigation of thermal performance of the graphene-coated Al heat sink

To get rid of the heat better by improving the thermal performance of a heat sink, Al substrate was coated by a graphene layer with a different thickness by using a chemical spray method. The thickness of layers was changed by changing the spry time from 1000 to 5000 ms. Surface morphology was tested by using SPM to investigate the change that was occurred on the surface. In order to understand the performance of graphene-coated Al heat sink, a wind tunnel has been designed to investigate heat transfer coefficient, Nusselt number and thermal transmittance for each sample under turbulent flow condition with four values of Reynolds number. The results showed that graphene improves the thermal performance, and this performance is getting better with the thickness of graphene, up to critical thickness.

Experimental Investigation of Thermal Performance of Mesh Wick Heat Pipe Using Nanofluid

In the present world with the advancement in technology and development of devices with high speeds and continuous runs, it has become the most serious challenge to effectively manage the thermal dissipation so that the devices are able to run smoothly and efficiently. With an effective thermal management system, the performance of these equipments or machineries can be improved to a great extent. This can be done by using heat pipes with nanofluids. The suspension of nanoparticles within the size range of 1-100 nm in the base fluids like water, ethylene glycol, etc. is called nanofluid. The aim of this research is to prepare Aluminium-water based nanofluids and to study its various properties. The aluminium nanofluid was synthesised using De-ionized water as the base fluid. The characterisation of the nanofluid was done by scanning electron microscopy (SEM) and transmission electron microscope (TEM) techniques.

Experimental Investigation of Thermal Performance of Improvement a Solar Air Heater With Metallic Fiber

ABSTRACT The current research aims to study the overall performance of a solar air ‎heater ‎integrated system (SAHIs) under the Iraqi weather circumstances throughout the utilization of metallic fiber as a new method in absorbing the heat. Several experiments were conducted using a double pass triangular plate and compared with metallic fiber (SAH) as an absorber surface. These experiments were performed during February, March, and April of 2019 over the air mass flow rate range (0.0043–0.0125 kg/s) and depending upon environmental circumstances. Results evinced that the ultimate daily thermal efficiency of the solar air ‎heater was (63.77%) and (74.2%) with a triangular absorber plate and metallic fiber, correspondingly when using (0.012 kg/s) air mass flow rate and the instantaneous thermal efficiency of (SAH) increased from (30%) to (80%) and (30%) to (95%) when the air mass flow rate was increased from (0.0043 kg/s) to (0.0125 kg/s) and from (0.043 kg/s) to (0.0123 kg/s) for triangular absorber plate and metallic fiber, correspondingly. At an air mass flow rate of (0.012 kg/s), the temperature of the ultimate absorber surface and the outlet of air was (58°C) and (35°C) for triangular absorber plate, respectively and (49°C) and (44.5°C) for metallic fiber correspondingly. Also, the results demonstrated that the daily and instantaneous thermal efficiency of (SAH) with the metallic fiber was higher than that with a triangular absorber plate at the similar air mass flow rate. Additionally, the temperature discrepancy between the absorber surface and the outlet air when employing metallic fiber was less in comparison with the use of triangular absorber plate, and the temperature difference between inlet and outlet air temperature decreased when the air mass flow rate was increased. Moreover, the present study manifested a higher overall thermal efficiency than those obtained by previous studies. Abbreviations: HE: Heat exchanger; SAH: Solar Air Heater; SAHs: Solar Air Heaters; SAHIS: Solar Air ‎Heater ‎Integrated System

Application of a phase change material to a thermoelectric ceiling radiant cooling panel as a heat storage layer

The objective of this study was to propose and obtain a workable design of a phase change material integrated thermoelectric radiant cooling panel (PCM-TERCP) through numerical and experimental investigations of thermal performance. The proposed PCM-TERCP consists of thermoelectric modules (TEMs), heat sinks, insulation, and PCM layer between two aluminum panels. The PCM layer is a thermal energy storage which provides passive cooling without operation of TERCP by freezing the PCM during the operation period for shifting the electrical load to the off-peak period demand periods.A numerical model of the proposed cooling panel was developed to obtain a desirable configuration of the PCM layer such that it would maintain the surface temperature set-point of the panel during the operation period without the activation of the TEMs of the panel. The numerical model was validated by measurement and data acquired through a laboratory test of the PCM-TERCP mockup. The predicted results agreed well with the measurement data, within the 10% error bounds. A parametric study was carried out to determine the critical design parameters affecting the cooling performance of PCM-TERCP. The results indicated that the panel surface temperature was significantly affected by the number of heat fins inside the PCM and thickness of the PCM layer. A 10-mm-thick PCM layer with more than five heat fins per unit length of the panel was the most feasible solution among the several cases considered in this study for PCM-TERCP to satisfy the design requirements for application in a conditioned space. In addition, it was revealed that the liquid fraction of PCM should be under 0.6–0.65 for efficiently using the latent heat of PCM by enhancing the heat transfer of PCM.

Experimental investigation of thermal performance of indirect mode solar dryer with phase change material for banana slices

ABSTRACT This paper presents an experimental investigation on a natural convection indirect mode solar dryer with phase change material (PCM) for drying of banana slices. The drying system consists of one collector with PCM and a drying chamber with two equally spaced trays. The paraffin wax was used as PCM in the dryer which release latent and sensible heat after sunset that make dryer operate effectively for the next 5 h. For the experimental investigations, 400 g of banana slices were dried from 73.2% (wb) to 20% (wb) of moisture content in 18 h (13 h day time operation + 5 h PCM) during April 2018 at Gorakhpur, Uttar Pradesh, India. Fourteen thin layer models for drying of banana slices, available in the either empirical or non-empirical form, were fitted using experimental data. A statistical analysis software, XL-stat was used to evaluate the values of constants of models and errors through non-linear regression analysis. Modified Henderson and Pabis model was found best suitable for the drying behavior of banana slices among all the models of thin-layer drying characteristics. The average drying rate for the lower tray and upper tray were 0.1316 and 0.1310 kg of water/kg of dried product/h respectively. The moisture content was reduced at a faster rate for the lower tray with moisture ratio from 100 to 28%. The maximum and average dryer efficiency were 9.88 and 2.98%, respectively, and the maximum and average collector efficiency were 85.46 and 66.32% respectively. This study showed that indirect type solar dryer with paraffin wax is suitable for drying of banana because it takes considerable time for drying and can be used for drying of other agricultural crops.

Experimental Investigation of Thermal Performance of a Solar Chimney Provided with a Porous Absorber Plate


 Experimental investigation of the influence of inserting the metal foam to the solar chimney to induce natural ventilation are described and analyzed in this work. To carry out the experimental test, two identical solar chimneys (without insertion of metal foam and with insertion of metal foam) are designed and placed facing south with dimensions of length× width× air gap (2 m× 1 m× 0.2 m). Four incline angles are tested (20o,30o,45o,60o) for each chimney in Baghdad climate condition (33.3o latitude, 44.4o longitude) on October, November, December 2018. The solar chimney performance is investigated by experimentally recording absorber plate and air temperatures and velocity of air. Results indicated that the using metal foam absorber plate lead to reducing the mean temperature of absorber plate by 6.7 °C as a result, the values of chimney outlet air temperature increased. The daily solar chimney efficiency enhanced by 58.7% and the useful energy received also increased. The existence of metal foam caused higher air velocity at the exit and increasing in the ventilation rate that the maximum ventilate rate obtained from the solar chimney is 5.96 1/hr for 27 m3 volume of room at solar irradiance of 730 W/m2 for chimney incline angle of 60o. The results of the experimental work show that the addition of metal foam to the solar chimney as an absorber plate is an efficient method to enhance the characteristics of heat transfer and the thermal performance of the solar chimney in the weather condition of Iraq.

Experimental investigation of thermal performance of the graphene oxide–coated plates

AbstractThis paper experimentally investigates the conductive heat transfer of samples with different materials and coatings. A range of graphene oxide nanoparticle concentration has been employed. Results demonstrate that utilizing nanoparticles leads to enhancement of conductive heat transfer by 10.07% and 8.01% for EK2 and ST14 samples, respectively. The aforementioned nanoparticles also reduce coating thickness and yield an enhanced quality of the surface, in terms of mechanical properties. The convective and radiative methods of heat transfer have been ignored in this study.

Experimental investigation of thermal performance of a heating system combining solar air collector with hollow ventilated interior wall

A novel heating system combining solar air collector with hollow ventilated interior wall (SAC-HVIW) has the ability to supply thermal energy for the nighttime heating and improve the nighttime thermal comfort in residential buildings on Tibetan Plateau. In this paper, a test chamber is constructed to investigate the heating performance of this system. Nine cases with different ventilation rates and supply air temperatures in the channel are measured under steady-state conditions. Results show that the heating capacity of the hollow ventilated interior wall increases with the logarithmic mean temperature difference (LMTD). U-value of the interior wall changes smoothly with the ventilation rate and the LMTD of the system, but the effectiveness of the interior wall almost keeps constant for all cases with the mean value of 0.85. The radiant heat transfer coefficient of the hollow ventilated interior wall keeps the constant of 5.43 W/(m2•K), whereas the convective heat transfer coefficient increases smoothly with the ventilation rate and the inlet air temperature. Radiant heat transfer is dominant with the weight of more than 60%. Experimental data are used to evaluate the heating performance of HVIW, and it is also beneficial to the design of this system.

Experimental investigation of thermal performance of the oscillating heat pipe for the grinding wheel

A massive amount of heat is generated during the high-efficiency grinding process, which leads to a serious burnout problem that limits the increase of the material removal rate. The oscillating heat pipe (OHP) can augment the heat transfer in the grinding zone to avoid the burnout. An oscillating heat pipe grinding wheel that is a combination of a grinding wheel and OHPs was proposed in this paper. Aimed to determine geometric dimensions and operating parameters of the OHP, experimental investigations were carried out to study effects of working fluid, inner diameter, and heat flux on the heat transport capability of OHPs. The dynamics of flow change and coupled effects of geometric dimensions and thermophysical properties of working fluids were further analyzed by visualization. The OHP filled with acetone shows an advantage in heat transfer. Within the critical diameter range, a large inner diameter is better for the thermal performance. As heat flux increases, changes of flow pattern and motion modes from bubbly flow to annular flow and from oscillation to circulation enhance the thermal performance. The inner diameter of 3 mm and acetone as the working fluid are preferred for better cooling effects.