Hafiz Muhammad Ali - Academia.edu (original) (raw)

Papers by Hafiz Muhammad Ali

$Research paper thumbnail of Thermal performance of phase change material (PCM) based pin-finned heat sinks for electronics devices: Effect of pin thickness and PCM volume fraction$

Inclusion of paraffin wax reduces the base temperature of heat sink. An enhancement ratio of 2.64... more Inclusion of paraffin wax reduces the base temperature of heat sink. An enhancement ratio of 2.64 at w = 1.00 is achieved for a SPT of 60 °C at 3.174 kW/m 2 for 2 mm thick pin-fin heat sink. At heat input of 1.98 kW/m 2 , it took 145 min and 229 min to reach SPTs of 60 °C and 70 °C respectively. 3 mm Pin-fin thick heat sink outperform the 2 mm pin-fin thick heat sink for volume fractions of w = 0.33 and w = 0.66. An enhancement of 4.30 is achieved against heat flux of 3.174 kW/m 2 for 2 mm thick pin-fin heat sink. a b s t r a c t The present experimental investigation focuses on the passive cooling of electronic devices by using phase change material (PCM) based pin-fin heat sinks to increase reliability, to ensure sufficiently lower temperature, to stretch the operating duration and to improve the functionality of installed features. Paraffin wax is used as a PCM and filled in heat sinks made of aluminum. As the thermal conductivity of PCM is very low, aluminum square fins are used as thermal conductivity enhancer (TCE). A volume fraction of TCE is kept constant at 9% and the uniform heat flux is applied to finned and un-finned heat sinks. An un-finned heat sink is used for base line comparison. Fin thicknesses of TCE of 1 mm, 2 mm, and 3 mm with square cross sectional area are investigated with a constant height of 20 mm. Volume fractions of PCM are varied as 0.00, 0.33, 0.66 and 1.00 for each heat sink to determine the thermal performance. The present study reports thermal performance at various heat fluxes to enhance the operating time for different set point temperatures (SPTs) and to compare the latent heat phase duration for various heat sinks tested. The results reveal that maximum thermal performance in operating time is achieved for 2 mm thick pin-fin heat sink filled with PCM volumetric fraction of 1.00.

In this work, graphene nanoplatelets nanofluids (GNPs) thermal and hydrodynamic performance is ob... more In this work, graphene nanoplatelets nanofluids (GNPs) thermal and hydrodynamic performance is
observed experimentally in comparison with distilled water on integral fin heat sink. Water based
GNPs nanofluids is used with 10% weight concentration. Experimentation is performed in laminar range
at heat flux of 47.96 KW/m2, 59.95 KW/m2 and 71.94 KW/m2. Higher pumping power is noticed for GNPs
nanofluids as compared to distilled water. From inlet to outlet of heat sink, rise of local base temperature
is observed for both distilled water and GNPs nanofluids. With the increase of heat flux, GNPs nanofluids
thermal performance decreases. Using GNPs nanofluids, the lowest base temperature and maximum convective
heat transfer enhancement is noted as 36.81 C and 23.91% corresponding to Reynolds number of
972 for heat flux of 47.96 KW/m2, respectively. Pumping power requirement depends upon flow rate and
heat flux, and it is found to be maximum 0.04W for GNPs nanofluids at heat flux of 47.96 KW/m2.

In this paper, a generalized model has been developed to predict the condensate flooding (i.e. th... more In this paper, a generalized model has been developed to predict the condensate flooding (i.e. the portion
of the tube covered with condensate) on the horizontal pin-fin tubes during free convection condensation.
The model is based on the balance of forces act up on the condensate in upward and downward
directions due to the effects of surface tension of the fluid and gravity. The model has been compared
with the wide range of experimental data already reported by researchers for a wide range of fluid
and tube combinations. The model predicts the condensate flooding on horizontal pin-fin tubes to within
±15% over most of the experimental data.

This study reports an experimental work to examine the angle effect of pin fin heat sink channel ... more This study reports an experimental work to examine the angle effect of pin fin heat sink channel in terms
of convective heat transfer coefficient, log mean temperature difference and thermal resistance using
water based graphene nanoplatelets (GNPs) nanofluids in a flow rate range of 0.25–0.75 LPM. Three heat
sinks having channel angles, measured from positive x-axis, 22.5 degree, 45 degree and 90 degree are
used. The volumetric concentration of GNPs particles is 9.5% and these particles consist of overlapped
two-dimensional graphene layers. All heat sinks are fabricated with copper substrate, which is maintained
at uniform heat flux during experimentation. Heat sink with 22.5 degree channel angle shows better
thermal performance as compared to other tested heat sinks. For the same flow rate, 22.5 degree heat
sink shows lowest convective thermal resistance as compared to other tested heat sinks.

High heat flux at reduced wall super heat temperature difference is a major concern of researcher... more High heat flux at reduced wall super heat temperature difference is a major concern of researcher in the
area of pool boiling heat transfer. One of the techniques is the use of nanoparticles in base fluid which
provides high heat flux at relatively low super heat value. Current investigation concentrates on the
impact of TiO2-water based nanofluids on the wall super heat, boiling heat transfer coefficient, and heat
flux at atmospheric pressure. Experimental setup was validated by nucleate pool boiling of distilled water
and by retracing the Pioro correlation. Two different concentrations of 12% and 15% by weight of TiO2 in
water as base fluid were tested and on average, enhancements in boiling heat transfer coefficient (W/
m2 K) were found to be 1.38 and 1.24 for 15% TiO2 and 12% TiO2 nanofluids respectively, when compared
to the results of distilled water.

In this paper performance of an indirect evaporative cooler is experimentally analyzed in terms o... more In this paper performance of an indirect evaporative cooler is experimentally analyzed in terms of its
thermal effectiveness. A heat and mass exchanger (HMX) using a cross-flow pattern incorporating
Maisotsenko cycle (M-cycle) is designed and fabricated having an improved channel width to height ratio
and more efficient moisture absorbing material (felt) on the wet channel. Experimental investigations
are conducted under various operating conditions of inlet air including its humidity, temperature and
velocity along with water temperature. The experimental results indicate that the dew point effectiveness
and the wet bulb effectiveness vary in the range of 62–85% and 92–120%, respectively with inlet
air temperature variation from 25 to 45 °C at different humidity ratio ranging from 11 g/kg to 19g/kg.
Moreover, the overall performance of the improved design is found 5% more efficient in terms of wet
bulb effectiveness compared to the previous systems.

A flat sheet air gap membrane distillation (AGMD) model and an evaporative crystallizer model wer... more A flat sheet air gap membrane distillation (AGMD) model and an evaporative crystallizer model were
developed for design and optimization of the lab-scale zero liquid discharge (ZLD) water desalination
experimental plant. The models were validated by comparing with published experimental data.
Univariate analysis was utilized to investigate the influences of thirteen operating and dimensional
parameters of single stage and multi-stage AGMD modules on the permeate flux, evaporative efficiency,
water recovery, and gained output ratio (GOR). Optimization of the parameters were conducted aiming to
maximize the permeate flux, water recovery, and GOR of the AGMD module. Membrane distillation and
crystallization (MDC) process was then altogether modeled in Aspen Plus software based on the parameter
studies of the single and multi-stage AGMD model. The effects of water removal ratio in the crystallizer
and NaCl mass fraction of the MD retentate stream on the heat duty of the system were analyzed.
The operating condition with the minimum input energy for the current MDC design was determined,
and the input energy is 1651.5 kJ/kg-H2O. The process can be further optimized to tremendously reduce
the required input energy when the heat stored in the evaporated vapor from the crystallizer is
recovered.

The temperature of the photovoltaic module has an adverse effect on the performance of photovolta... more The temperature of the photovoltaic module has an adverse effect on the performance of photovoltaic modules. The photovoltaic module converts a small portion of energy from solar radiations into electricity while the remaining energy wastes in the form of heat. In this study, water cooled PV/T system was analyzed to enhance the efficiency by absorbing the heat generated by the photovoltaic modules and allowing the photovoltaic module to work at comparatively low temperature. For this system, four photovoltaic modules of two different types were used. To investigate the cooling effect, two modules were modified by making ducts at their back surface having inlet and outlet manifolds for water flow. The measurements were taken with cooling and without cooling of photovoltaic modules. The temperature was measured at inlet, outlet and at different points at the back of Photovoltaic modules. It was found that there was a linear trend between the module efficiency and temperature. The average module temperature of c-Si and p-Si modules without cooling was 13.6% and 7.2% lower respectively than the same modules without cooling. As a result of temperature drop, the average module electrical efficiency of c-Si and p-Si was 13% and 6.2% higher respectively compared to the modules without cooling. Flowing water also gains useful heat from PV module so the resultant overall energy of the system was much higher.

New experimental data are reported for the condensation of steam on square wire wrapped on horizo... more New experimental data are reported for the condensation of steam on square wire wrapped on horizontal
instrumented copper tube. 0.8 mm square cross-section wires made of copper and brass and 1.0 mm
square cross-section wire made of copper with pitches of 2.0 mm, 4.0 mm and 6.0 mm are used. For both
0.8 mm and 1.0 mm square cross-section wire wrapped tubes, best performing pitch was found to be
4.0 mm i.e. 1.53 and 1.5 for 0.8 mm and 1.0 mm square wire wrapped tubes respectively. The effect of
thermal conductivity was evident in case of 0.8 mm (copper and brass) square wire wrapped tube at
all pitches tested with significance at 2.0 mm pitch. Compared to equivalent round cross-section wire
wrapped tubes, 0.8 mm square wire wrapped tubes showed lower heat transfer enhancement than
0.8 mm diameter round wire wrapped tubes while heat transfer enhancement was higher for 1.0 mm
square wire wrapped tubes than 1.0 mm diameter round wire wrapped tubes i.e. 13.4%, 7.1% and 3.7%
higher enhancement than the round wire wrapped tubes at 2 mm, 4 mm and 6 mm respectively.

An experimental study has been carried out to measure the performance of commercially available p... more An experimental study has been carried out to measure the performance of commercially
available photovoltaic modules during summer months in the climate of
Taxila, near the capital of Pakistan. The modules used in the study are
monocrystalline silicon, polycrystalline silicon, and single junction amorphous silicon.
The analysis has been focused on the measurement of module efficiency, performance
ratio and temperature of each module at actual operating conditions using
outdoor monitoring facility. The measured results are compared with the
already published data of peak winter month at the same site. Overall, the
monocrystalline module showed high average module efficiency while amorphous
silicon module was better in term of average performance ratio. Furthermore, the
module efficiency and performance ratio has shown decreasing trend with increase
of module temperature. It was found that modules have much higher temperature in
summer months (about 20 °C higher) and showed low efficiency and performance
ratio than peak winter month. The average ambient temperature varied from 18.1-
-38.6 °C from winter to summer.

The performance of a dew-point cooler is analyzed in terms of various parameters including dew po... more The performance of a dew-point cooler is analyzed in terms of various parameters including dew point and wet bulb effectiveness. An experimental setup of a counter-flow heat and mass exchanger [HMX] based on Maisotsenko cycle (M-cycle) evaporation technique is established. The setup consists of 8 dry channels made of Aluminum sheets and 7 wet channels made of kraft paper. Experimental analysis is performed under wide range of operating parameters including air absolute humidity i.e. 12.7 g/kg to 18g/kg, air temperature i.e. 20 to 55oC, and inlet velocities i.e. 0.88 to 1.50 m/s. The results indicate that appreciably higher value of dew-point and the wet-bulb effectiveness can be achieved ranging up to a maximum of 93% and to 130%, respectively at various inlet air conditions. Apart from the ambient air conditions, influence of amount of air diversion to wet side of channel is also studied. It is observed that this design feature of HMX can lead to a substantial increase of dew-point and wet-bulb effectiveness. By varying the inlet to wet side air ratio, a suitable limit of the quantity of inlet air diversion to working side is also suggested.

The use of vacuum glazed windows is increasing due to their application in modern building design... more The use of vacuum glazed windows is increasing due to their application in modern building design. Among various types of vacuum glazed windows reported in literature, thermal transmittance of single glass sheet (conventional window) i.e 6 W/m2k is reduced by 66 and 77% using air filled double glazed and air filled triple glazed windows respectively. Using low emittance coatings thermal transmittance of double glazed windows is reduced by 53%, however it offsets the visibility by reducing light transmittance by 5%. Stresses due to temperature/pressure gradients if not eliminated may lead to reduction in service life of vacuum glazed windows. Vacuum created between the glass sheets is used to reduce conductive heat transfer. Degradation in the vacuum is caused by number of factors such as, permeation of gaseous molecules through glass sheets, leakage through sealing, thermal/optical desorption and photo-fragmentation of organic species have been critically reviewed and future trends are outlined.

The paper reports experimental results using simulated condensation on eight horizontal integral ... more The paper reports experimental results using simulated condensation on eight horizontal integral finned tubes with different fin spacing but same root diameter. Condensation was simulated with low approaching zero vapor velocity of condensate using three liquids (water, ethylene glycol and R141b) supplied to the tube via small holes between the fins along the top of the tubes. Controlling parameters of the investigation were fin spacing of condensation tubes, flow rate of condensate and surface tension to density ratio of the condensate. The results indicate that the retention angle (measured from the top of the tube to the position where the inter-fin space is completely filled with liquid) increases with the increase in fin spacing. Also, retention angle increases as the density of the condensate increases but retention angle decreases with increase in surface tension. Interesting finding is seen as retention angle remains constant with increase in condensate flow rate, starting from very low (nearly zero) flow rate to the flow rate at which the tube gets fully flooded. The critical flow rate for eight tubes of defined fin density against three working fluids is measured. Results obtained from simulated condensation for almost zero condensate velocity are in good agreement with earlier data and theoretical model for retention angle on such tubes [1].

In this investigation, deionized water was used as base fluid. Two different types of nanoparticl... more In this investigation, deionized water was used as base fluid. Two different types of nanoparticles, namely Aluminium oxide and Copper were used with 0.251% and 0.11% volumetric concentrations in the base fluid respectively. Nanofluids cooling rate for flat heat sink used to cool a microprocessor was observed and compared with the cooling rate of pure water. An equivalent microprocessor heat generator i.e. a heated copper cylinder was used for controlled experimentation. Two surface heaters, each of 130 W power, were responsible for heat generation. The experiment was performed at the flow rates of 0.45 LPM, 0.55 LPM, 0.65 LPM, 0.75 LPM and 0.85 LPM. The main focus of this research was to minimize the base temperature and to increase the overall heat transfer coefficient. The lowest base temperature achieved was 79.45 oC by Aluminium oxide nanofluid at Reynolds number of 751. Although, Al2O3/H2O nanofluid showed superior performance in overall heat transfer coefficient enhancement and thermal resistance reduction as compared to other tested fluids. However, with the increase of Reynolds number, Cu/H2O nanofluid showed better trends of thermal enhancement than Al2O3/H2O nanofluid, particularly at high Reynolds number ranges.

Oxidation and nitridation of nano aluminum particles (NAPs) were studied experimentally by using ... more Oxidation and nitridation of nano aluminum particles (NAPs) were studied experimentally by using
simultaneous thermal analysis (STA) which is combination of differential scanning calorimetry (DSC) and
thermogravimetric analysis (TGA) in the atmosphere of air and nitrogen at one atmospheric pressure
conditions. It was observed that in air the oxidation process of NAPs completed in three steps whereas in the
nitrogen it was a two stepped reaction. In air the major oxidation step was observed before melting of the
particles while in nitrogen it occurred after that. The particles were ignited in air whereas no such rapid
reaction was seen in nitrogen. It was also observed that the heat produced during the chemical reaction in air
was three times the heat produced in nitrogen atmosphere. Detailed characterisation of nano aluminum
particles (NAPs) before and after the experiments was done with scanning electron microscopy (SEM),
transmission electron microscopy (TEM), Nanosizer (DLS), energy dispersive X-ray spectroscopy (EDS) and
powder X-ray diffraction (XRD).

Performance of desiccant evaporative cooling (DEC) system configurations is strongly influenced b... more Performance of desiccant evaporative cooling (DEC) system configurations is strongly influenced by the climate conditions and varies widely in different climate zones. Finding the optimal configuration of DEC systems for a specific climatic zone is tedious and time consuming. This investigation conducts performance analysis of five DEC system configurations under climatic conditions of five cities from different zones: Vienna, Karachi, Sao Paulo, Shanghai, and Adelaide. On the basis of operating cycle, three standard and two modified system configurations (ventilation, recirculation, dunkle cycles; ventilated-recirculation and ventilated-dunkle cycles) are analyzed in these five climate zones. Using an advance equation-based object-oriented (EOO) modeling and simulation approach, optimal configurations of a DEC system are determined for each climate zone. Based on the hourly climate data of each zone for its respective design cooling day, performance of each system configuration is estimated using three performance parameters: cooling capacity, COP, and cooling energy delivered. The results revealed that the continental/micro-thermal climate of Vienna, temperate/mesothermal climate of Sao Paulo, and dry-summer subtropical climate of Adelaide favor the use of ventilated-dunkle cycle configuration with average COP of 0.405, 0.89 and 1.01 respectively. While ventilation cycle based DEC configuration suits arid and semiarid climate of Karachi and another category of temperate/mesothermal climate of Shanghai with average COP of 2.43 and 3.03 respectively.

New experimental data are reported for water based nanofluids to enhance the heat transfer perfor... more New experimental data are reported for water based nanofluids to enhance the heat transfer performance
of a car radiator. ZnO nanoparticles have been added into base fluid in different volumetric
concentrations (0.01%, 0.08%, 0.2% and 0.3%). The effect of these volumetric concentrations on the heat
transfer performance for car radiator is determined experimentally. Fluid flow rate has been varied in a
range of 7e11 LPM (liter per minute) (corresponding Reynolds number range was 17,500e27,600).
Nanofluids showed heat transfer enhancement compared to the base fluid for all concentrations tested.
The best heat transfer enhancement up to 46% was found compared to base fluid at 0.2% volumetric
concentration. A further increase in volumetric concentration to 0.3% has shown a decrease in heat
transfer enhancement compared to 0.2% volumetric concentration. Fluid inlet temperature was kept in a
range of 45e55 C. An increase in fluid inlet temperature from 45 C to 55 C showed increase in heat
transfer rate up to 4%.

Desiccant cooling systems provide new possibilities in air conditioning technology through the us... more Desiccant cooling systems provide new possibilities in air conditioning technology through the use of
either solid or liquid sorption air dehumidification. Such systems can be more reliable and environmental
friendly than the conventional systems. The focus of current study is to enhance the existing ideal system
component models of the desiccant evaporative cooling system (DEC) developed in an equation-based
object-oriented modeling and simulation program, Dymola/Modelica to address the real component
operation. Initially, the enhanced component models are calibrated and validated through the transient
measurements obtained from the real DEC system installation. Afterward, using the validated physical
models of individual components, complete system model has been experimentally calibrated and
validated. The obtained results are in good agreement with the actual measurements at the both
component and system levels. At the system level, in terms of specific enthalpy of supply air, the
resulting maximum and minimum root mean square error (RMSE) and mean percentage error (MPE)
between the simulated and measured transient performance is 0.96 kJ/kg and 1.53%. The results show
that the enhanced system model is able to predict the performance of the real desiccant cooling system
with good accuracy. As such, the current paper contributes to the efforts of bringing simulations closer to
performance of real systems under building operating conditions.

$Research paper thumbnail of Thermal performance of phase change material (PCM) based pin-finned heat sinks for electronics devices: Effect of pin thickness and PCM volume fraction$