Enhancement of thermal comfort in a large space building

Many large confined spaces in tropical countries employ a combination of natural ventilation and mechanical fans for space cooling purposes. However, due to low wind velocity and an inability of mechanical fans to remove warm air, this cooling method is not capable of providing a satisfactory thermal comfort to the occupants. This study aims to find out a simple strategy for improving the thermal comfort inside a mosque building in Malaysia. Field measurements were first carried out to acquire the airflow velocity, air temperature, relative humidity and mean radiant temperature inside the mosque, for a duration of one-year. These data were then used to calculate two thermal comfort indices namely predicted mean vote (PMV) and predicted the percentage of dissatisfied (PPD). A computational fluid dynamic (CFD) method was employed to predict airflow and temperature distributions and to examine the effects of installing exhaust fans on the thermal comfort condition inside the mosque. Parametric flow analyses were conducted to find out the arrangement of the exhaust fans that would produce highest improvement in the PMV and PPD thermal comfort indices. It was found that, under the present ventilation condition, both PMV and PPD values at the selected locations inside the mosque exceed the respective upper limits as recommended in the ASHRAE Standard-55, indicating that the thermal comfort inside the mosque is extremely hot. Results of parametric flow analyses show that installing ten exhaust fans with a 1-m diameter at the south-side wall, at the height of 6 m from the floor, has a potential of reducing the PMV index by 75–95% and the PPD index by 87–91%. This translates into a vast improvement in the thermal comfort inside the mosque building

Improvement of thermal comfort inside a mosque building

A combined natural ventilation and mechanical fans are commonly used to cool the interior space inside the mosques in Malaysia. This article presents a study on thermal comfort in the Al-Jawahir Mosque, located in Johor Bahru, Malaysia. The objective is to assess the thermal comfort inside the mosque under the present ventilation system by determining the Predicted Mean Vote (PMV) and the Predicted Percentage of Dissatisfied (PPD). These values were then compared to the limits stated in the ASHRAE Standard-55. It was found that the PMV varies from 1.68 to 2.26 while the PPD varies from 61 to 87. These show that the condition inside the mosque is quite warm. Computational fluid dynamics (CFD) method was used to carry out flow simulations, to identify a suitable strategy to improve the thermal comfort inside the mosque. Results of CFD simulations show that installing four exhaust fans above the windows on the west-side wall of the mosque is the most effective strategy to improve the thermal comfort inside the mosque. Both the PMV and PPD values can potentially be reduced by more than 60

Vapor pressure development in a FR4-CU composite structure during solder reflow

This article presents a study on the development of vapor pressure a FR4-Cu composite structure when heated to a solder reflow temperature of 215 °C. Abaqus® finite element software was used to develop a representative two-dimensional model of the composite structure and to simulate moisture absorption and desorption processes. Simulation of transient moisture absorption was performed to predict moisture concentration distribution in the structure after being preconditioned in 85°C/85 % RH environment for 15 days. Simulation of transient moisture desorption was carried out at the solder reflow temperature to predict the redistribution of the moisture. Results of the moisture desorption simulation were used to compute magnitude of the vapor pressure in the structure. It was found that the moisture redistributes itself during the solder reflow process. Moisture concentration in the vicinity of the FR4-Cu interface, below the longer copper trace increases during the solder reflow. The vapor pressure in nearly 70 % of the FR4 material and close to the FR4-Cu interface, below the longer copper trace is almost equal to the saturation pressure of vapor at 215 °C. Distribution of the vapor pressure is very similar to the new distribution of moisture concentration resulting from moisture desorption process

Analysis of air and airborne particles movements in a hospital operating theater

In this study a computational fluid dynamics (CFD) method was used to develop a validated model of a hospital operating theater. The model was employed to perform simulation to predict the distribution of airflow and movement of the airborne particles inside the operating theater at a steady-state condition. The airborne particles were modeled as discrete particles which were released from the exposed body surface of the surgical staffs at a rate of 10 CFU/s. The effect of laminar inlet air flow velocity on the airborne particles concentration around the operating table was examined. It was found that the air flows straight downward from the air-conditioning diffuser towards the middle of the operating table. However, the existence of the medical lamp causes a vortex air flow condition below it. Air also penetrates the ultra-clean area on the opposite side of the operating table. The airborne particles are washed away from the vicinity of the operating table by the air flow. This is more effective when the supply air flow velocity is high. At low air flow velocity, some particles appear to penetrate into the ultra-clean area near the edges of the operating table. At higher air flow velocity, the airborne particles seem to be more effectively washed away from this region. High concentration of airborne particles occurs underneath the medical lamp due to vortices created by the air flow. Higher air flow velocity increases the level of particles concentration in this area

Two step runge-KUTTA-nystrom method for solving second-order ordinary differential equations

In this research, methods that will be able to solve the second order initial value problem (IVP) directly are developed. These methods are in the scheme of a multi-step method which is known as the two-step method. The two-step method has an advantage as it can estimate the solution with less function evaluations compared to the one-step method. The selection of step size is also important in obtaining more accurate and efficient results. Smaller step sizes will produce a more accurate result, but it lengthens the execution time. Two-Step Runge-Kutta (TSRK) method were derived to solve first-order Ordinary Differential Equations (ODE). The order conditions of TSRK method were obtained by using Taylor series expansion. The explicit TSRK method was derived and its stability were investigated. It was then analyzed experimentally. The numerical results obtained were analyzed by making comparisons with the existing methods in terms of maximum global error, number of steps taken and function evaluations. The explicit Two-Step Runge-Kutta-Nyström (TSRKN) method was derived with reference to the technique of deriving the TSRK method. The order conditions of TSRKN method were also obtained by using Taylor series expansion. The strategies in choosing the free parameters were also discussed. The stability of the methods derived were also investigated. The explicit TSRKN method was then analyzed experimentally and comparisons of the numerical results obtained were made with the existing methods in terms of maximum global error, number of steps taken and function evaluations. Next, we discussed the derivation of an embedded pair of the TSRKN (ETSRKN) methods for solving second order ODE. Variable step size codes were developed and numerical results were compared with the existing methods in terms of maximum global error, number of steps taken and function evaluations. The ETSRKN were then used to solve second-order Fuzzy Differential Equation (FDE). We observe that ETSRKN gives better accuracy at the end point of fuzzy interval compared to other existing methods. In conclusion, the methods developed in this thesis are able to solve the system of second-order differential equation (DE) which consists of ODE and FDE directly

Computerized simulation of automotive air conditioning system: a parametric study

This paper presents results of a parametric study performed on an automotive air-conditioning (AAC) system of a passenger car. The goals are to assess the effects of varying the volumetric flow rate of supply air, number of occupants, vehicle speed, and the fractional ventilation air intake (XOA), on the dry-bulb temperature and specific humidity of the air inside the passenger’s cabin, and on the evaporator coil cooling load of the AAC system. Results of the parametric study show that increasing the supply air flow rate reduces the dry-bulb temperature of the cabin air, increases both the specific humidity of the air and the evaporator coil load. Increasing the number of occupants in the passenger cabin causes the cabin air temperature, specific humidity and the evaporator coil load to increase. Increasing the vehicle speed causes the specific humidity of the cabin air and the evaporator coil cooling load to increase but the dry-bulb temperature of the air is not significantly affected. Increasing the fractional fresh air intake (XOA) also increases the cabin air specific humidity and the evaporator coil cooling load

Field measurement of airborne particulate matters concentration in a hospital's operating room

In a hospital operating room, adequate air flow and cleanliness are crucial to protect the patient from surgical site infection (SSI) during a procedure. The probability of the patient to get the infection is related to the concentration of bacteria carrying particles inside the room. This paper presents a field measurement study to quantify the concentration of particulate matters (PM) in a hospital operating room which complies with the ISO Class 7 requirements. The operating room was equipped with High Efficiency Particulate Air (HEPA) filters and a vertical laminar air flow (LAF) system. The measurements were conducted at three height levels from the floor namely 1.2 m, 1.8 m and 2.4 m. The data was logged at a rest condition, in accordance to the ISO 14644-1 requirements. A HPC300 particle counter was used to measure the concentrations of particulate matters namely PM0.5, PM1 and PM5. The results show that the concentrations of all particulate matters were higher at the height level of 1.2 m compared to other height levels. The concentration of PM0.5 was relatively higher than PM1 and PM5 in the vicinity of operating table

Experimental study on a cold storage system with a variable speed compressor

Selection of a compressor for a refrigeration system is generally done based on a peak load operating condition. The energy consumed by the compressor can potentially be reduced by regulating the compressor speed using an inverter. This experimental study investigates energy saving and performance enhancement potentials in an experimental cold-storage system when the electric frequency supply is reduced from 45 to 25 Hz, with a 5 Hz interval. The system is equipped with a compressor with a power rating of 3 HP (2.25 kW) and R22 was used as the refrigerant. The cooling load of the system was provided using an electric heater placed at the bottom of the cold storage chamber. Results show that the power input to the compressor was reduced when the electric frequency supply was decreased. The highest reduction in the compressor power input occurred when the electric frequency was decreased from 45Hz to 40Hz. The results also show that the coefficient of performance (COP) of the cold storage system was improved when the electric frequency supply was decreased. The largest COP improvement occurred when the frequency was decreased from 30 Hz to 25 Hz

Performance of solar thermal collector using multi-walled carbon nanotubes: simulation study

A flat-plate solar collector (FPSC) using multi-walled carbon nanotubes (MWCNTs) was numerically studied. Multi-walled carbon nanotubes (MWCNTs) with outside diameters of (< 8 nm) and 0.1wt.% were utilized. A three-dimensional model was built and solved via ANSYS software and the inlet parameters as 1000 W/m2, inlet temperature of 30°C and the volume flow rates in the range of 0.2-0.8 kg/min. Using DW decreased the temperature of absorber by 0.840%, 1.437%, 1.909%, 2.308%, 2.616% and 2.869% for the varied flow rates. Relative to DW, the temperature of absorber decreased by 0.874%, 0.804%, 0.756%, 0.717%, 0.685%, 0.655% and 0.633% at the same flow rate ranges. Meanwhile, the thermal efficiency of MWCNTs nanofluid was increased by 6.080%, 6.322%, 6.311%, 6.337%, 6.450% and 6.857% for volume flow rate of 0.2-0.8 kg/min

Reducing soak air temperature inside a car compartment using ventilation fans

This article presents an investigation on the effects of using ventilation fans on the air temperature inside a car passenger compartment when the car is parked under the sun. It was found from a measurement that the air temperature inside the passenger compartment could raise up to 48°C. Computational fluid dynamics method was used to develop model of the compartment and carry out flow simulations to predict the air temperature distribution at 1 pm for two conditions: without ventilation fans and with ventilation fans. The effects of fan location, number of fans used and fan airflow velocity were examined. Results of flow simulations show that a 17% temperature reduction was achieved when two ventilation fans with airflow velocity of 2.84 m/s were placed at the rear deck. When three fans were used, an additional 3.4% temperature reduction was attained. Placing two ventilation fans at the middle of the roof also reduced the air temperature by 17%. When four fans were used a further 4.8% temperature reduction was achieved. Increasing the airflow velocity at the four fans placed at the roof, from 2.84 m/s to 15.67 m/s, caused only a small reduction in the air temperature inside the passenger compartment