Several Studies Deal With Thermal Models Solved By The Finite Difference Method

By Author: doris zhang
Total Articles: 76
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However, as explained by Ibanez et al. or Schranzhofer et al. , it is also possible to couple a PCM model with a thermal model based on the transfer functions method. As noted by Dutil et al. , the enthalpy method and the heat capacity method are the two main approaches when modelling heat transfers with phase change. The enthalpy method has been used by Dauvergne and Dauvergne and Palomo Del Barrio to model plasterboards with micro-encapsulated PCM. Some authors have used the effective heat capacity method, assuming that this heat capacity is temperature dependent: Borreguero et al. fitted the heat capacity model according to the experiment, and Chen et al. or Ahmad et al. chose a rectangular function. In the case of research by Athienitis et al. , the approach is different again: the heat flux due to phase change is modelled by a triangular function, and is injected as a source term in the heat balance equation. The aforementioned studies concentrated for the most part on the accuracy of the calculations, but did not necessarily target the application to the real needs of architects and engineers. For instance, whether ...
... or not PCM wallboards are suitable to ensure a satisfying level of comfort in summer is a question that has to be considered at the early design phase, because the answer can strongly influence the design of the building. Indeed, professionals need simulation tools which are accurate, but quick and easy to use, and able to help them during the whole building design process, especially in the early phase. This paper proposes a consistent response to this professional requirement.

First, both models are described, then the coupling methodology is explained. The simulation tool is then applied to two real case studies to illustrate the ability of the methodology and the resulting coupled models simulation tool to evaluate easily the performance of PCM wallboards: a project for a timber frame family house,glass desktop whiteboard and an existing lightweight office building. The results for the two case studies do not provide any general rules on integrating PCM wallboards in buildings. They do, however, illustrate the possibilities that the PCM wallboard-building coupled model can offer in predicting performance when using PCM wallboards in two real case studies. This performance depends very much on building use and its intrinsic properties . For example, according to the results given above concerning the heating load, the use of PCM wallboards is more successful in the timber frame family house than in the office building, but this result is mainly a consequence of the heating set point temperature in the office building being set to 15˚C after 6 pm, thus preventing the solar energy stored by the PCM during the daytime from being used effectively in the evening. Conversely, concerning summer comfort, the use of PCM wallboards is more successful in the office building than in the timber frame family house because the internal gains are higher in the office building during the day; the temperature during the day tends to be higher in the office than in the house, leading to a higher temperature difference between daytime and night-time for the office than for the house, i.e. conditions that are more favourable for the PCM wallboards to achieve their complete melting/solidification cycles.

The two case studies highlight the fact that the PCM thermal effect interacts strongly with the night ventilation or the use of the window shading device, hence the influence of the PCM wallboards on summer comfort depends strongly on occupant behaviour. As already pointed out, the PCM wallboards need a sufficient temperature difference between daytime and night-time to be efficient, thus the occupants who shade the windows during the day and open the windows during the night have a strong impact on the level of utility of the PCM wallboards. For instance, concerning the south zone of the office building, DH dropped from almost 2000˚C∙hours to 1200˚C∙hours when the night air change rate varied from 1 h−1 to 4 h−1 : the night air change has a significant influence on the temperature inside the office, thus increasing the night air change rate facilitates PCM solidification and beyond its complete melting/solidification process, and consequently contributes to increasing the potential for using the PCM wallboards. By varying the number of PCM wallboard layers from 1 to 2, the question of the PCM wallboard thickness was considered for the second case study . Although when considering DH and UF, the beneficial effect of a second layer of PCM wallboards is less than that of the first layer, this second layer becomes particularly useful when the days are extremely hot: the first layer then only has an influence in the morning when the PCM melts almost completely, with the second layer providing additional PCM for cooling the building in the afternoon . In the Internet of things, wireless connectivity forms the basis for connecting the devices to the Internet, especially in Smart Home or Smart office type networks. The number of devices is not less than four or five per person. Therefore it is imperative to have a robust security mechanism implemented so that only authorized devices can connect to the network; otherwise, it can lead to leakage of information or other malicious activities that will lead to different types of losses.

In the Internet of things, speed and throughput are also equally important. So the choice of technology is equally important. Wi-Fi being suitable technology for future IoT things other than Bluetooth Low Energy and 6LoWPAN . Wi-Fi Technology provides the feasible data rates and throughput needed for IoT types of applications in Home or office networks. Therefore, it is important to look into the security aspect of Wi-Fi technology to secure IoT networks. So far as wireless network security is concerned, there are different types of security needs that need to be fulfilled, right from device authentication to data security. In this paper, our focus is on device association and security using Wi-Fi technology. We propose a solution to the existing Wi-Fi technology resistant to attacks like a dictionary or attaining a preshared key for network authorization. Wi-Fi Protected Access-II, which uses Advanced Encryption Standard , is the most robust and secure protocol. WPA 2 supports two modes of security viz “home User” and “Corporate User”. A pre-shared passphrase or passkey is used in home user mode, and Access points are manually configured for the authentication . However, it is not resistant to the attacks that can be carried through Aircrackng or Dictionary Attack for obtaining the Preshared Kay in Personnel Mode, i.e., Home or Small Office networks. Although Enterprise mode is available with WPA2, authentication is carried through the RADIUS server, and no Pre Shared Key is used. However, it suffers from the vulnerabilities of accessing the open network devices like Camera, etc., and hence enterprise mode of WPA2/PSK is not secure. The following are the vulnerabilities that exist in Wi-Fi networks and are addressed by our proposed solution. Rogue Access Point: the adversary creates the rogue Access Point and broadcasts the Legitimate SSID, allowing the legitimate device to connect to the Fake access point with a legitimate Pre-shared Key. Hence obtains the Key which the adversary uses for authentication to the network.

De-authentication: the attacker imitates the Access Point with the MAC address of the Legitimate device and forces the device to re-associate. And eavesdrop on the beacons transmitted for re-association by the device which contains the legitimate Key. And Key can be easily acquired using Dictionary attack or Aircrackng, using Kali Linux. The network standards discussed above provide security that is insufficient to meet the present demand of security, especially in a wireless environment with no defined boundaries. The researchers have proposed several solutions,shelf gun concealment as discussed in the forthcoming section. Mannon Mustafa et al. proposed a one-time pad solution requiring the active cell phone number of the user to send the unique ID. Mina Malekzadeh et al. suggested using HMAC-SHA-1 to secure management frames against the Deauthentication and re-association Attacks . Bicakci et al. WPA2 security protocols are vulnerable to Denial of Service Attacks using re-authentication and re-association. Zhang et al. proposed using the MAC filtering mechanism where a smart client can differentiate between legitimate and non-legitimate frames. Odhiambo et al. proposed an Integrated Security Model, which incorporates a drop policy to avoid DoS attacks. As described by Aqeel-ur Rehman et al. , Wi-Fi is suitable for future IoT. Therefore, it is obvious to emphasize on security concerns of Wi-Fi technology. Data rates and bandwidth available in Wi-Fi best among other technology for interconnection in IoT, which is the biggest motivation to make Wi-Fi technology better. WPA2 being a robust protocol in terms of authentication and confidentiality. WPA2 comes in two versions for home and enterprise use. Other security schemes like RADIUS server authentication in the Enterprise version are robust and provide authentication with other openness. However, it is still vulnerable to several attacks as an association to the network is without any security, allowing them to attack networks. In-home networks, especially IoT, it is expensive to have a RADIUS server in place. So based on the available technology , use of pre-Shared Key for authentication to the Devices, is still a good choice for the Home IoT infrastructure. But WPA2 protocol is weak in terms of the attacks carried through Kali Linux.

It is easy to obtain the Pre Shared Key, the reason being the key length is 128 to 256 bits which even encrypted using AES is still vulnerable to dictionary attack. In this paper, we propose wherein authentication does not involve any preshared key transmission at the time of association or re-association. Pre Shared Key will be shared among the users through manual means. Once the authentication process is to be established, the Hash of the Pre Shared Key will be transmitted and checked for the authenticity of the users to be connected to the Access point in Home or Enterprise networks. The process of the handshake is shown . The United Nations estimates that the population of the world increased from 2.5 to 7 billion between 1950 and 2011 . Fertility and future projected population growth are much higher in sub-Saharan Africa than in any other region of the world; furthermore, the population growth rate is of major international concern because it has the potential to hinder attainment of health and other development goals in the sub-region . Family planning aims at empowering individuals and couples to anticipate and attain their desired number of children whilst appropriately spacing and timing their births. FP can prevent between 20% and 35% of maternal deaths, but social norms and limited FP supplies prevent correct and consistent FP use in most low- and middle-income countries . In Ghana, FP uptake has not kept pace with the targets of national population policy adopted in 1969 and 1994 . There was a rapid increase in contraceptive use from 12.9% in 1988 to 25.2% in 2003, and since then contraceptive use has not significantly changed . The area of FP is a high interest to policy makers in Ghana as such quite a number of studies have been performed in this area. Research in this area has however been focused mostly on females and for that matter married females. Findings from some of these studies describe contraceptive use, attitudes towards FP and constraints associated with their use -. Most of these studies have also been cross-sectional i.e. performed at one point in time. The current study has focused on a wider population including adolescents, as well as bridging the gender gap by involving male partners of females. The paucity of longitudinal data to facilitate the understanding of the social dynamics of FP intentions and choices is a major drawback to the development of the next generation of FP interventions, which is particularly important for developing countries like Ghana.