Pros and Cons of Using Water and Steam as a Heating Medium in Heat Exchangers

Although water is abundantly available for commercial use, it contains various minerals that create corrosion and scaling in heat exchangers. The process of scaling adversely affects heat transfer and can lead to equipment failure. Chemical treatment is required to prevent corrosion and scaling deposits. Microbiological fouling is also an important factor when selecting water as a heating medium in heat exchangers. Properties of water and the functionality of heat exchangers are reviewed in PE exam prep courses.

Steam is used as a heating medium in heat exchangers. Pressure steam is classified as low pressure steam and high pressure steam. Low pressure (LP) steam carries more latent heat, is normally of higher quality, reduces scaling, and reduces the fouling factor. LP steam typically requires pressure reducing values, which require more space and require large pipes for condensation. The space requirement and size of the pipes add maintenance and operational costs. High pressure (HP) steam requires smaller pipes and has a lower installation cost than LP steam piping. Professional Mechanical engineers design and create drawings of piping systems prior to installation. Our PE Mechanical exam review course offers a thorough refresher of HVAC principles and topics related to heat exchangers.

Table of Contents

1. Water vs. Steam as a Heating Medium

2. Factors That Influence Heat Transfer Rates

3. How to Find Rate of Heat Transfer

1. Water vs. Steam as a Heating Medium

1. Water does not change state while it is being used as a heating medium. As it gives up heat energy to the secondary medium, its temperature drops. If one pound of water drops one degree Fahrenheit in temperature, it produces approximately 1 British thermal unit (BTU) of heat.
2. Steam also does not change state while it is used as a heating medium, and it gives up heat energy to the secondary medium. During the process, its temperature drops, but the fluid condensate remains at the same temperature. One pound of steam at a pressure of 30 psi gives up approximately 929 BTUs of heat. Steam gives up more energy per unit mass than water.

2. Factors That Influence Heat Transfer Rates

The following factors influence heat transfer rates:

1. Surface area
2. Temperature
3. Flow characteristics
4. Fouling/Scaling
5. Film coefficient of fluid
6. Thermal conductivity of metal

3. How to Find Rate of Heat Transfer

For fluids that change state, the rate of heat transfer "Q" is given by:

Q = W*C* Temperature change of the fluid (△T) + W* Latent heat of vaporization (△H)

W = Flow rate of fluid (kg/hr.)

C = Specific heat of fluid (BTU/kg/degrees C)

△T=Temperature change of the fluid (degrees C)

△H = Latent heat of vaporization (Btu/kg)

For fluids that do not change state, the rate of heat transfer "Q" is given by:

Q = W*C * Temperature change of the fluid (△T)

If the rate of heat transfer is higher, then the heat exchanger's efficiency is higher and vice versa.

The above equations are important for engineers who plan to take the Principles and Practice of Engineering (PE) exam for their career advancement.

An Introduction to Welding from a Structural Engineering Perspective

Table of Contents

1. Introduction

2. Uses of Welding

3. Types of Welded Joints

4. Comparison of Riveted Joints and Welded Joints

5. Properties of Welding Materials

6. Welding Processes for Different Metals

1. Introduction

Welding is the process of joining metals in which the parent metals are fused together to form a single piece. Welding is used wherever strength is required, whereas soldering and brazing are primarily employed to handle only light loads. Structural engineers require knowledge of the welding process because many structural frames require field welding during assembling operations. Professional structural engineers preparing for their SE exam certification need the technical knowledge of various welding procedures.

2. Uses of Welding

Welding is:

1. A substitute for castings and forgings 
2. A fabrication medium to join parts permanently and to form built up members 
3. A connecting medium, in lieu of nuts and bolts 
4. A repair medium to replace broken and worn out sections of members 

3. Types of Welded Joints

Welded joints are classified based on the welding method needed. Some examples include the following: butt, lap, strapped, tee, fillet, square butt, single and double V butt, single and double U butt, single and double bevel butt, single and double J butt, and corner joints. Technical and functional aspects of each joint are reviewed in SE exam review courses. 

4. Comparison of Riveted Joints and Welded Joints

When compared to riveted joints, welded joints are: 

1. Lighter in weight 
2. Stronger as there is no weakening of section due to punching or drilling 
3. Laborless as several operations, such as punching, drilling, riveting, fullering, or caulking are replaced by a single operation, namely welding. 

5. Properties of Welding Materials

Many materials can be welded, but the ease of welding varies depending on the material. At a high temperature, the structure of a material changes, as well as the physical properties and corrosion resistance of the material. Gaseous oxides cause blow holes, soluble oxides in the molten metal reduce the strength of the weld, and insoluble oxide causes slag inclusion in the weld. 

1. Metals, such as zinc, may vaporize and cause the weld to be more porous 
2. Metals of high thermal expansion and low thermal conductivity are subjected to high cooling stress as the metal cools after welding 
3. All carbon steels, except for spring steel and tool steel, can be welded satisfactorily, but the low carbon steels are most readily welded 
4. Cast iron is difficult to weld, but satisfactory welds can be produced if due care is taken while pre-heating prior to welding 

6. Welding Processes for Different Metals

Arc welding, submerged arc welding, and electro-slag welding methods are employed for welding ferrous metals, as the gas welding process is used for welding metal alloys such as brass and bronze.

Types of welding processes, welding joints dimensions, and welding angle specifications are very important for professional engineers who plan to take the structural engineering certification exam.

Corrosion Protection for Steel in RCC Bridge Structures

Table of Contents

1. Introduction

2. Corrosion Control Measures

3. Corrosion Control Methods

4. How to Prevent Corrosion of Steel in Concrete

5. Techniques Used for Protection of Reinforced Steel Against Corrosion

1. Introduction

Corrosion is the wearing of a metal due to a chemical or an electro-chemical reaction by its surroundings that indicates the damage and loss of material due to a chemical attack. In this process, metal is converted into an oxide, salt, or some other compound that may lead to the development of rust. 

The implementation of corrosion protection is a new construction technique to avoid the loss of materials through corrosion. Corrosion protection uses corrosion inhibitors, low-permeability concrete, and coated reinforced steel that considerably reduces the amount of reinforced steel corrosion in new bridges.

2. Corrosion Control Measures 

Concrete provides a protective environment for steel to avoid corrosion. Due to high alkalinity, the thin passive film of ferric-oxide (Fe2O3) is automatically formed on the surface of steel. This layer effectively protects the steel from corrosion and will stay effective as long as the material maintains a high alkalinity. Therefore, by preserving an alkaline environment, the corrosion of steel can be effectively prevented, and the durability of the structure can be ensured. The alkaline medium must be maintained for a longer period by making the concrete impermeable. The factors that impact the corrosion of reinforcing steel bars that are embedded in concrete depend on the amount of chloride ions in the concrete, the resistivity of the concrete, temperature, and the concrete microstructure. Structural material characteristics of rebars and cement concrete topics are reviewed in SE exam review courses. 

3. Corrosion Control Methods

Mechanical Methods: The physical barriers that prevent the access of chlorides, oxygen, and moisture to the reinforcing steel.

Electro-Chemical Methods: This method forces the steel reinforcing bars to be cathodic. It includes chloride extraction and protection.

The above methods are widely used for preventing corrosion; a qualified structural engineer with their structural engineering exam certification will recommend the implementation method for each project.

4. How to Prevent Corrosion of Steel in Concrete

A major issue of a reinforced concrete structure is deterioration. The cost of repairing deteriorated structures has become a major liability for highway agencies. The primary cause of deteriorations is cracking, spalling, and delamination. To minimize the development of corrosion of steel in concrete, the following steps should be taken: 

• Avoid heavily congested reinforcements at the intersection of beams and columns 
• Avoid the use of materials that speed up the process of corrosion 
• Clean rebars to remove rust scales before placing concrete 
• Provide cathodic protection to the steel 
• Use high quality and impermeable concrete, as well as an accurate water-cement ratio 

The above quality control and assurance measures are refreshed in SE exam review courses for engineers who are interested in becoming a certified professional structural engineer.

5. Techniques Used for Protection of Reinforced Steel Against Corrosion 

Protection techniques are used to improve the adhesion of epoxy coatings to steel. One method involves pretreatment of uncoated steel with zinc chromate. This procedure is used for all epoxy-coated reinforcement. Epoxy-coated reinforcement steel is one of the protection systems for new bridge deck construction. Calcium nitrite [Ca(NO2)2] is the most popular inorganic corrosion inhibitor, and it is used to prevent chloride ion reactions on steel surfaces. The use of a corrosion-inhibitor admixture in the concrete provides adequate corrosion protection.

The Importance of Networking and Communication Systems in Electrical Engineering

Table of Contents

1. Routing and Transmit Design in Computer Networks Terms

2. Network Protocol Used for Data Transmission

3. Advantages of Computer Networking

4.Challenges of Networking

1. Routing and Transmit Design in Computer Networks Terms 

A router is defined as a network connected with two or more computers to share resources. These networks can be linked through cables, radio waves, satellites, or infrared light beams. 

Network topology is the arrangement of a network, how the nodes are connected to each other, and their communication methods with other nodes in the same network. 

Network optimization problems include routing restrictions, traffic load, overall reliability, and cost. The electrical industry is focused on network development and optimization. 

Routing and network topologies topics are refreshed in PE review courses for electrical engineers. 

2. Network Protocol Used for Data Transmission 

Protocol is a set of rules that manages the communication between computers on a network. These rules provide the guidelines that regulate the access, allowed physical topologies, speed of data transfer, and types of cabling used for transmission. The most common protocols are: 

Ethernet: Carrier sense multiple access/collision detection (CSMA/CD) access method is used in Ethernet protocol. This protocol listens to the network cable before sending any transmission through the network to avoid collision. When a computer knows that the network is free and there is no traffic on the network, data will then be transmitted. Otherwise, each system waits until the cables are clear before transmitting data. 

Local Talk: This protocol was developed by Apple and is considered carrier sense multiple access/collision avoidance (CSMA/CA). Local Talk adapters and a twisted pair cable is used to connect a series of computers through the serial port. 

Token Ring: In the mid-1980s, IBM developed this protocol. This protocol uses the token-passing method, where computers are connected through network so that the tokens travel around the network from one computer to another in a ring. If a computer does not have the information to transmit, it simply passes the token. If the computer needs to transmit the data, it attaches the data to the token. 

Asynchronous Transfer Mode (ATM): ATM is a universal networking technology that handles audio, video, and data transmission. It creates a virtual channel (VC) and utilizes the channel for communication and then terminates it. This can be implemented by one or more ATM switches; it places an entry for the VC in its forwarding table. 

3. Advantages of Computer Networking 

1. When using a network, people can communicate efficiently with a group of people through instant messaging, video conferencing, social media, chat rooms, etc. 
2. It is easy to share files, data, and information. This can be beneficial for large organizations to maintain their data in an organized manner and easily sort based on preference. 
3. The files and programs on a network can be protected using passwords. The protected files cannot be accessed by any unauthorized users.

4. Challenges of Networking 

1. Networks may sometimes crash or breakdown due to an issue with the server. When this kind of issue becomes frequent in networks, it could cause a loss of funds as well as a decline in productivity. It is necessary to maintain the network properly to prevent disastrous breakdowns. 
2. It is very expensive to build a network in large scale organizations. Cables and other hardware costs are very costly to buy and replace. 
3. Security threats are a major issue in large networks. Careful measures must be taken to facilitate the required security.

Professional electrical and computer engineers may have studied topics related to computer networks, communications, computer systems, and software development during their undergraduate studies. PE exam review courses recap these topics once again for engineers who are preparing for their professional engineer exam certification.