Showing posts with label process heat. Show all posts
Showing posts with label process heat. Show all posts

Considerations in Selecting Industrial Heat Exchangers


The information below, courtesy of Standard-Xchange, outlines various design types of heat exchangers along with their advantages, limitations, and selection tips. For more information on applying heat exchangers to industrial process, contact Mountain States Engineering and Controls.

Non-Removable Bundle, Fixed Tubesheet

  • Less costly than removable bundle heat exchangers
  • Provides maximum heat transfer surface per given shell and tube size
  • Provides multi-tube pass arrangements
  • Interchangeable with competitive models
  • Shell side can be cleaned only by chemical means
  • No provisions to correct for differential thermal expansion between the shell and tubes. (Exception: expansion joint, available only on C200 and C210 exchangers)
Selection Tips
  • For lube and oil and hydraulic oil coolers, put the oil through the shell side
  • Corrosive or high fouling fluids should be put through the tube side
  • In general, put the coldest fluid through the tube side

Removable Bundle, Packed Floating Tubesheet

  • Floating end allows for differential thermal expansion between the shell and tubes
  • Shell side can be steam or mechanically cleaned
  • Bundle can be easily repaired or replaced
  • Less costly than full interval floating head-type construction
  • Maximum surface per given shell and tube size for removable bundle designs
  • Shell side fluids limited to non-volatile and/or non-toxic fluids, i.e., lube oils, hydraulic oils
  • Tube side arrangements limited to one or two passes Tubes expand as a group, not individually (as in U-tube unit); therefore, sudden shocking should be avoided
  • Packing limits design pressure and temperature
Selection Tips
  • For lube oil and hydraulic oil coolers, put the oil through the shell side
  • For air intercoolers and aftercoolers on compressors, put air through the tube side
  • Coolers with water through the tube side: clean or jacket water, use 3/8” tubes; raw water, use 5/8” or 3/4” tubes
  • Put hot shell side fluid through at stationary end (to keep temperature of packing as low as possible)

Removable Bundle, Pull-Through Bolted Internal Floating Head Cover

  • Allows for differential thermal expansion between the shell and tubes
  • Bundle can be removed from shell for cleaning
  • or repairing, without removing the floating head cover
  • Provides multi-tube pass arrangements
  • Provides large bundle entrance area
  • Excellent for handling flammable and/or toxic fluids
  • For given set of conditions, it is the most costly of all the basic types of heat exchanger designs
  • Less surface per given shell and tube size than C500
  • Selection Tips
  • If possible, put the fluid with the lowest heat transfer coefficient through the shell side
  • If possible, put the fluid with the highest working pressure through the tube side
  • If possible, put the high fouling fluid through the tube side

Removable Bundle, Internal Clamp Ring-Type Floating Head Cover

  • Allows for differential thermal expansion between the shell and tubes
  • Excellent for handling flammable and/or toxic fluids
  • Provides multi-tube pass arrangements
  • Shell cover, clamp-ring and gloating head cover must be removed prior to removing the bundle.
  • More costly than fixed tube sheet or U-tube heat exchanger designs
Selection Tips
  • If possible, put the fluid with the lowest heat transfer coefficient through the shell side
  • If possible, put the fluid with the highest working pressure through the tube side
  • If possible, put the high fouling fluid through the tube side

Removable Bundle, U-Tube

  • Less costly than floating head or packing floating tubesheet designs
  • Provides multi-tube pass arrangements
  • Allows for differential thermal expansion between the shell and tubes, as well as between individual tubes
  • High surface per given shell and tube size
  • Capable of withstanding thermal shock
  • Tube side can be cleaned only by chemical means
  • Individual tube replacement is difficult
  • Cannot be made single pass on tube side; therefore, true counter-current flow is not possible
  • Tube wall at U-bend is thinner than at straight portion of tube
  • Draining tube side is difficult in vertical (head-up) position
Selection Tips
  • For oil heaters, wherever possible put steam through the tube side to obtain the most economical size

Removable Partition Plates With Compression Endplates and Frame

  • Ease of disassembly for cleaning or replacement parts
  • Not Suitable for pressures over 300 psig
  • Not Suitable for change of state or gaseous applications
Selection Tips
  • For applications involving temperature crossing
  • Economical when exotic metals are required

Brazed Plate

  • Very compact and rugged
  • Lightweight
  • Many design options, including multiple passes, different plate styles, nozzle sizes and orientation
  • High heat transfer performance
No gaskets
  • Limitations
  • Can only be cleaned chemically
Selection Tips
  • For applications involving temperature crossing or close temperature approach
  • Ideal for refrigerant-to-liquid or refrigerant-to-gas applications
  • Very economical when compared to all-stainless tubular construction

Heavy Duty Removable Core Type

  • Tubes free to expand individually
  • Heating elements totally removable for maintenance or replacement without disconnecting outer casing from ductwork
  • Embedded or extruded fins available for higher design temperatures (750° F max.)
  • Individual tubes cannot be cleaned or plugged


Shell and Tube Heat Exchanger Fundamentals

shell and tube heat exchanger diagram and cutaway view
Shell and Tube Heat Exchanger
Shell and tube heat exchanges are found throughout fluid based industrial process control operations where heat must be transferred between two closed fluid systems. There are numerous design variants intended to provide levels of performance tailored to specific process requirements.

Provided below is a white paper that illustrates and explains the fundamentals of heat exchanger performance for shell and tube units. Covered are the three modes of heat transfer: conduction, convection, and radiation. Three sample application cases are covered, showing how the formulas are applied, and illustrations provide for even better understanding of basic operating principals. The article is sure to refresh or enhance your heat exchanger knowledge.

MSEC brings many years of heat exchanger application experience to bear on your application requirements. Share your new or drop-in replacement heat exchanger challenges with MSEC and work toward the best installed solution.

Heat Exchangers for Liquid-Gas Vaporization

Tube bundle for heating
Tube bundle for heat transfer.
Hydrocarbon and non-hydrocarbon based gases can be more efficiently stored and transported in a liquified state, providing higher media density and corresponding product weight per container. Upon reaching their final destination, the liquid can be reheated, returning to a gaseous state for distribution and use. Typical liquified gases include natural gas, oxygen, butane, propane, and nitrogen.

There are several ways to affect the physical change from liquid to gas, and picking the best option is dependent on criteria such as; 1) available energy sources; 2) plant location; 3) climate conditions; and 4) plant infrastructure.

The change from liquid to gas phase usually requires one or more vessels properly sized and designed to accommodate the vastly increased volume of the evaported liquid, handle the storage or distribution pressure of the gas, and be compatible with the process media. In most plants today, the gradual process of warming the liquified gases is done with steam-heated or oil-heated "heat exchangers" or "tube bundles".

Some heat exchanger systems may, instead of steam, use steam-heated intermediary fluids such as oil, water, or glycol-water solution to provide a smoother rate of heat transfer to the evaporating liquid. This method can employ two heat exchangers, one transferring heat from steam to the intermediary fluid, then another to transfer heat from the intermediary fluid to the liquified gaseous product to evaporate it.

Steam heated, closed-loop circulation systems play an important role in providing an efficient, low-cost and compact method to accommodate liquid vaporization. Steam is available in many industrial plants, providing a comparatively inexpensive and readily available source of heat energy. Heat exchangers are available in a range of pre-engineered capacities and forms, but it is quite common for these components to be custom fabricated to meet very specific requirements. Engineers can design their own systems from the component level, or provide performance requirements to the manufacturer and have a skid mounted unit produced, ready for connection to electric power (for control systems), energy source (steam, oil or water) and process inlet and outlet lines.

These systems can be quite technical, with numerous design considerations. The path to maximized safety and efficiency includes consultation with a heat exchanger expert as part of specification and design process. A combination of your high level process knowledge and their product and application expertise will yield the best outcome.

Shell and Tube Heat Exchangers for Industrial and Commercial Application

tubing bundle
Tube Bundle
A shell and tube heat exchanger is a type of heat exchanger consisting of a shell (a pressure vessel) with a tubing bundle (or core) inside. Two fluids are used, one inside the tubing and one outside the tubing, to change temperature of the fluid contained in the shell. The amount of surface area provided by the tubes determines the efficiency of the heat transfer, and is sometimes augmented by additional lengths of tubing, or with fins.

The function of a shell and tube heat exchanger is very basic. Two different fluids, physically isolated from each other, and at different temperatures, are allowed to transfer thermal energy from one to the other through thermal conductivity.

Cooling Tower Terms and Definitions

Delta Cooling Tower
Delta Cooling Tower
(definitions courtesy of Delta)
Cooling Tower Terms and Definitions

BTU (British Thermal Unit) A BTU is the heat energy required to raise the temperature of one pound of water one degree Fahrenheit in the range from 32° F to 212° F

Cooling Range The difference in temperature between the hot water entering the tower and the cold water leaving the tower is the cooling range.

Approach The difference between the temperature of the cold water leaving the tower and the wet- bulb temperature of the air is known as the approach. Establishment of the approach fixes the operating temperature of the tower and is a most important parameter in determining both tower size and cost.

Drift The water entrained in the air flow and discharged to the atmosphere. Drift loss does not include water lost by evaporation. Proper tower design can minimize drift loss.

Heat Load The amount of heat to be removed from the circulating water within the tower. Heat load is equal to water circulation rate (gpm) times the cooling range times 500 and is expressed in BTU/hr. Heat load is also an important parameter in determining tower size and cost.

Ton An evaporative cooling ton is 15,000 BTU’s per hour.

Wet-Bulb Temperature The lowest temperature that water theoretically can reach by evaporation. Wet-Bulb temperature is an extremely important parameter in tower selection and design and should be measured by a psychrometer

Pumping Head The pressure required to pump the water from the tower basin, through the entire system and return to the top of the tower.

Makeup The amount of water required to replace normal losses caused by bleed off, drift, and evaporation.

Bleed Off The circulating water in the tower which is discharged to waste to help keep the dissolved solids concentration of the water below a maximum allowable limit. As a result of evaporation, dissolved solids concentration will continually increase unless reduced by bleed off.

Explaining Heat Exchanger Stall

Spirax APT
Spirax Sarco APT
The most common process heating, heat exchanger hookup uses a temperature control valve on the steam line to the heat exchanger, and a steam trap on the condensate line from the heat exchanger.

The shell side is this steam space. A control sensor signal at the tube side outlet is used to throttle the steam control valve to maintain set point temperature. Higher pressure in the steam space than in the condensate recovery line produces effective condensate removal and lift to the return system.

Under a steady high load, differential pressure removes the condensate from the heat exchanger. Under reduced heating load, the control valve throttles down, reducing the steam pressure inside the heat exchanger. This also reduces the differential pressure across the steam trap making the trap unable to remove the condensate. This happens in all heat exchangers, whether properly sized or oversized.

This causes condensate to flood the steam space, known as heat exchanger stall. In other words, the pressure in the heat exchanger is equal to, or less than, the total back-pressure imposed on the steam trap, sometimes even attaining vacuum.

Some operators address vacuum in the steam space by installing a vacuum breaker on the shell. This practice introduces atmospheric gases that dissolve readily into the cooler condensate. These dissolved gases form corrosives that attack wetted surfaces, while doing nothing to eliminate the stall condition.

The simplest way to cure stall is to install a steam-powered automatic pump trap, such as a Spirax Sarco APT series. Pump trap operation is based on condensate level alone, with live steam pressure removing condensate under all load conditions, even vacuum.

By not using a vacuum breaker, you can reduce condensate acidity and large temperature swings in the heat exchange equipment. Heat transfer and control improve. Corrosion, water hammer, tube failure, excessive treatment chemical dosing, and high maintenance costs become distant memories.

A survey of your heat exchanger and condensate return system operating and maintenance data can uncover the below-par performance that indicates stall. If present an automatic pump trap is an easy solution that quickly returns dividends in process quality, energy savings, and reduced maintenance costs.

For more information on how to prevent heat exchanger stall, contact Mountain States Engineering and Controls at 303-232-4100 or visit

Always Looking for Ways to Add Value and Help Customers Solve Industrial Process Control Challenges

We opened our doors in 1978 with the mission of creating the most technically competent and application savvy industrial process control rep in the Mountain States. Headquartered in Lakewood, Colorado, MSEC established itself as a premier Manufacturer's Representative and Distributor of process equipment, industrial controls, engineered valves, heat exchangers and cooling towers. Serving the markets of Colorado, Wyoming, Montana, Utah, Nevada, Southern Idaho, Western Dakotas and the Panhandle of Nebraska, we earned a reputation for outstanding customer service. Now, with the reach and convenience of the Internet, we'll use this blog as another way to provide value to our customers - both existing and prospective.

We plan on sharing years of experience and knowledge here. Steam management experiences, process control application case histories, new industrial control products, automated valve packages and interesting jobs we've done. We hope this will be a place where information can be exchanged. If you like what you see, please tell others in your industry about us.